Wikipedia:Reference desk/Science

August 21

Quantum Immortality....WTF?

I read the question posed earlier about the possibility of immortality because of the random nature of quantum mechanics and my confusion can be summed up in my headline (excuse my French…err…acronym). I just want to have one thing cleared up to start. In such an experiment, according to quantum mechanics, the actual state that we see “forms” (or collapses to that state) when we observe it. Is the state that we see (dead or alive) the “real” (and only) state or do both states still exist? (theoretically). If it is the former than perhaps WTF was an understatement.67.70.29.35 00:07, 21 August 2007 (UTC)

Well, that's really at the heart of the problem. Rather than think about quantum immortality (which is controversial for lots of other reasons as well as this one) - let's just think about Schrödinger's cat. The question boils down to: What is the state of the cat between the quantum event setting off the poison gas (or not) and when the experimenter opens the box? What you believe depends on how you interpret the results of some very weird experiments. If you go the 'many worlds' approach then the whole 'collapse' thing doesn't really come up - dead kitty in one universe, live kitty is in the other - both things happen at once - but not in the same universe - hence no 'collapse'. But there are other ways to interpret the results that say that indeed the cat is both alive and dead at the same time in a 'superposition' that is only resolved into an actual state when someone "observes" it (this is the 'collapse' of multiple superposed cat states back into a cat that is most definitely either alive or dead). But other people claim that far from the state of the cat collapsing, instead the scientist has now entered into the superposition - so when he opens the box, the scientist is now in a superposed state of knowing that the cat is alive and knowing that the cat is dead - if he's disgusted by the stink of the dead cat and doesn't eat his lunch - then his sandwich gets dragged into the superposition - then his wife phones and asks how he enjoyed his lunch - and now she is dragged into the superposition...and so on until all of the universe is superposed...which is a lot like 'many worlds'. There are several other ways to look at it. But the effect is definitely there. Work on quantum computers and quantum cryptography rely heavily on the fact that superposition or multiple universes or SOMETHING weird is happening in actual reality. SteveBaker 00:39, 21 August 2007 (UTC)

Oh come on, are you actually saying that if you built a schrodinger's cat box in real life something weird would "happen in actual reality"? The cat would either die or not, period.. it might mess with quantum theories or whatever but real life? Are you sure? --froth^t 04:11, 21 August 2007 (UTC)

They come up with macroscopic examples like the cat in the box to illustrate something that *really is happening* in the world. Yes, it's real, in the real world (unfortunately, for people like me who will never understand QM). The world making Newtonian sense is just not true. See double-slit experiment#Quantum version of experiment. --Sean 05:09, 21 August 2007 (UTC)

Yes - sure we're saying that's EXACTLY what would happen in real life. The cat would simultaneously be alive and dead until the scientist looks into the box...according to SOME interpretations of the experiment. In other interpretations, the entire universe is duplicated at the moment the unstable atom decides to split (or not) - and the only difference between the two resulting universes are that one contains a dead cat and the other contains a living one. In other interpretations, the atom is in a superposition state but as soon as it tries to influence a macroscopic effect it's quantum state collapses. (Of course this is a thought experiment - and a practical experiment would have to ensure that the box was perfectly soundproof, etc so the experimenter wouldn't be able to know the state of the cat until he opened the box. That may be entirely impractical in practice - but as a thought experiment, this is entirely valid!) SteveBaker 13:28, 21 August 2007 (UTC)

Shouldnt this be rather easy to disprove? Just perform the experiment a couple hundred times and if you're still alive, proudly declare that you just killed a couple hundred people and that your universe is spectacularly lucky to be the only one who has proof that quantum immorality is real. Of course nothing is proved or disproved if you die.. --froth^t 04:23, 21 August 2007 (UTC)

Quantum immorality is a different issue altogether :) Capuchin 07:20, 21 August 2007 (UTC)

The problem with your argument is that only your consciousness has proof that quantum immortality is real. The chances are tiny that anyone else in that universe has proof of quantum immortality besides you. You are a statistical anomaly. In a way it is "your" universe caused by your consciousness being quantum immortal. Capuchin 07:20, 21 August 2007 (UTC)

The deeper problem (if we're talking about quantum immortality again - and IF it's true (which it's probably not)) is that there are an infinity of universes. If you believe in the theory, you can put a gun to your head, pull the trigger and find that it mysteriously fails to fire. You do this 100 times with 100 different fatal suicide techniques - and you find you'll survive all of them. Everyone around you is convinced that quantum immortality is true - you win a nobel prize - science, religion and philosophy changes everything. However, it's only been proven in that (very, very rare) universe where the gun jammed, etc. In the majority of universes (such as the one I currently inhabit) your brains splattered everywhere and you died - and we all find it hard to believe in quantum immortality because we have no evidence that it ever happened. The fact that nobody in all of history appears to have been saved miraculously after a series of wierd suicide efforts doesn't mean it won't happen - it just means that in almost all of the universes, you died the first time you tried it. People die all the time in the universe that you and I happen to inhabit right now - but quantum immortality would say that there are other universes in which those people are still alive. There are universes where Julius Ceasar is still alive - amazingly! We just don't happen to live in one of those because such things are astronomically unlikely. SteveBaker 13:28, 21 August 2007 (UTC)

Hold your horses there steve. We were talking about purely random events like radioactive decay. Despite the most fortuitous universe possible, ceasar would not be alive 2000 years later (unless the human race were drastically different, and then it wouldn't be ceasar). And suicide weapons don't jam randomly- only quantum experiment rigged suicide weapons. Right, right? --froth^t 20:50, 21 August 2007 (UTC)

I disagree. Atoms in liquids, gasses and solids are vibrating and bouncing around at random - and at the lowest level, these are affected by quantum events. So it's perfectly possible (although astronomically unlikely) that all of the oxygen molecules in the room you are sitting in might randomly migrate to within a few inches of the ceiling and stay there for 10 minutes - leaving you (sadly) breathing only nitrogen. Nobody I've ever heard of died like that. But you have to grant that it's possible. Similarly, when Brutus and his buddies were about to stab Caesar (just after "Beware the ides of March", "Et tu Brute?" and all that stuff), all of the molecules in their knife blades could choose that moment to vibrate out of the way or spontaneously disintigrate - or all of the molecules in the air might happen to line up and a brief but violent gust of wind blow Caesar away to safety, or the clasp holding up Brutus' toga might slip through a gap caused by random fluctuations in the molecules of the cloth - causing a wardrobe malfunction that has all of his co-conspirators falling over laughing...who knows? Sure these things are amazingly, ridiculously unlikely - and they have to happen with increasing frequency as Caesar gets older and more decrepit - but if we have an infinite number of parallel universes in which all possible variations of quantum events happen - Caesar must live on in a tiny (but still infinite) fraction of them. Suicide weapons can similarly be affected by crazy-unlikely quantum-triggered events. A belief in many-worlds essentially requires a belief that Caesar is still alive in a bunch of them. Just keep thinking "INFINITE NUMBER OF DIFFERENT UNIVERSES" when you think of "ALMOST ZERO PROBABILITY". Infinity multiplied by almost zero is still infinity. Only events that have utterly zero probability are not going to happen. SteveBaker 16:26, 22 August 2007 (UTC)

So how do you think a 2000 year old caesar would look, hm? Do you think his brain matter would even still be cohesive after that long? His body's not a gas, it's not subject to such random interaction --froth^t 02:18, 23 August 2007 (UTC)

His body is not a gas, but who cares? Everything is subject to random interaction, the molecules in your very own body included. Like I said in another question down there, behold the ALL POWERFUl wave function! The very bound molecules of the solids (and the less bound, but still bound!, molecules of the liquids) in your body still have wave functions, and as all wave functions do, they spread over the entire universe. It just so happens that molecules that are bound somehow are less likely to quantum tunnel to a new position (the source of most of these freaky quantum possibilities) than a gas is, as they have to overcome a greater energy barrier to move in that manner. Nonetheless, it remains possible, just exceedingly unlikely; there is a possibility right now off the molecules in your body quantum tunneling to Mars, but chances are that even in the entire life of the Earth, no living thing on Earth has every experienced this. As for how Caesar would look, it's possible for his molecules to randomly reverse all of his organ and cellular degeneration and return him to a young man, and even correct all genetic mutations that have occured to stave off cancer (and lengthen the telomeres back to normal to stave off senescence!). Quite unlikely, but it's somewhere out there...in all the random possibilities. Someguy1221 03:17, 23 August 2007 (UTC)

Thanks! Nicely explained. In many-worlds, you have an infinite number of worlds - in the vast majority of them, Caesar is remembered just as he is in this universe. In others, he's just barely alive - but surviving against all the odds. In yet others, he's miraculously surviving in full health. In others, he just spontaneously turned into an Aardvark...just now! While I was typing this message. But the odds of those things are so astronomically small that we can be extremely confident that our universe won't have any of those weird things happening in it...except that the 'strong anthropic principle' (if you believe it) says that you, personally, must be living in one of those universes where you havn't died yet...and you'll always live in such a universe - so you'll never die. SteveBaker 12:01, 23 August 2007 (UTC)

Original questioner speaking. Hmmm... perhaps I should rephrase the question. First I’ll start out with a few premises.

1) 1 state is actually seen when the cat in question is observed. 2) All subsequent observers will agree with the claim of the first observer (who’s only claiming what he saw). In other words, they will agree on the state of the cat.

If the premises above are accepted (I doubt they will be), then I can only say it is utterly absurd to say that only 1 state exists after the observation and yet 2 states before, as if observing the object somehow changes the reality of it. And what about each subsequent observer? If the first observer sees the cat as dead, then how can the cat still exist in only 1 state for the next observer who hasn’t yet observed the cat, because to him it should still exist in both states!? Again...wtf? This can only, I repeat ONLY, work if there are multiple (parallel) universes. Therefore, why can’t QM assert the existence of these universes as confidently as it can assert the seemingly absurd existence of a cat that is both dead and living at the same time? 67.70.29.35 07:54, 21 August 2007 (UTC)

Utterly absurd? Sounds about right. "If you think that you understand quantum mechanics, then you don't understand quantum mechanics" - Richard Feynman. Capuchin 10:00, 21 August 2007 (UTC)

Yep - wise words. (Feynman is my hero!) Quantum and relativistic effects are so totally alien to us, it's essentially impossible for us to truly 'feel' the consequences of them. We've evolved over millions of years to live within a range of sizes, speeds, gravitational pulls, etc. We see everything within those ranges as 'normal' and 'intuitive' - and things that only happen at other sizes, speeds, etc as utterly beyond our minds to fully comprehend. That's no surprise. A hypothetical creature that existed only at quantum scales would find our existance utterly incomprehensible. The important point here is that you cannot - must not - use common day-to-day experience as a way to interpret the universe at scales beyond that experience. The universe isn't weird - we're just hopelessly limited in range. But many of these seemingly impossible things are actually used in day-to-day devices. You have a flash memory in your PDA/Phone/MP3 player? Well, those devices only work because electrons can (essentially) spontaneously teleport. Super-secure communications systems are just beginning to be developed (eg between banks) that use quantum entanglement (which is a related phenomena to superposition). These things actually WORK - so the underlying science must be pretty close to the truth no matter how weird you think it is. SteveBaker 13:28, 21 August 2007 (UTC)

Steve, Perchance did you watch Richard Dawkins' talk at TED about why we percieve reality as we do?

And to the OP, don't worry, everyone else thinks that it's weird too, just that it being weird doesnt prevent it from being accurate. Capuchin 14:12, 21 August 2007 (UTC)

No, I didn't. Watching it now... SteveBaker 19:20, 21 August 2007 (UTC)

Share a link please? :) I always get a good smile out of physical scientists trying to dismiss the entire school of metaphysical philosophy at a stroke with empirical evidence. --froth^t 20:53, 21 August 2007 (UTC)

I think it's this. But he doesn't say anything that would interest a physicist or philosopher of science. It's sort of Metaphysics 101. -- BenRG 22:53, 21 August 2007 (UTC)

The physics of quantum mechanics is all contained in the mathematical formalism, which makes clear predictions about the outcomes of experiments of this kind. Your two premises are both empirically testable statements about the world, and the theory says they're both true. Where you get into trouble is when you start asking what the outcome of a measurement would have been, in the absence of any actual measurement. Asking whether the cat was alive before opening the box is a question of this type. Quantum mechanics doesn't answer this kind of question, and the formalism doesn't suggest any obvious way to answer it in general, and there's no real consensus about whether there is a sensible answer, or what it would be. In other words, it's not clear what quantum mechanics is saying about the nature of the universe. The interpretations are various people's guesses about what the nature of the universe might be, to give rise to rules like this. This isn't just a metaphysical question, since the interpretational difficulties become impossible to ignore when you try to quantize gravity. Hopefully a theory of quantum gravity will rule out some of the interpretations, or make it clear that they were on the wrong track. Of course, quantum gravitational effects are so weak at ordinary energies that this may remain metaphysics for a while.

Contrary to what many people seem to believe, the formalism does not say that the cat is "both alive and dead" before the measurement, or that the double-slit electron "goes through both slits". There's a wave function which may be in a superposition of alive and dead states, but (a) there's nothing in the formalism to connect superpositions in the wave function to anything empirically real, and (b) a superposition of X and Y is totally different from a state that's both X and Y. For example, a superposition of a cat in one box and a cat in another box is entirely different from a state with cats in both boxes, or half a cat in each box (assuming you could even define what that means). There's nothing "ghostly" about superpositions: the live cat and dead cat in the superposition are in no sense superimposed in the box.

Schroedinger's cat is not really a very good thought-experiment, because there's nothing essentially quantum about it. Cats are classical objects, and everything about the experiment is classical: you randomly gas the cat, and open the box, and the cat is alive or dead. The uncertainty principle doesn't meaningfully apply in cases like this. So my last two paragraphs were really about thermodynamically reversible systems, which are inherently quantum in their behavior. -- BenRG 16:22, 21 August 2007 (UTC)

But that's the whole point of the thought experiment. Schroedinger wanted to point out (in an especially memorable manner) that these teeny-tiny quantum weirdnesses can't simply be buried as something that doesn't have huge consequences. Because it's possible to amplify a small quantum event into something as macroscopic as a dead/not-dead cat, we have to start really worrying about what this means to our perception of macro-scale reality. SteveBaker 19:17, 21 August 2007 (UTC)

I've never really understood what Schroedinger was getting at in the original presentation ([1]), but he seems to have been saying that a microscopic superposition like 1/√2 ( |0> + |1> ) can be amplified into a macroscopic state which (by linearity) will look like 1/√2 ( |dead> + |alive> ). The problem is that there's no reason to believe that this is the case. Operationally, what it means to be in the state 1/√2 ( |0> + |1> ) is that when you measure with respect to a basis containing the state 1/√2 ( |0> + |1> ), you get that outcome with probability 1. No similar definition is possible with the dead-or-alive wavefunction, because it's impossible to measure along the axis 1/√2 ( |dead> + |alive> ). Since you can only measure in the dead/alive basis, the wave function might as well be a classical distribution 1/2 (dead) + 1/2 (alive). Probabilistic superpositions aren't new to quantum mechanics. What's new and strange is the way classical observables are mixed together in the wave function, and that doesn't apply here.

Additionally, there's not even a good theoretical justification for describing the system with the wave function 1/√2 ( |dead> + |alive> ). Cats, even when dead, are thermodynamic systems in constant interaction with their environment. You need to use the density matrix to describe this, not the wave function, and what you'll get is an almost exactly classical probability distribution, 1/2 |dead><dead| + 1/2 |alive><alive|. Even if you suppose, implausibly, that the box is perfectly insulated and apply the wave function to the whole box, I can still come along and claim that the wave function collapsed long before you opened the box, and you have no way to prove me wrong. In fact nearly any interpretation except many-worlds will predict that the collapse happens before the signal can grow large enough to break the vial, much less kill the cat. Even people like Wigner and Stapp who think consciousness has something to do with it are likely to believe that cats are conscious. -- BenRG 23:44, 21 August 2007 (UTC)

You can replace the cat with a computer that records the result of the quantum event and one hour later emails that result to the scientist - which would allow Copenhagen interpretationists to argue that the email remains superposed until someone reads it. A reasonable theory obviously shouldn't care whether it's a cat or a computer that's inside the box. I personally believe that many-worlds is by far the simplest explanation - but I also recognise that this is definitely a controversial viewpoint. SteveBaker 05:40, 22 August 2007 (UTC)

Psychomotor Retardation

What are the sympotms of psychomotor retardation and is it cureable/treatable?

I've created a new section for the OP. We have a stub article on psychomotor retardation. Wikipedia is not a source for medical advice, so if you're asking for such, please consult a doctor. Splintercellguy 03:42, 21 August 2007 (UTC)

Travel adaptors

My roommate is a student from Cambodia on a study abroad program.. his laptop power brick ends in a frightening power plug with big blades and a spike! He brought a little travel power adaptor so that he could plug it into our power socket.. with wide eyed horror I insisted that he plug it in across the room, lest he fry my computer when the device fails. My question is: are these travel adaptors safe? How can a AC-to-DC power converter just work on some random cambodian power network, and then suddenly (literally) adapt to 120V/60Hz? And will plugging it in across the room do anything to protect my power supply? :) By the way, I already saw our article on the subject, and it didnt help --froth^t 03:54, 21 August 2007 (UTC)

What do they look like? A simple cubic structure with your local plug on one side and his local socket on the other? Or is like a slab or box with something more in between? If it's the first one it's simply changing the physical contacts and maintaining direct electric contact between the two incompatible plugs, and doesn't contain any electronics at all; If it's the latter it's probably a transformer and some regulators that converts American voltages to the voltage that most of the world uses (240V). Either way it's not gonna blow up your computer (unless you have a very bad power supply and it happens to send a surge through the mains). --antilived^{T | C | G} 04:20, 21 August 2007 (UTC)

It's the first. Like I asked before, how does the power brick handle the unexpected electricity specs? --froth^t 04:25, 21 August 2007 (UTC)

I believe they can automatically switch between ~120V and ~240V, the same range of voltages any US made power supply can handle. Just take a look at the back of your own laptop's supply and see its specs. Someguy1221 05:20, 21 August 2007 (UTC)

See also Switched-mode power supply. When I went to Dublin last year (from the US), I just had a small set of adapters. When it was time to plug in my laptop or digital camera, I simply found the adapter that took my friendly-looking two blade American plug and converted it for the gigantic socket in my hotel room. The power supplies took care of recognizing the higher voltage/lower frequency and putting out the 5 or 12V DC that my electronics wanted. --LarryMac | Talk 15:53, 21 August 2007 (UTC)

For many of these power adapters, they don't actually "switch" between 120 VAC and 230 VAC power. Instead, it's more accurate to think of them as being "satisfied" by any voltage greater than (say) 100 VAC and they won't blow up until they get some voltage higher than 240 VAC. They're also happy with any frequency greater than 50 Hz and (probably) less than 400 Hz. That is, their internal electrical design is sufficiently flexible that any power source within those ranges of voltages and frequencies will satisfy their needs; they automatically adapt to any power sourcer within those ranges.

Atlant 12:32, 22 August 2007 (UTC)

Your friend's adaptop is not likely a voltage transformer. According to some quick Googling, Cambodia's power system operates at 50Hz, but voltages are either 120v or 230v. It is possible that the laptop's power brick is accustomed to accepting 120v/50Hz, but just has a different style of plug. Additionally, AC to DC converters are notoriously satisfied when being provided with any voltage between 100v and 250v, such as my laptop, cell phone, and camera charging perfectly while traveling in Italy, which uses 230v.

It is probably safe to use your friend's laptop with any adaptor. 71.185.112.107 14:06, 23 August 2007 (UTC)

Earth science

Why Himalayan orogeny is explained to have happened in an episodic manner that is sometimes 'faster' and at other times passing through a 'lull"?

Sorry, but the simple answer to this is that that is how it happened. As a historical event the Himalayan orogeny happened the way it did, and if the evidence suggests it was episodic, then that's what has to be said in explanations. Or was your question meant to be more along the lines of "why can orogeny occur in an episodic manner?" --jjron 10:04, 21 August 2007 (UTC)

I believe the question is why the two plates don't move together at a constant rate, but rather at a variable rate. That is, what causes this variation ? StuRat 13:00, 21 August 2007 (UTC)

Complex systems such as the convection inside the earth's mantle are not simple at all. The real question is, why would the rate be constant? Density irregularities, thermal differences - all these fluctuations, on geological time scales contribute to the rate of mountain formation and tectonic activity. Nimur 05:39, 22 August 2007 (UTC)

I believe the source of energy for the whole system is primarily radioactive decay in the Earth's core and mantle, which should theoretically be constant (or decreasing at a slow and steady rate), so some explanation is needed for how this constant heat supply doesn't lead to constant convection cells and plate movement rates. StuRat 11:17, 22 August 2007 (UTC)

Possibly internal strain energy within the mantle builds up it reaches a critical point, when is released by a period of mountain building, then it starts to build up again and repeats the cycle - a type of catastrophe theory model, or stick-slip phenomenon. The elastic-rebound theory of earthquakes works this way, on a shorter time scale. Gandalf61 13:27, 22 August 2007 (UTC)

One reason for the episodic nature of the Himalayan Orogeny is that it was not as simple as usually portrayed - it was not just two big blocks, India and Eurasia, coming together. There were island arcs, oceanic crustal terranes, sedimentary basins with various "floors", etc. that were all swept up in the collision between the two big blocks. Thus the rate of mountain building would vary depending on exactly what was going on - sometimes partial subduction, sometimes out-and-out collision, sometimes other kinds of interactions. And they were not always all head-on, either.. Cheers Geologyguy 14:30, 22 August 2007 (UTC)

pitcher plants

How do pitcher plants pollinate if they eat the pollinator? Clem 08:17, 21 August 2007 (UTC)

They don't eat the pollinator, see the reply to your identical question 3 days ago. Capuchin 09:26, 21 August 2007 (UTC)

Sorry, couldn't find it. Clem 13:37, 21 August 2007 (UTC)

No problem :) Capuchin 14:17, 21 August 2007 (UTC)

What is true

People use to fall in love at the first sight...This has happened many ion front of my eyes..OUt of this few loves have led to marriage and few have dropped...And there are another type of love which appears in lovers heart after spending a long time with them by working in same project or studying in same class or so...In this the later one can be accepted that each one understands each other in their working days and then begins to love...BUt the former case is unpredictable...How can a love at the first sight be a true love?..Isn't it due to facial attraction?..If he and she are beautiful enough to fill in their heart, then an attraction in name of love appears...So is the 1st case a true love?..As you see many such love at the first sight has proved too...what's the big thing behind this? — Preceding unsigned comment added by 122.164.117.111 (talk)

• "No, this trick won't work...How on earth are you ever going to explain in terms of chemistry and physics so important a biological phenomenon as first love?" --M@rēino 14:17, 21 August 2007 (UTC)

You get preprogrammed by several factors; your parents, tv and movies, experiences with other people, etc. then when you meet somebody who fits this preprogrammed template, you project a lot onto them. Most of the time, they don't turn out to be that ideal person you have in your head after all, even though they reminded you of him/her. Gzuckier 14:20, 21 August 2007 (UTC)

all such questions pale before the crushing power of DETERMINISM!! --froth^t 20:55, 21 August 2007 (UTC)

Which is then eaten by tiny particles, ordered so by quantum mechanics  :-p 151.152.101.44 21:37, 21 August 2007 (UTC)

Ha, determinism consumes all- it is at the very top level of science and no amount of tom-quantumerry can overwhelm it. Even completely unpredictable, random events would have happened that way anyway! Same for outcomes influenced by observation- the universe knows whether you would have observed it or not :D Not that I'm a fan of determinism, but Gzuckier's response begged a sarcastic, sweeping statement --froth^t 23:01, 21 August 2007 (UTC)

What does determinism have to do with it? In fiction, I've seen a lot of love at first sight combined with fate, which is deterministic. I've never heard of this in real life, and I always thought it only happened if fiction. — Daniel 23:02, 21 August 2007 (UTC)

"You get preprogrammed by several factors..." is what he said --froth^t 23:55, 21 August 2007 (UTC)

Pneumatics Vs Hydraulics

HI There are many systems using Pneumatics and Hydraulics for lifting or generating enormous thrust power in some stuffs like a bulldozer or a crane or maybe a driller machine or in locomotives etc...But the key point of my doubt is that which among these two technique is powerful?..A pneumatics based system(air pressure) is used in many things such as in Trains and automobiles that require air brakes at very high PSI and in some boring(earth Bore) machines for getting a water hole in earth..Such machines generate air from the big fans and compress it through various chambers and then increase it to high presure..whereas in Hydralics many applications will be based on pulling or lifting...such as brakes in automobiles, bulldozer using it to move the arm to lift or crush...and even in car crusher(correct me) too...What I understand is that air is compressible at high pressure(compression rate) where as a fluid based system (hydraulics) isn't compressible..I maybe wrong but is this correct?..Or is there any valid physics laws for this?.... —Preceding unsigned comment added by 122.164.117.111 (talk • contribs)

The compressibility and thus density isn't very important, I believe that only the pressure (in PSI or Pascals) is important in determining the amount of work done. One advantage to using hydraulics with oil as the liquid is that such a system is self-lubricating. An advantage of using pneumatics is that gases can be moved more quickly, especially over long distances, without generating as much heat. If air is used, the gas is free and does no harm when released. Water is almost free, but can rust steel. StuRat 12:54, 21 August 2007 (UTC)

(EC) See Pneumatics#Comparison_to_Hydraulics. Note that air is also a fluid; it's just not (normally) a liquid. --Sean 12:57, 21 August 2007 (UTC)

In fact, compressibility does make a difference. Because liquids aren't compressible, whatever happens at one end matches whatever happens at the other. If the brake pedal goes down, the brake pads squeeze. Period. (barring springing a leak or other failure). With gases, you can have a lot of action at one end and nothing at the other, just build up pressure. The other important factor is that when the gas is compressed, if it is released there is a lot of residual energy built up which now expends itself, which is not true with liquids. This can be useful, but more often not. For instance, when a container of compressed gas springs a sudden leak and starts rocketing around; with liquid under pressure, a sudden leak just spits a bit and that's it. Gzuckier 14:25, 21 August 2007 (UTC)

That's why one has to bleed the air out of hydraulic brake systems. If you get even quite a small bubble in your brake lines, you certainly notice how spongey your brakes feel! For systems that need a large reservoir of stored energy (like the air brakes in busses), pneumatics may be preferable because air is lighter than hydraulic fluid. SteveBaker 18:27, 21 August 2007 (UTC)

The compressibility question is actually very important. Picture two backhoes, one using compressed air and one using hydraulic fluid. Place the bucket against a rock and start trying to move it. With the hydraulic backhoe, because the working fluid is essentially incompressible, the pressure on the rock is released the instant the rock moves, even just a little, and further fluid volume (renewed pressure) needs to be manually admitted to the cylinder to move the rock further; as a result, the operator has very fine control over the motions of the bucket and the impacted rock. By comparison, with the pneumatic backhoe, the operator pressurizes and pressurizes the cylinder. Finally, the rock moves, but the pressure in the cylinder doesn't drop very much because the volume of the cylinder hasn't changed much and Boyle's law applies. So once static friction has been overcome and the pneumatic backhoe starts moving the rock, the arm on the backhoe can probably move all the way to the end of its travel and still have pressure remaining in the cylinder! The odds are that our pneumatic backhoe will proceed to hurl the rock with great force right at the operator!. A pneumatic backhoe would be almost uncontrollable.

Atlant 12:40, 22 August 2007 (UTC)

Wow! Awesome answer! Good one Atlant! SteveBaker 16:05, 22 August 2007 (UTC)

Thank you. You can tell I spent too much time staring out of my then-office window at backhoe operators working on The Big Dig. I became very impressed with the very fine level of control they had even as they dealt with many-ton forces.

Atlant 16:20, 22 August 2007 (UTC)

Fine control indeed. One thing you sometimes see at heavy equipment demos is an operator using the bucket to crack an eggshell without crushing the egg. No idea how hard it actually is, but it's pretty impressive to see it. Friday (talk) 17:35, 22 August 2007 (UTC)

Nettles

Why are dock leaves always found where nettles are growing? - Kittybrewster (talk) 11:41, 21 August 2007 (UTC)

I'm not sure that's always true - but even if it was, it shouldn't come as a surprise. When someone first got stung by a nettle, looked around to find something to ease the pain - they wouldn't have tried a plant that only grew 100 miles away! If there were a 'cure' for nettle stings, it would have to be a plant that shares similar habitats to nettles - similar soil conditions, similar moisture and sun requirements and so on. Hence, it's far from a coincidence that these plants tend to grow nearby. Sadly, I believe though that dock plants are becoming relatively rare - and I've seen plenty of places in the Ipswitch area where there were a ton of nettles - but no dock leaves anywhere to be found. SteveBaker 13:01, 21 August 2007 (UTC)

I looked for this information less than a month ago and found nothing. I hope someone knows! Capuchin 14:21, 21 August 2007 (UTC)

And Steve, Ipswitch??? Capuchin 14:21, 21 August 2007 (UTC)

Docks and nettles have similar ecologies, which is to say in a word what S.B. proposed above. They're both ruderal and thrive in the high nutrient levels supplied by fertilizers. Thus they colonise what is (sometimes sardonically) called improved land that has fallen into neglect (such plants are called "apophytes"). Plants adapted to poorer soils, consequently unable to make use of the nutrient glut, are crowded out. Some examples would be Scabiosa columbaria and, to an even greater extent, Deschampsia flexuosa. Docks still abound up here in the Scottish central belt. Can't fathom what's happening to them elsewhere. Bendž|Ť 20:48, 21 August 2007 (UTC)

Where I live in Central Europe, there are a lot of nettles but no dock leaves. As I regularly sting myself, I would be interested to know if anyone knows of any other quick herbal treatments. Regarding the question, I know nettles grow where there is a lot of nutritious waste, eg, near the septic tank, maybe dock leaves like the same kind of ground?Dianayork 21:08, 21 August 2007 (UTC)

That would be offering medical advice - which is not allowed here. SteveBaker 01:29, 22 August 2007 (UTC)

I see antihistamines advertised to treat nettle rashes but I don't have any first-hand experience with them. I'm sure that a pharmacist could sort you out. Plasticup ^T/C 03:50, 22 August 2007 (UTC)

I think that's taking the doctrine a tad far. GeeJo ^(t)⁄_(c) • 19:48, 22 August 2007 (UTC)

I didn't know that stings can be treated with dock leaves, but as for alternatives - I usually apply something wet -- Xil/talk 19:43, 22 August 2007 (UTC)

In my experience, spittle can smooth nettle stings in the absence of dock leaves. DuncanHill 19:50, 22 August 2007 (UTC)

Nettles grow better where chickens have been, Docks better where horses have been. The short term pain from nettles is nearly always only for a few minutes. (Longer pain when lots of contact is made).Polypipe Wrangler 08:31, 27 August 2007 (UTC)

isoxazole

what are the reactions and medicinally important compounds of isoxazole? —Preceding unsigned comment added by Dineshbph (talk • contribs)

Our article on isoxazole provides some information on this. If you have specific questions, we can try to help you out—but please don't post entire homework questions directly on the Reference Desk. TenOfAllTrades(talk) 12:53, 21 August 2007 (UTC)

Palmetto Bug communication

I have many precautions against bugs entering the house and surviving for very long. However, over a number of years the following scenario has occurred over and over again. I'll notice that for some reason I am unable to go to sleep as when perhaps you forget to take out the garbage and your mind will not shut down until that task is complete. Try as you will, you can not go to sleep, until you recall that the garbage needs to be taken out. In this scenario after anywhere from one day to a week or so of not being able to go to sleep you may realize that something like not taking out the garbage is responsible so you stop trying to go to sleep and get out of bed, turn on the lights and see a Palmetto Bug. My theory is that it may have crawled on you while you were asleep but also that you may have become subconsciously aware of its presence by some sort high or low pitched noise that it makes beyond the normal range of hearing. So my question is do Palmetto Bugs produce such a sound which might subconsciously alert you to there presence? Clem 13:50, 21 August 2007 (UTC)

Are you asking if cockroaches are psychically telling you that you need to put the garbage out? Capuchin 14:08, 21 August 2007 (UTC)

No, although the last consultant bill they sent me was way to high for me!...;D

No, what I am asking is if Palmetto Buds, in particular, make any kind of sound that might alert you to their presence but which is below or beyond normally audible hearing. Clem 14:20, 21 August 2007 (UTC)

Like crickets, only inaudible. Clem 18:25, 21 August 2007 (UTC)

If it's inaudible, how will you be able to hear it? Your ear doesn't have extra nerves that only connect to your subconscious mind. — Daniel 22:49, 21 August 2007 (UTC)

Not consciously audible, but still registering somehwere. Anyway, the point is, do cockroaches make a noise which could awake a sleeping person, specifically, do they make noise at the limits of human hearing? DuncanHill 22:58, 21 August 2007 (UTC)

Not maybe so much as wake a sleeping person but to keep them from going to sleep. Clem 06:07, 22 August 2007 (UTC)

I have heard them walking on hard surfaces like plaster or wallboard. The ambient noise has to be pretty low, like it usually is when you are sleeping. But I have heard them when I was awake and then found them by locating the sound. It isn't a sound like crickets make rubbing their legs together. It is just the sound of their hard chitinous legs contacting the hard surface.Alfrodull 23:01, 21 August 2007 (UTC)

Yes, this is close to what I'm thinking; a coincidental noise perhaps but also possibly a noise they more or less make intentionally, similar to the chirp(?) of a cricket or the croak of a frog, whether used for mating or saying "I'm here." or whatever. Clem 06:05, 22 August 2007 (UTC)

Maybe the cockroaches are there every night but on the nights that you sleep well you remain blissfully unaware of them. Plasticup ^T/C 03:52, 22 August 2007 (UTC)

I don't think so since no food is left out and the only place they can find drinking water is in either the kitchen or the bathroom which are loaded with baits and traps, in addition to the bedroom in precaution. Clem 06:05, 22 August 2007 (UTC)

You're kind of off topic there, but in the four years I spent in a place where Palmetto Bugs could be expected to be walking on the walls/floors/ceiling of my residence, I never slept well. Hoping you are in a situation where you can expect them not to be doing so:-) Alfrodull 04:51, 22 August 2007 (UTC)

Yes, this is a possibility too that maybe after not seeing them for awhile I forget they can still eventually enter such that I sleep well until... until... I hear them again? Clem 06:05, 22 August 2007 (UTC)

Every time that you check, you find cockroaches. Therefore it seems reasonable to suspect that they may be there on the nights that you do not check. Plasticup ^T/C 16:38, 22 August 2007 (UTC)

I agree with plasticup. Cockroaches avoid the light. Therefore at night they are moving around in the open. When you turn on the light (for any reason), surprise, there they are. This is the simplest explanation. Occam's razor says that it is therefore the most likely explanation.--Eriastrum 17:47, 22 August 2007 (UTC)

So then I first need to determine whether the bugs are also present when I am sleeping well, before an accurate conclusion as to my hypothesis that hearing them is keeping me from going to sleep can actually be reached. Clem 14:00, 24 August 2007 (UTC)

Just joining this thread... palmetto bugs, unlike cockroaches, have a distinct fluttering sound when they fly around. So, there is some sound there. As for finding out how many you have in the house, bug-bomb the place with some sort of fogger. I do it three to four times a year. Each time, I find dead palmetto bugs on the kitchen and bathroom floors every morning for a good week. It is difficult to keep them out. I've personally seen them crawling up out of the sink drain, squeezing in under the back door, hanging out along the edge of the front door waiting for me to open it so they can come in. -- Kainaw^(what?) 14:19, 24 August 2007 (UTC)

telescope design

on all telescopes using mirrors you have to have a small mirror at the focal point to reflect the image to where your detector is. but off course having the small in the way of the big mirror means that a) you have a small area that's unusable on the big mirror and you would get diffraction happening round the small mirror's support struts.

why is it then that astronomers don't just angle the main mirror so that its focus is no longer between it and the stars ie it focus of to one side (like making a telescope a V shape with the main mirror at the intersection of the two sides) surely this would allow better images to be formed as you can use all of the mirror and you wont have diffraction problems? is it that either its not much of a problem or does my idea cause more problems then it solves?--Colsmeghead 14:35, 21 August 2007 (UTC)

The size of the central obstruction caused by the secondary mirror is pretty tiny relative to the total area of the primary mirror, so the answer usually boils down to 'it's not worth the hassle'. Mounting the secondary mirror off-axis would add a great deal to the size, complexity, and cost of the telescope and its mounting; it's also likely to add unusual asymmetric distortions that would bug the hell out of scientists trying to do anything quantitative with the instrument.

Worse still, the shape of the primary mirror would not be a nice simple surface of rotation. In order to move the focal point off-axis, the mirror would have to have a complex shape. This increases the cost of manufacturing, and also increases the likelihood of errors. TenOfAllTrades(talk) 15:00, 21 August 2007 (UTC)

Actually, there are such telescopes - they are called Schiefspieglers, and most follow a design published by Anton Kutter in 1958. There is an overview here, construction drawings here, a picture here and a copy of Kutter's original article here. The design appears to be mainly used by amateurs, so I imagine that, as Ten says, the problems outweigh the benefits for professional use. Gandalf61 15:30, 21 August 2007 (UTC)

Those are some great links. The third link above seems to summarize the problem with using a Shiefspiegler design for large instrument:

"The tilt of the primary mirror...induces significant image errors (astigmatism and coma) in the central part of the image (and even more off-axis).

A defined tilt of the secondary mirror...can produce the same image errors with opposite sign and allows for its compensation.

Unfortunately, these errors can not be compensated completely, because the optical design owns not enough degrees of freedom. The image errors can be minimised by realising Schiefspieglers with small apertures and low f-ratios (smaller than about f/18)."

