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April 13

Speed of Earth's orbit around the sun

I read that earth orbit's the sun at a speed of 107,000 KM/H, which seems mighty fast. Given this imense speed, I find it somewhat surprising that we do not feel any wind resistance here on earth. I mean if you stuck your head out of a car window travelling at 100 KM/H you would feel a strong gust of wind in your face, yet we are tearing through space at 107,000 KM/H without so much as a feint breeze? Perhaps somebody might be able to enlighten me as to why this is! Kind Regards. Paul —Preceding unsigned comment added by 79.71.91.21 (talk) 02:09, 13 April 2011 (UTC)

If you keep your head inside that car window, and keep the window closed, you also don't feel any breeze, yet you're still travelling at 100km/h relative to the road surface, because the air in the car is also travelling with you at 100km/h. Same with the Earth. Its air comes with us as we hurtle along, so we don't feel a thing. — Preceding unsigned comment added by HiLo48 (talk • contribs) 02:22, 13 April 2011

Yes, the speed of the Earth relative to the sun is very fast, but the sun is a very long way off. The sun is at such a great distance that even though the relative speed is 107 km.hr^-1 it takes the Earth one whole year to complete one trip around the sun. That is an angular speed of only 0.0411 degrees per hour which is extremely slow. There is no atmosphere between Earth and the sun, and no atmosphere means no wind when moving relative to the sun.

Earth's linear speed relative to the other planets in our solar system is also extremely large, but the angular speed is extremely small so we experience no effects from our speed relative to those planets.

A jet airliner might pass overhead at a speed of 1000 km.hr^-1 and a height of 40,000 feet (12 200 m) but you experience no effects because of the great distance between you and the airliner. If the jet airliner passed near you (close to ground level) you would experience many effects! Dolphin (t) 06:48, 13 April 2011 (UTC)

Paul you may be interested in the Michelson–Morley experiment that was carried out in an attempt to detect some kind of "wind" due to the Earth's motion, and is famous for having completely failed. (I simplified this story). Cuddlyable3 (talk) 13:52, 13 April 2011 (UTC)

Those experiments strongly (and unexpectedly) demonstrated a phenomenon that the then-current theories were totally unable to explain. For a physical experiment, that counts as a spectacular success -- the opposite of a complete failure. –Henning Makholm (talk) 16:14, 13 April 2011 (UTC)

Once again proving that there are no failures in science; a negative result is still a result, and it is all data. --Jayron32 18:56, 13 April 2011 (UTC)

Well, you can have failures, like when an experiment results in a vague result that's of no use at all, or when different people doing the experiment get different results. These usually mean the experiment was poorly designed. StuRat (talk) 06:33, 14 April 2011 (UTC)

No Henning Makholm. Lorentz-Fitzgerald length contraction was a theory that explained the negative result of the MM experiment. If Albert had not come along later with his special relativity we would probably still find Lorentz's aethereal hypotheses plausible. Cuddlyable3 (talk) 21:31, 13 April 2011 (UTC)

I would like to point out that the diameter of the Earth is 12,750 km, so the planet takes seven minutes to travel its own width. Meanwhile, your car travels its own width in a tenth of a second and a turtle walks its own width in maybe five seconds. If you were watching the Earth from above, it would look very slow. —Preceding unsigned comment added by 205.193.96.10 (talk) 16:03, 13 April 2011 (UTC)

Using decay heat in a nuclear reactor to spin a turbine

I did a presentation in a class of mine, and part of it discussed nuclear energy. The professor asked me if it was possible to use the decay heat produced in a nuclear reactor in a scram situation to spin a turbine which would power a water pump to cool the reactor. I was fairly certain that this idea was not possible simply because it does not generate enough steam to spin a turbine, but I'm not entirely sure. I'm pretty sure they disconnect the reactor from the turbine anyway during a scram for safety reasons. Can anyone confirm my guesses? ScienceApe (talk) 02:33, 13 April 2011 (UTC)

In principle the waste heat could be used to turn a turbine, though probably not the main turbine(s) used for regular electrical generation (the initial decay heat will be less than 10% of the reactor's regular output, and this will decline in the days following the scram). In practice, adding a second turbine (with all of the associated mechanical complexity and necessary preventive maintenance on parts that would be in working contact with radioactive coolant) isn't worth the complexity and cost over other solutions to drive the pumps. (Generally, grid power as the first option, and backup diesel generators as the second.) TenOfAllTrades(talk) 03:27, 13 April 2011 (UTC)

Wasn't that a system in place at Chernobyl that they were testing when the accident occurred? And I thought they referred to s similar system at the Fukushima 1 plants. A scrammed reactor should produce plenty of steam for a while to ruin emergency cooling pumps. Nuke plants are all about complexity and cost, with backups to backups. Edison (talk) 16:14, 13 April 2011 (UTC)

Did you mean to say "run" instead of "ruin" ? StuRat (talk) 06:27, 14 April 2011 (UTC)

The system being tested at Chernobyl was to run the cooling pumps off the residual kinetic energy of the turbine for the 60 seconds it would take to activate the emergency generators. --Carnildo (talk) 00:17, 14 April 2011 (UTC)

This system exists already, at least on french nuclear reactors (PWR). I think it exists also in the US since french reactors were originally constructed with a Westinghouse licence. This kind of steam turbine was also in place in Fukushima I nuclear reactors but you still need a cooling function to remove heat from the system if you want to operate with a closed cycle. You also need a minimum electrical supply to control it (this can be supplied with batteries). — Preceding unsigned comment added by Franssoua (talk • contribs) 12:49, 14 April 2011 (UTC)

whey gel

what exactly is whey gel? —Preceding unsigned comment added by 80.1.216.243 (talk) 03:39, 13 April 2011 (UTC)

It is a gel formed from Whey protein. You can read both of those articles to learn both what a "gel" is and what "Whey protein" is. --Jayron32 04:03, 13 April 2011 (UTC)

Universe = black hole, for some of time... or wait, only in the sideways version of time, which is length (*confused mumbling*)

OK I've been doing some thinking about the universe. Let's say there's this guy, and he's just chilling looking at our universe from the outside right before the big bang. Now, because the universe is ridiculously massive and small, it will appear to him like a black hole. And he is sitting right outside the event horizon (naturally this is the mother of all black holes - being the mass of the universe at ~1.6×10^55 kg and a Schwarzschild radius of approximately a two trillion light years [1] [2] - can this be right?!).

