Wikipedia:Reference desk/Archives/Science/2007 August 21

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August 21[edit]

Quantum Immortality....WTF?[edit]

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? --frotht 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.. --frotht 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? --frotht 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 --frotht 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. --frotht 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[edit]

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[edit]

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 --frotht 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). --antilivedT | 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? --frotht 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[edit]

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[edit]

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[edit]

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)

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!! --frotht 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 --frotht 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 --frotht 23:55, 21 August 2007 (UTC)

Pneumatics Vs Hydraulics[edit]

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 (talkcontribs)

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[edit]

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[edit]

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


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[edit]

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[edit]

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[edit]

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.." --frotht 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 --frotht 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[edit]

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[edit]

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[edit]

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?

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

boat in current[edit]

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 --frotht 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[edit]

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[edit]

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[edit]

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? --frotht 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.. --frotht 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 --frotht 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 --frotht 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 --frotht 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[edit]

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)