In other words, the flaws of the instrument are minimized if you make it very long and with a small aperture—exactly the sort of things you don't want to have to do when you're trying to construct a large telescope. That article also describes a system that gets around most of the aberration by using a three-mirror system, but that has the drawback of involving four reflections (loss of light, introduction of distortion) and requires two large mirrors. I can see where they would fill an interesting niche for hobbyists, though. TenOfAllTrades(talk) 19:07, 21 August 2007 (UTC)

Plus, astronomers love those cool little starbursts caused by the struts. --Sean 17:42, 21 August 2007 (UTC)

Plus you don't have this problem with catadioptric telescopes. --80.229.152.246 21:59, 21 August 2007 (UTC)

Which problem do you mean ? A catadioptric scope doesn't have struts to cause diffraction effects, but the secondary mirror still blocks some light. Gandalf61 10:10, 22 August 2007 (UTC)

Just FYI: The "off-axis" design is pretty commonly used with microwave dish antennae.

Atlant 12:50, 22 August 2007 (UTC)

Hyperventilation

In American films and TV programmes, one often sees characters hyperventilating and being given a paper-bag to breathe into. However, I have never (in real life) heard of anyone actually hyperventilating. Is it more common in the USA than in Britain? DuncanHill 14:47, 21 August 2007 (UTC)

I suspect the the film industry – as they usually do – have taken a not-particularly-common disorder and enjoy overusing it as a plot device for comic or dramatic effect. You may be shocked to discover that American film and TV writers are sometimes prone to laziness and will resort to stock clichés in lieu of actual research or creative writing.

From this link, hyperventilation syndrome (HVS) may affect up to 6% of the general population. (But of course one should take that 'up to' with a hefty grain of salt.) Acute hyperventilation (the panicking, breathe-into-a-paper-bag, tingling, possible-loss-of-consciousness, saw-it-on-television sort) has a fairly low incidence. It represents only about 1% of total HVS cases. Unless you're a physician, you'll probably never run into an acute HVS case. TenOfAllTrades(talk) 15:12, 21 August 2007 (UTC)

Thank you, I had suspected something of the sort. DuncanHill 15:15, 21 August 2007 (UTC)

I particularly enjoyed this part of your excellent link -

Prehospital Care:

Because respiratory distress or chest pain has many potentially serious causes, this diagnosis should never be made in the field. Even when a patient carries a prior diagnosis of HVS, transporting patients with these complaints for a more complete evaluation than is available in the field is prudent. Rebreathing into a paper bag is not recommended in the field. Rebreathing should not be initiated in the ED until after more serious etiologies have been excluded. Deaths have occurred in patients with acute myocardial infarction (MI), pneumothorax, or pulmonary embolism misdiagnosed as HVS and treated with paper bag rebreathing.

So lazy scriptwriters may be killing people! DuncanHill 15:20, 21 August 2007 (UTC)

Indeed, I have often wondered if dangerous misleading of people shouldn't be punishable ("There should be a law against it!" :) ). How often does one see someone in a film crash a car and walk out merely in a daze? Even a crash at low speed (by car standards) is easily lethal, even when wearing a seatbelt. The misconceptions based on that lie are bound to have cost thousands of lives (considering over 30 million people have died in car crashes). Ironically US movies are chuck full of warnings against smoking but promote unsafe driving, which is much more lethal (and to other people to boot). DirkvdM 18:53, 21 August 2007 (UTC)

Well what are you supposed to do? OK so they may have an even more rare condition, making paper bag rebreathing fatal, but are you seriously going to stand there refusing to give a dying person the paper bag that they're screaming for? "WHAT IS WRONG WITH YOU I NEED A PAPER BAG OR IM GOING TO DIE!! THIS HAPPENS TO ME ALL THE TIME I KNOW WHATS WRONG WITH ME!" "sorry, can't do a field diagnosis, have to get you to a doctor.." --froth^t 20:58, 21 August 2007 (UTC)

I suspect that if it happened all the time, that person might just take the precaution of keeping a paper bag about their person. DuncanHill 22:55, 21 August 2007 (UTC)

Of course the knowledge that it may in fact be harmful is quite useful but I just couldn't help but take exception to "Rebreathing should not be initiated until after more serious etiologies have been excluded." I guess it's not as much of an issue if you're in a hospital since they can just be resuscitated, but I wouldn't want to be that patient who they let turn blue and pass out while waiting for tests --froth^t 21:01, 21 August 2007 (UTC)

While this is only a one-sample case, I used to hyperventilate when I was little (4-10 yrs. old). My mother (a nurse, my dad was a pediatric emergency doctor) would give me a paper bag and it would always calm me down. I was always supervised, and I don't know whether the effect was biological or psychological. Micah J. Manary 23:07, 21 August 2007 (UTC)

Interesting, I wonder if it could act in the same way as giving someone a hat if they feel sick (nauseaus). DuncanHill 01:33, 22 August 2007 (UTC)

It may be overused on TV, but I don't think acute hyperventilation is all that rare. Someone who is excited or shocked could easily hyperventilate. People with phobias come to mind. I have a friend who hyperventilated in front of me and passed out.
Mrdeath5493 03:53, 22 August 2007 (UTC)

DNA

Every human being has DNA that is completely (100%) distinguishable from any other human being. The only exception is twins (or triplets, etc.), who have the same DNA. So, first of all ... is my understanding correct so far? If so, when you take the case of twins ... is there any way whatsoever to distinguish their DNA or is the DNA a 100% match such that it is completely impossible to ever distinguish? Also, does this hold for all twins (identical and fraternal), or just the identical ones? Thanks. (Joseph A. Spadaro 17:10, 21 August 2007 (UTC))

Fraternal (dizygotic) twins share as much genetic material as between any two siblings of the same mother and father, they're just carried in the same womb. Apart from any mutations that occur after the zygote divides into the two fetuses, identical (monozygotic) twins have identical DNA. Fraternal twins have a higher likelihood of having identifiably different DNA than identical twins. It'd be difficult to distinguish identical twins by DNA alone, because they're essentially clones. However, they'll have different fingerprints and other characteristics defined by the environment. -- JSBillings 17:41, 21 August 2007 (UTC)

Regarding distinguishing identical twins by DNA alone: would it be merely "difficult" or scientifically impossible? (Joseph A. Spadaro 21:02, 21 August 2007 (UTC))

Barring any mutations that may have occurred, their DNA is 'exactly' the same. Most mutations will probably be destroyed with the mutant cells, so yes, their cells should have exact replicas of DNA. Micah J. Manary 23:05, 21 August 2007 (UTC)

On a bigger note, human DNA is not practically 100% distinguisable from other humans. It is true that (non-id. twin) people have completely different DNA sequences. It is ridiculously unlikely that two people would ever be born with the same DNA sequence, or even a vaguely close DNA sequence. But gel electrophoresis can get contaminated or misread (this is the most common method for DNA criminal matching etc). In this sense we may not distinguish, even if the people are different. Other problems include using other people's organs, blood, marrow, etc. which would retain the donor's DNA.

If we could sequence people's DNA quickly (isn't this an X-prize goal?) then we could be sure. Micah J. Manary 23:05, 21 August 2007 (UTC)

Note that when people do DNA identification they are only looking at a dozen or so sequences that are known to be independent of one another and with a high degree of variability (though exactly how high depends on the assumptions you make about the specific population are talking about—the rates vary by region, so assumptions about who you are testing can make the surity of the test drop by a few orders of magnitude). In most practical cases you don't need anywhere near 100% to distinguish between people. --24.147.86.187 23:10, 21 August 2007 (UTC)

Yep - in court cases where DNA identification is given, the forensics guy will give a probability of a match between some sample found on the crime scene and the supposed perpetrator. However, a mismatch is a much more certain thing. SteveBaker 18:31, 22 August 2007 (UTC)

I have another question on this topic, I understand that its highly impossible 2 people to have matching finger prints but is there proof to show this, and not on a couple thousand people in a survey, i mean out of 6 billion people is it impossible to not have 2 people that have the exact same finger print. I understand the science against my question but cant be satisfied until i see proof on the matter. If you wish to email me you can do so at a.marsters@hotmail.com, any assistance on this would be appreciated -- [User A.Marsters] 22:13, 02/02/2010 +12GMT

unidentified bird, mammal, insect

Hi. Recently I saw a bird on a power line. It was an estimated 2 in tall, and yellow. Its call, if I remember correctly, was a high-pitched chirp. Recently I saw this mammal. It looked almost exactly like a black squirrel. However, it was apparently much smaller, and its tail was so small that it was barely distinguishable. Finally, I saw this insect. It was light milky brownish-yellow, and about half a millimeter long. It typically is seen on old paper or wood. Can someone help identify these animals? If it helps, I live in southern Ontario. Thanks. ~AH1^(TCU) 17:30, 21 August 2007 (UTC)

The insect sounds like a termite. -- Kainaw^(what?) 17:38, 21 August 2007 (UTC)

The bird could be an American Goldfinch, although they're a bit bigger that 2 in. -- Flyguy649 ^talk _contribs 19:15, 21 August 2007 (UTC)

Hi. Thank you for your answers. However, I've seen a black winged termite before (presumably male?), and they're much larger than the bugs that I've been seeing. If they are termites, however, they would be female. The thing is, the bugs that I've seen are around 1/1000 the volume of a regular winged black termite. They are most likely not nymphs/larvae/juveniles, because the nymph/larva/juvenile of the bug is around 1/10 the volume of its adult. The article does not say how big it is, though. I found a website that said normal termites are around 1/8 of an inch. The bugs I am describing are more like 1/50 of an inch. If they are too small to be termites, could they be aphids or dust mites? If they are smaller than 50 microns in length, however, I'd probably have a lot of trouble seeing them. The bird does kind of look like an American Goldfinch. I only estimated their height by crude angular measurement, which is like trigonometry except done without a calculator and less accurate. Since the base of an equilateral triangle is longer than its height, I now estimate the bird to be around 3 in tall. I do admit that, becasue of potential innacuracies, they could be as large as 5 in tall. I'm not sure about the colour of their wings, though. Since the one I saw had a bright yellow breast, it's more likely to have been a male. There's also another bird I wanted to identify. It was bright red (not orange like a robin, but deep bright red, with some orange-red areas), and a bit smaller than a robin. It was seen about 500 m to the west of the yellow bird(s). Do you think the mammal was more likely to be a black rabbit or a black oversize chipmunk or a squirrel who had its tail mutilated, or something else? Thanks. ~AH1^(TCU) 23:37, 21 August 2007 (UTC)

Hi. Can someone please answer that last part? Also, I recently saw another yellow bird. It was seen in a river, and had black parts on its wing. It was actually about 2 in tall, and this time, almost small enough to be mistaken for an insect, particularily a large bee. Could it be another goldfinch, a beebird, a hummingbird, etc? It was seen north of another area near a river with ducks, canadian geese, and continental seagulls. What could it be? Thanks. ~AH1^(TCU) 01:35, 26 August 2007 (UTC)

Conjoined twins

What if, by chance, one conjoined twin committed murder. However the other twin tried, in all possible ways, to prevent this from happening. How will the murderous twin be judged? I mean, you can't sentence one to death/life in prison while the other is innocent. Another question is what if one female twin decides that she wants consensual sex with a man but the other twin (assuming they are joined at the waist) refuses this to happen. Can that twin charge that man for rape? --WonderFran 18:30, 21 August 2007 (UTC)

It's an interesting question although as far as I know, one that has remained hypothetical only. There's at least one film [2] on the subject, and quite a bit of discussion of the topic easily accessed via google. Donald Hosek 18:47, 21 August 2007 (UTC)

Note: a civilised society doesn't have the death penalty in the first place and life sentence only in very extreme cases. So that softens the dilemma a bit, but doesn't make it go away. One could of course make an exception for such an exceptional case. Have there ever been any such cases? I suppose a different kind of punishment could be devised. An interesting idea would be to have them separated (if the other twin gives their consent). Now this often comes with a risk, but one could decide to do it in such a way that the other twin is in no danger and the criminal twin takes all the risk. If the operation is successful, then the offender can be punished as a separate(d) person. Of course then a new problem arises - can a medical treatment that entails a risk be forced on someone in the course of a punishment? Consider this: suppose a wrongdoer is so unfit for prison life that imprisonment would almost certainly have a seriously damaging psychological effect on them (which must happen quite often). Well, they should have thought of that beforehand, shouldn't they? Maybe some people are too stupid to realise the consequences, but can that ever be an excuse in a court?

Linguistic note about the second question: if she want sex it's necessarily consensual, so that was a tautology. :) Also, why should it be a she? DirkvdM 19:11, 21 August 2007 (UTC)

Well of course WP has the plot summary of Chained for Life that Donald Hosek refers to above. - hydnjo talk 19:20, 21 August 2007 (UTC)

The positive side is that there will always be a witness to the crime! :D Sorry… —Bromskloss 23:07, 21 August 2007 (UTC)

Dirkvd - your agrument contains so many tangents that it hardly answers the questions let alone make sense. It is known that there have been rare cases where a female has raped a male however difficult it be so. To make things "easier" I chose female twins than male. I threw in "consensual" for legal sake. You can want sex when your drunk and not remember the next day. But in legal jargon, consensual means consensual.... --WonderFran 19:30, 21 August 2007 (UTC)

Hmmmmmm. These are extremely interesting legal questions. However, I am sure they have rarely -- if ever -- been encountered in the real world, as opposed to the hypothetical world. That being said, one can simply ask: How are other (i.e., non-legal) matters handled? Then, perhaps, there can be some transferability from those non-legal principles to legal principles. I mean, there must be millions of non-legal examples that still make your point, WonderFran. Example: Twin A wants a medical treatment, Twin B does not. Twin A wants to go to bed at midnight, Twin B does not. Twin A wants to go to the beach, Twin B does not. Twin A wants to sit in a Chemistry Class for 2 hours, Twin B does not. Twin A wants to listen to an Elvis record, Twin B does not. Twin A wants to wear a blue dress, Twin B does not. Etc. Etc. Etc. Granted, these are not exactly the same as the legal hypotheticals that you proffer. Nonetheless, if we can answer the non-legal dilemmas (i.e., how to handle the beach or Elvis disagreement), perhaps we can begin to imagine how the legal system would handle the legal dilemmas. Of course, this is all academic, as the legal dilemma you describe is hardly apt to happen. But, personally, I would love to know how these conjoined twins even begin to handle these other (more trivial) dilemmas. And as interesting as your legal dilemma is, it will probably never really occur. However, a dilemma equally interesting that could very well occur someday is: Twin A consents to the medical operation / surgery to separate them, but Twin B does not consent to this operation. I wonder how the medical community would handle that? (Joseph A. Spadaro 21:17, 21 August 2007 (UTC))

Or what would be even more interesting to contemplate is the case of persons with a split brain. “Split-brain” is when the corpus callosum which connects the right and left hemisphere of the brain is cut. The result is essentially 2 consciousnesses within 1 body. Each side capable of potentially holding different reasoning capabilities and belief systems. I recall a speaker from the beyond belief conference by the name of Ramachandran, a Professor of neuroscience, who gave the example of a split-brain patient whose left hemisphere of the brain was an atheist while the right side was religious! A similar thing could happen if the sides differed on other values and morals. Perhaps 1 side could have pre-meditated a murder while the other objected to it but was powerless to stop it (since some parts of the body are controlled by 1 and not both hemispheres). No chance for splitting the twins here :(.70.49.136.89 22:13, 21 August 2007 (UTC)

A conjoined twin shares at least some of its organs with its twin (at least the blood, I would think). So if one twin were dead, wouldn't the other also die, at least eventually? In any case, wouldn't the dead twin have to be removed surgically before it became gangrenous?--Eriastrum 19:04, 22 August 2007 (UTC)

I wonder if there really are only so many question in the world, and if so, have we reached that limit?

• Wikipedia:Reference desk archive/July 2005 II#Legal dilemma arising from a random pub discussion.
• Wikipedia:Reference desk/Archives/Science/2007 April 25#Snakes (odd title, I know, but stick with it)
• Wikipedia:Reference desk/Archives/Humanities/2007 April 26#polygamy and adultery

-- Rockpocket 00:08, 23 August 2007 (UTC)

boat in current

A boat is to cross a river of width L to a dock directly opposite. The speed of the boat at full throttle in still water is constant = V. When crossing in constant current C, the boat is continuously directed at full throttle toward the dock on the opposite shore. At what angle A* will the boat dock? —The preceding unsigned comment was added by 71.102.172.150 (talk)

• Please do your own homework. Flyguy649 ^talk _contribs 20:18, 21 August 2007 (UTC)please don't remove valid points. This is obviously copied from elsewhere if you look in the edit window -- Flyguy649 ^talk _contribs 00:17, 22 August 2007 (UTC)

Math desk? Intuition tells me that it'll approach parallel with the shore as the river gets wider, as long as the current is more powerful than the vertical component of the boat's velocity even at extreme angle. I expect this has a fairly complicated answer --froth^t 21:04, 21 August 2007 (UTC)

Your intuition is wrong! SteveBaker 16:02, 22 August 2007 (UTC)

Vectors (This is not homework....) Since my remarks on this matter were removed from the math desk, I will attempt to pursue the matter here. As SteveBaker noted Froth's intuition was wrong. Note that the boat is continuously pointed at the opposite dock. Imagine a line between the boat and the dock along which the boat is reeled as it swings out in the current. As long as the speed with which the boat is reeled toward the dock = V - C cosA, where A is the angle along which the boat is pointing, then this is equivalent to the original problem.

Qauntum Decay

Leaving quantum immortality aside could someone enlighten me on the weird result of quantum mechanics with respect to decaying radioactive substance like in the Schrödinger’s cat experiment. Suppose there are 2 nuclei in a radioactive substance, 1 of which will decay in the substance’s half-life. Which 1 will decay is a matter of pure chance without any “hidden variables”. Now, besides telling me how my intuition fails me, could someone describe to me (or give me a link to) the physical/mathematical (I’m looking for the technical stuff here) of how this doesn’t violate causality (or the law of conservation of momentum) because, conceivably, 1 particle could go in one direction while the other in another direction, so what caused the decay in the first place and how is momentum still conserved?70.49.136.89 21:34, 21 August 2007 (UTC)

To answer the last part of your question, momentum is always conserved in any radioactive decay event. Summing up the momenta of each individual resulting particle will always give you back the momentum of the original particle. A substantial amount of the momentum can end up in the hands of photons (gamma rays) and more exotic species like neutrinos (which are nearly impossible to detect); this can make balancing the energy and momentum books more challenging. (To a casual observer, it will appear that the decay product particle suddenly shoots off, acquiring momentum from no apparent source.)

If you want to avoid any sort of hidden variable theory, then there isn't any deterministic process that governs the time until the radioactive nucleus decays; the directions that it and its other decay products go will be likewise random, as long as the process conserves momentum. If you'd like, you can invoke a many-worlds interpretation of quantum mechanics and say that every possible decay does occur—but you only happen to observe the one that ends up in your timeline.

You might find our articles on the interpretation of quantum mechanics helpful. TenOfAllTrades(talk) 21:56, 21 August 2007 (UTC)

The nuclei will form a wave function which takes into account all possible outcomes, and then, if you measure it, the wave function collapses into one of these possible outcomes. Which is randomly determined, by chance. ΦΙΛ Κ 22:01, 21 August 2007 (UTC)

STS-3xx

I was reading about the space shuttle recovery missions in the aboe article. It states that in some situations in International Space Station can be dropped into a lower orbit to pick up the crew of a stranded shuttle. I was wondering (as the article doesn't say) is the ISS itself recoverable after this? Or is it down an irrideemable path once it has left its orbit? SGGH ^speak! 22:21, 21 August 2007 (UTC)

Quite recoverable. Even if neither the damaged shuttle nor the rescue shuttle is able to boost the ISS back to its normal orbit, plans call for a Progress resupply vehicle to be launched, which, after delivering its cargo, can be used to put the ISS back in place. --Carnildo 23:54, 21 August 2007 (UTC)

Interesting, thankyou SGGH ^speak! 00:10, 22 August 2007 (UTC)

randomness mechanism

After classical physics, how does quantum mechanics just storm on in and introduce the concept of randomness? How can anything be truly random and not determined by previous events (even if previous events are non observable)? Where does the randomness come from, it makes no sense! Does quantum mechanics give any sort of explanation for what mechanism provides randomness? Or does it just dismiss chaotic systems and arbitrarily call it "random"? How is radioactive decay of a particular atom truly random and not just determined by tiny variations the stability of the atom? --froth^t 23:12, 21 August 2007 (UTC)

The "mechanism" of randomness is still a topic of debate (many worlds interpretation and the competing Copenhagen interpretation). A common source of misunderstanding of the nature of quantum randomness comes from the attempt to graft classical concepts of measurable values onto quantum wave-particles. Before the Heisenberg uncertainty principle it was often claimed that if one knew the momentum and position of every particle in the universe simultaneously, one would know the entire future (now, you can say that Heisenberg's principle makes it impossible to know this, but it was already impossible as it would take more matter than exists to store that information anyway :-p It's the idea that matters). So, a lot of novices think that in quantum there is a limit to your ability to know the position and momentum of a particle. The truth of the matter is that a particle doesn't even have a single defined position and momentum in quantum! The randomness comes from how the particle "decides" what position to occupy when an event occurs that would classically reveal its location. Think of Schrodinger's cat; it's not that we don't know whether the cat is alive or dead, but rather that it is alive and dead until an event occurs that would reveal which. Someguy1221 23:26, 21 August 2007 (UTC)

Tell that to the cat.. --froth^t 23:52, 21 August 2007 (UTC)

Classical physics is really only about medium sized objects going medium to long distances (I know these terms are purposely vague). Small objects (like fundamental particles) with very strong forces (the nuclear forces) were never considered. Similarly, relatively gives us a different picture at very great speeds and scales. Relativity can replace classical physics and it keeps all its predictability, for large enough objects.

As for randomness, its true that the ball you just threw always goes along a predictable path. For small particles (leptons, bosons, the such) a new theory was needed to describe their motion. The observation came first, just like in classical physics. Will the concept of randomness always exist? Maybe. The classical physics model was replaced by general relativity, so current quantum mechanics could easily be replaced. You might try reading uncertainty principle or ask about which random process you are most curious.

You may also be interested in grand unified theories, which put all of quantum mechanics, relatively, and the interaction of all forces on the same 'page'. Micah J. Manary 23:20, 21 August 2007 (UTC)

I think you're asking why physicists assume that the randomness in quantum mechanics is real randomness and not just a sign of an approximate description, as in classical Brownian motion. Well, they don't as such. But it's turned out to be very difficult to come up with any underlying system that quantum mechanics could be approximating. All of the reasonable-looking ideas are theoretically and experimentally ruled out. See hidden variable theory. -- BenRG 00:02, 22 August 2007 (UTC)

Well sort of the way I think about it is.. hm well OK how about quantum entanglement. Two particles interact so that they have certain special characteristics that relate them.. for example when one is positive spin the other is negative.. but there's no evidence that since that first interaction they've interacted at all.. as far as we know it's just a predetermined script, and due to "The Way Things Work(TM)" and the nature of the initial interaction, the scripts are automatically synchronized in a predetermined way. There's no actual interation and no spooky action at a distance. I recall the concept of weird, complex systems of equations (or setups in conway's Life) that seem reasonably stable for millions or billions of iterations but then explode wildly.. couldn't something similar be going on with entanglement? Or how about a bizarre trick where a computer across the internet is pre-programmed to (at an exact time) send you the ICMP packets that represent a ping response.. when you ping the computer, the premade response packets are just arriving at your router, so ping reports a 0ms ping. The flip to a different state would have happened anyway even if its entangled particle were never observed [or the ping was never requested], but we just wouldn't know about it [because the router wouldnt be interested in a response not registered with NAT]. Now if for example I have 2 pairs of identical, spatially separated particles that experienced identical interactions, and I observe particle B1, then observe particles A1 and A2 simultaneously.. and A1 and A2 are different, just because B1 was observed previously, then I would be pretty darn spooked (but probably write it off to experimental error due to the meaninglessness of "simultaneously" when dealing with quantum sizes).. however nothing like this has been demonstrated right? Forgive me for any gross errors but I'm a newbie at this. I'm highly unwilling to accept the spins of electrons as affecting a non-local particle.. it doesn't even make sense, what do electrons directly influence outside its own atom and atoms around it? Trying to make them into some kind of next-theory of physics has me pretty frustrated with the seemingly overcomplex theories, and very seemingly pulled-out-of-thin-air yammering --froth^t 00:40, 22 August 2007 (UTC)

There is an experimental proof that certain quantum characteristics cannot possibly be predetermined. Lemme dig up a link...Someguy1221 00:44, 22 August 2007 (UTC)

Aha! Right where I remember it [3]. Someguy1221 00:46, 22 August 2007 (UTC)

"You might argue that they could both be changing in some predictable way that keeps them in synch, but you can test (and disprove) this theory by moving one detector a little closer to the source than the other. When you do so the results are unchanged, whereas if the electrons were changing as they flew and you measured one earlier than the other you would expect again that you might get different results. If you still wanted to say they were changing as they flew then you would have to say that the instant one of them was measured the other for some reason stopped changing so that when you measured it later it gave the same result as its partner." LOL how does this prove that they're not changing in some predictable way? This is basically saying "we can't see how the pattern of change could complex enough to give the same result even when we move the sensor, therefore it can't possibly be changing. QED." Um what if the pattern dynamically changes over time to adapt to if I'm sensed right now I'd better be positive because my dynamic changing is synchronized with that of the particle I interacted with back there, and he'd be positive if he were sensed at whatever point down the road.. I'd find it much easier to accept (not to mention much more fascinating) if the particles operated on some fantastically complex, non-temporally-dependant, highly interdependent (AT THE TIME/PLACE/WHATEVER OF INTERACTION, NOT THE CURRENT MOMENT) pattern of oscillation such that they always read the same--- than to accept that they totally violate locality. IMHO pysicists can't just slap a "well that fundamental tenant that has never been disproven doesn't really fit into our new thories so it's outdated and false" on locality and call it science.. and while I'm thinking about it, isn't there a universe where the 2 particles released by a random emitter just HAPPEN to be the same every single time? Isn't that something to be considered as well? I just see so many gaping problems and unsolved questions with quantum theory, and so many totally unsupported or adequately-proven claims in quantum theory... like that paragraph I quoted above, which is little more than "assume that the particles change slowly and regularly, not fluctuating infinitely fast and infinitely complex, taking every value at once yet when observed just then happens to take on a value according to a predetermined system at moment of interaction, so that time isn't a factor in when it's observed. Now assuming that, 'since time is a factor', moving the sensor doesn't disrupt the results therefore there's spooky action at a distance. Mhm --froth^t 01:13, 22 August 2007 (UTC)

Your idea is just the sort of reasonable-looking idea that's been ruled out. Bell was the first to show that any such approach leads to predictions that are inconsistent with quantum mechanics, and I think Aspect was the first to show that the real-world outcome confirms quantum mechanics. Greenberger, Horne and Zeilinger came up with a non-probabilistic version of Bell's result, i.e. an experiment where quantum mechanics predicts one outcome with 100% probability and any theory like yours predicts a different outcome with 100% probability. -- BenRG 01:04, 22 August 2007 (UTC)

Here's an old post of mine describing a gambling-game version of Bell's theorem: [4]. This might be easier to understand than the other articles. At least it's shorter. -- BenRG 01:11, 22 August 2007 (UTC)

The OP asks how what the cause of these random things is - but that's really the point. If they had a cause then either:

• They aren't random after all because they are caused by a non-random event...or...
• The cause itself is random - and hence they are random. But that just leaves you asking what the cause of the cause was.

Ultimately, there has to be an utterly random cause-less event. SteveBaker 01:19, 22 August 2007 (UTC)

The point is that I'm denying anything random at all.. so yes #1, They aren't random after all because they're caused by a non random event. Where do physicists come up with this idea of randomness? Just because they can't model it they call it random and independent of all history before the random value was determined? How do they prove that it's not deterministic? Even if no pattern has ever been devised, how do they know that it's not just a sequence that repeats after a hundred billion trillion times? How can they possibly prove that randomness is random and not some inscrutable complexity that may be unobservable due to physical limitations but nevertheless totally non random? It seems like they're just claiming it as a fundamental tenant rather than actually trying to prove it --froth^t 01:40, 22 August 2007 (UTC)

Wait, wait. Am I to believe that the decay of a uranium particle has no cause, or at least that some event causing/leading up to its deacy has no cause? That is not scientific at all. Under such circumstances how can QM ever lead to a theory of everything if there is always at least 1 unexplained event NECESSARILY embedded into it!? If I were to flip a coin a billion times but show you only the result, you could very well be tempted to say the result is utterly random, and, seeing as you could never find out the factors associated with the flip (or the decay of an atom) becuase the universe's laws prevent you from seeing anything but the result, you will never know that it is actually deterministic in nature. Even if it is theoretically impossible to measure or deduce the mechanism by which something occurs becuase the act of measuring disturbes the original state (or is simply hidden from all possible observations), doesn't mean there wasn't a "real" state to begin with. "Absence of proof is not proof of absence." If there are multiple states or positions of a singular particle, only one of which is actually "revealed" to the observer, then there must be a reason for that particular state as opposed to another. Otherwise, science would remain an incomplete view of nature forever, which means there's no reason to assume the validity of a theory of EVERYTING based on QM if it can't explain EVERYTHING.67.70.131.238 03:18, 22 August 2007 (UTC)

OK so the decay of a uranium atom has no cause...yep - that's true. Well, to be exact - it decays because it's an unstable combination of neutrons and protons, so that's the "cause" - but we're really asking why it chose to decay at that exact point in time...but that is truly random, with a statistical distribution that matches the half-life of whichever isotope you're talking about. If you think about it, it has to be. All of the bazillion atoms in a uniform sample of uranium could be utterly identical. How would roughly half of them know to decay within (whatever the halflife of uranium is) while the other half do not? They don't talk to each other and agree what to do - yet the half-life stays remarkably stable over a range of temperatures and pressures and other conditions. It can only come about for the same reason that if you flip 100 coins, about 50 of them will come up heads...it's random.

Coin flips are somewhat random for an entirely different reason - chaos theory. The result of a coin flip is very sensitive to the "initial conditions" - ie the precise force you applied to the coin at the beginning, how you held it, etc. That extreme sensitivity makes it really hard to flip a coin so it'll reliably come up heads because the slightest amount of variation of force (either more or less) will result in the opposite outcome. We deliberately pick 'random number devices' like flipped coins, dice, magic-8-balls, etc such that they have that sensitive dependency that makes them almost impossible to predict. Now, there are some classical (non quantum) setups for which that sensitivity to initial conditions is INFINITE - that is to say, an infinitely small change in initial conditions (the force on the coin - whatever) will result in a change in the outcome. An example of such a system is the double pendulum. These systems exhibit true randomness without the needs for weird quantum effects. So, I'm afraid you'll have to just get over your dislike of this aspect of the universe - you're not alone in hating it - Einstein famously said "God does not play dice"...well, both he and you are wrong about that. The laws of nature have randomness built right in. Like it or not - that's it.

How do scientists know that this randomness is not merely an experimental error? Well, read Uncertainty principle - it explains that this aspect of quantum theory comes from the mathematics - it's not some experimental result that could be misinterpreted. The mathematical derivation is in the article. SteveBaker 05:28, 22 August 2007 (UTC)

I used the example of something like coin flips specifically as a non-random event as it has direct causes which explain the effect (gravity, surface texture, spin rate etc). Chaos doesn't imply non-casual or non-determined. In fact the opposite. In studying chaos we try to find (in mathematics) an equation (say) that describes an apparently random set of values. It is exactly the point I was trying to make. Chaos implies causality but at the same time, unpredictability, that is, that the system is too complex for us to be able to solve, nevertheless dependent on certain causal factors which a hypothetical entity like God, having all knowledge of initial conditions and laws of the universe, would be able to predict the outcome, however chaotic it may seem to us, of the experiment. Chaos isn't random, rather it is the apparent randomness caused by small changes in initial conditions which has a large DIRECT causal effect on the outcome. Even your double pendulum is deterministic[5][6]

As for decay, it can be modeled statistically in a deterministic way. The decay of a dead animal for example (or many other chemical reactions), still exhibits an obvious half-life yet is not dependent on quantum theory rather it has direct causal factors like surface area, concentration of bacteria etc. As for the example of uranium it is utterly false to say that exactly half the number of atoms will decay after its (expected) half-life. It is only the average, so it is not necessary that half of the uranium atoms “know” that the other half did decay so they wouldn’t. They could be decaying because of their own internal clocks of some sort which could be affected by factors like when the uranium atom was created in the first place and conceivably other factors that affect the stability of the atom. The half-life is only an approximation that works better with more atoms (to average it out) but if you would be wrong to say that given a sample of any 2 Ur atoms, 1 must decay after the (expected) half-life.67.70.131.238 06:05, 22 August 2007 (UTC)

Chaotic events are only theoretically predictable - because in theory, you can know all of the initial conditions to infinite precision and you have perfect ('classical') knowledge of all of the rules of the universe. However, in practice, you can't do the math to infinite precision - all computational devices have finite precision - and you can't measure the initial conditions to infinite precision. So in practical terms, chaotic devices are indeed quite utterly random - there is no possible way to figure out whether a double pendulum will or will not 'flip' given arbitary initial conditions. Note that truly (mathematically) chaotic devices are INFINITELY sensitive to initial conditions - that means that a (1/infinity)% change in the initial setup will produce a different result. As for half-life decay - I very carefully didn't say "exactly" half the atoms - I said "roughly". Also, it's not like the decay of an animal because it has no 'starting point'. If you measure the half life of two batches of uranium - one of which was purified from a sample produced in some kind of nuclear reactor a year ago - the other of which was just made - you can't tell the difference. The atoms don't know how long ago they were made. That's not true for dead animals. SteveBaker 15:54, 22 August 2007 (UTC)

As my own last edit before bed-time, I will risk a hand-wavy argument over this. I have often stated in both real life (and once right here on the reference desk), that quantum physics notoriously defies all attempts at explanation without using inaccurate analogies or generalizations. Events as described by quantum are entirely the result of the all powerful wave-function, and the operators that act on it. To fully and truly understand the proofs of why all theories non-quantum trying to describe the quantum are actually wrong requires a profound understanding of quantum itself (as evidenced by the near imposibility of placating all concerns originating from a sufficiently smart human being with no advanced education in the field. Alternatively you could claim that anyone who studied that much quantum is actually insane, and that's why the explanations don't always make sense, although the counter to that is they've designed some darned neat stuff). I consigned myself some time ago to stop trying to understand it, and simply answer the questions on my problem sets and tests. Someguy1221 06:53, 22 August 2007 (UTC)

That's a powerful point that I feel is never sufficiently strongly made. You can argue that it's nonsense and not possible and raise all sorts of objections - but the annoying problem for people who argue that is that the PC they are typing on at the instant they raise those complaints wouldn't work unless our description of quantum effects was significantly close to the truth. If you swallow your 'evolved-to-be-an-arboreal-ape' brain's objections and just do what the math says - then you can use quantum weirdnesses to make all sorts of useful real-world, macroscopic devices. We've only just scratched the surface of this with things like flash memory - just wait until we have those near-magical quantum computers that can do (essentially) infinite amounts of parallel calculations using superposition - or quantum cryptography in which you can use a variation of Schroedingers cat to tell you whether your email has been 'observed' by the bad guy depending on whether certain quantum entanglements are still present. This stuff is "indistinguishable from magic" as Arthur C Clarke would say. SteveBaker 15:54, 22 August 2007 (UTC)

Just as a note, if you feel like the random aspects of QM are distressing and confusing and potentially wrong — you're not alone! This was essentially Albert Einstein's objection against it, that QM was really just an "incomplete" theory that would someday be superceded by one that would get rid of these "you just have to accept that it is random." Was Einstein right? Not entirely. Some of his specific objections have been shown to be wrong (see EPR paradox vs. Bell's theorem), but there are other possibilities for recovering Einstein's "dream" and getting around the Copenhagen interpretation. You might check out this recent exchange in the New York Review of Books between two physicists, which I think demonstrates well that this is more alive an issue than your average physics student is taught. --24.147.86.187 12:47, 22 August 2007 (UTC)

Sea Shells

Hello, I have some sea shells from South Carolina that I got from a vacation. They were dead... I have tried everything from boiling them to bleaching them and I cannot get them to stop smelling. Any ideas?

Thanks!! --Zach 23:17, 21 August 2007 (UTC)

Baking soda is a traditional deodorizer - I have never tried it on sea shells, but it would not harm them. ON NO ACCOUNT USE ACIDS - acid will eat your shells! We did have a similar question about (I think) starfish a while ago, but cannot recall the outcome. DuncanHill 23:22, 21 August 2007 (UTC)

You say "they were dead". What kind of shells? Sand dollars or conch shells? A conch shell will smell as long as there is some rotting conch meat still buried deep inside. They are a pain to clean - which is why it is best to get one that is empty (usually meaning the crabs picked it clean). Sand dollars are normally taken (illegally) while they are still alive. If they are not bone-white, they are alive. All those little fuzzy looking things are the animals "legs". They smell as they rot. The guts inside the shell also smell as they rot. Since it probably died being out of the water so long - your best bet is to leave it in the sun until it bleaches white. Then, it will stop smelling. It is common to put it in water mixed with white glue to help strengthen it. Unlike other shells, they break with the slightest bump. -- Kainaw^(what?) 02:52, 22 August 2007 (UTC)

I would think that you need a no-scrub, soaking cleaner. I have used one called PBW (stands for powdered brewery wash). Homebrewers use it to clean hard to reach areas of brewing equipment. However, it would likely meet your needs. It removes thick organic deposits that you can not scrub as long as you soak it long enough. I'm fairly sure that it won't break down CaCO2. Just to be sure, though, you might soak a small disposable seashell in it before using it on larger ones. You can buy it from Northern Brewer @ this website.
Mrdeath5493 03:32, 22 August 2007 (UTC)

Here we leave shells with meat in them near an ants nest outside. Ants will get inside and pick them clean. Graeme Bartlett 03:59, 22 August 2007 (UTC)

I wonder if you can't treat them like bones -- boil them until the meat falls away. As a bonus, you'd also get some totally nasty soup. --Mdwyer 20:05, 22 August 2007 (UTC)

August 22

Medicine - The Spleen

Why does it appear that males are more suseptable to accidental damage to the spleen than females? Wally3178 —Preceding unsigned comment added by Wally3178 (talk • contribs)

What makes it appear that way? Mrdeath5493 03:21, 22 August 2007 (UTC)

I would take a guess that male humans are more likely to have accidents than females, as they do more risky things. There are more likely to drive fast, try extreme sports or want to take on that dare for a thrill. Graeme Bartlett 04:02, 22 August 2007 (UTC)

(edit conflict stole my sarcastic thunder) Spleen injuries tend to be impact related. Men tend to do more stupid physical stuff. I hope that is technical enough for you. Plasticup ^T/C 04:04, 22 August 2007 (UTC)

Also, men are probably more likely to falsely claim spleen trauma, which I imagine is what prompted the original question. -- BenRG 11:43, 22 August 2007 (UTC)

Really? I have never heard of anyone pretending to hurt their spleen. It seems like a rather wimpy organ to pick. If you are going to lie, go for something exciting like a liver or a kidney. Plasticup ^T/C 16:41, 22 August 2007 (UTC)

is this right?