Now do I understand properly, that because he is outside the event horizon, everything that occurs within will be unobservable to him? Time on the surface of the event horizon is frozen for him, and time inside is on an entirely different plane of existence (piece of trivia: I heard one theoretical physicist put it this way: time bends on the fourth dimensional level, and length becomes time, and time length). As such, the big bang will never exist for our friend on the outside of the black hole. At best, current theories indicate he might (or might not) be able to deduce what occurs inside only from an extremely accurate reading of the Hawking radiation (see Holographic principle#Black hole information paradox).

Thus, if I understand properly, it is entirely possible that we live in a universe which is encapsulated within another universe, but the second universe will remain forever unattainable to us. No matter how much the universe expands, because we are dealing with infinitely small meters and units of time (on the event horizon, from the perspective of the outside... god knows what the hell happens inside), we will never reach that universe. I realize this isn't an entirely new concept (I saw Leonard Susskind explain it similarly), but it... kind of made sense to me for the first time tonight, when I thought it up on my own.

So I have some questions about all this:

1. If something were to enter the black hole from the outside, when and how would we perceive it on the inside?
2. Could it be, with the super-screwed-up-ness of time and space, that tracing back to the big bang is really just tracing back to the beginning of the existence of the black hole? And we would experience it entirely backwards (instead of matter falling in, vice versa), in a mad confusing turn of events because time is all goofed up.
3. Addendum to above: possibly all matter that can fall in has already fallen into the black hole before the big bang? And the entire external universe has already all ended, because it took infinite time for even a second to pass within? I'd have to assume Hawking radiation turned out incorrect. Thus we experience the big bang as the beginning of time, but really it's the end of time for the external universe. Much in the same way as someone traveling on a photon would have the entirety of time pass before experiencing even a second.
4. My understanding is that, given the right conditions of a spinning black hole, the singularity can be exposed to the outside world. What would happen then? What would it look like?

OK, I hope I haven't textwalled here too much, and I've stated this clearly enough that you all can understand it. I know I haven't stated it clearly. Anyway, am I making any sense at all?Magog the Ogre (talk) 06:37, 13 April 2011 (UTC)

Unlike some of the people here, I'm no expert, but aren't there a couple of problems with treating the big bang as a black-hole style singularity. I believe time and space came about in the big bang, standing outside it makes no sense. (unlike standing outside a black hole, of course) Isn't the concept of observing anything flawed with no concept of time and space? Grandiose (me, talk, contribs) 08:18, 13 April 2011 (UTC)

I have two questions:

1) can black hole return to expand or exploding to produce new objects?

2) about the big bang and expanding of universe ,there is no boundary and centre for universe , is there remnant matter in first point which big bang started?(this helps imagining )-78.38.28.3 (talk) 08:37, 13 April 2011 (UTC)

[Fixed your formatting for clarity, 78] In brief:

1) It is thought that, given long enough, all black holes will eventually evaporate by giving off Hawking radiation, but the time this takes is in some inverse proportion to their size, so black holes of star-mass or larger might take longer than the Universe itself will exist to evaporate (from the first link: "For a black hole of one solar mass . . . we get an evaporation time of 2.098 × 10⁶⁷ years"). Otherwise (we think), no.

2) There is no one "first point where the Big Bang started" because that point itself has now expanded to form the whole of the Universe. The Big Bang was also an expansion of space (and time) itself, not just of some matter within pre-existing space. To put it another way, everywhere is that "first point". This is, of course, very difficult for us to visualise. {The poster formerly known as 87.81.230.195} 90.197.66.111 (talk) 12:53, 13 April 2011 (UTC)

The error in your hypothetical scenario is subtle—it presumes that there is somewhere for an observer to sit outside the Universe, where he can watch the show. (That scamp Douglas Adams can be blamed for this perception, as he offered us the Big Bang Burger Bar as the natural complement to Milliways, The Restaurant at the End of the Universe.) Outside the Big Bang singularity, there just isn't any space to be in, and no way to watch the big...bang as it happens. TenOfAllTrades(talk) 15:10, 13 April 2011 (UTC)

4 It look like black hole from outside —Preceding unsigned comment added by 77.127.207.138 (talk) 15:47, 13 April 2011 (UTC)

Outside ? It's confusing to think about these things because of the tendency to think of the metric expansion of space being like a 2-sphere expanding into 3D space....but it isn't. Sean.hoyland - talk 16:10, 13 April 2011 (UTC)

"Big bang theory". Phewy, bah humbug, hogwash. I can think of no other scientific postulation which has received such resounding, universal acceptance based on such flimsy empirical evidence(other than perhaps the flat earth theory). Oh yes another one might be "god done it". The big bang is no more an explanation than the bible is. Think about it.190.149.154.194 (talk) 17:08, 13 April 2011 (UTC)

Perhaps I should clarify. Befor the existance of time or space or the universe,(something?) went bang and brought everything including itself into existance. What? Metaphysical mumbo jumbo.190.149.154.194 (talk) 17:21, 13 April 2011 (UTC)

Read Big bang#Observational evidence for the empirical evidence for the big bang. Dauto (talk) 17:48, 13 April 2011 (UTC)

The Big Bang theory is one of the best-evidenced scientific theories in the world, provided you understand its inherent limitations (briefly, that it describes effects and not cause). — Lomn 17:50, 13 April 2011 (UTC)

Thanks guys. I have no difficulty with hubble's expansion conclusions or with penzias and wilsons observations of residual electromagnetic radiation. I do however have a problem with the general assertion that the logical back track of those observations indicate the origin of the universe. It seems clear that what is being learned is part of the history of the universe, not neccessarily the origin. I think that basically sums up my argument.190.148.132.153 (talk) 19:07, 13 April 2011 (UTC)

I think that most (if not all) cosmologists would agree, these days. -- BenRG (talk) 20:38, 13 April 2011 (UTC)

but agine it cold be cycle in time , and be black hole agine . —Preceding unsigned comment added by 77.125.91.113 (talk) 22:35, 14 April 2011 (UTC)

Contrary to popular belief, you can put a big bang cosmos inside a larger universe that didn't start at the big bang, at least in classical general relativity. From the outside, the big bang cosmos has the same gravitational field as any other object with that mass. (This means the mass has to be finite—which means that the homogeneous cosmos that we find ourselves in has to have an edge out there somewhere—but that's consistent with observations if the edge is far enough away.) The big bang appears from outside as a white hole. In a black hole there's an event horizon that can only be crossed from outside to inside, and anything that does cross it ends up at the singularity, while anything that doesn't cross it ends up at future infinity. A white hole is the time-reversed version of that: there's an event horizon that can only be crossed from inside to outside, and anything that crosses it started out at the singularity (the big bang singularity, in this case), while anything that doesn't cross it started out at past infinity. The big bang singularity is inaccessible from the outside universe, but all of the matter that originates from it crosses the event horizon, after which there are no restrictions on two-way travel between the big bang and non-big-bang regions.

However, if there's a positive cosmological constant, then long-distance travel eventually becomes impossible. In the real world, assuming future expansion is dominated by the cosmological constant, I think that it's already too late to reach the edge of the visible universe, much less the edge of the whole big bang cosmos (if there even is one). Also, I don't know how quantum gravity alters this picture. Classically, the white hole has to have existed forever from the outside universe's perspective, but I don't see why it wouldn't Hawking-radiate away once you add quantum effects. It may be that nothing I said above makes sense in quantum gravity. (And all of it is almost certainly wrong in any case, even if it works in theory.) -- BenRG (talk) 20:38, 13 April 2011 (UTC)

Finally I love supernovae for their brightness in exploding (as many people suppose they are new ) and their rule in sending our body and our earth elements here and their heart (neutron star )which have palpitation such as our heart does

akbarmohammadzade--78.38.28.3 (talk) 04:16, 14 April 2011 (UTC)

BenRG - thank you for your response. At the risk of sounding nasty, I'm getting kind of tired of hearing it repeated ad nauseum on RD/S that "time doesn't exist outside of the big bang" (I've run into this paradigm problem when asking questions here before). It's just wrong - from the perspective inside of the big bang, time outside would not exist if I'm not mistaken (hence the white hole). But there is no reason that anything outside of it couldn't exist. Now the only question is: how would a white hole that massive appear to the outside? And what would the time scales look like? Is it even possible it might appear like a black hole? Magog the Ogre (talk) 01:53, 17 April 2011 (UTC)

you need as i imagin to divide what is happening in our condition of life and way of our sensing the time and relativistic time, and the way which do our mind think , then comparing those to find better way of imaginary,and intering to place there is no time. the subject and question brout below I think be useful for you .

. akbarmohammadzade--78.38.28.3 (talk) 03:32, 17 April 2011 (UTC)

how dos god see us ?

Imagine the piston of your car , you do start your car and run , after one hour you may go 70 KM your car weels did rotate 70000 times and motor piston moved 180000times , for you time spends slowly and for apoint on car weel middle and for a point on piston very fast. our brain thinks abslotly free from time , so the future and passed time and recent is equal for it ,we are seeing big bang and its events with ability of our strong brain and its modeling , and out standing not to be nessesery. we round earth axis one time per day , our year is 365 days , but one day for sun is 27days and one year for sun is 225 million years . there is in holy kuran that one day in after death time equals our 50000years , and the earth had created in 6 days ,of course those are not equal our recent days . we dont know troughly god's mind .and his way of creation , some things will appear to us after death . that was examined for miones reached to sea side and observed on top of hill , the time spending is very slovly for mion and its half life .(for its speed %99.9C)

akbarmohammadzade--78.38.28.3 (talk) 03:32, 17 April 2011 (UTC)

Bear pit

The article says that a bear pit trap can deter bears from approaching a cabin. How could that be? If bears are smart enough to avoid falling in it, wouldnt they be smart enough to simply walk around it? Thanks 92.15.19.232 (talk) 13:11, 13 April 2011 (UTC)

Perhaps bears are just smart enough to keep away from anything that looks dangerous or smells human, but not up to complex route planning. Here is the editthat added the information to the article Bear pit. You might leave a message to the editor on their Talk page or raise the question at the article talk page. Cuddlyable3 (talk) 13:37, 13 April 2011 (UTC)

It's unreferenced and sounds pretty questionable to me. I'd just remove it and maybe leave a note about it on the talk page. --Sean 19:32, 13 April 2011 (UTC)