I'm thinking BS on this one. What could the speed at which you lower objects into it matter at all? In all cases, (I believe) you can lower it in and there's no additional tautness on the rope as you lower it even if it goes all the way down to singularity, but you're completely unable to budge it a nanometer outward.. and the effect is exactly the same whether you're moving it fast or slow. This section seems to be implying that if you go slow enough, you'll never even reach the event horizon and so no matter how much rope you play out you can always pull the guy back in. Is there any basis for this theory? --froth^t 00:26, 22 August 2007 (UTC)

You're right, the article is wrong. The event horizon is a finite distance away, and if you extend more than that much rope, it will go through. You'll never see it go through, because the light can't escape either.

You can't lower an object gradually all the way to the singularity, though, because once you're inside the event horizon there's no such thing as a stationary (dangling) state. Your rope will break -- it's a physical impossibility for it not to. -- BenRG 00:43, 22 August 2007 (UTC)

You can slow it down though, and if you have a really strong (and stretchy) rope shouldn't you be able to hold on long enough for it to reach the center and 'dangle' (hang there moving very slowly downward) for a bit? --froth^t 01:42, 22 August 2007 (UTC)

I just watched a documentary on super-massive black holes. It mentioned that many scientists believe the event horizon around them is fundamentally different than a regular black hole's event horizon. You can pass through the event horizon (which means a rope could pass through). Once through, the incoming matter will collide with matter trying to escape the singularity - turning it all into a scorching mess of exploding particles. So, there's no possibility of the rope reaching the singularity - but it could get past the event horizon. Of course - the documentary could have been a bunch of bull. At least I didn't see Michael Moore in the credits anywhere. -- Kainaw^(what?) 02:47, 22 August 2007 (UTC)

I'd call BS on that as well, at least working under a purely GR system (quantum relativity may prove me wrong). The only significant difference between a supermassive black hole and a normal black hole (of a couple of solar masses, say) is that tidal effects near the event horizon are negligible, so you won't be "spaghettified" when you pass through it. And it's not like the event horizon is a magical wall that lets you in and doesn't let you out again, it's the boundary where all time-like and null curves (i.e. those travelled by massive particles and photons, respectively) point inwards, so there's no way you'd run into particles "trying to escape the singularity" - at best you could accelerate yourself into the path of slower-moving particles but I don't think it would be much worse than running into them out in normal space.

I'm pretty sure froth is right - the rope going through the event horizon would pull on you, stretching further and further, until either (a) it breaks just outside the horizon, or (b) it pulls you in with it. Confusing Manifestation 06:56, 22 August 2007 (UTC)

In a Kerr black hole there are two event horizons, and the inner one is also a surface of infinite blueshift -- as you approach it you see the entire future of the outside world compressed into a finite time. This would certainly fry you, and may be what the documentary was talking about. Also, if you got past that, the singularity is timelike, so you might indeed run into something emitted from it. But I doubt very much that the interior portion of the Kerr solution has physical significance, and if it does then it applies equally to black holes of all sizes.

What you said after "I'm pretty sure froth is right" is right, but I'm not sure it's what froth said. Given an arbitrarily strong rope you can dangle things arbitrarily close to the event horizon, but not arbitrarily close to the singularity. (edit: Well, not from outside the hole. Once you've passed through both event horizons, I don't think there's anything in general relativity that prevents you from toasting marshmallows on the singularity.) -- BenRG 11:54, 22 August 2007 (UTC)

So what's keeping the rope from passing the event horizon? Sure you never see it pass the event horizon (what would this even look like from the ship's point of view? would the rope just get longer and longer out into the vanishing point of the 3d perspective?) but from the end of the rope's point of view it's gettin fried by apocalyptic energies inside the black hole --froth^t 02:11, 23 August 2007 (UTC)

Nothing keeps it from passing the event horizon, but there's no way to transmit tension from outside the horizon to inside. Inside the event horizon there's no such thing as a stationary (suspended) state -- the light cones point inward, and "staying in the same place" would require superluminal motion. In the Kerr solution, you can suspend an object above the singularity by a rope attached to a rocket that's inside both horizons, but not by a rope that crosses one or both horizons. -- BenRG 17:26, 23 August 2007 (UTC)

Whoa whoa whoa, you mean to say that the rope could actually pull you in with it? What if due to an extraordinarily powerful engine on your rocket ship you were hovering just above the event horizon and dangling a rope down and holding it so that it falls very slowly, and somebody down inside the event horizon tugs on the rope intermittently, sending a morse code message if you're measuring the pull on the rope? Seems impossible, yet inevitable if the rope can "pull you in" --froth^t 02:08, 23 August 2007 (UTC)

If you lower part of the rope past the event horizon, the rope must either break or fall through in one piece. If it falls through in one piece, and you don't let go, then by definition you fall in too. That's all ConMan meant by "pulls you in". -- BenRG 17:26, 23 August 2007 (UTC)

Could one (in theory) orbit the singularity indefinitely while inside the event horizon, just as you can orbit it outside the EH? --Sean 13:37, 22 August 2007 (UTC)

No, inside the event horizon all the timelines move towards the singularity, so no orbits are stable. Even outside the event horizon there is a zone where no orbits are stable and you would fall in if you did not have that rope holding you up! Graeme Bartlett 22:13, 22 August 2007 (UTC)

Power used by a car

Hello,

I am trying to determine the average power used by a car in joules or watts. I know it varies from car to car and from terrain to terrain but I am trying to get an idea.

Thanks, Bryan

The power produced by the engine (in kiloWatts) is frequently stated for European cars - but in any case, simply multiply the horsepower number by 0.746 to get kiloWatts. However, that's the peak output of the engine - most of the time it's going to be a lot less. Also, if you are interested in the energy USED by the car, a typical internal combustion engine is only 20% to 30% efficient. So, take my car (a 'tricked out' 215hp MINI Cooper'S) - 215hp is 160kW when it's redlined - but at 20% efficiency, we're consuming the equivelent of 800kW of energy from the gasoline. But most of the time, the engine isn't running at full power, so 80kW at the output of the engine (and 400kW of fuel consumed) would be about right for my car. SteveBaker 01:07, 22 August 2007 (UTC)

Spelling note: it's "kW" with capital W, but "kilowatts" with no capital. All metric units named after people work that way.

The 160 kW is right, and 20% efficiency is plausible, but I don't believe the last set of numbers. The problem can be seen by looking at the other part of the question and speaking of joules, which measure energy, not power. According to Wikipedia at gasoline#Energy content, one liter of gasoline produces about 34.6 megajoules (34,600,000 joules) of energy. (Checking other random sources on the web I see somewhat different numbers, but that's in the right ballpark, anyway.) So for Steve's car to be burning fuel at a rate that produces 400 kW of energy, it must be consuming 1 L every 34,600/400 = 86.5 seconds. That's 11 US gallons in an hour. You wouldn't get far on a tank of gas at that rate.

I think a car in a steady cruising state is actually running at much less than half of its full power. If someone can find figures for the air and frictional resistance of a car at highway speeds it might be interesting to look at the energy consumption that way. But if we assume that the cruising state is actually at 1/8 power and Steve's other numbers are right, then it takes 4 hours to burn 11 US gallons, during which you might drive 240 miles, giving about 22 miles per gallon, which is in the right ballpark at least. So I suggest Steve's final set of numbers are too large by a factor of something like 4.

--Anonymous, August 21, 2007, 03:26 (UTC).

Hmmm - good point about joules vs watts - of course you're right. As to the numbers being too large...well, for my car, horsepower is about proportional to RPM. 160kW is at 7000 rpm - redline. In 6th gear at 70mph, I'm turning about 3500 rpm. So roughly 80kW ought to be what the engine is putting out. Possibly the 20% efficiency number is wrong - I got it from internal combustion engine, but if I'm off by a factor of 4 then the car would have to be 80% efficient and that's not possible for any heat engine. I'll go away an look at the numbers more carefully tomorrow - I need sleep! SteveBaker 05:04, 22 August 2007 (UTC)

<offtopic> A computer programmer...sleeping? Steven, for shame...Someguy1221 05:11, 22 August 2007 (UTC)<offtopic>

Technically, I said I needed sleep - not that I was actually going to get any! :-( SteveBaker 15:35, 22 August 2007 (UTC)

Well, the mistake here is to assume that half the engine speed means half the power. If you're driving up a hill (on a straight road, and not one steep enough to downshift), you'll step on the gas and maintain the same speed at a higher power level. Conversely, go down a hill and you may be doing the same 3500 rpm at 70 mph with your foot off the gas pedal. This shows that engine speed does not depend on power alone. Your car may develop 160 kW of power at 5000 rpm under some conditions (gear and gradient), but under other conditions you could hit the red line before it ever got to 160 kW. Heck, that's why there is a red line: because the engine is capable of developing enough power to go above 7000 rpm and maybe destroy itself. --Anonymous, August 21, 05:30 (UTC).

Toads and warts

Can a human really catch warts from handling a toad? --Kurt Shaped Box 01:36, 22 August 2007 (UTC)

These sites say no. The second says that "[a] possible source of this myth are the poison glands located on the backs of some species of toad. People who develop an allergic reaction to the secretions from these glands may get bumps that look like warts." — Matt Eason ^{(Talk &#149; Contribs)} 03:17, 22 August 2007 (UTC)

Thanks. I thought that it was an old wives' tale - but it seems to be very deep-rooted. I remember being on a school field trip as a teen and hearing another kid being shouted at for picking up a toad. The (science) teacher was like "OMG! Put it down now! You don't have any cracks in your hands do you? Go wash them now! Don't touch your face! You'll get warts!". I know otherwise sane and rational people who just have to 'greet/salute the lone magpie' too. --Kurt Shaped Box 08:19, 22 August 2007 (UTC)

Aw, but you gotta admit — terrifying children sure is fun! --24.147.86.187 13:08, 22 August 2007 (UTC)

insuline

to maintain the sugar balance of one of my patient i would like to suggest dose of human mixtard insuline of concentration 50:50 as 20 units before breakfast and dose of human mixtard insuline of concentration 30:70 as 8 units before dinner............... so my Q. is whether using this type of combintions at same time is advisable or not? and r there any drawback of of this type of treatment? please help me..... —Preceding unsigned comment added by 59.95.16.110 (talk • contribs)

Please read the medical disclaimer. We cannot give medical advice. — Matt Eason ^{(Talk &#149; Contribs)} 03:05, 22 August 2007 (UTC)

I seriously doubt you are treating a patient. If you are, you might consider going back to medical school.
Mrdeath5493 03:19, 22 August 2007 (UTC)

And ask the patient to wait till he completes his medical course ? ;-) -- WikiCheng | Talk 05:03, 22 August 2007 (UTC)

Per WP:BITE and {WP:NPA it is sufficient to cite the medical disclaimer, without the need to attack and insult the questioner. Those new to Wikiedia may not be familiar with the "no medical advice policy." Thanks. Edison 14:36, 22 August 2007 (UTC)

PHYSICS D/L

I am unable to download the artiicle on 'Physics': the main page is opened , pictures etc uploaded and then the phrase '1 item missing ' appears, which prevents d/l at my end! Clear the glitch if you may. ……Autistic49 04:20, 22 August 2007 (UTC)

If you mean Wikipedia, then the article works fine for me. What's your browser? Splintercellguy 04:42, 22 August 2007 (UTC)

Physics seems to be working here as well. Maybe you have a proxy server problem, if not a browser problem. Nimur 05:49, 22 August 2007 (UTC)

*Jumps on the spot*. Yup, working here too. Capuchin 09:16, 22 August 2007 (UTC)

I dunno - I think my string theory might be broken. :-) SteveBaker 15:32, 22 August 2007 (UTC)

BOTANY

Smallest chromosome number in angiosperms 2 is seen in which plant 123.108.203.82 9:48 UTC did not sign the question.

Please do your own homework.

Welcome to the Wikipedia Reference Desk. Your question appears to be a homework question. I apologize if this is a misinterpretation, but it is our aim here not to do people's homework for them, but to merely aid them in doing it themselves. Letting someone else do your homework does not help you learn nearly as much as doing it yourself. Please attempt to solve the problem or answer the question yourself first. If you need help with a specific part of your homework, feel free to tell us where you are stuck and ask for help. If you need help grasping the concept of a problem, by all means let us know. --Sean 14:10, 22 August 2007 (UTC)

sea

why water in seas flows towards bank? are waves occur bec of collision between coming water towards bank and returning water from bank? —Preceding unsigned comment added by Prasanth prav (talk • contribs)

The reason waves come towards the shore is that they are produced in the ocean and not by the land. So waves will always be travelling towards the coast when you are at the coast. There is a secondary diffration effect where waves approaching a coast with a shelving floor will be turned around to approach more perpendicularly. Graeme Bartlett 09:54, 22 August 2007 (UTC)

I don't buy your first answer (think about a large circular island in an infinite ocean). The diffraction answer is the correct one. Water waves slow down in shallower water (especially when the depth of the water is less than about one and a half wave lengths). So if you imagine a gently shelving beach and a wave approaching it from far out at sea at 45 degrees - the part of the wave that hits the shallower water first slows down and the part that's still over deep water doesn't. So the deep water part quickly catches up with the shallow water part until they are both moving over the ocean bottom at the same depth. This makes the wave turn inwards so it's coming in parallel to the beach because that's the only way that the entire length of the wave can be travelling at the same speed. You can see this most clearly in a curved bay where a wave entering the bay bends outwards to precisely follow the line of the beach. In cases where there is no gently sloping bottom (eg where a cliff-face drops straight down into deep water), the waves crash against it at any angle they happen to be moving at. In the case of that large circular island in an infinite ocean - the waves will come ashore all around the island - including on the side where the waves are generally moving away from it! SteveBaker 15:30, 22 August 2007 (UTC)

May be the question and answer are not clear enough. In the case of the circular island in the large ocean, the island will block waves coming from the other side of the island, so on the eastern shore, there will be no waves coming from the west (or north west or south west). Graeme Bartlett 23:43, 22 August 2007 (UTC)

That's not true though - the refraction effect will wrap waves around to the back of the island. You'd expect maybe dead calm water? Nope - you still get waves. SteveBaker 00:52, 23 August 2007 (UTC)

On the OP's question, note that waves do not involve the "flow" of water. Waves move, but the water does not move with the wave (not much anyway). See Ocean surface wave and Ocean current. Pfly 04:01, 23 August 2007 (UTC)

Right. If you put a neutral-bouyancy object into the ocean, it moves with the water in a vertically circular motion. As the depth of the water starts to get close to the diameter of that circle, the circle is forced to squash down into an ellipse - until right at the edge of the beach, the water is moving horizontally up and down the beach. The act of squashing that circle down into an ellipse extracts energy from the wave and therefore slows it down. Which is the cause of the diffraction effect described earlier. SteveBaker 22:43, 25 August 2007 (UTC)

Waves carry energy. That energy is provided by winds and other forces in the open water, and is dissipated as friction at the shore. Therefore waves travel towards the shore. For waves to travel away from the shore, something would have to exert energy to move water up and down at the shore. --Spoon! 02:23, 25 August 2007 (UTC)

That's bogus. Suppose there was a planet that was all ocean with no islands - what would happen with the waves then? What you are describing is akin to arguing that sound waves get sucked into your ears! SteveBaker 22:43, 25 August 2007 (UTC)

Death by Fire

I have heard that when people die in a house fire, it is typically from smoke inhalation (that is, they can't breathe) and not from the burns / flames of the fire per se. However, if the human body is set afire / burned, what would be the specific biological reason / cause of death? What exactly would you die from? In other words, would it be organ failure, heart attack, shock, ... what does the fire do to the body that causes the death? Thanks. (Joseph A. Spadaro 08:49, 22 August 2007 (UTC))

Burns victums can have massive fluid loss, and after a while major infections. The heart would probably stop when there was not enough blood. Graeme Bartlett 10:04, 22 August 2007 (UTC)

Pertaining to death while burning, there is also suffocation. Attempting to breath flames will damage the throat and lungs to the point that the person cannot continue to breath. This may be considered organ failure of the lungs. -- Kainaw^(what?) 11:02, 22 August 2007 (UTC)

Not to mention the effects on the brain.. I'm not exactly sure how this works, but think of how delirious you get when you have a 10 degree (F) fever.. imagine a 1000+ degree fever. --froth^t 02:05, 23 August 2007 (UTC)

This is a bit of a circular argument. In the contemporary definition of death there really is only one answer to any question that ends with "what would be the specific biological reason / cause of death?" And that is "cessation of electrical activity in the brain" which is caused by lack of oxygen. No matter if you fell from a great height, had cancer, a heart attack or were burned alive, ultimately you die because your brain doesn't get enough oxygen. Vespine 06:38, 23 August 2007 (UTC)

That's not true for situations in which your brain is destroyed (if what's left is spread out and open to the air, it could very well have plenty of oxygen). Someguy1221 06:52, 23 August 2007 (UTC)

But your brain does not have the capacity to process oxygen out of air, only your lungs can do that, your brain can only get oxygen out of blood. What you are saying is like saying you couldn't die of thirst stuck on a boat in the middle of the ocean since you are surrounded by water, when in fact, that's probably the 1st thing you'd die of. Vespine 00:50, 27 August 2007 (UTC)

physics

what is the use of neutral wire in a circuit?

Neutral wire. Just because it's called neutral doesn't mean it actually does nothing. The Neutral and Live wires are both "live", they form the circuit. Capuchin 09:55, 22 August 2007 (UTC)

Electric current flows in a circuit, rather than just one way down a wire. This means that current flowing from a wire from a power point has to return someway. The desirable way is for the current to return in a neutral wire. The neutral wire will have a voltage near earth potential much lower than the active wire. However don't rely on this as a power point may have wires reversed by accident. In a three phase system if the currents are not balanced in the three phases, some current will return on the neutral wire. Graeme Bartlett 10:00, 22 August 2007 (UTC)

When electricity flows one way on one wire for a while and then stops we call it "static electricity." Current electricity requires a return path, which is the neutral. Household wiring normally has a "phase" wire which is at the highest potential from ground, a "neutral" which is connected somewhere near the main circuit panel to a ground, and a "ground" or "earthed" conductor, which is present for safety, to provide a return path to ground in the event there is a circuit fault, such as a frayed wiring on the phase conductor allowing it to touch the grounded outer metal shell of an appliance. Edison 14:24, 22 August 2007 (UTC)

"Neutral" means neutral with respect to ground. Properly designed, there is never a potential between the neutral wire and the person. SInce people are often connected to ground, the neutral wire is normally grounded. It is code to ground the neutral wire at point of entrance in residential and most commercial locations to ensure that it is neutral with respect to ground. In a standard 120/240 single-phase entrance, the neutral is the center tap of the transformer. In 120/208 three-phase system, the neutral is the center of the wye transformer. In 120/240, three-phase systems the neutral is the center tap of one coil of a delta transformer. In all cases, the neutral is grounded to ensure that it is neutral to people. --Tbeatty 06:47, 23 August 2007 (UTC)

Conjoined Twins

Referring to my earlier question, has there ever been a case known or documented that there were three or more twins conjoined? If that is not possible, please explain why. I am trying to sound smart to my little nephew..... thanks! --WonderFran 12:18, 22 August 2007 (UTC)

A web search for "conjoined triplets"[7] suggests there have been several cases of conjoined triplets and quadruplets.--Shantavira|^{feed me} 13:56, 22 August 2007 (UTC)

If you want to sound really smart, I'd respectfully suggest you drop expressions such as "three or more twins". That might tend to confuse a lot of little 'uns. -- JackofOz 02:21, 23 August 2007 (UTC)

THREE twins!? That would be six conjoined kids! --24.249.108.133 03:10, 23 August 2007 (UTC)

Maybe he/she means three sets of conjoined twins? :-P Nil Einne 01:27, 24 August 2007 (UTC)

How many islands are there?

This question could be split in two, oceanic or inland, I am interested initially in oceanic islands but the other would be interesting too.

For anyone interested in the geography of islands, the following link is amusing, and is what set me off on this train of thought: http://www.elbruz.org/islands/Islands%20and%20Lakes.htm

— PhilHibbs | talk 14:13, 22 August 2007 (UTC)

I think this is another unanswerable question along the lines of Coastline of the United Kingdom - you might start off by counting the islands you can see at the scale of a 1" to 100 miles map - then discover that if you got a 1" to 10 miles map, you'd see a lot of smaller islands that you missed before. When you ran out of high-precision maps, you'd go and visit one of the islands - only to discover some very tiny islands - just a few feet across - scattered around it. Closer up, you'd find large rocks protruding from the ocean and have to conclude that those too have to be counted as islands. Where do you stop? Individual grains of sand on the beach are technically islands in that they are bits of land surrounded by water. The answer is 'fractal' - and in just the way that you can't come up with any kind of a number for the length of a coastline, I'd argue that you can't ever count the number of islands. SteveBaker 15:19, 22 August 2007 (UTC)

Still, you might like to start counting them with the help of our list of islands.--Shantavira|^{feed me} 18:10, 22 August 2007 (UTC)

As with the coastline question, there is no problem with getting an exact number from any of several sources - the problem is that it's doomed never to be "correct". Perhaps if a minimum size of island were specified? SteveBaker 18:22, 22 August 2007 (UTC)

The tinier bits of this volcanic archipelago near Iceland form and erode on time-scales of a few days.

There's also a fallacy in assuming that islands are permanent. How many islands are there at any given instant? This is not even a question of geologic time; Jolnir and Surtsey are examples of large island formation (and total erosion) in the time scale of weeks. Nimur 18:32, 22 August 2007 (UTC)

Light Bulb Pressure

What kind of pressure is the low pressure inert gas in a standard tungsten filament bulb? Light bulb doesnt give a ballpark figure. Capuchin 15:21, 22 August 2007 (UTC)

I have always assumed it was roughly atmospheric pressure (since nothing dramatic happens if you break an ordinary incandescent lightbulb: you get neither a noticeable explosion nor implosion), but I have no data at hand to back that up. The point of the gas is to partially offset the vapor pressure of the tungsten that would otherwise boil off the filament owing to the very high heat of the filament. I've always (further) assumed that "low pressure" was just a comparative with other lamp types such as quartz-halogen lamps. In QH lamps, the filling gas is at a fairly high pressure and these lamps have been known to explode, especially upon failure of the filament (when the brief arc can overheat the filling gas)..

Atlant 16:33, 22 August 2007 (UTC)

according to these lecture notes [8], it's 0.01 - 0.1 torr. That would be for a light bulb that's actually evacuated (as used to be the usual case). Apparently, though, many light bulbs are now filled with argon and nitrogen at somewhere below atmospheric pressure; in that case the pressure probably changes a lot with temperature. --Reuben 16:45, 22 August 2007 (UTC)

The first practical light bulbs in the 1870's 1880's, with a carbon filament, had to have the vacuum pumped down to an excruciatingly hard vacuum, because any residual oxygen caused early burnout, and because the convection currents of an inert gas also buffeted the fragile filament and caused early failure, as well as cooling the filament and lowering light output. Today only small tungsten filament bulbs have a vacuum, and those over 20 watts or so have an inert gas fill. I have tried carefully venting such a modern 60 watt bulb under water to collect the internal gas and found that it is roughly 3/4 of an atmosphere, but manufacturers could provide a more accurate figure. [9] which is the site of Universal Industrial Gases, Inc., an Argon supplier says "93% argon and 7% nitrogen at a pressure of 70 kPa (10.15 psig)." This would be 69% of atmospheric pressure. When hot, the pressure would increase considerably. [10] says that tungsten halogen bulbs use several atmospheres of fill pressure. Modern tungsten filaments are a fine wire tightly coiled, which resists the cooling effect of the gas. Edison 17:13, 22 August 2007 (UTC)

Those early vacuum bulbs were a popular plot point in old movies. The good guy is trapped without a gun by the bad guy - so he unscrews a few light bulbs and at a strategic moment tosses them across the room. Aparrently they imploded with such an impressive bang that it sounded much like a gunshot going off! This idea carried on well after that kind of bulb were no longer around! SteveBaker 18:18, 22 August 2007 (UTC)

Why is warm cheese more flavorful than cold?

Just curious why room temperature cheese has more flavor than the same cheese that has been refrigerated? --24.249.108.133 15:26, 22 August 2007 (UTC)

I imagine it has to do with increased volatility of odour molecules when cheese, or indeed any food is warm. (Most of what we call taste is really smell; taste is only sweetness, saltiness, bitterness, and sourness. Oh and umami). The cold cheese may also affect the way the taste buds sense as well. Flyguy649 ^talk _contribs 15:38, 22 August 2007 (UTC)

I find this is true of many many foods. When beer is ice cold, you taste it less than when it's a bit warmer than that. (Of course if you're drinking ice cold beer you probably don't WANT to taste it..) Friday (talk) 15:45, 22 August 2007 (UTC)

Errr.. it isn't? Or at least, it depends on the cheese.81.83.82.123 21:10, 22 August 2007 (UTC)

In the interest of science, I propose that the submitter eat cold cheese through his nose to see if it taste better. --Tbeatty 06:52, 23 August 2007 (UTC)

Swallowing toothpaste

Toothpaste (esp. with fluoride) always caution people not to swallow the toothpaste, but what happens to a person if he really does swallow some toothpaste, say, a mouthful? Thanks.

I would imagine Fluoride#Toxicology might give some information. Rawling4851 16:00, 22 August 2007 (UTC)

Also see Toothpaste#Ingredients_and_flavors near the bottom re: nausea. Many toothpastes contain detergents such as SLS that would irritate mucous membranes in the digestive tract if present in high concentrations. -- Flyguy649 ^talk _contribs 16:33, 22 August 2007 (UTC)

At last, I discover why some toothpastes make me urge. DuncanHill 19:37, 22 August 2007 (UTC)

When I was younger no one ever told me not to swallow it. I didn't learn that until a teacher mentioned it in 3rd grade and I seem to be alright. Plasticup ^T/C 16:43, 22 August 2007 (UTC)

Nothing said on Wikipedia may be taken as medical advice, per the disclaimer at the top of the page. The tube of Crest says ""Keep out of the reach of children under 6 years of age. If more than used for brushing is accidentally swallowed, get medical help or contact a Poison Control Center right away." This also presumably applies to the deliberate swallowing of the product. See also Fluoride poisoning. Edison 16:47, 22 August 2007 (UTC)

Toothpaste, especially the thick pastes of most popular brands, is a choking hazard in young children, which is another reason why it should be kept out of their reach and only very small (pea-size or smaller) quantities used. Flyguy649 ^talk _contribs 19:01, 22 August 2007 (UTC)

I don't know how much flouride is in toothpaste in relation to the flouride in those trays at the dentist, but when I was about 10 years old I swallowed a whole mouthful of delicious orange tasting flouride... the most intense stomach pains I've ever experienced before or since.... x_X --froth^t 01:59, 23 August 2007 (UTC)

Far, far less flouride is in toothpaste. StuRat 02:34, 23 August 2007 (UTC)

I knew a guy who had stomach ulcers because of fluoride in the water. He drank bottled water, but the fluoride wasn't filtered out (a lot of filter companies advertise that they don't filter fluoride out like it's a benefit). Juanita Hodges 21:24, 23 August 2007 (UTC)

It generally is a benefit, in the quantity added to drinking water. If I were a betting man I'd wager that the tiny amount of fluoride added to tap water had nothing to do with your friend's ulcers. --24.147.86.187 23:49, 23 August 2007 (UTC)

Astronauts swallow toothpaste regularly. It is simply the easiest way to get rid of it in space, where water is in short supply and everything tends to float around heading for expensive electronics.

Children can develop fluorosis if their adult teeth are not in. While not the end of the world it is not a pleasant-looking condition and cannot be reversed (you can cover it up, but that's about it). --24.147.86.187 23:47, 23 August 2007 (UTC)

helium ballons

hi all, i think i know the answer, but wish to run it past the collective anyway. Our children have several of the small, cartoon character shaped, helium filled 'foil' ballons; nemo, piglet etc which have retained all their gas and ergo there shape for upto several years, but any large, round 'birthday' ballons we have bought, seemingly made from the same material, have rapidly lost their gas (dependant on temp) after only a few days. I feel that it is a marketing ploy, encouraging you to buy more of the larger ballons, but this theory falls short, when the same ploy could be used to encourage you to buy more character ballons. Has anyone any suggestions for the disparity between their 'inflation life'? thanks Perry-mankster 15:52, 22 August 2007 (UTC)

The foil balloons are made of mylar. Assuming the large ones are also mylar (and not latex like most cheap balloons), it could be a quality issue. If the mylar used for large balloons is made from lower quality mylar, it may have larger pores that allow the helium to escape. Another possibility is that the larger balloons have more seam length. Seams are likely to be the weakest part of the balloon. As for marketing, I have no idea. Flyguy649 ^talk _contribs 16:10, 22 August 2007 (UTC)

Pre-made balloons may have a heat-sealed filling point, whereas balloons bought at florists and the like probably just use some sort of clamp; I'd guess that most of the difference in leak-down rates occurs there. Latex balloons, of course, leak through pores in the latex; remember that helium is the smallest "molecule" so it is very capable of leaking through the tiniest holes. This is what makes it valuable in leak detection: see Helium mass spectrometer.

(Yes, I know I'm using "molecule" in a rather loose way, but I wanted to capture the idea that a diatomic H₂ molecule, the next most-likely competitor, is larger than a helium atom.)

Atlant 16:44, 22 August 2007 (UTC)

I wonder whether the 'character' balloons had more paint on them too? It's possible that the paint seals up whatever teeny-tiny holes the mylar might have? It's a long shot though. Mathematically, we know that seam length is smallest (as a proportion of volume or surface area) in a circular balloon - so I don't by Flyguy's 'seam length' argument unless the two classes of balloon are radically different in size (which in itself could explain everything). I like Atlant's answer best - the nature of the seal has to be critical. SteveBaker 16:57, 22 August 2007 (UTC)

Note that helium will leak through the spaces between molecules even if there isn't a hole. You can (slowly) collect helium out of the atmosphere by just pulling a vacuum on a sealed glass container. Part of the reason why people thought they had cold fusion. Gzuckier 17:25, 22 August 2007 (UTC)

If the "round" balloons are latex, there is a lot of pressure forced on the contents of the balloon because the balloon is attempting to shrink down to the original size. This gives the helium inside more incentive to escape any way possible. The mylar balloons I've seen do not stretch. Therefore, they lose helium primarily due to standard osmosis at a much slower rate. But, if both balloons are mylar, this explanation is useless. -- Kainaw^(what?) 17:31, 22 August 2007 (UTC)

Yeah - it's very clear that rubber balloons leak helium in a matter of hours where mylar balloons with hold helium for at least a week or two - maybe longer. But the OP said that they were "seemingly made from the same material" - so that doesn't answer the question. (V.Cool about the cold fusion experiment though! Thanks for that Gzuckier.) SteveBaker 18:15, 22 August 2007 (UTC)

You're welcome. A guy I used to know was a physics prof whose specialty in the 80s was cold fusion debunking. Making things even more complicated is that glass which has been exposed to the atmosphere for any length of time is sort of saturated with helium, the way a sponge will be moist after you take it out of a damp environment; so even if they eliminate helium from the outside of the cold fusion reaction chamber, they still have to establish that they have de-heliumed all the glassware in the system sufficiently before detecting anything from the fusion itself. Gzuckier 16:51, 23 August 2007 (UTC)

oxidative phosphorylation

71.97.110.36 18:10, 22 August 2007 (UTC)I am trying to learn about this process. what is it and what does it do, and is it a desirable outcome? Looking at L-carnitine Fumarate- The product states:"L-Carnitine is an amino acid found in high concentrations in heart and liver tissue, where it participates in metabolizing fatty acids into energy in the mitochondria. L-Carnitine also facilitates the metabolism of carbohydrates and enhances the rate of oxidative phosphorylation". Can you explain this in an understandable statement? I am curious about this, and would like to know if this is a good thing, and is this desirable? I understand what the statement is, but not sure about the outcome?

Original questioner's email address removed - Nimur 18:39, 22 August 2007 (UTC)

Have you looked at Oxidative phosphorylation? This is a particular biological chemical reaction involved in the metabolism, or energy use and storage, by cells. L-Carnitine is a catalyst for that reaction, helping it to occur. I'm not a biochemist, but I would think that any catalyst that enhances the formation of ATP is a desirable thing; that is probably why the cells generate the L-carnitine. Nimur 18:42, 22 August 2007 (UTC)

The dietary supplement industry is built on vague statements such as, "L-Carnitine also facilitates the metabolism of carbohydrates". The question you probably need to ask is if there is any evidence that a carnitine supplement will provide health/fitness benefits. Some small studies of carnitine as a dietary supplement have been published. For example: Effects of four weeks L-carnitine L-tartrate ingestion on substrate utilization during prolonged exercise. The results of more clinical studies are described here. --JWSchmidt 22:18, 22 August 2007 (UTC)

Vehicles Submerged in Water

Say that you are driving your car and all windows are up. By some accident, your car (and you) ends up in a body of water. I have heard that it is impossible to roll the windows down (in order to escape from the vehicle). Is that true? Is it just hard to do ... or actually impossible? And why? Also -- a related question. If you are in the above predicament, what are the best survival techniques? Thanks. (Joseph A. Spadaro 19:47, 22 August 2007 (UTC))

The extreme pressure of the water forces the window against its frame. There's too much friction to overcome. Even though the electronics and mechanical parts still function, they are unable to generate enough force to slide the glass against the rubber frames. This was recently investigated by the Mythbusters. --Mdwyer 20:00, 22 August 2007 (UTC)

So, are you saying that it is physically difficult to do or physically impossible to do? If the latter ... then, once you are in that predicament, there is literally nothing that you can do? Your fate is sealed, period? And, a related question: does it matter in any way whatsoever if the window is slightly rolled down (say, an inch or so rolled down from the top) ... or that makes no difference at all? Thanks.(Joseph A. Spadaro 20:11, 22 August 2007 (UTC))

Direct link: MythBusters (season 5)#Underwater Car —Keenan Pepper 20:45, 22 August 2007 (UTC)

In such a situation, you should at least try to open up a window, or break the glass. If that doesn't work, chill. The car will gradually fill up, and once it does (doesn't have to be all the way) you'll be able to open the door. Of course, if you end up at the bottom of the ocean, your chances of survival are pretty slim..

hehe, ok next time i'm in a submerged car and the windows won't wind down i'll just chill! ;-) --Cosmic joker 21:52, 22 August 2007 (UTC)

If the car does not leak, then would the trapped air inside be buoyant enough to float the entire vehicle? Nimur 22:22, 22 August 2007 (UTC)

Temporarily, but cars leak, so the point is moot. It's enough that a car doesn't (immediately) sink like a rock, though. — Lomn 22:27, 22 August 2007 (UTC)

Some cars can float for quite a while. It was even a selling point for the VW Beetle: [11] --Reuben 22:38, 22 August 2007 (UTC)

As for survival chances - my first thought was that one could use cell phone (which probablly would be still dry) to call for help, only question is if it would be within reach ---- Xil/talk 22:49, 22 August 2007 (UTC)

Almost certainly useless, as help not on the scene already will take too long. As Keenan's link above indicates, the best survival option once you're submerged is to (1) not panic, (2) allow the car to fill with water (faster is better, so open the window as much as possible) and (3) open the door and exit when pressure permits. Faster is better because you naturally want the car to be as shallow as possible when you do exit the vehicle. — Lomn 22:54, 22 August 2007 (UTC)

Yes, if you sit and wait for help to arrive after you make the call, but you have to wait some while for car to fill with water anyway so you 1) make a call 2) wait for water 3) try to swim out. So if you manage to call help you don't find your self in middle of nowhere soaked to skin and probably injured ---- Xil/talk 23:27, 22 August 2007 (UTC)

There could be a large air bubble in the passenger compartment that may provide breathable air for quite some time (say 20 minutes). StuRat 02:22, 23 August 2007 (UTC)

As for making a call from your sinking car, how much does water weaken a cell phone signal? Someguy1221 03:22, 23 August 2007 (UTC)

I'd expect it to dramatically cut the signal strength, owing to the density of water. Being under 10 feet of water would be about the same as being under 10 feet of soil or concrete. Then there is also the issue of the cell phone being submerged in water and shorting out. StuRat 21:27, 23 August 2007 (UTC)

I'm guessing that if you manage to break the glass, you should cover your face to avoid getting blinded? Skittle 23:41, 22 August 2007 (UTC)

That's a good question- unless in very deep water for some reason, I wouldn't even try breaking the glass. It probably wouldn't kill you because it's safety glass and it would explode into pellets, but it sure wouldn't be pretty. Any better answers? --froth^t 01:56, 23 August 2007 (UTC)

More specifically, side and rear windows in cars are tempered glass. Only the front windshield/windscreen is true multi-layer safety glass because safety standards require it to be strong enough to not allow you to burst through it in a crash. The fact that the side windows are tempered glass means they are susceptible to breaking if scratched or hit with a sharp object, BTW. This may be useful in the situation under discussion ;-). MacGyver would simply borrow his woman passenger's diamond ring et voila!