What about the girzzly bear that watched its mother and probably other older siblings get killed by a hunters and then continued to watch as the hunters gathered arount the mother to take pictures with it. The juvenile bear must have watched for a while as the hunters "hugged" and "played" with the mother. Later the same hunters were back and had the juvenile in their sights when the bear rolled over on its back and played dead showing submissive behavior while slowly coming closer to the hunters. it let them pet it and touch it as if saying here do what you want but don't kill me. it was on TV and it changed the hunter's life forever. —Preceding unsigned comment added by 98.221.254.154 (talk) 02:07, 14 April 2011 (UTC)

Maybe they are so "smart" that they know if they see 1 pit in the area there is likely to be others that they might not see.98.221.254.154 (talk) 02:50, 14 April 2011 (UTC)

That's what I think was implied, but that seems a bit beyond bear intelligence, to me. StuRat (talk) 06:23, 14 April 2011 (UTC)

Not really, did you read the question? He's asking why they DIDN'T walk around the one they saw. Does the juvenile bear's behavior in my previous example also seem beyond bear intelligence to you? —Preceding unsigned comment added by 165.212.189.187 (talk) 13:42, 14 April 2011 (UTC)

I was under the impression that bears were a fairly intelligent group of animals. Googlemeister (talk) 15:29, 14 April 2011 (UTC)

Fairly intelligent yes, probably on the order of dogs. But seeing one trap and then extrapolating that there may be others requires that it think about what you are thinking ("He's trying to trap me !"), getting into game theory. This is likely beyond all but the most intelligent animals. Although I suppose there might be a way to figure it out using less intelligence. If I found something bizarre in the woods, I might look for it again in the same spot, even if I had no idea who or what caused it to appear there and what their motivation, if any, might be. Perhaps a bear can work on this level. StuRat (talk) 18:14, 15 April 2011 (UTC)

Well, I may not be any smarter than the average bear, but I'm fairly certain the implication in that article is that the pit has to go 360 around your cabin. ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:41, 17 April 2011 (UTC)

Would that be called a pit ? That's more of a trench, or, if filled with water, a moat. StuRat (talk) 21:04, 17 April 2011 (UTC)

The key question is: Never mind the bear walking around the pit... how can you ensure that he will take a path that will even lead to the pit in the first place? ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:06, 17 April 2011 (UTC)

Mass-energy conversion of the human body

One of the sources I've read claims that the conversion of the human body mass to energy would produce a 200-300 TNT megaton explosion, Another source, however, states that because the basic human body components - carbon, hydrogen, oxygen and nitrogen - have low molecular weight and a lower proportion of internal energy, the released energy would be far less than that from the nuclear weapons. Which is right?--89.76.224.253 (talk) 16:17, 13 April 2011 (UTC)

My suspicion is the difference is in how you are proposing to convert the mass to energy. If you're talking about throwing a human into a human-sized chunk of anti-matter (a more or less pure conversion of mass into energy), then you'd get something like a massive nuclear explosion. If you're talking about any other, more conventional method (e.g. burning alive), you're getting considerably less than that. --Mr.98 (talk) 16:20, 13 April 2011 (UTC)

Going by the mass–energy equivalence, the human body would be around 4.5 to 11 EJ (ballpark estimate for adults - ~50 to ~120 kg). That is, very roughly, between 1000 and 2600 megatons of TNT. By comparison, the biggest bomb ever created by humans was around 50 megatons of TNT. --Link ^(t•c•m) 17:10, 13 April 2011 (UTC)

Evaporated Water Consumption

If one consumes water with absolutely no salts, what are the major disorders one might run into? Most of the disorders found in wiki and google search are caused by a single salt/mineral deficiency. Also what specifically does the body go through when there are no salts present in the water consumed? Does this affect kidneys? Is it true that salt deficiency causes body to borrow salts from bones resulting in calcial erosion of bones in process? —  Hamza  ^{[ talk ]} 17:29, 13 April 2011 (UTC)

Does this help? --TammyMoet (talk) 18:12, 13 April 2011 (UTC)

Actually, I think Water intoxication is more relevent; water intoxication is caused when consumed water causes the electrolytes (salts) in the bodies fluids to become diluted to a dangerous point. --Jayron32 18:53, 13 April 2011 (UTC)

Water intoxication can (and in practice usually does, as it's what people usually drink) involve regular tap water and mineral-containing spring water; it's not confined to demineralized or distilled water, and indeed the trace minerals present in most water don't make an appreciable difference to body or blood electrolyte levels. TenOfAllTrades(talk) 19:39, 13 April 2011 (UTC)

Note that you can get the salts you need from food, they needn't be in the water. StuRat (talk) 02:05, 14 April 2011 (UTC)

How did the hills of Rwanda form, and how old are the soils?

Rwanda is the "land of a thousand hills", but I can't work out how they were formed. In the UK, AFAIK, most hills were formed by the last glaciation - how do hills form on the equator? On a related note, can anyone find out roughly how old the soils in the south of Rwanda are (we'll be talking millions of years)? _{(google is not being my friend today)} SmartSE (talk) 18:35, 13 April 2011 (UTC)

Rwanda lies in the western branch, pretty much right under those two red triangles

Rwanda lies on the western fork of the Great Rift Valley, see the map to the right. The hills in Rwanda are thus caused by Plate Tectonics, i.e. in this case the area is literally being torn into two pieces as the Somali Plate seperates from the African Plate. Along plate boundaries, you get a lot of geologic activity, from volcanism to subduction to folding, and I suspect that, given where Rwanda is, despite being such a small country, you can find ample evidence of all of this. In geology, all of these process are called Orogeny, which roughly means "mountain birth". Sadly, I cannot find any articles on the Geology of Africa or of the Rwanda region. The template below, filled with redlinks, shows that this is likely a MUCH needed area of Wikipedia. Alas, I hear there is a new Pokeman coming out soon, so I think this is going to be pushed to the back burner for a bit longer while more important work gets done.--Jayron32 18:48, 13 April 2011 (UTC)

The geology of Rwanda is pretty complicated so it probably depends on which hills you are talking about. Generally speaking though, in the tropics like elsewhere, landforms like hills are formed by climate+the nature of the rocks+the biological activity...only much faster. Rock can be turned into soils through chemical weathering and high rainfall, transported away somewhere else either by water or landslides/soil creep/slow flow processes etc pretty quickly in the tropics. Well, that and whatever else is going on geologically that could effect the landscape like rifting, volcanic activity etc etc. Sean.hoyland - talk 19:12, 13 April 2011 (UTC)

I was going to go start linking the geography articles of those respective countries, then I realized... Not the same thing at all. Falconus^{p t c} 22:41, 13 April 2011 (UTC)

Follow-up on cleaning apple juice bottles for recycling

Referring to this question, I am happy to say I finally threw out the first of about half a dozen apple juice bottles.

Using hot water and dishwashing liquid, but mostly repeating the process of filing the bottle with water and adding dishwashing liquid and shaking it up every now and then when I prepared my bottles for recycling, I finally looked at one bottle and realized it was clean enough to go.

The others still look a mess. I suppose I could take them, but someone would have a lot of work to do and they might just reject them at whatever facility processes them.

Yes, it has been over a year. I had no idea.Vchimpanzee · talk · contributions · 18:40, 13 April 2011 (UTC)

At least you didn't send them to the recycling center Bluefist ^talk 13:26, 14 April 2011 (UTC)

It seems that you may have the wrong idea about what recycling is. It's true that if you wash out a bottle and put something else in it you can say that you recycled it, but that is not how a recycling facility does it. At a commercial recycling facility the sorted plastics are melted down and reformed into other products. Any contaminants (such as apple juice and other stuff) are iliminated by processing and melting. Therefor a simple rinse out one time with water will aid the processing slightly. It is not neccessary to make them clean enough to put food into.190.56.16.167 (talk) 20:18, 13 April 2011 (UTC)

Another thought. If your bottles are made of glass the same thing applies. The glass will be smashed up and melted down to make other bottles or maybe a window. You dont need to make them clean enough for food. Germs will not survive the melting process.190.149.154.28 (talk) 21:00, 13 April 2011 (UTC)

Where I live the recyclers say to just recycle the item without any cleaning at all, just leave remaining food or juice on it. I suspect it will get washed later anyway. Graeme Bartlett (talk) 21:39, 13 April 2011 (UTC)

My understand was the washing of recycling was more to prevent Rats or Cats or whatever other street creature from making a mess of your recycling box to get at that last bit of baked beans your tin didn't get clean (similarly to reduce smell given that my recycling is only collected once a fortnight). ny156uk (talk) 22:06, 13 April 2011 (UTC)

What is your goal? to help the environment? if so then you might want to consider all the electricity for the hot water, the good, clean potable water that you wasted cleaning the bottles, the soap you wasted and added to the once good water that now has to be removed by some water treatment facility. all because you wanted to clean some organic biodegradable material off the glass bottles? think a little farther than your nose. —Preceding unsigned comment added by 98.221.254.154 (talk) 02:17, 14 April 2011 (UTC)

I don't know what my goal is. I just didn't want to put those filthy bottles in with the regular recyclables. Ordianrily, the stuff left in the bottles will get washed out easily and the bottles will be clean. These were bottles I waited too long to wash out and they're disgusting. Maybe they would accept them. I do know if I'm not careful to clean some of the items, the perfectly good recyclables in the bin could get messed up. By the way, I didn't waste soap. I waited until the bottle of dishwashing liquid was nearly empty. I probably did waste water.Vchimpanzee · talk · contributions · 19:32, 14 April 2011 (UTC)

I'm surprised you responded to the IP's "think a little farther than your nose" comment. I'm sure the environmental impact of the equipment and infrastructure he used to post that comment far exceeded your bit of water and soap. Sean.hoyland - talk 19:58, 14 April 2011 (UTC)

That's stupid. Nobody bought a computer just to reply to this post.

The goal here presumably isn't to put the bottles in the recycling bin. The goal is to make a positive impact by doing so as opposed to throwing it in the trash. (By saving glass.)

98.221 made a perfectly valid point that water and energy have been wasted in the attempt to save a little glass. APL (talk) 15:07, 15 April 2011 (UTC)

I could be wrong, but it seems unlikely your recyclables are kept separate when they leave your bin. In other words, it doesn't really matter how clean your recyclables are, they're going to get 'messed up' by other people's recyclables... Nil Einne (talk) 20:40, 14 April 2011 (UTC)

I'm surprised they don't make an effort. We have a giant container we throw all the recyclables in. At one time the different types were separated. I don't have a bin of my own because recycling is a recent introduction in my community. I still take everything 'to the dump" as I always did. If I asked for a bin like my neighbors have, I'd have to remember to put it out every Monday. Chances are I wouldn't.Vchimpanzee · talk · contributions · 22:50, 14 April 2011 (UTC)

For those who may wonder, my father took the trash on Saturday, and at some point I started going with him but it was always after lucnh. I'm still in the habit of going at that time or, if the college library near my house is closed, later in the day. The recyclables go in what look like milk crates. I'm not sure how we started doing that. Once the town got trash pickup, I chose to keep doing what I always did, even after they added recycling pickup.Vchimpanzee · talk · contributions · 21:13, 15 April 2011 (UTC)

Do we feel heat from the sun because of Infra Red, or because of the energy in the entire spectrum?