Atlant 12:37, 23 August 2007 (UTC)

Pretty or not, your options are highly limited when you're in the water. If the car for some reason submerges or is slightly buoyant without filling with water, you will only have a finite amount of time before you asphyxiate. And most people given the situation will panic and hyperventilate, which will of course cut down on how long you can hold on the air supply.

And if the car is filling with water, of course, time is severely limited (the car's fill time plus how long you can hold your breath), so drowning is definitely a concern. Getting rescued in either situation is not a trivial issue, and given response time plus the amount of time getting geared up, you may be out of time. If I can't get the doors open after the car starts filling/fills up, I'll take my chances breaking the windshield or a window. Sure, I may get skin/neck lacerations or even blind myself, but it beats the alternative. –Pakman044 04:09, 23 August 2007 (UTC)

If the doors won't open I'd go for opening the windows next, as they aren't likely to be submerged as quickly as the doors. Surprisingly, power windows seem to operate for a few minutes. Also, the rate at which the car fills with water isn't constant. I'd expect it to be slow, at first, as only a small part of the car is submerged, meaning only a few routes for water to get it. Then I'd expect the rate of flooding to increase, but eventually taper off, as a car almost filled with water will have few routes for the air to exit. StuRat 21:34, 23 August 2007 (UTC)

But you want the car to be submerged as quickly as possible so the pressure equalizes --froth^t 22:20, 23 August 2007 (UTC)

I wouldn't say that. As long as you have breathable air, there's no hurry, and more time gives you more hope that rescuers will arrive, you can get your seat belt off, you can overcome the tendency to panic, make a plan, etc. StuRat 00:36, 24 August 2007 (UTC)

Write your last will and testament... (You did remember the waterproof marker that works under water right?) Nil Einne 01:21, 24 August 2007 (UTC)

See the following two videos recorded by Top Gear - [12] and [13]. If you end up in water start trying to open the door AS SOON AS POSSIBLE AND GET OUT AS FAST AS YOU CAN. 91.108.209.10 12:51, 23 August 2007 (UTC)

Alzheimer's Disease

My most basic and simplified understanding of Alzheimer's Disease is this: when you get very old, your mind / mental faculties fail to work 100% properly and you start to lose your memory and to forget a lot of things. That is overly simplified, of course -- but, I believe, the gist of Alzheimer's Disease. Basically, it comes dowm to losing your memory and forgetting / not remembering things. How then, exactly, can Alzheimer's Disease be a cause or reason of death? How would a person's physical body die just because, in their mind, they have become forgetful and lost their memory? Thanks. (Joseph A. Spadaro 21:41, 22 August 2007 (UTC))

Alzheimer's disease is a lot more complicated than simply becoming forgetful. See Alzheimer's Disease and Biochemistry of Alzheimer's disease. Though to answer how forgetting things can lead to death, imagine if you forget how to eat and drink (though that bit can be overcome by medical care). 151.152.101.44 21:47, 22 August 2007 (UTC)

In a nutshell, Alzheimer's is a neurodegenerative disease caused by a biochemical abnormality in protein folding which leads to accumulation of these mis-folded proteins. The exact pathological mechanism is still under investigation. -- MarcoTolo 21:53, 22 August 2007 (UTC)

Number of deaths for leading causes of death. Memory loss is a common symptom, but as the disease progresses other brain functions are increasingly disrupted, making patients more at risk for illness and death. --JWSchmidt 22:27, 22 August 2007 (UTC)

Joseph, what you describe is just the normal decline of cognitive abilities with age. Just forgetting things a bit more often than usual is really quite harmless as compared to real dementia, where forgetfulness is only the very start. Simon A. 08:38, 23 August 2007 (UTC)

I have cared for a large number of people with Alzheimer's Disease and all of them eventually passed away from an associated illness. As the illness progresses the person (and this varies enormously from person to person) becomes less and less able to use their vital functions, feeding, drinking and moving. The nutritional problems can be overcome but eventually the lack of spontaneous movement can raise the person's susceptability to chest infection caused by diminished ventilation. Of course if the hydration problem isn't properly addressed there is a likelihood of renal or bladder infection with the consequent risk of generalised septicaemia and then multi-organ failure. Witnessing this raises the vexed question between quantity or quality of life. Richard Avery 18:48, 23 August 2007 (UTC)

Quick, slightly vulgar question...

Why do pigs choose to roll around in their own shit? --Kurt Shaped Box 23:49, 22 August 2007 (UTC)

Pigs cannot sweat, so roll in mud to cool themselves, and also use it as a sunblock. In my experience, most pigs will prefer good clean mud, but many are kept in conditions which deny them access to this, so use whatever is available. DuncanHill 23:54, 22 August 2007 (UTC)

Exactly right - pigs only roll in excrement when alternative forms of cooling are unavailable (see this paper for more than you want to know about the mechanics of cooling in hogs). -- MarcoTolo 00:29, 23 August 2007 (UTC)

For more information about terrible pig habits, see Savaging. I'm always trying to get more eyes on this article to help improve it. Nimur 01:54, 23 August 2007 (UTC)

"Terrible" is an opinion, and the line "Aggressive behavior may be due to fear, discomfort, and unsanitary conditions" even implies that it is terrible human habits, not terrible pig habits, that are to blame. — PhilHibbs | talk 13:19, 23 August 2007 (UTC)

Indeed, although IANAPF I have known enough in my time to realise that such behaviour is a sign of poor husbandry. DuncanHill 13:22, 23 August 2007 (UTC)

I keep trying to find a reliable source for information about savaging in budgerigars to add to that article. I have a textbook somewhere that mentions it - but I've looked high and low for the thing today and still can't find it. Young hens in particular are known to savage their own chicks. --Kurt Shaped Box 17:05, 23 August 2007 (UTC)

On the other hand, I've seen dogs eat and roll in excrement. I can only speculate that this helps disguise their "dog smell", making it easier for them to sneak up on prey. StuRat 02:14, 23 August 2007 (UTC)

...who wouldn't notice a giant turd sneaking up on them. Someguy1221 03:20, 23 August 2007 (UTC)

They'd just think it was a visit from Mr Hankey. StuRat 00:31, 24 August 2007 (UTC)

Or a Baby Ruth bar DuncanHill 12:28, 24 August 2007 (UTC)

actually, you should see them around horses. Makes a lot more sense then. And dogs seem to like it more. --Tbeatty 07:45, 23 August 2007 (UTC)

August 23

What is Lanalool?

I see this crazy sounding substance in more and more shampoos and conditioners. What is it? And where does its name come from? --24.249.108.133 03:14, 23 August 2007 (UTC)

Are you sure you spelled that right? Lananool has no ghits.Whoops, mispelled it. Someguy1221 03:20, 23 August 2007 (UTC)

Lanalool does, but I'm still unsure exactly what the diff is between that and linalool. --jpgordon^∇∆∇∆ 03:57, 23 August 2007 (UTC)

I don't know what it's fashionable to put in shampoos these days, but maybe you mean lanolin? --Anonymous, August 23, 2007, 03:50 (UTC).

See Acetylated lanolin alcohol (aka Lanalol). -- MarcoTolo 04:04, 23 August 2007 (UTC)

No, I mean Lanalool. I'm quite familiar with Lanolin, silly. --24.249.108.133 19:40, 23 August 2007 (UTC)

I'm not trying to be obnoxious, but you're sure it's "lanalool"? Linalool (with a i) is "one of the most frequently encountered floral scent compounds".[14] -- MarcoTolo 20:02, 23 August 2007 (UTC)

sun and moon simultaneously visible

When the sun and moon are simultaneously visible, how do they appear to people on the other side of the world?

Literally on the other side of the world, i.e., a full half-rotation away? It would be night time, and a very dark night, as there'd be no moon visible. --jjron 08:39, 23 August 2007 (UTC)

Only half a rotation? What about a full one?  :) --Bowlhover 15:18, 23 August 2007 (UTC)

No! Ignore jjron! If it's dawn for me - then someone on the exact opposite side of the earth will be seeing a sunset. So it is certainly possible. There will be some difference in the relative position of the sun and moon because of parallax. This is most noticable during a solar eclipse. The amount of the eclipse is different depending where you are on the surface of the earth. Some places are seeing the moon precisely aligned with the sun (a total eclipse) - other places nearby (a couple of hundred miles away) see the moon slightly overlayed on the sun (a partial eclipse) - and further away still, a few thousand miles away, the moon is just off to the side of the sun (no eclipse at all). SteveBaker 11:52, 23 August 2007 (UTC)

This is the summertime, so if it's dawn for you in the United States (5:30 a.m.), it would be a hot late-afternoon somewhere in China (5:30 p.m.). But it would be nighttime in Australia at the point exactly half a world away, both in latitude and in longitude. Their time would also be 5:30 p.m. but it's winter for them right now; thus the day is shorter.

The same applies with the Moon, except there's a two-degree paralax error that SteveBaker mentioned. The actual parallax error will be smaller if one observer isn't exactly half a world away from the other. --Bowlhover 15:16, 23 August 2007 (UTC)

No! Oh come on guys - THINK! Forget about summer/winter, day/night, USA/China/Australia, whatever! Just take a near-perfect sphere - hold it up in the light of an object that's a very long way away (like the Sun for example) and you'll see that exactly half of the sphere is illuminated. Take one point that's right on the edge of the shadow - now find the point on the opposite end of a line through the center of the sphere - and guess what? It's right on the edge of the shadow too. PLEASE! Simple geometry! Hence if the sun is rising at one point on the surface of the earth then the sun is setting on the exact opposite point. QED.

Now, you may try to argue that the sun isn't infinitely far away and hence slightly less than half of the sphere of the earth is illuminated by it - but that's not true because the sun isn't an infinitely small dot - it's a large disk. Hence the some fraction of the suns disk is definitely visible from two opposite points on the earth at some point during sunrise/sunset. Now you're going to think to argue that the earth isn't a perfect sphere - but the error is of the order of 20km - 0.3% which isn't going to make enough difference to matter. Additionally, refraction of light through the atmosphere actually bends the suns light somewhat into the dark side of the planet - which prolongs both sunrise and sunset somewhat - so in fact, more than half of the earth can see the sun at any given time. SteveBaker 17:29, 23 August 2007 (UTC)

How did sunrise/sunset come up? haw haw pun. I thought he was asking about when you can see a white "ghost" of the moon in the daylight sky.. the answer would be maybe under the best of circumstances a person on "the other side of the earth" - I don't think he means literally 180 degrees, rather just generally on the dark side - could see a sliver of the moon. See this top down view. http://img212.imageshack.us/img212/1687/moonvz3.png --froth^t 22:17, 23 August 2007 (UTC)

No! Ignore SteveBaker! ;) His answer deals only with the extreme conditions at sunrise and sunset. My original answer, and Froth's answer above, deals with the 98% of the time (I don't want an argument on the exact percentage) when it's not sunrise and sunset. Surely that's what the original questioner meant. The sunrise/sunset issue is simply an addendum to this. --jjron 23:07, 23 August 2007 (UTC)

WHAT!? When did the OP mention that it couldn't happen at dawn? In fact, if the question has meaning, the OP must have been talking about dawn/dusk since it's the only way for it to happen. Then YOU flippantly (and utterly incorrectly) suggested that the OP was asking a stupid question (when in fact, it's a perfectly reasonable question) - when I corrected you, Bolhover claimed I was talking nonsense - so he also had to be corrected. And now you are pathetically trying to change things around to make it sound like your first comment was valid. Froth's answer is also nonsense - the OP specifically said "When the sun and moon are simultaneously visible" - so OP was not talking about anyone on the dark side (duh!). So, my answer (which said - precisely - that people on the exact 'other side of the world' when 'sun and moon are simultaneously visible'...can see the sun and moon in different relations to each other in the sky. I answered the actual question that was asked - not some other question as you guys did - and without invalidating what the OP specifically asked for. What's more, I went the extra mile and corrected your collective errors...and I'm in trouble?!?! Bah!  :-) SteveBaker 00:31, 24 August 2007 (UTC)

Hmmm, OK...

1. Now, who said the original question said it couldn't be at dawn? All I said was that without further clarification the logical assumption is that they're asking about the 98% of the time when it's not sunrise/sunset. Now perhaps they did only want a sunrise/sunset answer, but that's nowhere in the question, and has not been clarified any further.
2. I neither flippantly nor incorrectly said the original question was stupid - you're the only one who's mentioned that.
3. Bowlhover might appreciate you getting his name right.
4. I don't know about other users, but I feel that some of your comments are verging on personal attacks, e.g., saying my answers are pathetic. This is not the first time I've noticed this type of behaviour directed towards other users. I would thank you to desist with these actions.
5. Time to cut down on your tirades, and accept that you're not always right, and don't have a monopoly on giving answers. This is not the SteveBaker Reference Desk, it's the Science Reference Desk. --jjron 09:43, 24 August 2007 (UTC)

Ummm, one can see both sun and moon at other times than just dawn and dusk..... (runs away and hides). DuncanHill 00:36, 24 August 2007 (UTC)

You're completely right DuncanHill. It's only in SteveBaker-land that the moon and sun are only ever both visible at sunrise/sunset ;) . --jjron 08:56, 24 August 2007 (UTC)

Don't forget that special circumstance which allows people to see the Sun and Moon not only at the same time, but also in the same space! At this time, the other side of the world is indeed in a dark night (and generally experiencing quite high tide). Laïka 09:59, 24 August 2007 (UTC)

[edit conflict] SteveBaker must be considering the case where the sun and full moon are simultaneously visible. --Allen 10:02, 24 August 2007 (UTC)

Let me try to summarise:

• Most of the time the Sun is not simultaneously visible from two fixed antipodal locations on the Earth - it will be day at one location and night at the other.
• There are two short periods that are exceptions to this - around sunrise and sunset the Sun (or at least part of its disk) may be simultaneously visible at two antipodal locations.
• Similar considerations apply to the Moon - most of the time it will not be visible simultaneously from two fixed antipodal locations. There may be short periods around moonrise and moonset that are exceptions to this generalisation - although the relative neareness of the Moon to the Earth may rule this out too.
• So the only possible times that the Sun and the Moon could both be simultaneously visible from two fixed antipodal locations (even if only in theory) would be when moonrise or moonset conincide with sunrise or sunset i.e. when the moon is close to conjunction or opposition. Gandalf61 10:37, 24 August 2007 (UTC)

Looking back at OP's question, "When the sun and moon are simultaneously visible, how do they appear to people on the other side of the world?"

I don't think the question is asking when or where would one be able to see both sun and moon at 2 opposite positions are earth. The question asks when you can see both sun and moon at the same time, what does the sky look like at the exact opposite position on earth. Seeing both sun and moon can happen most time of the day. I was able still able to see the moon at around 11:30am in chicago during mid-fall. MOST of the time the opposite side wouldn't see either object. But during early sunrises or late sunsets (given you can still see both moon and sun), the other side may be able to see either one or both sun and moon.192.53.187.183 15:25, 24 August 2007 (UTC)

I agree- gandalf's answer is useful but not what the OP was looking for. If one of the antipodes sees the sun and moon simultaneously, what would the other see? Not, "under what circumstances would two antipodes both see the sun and moon simultaneously" --froth^t 16:24, 26 August 2007 (UTC)

Megapixel equivalent of eye

Had a discussion today about the sensitivity of the human eye versus digital camera sensors, VDUs, photographs, etc. We were trying to work out a megapixel equivalent of the human eye. I reckon I came up with a reasonable solution, my friend reckoned I was hugely underestimating. I won't give our figures at this stage, as I'd be interested to see what others come up with independently. What do you think? --jjron 08:35, 23 August 2007 (UTC)

You might want to check out the article on the Eye#Acuity, since it does cover this. Also, keep in mind that the density of photoreceptors differs in parts of the retina, as well as the type of photoreceptor (rod or cone), so comparing the megapixel resolution of a digital camera (which has a constant density across the whole width) to an eye is bound to have problems. -- JSBillings 11:37, 23 August 2007 (UTC)

There are some subtle issues that make direct comparisons with a digital camera tricky:

• The eye has more resolution in the center of its field of view than the edges.
• The edges of your retinas are more sensitive to motion and less sensitive to colour than the center of the field of view.
• Your eye continually vibrates back and forth so that each "pixel" samples the scene in different places which greatly increases the effective resolution for still scenes - but doesn't help much for moving scenes.
• There is the matter of being able to see brightness changes with maybe 4 to 6 times more precision than colour changes.
• All sorts of strange adaptations happen in low light conditions that trade "image quality" for night vision ability.
• We have a continually variable lens on the front end of the eye. This means that those (however many) pixels are sampling a different amount of the world when we are focussing at long distances than at short distances. Because this adjustment is continual and unconscious, it can result in a perception of higher resolution for things closer to the eye than at long distances.

So you just can't come up with a single meaningful number. Do you count the motion due to the vibration of the eyeball? Well, you should if you were deciding the resolution you should print a photograph (say) - but you probably shouldn't bother when planning a movie theatre that's going to show mostly fast-moving pictures. Should you count the monochrome 'pixels' at the edges of the eye? Well, again - "it depends" - those pixels are really good for attracting your attention to potential dangers sneaking up on you from the sides - but terrible at (say) reading a book. That vibration of the eye to improve resolution tends to vanish when you are extremely tired (or sick or drunk) - which is why you may get blurry vision under those circumstances. Black and white pictures can be seen with much, much better resolution than (say) red and green pictures. Switch your Windows colour scheme to red text on a green background and see how long you can stand it! Red and green are about the same brightness - so only your low-resolution colour sensors are helping you out...which makes vision much more blurry than for black and white text.

The whole question is a bit dubious...there just isn't a 1:1 comparison between our eyes and a digital camera. But if this information is not to to be used to settle an argument (or worse still, to win a bet!), I'd say this: In the flight simulation business (where I used to work) we would consider a graphics display of something like 6000x4000 resolution over a 60 degree arc to be roughly "eye limiting resolution" - ie there is no point in making the display sharper than that because the human eye would be unable to see the improvement. So - very, very roughly, 24Mpixels is about it. However, this is a tremendously variable thing and I wouldn't want to be held to that number under all circumstances. SteveBaker 11:41, 23 August 2007 (UTC)

I say roughly 100-200 MegaPixels. Something like 17320 x 11547 digital camera capturing images at 80 times a second. 202.168.50.40 22:25, 23 August 2007 (UTC)

I'm a bit doubtful about that. Suppose we go with (roughly) a 60 degree field of view...at normal reading distance (say 30cm) you'd be able to resolve an object that is 0.3/17320 = 1.7 x 10^-5 meters across. That's 17 microns - you'd be able to see some of the larger bacterium if your eyes were that good. I don't think so. SteveBaker 00:17, 24 August 2007 (UTC)

Hmmm, well the width of human hair ranges from 18 to 180 µm, with an average value of about 80 µm. I personally have no problem seeing a normal human hair from 30cm. Now I may not be able to resolve the very smallest/thinnest ones at that distance, but it's certainly not as absurd as you are trying to suggest. --jjron 08:30, 24 August 2007 (UTC)

Firstly, how do yo know you can see the finest hairs? After all, if you can't see them you won't know they are there! People have very, very fine hairs on some parts of the body. Maybe you can only see the thicker ones. 180um is no problem - you can see that with just 1Mpixel. Are you telling me you can see bacteria? I'm saying that 24Mpixels is reasonable and 100 to 200Mpixels is not. 24Mpixels is only 4x the 'area' resolution of 100Mpixels - just half the linear resolution. So I wouldn't be so surprised if you could see a 34um hair - but I'm pretty darned certain you can't see a single bacterium at 5cm - let alone 30cm. SteveBaker 18:18, 24 August 2007 (UTC)

OK, thanks for answers given so far (no kidding there's lots of complexities to it, I never said the sensitivity of the eye could be directly stated in megapixels; and get down off your high horse, whoever it is that's up on it...sheesh! It's a thought exercise for crying out loud. I thought my original question was pretty clear on that.). Anyway, for the record the answer I proposed was just over 100 megapixels per eye, based essentially on the number of photoreceptor cells. My friend thought it would be more likely in the gigapixel range. Since then though I have also noticed the article on the optic nerve says that the nerve itself contains only 1.2 million nerve fibres, indicating that the retina preprocesses the image before sending it to the brain. This would probably impact the effective sensitivity, i.e., what would get to the brain would not actually be the maximum possible figure that the eye could theoretically detect. Therefore my figure may be too high for the reality of the situation, and what our brain can actually detect may be closer to the figure given by SteveBaker from his practical experience, or possibly even less. Any other thoughts still welcome. --jjron 08:29, 24 August 2007 (UTC)

The optic nerve doesn't transmit pixels - or anything remotely like pixels. It's sending higher level things like "There is a vertical line 20% across from the left and it's moving at such-and-such speed" - the idea that our brain is fed a bunch of pixels is very far from the truth. Hence, you can't deduce anything whatever about resolution from examining the number of nerve fibres. (And even if it was sending pixels - I'd point out that my antenna connects to my TV with just two "fibres" - video and ground - that tells you nothing whatever about its resolution!) SteveBaker 18:18, 24 August 2007 (UTC)

Just noticed this in the eye article - equivalent resolution. Interesting. One calculation gives 81 megapixels, but goes onto to say that the area of sharp vision gained from the fovea is closer to just 1 megapixel. --jjron 08:42, 24 August 2007 (UTC)

Yes, it's an interesting question and odly - one I too was recently thinking about - I wanted to know how many megapixels an EVF would need to be as good as or better than the viewfinder in a SLR - i got 10,000 x 10,000 to be better - 100Mpixels - so I would agree with the 81megapixels figure above .87.102.79.29 13:12, 24 August 2007 (UTC)

where is the sun in google sky?

hi, on google earth "sky" mode.... I cant find the sun (it hasnt gone out has it?)

also how old are the pictures of earth and how often are they updated?

TIA —Preceding unsigned comment added by 91.105.76.65 (talk • contribs) 7:47, 23 August 2007

The images used in Google Sky were collected from telescope images, which don't include the sun. Like the images in Google Earth, they aren't "live" images, but come from archives of images collected by different agencies around the globe, some more frequent than others. Google answers the question of the age of the images in their Help section. -- JSBillings 14:19, 23 August 2007 (UTC)

Now that I think of it, I'm surprised that Google hasn't included high-resolution imagery of the Sun in it's Google Sky, with the option of turning it off. After all, it is a star in our sky. Maybe I'll suggest it. -- JSBillings 14:23, 23 August 2007 (UTC)

Why don't telescope images include the sun?! My telescope can view the sun jus-- I CAN'T SEE!!! AUUUUGGGGGH! :) --Mdwyer 05:15, 24 August 2007 (UTC)

They do have telescope images. They were mostly taken during sun elcipse to get rid of the intense glare. I'm sure it can also be done with some sort of filter though...

Recovering wet electronics

If the interior of a simple electronic is wet, should I dry it until it works again, or slightly longer to ensure no additional water remains? I'm keeping a previously-wet (still wet?) device warm right now with a hair blower even though it became functional half an hour ago. --Bowlhover 14:54, 23 August 2007 (UTC)

Water will rarely destroy electronic devices when there is no electricity running through them. However, it can leave corrosive and/or conductive deposits on the electronics when it dries. For that reason, you should dry the electronics and then clean them (I use rubbing alcohol). -- Kainaw^(what?) 14:58, 23 August 2007 (UTC)

You should probably avoid using a hair dryer to keep the device warm, since it'd probably produce a static charge, plus, heating the electronics can damage the components. Try a normal table fan. -- JSBillings 15:50, 23 August 2007 (UTC)

It sounds like this ship has sailed, but if it happens again, you shouldn't even attempt to turn the device back on until it is completely dry. kmccoy (talk) 16:56, 23 August 2007 (UTC)

Yep - exactly. The best procedure is:

1. Turn off the power, pull out the batteries - as fast as possible! Seconds count!
2. Dab off as much of the liquid as you can with something absorbant like a paper towel. Don't wipe it because you'll spread water from wet areas into dry areas.
3. If the liquid has 'stuff' in it (like a sugary drink for example) - then you may need to wash the stuff off. If so, use distilled water - not tap water. Don't use any detergent or soap...just plain water...and definitely don't used bottled mineral water (the minerals are what we're trying to avoid by using distilled water).
4. Leave it to dry SLOWLY - don't apply heat - don't blow air over it. You'll want to keep it somewhere not too cold - but don't deliberately heat it up.
5. Only after many days - when it's UTTERLY dry - in all the little nooks and crannies - try turning it back on again.
6. If it totally doesn't work - you can try using some of that oily stuff they sell in car parts stores for displacing water from car electrical systems. I've never had any luck with it - but some people claim it worked for them. Definitely a last resort though.

It's a crap shoot though - sometimes it survives - othertimes not. My favorite keyboard died of a diet coke overdose and couldn't be revived - my inkjet printer works just fine after a friends child dumped about a half pint of sticky orange juice inside! I'd never have believed it would still work after I had to pull out soggy paper - and re-wash with fresh, distilled water several times to get rid of the stickiness that pervaded every crevice of that mechanism! SteveBaker 20:01, 23 August 2007 (UTC)

Nobody actually said why to wait until there is no possibility of a drop of water remaining before starting it. The reason is that a drop of water can create an arc and short-circuit the electronics, which will likely cause permanent damage. StuRat 21:18, 23 August 2007 (UTC)

It's not just arcs. What you're really trying to avoid by instantly removing all power and batteries is the movement of ions. For example, you don't want to see all those nasty little chloride ions (from salts) migrating into the guts of the electronics where they'll rapidly murder everything.

It's on this point that I disagree with one bit of SteveBaker's advice: once I'd rinsed away any sticky stuff, I'd use mild heat and/or plenty of air motion to try to dry the circuitry as rapidly as possible. But keep mindful of the idea of mild; lots of electronics won't think well of you above 70°C (the top end of the "commercial" temperature range).

And yes, like so many of you, I rescued something. In my case, it was a TV that was given a drink of egg nog one New Year's Eve; I ended up mechanically removing a lot of the congealed nog the next day.

Atlant 23:10, 23 August 2007 (UTC)

Further to Steve's advice, while I agree that distilled water would be better than tap water to wash away a drink, I'd certainly do it with tap water if I had nothing else available. If the drink dries up in place, it will surely produce more residue than the tap water. --Anonymous, August 23, 22:10 (UTC).

The main reason to chop the power ASAP is because the water connects bits of electronics to other bits of electronics in ways that they were never designed to be connected! Who knows what that might do? Lots of chips are very sensitive to (for example) being driven with negative voltages. Shorting out the power supply ought to just blow a fuse - but these days, fuses cost money - so cheap power supplies are designed to just fail instead. Shorting out a resistor could result in too many volts going to the next device along the chain. Shorting a capacitor could shove a huge spike of current through something down the line - or cause the capacitor to discharge a stored charge suddenly, which might well wreck it. It's unlikely you could get to the power switch fast enough to stop any of those things happening where the circuits are already wet - but water spreads out fairly slowly so if you can cut the juice within just a few seconds, you are definitely improving your chances. The reason to prefer distilled water is that it's less corrosive than water with minerals in it - and also it doesn't conduct electricity anywhere near as well (although you aren't going to turn the thing back on until it's utterly dry - so maybe that doesn't matter. You need to avoid applying a lot of heat to the electronics as they dry because warm water is more corrosive than cold water - and most electronics don't like being overheated (eg with a hair drier). SteveBaker 17:48, 24 August 2007 (UTC)

This thread has prompted me to innovate Dweller's Ref Desk thread of the week award, and I hereby give the inaugural award to those who contributed here. Congratulations. --Dweller 13:00, 24 August 2007 (UTC)

What? No cookies? No barnstar-of-refdesk-goodness? No massive cash prizes? Not even a teeny-tiny penguin to put in the top-right corner of your user page? Where's the incentive here?! :-) SteveBaker 17:36, 24 August 2007 (UTC)

First, shake off any loose drips, then leave to drain (on a draining board) for say 30 mins. If you have a switched on dehumidifier, place the electronics in front of its output and leave there for for 24 hrs. After this time it should be safe for you to reapply power to the circuit. If you have an A/C unit set to dry/cool, this should also work. I have performed this on circuit boards from a TV. Worked perfectly afterwards (the picture ,however, was not noticeably cleaner)--88.109.139.255 18:43, 25 August 2007 (UTC)

The Federal Puke Ray: How does it work?

The government is working on something called a puke ray. http://www.theregister.co.uk/2007/07/27/dhs_chunder_cutlass/ The article claims it just uses light. Anyone know any more about it? I would like to try to build my own. Juanita Hodges 21:29, 23 August 2007 (UTC)

Mythbusters claimed an infrasonic beam could affect the intestines of a person. It did not work when they built it. It would work by shaking the contents loose! Graeme Bartlett 22:35, 23 August 2007 (UTC)

Wasn't there some research done (by the Soviets?) at some point into creating a 'gay beam' and a 'make them shit their pants' beam? --Kurt Shaped Box 22:39, 23 August 2007 (UTC)

I seem to recall the KLF getting hold of some American experimental kit and exploding a cow using sound waves some time ago. DuncanHill 22:43, 23 August 2007 (UTC)

Brown note? Capuchin 06:36, 24 August 2007 (UTC)

On a more serious note, I see we have a Less-lethal weapons article, with some interesting links from the see also section. DuncanHill 22:50, 23 August 2007 (UTC)

• I would guess that one way to do it would be with microwaves: since they (when focused right & all that) heat up water molecules, they should be able to cause serious damage to a gastrointestinal system. --M@rēino 23:01, 23 August 2007 (UTC)

How come it's a "federal" puke ray? I think each state should have its own. ◄Zahakiel► 23:10, 23 August 2007 (UTC)

How absurd. Next you'll be suggesting that each individual state administration should be privy to the records of the CIA's dream-stealing psychoelectronic satellites and the recordings from the microdot cameras hidden in that eye on the back of a dollar bill... --Kurt Shaped Box 23:22, 23 August 2007 (UTC)

Say, are you running for president on 08? ◄Zahakiel► 23:32, 23 August 2007 (UTC)

The news article appeared to claim it was by light, not sound. My neighbors' car stereos already are a sonic attack that cause me so much pain and naseau I nearly puke, but the article said this was with light. Juanita Hodges 01:10, 24 August 2007 (UTC)

Could they be showing the victim sickening images? Also a flashing light at a customized rate around 15 Hertz could cause some interesting effect on people including epileptic fits. Graeme Bartlett 11:47, 24 August 2007 (UTC)

I thought it might be flashing. They did claim there was this specific frequency they hit that did bad things. The TV, computer monitor stuff, etc. is all just red, green, blue stuff and maybe blacks and whites. The sun and light bulbs are all white-yellow variations usually. So it could be a specific frequency of light people don't see. Juanita Hodges 18:11, 24 August 2007 (UTC)

Remember the Sick Sticks in Minority Report? One touch and you'd lose your lunch! I could see a nausea induced weapon if it upset your inner ear and made you dizzy (like sea sickness). Not sure how lights would make you sick unless you were wearing VR goggles and your environment was spinning out of control --24.249.108.133 20:46, 27 August 2007 (UTC)

Which animals sweat?

Horses and humans perspire. Dogs and pigs don't (much). Is there some common thread or selective pressure that makes some animals sweat and others not? Which other animals sweat? Thanks! --Sean 23:11, 23 August 2007 (UTC)

The body surface-to-mass ratio might have a hand in that. If the animal is too large to efficiently siphon off heat, the skin is as good a place as any to get rid of the excess. ◄Zahakiel► 23:19, 23 August 2007 (UTC)

There was an article on sweat not long ago in the New York Times Science section titled "sweatology" or something like that. The basic drift of it as I understood it is that humans are actually pretty unique in this regard, and our copious, full-body sweat glands are among the reasons we can tolerate so many climates. One of the other interesting facts in the article is that while human internal temperatures can regularly be lowered without too much ill effect (hypothermia, but there are some professions where that occurs all the time), but if you raise the internal temperature by just a few degrees you get delusional and often quickly die. Ergo the importance of sweat glands, etc. --24.147.86.187 23:42, 23 August 2007 (UTC)

The lack of thick body hair on humans makes sweating work better. The question should really be why horses sweat. It does seem to cause them problems, as a horse that runs hard in cold weather gets soaked with sweat, then gets cold when it stops running. Perhaps being bred by humans has increased their tendency to sweat, as humans are likely to ride them hard (for which sweating helps to keep them cool) and then keep them warm (say in a barn with a blanket on them) and provide water. Thus, those which sweat profusely were more likely to survive with humans than they would on their own. StuRat 00:24, 24 August 2007 (UTC)

That happens with humans too - they always tell you that in arctic conditions, it's essential not to over-exert yourself to the point where you start to sweat because the moment you stop exercising, you die. SteveBaker 15:22, 24 August 2007 (UTC)

The article Sweat says that "Primates and horses have armpits that sweat similarly to those of humans." -- WikiCheng | Talk 06:15, 24 August 2007 (UTC)

One source states pigs can only sweat 3% the volume we can. Bendž|Ť 08:08, 24 August 2007 (UTC)

August 24

Weak bosons

Can a W⁺ or a W^- emit a Z⁰ I saw this in a list of fundamental interactions but it seems to violate conservation of angular momentum. So how does this work? Thanks, *Max* 01:05, 24 August 2007 (UTC).

Yes, it's possible, and no, it doesn't violate conservation of angular momentum. In order to fully understand how such things work, you must master the Table of Clebsch-Gordan coefficients, no easy task. It's somewhat arcane, but basically this table tells you all the ways that angular momentum vectors can be summed in quantum mechanics. In this case, you want the entry under j₁=1, j₁=1. This means that you have two things that both have angular momentum 1: the W and Z in the final state. Now we need them to add up to a total j=1: the W in the initial state. The entries for m₁, m₂, and m tell you the z component of these three spins. You can ignore the first table there, since it's for j=2. The second and third tables tell you how the state of the final W and Z relate to the initial W. --Reuben 05:41, 24 August 2007 (UTC)

I don't really understand it, but thanks for telling me it's possible. Also, I noticed that my list left out a W decaying into leptons of different generations. Is this just an oversight (they also forgot quarks emitting gluons)? Thank you *Max* 13:31, 24 August 2007 (UTC).

You could also think of the angular momentum as classical. If you put the two final spin vectors along edges of an equilateral triangle, then they add up to the third edge, which has the same length (that's how spin 1 + spin 1 = spin 1). Quantum mechanically the idea is the same, but the mathematical formalism looks very different. There's no simple vertex for W -> leptons of different generations. You can have W -> charged lepton + neutrino, and then the neutrino's flavor oscillates. --Reuben 19:33, 24 August 2007 (UTC)

Wouldn't it sensible if Nature made us all hermaphrodites?

In a species that reproduces sexually, half of their numbers – the males – do not give birth, but continue to compete with females – who do give birth – for the available food. Wouldn’t a hermaphroditic species have all the benefits of genetic mixing that comes via sexual reproduction, while doubling the number of its members who are capable of becoming pregnant, and thus placing the survival of the species on a firmer footing? And yet no animals more advanced than some lizards are hermaphroditic. Myles325a 04:06, 24 August 2007 (UTC)

And tell us why there does NOT exists any species whose individuals CANNOT impregnate themselves but can impregnate other individuals. 202.168.50.40 04:43, 24 August 2007 (UTC)

(OP myles325 back). Don't understand what you mean. Humans are a species whose members CANNOT impregnate themselves, but who can impregnate others. Maybe you could rephrase your point without the use of double negatives. They can be confusing. Myles325a 05:23, 24 August 2007 (UTC)

When you say 'species' how far are you willing to go? Outside of the animal kingdom, there are a large number of species that have both sexual parts, but cannot impregnate themselves. Think flowers. --Mdwyer 05:12, 24 August 2007 (UTC)

(OP myles325 here). My question was simply why hermaphroditism is not found amongst the "higher" animals, when it is notionally so sensible. I don't understand your point at all. Myles325a 05:23, 24 August 2007 (UTC)

As far as I know, the offsprings produced by mating of different individuals (of the same species) are more robust. Genetically the farther the mating individuals are, the better. -- WikiCheng | Talk 06:13, 24 August 2007 (UTC)

One possible answer, although this is all speculation, is that it provides an easy division of labour. While you think men are competing for food without giving birth, in humans (traditionally anyway) it is the men who are hunting for food while the women raise the children. This system provides a safe environment for child raising and allows men the freedom to hunt. A hermaphrodite species would have to look after a baby while at the same time hunting or gathering, hardly a safe environment for a child. In some species the relationship is more equitable, for example in penguins, the males keep the eggs warm while the females hunt for months, and the men lose much of their weight doing this. The females return, after hatching, take over the job of warming the baby, while the males go off hunting for a long time and this continues. I assume you meant hermaphrodite but not self impregnating, so I don't know if the two sex solution may provide increased competition benefits as well? Cyta 07:17, 24 August 2007 (UTC)

Except that sexual differentiation goes back WAY before humans, way before even division of labor. You can't figure out the origins of sexual differentiation by looking at humans; that's why people like Darwin tried to think about it by looking at animals where the advantages were less obvious to the naked eye (like barnacles and orchids). (And in any case, be aware that speculating on the evolutionary roles of human sexes is a scientific and political minefield. Characterizing men as just "hunters" and women as just "baby raisers" is overly simplistic, and such "naturalistic" explanations often end up enshrining the worst of contemporary social mores and gender roles.) --24.147.86.187 11:35, 24 August 2007 (UTC)

Sorry I didn't intend to offer an evolutionary explanation for gender with my human example, just an example of why it might not be sensible for nature to make us all hermaphrodites, as the original questioner suggested. As for political and scientific minefields, I like to keep the two seperate. And while I appreciate your point on not misusing science to influence politics, I won't avoid what I think is a reasonable "naturalistic" explanation in order to fit in with the "best" of contemporary social mores and gender roles. Cyta 12:59, 24 August 2007 (UTC)

I'm not implying you should embrace political correctness, I'm just implying that if you haven't really taken any serious time to think about gender roles then you should try to avoid speculating wildly on their "natural" origins. I don't claim to know enough about them to sort out the "natural" components or not (and there are surely some there), but I know that I don't know enough to do so with any success at all, and so I avoid speculating. (Put in more religious terms, I am a naturalistic-gender-role agnostic, not an atheist or a true-believer.) --24.147.86.187 00:47, 25 August 2007 (UTC)

OK well I don't consider my speculation wild, although as I admitted in my original post, it is just my speculation. It makes sense to me, that, hunting being a dangerous activity, babies should not be brought along, so someone has to stay home and look after them. Men are on average, faster and stronger and would make better hunters. I can't see any reason why women can't gather as well as men though. And atleast for the first few months of life, there is the obvious advantage that women can breastfeed! None of these things of course apply in the modern world. If I never speculated I'd never answer any RD questions, so I will continue to do so with disclaimers. Cyta 07:02, 27 August 2007 (UTC) ps Simon A's evolutionary answer below seems a much superior one to mine anyway.