Whenever people talk about being warmed by infra red radiation from the sun, I always grumble and say that the entire spectrum of light contains energy, and that infra red just happens to be the frequency that warm bodies on earth emit, and so we think of that as heat.

However, I recently read in [3] that "Far infrared waves are thermal. In other words, we experience this type of infrared radiation every day in the form of heat." So this NASA site seems to be saying that there really is a difference between IR light and other light when we are feeling heat from the light source. Is that right? Have I been confused all along? Can we not get warm from just the visible/UV spectrum of the sun (if there is enough of it)?

Thanks! — Sam 71.184.188.110 (talk) 22:30, 13 April 2011 (UTC)

You are not wrong. The sentence you quoted is about perception, we experience some frequencies as vision, and others as heat. But both can cause warming. However there is a somewhat more light energy available as infrared than as visible light (from the sun), so most warming is from the infrared. Ariel. (talk) 22:41, 13 April 2011 (UTC)

But you can have very bright, but "cold" light right? Vespine (talk) 22:44, 13 April 2011 (UTC)

I think the reflectance characteristic of each frequency is very relevant. See Spectral reflectance curve. The frequencies we associate with visible light are readily reflected from opaque surfaces and that is one of the reasons we can see things with the naked eye, but little of the energy with those frequencies is transmitted into the opaque surface to raise its temperature. The frequencies we associate with the infra-red band are not so readily reflected from opaque surfaces so most of the energy in the IR band is transmitted into the opaque surface and so raises its temperature. Also see Infrared#Heat and Thermal radiation. Dolphin (t) 22:55, 13 April 2011 (UTC)

The so called "cold" light is a light bulb that produces little Infrared while producing visible light. Of course, visible light is also a form of heat so "cold" light does produce heat. Dauto (talk) 23:58, 13 April 2011 (UTC)

"But you can have very bright, but "cold" light right?" Not if the source is blackbody radiation. The spectrum emitted because of thermal energy is a well-defined function, and the intensity is rigidly bound to the frequency-distribution. Both of those parameters are determined by the source object's temperature.

A non-thermal source of radiation can provide any spectral distribution; it can radiate at specific frequencies (observable as individual spectral emission lines), or can radiate over a wide range of frequencies, with continuously varying intensities.

But again, if the source is due to thermal emission, then the total amount of energy radiated is defined by the temperature of the source (which also defines the spectral distribution that gets radiated). The mathematical formula that defines this relationship is Wien's displacement law. Loosely speaking, it's not possible to have very bright radiation from a very cold source: decreasing the temperature decreases the total amount of radiated power and changes the shape of the spectrum. Nimur (talk) 00:17, 14 April 2011 (UTC)

Just as an aside - "cold" lightbulbs, such as a cold cathode fluorescent lamp, are not thermal radiators: they fluoresce (producing photon-emission via a totally different physical process), and thus are not a blackbody radiator. This is very different than an incandescent lightbulb. Nimur (talk) 00:20, 14 April 2011 (UTC)

Not if the source is blackbody radiation But we're not talking about "the source", we're talking about the "light" it self. if you have some IR and heat shielding that transmits only visible light, then that light can be bright and "cold" right? As in if you shine it on a thermometer it won't heat it up? Vespine (talk) 02:00, 14 April 2011 (UTC)

The only thing that matters is the total irradiance, and how well light of that wavelength is absorbed. If a surface has equal absorptivity for visible light and infrared, then a 1 W beam of infrared will heat it up exactly the same as a 1 W beam of visible light. Talking about light being "cold" is meaningless.--Srleffler (talk) 02:38, 14 April 2011 (UTC)

Correct. The mathematical model of color temperature is an attempt to fit a black-body curve to a light-source. But if the light source isn't black-body-like, then its effective temperature has very little physical meaning. Nimur (talk) 02:49, 14 April 2011 (UTC)

Heat is the sum of all of the kinetic forms of energy experienced by a molecule, these are usually classified into 3 types of motion: translation (that is, moving in a straight line), rotation (spinning around an axis) and vibration (deformations of the molecule along bonds). Photons in the IR range cause molecules to vibrate, basically by exciting the electrons that occupy the molecular orbitals that hold the molecule together. The article and section Infrared_spectroscopy#Theory and stuff in that area describes how IR photons do that, and the various ways that a molecule can vibrate. Here's the important connections to make, for the layperson: Vibration of molecules is heat. Its not that we "perceive" it as heat, it not that we "sense" it as "warmth" or anything like that: vibration is heat. Since IR photons cause electrons to become excited in such a way as to cause molecules to vibrate, quite literally IR light causes heat. In a very direct sense, by the most basic definition of what heat is. --Jayron32 02:23, 14 April 2011 (UTC)

But visible light and UV cause heat too. Anytime electromagnetic radiation is absorbed in a material, the result is heat.--Srleffler (talk) 02:38, 14 April 2011 (UTC)

Not necessarily. Absorbed light will always cause electronic transition from one quantum state to another. However, this transition does not necessarily cause the substance to gain thermal energy. Thermal energy (heat) is only that energy that involved increases in kinetic energy of the molecules themselves; an electron moving to a higher energy quantum state does not necessarily cause the molecules of the substance to move faster; it MAY cause that to happen, but only in situations where there is significant coupling between, say, electronic states and vibrational states (vibronic coupling). Absorbed light may cause other things to happen as well, such as chemical reactions (Homolysis being a major one), fluorescence, phosphorescence, or simply immediate re-emission of the same wavelength photon. --Jayron32 04:07, 14 April 2011 (UTC)

Jayron, you're making the very common mistake of confusing the word heat (which is energy transferred to a substance by a variety of methods including radiation - IR, UV, visible, etc, all included) with the internal kinetic energy. Besides, most of the visible light that is not reflected and does get absorbed eventually does find its way into the vibrational modes of the molecules. Dauto (talk) 14:52, 14 April 2011 (UTC)

Procession of the Perihelion

Prior to the acceptance of GR what other attempts had been made to explain the peculiar mercurial motion. So far I have:

1. Planet Vulcan
2. Gravity as an $r^{2.00000016}$ instead of $r^{2}$ law

Please add to the list if you know of any! Thanks. —Preceding unsigned comment added by 92.20.205.185 (talk) 22:46, 13 April 2011 (UTC)

For one thing, gravity is a $r^{-2}$ law, not a $r^{2}$ law. (Sorry for the nitpicking). Dauto (talk) 00:07, 14 April 2011 (UTC)

Why not at all, Newton claimed the source mass required to produce a unit force on a test particle at a distance $r$ scaled as $r^{2}$. —Preceding unsigned comment added by 92.20.205.185 (talk) 00:46, 14 April 2011 (UTC)

April 14

Pseudoscience: suspended water

I know this seems ridiculous, but there is no harm in asking. This video on youtube (of course) has a person do a magic trick where he removes a cup leaving water in suspended animation. I highly doubt this as possible and is probably just a joke, but how did he fake it in the first place? Even faking this stunt seems inconceivable. Bugboy52.4 ¦ =-= 03:28, 14 April 2011 (UTC)

Looks like CGI to me. The "suspended" water seems to be obviously added in post production; it becomes even clearer when frame through the video. There are certain frames where it seems rather obvious that the water isn't "sitting" on the desk. This sort of thing is relatively easy to fake with pure CGI alone. Modern computer animation is fully capable of placing an animated object in a virtual 3D space and tracking camera movements such that you can view the object from all angles. I see no reason why a sufficiently talented animator couldn't have done this. --Jayron32 04:38, 14 April 2011 (UTC)

I found something for you: [4]. It seems you can find glitches in his animation; where for a few frames, the "suspended" water jumps illogically; in the middle of a normal pan, for a few frames, the water moves the wrong way before resuming normal motion. Its plainly an effect added after the fact. --Jayron32 04:45, 14 April 2011 (UTC)

I spotted another glitch myself. If you watch the inverted image of the countertop behind the "suspended water", around the 1:45 mark, the image illogically jumps from one place in the "suspended water" to another, without a smooth transition. There's no reason it should do that. If you play the 2-3 seconds before it, and the 2-3 seconds after it, you can see what I mean. Just rock back and forth over that, and you see where there's an obvious glitch in his animation. --Jayron32 04:49, 14 April 2011 (UTC)

Ha, very good! I wonder how many people will "try it". lol.Vespine (talk) 05:43, 14 April 2011 (UTC)

If I were going to fake this, I'd use clear gelatin or a carefully frozen cup of ice to get the basic form and then animate in effects to make it look more like free-standing water. a good afternoon's work, but easy enough or a bored high-school kid with time on his hands. no complex cgi involved. --Ludwigs2 06:10, 14 April 2011 (UTC)

Probably a parody of this comic strip by B. Kliban that has been making the rounds on the internet recently. Flicker Link.

I'd like to see someone try that second one. APL (talk) 13:27, 14 April 2011 (UTC)

I don't know, I'm not convinced about this. The image through the water seems amazingly believable, and above all... where does the water come from when he breaks the water cone? I'm leaning toward believing that there is some kind of physical transparent membrane involved. I see the slight dimming at 1:45, but that might plausibly be the effect of reflection hitting the videocamera's light meter. The shift to include more at the top of the image in the water cone matches a slight lowering of the camera. If it's a CGI fake it's pretty impressive! And the cartoon seems more a parody of this than the other way around. Wnt (talk) 05:03, 15 April 2011 (UTC)

Spilling water across a surface isn't a difficult thing to animate... --Jayron32 05:19, 15 April 2011 (UTC)

1) Prank "Science" videos are very common on YouTube. They're practically a genre in and of themselves.

2) The match-moving techniques needed for this sort of thing were impressive and Hollywood-only a few years ago, but commonplace now.

3) The guy who posted this is a computer animator!!! Look at his other videos!

Also, the cartoonist I just linked died twenty years ago, he's not drawing parodies of youtube videos. APL (talk) 14:56, 15 April 2011 (UTC)

This reminds me of similar physics experiment [5] in which you turn a glass of water upside down, but the water stays in. If it is real perhaps it can be done by similar mechanism ? ~~Xil (talk) 18:04, 17 April 2011 (UTC)

FIBONCCI NUMBER

what cause the nature to obey fibonacci number? --78.38.28.3 (talk) 05:38, 14 April 2011 (UTC) —Preceding unsigned comment added by 78.38.28.3 (talk) 05:37, 14 April 2011 (UTC)