Don't worry about it. The idea that men and women were not designed for different purposes (either by God or at random, thank you Darwin!) is scientifically nonsensical. The key idea to keep in mind is that there is no evidence we are confined to operating within these purposes (besides the obvious ones, of course, until some truly sadistic biologist finds a way to allow men to bear children). Someguy1221 07:12, 27 August 2007 (UTC)

[Edit conflict]

Myles, first of all: Beware of group selectionism. It is the not that uncommon fallacy in thinking about Darwinian evolution to assume that a species will thrive if its characteristics is of benefit for the species. Evolutionary selection only acts on the level of individual organisms (or even of single selfish genes). Now, I'll try to speculate a bit on the reason: Imagine a higher hermaphroditic species and assume that one individual has, due to some mutation, lost the functionality of its female reproductive apparatus. (Let's say the the organ simply got too small and does not work properly.) The individual hence does what it (or now rather: he) can do best, namely impregnate other animals. Given that it costs much more time to grow an egg or even allow an fetus to develop in a womb than to simply inject some semen, our mutated animal uses its time quite productively to spread it genes and the new male-only form will flood the species's gene pool. This results in over-abundance of male mating partners, which requires those of the hermaphrodites who choose to act as females to choose their partner carefully in order to not waste time on bad gene material (which would cause their gene-line to die out, see sexual selection). This renders being female a full-time job, where producing male genitalia is only a waste of energy, and so, a dimorphic species arises. In lower organisms, it seems to me, the disparity in the energy costs of producing eggs and semen is not that large yet, and hence, the advantage of this division of labor does not yet outweight the opportunity cost of not having the flexibility to perform both roles, and hence hermaphrodites occur. (Note, by the way, that many fish retain this flexibility: they can change their sex when needed. Also, observe that unisexuality and bisexuality seem to be quite on equal footings in plant sexuality) You may also like our article on evolution of sex. Simon A. 07:28, 24 August 2007 (UTC)

Sharks have been known to reproduce asexually, but why this is rare is explained in the article. Bendž|Ť 08:14, 24 August 2007 (UTC)

I presume that this is why (in higher species where the cost of child bearing is greatest) the females have evolved to demand often ridiculous adaptations in males. A male bower-bird doesn't have to suffer the 'cost' of producing gigantic eggs and keeping track of the young - which would suggest that the males would out-compete the females for food and such. To counter that, the females have evolved a strategy which requires the males to collect all sorts of junk - carefully arrange it into a bower and do complicated (but ultimately meaningless) dances to attract them. This disadvantages the male to level the playing field when it comes to hunting for food. Many male animals have to produce brightly coloured plumage/fur/scales in order to attract females. This puts them at a terrible disadvantage when it comes to hunting or hiding from predators - but it's the price of doing business...so they bear it. In humans, there is good evidence that females prefer the 'reliable type' of men who are going to stick around and share the cost of child rearing - rather than running off with other women. Females who make this demand are more likely to produce viable young that live to reproduce - so from the male's perspective, it's worth the price. This balances out the disparity of energy costs to the point where the advantage of being a male reduces enough that there is a reasonable population balance. SteveBaker 15:16, 24 August 2007 (UTC)

I've always thought the most enlightening example of gender distinction in animals to be the rotifer. The males can't eat or swim like their female counterparts, and merely twirl around trying to reproduce until they starve to death. Make your own conclusions as to what that means about us guys ;-) Someguy1221 20:56, 24 August 2007 (UTC)

Geometry of complex

I want to know the geometry of potassium trioxalato aluminium trihydride complex?

[K⁺]₃ [Al(C₂O₄)₃]^3- Potassium trioxalatoaluminium complex has 6 coordinate aluminium with oxygens bonded to Al (can be chiral)

I can't see how the 3 hydrogens can be incorporated - have you missed a bit of the name - or can you give more details (eg its synthesis)...87.102.79.29 13:21, 24 August 2007 (UTC)

This link http://classes.uleth.ca/200401/chem2810a/lecture_15.pdf page 91, first set of diagrams, last (rightmost) diagram shows Iron (III) trioxalato complex which has the same structure as the aluminium complex.87.102.79.29 13:27, 24 August 2007 (UTC)

Colour question (related to one above)

How many colours should I be able to distinguish on a monitor - eg what's the 'bit equivalent' of the eye - and is 24bit colour beyond what the eye can percieve in terms of hue..87.102.79.29 13:51, 24 August 2007 (UTC)

This is another question that comes up a lot...and once again, a clear, simple answer is impossible because our eyes simply don't work like a digital camera:

• The eye is very sensitive to brightness variation - but much less sensitive to colour. Our eyes work in Red+Green+Blue+Brightness, not Red+Green+Blue like a TV set, a computer or a digital camera. Interestingly, there is a lot of work out there on RGB+Brightness displays (they are called 'RGBS' or 'RGBE' depending on who you read). Many modern computer games work in RGBE and convert to RGB at the last moment inside the graphics card (I do this stuff for a living!).
• In a computer monitor, the voltage sent to the monitor is directly proportional to the number used to represent it - so 8 bits per colour gives you 256 equally spaced voltages - however TV and LCD monitors aren't very linear - so equal changes of voltage do not produce equal brightness changes. In order to correct for this, computers and such have to perform a trick called 'gamma correction' which re-maps the numbers from a linear-voltage to a linear-brightness. This process causes a loss of precision over some of the brightness range - so the 8 bits you thought you were getting is more like 6 bits over the mid-range brightnesses. Cameras do similar tricks. Our eyes are also non-linear. We can tell the brightness differences between dark things much more easily than between bright things - so you can't directly compare bits-of-computer-colour-resolution to bits-of-human-eye-resolution...it's just not an apples-for-apples comparison.
• The eye is vastly more sensitive to green (and to a lesser extent, red) than it is to blue. However, in computer graphics, we tend to use the same number of bits for all three colours. We can easily see MUCH more than 256 brightnesses of (say) green - so 8+8+8=24 bits is simultaneously more bits of blue than we really need - and not enough green bits. The choice of 8 bits per component for computer graphics, etc is more because of the limitations of the display than of our eyes.
• Our eyes have all sorts of sneaky tricks for grabbing more light - by adjusting the amount of light let into the eye through the iris - and by releasing chemicals that sensitize the retina after you've been in the dark for maybe 20 to 30 minutes. So in a dark place - with dark-adapted eyes, you can see very dim things indeed - but you can't simultaneously see very bright things because as soon as a bright objects enters your line of sight, it erases your dark-adaptation and you don't get it back for another 20 to 30 minutes. So whilst 'instantaneously', 8 bits might be enough - over the entire range of your vision from something as bright as the sun down to something as dim as a candle a couple of miles away, you'd need maybe 24 bits for each of red, green and blue!
• Our 'resolution' is better in terms of brightness than in terms of colour - so for very small objects, colour doesn't work very well. You could imagine using fewer bits of colour for drawing text than for (say) cartoons.
• We are very good at spotting changes in colour - but less good at absolute colours. If you take two swatches of colour and place them a couple of inches apart on a grey background, you can only distinguish differences in the colours when they differ by maybe one or two percent. But if you place the two colours next to each other, then under the right circumstances (muted room lighting - brightly lit colour swatches, etc), you can see a change between the two of maybe 0.02%
• Our brains are designed to recognise the shapes of objects from subtle differences in shading. This is how you can tell the difference between a sphere and a flat circle. But we're pretty astoundingly good at that. Using subtle differences in lighting, we can look at a cylinder (which is just a shaded rectangle on our two-dimensional retinas) and tell whether it has a circular cross-section or a slightly oval cross-section. Remarkably, we can do this using shading cues that have less brightness difference than the smallest brightness differences we can recognise when comparing side-by-side colour swatches. This suggests that our eyes produce 'better' quality images than our brains actually need so that much of that precision is lost when performing unimportant tasks like comparing colour swatches - but which is fully utilised when deciding on the shape of a roughly cylindrical object. This makes sense from an evolutionary standpoint because telling which of two apples is the ripest to a precision of one part in a thousand is definitely overkill - but estimating the cross-sectional area (and hence the strength) of a branch whilst swinging through the trees might well be a life-or-death kind of a thing.

So, the disappointing bottom line is the same as for your last question...we don't really have a way to come up with a good number. The number that's used most often is 12 bits of green, 11 bits of red and 9 bits of blue...but that's by no means a "correct" answer. SteveBaker 15:03, 24 August 2007 (UTC)

Thanks - that was a long and good answer87.102.75.201 15:21, 24 August 2007 (UTC) (I didn't ask the previous question - just to be clear and prevent any confusion)87.102.75.201 15:51, 24 August 2007 (UTC)

Oops! My bad! SteveBaker 16:42, 24 August 2007 (UTC)

Thanks from me, too. I raised the question on the Computing desk (someone else copied it here) because I created an image containing all 2**24 colors (see the top entries here) and found that I cannot distinguish some adjacent colors no matter how much I blow it up. —Tamfang 21:15, 24 August 2007 (UTC)

True - I've tried similar things with long bands of colour varying by one unit. I couldn't see the join - it looked continuous- but I didn't look at every combination; specifically the green colours which I now know I should have been checking..87.102.6.217 22:11, 24 August 2007 (UTC)

But read what I wrote above. Unless your monitor gamma is set up perfectly - and even if it is - and room lighting conditions and that your eye is more sensitive over some of the bit range than others...it's inevitable that there will be some regions and some sets of conditions where you can't see single steps. The best region to see single bit variations is with a properly gamma-corrected monitor in a dark room - looking at only dark shades of colour. That (wonderful!) 4kx4k fractal with all 2²⁴ colours is great - but it puts light colours next to dark ones so it's hard to get a total screenful of dark colours. When I worked in flight simulation, we'd draw a night sky as a subtle blend from some kind of soft glow at the horizon to total black at zenith. In a darkened flight simulator cockpit, it was easy to see single bit steps in brightness - and it was impossible to fix with 8+8+8 bit graphics - so I know for sure that 8 bits isn't enough under all conditions. But this isn't a simple thing - eyesight is very complicated with lots of interacting phenomena. Even under controlled conditions, the amount of time you spend in darkness or how tired you are - all of those things interact. SteveBaker 20:47, 25 August 2007 (UTC)

Scary Movie

Hi, I've recently watched a scary movie about vampires n that sort of stuff... yeah, i know I shouldn have done so , but what's done is done... the problem is that I'm really scared now I know this may sound stupid, but is there a way to stop being scared? I've tried pushin it out of my mind but in vain... Thanks.

Maybe watching Buffy the Vampire Slayer would help?87.102.75.201 15:55, 24 August 2007 (UTC)

I remember getting really scared after watching "The Ring" alone. I tried watching spongebob to counter the effect. :D

Yes, read the How to be saved instructable. That should do the trick. Either that or make it worse. Clem 17:05, 24 August 2007 (UTC)

I've always found that reciting the Litany against fear helped.  :) -- JSBillings 18:04, 24 August 2007 (UTC)

Just remind yourself it's a movie. Maybe after watching a scary movie, watch Scary Movie (a parody of scary movies). Juanita Hodges 18:08, 24 August 2007 (UTC)

I've done the same thing numerous times. The thing to remember is that the vast majority of the time you are afraid of what you don't know. For instance, you are afraid of a dark room because you don't know what is there (i.e. a vampire or werewolf). You could also be afraid of water because you don't know what's under you (i.e. a hungry shark). Of course, your assumption is that these creatures' intentions are to kill you or otherwise commit unspeakable harm to you. The point is that you don't know, which is what you really fear. It's not a huge help, but it gives me some comfort to put it in perspective. --204.23.231.181 18:35, 24 August 2007 (UTC)

Don't be scared. I mean, if the vampires are going to get you, you're not going to be able to do much to stop them. ;-)

Personally I find scary things less scary once I know how they work. Look up how they did the special effects for the movie. Once you see a few "behind the scenes" photos of the actor looking like a doofus it'll be easier to think of it as a staged production. After I saw The Ring (I don't watch very many scary movies) I took some time to look up all of the "scary" death scenes, which are really scary because they are flashed really quickly on the screen in the movie. Once I got a good long look at them and how the special effects were done I didn't worry so much anymore. --24.147.86.187 00:53, 25 August 2007 (UTC)

I still can't bear to look at any shots from The Ring. What did help is that I saw the movie Underworld right afterwards; it is another horror movie, but one where the protagonists have more direct abilities to confront their enemies. That might help. Eran of Arcadia 18:56, 27 August 2007 (UTC)

Next time listen to what mummy and daddy say and don't watch a movie you're too young to watch :-P Nil Einne 14:06, 25 August 2007 (UTC)

Salt in processed foods

Is it possible that there might be so much salt in a processed food that if you ate it without having any water to delude the salt that the salt content would actually be enough to kill you? Clem 17:01, 24 August 2007 (UTC)

Well LD50 of table salt is about 3g/kg body weight - so if you weigh 50-100kg you'd need 150g to 300g of salt to give you a 50/50 chance of survival.

That's about 10kilograms of corned beef.. (22lb) That said you could make yourself pretty sick by just eating a lot less .

You'd probably gag first before you eat enough.87.102.75.201 17:32, 24 August 2007 (UTC)

Since 1kg of seawater contains 35g of salt - if you weighed 50kg, your LD50 is 150g of salt - you'd only have to drink 5 liters of seawater. That's still an awful lot - but it seems like you could maybe do it. But processed food isn't ever even close to being that salty. SteveBaker 20:12, 24 August 2007 (UTC)

(OH! ...and of course, the LD50 dose is the dose at which half of the subjects die - at good proportion of people would drop dead with a lot less than the LD5- amount.) SteveBaker 20:14, 24 August 2007 (UTC)

I dont know how true this is but i thought the thing that killed you was that you drunk too much water after consuming too much salt? Tiddly-Tom 00:24, 25 August 2007 (UTC)

Per the point several people have made, the LD₅₀ is the median lethal dose. Of more interest perhaps is the Template:LDLo which according to [15] is 1000mg/kg in humans. I.E. 50g of salt may be enough to kill a 50kg human. Nil Einne 11:50, 25 August 2007 (UTC)

Could try Dead Sea water. bibliomaniac15 Prepare to be deleted! 01:23, 27 August 2007 (UTC)

Editing Wikipedia telekinetically

I think I read about a kind of advanced, artificial limb that just came out that is designed such that the user can move his/her fake arm just by thinking about it. I think this is prety cool (does someone have a link to that an article about this, btw?). I'm wondering what other types of machines we'll eventually be able to operate just by thinking about their use... Are there other examples of this technology? In the future, could I, for example, edit Wikipedia articles just by thinking about the edits I'd like to make?--The Fat Man Who Never Came Back 18:07, 24 August 2007 (UTC)

You may be thinking of technology similar to this. This company (article) claims to have developed technology which allows players to control video games with their mind. I've read news articles about similar technology in the past but I can't find any of them - sorry — Matt Eason ^{(Talk &#149; Contribs)} 18:14, 24 August 2007 (UTC)

There have recently been a lot of studies about brain waves which have produced experiments using these brain waves to control mouse movement, prosthetic movement, etc. I would suggest you do a google search on brainwave experiments, brainwave studies, or brainwave control. I'm sure you will get many sites on it. To be clear, these experiments use a "cap" of sorts that fits on your head and it connected to whatever device you want to move, it isn't telepathy as we think of it in science fiction. --204.23.231.181 18:46, 24 August 2007 (UTC)

Yes, this stuff exists - but it's not at the level of you thinking "I really wish such-and-such would happen" - and it magically happens - you either have to make a peripheral nerve do something (eg by trying to move an amputated arm) - or in some implementations, you concentrate on modifying your alpha brain waves, which is something you have to learn to do with biofeedback techniques. Either way, we're a long way from being able to think words and have them appear on the page. These are at best fairly slow one or two bit binary inputs. There is plenty of scope for improvement on this though. I suspect the worst part will be in getting electrodes that can be worn comfortably and easily and which don't have to be positioned too precisely. Failing that, we need implantable technology and medical ethics being what it is, I don't think doctors will be routinely implanting brain probes into perfectly healthy individuals. It's possible that in the future, you'll have to take a trip to some country with less medical ethics than in (for example) the USA in order to get your bio-implant widget implanted. The real problem then will be getting it upgraded every few years as the technology improves. SteveBaker 19:22, 24 August 2007 (UTC)

For the sensors to be precisely positioned, they do not need to be implanted in the brain. In the skull would also do the trick and would be a much less tricky operation. Actually, the sensors need only be 'anchored' this way and don't have to be in the skull. All the electronics can then be at the surface. Maybe that would require shaving the head and maybe wearing a whig, but that's hardly a medical issue and I'd be willing to do this if it really gave me direct mind control over electronics. DirkvdM 08:03, 25 August 2007 (UTC)

Some early work on this was done by Miguel Nicolelis, who gave a monkey the ability to control a computer game. An extremely simple one, but it proves the principle. Given that it's a fairly unobtrusive experiment, I wonder why he didn't use a human (such as himself).

Similar work is also done with pilots controlling planes through thought. DirkvdM 08:03, 25 August 2007 (UTC)

Unobtrusive? Did you read the article you linked to "He and his colleagues implanted electrode arrays into a monkey's brain that were able to detect the monkey's motor intent and thus able to control reaching and grasping movements performed by a robotic arm". If you consider that unobtrusive I guess you can volunteer for the next human trials but I'm guessing Miguel himself didn't. BTW, this sort of thing has actually been done in humans [16] [17], not surprisingly in people who had a good reason for being willing to take the risk. Oh and I just found we have a surprisingly detailed article Brain-computer interface Nil Einne 14:05, 25 August 2007 (UTC)

Running On Water

I am aware that there are several species that are able to traverse the surface of water. Plumed basilisk seem to be able to do with speed that counteracts their low weight, while water striders rely on the hydrophobic nature of their legs to beat surface tension. My question, however, is not a biological one, but more in the realm of physics. How fast would a human being need to run to run on water? If you know of some forumlae that can provide the answer, you need but provide it - I am capable of plugging in numbers. If you choose to run the numbers yourself, choose any arbitrary variables that please you (for instance: mass, weight, surface area of foot, etc) as long as you state what variables you assumed at what value, and that they are within human norms. I am fully aware that it is not possible, and that there are likely a number of complicating factors. Let them trouble you not. :) Thanks. -- Sapph42 18:25, 24 August 2007 (UTC)

You can barefoot ski at ~35 mph, according to the article. --Reuben 18:34, 24 August 2007 (UTC)

I'm assuming this takes advantage of hydroplaning, which is hydrodynamically very different than running on the surface. Its a good start, though. Thanks. -- 69.255.155.141 18:57, 24 August 2007 (UTC)

Well, let's think about this. As you push one foot into the water, you are displacing water out to the sides. That requires a force to be applied to the water - which will operate to counteract your weight. The ikky snag is that as you pull your foot out of the water, you have to suck back enough water around the sides to fill in the hole you left. At first thought (and I confess I've spent about 20 second on this one so far!) I suspect those forces are about equal - meaning that you could obviously push yourself up out of the water by stamping down very hard - but in pulling your foot up for the next 'stamp', you'd pull yourself back down into the water to the same degree. So I think a simplistic "running very fast" kind of thing can't work. But maybe with some kind of extreme speed (now purely hypothetical) - you could be trying to make the water move faster than the speed of sound in water - and then maybe something interesting and non-linear might happen. Hmmm - tough. The Plumed basilisk can only do this for a relatively short distance - it's possible that it's feet sink slightly deeper into the water with each step - which is about what you'd expect to happen - but the shape of it's feet maybe minimise the losses so it can stay up for much longer than we might expect. If it could run on water indefinitely (or at least until it got tired) then maybe we'd have to say there was a way for humans to walk (or run!) on water. Hydrodynamics is a tricky subject though - I could easily be way off base on this one. SteveBaker 19:32, 24 August 2007 (UTC)

My initial thought is that the only way this could work and avoid the force/counterforce problem you outline is if the surface is never breached. Is there a minimum response time for surface tension, below which no contact will break it? If so, a sufficiently fast stride could circumvent your objection. Further, in the case of the Plumed basilisk, if it could move twice as fast, would it be able to travel twice is far? If so, regardless of non-linear affects, could a supersonic basilisk travel miles? -- Sapph42 20:24, 24 August 2007 (UTC)

Surface tension is far too weak to have a measurable effect on something the size of a human. It's not a matter of speed. I've had some revised thoughts about this. As your foot strikes the water, the space it wants to occupy is full of water - so if your feet sink into the water (say) an inch - then a volume of water equal to the area of your sole times one inch deep has to be moved out to the sides. In so doing, it accellerates from a standstill to some speed that's determined by how fast your foot comes down. Since force equals mass times accelleration, in order to get a force that's enough to support your weight under gravity - you'd have to move the water out of the way with an accelleration that's proportional to your weight divided by the mass of the water you are displacing. If you displaced (say) 1 liter and you weigh 100kg - then you're going to have to push the water out the way with an accelleration of about 100g's! That's very fast...but in principle you could do it. So for as long as you are pushing your foot deeper and deeper into the water, you are not sinking. But there comes a point where that foot is down as far as it will reach - so you have to stamp with your other foot WHILST PULLING THE FIRST FOOT OUT! But to get your foot out of the "hole" it made, the water has to flow back in beneath it - and if your two feet are moving at the same speed, it seems likely that the upward force required to pull the water back in would be pretty similar to the downward force you get by stamping down on the water. I guess the saving grace here is that when you push down, you are trying to raise the depth of the water slightly - so you are also lifting water upwards vertically. Gravity opposes that so you can apply a bit more force to overcome it. When you pull your foot back out, gravity is helping the water to flow back underneath again - so maybe you have more water resistance in the foot that's going down than you do on the one that's moving up. That tiny amount of difference might be enough for a very light creature with proportionately large feet. Those basilisk guys are small - and skinny with big feet. Since the weight a creature has to support increases as the cube of it's height and the area of it's feet as only the square of the height - the amount of water displacement - as a fraction of weight gets worse the bigger you are. Perhaps that explains how the basilisk does so well at this? SteveBaker 20:54, 24 August 2007 (UTC)

Bored physicists to the rescue. From The Physics of Superheroes by James Kakalios: "The density of water is much greater than that of air - water molecules are in contact with one another, while there are large open spaces between air molecules. . . . [F]or the Flash, when running in top of the water's surface, this is a good thing. Just as someone is able to water-ski if he or she is towed at high speed, the Flash is able to run faster than the response time of water molecules. As his foot strikes the water's surface at speeds greater than 100mph, the water is not able to move out from underneath his boot fast enough and instead forms a shock front, similar to the shock front that forms in front of a supersonic airplane." -- Sapph42 22:33, 24 August 2007 (UTC)

I think that's an unnecessarily exotic explanation. I just point my -- um, that is, the Flash, yeah, that's the ticket -- just points his feet. He leans forward and pushes against the water at an angle with his forward foot. He slides the back foot backwards out of the hole in the water; this requires very little force because he doesn't have to move any water out of the way, except what sticks to the foot. --Trovatore 06:50, 25 August 2007 (UTC)

It's an easy question to answer; the only variable you need to control is the temperature. Just get the water down to around -20C for a while and it should be solid enough to walk, run, and skate on. Matt Deres 14:48, 26 August 2007 (UTC)

Space-time continium

Hi, im writing a science fiction story which involves a device that is able to look back in time, problem is i can't describe how it works because i don't know. I think it would be something to do with the space-time continium, but i'm not sure, i've already checked wikipedia for information, so i was hoping you could give me some info on how such a device could work. Thanks for taking the time to read this. (I would also like to thank everybody who has taken the time to provide answers for my question).

Best regards Sci-fiGOD2k7 18:51, 24 August 2007 (UTC) Sci-fiGOD2K7

A popular idea I've seen in a lot of science fiction is to take advantage of the Multiverse theory, and to view an alternative universe that is identical to our own, only that it is 20 years younger (or whatever time you want to look at). -- JSBillings 18:54, 24 August 2007 (UTC)

Look at info on pages like black hole and event horizon. Looking back in time is what we do all the time. What you see is not happening right now. It took time for light particles to bounce off stuff and then hit your eye. So, seeing far into the past simply means having some old light particles around to catch a peek at. -- Kainaw^(what?) 18:55, 24 August 2007 (UTC)

Or if something less scientific appeals to you, perhaps this device could access the Akashic records.--Shantavira|^{feed me} 19:17, 24 August 2007 (UTC)

Merely looking back seems maybe possible. Firstly, all the information about what was happening back then may not have been lost (talking about a scifi plot rather than reality here). Suppose a book slid across that table an hour ago. The energy of it's motion got turned into heat - perhaps some amazing scifi gizmo could examine the energy present in the world now - and track that backwards in time to someplace in the past. Not possible in reality for all sorts of thermodynamic and heisenburg-ish reasons - but maybe a good writer could make it seem plausible! Alternatively - if we don't have to look back into time before the creation of the technology, it could merely be recording where things in the world are right now - and replaying them later. In a sense, a VCR does what you ask. It's a spooky device that lets you watch TV from the past! A camera and a VCR lets you see into the past. So a device that recorded MUCH more information than a camera and a VCR could record EVERYTHING that happened. Maybe a ubiquitous array of sensors made out of nanotechnological 'dust' and sprayed from the air over everything and everyone - recording in massively complex nanotech memory and replayed via some kind of holistic network which allows you to broadcast a command for any mote of dust that was around 10 years ago at this location to please return data to me. But that limits you to not seeing further into the past than the invention of the machine. Most of the hypothetical relativistic/black-hole/wormhole time-machine contraptions that people come up with would have the same restrictions - but my way is a lot more do-able in reality. To actually see far into the past - before the invention of a machine to do it is exceedingly dubious. Parallel universes (as far as we know) are undetectable and cannot communicate information to us - so they don't really help - although if you are prepared to bend science enough, you could argue for it.

Do me a favor though. If you write this story - think about this: If you have a machine that can see back in time, it also has to be able to see different locations in space too - the earth is orbiting the sun - if you look back at the spot you are at right now, but 6 months ago - all you'll see is vacuum - because the earth was a long way away back then! So your device has to be able to look at any place as well as any time. If it lets you look back (say) 1 millisecond ago - but anywhere in space - then it's able to spy on anyone right now! It would be a tremendously useful instrument because we could (presumably) use it to explore the bottoms of the oceans - or the innermost parts of the earth's core. If the device were cheap enough so that (for example) a major newspaper publisher could afford one, you just know that nobody would have ANY privacy anymore. Forget being able to see into the past! Seeing any place here in the present would be an earth-shattering thing. SteveBaker 19:54, 24 August 2007 (UTC)

This is the plot for an old Isaac Asimov story. The government suppresses the technology because it allows someone to spy on anybody. Delmlsfan 02:31, 25 August 2007 (UTC)

I thought it measured the trajectory of neutrinos.. it's a pretty stupid idea. Based off of "if you know every particle's location and trajectory then you know the future".. of course it's impossible to define exactly where a particle is at quantum size, and it makes even less sense to try to pull off that calculation with only a miniscule data set --froth^t 04:05, 25 August 2007 (UTC)

There's a fairly famous old story on this premise, "E for Effort" by T. L. Sherred. Damon Knight revisited it, in a mellower key, in "I See You" (1976?), which i think assumed a sort of slow light. —Tamfang 21:56, 24 August 2007 (UTC)

I want to thank people for helping me with this matter, as its driving me nuts. My original idea was that it was a system of satellites all hooked up to a quantum computer, and the satellites were somehow able to look back in time, but i'm not sure how this would work. Thanks again, Sci-fiGOD2k7 22:30, 24 August 2007 (UTC)

I'm a big fan of this kind of 'hard-core' scifi - and in my view, I'll allow any story writer ONE ridiculously impossible invention providing that:

• It's self-consistant (like with what I said about it being able to see any PLACE as well as any TIME) - if there is a glaring inconsistancy - it'll bother me through the entire book!
• That all of the implications of the thing are properly explored.
• That it's actually necessary for the plot.

What I hate is when some device is postulated - and I find myself saying "But if you had a thing like that - why wouldn't you use it like this?!?" - or "Why did the author need to invent such a thing when the story would have been just the same with more reasonable technology". So I'd be happy to read a story where you handwave the details of why some quantum effect in a satellite allows you to look into another place at another time - so long as you tell me about the consequences of using it for spying on your boss one second in the past (or whatever). (I'm also trying to remember another story based around the "machine that looks into the past"...something to do with investigating the history of Christopher Columbus...I don't recall. SteveBaker 01:05, 25 August 2007 (UTC)

A looking-back-in-time machine

At right is a real-world device that once looked 13 billion years back in time. --Sean 01:10, 25 August 2007 (UTC)

I remember an Isaac Asimov short story had such a device. I can't remember if it had much explaination. Basically someone came up with the theory. The device was invented and under the control of the world government science ministry. They controlled the information about the device that was release. They did regularly release 'discoveries' from the past. Then a history professor got annoyed when his proposal to study something never received any attention and enlisted a student to help him (illegally) make a device. The student accepted but after a while realised that the government had been bullshitting as the device couldn't look back that far as it got more blurry the further back you go. The professor's wife found out about the device and was very interested. The professor himself lost interest because 1) It couldn't study what he wanted to 2) His wife wanted to look at their dead daughter which was bad because a) It was unlikely to be beneficial for her well being to keep look at her dead daughter b) He was a smoker and was afraid he may have been responsible for the fire that killed his daughter. The government meanwhile found out and was watching the involved parties with their version of the device. They professor intervened and tried to get the student to stop making the device. The government joined in and pointed out the reason they'd been protecting the device was because it completely destroy society as it would destroy privacy; as the past is basically the present. Unfortunately it was too late as the student had already given his research to his uncle who had then given it to the press and the government had not noticed the uncle's involvement so had not watched him. Anyway the point of my retelling here was to concur with SB. If you want to include such a device you have to think of the implications it will have. I mean there's already enough of Britney and Paris in the media without "watch Britney drinks a glass of water" or "watch Paris try out 3 dresses before deciding just to go naked (everyone's already seen her naked anyway)". Unless you take the easy way out and do the opposite Asimov's device, it can't look into the near past but only the far past. But this makes far less sense to me... Nil Einne 12:55, 25 August 2007 (UTC)

I have thought of what i want the device to be, a series of satellites linked to a powerful earth based quntum computer. The device can look a far distance back in time and as its a system of satellites it can look any where on earth. But i have a problem, as im not sure how i could get it to look back in time, does anyone have any ideas to how it could look backwards through time, because personaly i'm no good with the whole spacetime thing, but i was thinking it could use a series of light cones to look through a closed time like curve, but im not sure how it would do this and if it would work (in a fictional stand point). So if anyone has any ideas of how this would work i would love to hear them. Thanks for all answers past and future

Sincerly Sci-fiGOD2k7 16:29, 25 August 2007 (UTC)

A large mirror placed 2 light-years away - coupled with a really powerful telescope - would allow you to see exactly four years into the past. But as with all such devices, even if you launched it at some insane speed, close to the speed of light, it would take more than two years to get to the right place and by the time the light reflected from it got back to our telescope, it would be another two years - so the machine would only be able to look back to points in time AFTER its initial creation. This does seem to be a fundamental limitation of all such contraptions. SteveBaker 22:06, 25 August 2007 (UTC)

user knowledge

I have developed an indicator circuit to display the status of a Hall sensor. A friend says the user of the device it is in will not buy it because it is diagnostic tool only a technician would find of any value. I contradict saying that knowing is far better than not knowing regardless of whether the knowledge is useless of over your head. Who is right? Clem 20:54, 24 August 2007 (UTC)

I'd say you and your friend are right, whereas the user is wrong, and you might want to adapt to the user. As you say, for a completely rational person, more knowledge is always good. Your user, however, might find it intimidating or something, because he does not understand it. I did a similar thing at the supermarket the other day. I was going to buy ham, but there was too much to choose from so I ended up buying nothing! Stupid of me, but that's what I did. —Bromskloss 21:38, 24 August 2007 (UTC)

Perhaps a compromise is in order. I agree that displaying something all the time which the typical user won't understand would be annoying to them. Instead you could have them hold some combination of buttons down to get the status of the Hall sensor. That way, the user won't be annoyed by it, but techies can still get the info if they want it. StuRat 03:42, 25 August 2007 (UTC)

Good idea. An on/off switch. Clem 22:45, 26 August 2007 (UTC)

Maglev technology & Meissner Effect/Flux trapping

I know about the Japanese maglev system that uses superconducting coils for efficiency in its EDS system, but why has no-one tried using the Meissner and flux-trapping effects demonstrated by super-conductors (below their critical temperature) to create a stable maglev platform? The technique has been demonstrated on 'toy' maglev trains, videos of which can be found on YouTube ie. http://uk.youtube.com/watch?v=rfUWDYm0ewI

Would such a design not be favourable over both electrodynamic (EDS) and electromagnetic (EMS - eg. Transrapid) suspension, EDS requiring the movement of the train to create the levitating force, and EMS being naturally unstable and requiring a computer control system?

Or are there technical limitations that I am unaware of? For example can this method carry the weight of a laden train?

Thanks, Jonaboff_talk

22:41, 24 August 2007 (UTC)

Just an idea. I believe the superconducting property vanishes in the precense of too strong a magnetic field (right?). Carrying a full-size train would require a stronger magnetic field than carrying a toy. Perhaps it would be too strong. —Bromskloss 23:01, 24 August 2007 (UTC)

It would be a matter of price. A superconducting coil in the train is one thing, but making hundreds of kilometers of superconducting track would exceed the budget of the train company. The material costs on the order of $100 per gram, or $100,000,000 per ton. Graeme Bartlett 23:16, 24 August 2007 (UTC)

A minor note—the toy shown uses conventional (albeit fairly powerful) magnets in the track. The only superconductor in the toy is aboard the train. Of course, sufficiently powerful permanent magnets for such an application would also be quite costly. I'm not prepared to comment on whether it would even be possible to scale up such a system to operate at hundreds of kilometers per hour and with cars weighing tens of tons. TenOfAllTrades(talk) 13:09, 25 August 2007 (UTC)

I'd say Graeme is right. No chance to make such a large installation superconducting. The largest device build so far to my knowledge is the Large Hadron Collider: The 30 kilometre circumference ring is kept at liquid helium temperature to be able to use superconducting magnets. Simon A. 08:39, 25 August 2007 (UTC)

It there any reason why you have to use low temperature superconductors? Most maglev systems in development using superconductors are using 'high' temperatures ones cooled by liquid nitrogen Nil Einne 12:58, 25 August 2007 (UTC)

As Ten said, only the bogeys of the train would be superconducting, the track would be ferromagnetic. Do the superconductor effects only work with permanent magnets, or could electromagnets be used?

I also have a feeling that the $100 per gram estimate is a little high, that puts it at around £50, right? I can buy a kit like the one shown in the video for little more than £100, and the superconductor block weighs much more than 1 gram.

Thanks, Jonaboff_talk

14:05, 25 August 2007 (UTC)

I'm not 100% sure if I understand the difference between what you're proposing and what's be done but, are you sure this has never been attempted? What about the Southwest Jiaotong University, China test (see Maglev train). Our article has limited information but there is more information in various journal articles. Nil Einne 14:46, 25 August 2007 (UTC)

The Southwest Jiaotong University, China maglev is actually exactly what I meant by the sounds of the article, I'm not sure why I haven't noticed that in the article? I'll check the history, see how recently the section was added. Thanks anyway. My point still stands, that it seems strange to me that this approach isn't more popular, when it eliminates the problems of stability, power failure, does not require wheels etc.

On a side note, does anyone know if electromagnets can be used in such a system, or can only ferromagnetism achieve these effects? Is there a physical difference between electromagnetism and ferromagnetism besides the source?

Thanks, Jonaboff_talk

15:45, 25 August 2007 (UTC)

August 25

Mountain height limit

I recall learning about a height at which mountains 'melt' their base, implying a hard limit on the physical height of mountains (on earth, etc). Is this true, and can anyone find details? Thanks :) --Quiddity 00:50, 25 August 2007 (UTC)

Regarding erosion... Angle of repose. —Preceding unsigned comment added by 138.29.51.251 (talk)

There are a few limits you can put on the size of a mountain, depending on exactly what failure mode you're interested in. It turns out that there are different things keeping mountains up: some are effectively floating, some are totally unstable and start to sink as soon as nothing is building them up again... the article at isostasy has some more information. Here's a paper where the author estimates the maximum height of a mountain: How high can a mountain be? by P.A.G. Scheuer, J. Astrophys. Astr. 2, 165 (1982). This primarily considers the failure mode where the mountain simply falls apart. As you make the base wider and wider, it's possible to make the mountain taller and taller. The paper also describes an odd "tower" of blocks that can be arbitrarily tall. There might also be a largest mountain that can be statically compensated, but I'm not sure about that. I don't think that melting as such should be a problem. You have to go all the way to the outer core to get liquid. It's more a matter of overstraining the material until it breaks. --Reuben 06:51, 25 August 2007 (UTC)

To elaborate on Reuben's point, the outer core starts at a depth of several thousand km, whereas mountains grow up to heights of several km or at most tens of km if you measure from the deepest sea trenches instead of the sea surface. However, I imagine there would still be some effect, even if it is not the most decisive. Also, some volcanoes (which are mountains of sorts) arise at hot spots, where the crust is much thinner. DirkvdM 08:28, 25 August 2007 (UTC)

So we know that for most substances, the melting point decreases with increasing pressure - so at what pressure does rock melt at (say) 20 degC ? Once you know that it should be a simple matter to discover the answer to this question. Sadly, I don't know how to find out that first answer. SteveBaker 21:13, 25 August 2007 (UTC)

I don't know if "melting" is the right model, but that's the basic reason why Olympus Mons is on Mars, and could never exist on earth with its greater gravity. Gzuckier 15:15, 27 August 2007 (UTC)

Monounsaturated and Polyunsaturated Fats

Hi, I've learnt that mono- and poly- unsaturated fats are beneficial to one's health, yet which is more important or more beneficial? I don't mean totally cutting out the other, but I just wanna know which is better. Thanks

There was a time in living memory when the conventional wisdom was, the more double bonds, the better; polyunsaturated fatty acids were considered to have better properties as regards preventing plaque accumulation in the arteries. I'm not an expert on this, but I believe the mainstream thinking has changed, and nutritionists think that most people would be well advised to increase the proportion of their fat intake that consists of monounsaturated fatty acids such as those found in olive oil and peanut oil (while reducing their total fat intake overall). Supposedly the polyunsaturates are more likely to cleave at the double bonds forming dangerously oxidative free radicals.

But you never know. These guys change their story a lot; five years from now we may be hearing something different. One exception to the "polyunsaturates bad" current conventional wisdom is that people are considered to require a certain intake of omega-3 fatty acids for proper brain function. --Trovatore 06:28, 25 August 2007 (UTC)

regarding heat

I understand that as an electron goes down an energy level it will release a photon or cause the atom or impart more kinetic energy to the atom. Could you please explain how this kinetic energy is imparted?

It still happens by a photon being emitted, but the photon is absorbed by a neighboring atom. Some other effects also come into play. When the photon is sent out it carries some momentum, and the atom moves off in the opposite direction to compensate. The photon is lowered in frequency or energy to compensate. Another way is that energy is shared amongst several atoms. One way to visualize it it to imagine the activated atom to be larger, and it suddenly shrinks or changes shape. If it is attached to other atoms in a chemical bond, it will shake around all the atoms involved disapating the energy. Graeme Bartlett 22:12, 25 August 2007 (UTC)

thanks

bird blood

Hello, if birds have hollow bones how do they synthesise blood ?Boomshanka

I asked the same question a while ago. turns out that bird bones aren't really hollow at all. They have air pockets, but apperently they also have bone marrow the synthesize new blood cells. PvT 17:07, 25 August 2007 (UTC)

Anyone who's sucked the marrow out of a chicken bone has seen it first hand. It's also worth noting that flying birds don't seem to have a lot of blood. I've hit birds with my car windshield, and it was all just feathers and grey guts with little or no blood. --Sean 12:20, 26 August 2007 (UTC)

Toxicity of unrinsed dishes

In the Netherlands (and in the UK, it seems) many people do not rinse the dishes after washing them. Washing-up liquid has a link to a suggestion that that is no problem if the right concentration was used, but I doubt that that happens often (most people use way too much, especially in the US). So is any remaining washing up liquid on the dishes a health risk? Btw, I once heard that swallowing pure washing-up liquid is unhealthy because it makes your intestines stick together, but that's a different thing. DirkvdM 06:22, 25 August 2007 (UTC)

Not in the short term - apart from the taste the small amounts should have no ill effects

In the long term - who knows? Myabe you'll just have a nice clean intenstine!87.102.84.56 12:59, 25 August 2007 (UTC)

It would depend on the composition of the dishwashing detergent used. Since it's not normally intended for human consumption, they may put things in which are somewhat toxic (not highly toxic, mind you). If you consume a substantially larger quantity than they expect, you may suffer from health issues. Of course, my observation is that food contaminated with even tiny quantities of dishwashing detergent is so unpalatable that I can't eat it anyway. This is why you should clean dishes in the organic way (have your dog lick them clean). StuRat 16:58, 25 August 2007 (UTC)

Disclaimer: this is my opinion, and I'm a very opinionated person.. I'll never understand people who don't rinse their dishes. It's like taking a shower and leaving the shampoo in your hair. Rinsing not only removes the detergent leftovers, but it's also an important part of the actual cleaning process. After all, the whole point of detergent is to make the grease come off. The grease will indeed come off the plate and attach itself to the soapy water, but if it isn't rinsed off, then you effectively haven't cleaned the dishes at all. Oh well.Nimlhûg 20:32, 25 August 2007 (UTC)

Exactly, that's what I tell people too. It's the rinse that counts, the soap or whatever is just an aid. I once saw in a hospital how the floor was 'cleaned' by applying a detergent solution (what do you call that?) and then simply sweeping it up again. No rinsing. That's just redistributing (most of) the dirt and adding toxic stuff to it. In a hospital! But a lot of people do that, more than with the dishes.

Anyway, it may be clear that I always rinse, but since a lot of people don't (including my mother) I wondered what the health risks might be, if any. And might washing up liquid be designed with this in mind? DirkvdM 06:13, 26 August 2007 (UTC)

While the thing about the hospital doesn't intuitively sound great, it strikes me as possible that things are not quite as bad as they sound. The "toxic stuff" may well be the point. There are actually two components to washing things -- mechanically removing nasty stuff, and chemically/physically killing it. The balance between the two depends on the context -- those "hand sanitizer" things you see people using a lot these days rely entirely on the second modality. Antibacterial soaps are a separate thorny issue; some people are worried about triclosan getting into the water supply, and about bacteria becoming resistant to it. --Trovatore 16:49, 27 August 2007 (UTC)

It also has to do with how much wash water is left on the dish to evaporate. If your dishes were reasonably hydrophobic and you set them vertically to drain and air-dry, the rinsing step might not make much difference because there might be very little wash-water (and its detergent) left on the dish anyway. By comparison, if the dishes were hydrophilic and/or you set them down horizontally with a puddle of dirty, soapy wash water standing in them to evaporate away, then your results would be quite different. But I'm American, so I'm a rinser.

Atlant 11:47, 27 August 2007 (UTC)

Spherical Magnet?

Why is it impossible to repeat a simple bar magnet onto a sphere at an angle that's perpendicular to the tangent of the surface so that whole of outside have one pole while the whole of the inside have the other pole? --antilived^{T | C | G} 07:15, 25 August 2007 (UTC)

I haven't made the calculation, but perhaps if you added together all their magnetic moments they would sum up to zero? —Bromskloss 10:48, 25 August 2007 (UTC)

I'm not sure that it is impossible - why do you think so (excluding the difficulty gluing the thing together).87.102.84.56 10:56, 25 August 2007 (UTC)

My Physics teacher said so, because of "the field lines would intersect the magnet itself". However is there any other explanation on why is it impossible (or not)? --antilived^{T | C | G} 12:14, 25 August 2007 (UTC)

There's this thing with that the magnetic field should be divergence free ($\nabla \cdot \mathbf {B} =0$), that is, there are no magnetic monopoles. The discussed spherical magnet, however, would have such a monopole in the middle, from which the field lines would originate. —Bromskloss 12:25, 25 August 2007 (UTC)

That would have to be a perfectly made example though - if there were gaps between the magnets there would be no problem.?

(Secondly what if Maxwell is just wrong - does the spin of a neutron not represent a magnetic monopole??)87.102.84.56 12:55, 25 August 2007 (UTC)

If there were gaps, the magnetic field inside would leak out there and cancel the outside field and we would no longer have a magnet. Spin would correspond to a magnetic dipole, I guess. —Bromskloss 16:48, 25 August 2007 (UTC)

Surely if there would be gaps the situation would be just one of having N magnets all arranged about a point - erm - so they would still function as magnets.?

Actually I don't get the original poster's physics teachers response "the field lines would intersect the magnet itself" - say I take a rectangular bar magnet and force (literally) 11 other similar magnets around it (not all N-S alligned) - then the magnetic field lines might be forced inside the magnet - with possible demagnetisation.??

MY ANSWER TO ORIGINAL POSTER I think to be honest your physics teacher has 'dodged the question' - though to be honest I'd like to dodge it also - it's a complicated situation really. And the answer depends on whether there are gaps between the magnets (Ithink) and also has to take into account the possibility of some demagnetisation near the centre due to the concentrated magnetic field.

If you could do it - with specially 'wedge' shaped magnetic peaces then it would be interesting to consider if the thing you would have made is effectively a monopole (from outside). I'm guessing some demagnetisation would stop this happening due to the highly concentrated field lines..87.102.84.56 18:16, 25 August 2007 (UTC)

I remember reading somewhere that mathematically a sphere with uniform density has the same gravitational pull as it would if it was all compressed into a point in the center. Because gravity and magnetism both obey the inverse square law, the same applies to a magnetic monopole. If you had a larger sphere that was a northern monopole, and a smaller one that was a southern one, and you put the smaller inside the larger so they shared the same center (effectively making the magnet you described), from anywhere outside the sphere it would be the same as if they were both in the same point in the center, where they'd counter each other out. In short, the southern magnetic field emanating from the center of the sphere and the northern field emanating from the outside would be the same everywhere outside the sphere and counter each other out. Get it? — Daniel 18:43, 25 August 2007 (UTC)

Yes - thats right - though I'd expect a very weak residual field from the magnets.

I don't know if you'd be able to explain what happens to the 'magnetic field lines' in the case where 'cone/wedge shaped magnets' make up a perfect sphere - (you answered question 1 pretty well - just hoping) - I think they must go through the magnets so there must be some blanking as well?87.102.84.56 18:56, 25 August 2007 (UTC)

Let's just take Maxwell's laws to their natural conclusion. $\nabla \cdot \mathbf {B} =0$. From this, we know that the same number of magnetic field lines enter the sphere as leave it. Further, let's just look at the wedge shaped magnets you'd need to make such a sphere. The same law holds for them, the same number of magnetic field lines entering the north end emanates from the south end. I'd imagine that in a realisticly constructed sphere, you'd have magnetic fields leaving the magnet (in standard magnetostatics, the field lines leave the south end, and enter the north end) through gaps between the wedges, and re-entering across the wedge surfaces. Now, if you could have a flawlessly spherical and uniform magnet, well, let's turn to electrostatics. The laws governing electrostatics and magnetostatics differ only due to the absence of magnetic monopoles. However, if such things existed, magnetic monopoles would interact with one another exactly as electric charges do (except the left-hand right-hand rules get switched somewhere, this has been a while for me!). So, one "monopole" spread over the surface of a sphere, and an equally strong but opposite monopole in the center. From Gauss's law, the monopole on the surface creates a magnetic field outside the sphere identical to one that would be created if it were concentrated at the center of the sphere. Since electromagnetic fields obey superposition quite perfectly, the two poles cancel out completely everwhere outside the sphere, and your long sought after spherical magnet is completely dead. Someguy1221 20:34, 25 August 2007 (UTC)

I think is worth noting (with reference to the later part of your argument) - that the field due to a spherical surface charge is not exactly the same as that of a point charge centred at the sphere centre - there's a (small difference) - which varies with distance... (that difference depends on the nature of the 'field' variation with distance and of course if the field is a vector or scalar quantity matters as well)... 87.102.84.56 21:16, 25 August 2007 (UTC)

Meaning that the spherical magnet is not dead (possibly very weak) but with a <literary effect>unmistakeable feeble pulse</literary effect>...87.102.84.56 21:21, 25 August 2007 (UTC)

That arises from the failure of the assumption that the charge can be uniformly spread over the surface. If it could be, the magnet would, literally, be completely dead on the outside. But since electrons have finite distance between them, this is not the case. Someguy1221 21:35, 25 August 2007 (UTC)

No the effect still arises when the charge is uniformly spread on the surface.87.102.23.4 00:36, 26 August 2007 (UTC)

I'm confused, why? Someguy1221 01:06, 26 August 2007 (UTC)

Consider the gravitational effect from a point mass M

and the gravitational effect from a evenly distributed spherical surface with total mass M (gravity follows the same inverse square law as electrostatics yes?)

The functions of field/force are very similar at great distances

But differ fundamentally - the field is given by a different equation for each case.

You'd need to work out the field due to a distributed mass/charge around a spherical surface as a function of distance - probably you'll end up with a function with two integrals - you don't need to be able to do the integration to show that the function is not the same as the 1/r² that comes from a point mass/charge. (this may be a maths desk problem)

Because the two functions are different - subtracting one from the other results in a non zero field (in fact there is a surface where the field is zero - but everywhere else it is non zero) - in fact the field changes sign. 87.102.23.4 01:16, 26 August 2007 (UTC)

(the gaussian law holds when r (the distance) is greater than R (the radius) r>R but is not 100% correct at finite distances - there is a minute error - which is much more noticable when r approaches R - in fact when r=R the field becomes infinite just as it does when r=0 with a point charge. Gausses law is an approximation - that's why I said that the noticable effect would be 'very feeble' - this is especially true when r>R because the approximation is very good.87.102.23.4 01:25, 26 August 2007 (UTC)

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/elesph.html#c3 gives the approximations for field according to gauss inside and outside the sphere - note for inside a sphere of radius R the field according to gauss is Qr/4pie₀R³ - not the same as a point charge - I can't find a link to a more detailed analysis right now but can explain if if needed.87.102.23.4 01:33, 26 August 2007 (UTC)

Your own link states, if I may quote: "The electric field outside the sphere (r > R)is seen to be identical to that of a point charge Q at the center of the sphere." Their equations for both inside and outside the sphere are trivial applications of Gauss's law. Someguy1221 01:46, 26 August 2007 (UTC)

I linked just to show that a different equation exists (under guasses approximation) for r<R - there is under gausses approximation - a discontinuity at r=R - this is not the same as being 'identical to a point charge' because for a point charge there is no discontinuity at r=R. How exactly do you explain gausses equation for the field inside the sphere

Qr/4πє₀R³ (inside the sphere) compare Q/4πє₀r² for a point charge?

in terms of a point charge?87.102.44.85 10:54, 26 August 2007 (UTC)

It's actually completely consistent. The example given was that of a sphere whose charge is uniformly distributed through the entire sphere, not just the surface. If you accept that charge distributed across the surface of the sphere creates no electric field within the sphere, then at any point inside the sphere in the example, the charge you are "exposed to," in a sense, is proportional to the cube of your distance from the center. So, as you move out from the center, the apparent point charge increases in magnitude as r³ while the field strength/charge ratio remains proportional to 1/r², yielding the linear relationship Qr/4πє₀R³ (where R is the radius of the sphere, constant). At r = R, the two equations give the same result, there is no discontinuity. Someguy1221 22:24, 26 August 2007 (UTC)

In the example you gave originally "So, one "monopole" spread over the surface of a sphere, and an equally strong but opposite monopole in the center. From Gauss's law, the monopole on the surface" and in the example linked (which isn't connecting unfortunately) the charge was on the surface - I've underlined those parts that refer to the monopole/charge being on the surface. It looks like you don't know this.

You're analysis above is just wrong( the first part). The second part you have just turned into words what was stated in the equation. There is discontinuity in terms of the first and other differentials. If you want to discuss this further can you start a new question because we are getting very far away from the original magnets problem.87.102.45.106 12:01, 27 August 2007 (UTC)

This is all because, from a mathematical perspective, Gauss's law and Coulomb's law are actually identical. The only difference is that Gauss's law does not inherently imply that the electric field of a point charge is radially symmetric, so you must make this assumption (which everyone does). Someguy1221 22:29, 26 August 2007 (UTC)

Note - gauss's law inside the sphere surface is mathematically different from coloumbs. Please be careful when you say things like 'mathematically ... identical'87.102.45.106 12:01, 27 August 2007 (UTC)

Bacteria in human mouth vs. at the end of the digestion process

I know in some species like the kimono dragon their mouth has so much bacteria that it's what kills people and not their bite, so they may even have worse bacteria in their mouths than at the end of the digestion process (rectum). But what about humans who have bad breath, tooth decay, and that white-yellow film on their tongue from bacteria... how much, how deadly, etc. is that bacteria to the bacteria at the end of the digestion process? mouth (human) is a brief article that says nothing of this. Juanita Hodges 07:18, 25 August 2007 (UTC)

Very little bacteria survives the beginning of chemical digestion in the stomach—the low pH (high acidity) pretty effectively kills most bugs. Intestinal flora are usually quite different from the stuff in your mouth.

Meanwhile, the toxicity of komodo dragon saliva depends partly on the bite; it's not just the saliva by itself. By puncturing your skin, pathogens in the komodo dragon saliva get a free pass into deeper tissues and (potentially) your blood. While your mucous membranes and skin are (somewhat) resistant to many nasty things, most of the rest of your body is more poorly defended against pathogens. (This is one of the reasons why gastrointestinal perforation is so serious—the normally harmless and helpful bacteria in your gut get spilled out into the abdominal cavity, where they cause massive infection.) TenOfAllTrades(talk) 18:33, 25 August 2007 (UTC)

How bad are the human mouth bacteria compared to intestinal bacteria? Juanita Hodges 22:07, 25 August 2007 (UTC)

When placed where they shouldn't be, intestinal bacteria are generally worse. Someguy1221 01:48, 26 August 2007 (UTC)

Can human mouth bacteria be deadly or infectuous in the wrong place? Juanita Hodges 02:26, 26 August 2007 (UTC)

Depends how far along the road to decay the mouth is. If there's an actual infection with bacteria chewing away at the gum tissue, you can correctly imagine that those bacteria will be more than happy to chew away at your arm tissue or foot or whatever as well. This is the basic reason why people with pacemakers for instance have to be careful with dental surgery because those serious bacteria could enter the blood stream and infect the wiring to the pacemaker, etc. Regular tooth-cavity bacteria, not so much. Their big trick is turning sugar into cement, which is not that handy for infecting a puncture wound. Also, scientists currently are beginning to doubt the komodo dragon story, and theorizing that maybe it's a real toxin they secrete. Other reptiles get pretty good mileage out of the poison-bite trick, of course. Gzuckier 15:10, 27 August 2007 (UTC)

Camera emulating the human eye

In a question hereabove, SteveBaker says the human eye uses a combination of colour and brightness detection, a technique also being developed for monitors under the name RGBS or RGBE (note that RGBE is about something different, although related). I had previously thought of making a camera sensor that way. Put a layer in front of the colour sensor that does two things - measure the brightness and darken according to the brightness. Thus, the light passing through it to the colour sensor will be of equal brightness and the colour sensor needs only detect the colour. The idea is that if you split the two functions they can be more precise at what they do - more detail in brightness and shadows and a higher colour depth. Also, performing a more limited task means it can be done in a smaller area, so the pixels can be packed closer together, so the resolution (and with it the pixel count) goes up. Does this make any sense? DirkvdM 07:38, 25 August 2007 (UTC)

After a couple of reads .. yes... You get higher dynamic range (in the overall image) - a pixel seeing bright light can get a good exposure without being overexposed (whiteout) at the same time as a pixel getting low light can also get a good exposure - makes sense..

As for the second part "Also, performing a more limited task...." I'm not sure I agree - wont the pixels just be the same size as normal?87.102.84.56 11:01, 25 August 2007 (UTC)

I seem to remember a vaguely similar system - were there are four sensors - rgb and intensity - the intensity sensor controls the sensitivity of the rgb sensors electronically though - possibly this was in a fuji camera 'ccd' can't remember more though.87.102.84.56 13:39, 25 August 2007 (UTC)

One problem I see is that the time it would take for the first layer to darken wouldn't be enough to block the light from hitting the second layer. With flash photography, perhaps a double flash could be used, where the first flash darkens the first layer and the second flash is used for the second layer. Another problem might be that the first layer would refract light and cause a fuzzy image. The closer the two layers are to each other the less of a problem this would be. StuRat 16:46, 25 August 2007 (UTC)

Someone said something about pixels. This isn't to increase the number of pixels, it's to increase the accuracy of the color in each pixel. Why is it red green blue and brightness instead of hue sat and lum? I know one of those is brightness. — Daniel 17:04, 25 August 2007 (UTC)

It's hard (maybe impossible) to build a 'hue' detector without building it from a set of red, green and blue detectors. Hue is a measure of where on the rainbow spectrum you are - so you'd think it would be a measure of light frequency or something - but then we have 'hues' like Magenta (purple) which is a mixture of red and blue that doesn't ever appear as a single frequency of light. Alternatively, we have the colour humans call 'yellow' which is really one of two totally different physical phenomena. It's either pure light of a frequency somewhere between red and green - or it's a mixture of pure red and pure green. Humans can't tell the difference - but a frequency-measuring-sensor would have to do so in order to produce realistic colours. The concept of 'hue' as we describe it only works for creatures like humans who happen to have red, green and blue sensors. So when you are making a camera, the simplest and most realistic thing to do is to emulate the human eye - producing the exact same artifacts as the human eye does. Hence, our cameras have the exact same problem (that they can't tell the difference between the two kinds of yellow) as we humans do. So RGB is here to stay - adding intensity sensors would perhaps be useful though. SteveBaker 21:25, 25 August 2007 (UTC)

I'm not sure I follow. I'm not suggesting to eliminate the rgb sensor, just present it with a light that is always equally bright, so it can focus more on its own task and thus be better at it. The image at the top of Munsell color system is rather illustrative. I want the first sensor to measure the brightness and 'equalise it' for the second sensor, which then measures hue. Now I wonder how chroma is measured. Or does that go with hue? DirkvdM 07:24, 26 August 2007 (UTC)

The colour system you are talking about is Hue/Saturation/Value (HSV). Hue is best descriibed as 'where on the rainbow you are' - all shades of red through bright red to dark red and including pinks have about the same hue. Saturation is the distinction between red and pink - or blue and 'baby blue' - it's the amount of 'colour' in the colour so to speak. Value is brightness. HSV is a useful way to pick colours if (for example) you are worrying about colours that look good together, concepts of contrasting shades are easier to understand in HSV than in RGB - but there is relatively simple math to convert one into the other and back again. There are many different variations on the HSV theme though. So your idea for the sensor is to normalise the brightness of the incoming signal so that the RGB sensors are operating at higher brightness levels. Essentially, that's what RGBE/RGBS does - it decouples the overall brightness of the signal from the sensitivity of the RGB number range. But whether you can come up with a sensor that physically implements RGBE is a tougher question - as far as I know, all existing high-dynamic-range systems work by taking pictures at a range of different exposures and merging the results. SteveBaker 13:32, 26 August 2007 (UTC)

Ah, that last bit sounds interesting. A disadvantage of that method is that you need to expose several times, which means longer exposure, which becomes a problem at low light and/or a fast moving subject. My system requires only one single exposure with two sensors, the results of which are then combined. Sounds better, doesn't it? If it can be implemented, that is. DirkvdM 18:50, 26 August 2007 (UTC)

Stu, you say the first layer might not react fast enough. But I forgot to mention that the idea is that it takes its measurement-energy from the light. It's sort of like how an analogue film works - the silver halide grains that get hit by light darken and I assume they do that by absorbing the light energy. The idea is that this layer does that too. Since it does this by absorbing the light energy, the reaction is instantaneous. But it also needs to measure the light intensity. Maybe that could be done after the photo is taken, by letting the layer 'leak' its energy and measuring that.

But I just realise this might require wiring in front of the sensor, which is not a good idea. Maybe it could be a mirror that sends the image to the side, where the colour sensor is. There's another thought - why don't we have newtonian cameras? I'll make that a separate question. DirkvdM 07:24, 26 August 2007 (UTC)

Are you sure that reaction is "instantaneous" ? I don't know enough about it to say, but don't many such reactions involve electrons staying in one shell for a fraction of a second, then jumping to another ? StuRat 22:31, 26 August 2007 (UTC)

Maybe the darkening of photographic film is indeed not instantaneous, but in retrospect that might not be a good comparison. What counts is that the energy is taken out of the beam of light. Letting an electron jump to a higher energy state sounds like a good (the only?) way to do that. And maybe the falling back could then be measured somehow. But I now realise that this will probably not let through light of equal distribution. More likely, it will let light through at a fixed percentage of the incoming light. So the brightness is still measured, but the rgb sensor behind it will still have to deal with variable light intensities, and the idea was to be freed from that so the sensor can be made better at colour measurement.

Just in case that last bit needs clarification, think of different scales used for different weights - a very precise scale that weighs to the precision of milligrams will not be able to withstand the weight of, say, a car. A multimeter also has different 'scales' for different inputs, for similar reasons. DirkvdM 07:32, 27 August 2007 (UTC)

WHAT HAPPENS DURING MULTIPLE PERSONALITY DISORDER?

PLEASE LET ME KNOE THE PATHOPHYSIOLOGY OF THIS DISORDER I HAVE CHOSEN THIS TOPIC FOR MY SEMNINAR PRESENTATION AND SO I NEED THE HELP OF ALL THOSE WHO STUDY PSYCHIATRY SPECIALLY PLEASE STRESS ON WHAT HAPPENS TO THE BRAIN

Firstly, using all caps is not a very good idea, as some people may construe your statements as disrespectful. Secondly, Wikipedia is an encyclopedia, have you read our article on multiple personality disorder? Splintercellguy 09:15, 25 August 2007 (UTC)

Yeahhhhhh, using all caps when discussing mental health...? It makes me wonder about the poster's own mental stability. =/ Not a good combonation! --24.249.108.133 20:50, 27 August 2007 (UTC)

WHAT HAPPENS TO THE BRAIN DURING THE DISSOCIATIVE IDENTITY DISORDER?

i AM GOING TO DELIVER A SEMINAR ON THIS AND SO I NEED THE HELP OF ALL PSYCHOLOGISTS NO WEBSITE CLEARLY MENTIONS THE PATHOPHYSIOLOGY OF THE BRAIN AND SO I IMMEDIATELY NEED THE RELATED INFORMATION PLEASE MAIL ME IF POSSIBLE <e-mail removed>

See my response for your other question. Splintercellguy 09:16, 25 August 2007 (UTC)

Oh yeah, it's not a good idea to publicly post your e-mail, it's an invitation for spam. Splintercellguy 09:53, 25 August 2007 (UTC)

21 grams

Does the life force in humans have a discernible weight? - Kittybrewster (talk) 11:01, 25 August 2007 (UTC)

Well there isn't any tangible thing as a "life force" in modern medical science. "Life" itself is defined very differently by many different people, but generally speaking it is often considered to be processes which decrease entropy. These processes can have no independent weight of their own, and indeed are not independent from the functioning of the organism itself. Think of a wind-up toy—would you say the winding of the spring (we'll call it the "mechanical force") has a discernible weight, or was even something physically different from the toy as a whole? --24.147.86.187 12:08, 25 August 2007 (UTC)

Actually ... in 1907 Duncan MacDougall measured the weight of a soul and found it to be 21 grams. However, I think you'll find few people today that believe that the life force in humans has a discernible weight, and there is no scientific rationale to support such a belief. --Ed (Edgar181) 14:28, 25 August 2007 (UTC)

I think you you need to define what a life force is and try to prove it exists. What exacttly was he measuring? --72.202.150.92 18:41, 25 August 2007 (UTC)

Weigh someone just before they die - then again afterwards - the difference (if the experiment is done carefully enough) will certainly be zero. There is simply no such thing as 'life force' in modern science. SteveBaker 21:59, 25 August 2007 (UTC)

The air in your lungs has a weight. If on dying the ribs and diaphragm relax, the chest cavity would collapse slightly and expel some air; probably just over 0.5 litres, which would weigh about a gram, so the mass of the body would decrease slightly. The studies into the mass of the soul were fatally flawed for a number of reasons, though: people dying of terminal diseases tend to be moving quite a bit which can interfere with scales, it is very difficult to work out whether someone is alive or not with late 19th century science (even more so to do it without disturbing the scales), and of course, as the body dies, sweating, breathing and respiration will all decrease the total mass. Laïka 23:42, 25 August 2007 (UTC)

The air in your lungs is at the same pressure as the surrounding air, and therefore has the same density. It contributes to your body's mass, but not to its weight as measured in the normal way with air surrounding it. --Anon, August 26, 2007, 16:23 (UTC).

If you give any credence to the thoughts of naked space vampires, you may want to see Lifeforce (film).

Atlant 11:52, 27 August 2007 (UTC)

Hooke's law and its integral

If Hooke's Law is $F=-kx\,$, why is its integral $U={1 \over 2}kx^{2}$? Shouldn't it be $U={-1 \over 2}kx^{2}$, although it gives rubbish results? Why does the negative sign suddenly disappears when it's calculating energy instead of force? --antilived^{T | C | G} 12:23, 25 August 2007 (UTC)

I think you should see it as follows. Your $F$ is the force the spring exerts on your hand, which compresses the spring. Your hand, however, exerts the force $-F$ on the spring, and this is the force you should integrate (since this is the force acting on the spring, transferring energy to it). —Bromskloss 12:30, 25 August 2007 (UTC)

So we are not actually integrating Hooke's law to get the energy formula? Shouldn't that be changed in the articles to reflect that? --antilived^{T | C | G} 12:34, 25 August 2007 (UTC)

You're probably right. Of course, it's not a very big thing so a short note would be enough. —Bromskloss 12:38, 25 August 2007 (UTC)

No,no - not right the energy equation is the integral - but the force (opposing) is in the opposite direction to the movement - hence the change of sign - maybe the article needs clarifying.

But the force needed to move the spring is kx not -kx since it is in the opposite direction to the force the spring makes itself - (make sense or not?)87.102.84.56 12:46, 25 August 2007 (UTC)

—Bromskloss has it right.

Work is force x distance. The force exerted by the spring is -kx The force needed to move the spring therefor is kx. Hence the change of sign.87.102.84.56 12:48, 25 August 2007 (UTC)

OK now a new problem comes up. If W = F × D, then isn't W = kx² only? Where does the 1/2 come from? --antilived^{T | C | G} 05:56, 26 August 2007 (UTC)

Work equals the integral of force with respect to distance. Normally this would just be force times the distance co-directional with the force, but for a spring, the force is not constant, but rather is directly proportional to the distance, so you must take the integral of the force this time. The integral of kx with respect to x is kx²/2. Someguy1221 06:16, 26 August 2007 (UTC)

Yea I know that, but I'm wondering WHY is it the integral of force? Why isn't it just a product of manipulating several other formulae like many others? --antilived^{T | C | G} 06:24, 26 August 2007 (UTC)

Well, if you'll accept that the force at a given instant, multiplied by the distance traveled over that instant equals the energy transfered in that instant...This only works for non-infintesimals if you use integrals, as integrals are infinite sums of infintesimals. If I'd remembered my physics better, I could derive for you the relationships from Newton's laws, but that's a few years in the past. The simplest I can put it, short of that, is that simply combining formulae algebraicly doesn't yield every possible physical relationship. Newton created the calculus for the primary purpose of answering physics questions that were beyond contemporary mathematics. Someguy1221 07:43, 26 August 2007 (UTC)

Mains adapter

I just bought a digibox and the mains adapter that came with it was small and surprisingly light, only about 50gm, almost as though there was nothing inside the box, but it works just fine (12v DC from 240v AC). They are usually up to ten times heavier than that. Is this some new technology?--Shantavira|^{feed me} 12:43, 25 August 2007 (UTC)

Digiboxes don't use much power and electronic things are getting more and more energy efficient - so maybe it just has a much smaller transformer than you were expecting?

Alternatively a wholey electronic power supply - (no transformer) could be made - which might be lighter.

I expect the former though - what is the rating of the power supply?87.102.84.56 12:51, 25 August 2007 (UTC)

12w.--Shantavira|^{feed me} 12:55, 25 August 2007 (UTC)

mmmh (I've got one of those too and it is very light) - a web search confirms what I used to think - that a conventional 12va transformer weighs much more about 125g at least...87.102.84.56 13:04, 25 August 2007 (UTC)

It sounds to me like this is a switching power supply and you're thinking of more traditional transformer based power supplies... Switching power supplies are hardly 'new technology' for example they've been used in computers for a long while. However it's perhaps only recently that they've began to become common as replacements for more traditional transformer based 'power brick' type mains adapters. Most mobile phone adapters nowdays are switching ones I presume because of the weight and universal use advantages Nil Einne 13:08, 25 August 2007 (UTC)

Edit: I also noticed this from the above article "In early 2006 even very low power linear regulators became more expensive than SMPS when the cost of copper and iron used in the transformers increased abruptly on world markets." It seems likely that in 10 years time, people will be asking 'why is this old power adapter I found so heavy?' Nil Einne 13:10, 25 August 2007 (UTC)

The article says switching power supplies are more efficient. So they may have been cheaper from the beginning, but alas people usually only look at what something costs now, not in the long run, which is what really matters. If people would wisen up in this area, that might just 'save the world' (climatologically speaking). Or at least it would help. (Of course it becomes totally irrelevant if you occasionally use a car when you don't need to - not to mention gas guzzlers.) DirkvdM 07:44, 26 August 2007 (UTC)

+ & - chargged metals

I am running an inhome experment and would like to use the maximum differencial in possitively and negatively charged metals. Is there an oppisit to isatobe 235, or a less radioactive metal? Is there isatobe 100 and an anti-100? A 50 and anti-50, anything? Can you stear me in the rite direction? Thanks, Gods— World Changer161.51.11.2 13:44, 25 August 2007 (UTC)

Um what? Isatobe 235? You mean Uranium-235 (uranium isotope 235? Um little hint. If you're planning a 'in home' experiment you want to consider elements you can actually obtain easily. Also I don't quite get what your doing. Are you trying to make a Galvanic cell? If so take a look at Standard electrode potential (data page). However personally I would recommend you steer away from anything which produces hydrogen flouride. Nil Einne 13:50, 25 August 2007 (UTC)

Not sure +3 is the usually max charge on a metal as found in Aluminium, maybe you were thinking of electronegativity and electropositivity?87.102.84.56 13:53, 25 August 2007 (UTC) If so gold and lithium would probably be your choices..

There is as far as I know no thing as an 'opposite to isotope 235' or an opposite to an isotope that can be got.87.102.84.56 13:56, 25 August 2007 (UTC)

It would help if you told us more..87.102.84.56 14:09, 25 August 2007 (UTC)

Sacrificial Anode - Aluminium

I have read that aluminium forms an oxide coat that prevents it from oxidising and hence is it quite unreactive. Yet I have been told aluminium could be attached to those drilling stations in the ocean to protect the iron from oxidation. Doesnt the oxide coat prevent this?

What you have been told may or may not be true - I've no idea - but it's a possibility.

The alkaline nature of sea water will tend to dissolve the aluminium oxide - so yes I imagine that aluminium could be used as a sacrificial anode..87.102.84.56 14:04, 25 August 2007 (UTC)

From Galvanic corrosion " Boats and vessels that are in salt water use either zinc alloy or aluminium alloy. If boats are only in fresh water, a magnesium alloy is used. "87.102.84.56 14:07, 25 August 2007 (UTC)

So are you saying the Cl- ions play a factor in this? And why would you use an alloy instead of pure Al? Thx58.107.237.74 15:13, 25 August 2007 (UTC)

The use of an alloy is probably for ease of welding and structural integrity. Nimur 15:44, 25 August 2007 (UTC)

The Cl- ions may help dissolve the Al, but the pH of the sea water is important too.87.102.84.56 16:32, 25 August 2007 (UTC)

Fused NaCl

What does fused mean? (This is at Downs Cell in the diagram) but there is no explanation. Note it says "The electrolyte is sodium chloride that has been fused to a liquid by heating." can someone explain further? Phgao 15:27, 25 August 2007 (UTC)

I think it's a strange usage of the term to mean "melting." I might venture to say "incorrect usage" of the term fusion, which in chemistry and thermodynamics usually means the transition from liquid to solid (latent heat of fusion, for example). In this sense, the molecules "fuse" close together to form a solid phase (not to be confused at all with nuclear fusion, a totally different process). However, Wikipedia is edited by users from many locations, and some regions tend to use dramatically different terminology from the stuff I learned in school in the US. Nimur 15:47, 25 August 2007 (UTC)

It's not incorrect. I admit it's a little con--wait for it--fusing, though. This is one of those words that's its own antonym, like "cleave". I think there's a name for such words, but I forget what it is. --Trovatore 03:31, 27 August 2007 (UTC)

Though 'fused' usually means to us 'set solid' in this case it means melted - it's a standard chemistry term - (search for 'fused salt' if you want to check) Note electrical fuses melt when they fuse..87.102.84.56 16:26, 25 August 2007 (UTC)

Specifically 'to fuse' just means 'to melt' - to be pedantic fused ice is water.87.102.84.56 16:30, 25 August 2007 (UTC)

Just to confuse things 'fused' can also refer to substances that have been melted. Such as fused magnesia.87.102.84.56 18:03, 25 August 2007 (UTC)

Recharging a Lone Ranger atomic bomb ring

Oh boy oh boy. I got a pair of Lone Ranger atomic bomb rings, one of which is in good condition that I won't mess with, one of which is basically just the spinthariscope component and so I don't mind playing with it a bit.

I'd like to "recharge" it. I gather than the original alpha source was polonium-210.

I imagine that "recharging" it basically will come down to figuring out how to open up the isotope chamber, cleaning out the old stuff (now long since decayed into lead), and putting in a new isotope source.

My question is: what sort of radioisotope should I go with? I know that Po-210 was used because it had a high level of activity, and thus would produce more exciting flashes, but its short half-life (138 days) means that to keep it running at a reasonable level I'd have to "recharge" it once a year. Seems like a pain. If I could find something a little less active, but with a better half-life, that might be more ideal. The only site I know of to get radioisotopes seems to only offer Po-210 as its alpha emitter, so I might be stuck with that.

Could I use the Americium-241 sources in a smoke detector? Am I right in thinking that the only way to get a comparable number of alphas as from the original Po-210 source would be to have much more of it? (Obviously I can't get too comparable, as—if I understand half-lives correctly—that means I would need hundreds of times more.) Is it worth trying, since the half-life is a lot longer and the sources are a lot easier to get a hand on?

My next question is: is this even reasonably a good idea? Obviously exotic radioisotopes can be quite toxic though I imagine I am not going to want to be using more than a speck and my understanding of strong alphas is that as long as it doesn't get inside me I should be okay (skin will stop the alphas easily). If I got a needle source of Po-210 from that site, and made sure not to, say, eat it or inhale it, would it be safe to put inside the ring?

If I am totally backwards on any of this please let me know. I'm no physicist and no chemist. --24.147.86.187 15:36, 25 August 2007 (UTC)

I wonder if the interior of the chamber is filled with inert gas (or possibly even vacuum)? If so, opening the case to replace the radiation source would vent the chamber. I suppose, since alpha particles have a mean free path of a few centimeters in air, and this thing is pretty small, that this is a total non-issue. Nimur 15:55, 25 August 2007 (UTC)

Sounds like a bad idea to me. First, even though the skin may stop the radiation, it may do damage to the skin in the process, which might potentially cause skin cancer down the road. Second, handling such material without risking inhalation or ingestion requires specialized equipment and training. In other words, "don't try this at home, kids". StuRat 16:18, 25 August 2007 (UTC)

I agree bad idea - see http://www.hse.gov.uk/laU/lacs/42-6.htm what the article reveals is that "less radiotoxic alternatives have replaced radium in radioactively luminised articles such as tritium (3H) or promethium-147 (147Pm)" - these are beta emitters - I imagine they would still activate a scintillation device?

The major hazard here is inhalation of any dust when cleaning it out, amongst the others - I wouldn't go scraping out a fire sensor or what ever unless I had a device that would keep any dust away from ME. Thinking about glove boxes, breathing filters - note also that the materials used may be harmless when contained in their devices but when exposed can be really bad - this for instance applys to radioluminous watch dials which are consider safe? but if you break the glass it's a case of forget it - and don't even think about touching it - 2mm of glass provides a lot of protection - which out that you could expect 'burns' on your skin.

Specifically all this work needs to be done with tools eg pliers - don't even think of doing it if you would need to manipulate the things with your hands.

I know that there is a lot of 'scare' about radiation - but inhalation of any radioactive dust can be a very serious problem.

See http://www.bhi.co.uk/hints/poison.htm "The hands of the watch or clock should be scraped while immersed in oil and the scraper left submerged in the oil to prevent the particles entering the air being breathed."87.102.84.56 18:34, 25 August 2007 (UTC)

I really wouldn't try this at all.87.102.84.56 18:51, 25 August 2007 (UTC)

Well, obviously I don't want to be handling raw materials here. Am-241 in a smoke detector comes in an insoluable dioxide form inside a gold matrix. I would just be transferring that bit into the ring; I find it unlikely that it would be a significant health hazard, no? Anyway I would not be handling this with my bare fingers in any case.

Cleaning out the existing material is probably the toughest bit. What exactly is the existing material at this point? Po-210 decays to a stable element of lead (Pb-206), which doesn't sound all that dangerous. After 60 years there should only be 1.57 * 10^-48 of the original material left, according to my calculations; I find it hard to believe that this would be a significant amount. I'm also suspicious that the Po-210 was originally in a form that would be prone to be a health hazard if messed with, since it was distributed in children's cereal, but I'm well aware that making assumptions about the safety standards of the past is a losing game!

Anyway, I don't say that to be contrary, but some of the concerns above don't seem to be to be very tailored to this particular situation, and some strike me as being a little uninformed (e.g. replacing it with tritium, for which there is no way in hell I'd be able to get it into such a ring without very sophisticated tools, or the concern about skin cancer from brief contact with a tiny amount of a relatively weak alpha emitter, which is no real threat at all). --24.147.86.187 18:57, 25 August 2007 (UTC)

Yes - it's not 100% applicable - and the Po is in an insoluble form - but what bulk form does that dioxide come in - as a beed or powder - if it was me I'd like to know before opening the gold case.

If it's insoluble you could then make the transfer under water - which does give you additional safety. I deliberately ere on the side of caution here. The radiation (alpha or beta) from an unshielded source can burn you - (unrelated to radiation poisoning as such) - although it would be little more than a 'tiny speck of hot ash' in magnitude.87.102.84.56 19:33, 25 August 2007 (UTC)

The Americium in smoke detectors comes on a little disc, according to this fellow. It'd be nice to know exactly how it is put together, though, because the disc itself is too big to fit in the ring, obviously. The more I think about the cleaning aspect the more I think it is probably a non-issue—there's going to be for all intents and purposes no radioactive material left inside the ring, it is all going to be lead, yes? --24.147.86.187 23:00, 25 August 2007 (UTC)

I read (but can't find the source now) that the Am (don't know if the metal or oxide - think the oxide) is rolled into a very thin gold sheet - i guess that the AmO2 becomes embedded in the gold, as I remember another thin metal sheet is rolled onto this (too thin to stop the alpha particles), there was also a silver? thicker backing and some other metals plates involved - so what you should have is effectively a sandwich of AmO2 between gold - the rolling probably fuses the gold/silver sheets so it shouldn't be separable.. Apparently 0.2mg is the very approximate amount involved, another site says they detected 2000 alphas per second using some sort of counter?87.102.23.4 00:22, 26 August 2007 (UTC)

Here http://www.madehow.com/Volume-2/Smoke-Detector.html

The process begins with the compound AmO2, an oxide of Am-241. This substance is thoroughly mixed with gold, shaped into a briquette, and fused by pressure and heat at over 1470°F (800°C). A backing of silver and a front covering of gold or gold alloy are applied to the briquette and sealed by hot forging. The briquette is then processed through several stages of cold rolling to achieve the desired thickness and levels of radiation emission. The final thickness is about 0.008 inches (0.2 mm), with the gold cover representing about one percent of the thickness. The resulting foil strip, which is about 0.8 inches (20 mm) wide, is cut into sections 39 inches (1 meter) long.

87.102.23.4 00:28, 26 August 2007 (UTC)

http://www.rampac.com/certificates/1030036.PDF shows a structure for a laminate.

87.102.23.4 00:32, 26 August 2007 (UTC)

And the average amount of radiation is 1 microCurie. http://www.epa.gov/radiation/sources/smoke_alarm.htm87.102.23.4 00:34, 26 August 2007 (UTC)

Polonium 210 has been in the news quite a lot over the past year or so since it was used to murder an ex-Russian spy in the UK. What we can learn from that is that Polonium (in very, very small quantities) is insanely toxic if you ingest it or breath it in. But in general, the radiation it produces is stopped by a few centimeters of air or a sheet of paper - so it can be handled safely - with suitable precautions. So once inside the ring, it ought to be pretty safe - but getting it in there safely is going to be tough. The most likely way would be to buy one of those antistatic brushes that photographers use that contains polonium 210 in tiny quantities embedded in a matrix of more inert stuff. Whether the spintharoscope in the ring would be able to detect it - I don't know. At any rate, you ought to go to United Nuclear - those guys will sell you all manner of radioactive samples - and spintharoscopes and whatever else you are likely to need. SteveBaker 21:45, 25 August 2007 (UTC)

It is toxic, yes, but not in the quantities that you can buy on the internet, and not in the forms that you can buy on the internet. Big differences there. Notice that Litvivenko was killed with 50 mCi of Po-210; United Nuclear sells it in 0.1 μCi amounts — a difference of four orders of magnitude! The median lethal dose is still over two thousand times more than you could buy online. So again, I think we're maybe drawing on the wrong associations here, letting our imaginations get a little out of control with all of the scary imagery that surrounds all things nuclear... --24.147.86.187 22:48, 25 August 2007 (UTC)

Sorry - yes, the impression I was trying (and evidently failing) to convey was that the tiny amounts you get in antistatic brushes and from United Nuclear are safe - they wouldn't be sold so freely otherwise. But in much larger quantities, this is nasty stuff. The main point is that the radiation is stopped by your skin before it can do any damage - but if it gets inside your body, it can cause nasty problems (in enough quantity). However, we don't know how much was in the original ring - and we don't know how sensitive the spinthariscope inside the ring was (or indeed still is). It might be that larger quantities are needed to make the ring work - and attempting to make larger quantities (eg by buying a heck of a lot of photographer's brushes and refining the resulting stuff would be a very bad idea indeed. Back in the 1940's, this kind of stuff was not at all well understood and some pretty lethally dangerous products were made before we realised the long term consequences of radioactivity. Note however that Polonium 210 has a pretty short half-life (about 4 months) - so even if our OP sucessfully recharges the ring, it's likely to stop working again after a year or two - and the activity of any "polonium" you do buy may be critically dependent on how old it is - Po₂₁₀ turns gradually into boring old lead and stuff that's a year old has about 1/8th as much active ingredient than 'fresh' Polonium straight from the reactor! But, as I said before, I strongly recommend the United Nuclear web site - they have tons of safety information and will sell you reasonable quantities of several radioactive elements. SteveBaker 13:13, 26 August 2007 (UTC)

Something that concerns me in this whole discussion is the liability of manipulating radioactive materials or telling people to manipulate them to put them in what is clearly a toy, however expensive and collectable a toy it has become. There is a likelihood of such a ring or toy in the future being in the hands (or on the finger) of a child, and of it making its way into said child's mouth. So do not go there. Keep the ring as a collectable. Do not start scraping radioactive material off of something, whether it is the spinthariscope ring, a smoke detector, or an old radium watch dial. It is bad enough when children are harmed by swallowing magnets. Now on to playing with asbestos, mercury, lead, and other 1950's science experiment hazards. Edison 15:07, 27 August 2007 (UTC)

Fields of science

What field of science begins with the letters "Q", "J", "W", and "Y"? Thanks68.78.73.144 16:36, 25 August 2007 (UTC)

Quantum theory Algebraist 17:12, 25 August 2007 (UTC)

Homework question? lol Jonaboff_talk 19:37, 25 August 2007 (UTC)

Yes. please help.

Searching the lists turns up nothing obvious under j,w,y - maybe you'll have to get creative? eg Jungle science - the scientific study of jungles?87.102.84.56 20:02, 25 August 2007 (UTC)

Jupiterean studies, Yttrium chemical science, wastewater science, wetland science, wavelets? (ideas from http://www.dmoz.org/Science/J/)??87.102.84.56 20:06, 25 August 2007 (UTC)

This list might help http://www.daviddarling.info/encyclopedia/alphindexy.html Yeast studies?87.102.84.56 20:08, 25 August 2007 (UTC)

Wet chemistry? Laïka 20:14, 25 August 2007 (UTC)

Jungian Psychiatry? I don't think it's science, but a lot of people do. -Arch dude 01:33, 26 August 2007 (UTC)

See Special Pages (top left) > All Pages (Special:Allpages) and fill in those letters. No, sorry, that hardly narrows it down. DirkvdM 07:53, 26 August 2007 (UTC)

W and Z bosons ? (At least it satisfies the w... Nimur 17:59, 26 August 2007 (UTC)

You could go with Quaternary studies for Q Mac Davis 19:13, 27 August 2007 (UTC)

Elasticity and Strain

The elasticity of a string is its property to resist any deformation when a force is applied. So is it that an elastic string will have a greater strain value than a relatively non-elastic string ... ??? or is it the other way round ???

Please enlighten.

Probably you should read Deformation, Strain (materials science) and Elasticity (physics) - at least the first bits.

The answer is yes - and not the other way round - an 'elastic' string strains/stretches more than a less elastic one for a given weight/force- strain is given by the amount of stretch.87.102.84.56 20:14, 25 August 2007 (UTC)

Animal intelligence testing

Have any intelligence tests been devised that will give meaningful results, on the same scale, for both human and animal subjects? NeonMerlin 20:34, 25 August 2007 (UTC)

The days, at the most technical level, intelligence is usually considered to be a uniquely human concept, but our efforts to investigate the non-human animal equivalent is detailed at Animal cognition. Some of the more simple tests - that we use in testing human children, for example - are also used in animals. You might also see Comparative psychology. Rockpocket 21:42, 25 August 2007 (UTC)

There are plenty of tests - but they tend to be of a qualitative rather than quantitive nature. We have discovered (for example) that Chimpanzees and Dolphins can recognise 'self' - they recognise that the animal they see in a mirror is themself - but that dogs and cats can't do that. Grey parrots can learn the concept of numbers and can count to at least five. Dogs can learn to understand 500 words of English - but have no concept of grammar or word order. But intelligence tests that come up with a distinct number are likely to be impossible. Even IQ testing amongst humans is considered a very dubious science since it's very easy to allow cultural or age biasses to creep in. So I think the answer is a definite "NO!". SteveBaker 21:52, 25 August 2007 (UTC)

But you have to admit, it'd be rather enjoyable if you could confidently say, "My friend, I have quantitative, scientific proof that you are stupider than a hog." --24.147.86.187 23:56, 25 August 2007 (UTC)

Surely animals have intelligence. At least, I define it as the ability to solve problems and learn (the other traits the article mentions, reasoning, planning, abstract thinking, comprehension of ideas and language are all subsets of those two, if you ask me). And all animals can do those two things to some extent. For example, you could put a fence (of finite length) between a dog and a bowl of food. Stupid dogs will run into the fence and start barking in frustration. Intelligent dogs will walk around the fence. I once saw that done with two dogs at the same time. The stupid dog didn't even pick up the smart dog's solution. And that is another intelligence trait. For sheep dogs there are problem-solving contests called sheepdog trials (as shown on BBC), which can qualify as intelligence tests. The dogs are presented with a new situation and have to decide what to do (much the same way in which hunting animals do), possibly under the direction of a shepherd's whistle, which qualifies as language. The herding tests may be fairly standardised, but there are also other tests, where the dog has to follow a course and overcome obstacles they have never seen before. You can actually see them think, standing in doubt about what to do next. A stupid dog wouldn't even understand it was being tested.

However, the question was for a test that can be used for different species, and that would be trickier. Even among humans, there are different tests for different levels of intelligence. So one test for different types of intelligence seems impossible. Of course, it gets even more difficult for the 'lesser species'. Such as plants. Can they be said to have intelligence? DirkvdM 08:08, 26 August 2007 (UTC)

If you choose your own definition of intelligence, then surely they do. Rockpocket 05:08, 27 August 2007 (UTC)

May I politely suggest that sheepdogs are comparatively intelligent but in a limited way. They have a very strong instinct to herd other animals but this ability should not necessarily be assumed to be intelligence. Having watched sheepdog trials on TV it is very clear that the skill of the shepherd in signalling to and guiding his dog or dogs is of paramount importance. When dogs have no contact with the shepherd they frequently herded the sheep in a random way, showing little knowledge of the point of the competition. Richard Avery 09:12, 26 August 2007 (UTC)

I assume that is because they haven't been trained to do that. If they were, an interesting test would be to see how well they would do compared to humans - so dogs without the help of humans and humans without the help of without the dogs. I wouldn't be surprised if dogs would perform better, and that is what I meant with 'different types of intelligence'. Overall humans may be more intelligent (and certainly in tests designed for humans of course), but at specific tasks other animals might perform better. But of course we don't design such tests, as intelligence tests, that is, because we perform worse, so we think that that isn't intelligence. And that is a central problem here. We define intelligence based on what we are good at, so of course other animals are then by definition less intelligent. We've got a bad case of intellectual parochialism. We're human chauvinist pigs. :) DirkvdM 19:17, 26 August 2007 (UTC)

The difficulty and controversy of quantitative intelligence testing of humans has not yet been solved. Our article IQ explains the various criticisms of standardized testing. In my opinion, this boils down to a philosophical question - does "absolute intelligence" exist at all? If so, how can we effectively probe it with standardized testing? If not, what qualities do we generally associate with intelligence? Once these issues are definitively settled in humans, it will be easy to extend the concepts to other creatures, bridging the natural language gaps and so forth. Until then, we will have to use operational definitions with limited scope (such as "time to complete a mouse maze") as a metric for intelligence. Nimur 18:07, 26 August 2007 (UTC)

Yes, nicely put Nimur. I guess without defining what we mean by intelligence (with all its connotations and variations) comparing the intelligence of different species is a problematic excercise. Hey, Dirkvd that's a big tough on the pigs :)) Richard Avery 10:30, 27 August 2007 (UTC)

The root of the problem of intelligence testing is that we don't have a solid definition of what the word means. We originally (I believe) used the term to mean "those intellectual capabilities that man has but animals lack" - we named our own species "Homo Sapiens" (thinking man) as if no other animal has that ability. That definition would mean that all animals would have to score a zero on any true "intelligence test" because if any of them ever managed to score higher, we'd have to admit that the test wasn't testing intelligence at all.

But over the past 50 years or so, we've learned a lot more about animal intellectual capabilities and it's getting harder and harder to draw a line. We have dolphins and chimps who we have proven to have a sense of 'self'. We have all sorts of animals that make and use tools. When I was in high school in the 1970's, we were taught that only Man uses tools - in the 1980's that only Man makes tools - now, we've quietly abandoned the whole tool thing because we've found that even some really small and "stupid" fish make and use tools. In the early 1990's my son was taught that only humans have 'language' - but that's indefensible in the face of things like the lowly cuttlefish's visual 'language' and interpretations of whale 'song' in which personal names seem to make an appearance. Now we have gorillas who can not only learn sign language but also teach it to their children.

We'd probably claim that only humans have written languages - but then we'd be in trouble because plenty of human societies never developed it. Math is similarly problematic. There are human tribes who don't have words for numbers higher than three - yet we have a grey parrot who can clearly understand quantities as high as five.

One by one, things that separate us from the animals are being shown to be quantitative rather than qualitative. We use MORE tools, MORE language and have MORE "intelligence" than the animals. So now, we have to ask ourselves what intelligence is - because it's clearly not "what we have but animals don't have".

Worse still for our definition of 'intelligence' is that a lot of people dislike getting a low score on IQ tests (because it gives them no way to avoid thinking of themselves as "stupid") - so we start insisting that they have "different kinds of intelligence". So I hear that dancers (some of whom might maybe score low on a conventional IQ test) ought to get extra credit for their 'kinesthetic' sense, and that someone with a great memory should score some extra points for that too. That dilutes the meaning of the word - for unhelpful reasons of political correctness rather than as a result of scientific investigation.

We also want a score that allows some kind of absolute measure of intelligence that's irrespective of age or educational level - but it's becoming increasingly obvious that our brains change as a result of learning and that age most definitely is a factor. But without a solid definition - we'll never come up with a scoring system. With the rise of 'political correctness' - it's even less likely that such a measurement can be made without upsetting a lot of people. We dislike anything that discriminates on the basis of the way we were born - so you are in trouble if you try to measure that exact thing with an IQ test.

So it's a bust. The best science can do is to invent a new word and start over with the whole messy business. SteveBaker 17:46, 27 August 2007 (UTC)

liquid pressure

Is it possible, as it is with a gas, to cram an ordinary cup of water into a half-cup sealed container with enough pressure? If you dive a mile under the ocean and seal a flask of water, then return to the surface and open it, will it gush out of its container like a geyser? If you go down to the floor of the ocean with 6 sheets of metal and some really strong tape, and you construct a watertight box around yourself, will the water inside still be at high pressure or will the metal take the strain? What if you run a hose from your box up to the surface and keep it clear of water, but the box is still filled? --froth^t 21:57, 25 August 2007 (UTC)

Water's compressibility is very tiny compared to any sort of gas; the sort of question that you're asking is addressed on this external site. Working from those figures, the pressure at six miles depth should be about a thousand atmospheres, giving a decrease in volume of about five percent. In other words, it would be a very short-lived geyser.

If you wanted to keep that pressure inside a metal box, you're going to need something stronger than tape to hold it together. A thousand atmospheres is about fifteen thousand pounds (nearly eight tons) per square inch.

It is possible to increase the density of water by a factor of two, but you need absurdly high pressures to do it. This page has diagrams and details of all the exotic ices that are formed at extremely high pressures; to get water down to half it's normal volume, you'd need pressures closer to a million atmospheres. It also wouldn't be a liquid at that point; it would be an unusual type of ice. TenOfAllTrades(talk) 22:26, 25 August 2007 (UTC)

Here's an interesting bit of trivia. If water weren't compressible, sea level on Earth would be about 40 meters (130 feet) deeper, and the Earth would have about 5% less uncovered land area as a result. TenOfAllTrades(talk) 22:28, 25 August 2007 (UTC)

[EC] For the water flask: No. Fluids are said to be incompressible. If you compress gas the pressure to the walls increases because the density has increased and the particles now hit the wall more often. In a fluid, the particles are so close to each other that you cannot compress them more without forcing them into a crystal. Of course, water is not exactly incompressible, but you need huge pressure to just compress it a very tiny bit. There is no longer proportionality between volume and pressure. For the metal box: Yes, one can construct a metal box that is able to withstand the water pressure from outside and keep atmospheric pressure inside: it's called a submarine. Usually, submarines are filled with air and sailors and torpedoes and all this, but if you insist, you can also fill them with water. (Ok, before someone corrects me: A military submarine is not built to take the pressure at the deep ocean floor, but there are Bathyscaphes). Simon A. 22:32, 25 August 2007 (UTC)

Just a minor nit here: It's liquids that are (almost) incompressible, not fluids. A fluid, technically, is either a liquid or a gas (anything that flows, which is the etymological root of "fluid"). --Trovatore 03:12, 27 August 2007 (UTC)

Wikipedia needs a bit of work on the different forms of ice, and could do with an ice phase diagram. There are no articles on ice II IV V VI VII VIII X XIII or XIV! Graeme Bartlett 22:41, 25 August 2007 (UTC)

Thanks for the answers so far but I think you've missed the main thrust of my question. If you build a metal box around yourself at great depth, will there still be crushing pressure from the water above? Or will the box take the pressure and the water inside have pressure of surface water? Basically I mean like if you seal gas in a container then it retains its pressure, but if you seal high-pressure water in a container so that there's no longer a mile of water on top of it is it still high pressure? Do you see what I'm saying? Let me put it another way.. some guy puts on some super strong diving suit and dive down a mile underwater. He takes off his suit and promptly dies from the crushing pressure. The next guy comes along and has the idea of taking a sheet of metal to hold above his head, hoping that it'll hold up the massive column of water above him. He braces it between some rocks and crawls underneath, then takes off his suit. He's crushed too because the pressure "gets in" from the sides. The next guy decides to totally protect himself from the pressure above by taking down 6 sheets and building a box around himself. Now the gigantic column of water above him is supported by the box, and his body doesn't have to try to push back. Right? That's my question- would it work? Or would it act like gas, and retain its pressure? --froth^t 00:17, 26 August 2007 (UTC)

Your talking about a sealed box that the diver goes down in right (made of super tape that doesn't break) - like a submarine? The answer seems to be yes - because the box he's in isn't crushed or compressed - neither is he?

Or did you mean he builds the box when he's really deep - in which case the box will contain water under pressure when he builds it around him and he'll be crushed.

Or? 87.102.23.4 01:40, 26 August 2007 (UTC)

The original question - build a box/bottle down below and bring it up - as it is raised the pressure from within the box gets greater and greater - if it's opened at the top and it's kept its shape then - yes - water will come out ( a bit) as it expands.

If you build the box at deep pressure the water inside will still be pressureised.

If you take a pipe from sealed box up to the surface - nothing changes - the column of water above the box causing the pressure is the same height.87.102.23.4 01:45, 26 August 2007 (UTC)

I agree with the last guy;

1. if you build a sealed box underwater, the pressure inside when you seal it will be the same as the pressure outside.
2. if you run a hose to the top, as long as the top of the water inside the hose is at the same level as the top of the water outside the hose, the pressure in the box will be at the same pressure as outside. if you pump the water out of the hose until the top of the water is at the top of the box and the rest of the hose is full of air, the pressure in the box will be at atmospheric pressure, plus whatever extra atmospheric pressure you get for being that further down. Odd but true; the height of the water in that hose, even if it's like 1 mm in diameter, governs the pressure in the box. Gzuckier 14:56, 27 August 2007 (UTC)

Accents

This is a strange one, but since it concerns the brain it presumably belongs here. One night several months ago I stayed up all night, drank espresso, and watched episodes of QI. I must have watched every episode. The strangeness began when I went to class in the morning, having just watched the last episode about thirty minutes earlier. Every background voice sounded British or Irish to me. I will explain. Every vocal sound I overheard was analyzed as if it had been spoken by a Briton or Irishman - not at the level of words, but at the level of phonemes. I would be unable to say what was being said. If I listened closer, the effect would vanish. Also, certain phonemes would disrupt the effect, and the American accent would return fleetingly. Also, the effect was less apparent when the overheard voice was one familiar to me. All other background voices appeared to fluctuate between English, Scottish, or Irish. People with non-American accents, such as speakers from India, were no exception. Once I had some sleep, the effect waned, but it was another ten hours or so before it had vanished altogether. It has not happened again. I strongly suspect caffeine and/or lack of sleep was the root cause, but I was just wondering if this effect is known to psychiatry, if it has a special name, etc. Thanks! Bhumiya (said/done) 22:37, 25 August 2007 (UTC)

When I listen to a single voice for too long, my internal voice starts immitating that voice. A.Z. 01:38, 26 August 2007 (UTC)

You say the effect disappeared when you listened more closely. That suggests difficulties in concentration, which could easily have been caused by a lack of sleep. However, that doesn't explain this specific effect. In line with what AZ said, if you expose yourself to something long enough, you will start to expect that in your surroundings and pick up any hints of it and amplify those. So any 'English' traits' in what you heard in the pronunciation of those people would take the overhand. Similar to the effect of walking out of a movie theatre and seeing the world in the perspective of the sort of movie you've just watched. DirkvdM 08:31, 26 August 2007 (UTC)

Perhaps the experience described is akin to what happened to me when I lived for several months in a French-speaking city: if someone spoke English to me when I wasn't expecting it, I sometimes didn't understand it; I only recognized that it made no sense in French. —Tamfang 07:34, 27 August 2007 (UTC)

Haven't heard this one before but the opposite has been seen: "Foreign accent syndrome (FAS) is a rare speech disorder characterized by the appearance of a new accent, different from the speaker's native language and perceived as foreign by the speaker and the listener. In most of the reported cases, FAS follows stroke but has also been found following traumatic brain injury, cerebral haemorrhage and multiple sclerosis.", so it's not altogether surprising that it would go this way as well.

Prozac and Weight Change

I was wondering what Prozac does to cause weight loss and weight gain in some people. Is it from a change in appetite or does it have to do with something else? Which is more common? Weight loss or gain?

Prozac is a psychoactive drug. "Weight loss" and "wieght gain" are terms usually used to describe human behaviors. Prozac can have major effects on human behavior. I cannot cite any specific studies, but I I would guess that any effect on weight is a secondary effect. For example, Prozac is apparently used to treat bulemia nervosa. -Arch dude 03:54, 26 August 2007 (UTC)

I don't know either but I think the answer is easy to guess. Change in appetite is a very common effect in depression. I suppose everybody knows people who start eating a lot when they are depressed or stressed or whatever, and other people who eat less and less in such times. So, given that our appetite is so much coupled to our mood, shouldn't it be obvious that any mood-influencing drug changes appetite and hence over time body weight? Simon A. 10:28, 26 August 2007 (UTC)

Yes many depressed people tend to eat more to comfort themselves and gain weight, but many also gain weight rather then lose weight when taking prozac. I don't think the answer is that easy.

I gained thirty pounds while taking Prozac in 1996, and forty more over the next two years. During that time I had no acute depressive episodes, and they came back when I stopped gaining weight, or vice versa. Draw your own conclusions. —Tamfang 07:37, 27 August 2007 (UTC)

August 26

Psychology

I am currently in grade 12 and thinking of entering the field of psychology, specifically criminal psychology and I was wondering what route I should take regarding schooling. And what schools in Canada would be best? 75.154.106.228 04:47, 26 August 2007 (UTC)

Don't make hasty decisions, just because you think CSI or Criminal Intent or whatever it is on TV these day is cool doesn't necessarily mean it's true (if you are one of the millions of 'kids' that decide your career on TV programmes). --antilived^{T | C | G} 05:54, 26 August 2007 (UTC)

Don't condescend. He/she's a senior in high school and asked a well-directed question, I think we can afford to take it seriously. Anyway CSI is all about forensic investigation, not criminal psychology, if I recall, so if you are going to cast aspersions about his/her motivations, you might as well get the reference right! --24.147.86.187 13:05, 27 August 2007 (UTC)

I have not made this career choice because of shows on TV I have never watched any of the CSI shows or anything like that. I have done extensive research on this career, and chose it because it interested me.

You'll presumably want a general sciences background, with perhaps some pre-law stuff thrown in. Keeping your education focused on fundamentals will afford you the greatest flexibility later on. As for schools, I personally would go to University of British Columbia, as it's a great school in a world-class city. --Sean 19:47, 26 August 2007 (UTC)

I don't think there's anything wrong to having a goal for your education to a specific goal career — we can't all be generalists, and most people who graduate from undergrad these days have so inspecific of skills that they can't do anything without an additional year or two of education. Unfortunately I don't know the specifics of what that particular career requires, and I'm averse to just speculating on it. My recommendation would be to find a university with a criminal psychology program (even one you are not planning to go to) and try to contact someone there for advice. Someone "on the inside" will be able to give you good advice as to what sorts of backgrounds are more desirable, what level of education is normal for a practitioner (does it require a master's degree?), and what universities have good programs for that sort of goal. --24.147.86.187 13:03, 27 August 2007 (UTC)

Two general routes to becoming a shrink; one via MD one not. If you don't have an MD, you're not allowed to prescribe drugs, which is kind of a big part of the biz these days. But, not everybody is cut out for med school, for sure. They have to send patients out to an MD to do the drug prescribing and periodic monitoring and so on. Anyway, something to think about when you're sort of thinking through your plans. Gzuckier 14:48, 27 August 2007 (UTC)

• The MacLeans survey might help (most of it requires a subscription, sadly). --M@rēino 17:24, 27 August 2007 (UTC)

Newtonian camera

Would it be possible to make a camera (lens) that uses the same principle as a newtonian telescope? I imagine it could be done simpler, with a mirror behind the lens (if any) that reflects the light to the side, where the sensor then should be. That would be a way to make the camera flatter, a solution to a substantial practical problem, especially with the better lenses, which are always too bulky to always carry around. Actually, come to think of it, why aren't photo cameras made the way film cameras are, with the lens at the narrow end? That would also get rid of the sticking out lens. Actually, some cameras are moving in that direction, but why don't they take the final step? DirkvdM 09:09, 26 August 2007 (UTC)

partial answer - newtonian telescopes don't make very good zoom lenses...that said some lens do utilise mirrors - Catadioptric systems

traditionally photo cameras were that shape because of the shape of the negative+film roll..

For maximum stability of a camera holding it with two hands helps - it could be argued that the classic shape is better for two hands holding than a cine-camera shape?87.102.44.85 10:41, 26 August 2007 (UTC)

It's actually quite difficult to make a 'fast' Newtonian reflector – that is, one with a small focal ratio that will fit in a short tube – that produces good images. Consider the workhorse zoom telephoto lens on my camera. It gathers light through an opening 72 mm across, and focuses it onto a film plane only about 150 mm away. In that length, I also get all the optics I need to focus, control my depth of field, and zoom the apparent focal length from 28 mm to 80 mm. In contrast, a typical Newtonian reflector will tend to have a length that is at least four to six times its diameter (and often quite a bit more). The highly curved mirror needed for a short body is costly and hard to manufacture precisely. The particular aberrations associated with the Newtonian optics (particularly coma) are also worsened with short focal ratios.

Telescope manufacturers have adopted (at least) three strategies to deal with this. 'Slower' optics with longer focal lengths relative to the telescope's diameter reduce the effect of the aberrations, but at the cost of a longer instrument. In astronomy, ignoring the problem is actually often an acceptable solution—stuff in the middle of the field is bright and sharp, and any weirdness can be confined to material off at the edges. Finally, telescope makers have started to add lenses to reflecting telescopes: catadioptric systems. It's that final solution that most often appears in the world of non-astronomical photography. Nevertheless, it's still only used where the cost and weight of glass lenses would be prohibitively high. TenOfAllTrades(talk) 11:23, 26 August 2007 (UTC)

Mostly agree - but.. (note not technically a newtonian - but still a reflector) consider this http://www.zenit-camera.com/rubinar_1000_lens.htm a 1000mm lens - note the short length to width ratio (especially when compared with the equivalent 'glass' lens).. also consider the reduced weight (not such a big factor nowadays with plastic lens) - I just wanted to pick up on that "length that is at least four to six times its diameter" bit - newtonians can be better than glass in this respect due the 'folded' nature of the light path.(and can get very wide for good light collection..

OK I admit I'm just trying to sell this lens (also available in other fittings!).87.102.44.85 13:14, 26 August 2007 (UTC)

You need to be careful with your terminology—while all Newtonians are reflectors, not all reflectors are Newtonians. All commercial (as opposed to home-built) reflecting camera attachments will contain lens elements as well as reflecting elements, both to correct the aberrations of the basic Newtonian design and to greatly reduce the length of the instrument. The focal ratio caveat obviously doesn't apply to catadioptric systems.

Finally, you can't 'fold' the light path in a Newtonian system down to much less than its focal length. The closer the secondary mirror is to the primary's surface (and the further it is from the primary's focal point) the larger the secondary needs to be to capture all of the light. This, in turn, increases the size of the central obstruction, reducing the telescope's light-gathering ability. TenOfAllTrades(talk) 14:39, 26 August 2007 (UTC)

Interesting - looks like I meant a Schmidt-Cassegrain telescope or similar - in my ignorance I assumed it would be considered just a variation on the newtonian - thinking all mirrored telescopes/lens were newtonians. Oops!.87.102.11.213 16:51, 26 August 2007 (UTC)

My oops. When I said newtonian telescope I meant reflecting telescope. So the title should read 'reflecting camera'. DirkvdM 09:23, 27 August 2007 (UTC)

87.102.11.213, you said that reflective telescopes don't make very good zoom 'lenses', but I get the notion that the opposite is true (or did you mean that reflective telescopes have a limited range of zoom?). They're very good at zoom (after all, that's what telescopes do) and are much more portable than comparable lenses. But I just realise there might be another problem here if the secondary mirror is in the path of the light, as indicated by the macro-limit of the Zenit 'lens' linked to by you. In a telescope that mirror being in the way doesn't matter too much because the objects are huge and far away, so it will only affect the overall light intensity. But for objects closer by there is a more serious problem. Take macro photography. If the object is small and only a cm away from the camera then its light might be completely blocked out by the secondary mirror. That is an extreme example, but for objects not that close but still close the 'blockage' of light would still be unevenly distributed. Does that make sense and from which distance would it no longer be a (serious) problem?

That would be solved by not having the secondary mirror in the path of the light, but I remember from a previous thread here that that would cause more problems in constructing the primary mirror. Then again, maybe economics of scale might solve this if the cost is largely in the development of the technique and the production of the machine that makes the mirrors. Telescopes are never mass produced, but cameras are. Once you have a (polishing) machine that can make this type of mirror then the production of each individual mirror would not be so expensive, so it's just a matter of how many you can sell. Right? DirkvdM 09:23, 27 August 2007 (UTC)

Re - zoom - by zoom I meant the ability to change the focal length. I never heard of a 'zoom' telescope as such, but I know different eyepieces can change the magnification - is that the same.. Otherwise I agree the other points. I think the question is (in the case of a camera) why use mirrored optics in preference to lenses - especially when the abberations due the the second mirror are avoidable with a lens system..?87.102.45.106 11:45, 27 August 2007 (UTC)

disclaimer I'm no optics expert - it's probably the thing I know least about - I think you DirkvdM should ask a new question about the reasons why we are not using newtonians in cameras - I'd be interested to see a proper answer. 87.102.45.106 12:10, 27 August 2007 (UTC)

stepped transmission

why geometric progression of speeds is preferred in stepped transmission systems? thank you210.212.24.7 09:55, 26 August 2007 (UTC)

you mean like gear ratios 1:1,1:2,1:4,1:8 etc?

a geometric progression gives a wider range of gear ratios than a linear progression cf 1:1,1:2,1:3,1:4

So that enables both slow crawls and high speed driving.

There may another reason I've missed?87.102.44.85 11:42, 26 August 2007 (UTC)

It's not just automatic transmissions, the gear ratios (reverse, 1st, 2nd, ...etc) for four manual transmission cars I've owned recently are:

• 1963 Austin Mini (37hp): 13.66, 13.66, 8.18, 5.32, 3.77
• 2003 BMW MINI Cooper S (165hp): 11.13, 11.42, 7.18, 5.40, 4.40, 3.66, 2.99
• 2005 BMW MINI Cooper S (172hp): 11.94, 12.79, 7.79, 5.65, 4.61, 3.83, 3.13
• 2007 BMW MINI Cooper S (178hp): 11.78, 12.06, 7.77, 5.41, 4.15, 3.46, 2.97

All of them have the property that the difference between consecutive ratios reduces by smaller and smaller amounts as you get into higher gears. I believe this is because they wish to move the optimum shift points closer and closer together (in RPM terms) so that the car may be kept running within narrower and narrower torque bands - allowing you to employ more torque at higher speeds when air resistance becomes a significant factor. They also seem to have been chosen to provide efficient cruising at typical speed limits. If you look at the differences in gear ratios between 2003 and 2005 - and note that the 2005 model had just 7hp more than the 2003, you can see that careful selection of gear ratios to match small engine changes is sufficiently important to car manufacturers that even a 4% engine performance improvement warranted redesigning the gearbox! This tells you that there is a lot of science going into picking those ratios. SteveBaker 12:48, 26 August 2007 (UTC)

Building a wall or fence to block traffic noise

A noisy road has been built about 70 metres away from my house. I was wondering if I could reduce or remove the traffic noise by building a wall adjacent to my house so that I would have a small enclosed courtyard area that was open to the sky yet comparatively quiet.

The main determinant of how silent the courtyard would be, I think, would be the noise coming over the top of the wall and diffracting into the space beyond it. Thus even though below the height of the wall, you would still hear noise because of the sound waves diffracting from the top of the wall. Does anyone know how to calculate this effect? A taller wall would be better, but I'd like to estimate if an acceptable height of wall (say two metres) would still reduce the noise enough to be worth building.

I'd be grateful for any practical ideas about how to reduce the noise - for example trellisses that may reduce noise by acting as diffractors and creating destructive interference of the sound waves. Thanks. 80.2.200.132 10:33, 26 August 2007 (UTC)

I can't give you an equation - but can confirm that a wall (taller than you) will significantly cut the noise.

The other methods are pretty much as you describe - anything that can absorb a sound wave - anything solid - trees may help.

A wall would definately be 'worth building' the sound reduction effects would be significant. A hedge or row of trees would also help - pines grow fast and tall.87.102.44.85 11:46, 26 August 2007 (UTC)

This page says: A noise barrier can achieve a 5 dB noise level reduction, when it is tall enough to break the line-of-sight from the highway to the home or receiver. After it breaks the line-of-sight, it can achieve approximately 1.5dB of additional noise level reduction for each meter of barrier height". I've also seen rows of fast-growing cypress trees that are very dense, nice to look at, and apparently good for noise abatement. --Sean 12:08, 26 August 2007 (UTC)

My first guess would be that trees (especially the thick cypress variety) would form a better sound barrier than a brick or concrete wall. The trees will block the line-of-sight as effectively, but will muffle the sound better. Also, they can grow to very tall heights, which has been empirically shown (as above - 1.5 dB per meter of height) to reduce the noise significantly. Nimur 18:16, 26 August 2007 (UTC)

• Another way to reduce noise is rubberized asphalt. If this is a new road built near existing houses, your community might be able to force the use of a surface of rubberized asphalt. --JWSchmidt 00:04, 27 August 2007 (UTC)

There are many street-noise blocking walls where I live. They are 12-15 feet tall, corrugated steel walls. Very ugly, but work well. -- Kainaw^(what?) 00:23, 27 August 2007 (UTC)

I've studied sound breaking and pretty much what you'd need is a really dense, solid wall with lots of mass. Brick and concrete probably. Traffic noise is often low frequency so the wall would need to be a ways into the ground (I think--anyone know for sure??) and then I know it'd need to be high and pretty fully surround your home at least in the noise's direction. Traffic noise is worst as loud engines and loud car stereos. Juanita Hodges 01:34, 27 August 2007 (UTC)

This question has been asked before, last year I believe. Alas I don't know of an easy way to search for that. But 'the answer' I believe was a plant-barrier. This might have the added advantage that you will be allowed to make it taller than a wall. For an obvious reason - it's not as ugly. I don't know how the costs would compare, especially if you don't want to wait and want to plant big trees (with plants below them). DirkvdM 09:31, 27 August 2007 (UTC)

You'll want to wait for winter when plants are dormant for a bio-solution, but a fence of living willow would work. You can use a species that grows at a rate to match your need. Bendž|Ť 09:42, 27 August 2007 (UTC)

Unidentified disease of Marigold

I have a marigold plant. It was flowering really well. Suddenlty one day I saw cobweb like stuff had developed on the flowers. On close inspection I saw small dot like white things moving in that web. This web is more like a thin veil of cotton rather than a web actually. I wasn't sure what to do so I banished the pot to the fire exit and closed the window. I did not want my other plants to get whatever it is and I thought sun might be helpful. I live in NY but am used to a more tropical weather garden. The questions are:

What is this disease? Is it harmful to other plants or to humans? How do I cure it?

Some added information: It rained heavily and the plant was soaked. I brought it indoors so that it is not harmed by the cold rain. It remained indoors for 4 days before it developed this thing. --Kaveri 13:59, 26 August 2007 (UTC)

Sounds like red spider mite. Easy to get rid of if you spray with water mist daily. (Or possibly mealy bug.)--Shantavira|^{feed me} 15:25, 26 August 2007 (UTC)

I agree, red spider mite. They love hot, sunny, dry places so giving them a fine water spray once or twice a day will certainly control them. Check your other plants because these little monkeys can spread round a greenhouse at the speed of light. Richard Avery 10:13, 27 August 2007 (UTC)

Uh oh, looks like we're going to have to augment our disclaimer: no medical, legal, or horticultural advice! :-) --Steve Summit (talk) 17:35, 27 August 2007 (UTC)

lenses

Can't seem to find a page on 'lens manufacture' other than history of lensmaking. Is there one? I'm thinking specifically on how plastic and glass lenses are made (cast, then ground ??) rather than lens design.87.102.11.213 16:55, 26 August 2007 (UTC)

Float glass details the process of float glass, but I think this is not the common procedure for small lenses. We seem to have the historical perspective well-represented, but I can't find much on modern lensmaking either. Nimur 18:19, 26 August 2007 (UTC)

????Does "ref desk collaboration of the week" still exist - if so I'd like to put this forward. Where is it. I've also made a requested article thing as well..87.102.11.213 19:23, 26 August 2007 (UTC)

Acoustics

When, say a trumpet plays a note, and then a piano play a note of the same pitch, what is the difference between the sound waves that the two instruments make that allows us to distinguish between them? Imaninjapirate^{talk to me} 17:31, 26 August 2007 (UTC)

The second,third,fourth etc harmonics differ. Overtones is probably the easier/better article to read here and both give you the answer.87.102.11.213 17:37, 26 August 2007 (UTC)

Also you are listening to different waveforms. See the various articles linked from that one, some of which have samples of what different waveforms sound like. The only thing the two notes have in common is their wavelength.--Shantavira|^{feed me} 17:45, 26 August 2007 (UTC)

It's worth noting (as it's not in the article waveform) that the waveform consists of the (wavelength) fundamental frequency plus all the overtones or harmonics - bringing all three articles together.

Effectively the presence of harmonics or overtones is means that the 'note' consists of multiple pure tones - there are multiple notes being played simultaneously when a piano key is pressed - the note (on the musical score) corresponds to the first harmonic.87.102.11.213 18:07, 26 August 2007 (UTC)

Also, "imperfections" in each instrument (such as breathy noise in the trumpet) result in non-harmonic elements of the sound spectrum. You might want to investigate psychoacoustic perception, which is an ongoing research topic. Nimur 18:22, 26 August 2007 (UTC)

Then there is also the rate of attack and decay (how quickly the sound reaches max volume and how quickly it ends), which tends to vary by instrument. A grand piano, for example, will have a slower decay rate than an upright piano. StuRat 22:13, 26 August 2007 (UTC)

And the technical term for it is timbre. Confusing Manifestation 22:26, 26 August 2007 (UTC)

And Stu is referring to the adsr envelope (at least, that's the simplified model used in electronic musical instruments). Note that during attack, the pitch may also be different. DirkvdM 09:37, 27 August 2007 (UTC)

Also, the relative amplitude of the overtones can change with time. Also, some partials can be more or less out of tune (as per the 7th on a piano).

In truth, this question is being asked backwards! There is almost nothing the same between the acoustic waveform of a trumpet and a piano playing the same note. Just about all you can say is that the majority of the energy present in the sound is delivered at some specific frequency for most of the duration of both notes. All else is up for grabs and will be different. It's interesting that our brains are able to discern any similarity between the two notes at all! I suspect that some aspect of the way we percieve sound is responsible for that - but I'm no audio expert. My domain is in the world of light and eyes - and our ability to see hundreds of shades of red as all being fundamentally more or less the same "colour" is perhaps a similar ability. If so, it's an artifact of the approximate way we percieve such things ("It's a bug - not a feature!") SteveBaker 16:30, 27 August 2007 (UTC)

If a tree falls in the woods, does it make a sound?

answer the question!!!!--arab 20:56, 26 August 2007 (UTC)

If a tree falls in a forest — Matt Eason ^{(Talk &#149; Contribs)} 21:05, 26 August 2007 (UTC)

And this entire discussion, from June 30. Without doubt, sound is produced. Nimur 21:54, 26 August 2007 (UTC)

Without doubt? That's not the answer. The answer depends on what kind of question you are really asking, as the normal one requires qualification to be precise. --24.147.86.187 22:00, 26 August 2007 (UTC)

Not really. Nobody was able to come up with any kind of reasonable version of the question in the June 30th discussion that produced a tree that falls in a forest without making a sound. The nearest anyone came (IMHO) required a redefinition of the word "sound" in a way that fits no dictionary definition. What do you think is unclear? SteveBaker 23:47, 26 August 2007 (UTC)

OK, I made many comments that I removed now. Science simply cannot answer any question, including this one, as the article on science correctly states. A.Z. 03:11, 27 August 2007 (UTC)

This thread is at grave risk of turning into the kind of debate which the reference desks frown on, but: this last is of course nonsense. Science can answer many (if not most) questions, and it can answer them to an arbitrary degree of accuracy. There are, to be sure, untestable philosophical questions which science cannot answer, and it's also true that "an arbitrary degree of accuracy" is not synonymous with "absolute accuracy". But if science can't answer anything, then how is it we're not all still living on nuts and berries? —Steve Summit (talk) 03:42, 27 August 2007 (UTC)

I'm sorry, but I do not know if we are living on nuts and berries. I do not know absolutely and unquestionably that a berry or a nut have ever existed. If you can't realize that science is nothing, and that it doesn't make you know nothing and that no truth comes from it, you are just fooling yourself. A.Z. 03:44, 27 August 2007 (UTC)

Yes, yes, it's fun to play the I-can't-prove-that-all-of-observable-reality-isn't-a-figment-of-my-imagination game. We've all played that game before. But if you want to cure disease or feed the masses or travel faster than you can walk, it's not a useful game to play. The "practical everyday purposes" which you seem to be pooh-poohing are (for practical everyday purposes) the only purposes that matter. Scientific truths may not be isomorphic with philosophical truths, but neither one has a monopoly on the concept of truth.

To A.Z.: This will be my last post in this thread. To everyone else: I apologize for prolonging a philosophical debate on this science desk. —Steve Summit (talk) 03:57, 27 August 2007 (UTC)

I profoundly disagree with you. I'm not playing a game, and I'm sorry you're mocking me. Believing in science is like believing in the Bible. You don't know if there are masses, you don't know if there is food, and that does matter. I feel really sorry to see a question that does matter being mocked here, and philosophers who are just people that don't have a blind faith in science or the Bible being called pathetic. You should admit that no, you don't know if a tree makes a sound or not when it falls, either in the forest or in front of you. I think we should feed the masses and live our practical ignorant everyday life, and I belive there should be science, but I won't pretend to know truths, and pretend I'm not ignorant. A.Z. 04:07, 27 August 2007 (UTC)

Here's the problem for the "nothing can be proven to be real" folks. If nothing were real outside of your thoughts then you could simply cease to interact with this phoney world. So shut off your sensory inputs and just sit inside your mind and all should be well. The trouble is that after you have thought a significant number of thoughts (what we scientists would describe as "a few hours of time passing"), your "fake" sensory devices are going to start making some alarmingly real demands on your thoughts. You'll find that you get sleepy, hungry and thirsty. There is simply no way to shut out those demands no matter how unreal you believe them to be. So whether or not these things are real, you have to act in pretty much every way as if they were. If the demands of food and sleep were illusions brought about by our senses - why are your thoughts so utterly dependent on them? If you go for 48 hours without sleep - you'll find your "inner thoughts" become very hard to keep on track...which would be a surprising thing if the real world were utterly illusionary. So the value of an unprovable (and unfalsifiable) hypothesis such as yours drops to zero within a surprisingly short period of time. The "real world" (as I would prefer to describe it) is 100% compelling - you can't shut it out no matter how hard you try. Time passes in your mind at a rate not too dissimilar to the real world - you can't count to 100 in your head (or think 100 interesting thoughts or...whatever) without at least (say) half a minute or so passing in the real world. Increasingly, we scientists out here in the real world can tell (in the form of various brain scanners) approximately what's going on in your 'inner thought world' - we can see regions of your brain relating to vision light up when you think about pictures and regions related to reasoning light up when you think about math problems. In an increasingly real sense, I can compare what's going on in your mind with what's happening in mine - and find some sharp correlations. So your personal 'inner world' is also increasingly able to be viewed from within my personal 'inner world' - and as far as can be discerned, they work the same way. So what is the point (other than to annoy Steve Summit - which, I agree may be entertaining!) in holding the bizarre view that the outside world is fake and your thoughts are all there is - when the reverse seems to be the only thing that actually works for you? You have absolutely no evidence for the view that your inner world is all that there is and that the real world is faked - yet there is a mountain of evidence that says the opposite. If all of that evidence was out here in the 'real' world - you'd have some grounds for regarding that evidence as illusionary - but it's not - some of the evidence for the existance of a real world exists inside your inner world. Your absolute inability to keep your inner world from turning to thoughts of food, drink, sleep, etc as the real world places demands on it reveals evidence that is totally independent of your senses. Sure the 'feeling' of hunger is a sensory input from your stomach - but if it were illusionary, you could have it not affect your inner world...but you just can't do that. Try this: Try counting to 100,000 in your head without getting hungry. If the world were illusionary, you'd be able to do it...you can't. You just can't. Ergo, the real world is...real. QED. SteveBaker 16:21, 27 August 2007 (UTC)

[response to now-deleted prior comment referring to our article on Science]

While the statement, "Science does not and can not produce absolute and unquestionable truth" is certainly true in the context of the philosophy of science, it's profoundly misleading in the context of everyday life. If you've heard that scientific truths aren't absolute, you can easily conclude that (say) biblical truths are just as good as scientific ones. In a way, it'd be really great if we could publicly claim that scientific truths are absolute.

For everyday purposes, saying that scientific truth is not absolute is like saying that falling trees do not produce sound, or that the sky is not blue, or that 1+1=3, or that gasoline doesn't power automobiles, or that heavy objects fall faster than light ones, or that death from cholera is inevitable, or that easy transmutation of lead into gold might be possible tomorrow. —Steve Summit (talk) 03:31, 27 August 2007 (UTC)

But the tree question couldn't care less about everyday life. It's a question about truth, not a ridiculous question about whether your recorder will record something if you place it next to a tree that is about to fall. And, yes, I admit not to have a clue about whether the sky is blue. When I say it's blue, I'm assuming everyone knows that's just for practical everyday purposes. A.Z. 03:38, 27 August 2007 (UTC)

If you take the view that you cannot trust your senses then you have deeper problems. It's not just that you have to doubt that the tree makes a sound - you have to say that the words "tree", "fall", "forest" and "sound" are completely neutral audio signals that your senses are feeding to you with no verifiable meaning whatever. You don't know that you read the question correctly (or at all) or that you did in fact answer it. You don't know whether you are reading what I wrote - you don't even know that anything exists. If that is indeed your belief - then why are you trying to answer this question? In any not-believing-ones-own-senses situation, the question may never have been asked.

The truth is that the question (like everything else we do or say in the real world) is merely shorthand for: "If 'trees' (defined as the following bundle of possibly-illusory sensory inputs....) existed in the way our senses depict them - and if one 'fell' (defined as...) in a manner subsequently seemingly revealed to our senses but not reported directly to our senses at that time..."...and so on for about another four pages. The answer is: "If all of those things were hypothetically true then the answer would be (with many, many more caveats) - Yes!"...which is all you can ever answer about any question on any topic. The point being that you have to understand that the question is wrapped around with all manner of unwritten caveats and assumptions about the real world existing as perceived - and it is implied and understood that your answer should strictly be wrapped in the same unwieldy bundle of linguistic torture. If you accept the question under those terms then the answer is unquestionably "Yes" under those same terms. If you don't accept the question because you refuse to accept those layers of implied meaning then why are you answering it? If the sound of the tree might not exist - then neither might the question be about trees in forests at all - so you can't have a valid answer either way. SteveBaker 18:38, 27 August 2007 (UTC)

That 1+1=2 is an absolute and unquestionable truth, not discovered by science. A.Z. 03:42, 27 August 2007 (UTC)

I don't know about that. It's (essentially) an axiom built into mathematics - and math (done that way) happens to be useful. But there are other ways that don't come out with that. Suppose you did all of your math in logarithmic domain or perhaps if math were invented by creatures who lived their lives moving at speeds close to the speed of light relative to each other and who learned to add velocities, times and masses using the Lorentz transform: 1c+1c doesn't equal 2c, it equals 1c. Sure they'd have to come up with some new, fancy representation for counting apples - but then we had to go to quite a lot of trouble to bend our math to do relativistic stuff that would come naturally to them. That doesn't make either their or our math 'wrong' - it just doesn't apply. Just as we say that the three angles of a triangle add to 180 degrees - that's not true in a severely warped gravitational field and beings who lived in proximity of a black hole would never have believed what Euclid had to say. It's not entirely obvious that every imaginable culture would see addition of integers as particularly useful. We can imagine beings who can only count to three (one, two, three, many) - who would have an entirely different arithmetic system. 1+1=2 and 1+2=3 but 2+2=many and 2+3=many. Also 2-1=1 but many-1=undefined. You would say that 1-1=0 was also an absolute, unquestionable truth - but the ancient Greeks had an entire system of arithmetic that didn't even contain the concept of zero. You could come up with an entire self-consistent (but not very useful in our world) set of mathematics based around denying our basic rules of arithmetic - in which 1+1=2 would not be quite the slam-dunk you think it is. SteveBaker 18:08, 27 August 2007 (UTC)

To the Original Poster: the answer to your question is, "yes". (Why do you ask?) —Steve Summit (talk) 02:56, 27 August 2007 (UTC)

The answer is yes. Those kids at the Humanities desk may tell you something different, but here we value objective reality and empirical verifiability. Unless you ask the quantum people, who will likely disagree as to whether the falling tree even hits to ground... Plasticup ^T/C 03:31, 27 August 2007 (UTC)

Sound of a bong bubbling* *Cough* Wow, like, you guys just totally blew my mind. 24.22.163.169 06:58, 27 August 2007 (UTC)

This requires the true definition of the word "sound" in a way that newer dictionary nolonger use. According to Webster's new international dictionary published 1931 2620 pg. Definition "Sound": 3. To Speak; utter; express "audibly". Now Rare. Definition of audibly which is an adv. form of "Audiblo" its definition is "Audiblo"- Capable of being heard. Not the word capable, as in if present or not present! key. it will be capable of being heard., it is capable of being heard even if no one there. Key word capable so it someone happens to be there it can be heard but does not require someone to be there, then it would be heard, not just capable.... Sound waves being produced,, case solved!!! Q.E.D. --Aaron hart 09:50, 27 August 2007 (UTC) so the ansuer is yes no matter how you twist your modern definitions......

Like in any debate, the person who defines the terms wins the argument. -- JSBillings 10:22, 27 August 2007 (UTC)

Answer=yes.87.102.45.106 13:19, 27 August 2007 (UTC)

How do you demolish a skyscraper?

What is the normal non-terrorism way to demolish a skyscraper? Mapper of the streets 22:54, 26 August 2007 (UTC)

Tall buildings are typically demolished using excavators. Controlled implosion has been used on buildings ~40 stories tall, although the danger and environmental hazards make this a non-prefered method of doing it (and this would imaginably be impossible in sufficiently dense urban areas). The tallest building ever demolished (not by terrorists) was only 47 stories tall. See also, demolition, high-reach excavator. Someguy1221 23:13, 26 August 2007 (UTC)

Explosives are planted in the base of the tower and then the tower falls vertically rather than on its side. It takes a lot of planning to get a tower to fall vertically. Juanita Hodges 23:25, 26 August 2007 (UTC)

Occasionally, buildings are dismantled piece by piece, in sort of the reverse order they were built. I watched this being done to the top floor or two of a building in Seattle that was being remodeled, and the same thing is currently and notably being done to the damaged Deutsche Bank building next to the WTC site. Presumably manual dismantling is more timeconsuming, more expensive, but less disruptive than either explosive demolition or excavator demolition. —Steve Summit (talk) 02:55, 27 August 2007 (UTC)

It is also noticeably less exciting. Plasticup ^T/C 03:33, 27 August 2007 (UTC)

Well, except for a couple of recent incidents at the Deutsche Bank building. :-( —Steve Summit (talk) 03:37, 27 August 2007 (UTC)

You can find a very good article on building_implosion at [18] -- WikiCheng | Talk 04:11, 27 August 2007 (UTC)

If you're (understandably) worried about the building falling to its side during demolition, think about the New York WTC (the terrorist thing you refer too, I presume). Both those towers fell straight down, despite the fact that they had been hit violently in the side. I can imagine that skyscrapers are even designed to fall like that if explosive demolition is so much cheaper than excavator demolition. Btw, funny that you specify non-terrorist. Loads of skycrapers must have been demolished (makes me wonder - how many?) and only once by terrorists. But the images have been repeated on tv so often that indeed I also instantly thought of the New York WTC when I read the header. We've been brainwashed. :) DirkvdM 07:13, 27 August 2007 (UTC)

A lot of people say there were explosives planted in the twin towers and people heard explosions at the base of the towers, too. Juanita Hodges 11:05, 27 August 2007 (UTC)

That would of course be the controlled demolition hypothesis. Worth noting is that – aside from a tiny minority of conspiracy theorists – it is widely acknowledged as bunk. Beware the 'major events must have major causes' trap in human psychology: [19]. TenOfAllTrades(talk) 13:27, 27 August 2007 (UTC)

You might enjoy David Macaulay's book Unbuilding, in which he descrbes the hypothetical dismanteling of the Empire State Building.

Atlant 12:00, 27 August 2007 (UTC)

The lesson the twin towers does bring is how relatively easy it is to bring buildings down more or less vertically. In that case, both essentially unplanned collapses happened fairly close to vertically. Demolition experts who are trying to achieve this kind of effect ought to be able to produce it on demand. One wonders how much thought about the ultimate demolition of the building goes into the original design process. Are architects inadvertantly making buildings that are going to be costly to demolish when the time comes? SteveBaker 15:49, 27 August 2007 (UTC)

Twin towers spilled debris out all over the place, presented a major health hazard, and rained concrete on the city. I doubt it is a good model for how things ought to work, demolition-wise. It superficially came straight down (under the massive weight of the top bits of it) but it was nowhere near a model for a safe demolition, and if you look at the footage/pictures you can see that there is a tremendous plume of materials as the buildings comes down (i.e. Image:South WTC Collapse.jpg). --24.147.86.187 18:22, 27 August 2007 (UTC)

August 27

Noise reduction history

What 'playback only' audio noise reduction techniques were available in 1989 in the US? IE how did they go about reducing tape hiss in those days?--88.110.232.152 04:24, 27 August 2007 (UTC)

Dolby noise reduction systems were quite common in 1989, but they are not "playback only". I'm not sure there are any reasonable techniques for reducing tape hiss on playback only. Since tape hiss occurs across a very broad frequency range you can't really reduce it without also reducing everything, signal as well as noise (I could be wrong, perhaps there are some Magical Algorithms out there I haven't heard about). Still, it's best to take noise reduction steps at the recording stage. Pfly 05:59, 27 August 2007 (UTC)

On prerecorded tapes at that time dolby B was common.87.102.45.106 11:34, 27 August 2007 (UTC)

The playback-only techniques that are commonly used depend upon having a "moment of silence" from which one can deduce the various noise sources in the system (hiss, turntable rumble, etc.). One way it is done is to take the Fourier transform of the noise and decide how much noise is in each of the frequency bins. The normal (non-silent) signal is then run through the transform and any frequency bin that has about the same energy as was present in the noise sample is just dropped (zeroed out). The signal is then inverse-transformed back into an analog waveform and voila!, some of the noise has been removed.

Other techniques look for discrete events like "clicks" and "pops"; the real sound source is muted during these events and inferences are drawn (again, often using the Fourier Transform) as to what the sound would have been had the click or pop not occurred.

Back in 1989, it would have been a possible but expensive proposition. Nowadays, you can buy reasonably-priced software for your PC or Mac that will do all of this automagically (e.g., Sound Soap).

Atlant 12:07, 27 August 2007 (UTC)

thanks you. l am aware of the modern spectral subtraction techniques such as is used in Cool Edit etc. I have a reissued CD digitally remixed in 1989, where they say on the sleeve note that they have managed to remove most of the tape hiss (caused by too low a recording level) on the original master tape. What noise reduction technique are they likely to have used? (BTW is not low pass filtering as the upper frequencies are OK) Oh yeah, and why would they keep the very low amplitude and refrain from eqing the tracks back to something acceptable?--88.110.232.152 13:53, 27 August 2007 (UTC)

Plants Water Purifacation

How plants can discern the particles of substances and elements , with what special characteristic of them?Flakture 07:42, 27 August 2007 (UTC)

As a general answer, the process is based on similar concepts in both plants and animals. Membrane transport proteins are generally sensitive to the charge and size of molecules and ions. Proteins can also be "designed" to take advantage of chemical characteristics of target molecules (ie, the propensity of oxygen to bind to iron in hemoglobin). Someguy1221 08:08, 27 August 2007 (UTC)

Photon duality

--Aaron hart 11:30, 27 August 2007 (UTC) An Old subject but could someone please explain the current theory of partical duality. I thought I had it figured out, "Transformes from energy to matter for a brief instant durring an interaction. Durring the interaction I thought that when it existed as matter is speed was <<C then back to energy propegating through space time at C. Like the particles in a accelerator that result from a smash, these particles exist as mass and in an electromagnetic field spiral and pop into energy Likewise in space-time particles are continually popping from energy fluxuations to matter, then back to energy!., not nececerrially the pairs just similar....--Aaron hart 09:25, 27 August 2007 (UTC) ANY IDEAS From top Physicist giving up secrets that are well kept. Has it been proven that photons always travel at c, is it possible that durring an interaction velcity is <C since it interacts and transforms into mass, then imidiatly back??? Just wondering I mean is anyone really sure at this time??--Aaron hart 10:18, 27 August 2007 (UTC)

You have a very distorted idea of what matter and energy are. The interactions you think you are talking about, transformation from matter to energy, is actually not this at all. The interactions you speak of are transformations from waves to particles. Light never slows down below C when it interacts with something, and it never stops being energy (the "m" in E=mc^2 is not matter, but mass. A lot of people think that mass and energy are two very different things that can simply be interconverted, but their distinction is actually quite non-apparent in high-energy physics. A photon of "pure energy" has a measurable mass, that given by E=mc^2, and an atom holds within it the energy calculated from E=mc^2, using its measured mass. If you remove through chemical interaction some measurable amount of energy from an atom, it actually weighs that much less as well, even though you removed no particles from it). Now, what it means when light turns from a wave into a particle is that it goes from having no definite position to having a definite position (it's a very difficult concept to wrap your mind around that an object can actually not have a position. The wave the photon is said to be is a sort of map of the probability that you will find it at any particular point at a given instant in time. The very important idea to keep in mind is that before the photon interacts, it isn't actually anywhere! It has no position before it interacts, merely a probability of being found at each point in space). Now, as to what's going on in those particle accelerators is that a pair of particles, typically those generally associated with matter (ie, protons) are smashed together, and interactions that can be described only by quantum mechanics (these interactions are impossible to understand, no point trying to explain them) transform the proton into new particles. As for the particles popping in and out of existence in space time, there are two sources for these. Some are photons or or something else transforming into another type of particle, and then back. Others just, well, pop out of nowhere. These are called virtual particles. They don't actually require any energy to pop into existence, they just do. You can't detect them unless you supply them with energy somehow, but that's another story. But back to the energy/mass/matter thing. Matter is typically used to describe "that which is tangible" (atoms and their constituents). Energy, well, I have no way of explaining that one. You can read energy if you like. The most basic physical idea is that energy is a property of all particles that is conserved (the total amount of it in the universe never changes) in all possible detectable interactions, but is not a measurable physical property like mass. And mass, of course, is merely that which has inertia. I'm sure my answer will not satisfy you, please ask more, and do consider taking introductory quantum physics when you enter college (if you haven't already). Someguy1221 10:25, 27 August 2007 (UTC)

About light dropping below C, while the waves of light can do very funny things indeed, and appear to speed up or slow down, the most basic answer is that photons cannot ever change speed. This is not something to be proven or disproven, but rather it is a mathematically necessary property of photons derivable from the fundamental laws of physics. Someguy1221 10:26, 27 August 2007 (UTC)

Yes I worded it rather incorectly I did mean waves to particles which I meant to refer to as mass. Now my question is how can a photon have mass when only massless waves can travel at the speed of light? Yes I did mean that the waves convert to particles of a mass with the equivalent energy. I also knew that when chemicals interact exothermically they lose the mass equivalent to their evergy, Is this not a form of mass to energy, and could it not similary be waves to energy and energy to mass, and back. could some of the mass be changed to energy, in a wavelike packet? But the part I am interested in is the mass leaving the molecules when energy leaves, is this itself not a transformation as I have proposed?!, is not energy from a exothermic reaction transmitted as a photon? Also The particles poping into existance being photons does this not support my theory. Also I tought this was from energy fluctuations in space time......--Aaron hart 10:58, 27 August 2007 (UTC) p>s> I really appreciate someone with your calaber repling to me thoughts.

Also I was refering to energy to mass, or wave to particle the mass being equivalent to the energy of the particle. It has been a while since I have studied any of this, and quite a while since I have thought of any of it, it started to interfear with my being quote "a normal person" sorry--Aaron hart 11:30, 27 August 2007 (UTC)

I'll try to answer the new questions point by point. To say that only massless waves can travel at the speed of light is not entirely correct. The relativistic equation for kinetic energy (γ-1)m where "m" is the measurable inertial mass of the particle at rest shows that a particle with non-zero rest mass requires an infinite amount of energy to move at the speed of light, since γ = ∞ at the speed of light. This is not to say that photons have no mass, and in theory this is measurable by their gravitational influence (I can hop over to one of my labs right now and measure their momentum easily enough, but this may not satisfy you). Simply all of their mass resides in what is defined as their kinetic energy. Now, back to this mass to energy bit. Firstly, I'll declare that a particle is actually a special case of a wave. If you are concerning yourself with waves that represent a potential particle's probable position in space, then an actual particle can be thought of (ignoring a tad bit of physics at the moment) as nothing more than a Dirac delta wave. Further, one can think of energy and mass as abstract mathematical properties of waves, calculable from the use of mass/energy operators if the wave form is known. Now, an atom is a wave, or rather a superposition of many waves representing the numerous particles that can be found within. The waves have a calculable mass, and therefore energy. When what you normally think of as "pure energy" is extracted from the atom (this can be through emission of a photon or as causing something else to speed up) the wave forms will change in some way. The new wave forms, while describing the same potential particles, will have a different calculable mass/energy. Sometimes it's very easy to ascribe to some nature the type of energy one is dealing with, ie, kinetic energy, thermal energy, photonic/phononic energy, gravitational/electrical potential energy, etc. When you're dealing with a static system, like a lone atom, for example, it's very hard to ascribe the location of the energy, and we generally shrug it off and say that it's all just mass. But in truth, the "energy" is merely a calculable property of the wave functions describing that atom, and this point of view happens to work for all other forms of energy as well. This is all simply to say that classical views of the distinction between mass and energy somewhat collapse in the presence of quantum mechanics. Now, to the last question, the nature of any possible "energy fluctuations" in space-time is largely a matter of interpretation of the meaning of vacuum energy. But if you prescribe yourself to believing that particles pop into existence, then by quantum mechanics, as hard as it may be to swallow this, they didn't actually come from anything. They just start existing, and very quickly stop existing. Now unfortunately I must go to bed, but I'll be back in about 8 hours. Someguy1221 11:29, 27 August 2007 (UTC)

measurable inertial mass of the particle at rest this is where I believe it is a particle, sice it acourding to quantum mechanics it can never be at rest. Also I don't completly believe in Quantum Mechanics, Is it not based on we can not know the position and the velocity since we have to interact with it, which messes with the velocity. But this is only due to scientific measurement, not actuall fact. In fact Relitivity states the Big bang began at a Singularity, Impossible for Quantum Mechanics, but only by our measurments, thus I believe it is basied upon an unkonwn, which is unkown to observers but not God. Thus I believe in singularities, and sure it stands up to evidence, since we are observing the phenomenon, thus it fits. From our observation.--Aaron hart 11:52, 27 August 2007 (UTC) P.S. thank you

It is actually a very good question you bring up, and a common and key misunderstanding of quantum mechanics. We are often taught in high-school or introductory college-level chemistry classes that Heisenberg's uncertainty principle prohibits us from knowing the simultaneous position and momentum of a particle at a given moment in time to greater than a specified accuracy. What we normally aren't told is that it is not our inability to measure these quantities, or our inability to measure one quantity without disturbing the other (that one is only partially true. After measuring a particle's position, applying the momentum operator to the new wave function of the particle, now something like a Dirac delta, will show a very large range of probable values). Rather, the uncertainty in a particle's position/momentum arises from the fact that it doesn't actually have a single defined position and momentum. This is a very alien concept to classical physics, and why it is a common misunderstanding. As I said in above posts, the wave function, through the application of operators, gives the probability of the particle having any given position, momentum, or energy. Before the measurement is made (any arbitrary event whose outcome depends on the particle's position/momentum/energy), the particle exists only as this wave, and occupies no actual position in space. And so, from a quantum perspective, it is not that there is a limit to what we can know about the universe, but rather there is a limit to how much information can actually exist in the universe. As to the singularity thing, Quantum doesn't forbid the existence of a singularity, it merely can't explain it. But neither can relativity. Someguy1221 19:22, 27 August 2007 (UTC)

   I misunderstood, I thought that a particles position and momentum could not both be measured at the same time, and that this was a conciquece of the observation.  Also I don't understand how something with mass can travel at the speed or light, You site rest mass, but this is the total energy of the particle, which can not exist at rest.  I just don't seem to get the concept; a particle with rest mass traveling at the speed of light, has all of its matter or more correctly mass converted to energy (i.e. electromagnetic wave), then when it interacts I believe it is possible however short lived, to transfer from energy back to mass, to interact.  Then the mass transfers back to a EM wave, due to its unstable form, (being so small).  Which I think all has to do with the properties of Space-time.  I am most likely way off, but it makes sence to me, and it is very hard to relate in words.  Note, I did not think Physicist completely understand Photon Duality at this time; only theorys with mathmatical formulas that all fit nice and neat (for the observer)--Aaron hart 21:08, 27 August 2007 (UTC)

Riverstone pebble tiles

Hi, under composite materials I have found the above product, which I require for my knitchen worktop. Problem is I cannot find any reference to a maker, where can I source this? MMany thanks <email address redacted>

^{Email address removed — Matt Eason (Talk &#149; Contribs) 11:01, 27 August 2007 (UTC)}

Do you mean like this http://www.alibaba.com/catalog/10880060/River_Stone_Natural_Stone_Stone_Tile_Cobble_Pebble.html or http://www.ecvv.com/offerdetail/I1424081.html ?87.102.45.106 13:14, 27 August 2007 (UTC)

True open circuit- calculation

How does one achieve a true open circuit (at RF) at the end of a piece of 50 ohm coaxial cable (or other sort of line) bearing in mind that the impedance of free space is always 377 ohms? Is it possible, or must one always have some radiation from the line end?--88.110.232.152 13:41, 27 August 2007 (UTC)

ie since :$\Gamma ={Z_{L}-Z_{S} \over Z_{L}+Z_{S}}$, is it true that gamma can only be a maximum of (377 -50)/(377+50) = 0.7658? as opposed to the ideal of 1?

A very good question, and I'm disturbed that I can't get my thought in order to answer it myself. My intuition tells me that if you enlarge the cable (keeping its impedance constant, of course) so that the centre conductor and shield are far apart, the situation would be more close to the ideal open circuit. Then again, you know how intuitions can be. Please, can someone help out here? —Bromskloss 19:23, 27 August 2007 (UTC)

I suspect that the 377 ohms is irrelevant in this case, but I can't be certain. At a guess, it's because the sequence of impedances is 50R-open-377R and not 50R-377R, so the wave is reflected from the "open" condition at the end of the cable and never sees the 377 ohms of free space beyond.

I can more easily tackle the OP's conclusion, because a simple ETDR experiment shows that an open-circuited cable has a reflection coefficient close to 1. See Figure 11 in LeCroy App Note 016 for an example. --Heron 19:32, 27 August 2007 (UTC)

Ah! but how close? cant be closer than 0.7658--88.111.124.125 20:44, 27 August 2007 (UTC)

OK to help anyone pursuing this line of inquiry, I quote from the article on coaxial cable:

• The characteristic impedance in ohms (Ω) is calculated from the ratio of the inner (d) and outer (D) diameters and the dielectric constant ($\epsilon _{r}$). The characteristic impedance is given by $Z_{0}={\frac {138}{\sqrt {\epsilon _{r}}}}\times \log({\frac {D}{d}})$.

Certainly a lower source impedance would make a better o/c, but still not perfect. Is perfection possible/

--88.110.52.40 19:35, 27 August 2007 (UTC)

toothpaste

does toothpaste ever expire? thanks.

The Chicago librarians who researched this question say yes. [20] --Sean 14:27, 27 August 2007 (UTC)

reaction machenism

conversion of suger to 2,5-dimethlyfuran with complete reaction machanism

• Check your spelling; I believe you mean 2,5-Dimethylfuran. The reference materials on that page should answer your question. --M@rēino 17:28, 27 August 2007 (UTC)

I looks like you might be thinking of a method with Hydroxymethylfurfural as an intermediate- that page has a lot of useful mechanistic infomation (on the production from sugar).87.102.85.15 17:32, 27 August 2007 (UTC)

Telescope Physics

I know how a telescope works, however, I am a little shady on the physics of light travel and a telescope. It's fairly simple when you talk about seeing a couple of miles away with binoculars as you are seeing what is happening right then. What I don't get is when astronomers look into space billions of light years away. I understand that light travels at approx 186,000 miles per second and so what is being seen happened billions of years ago. So the question is when you look through a telescope are you simply pin pointing an area of the sky as though it were a 2-dimensional image? So the more closely you can pin point an image, the farther away from earth you can see? If I were able to take an extremely high resolution picture of the sky would I be able to see as far away with the telecope? --Beckerj99 18:25, 27 August 2007 (UTC)

Your picture needs to be both high resolution and high sensitivity, as the images of distant objects will be very faint - but the basic answer to your question is "yes" - see Hubble Deep Field, Hubble Deep Field South and Hubble Ultra Deep Field. Gandalf61 18:40, 27 August 2007 (UTC)

Awesome, I always thought that was the case, but couldn't find an article specifying it. Thx!!