The fibonacci series is a type of power series; in that way it nicely models growth patterns. In other words, things tend to grow from themselves; one cell produces additional cells, which produce additional cells themselves, and so on. One way to model this is through exponential growth, but that only works where the growth occurs via individuals (i.e. one free bacterium divides into two, each of those divide into two, etc. etc.) When you have a situation where you have growth which is restricted by the new copies, for example the way a Chambered Nautilus shell grows is that each successive growth can only occur at the opening of the shell. The shell cannot grow in all directions, only in a highly constricted direction. This growth will not occur exponentially, since parts of the shell which have already produced new shell are now "surrounded" by that shell, and don't have any room to produce any more shell around them. It will only occur at the leading edge of the shell, and this is better modeled by an additive power series rather than a multiplicative one. Hence, the connection to the fibonacci series, the best known example of an additive power series. --Jayron32 05:57, 14 April 2011 (UTC)

Point of clarification for the purposes of general education. Nature does not obey mathematical formulae. Mathematical formulae are human inventions that describe different aspects of nature, often without any real understanding of why nature might behave in that fashion. Never forget the basic paradigm of modern science: if your formulae say one thing and nature does something else, it's not nature that's made a mistake. --Ludwigs2 06:19, 14 April 2011 (UTC)

True, that's why I stated that nature is modeled by the fibonacci series and exponential growth. Those are human-created explanations for nature. I recall what a chemistry professor of mine once said... "Molecules do what molecules do, and if they don't obey the rules that we give them, that's our problem and not theirs." The same is true for all of science. --Jayron32 17:28, 14 April 2011 (UTC)

On the other hand, Julia Robinson looked at it the other way around, that the mathematics of numbers is "the one real thing". Sean.hoyland - talk 18:25, 14 April 2011 (UTC)

The continued fraction expansion of the fibonacci number tells us that it is the number that is least good approximated by rational numbers. Depending on the physical context, this helps to avoid resonances. 95.112.246.93 (talk) 09:31, 14 April 2011 (UTC)

See http://www.evolutionoftruth.com/adm/contents.htm. -- Wavelength (talk) 23:17, 14 April 2011 (UTC)

I'm not sure spamming links to pseudoscience sites is appropriate here. Look, I am a professing evangelical Christian, and Jesus Christ is my lord and savior, and that website is still unmitigated bullshit. --Jayron32 05:18, 15 April 2011 (UTC)

Ian Stewart discusses the reasons for the appearance of fibonacci numbers in nature in chapter 1 of his book The Magical Maze. It's as 95.112.246.93 says: by rotating each floret by the golden angle, the plant can pack them in maximally. --ColinFine (talk) 21:32, 17 April 2011 (UTC)

Cardiomyopathy

What is the meaning of the term "constrictive cardiomyopathy"? aniketnik 08:21, 14 April 2011 (UTC) — Preceding unsigned comment added by Aniketnik (talk • contribs)

A number of useful definitions turn up when you google your term. Eg. [6]. Aaadddaaammm (talk) 09:02, 14 April 2011 (UTC)

Pycnodeuterium

How credible is the existence of Pycnodeuterium ? My google hits all relate it to cold fusion which raise some extra doubts about it. 95.112.246.93 (talk) 09:39, 14 April 2011 (UTC)

Palladium is well known to absorb large amounts of hydrogen (of which deuterium is an isotope) into its crystal lattice: see Palladium hydride. I'm not sure what the particular qualities are attributed to "Pycnodeuterium" are: is it just deuterium adsorbed into the palladium crystal structure? Because that absolutely does happen, even if it doesn't allow cold fusion. Buddy431 (talk) 23:29, 14 April 2011 (UTC)

The article tells of "ultrahigh density deuterium lump" and does not mention simple hydrogen. As D is a boson whereas H is not, Bose–Einstein condensate comes to mind. Regrettably, the article does not even specify how "ultrahigh" the density really is. 95.112.143.65 (talk) 08:46, 15 April 2011 (UTC)

Here's the journal article that it came from: [7], and the pdf of the full article where it is specifically mentioned that both regular hydrogen and deuterium are absorbed similarly. The fusion they're talking about is real , hot fusion that occurs in stars (where pressure forces the deuterium to form a metallic solid). The authors were exploring the possibility of reproducing this hot fusion that occurs in stars by forcing deuterium into a palladium crystal, essentially forcing the hydrogen (deuterium) into an orderly metallic solid state, due to the nature of the palladium crystal. The ideas and terms from the paper might have been misappropriated by cold fusion advocates, but it looks like the research is relatively sound, if not nearly as exciting as some would like us to believe. Buddy431 (talk) 16:53, 15 April 2011 (UTC)

physical education

what are the effects of physical activities in human body? —Preceding unsigned comment added by 41.59.1.50 (talk) 10:28, 14 April 2011 (UTC)

As from my experience, mostly Abrasions and Hematoma, but probably this is not what you are asking for. 95.112.246.93 (talk) 12:02, 14 April 2011 (UTC)

See physical exercise. --Tango (talk) 12:56, 14 April 2011 (UTC)

Hmm, "Physical exercise is any bodily activity that enhances or maintains physical fitness and overall health and wellness." (from physical exercise). If so, then it is well different from what our (or at least, my) teachers forced us to do at school. At times I was so depleted I had to vomit. I remember a class mate left with a broken nose. But as the OP's question is probably homework, this is no thing to say to the teacher who is in power to have get your nose broken and get away with it. 95.112.246.93 (talk) 17:24, 14 April 2011 (UTC)

Differences between conservative and liberal brain

Please help to expand this article. — Preceding unsigned comment added by Brain Researcher (talk • contribs)

No, see wp:MEDRS in relation to single sourced studies and media reports. There's no literature review available on the field, the article ought to be deleted until multiple studies are available. Remember cold fusion? Fifelfoo (talk) 11:34, 14 April 2011 (UTC)

(after EC) The reference desk is a good place to ask questions or request information. If you have questions about the article in question, feel free to post them. However, as it appears that you created the article in question and are now trying to recruit assistance in its development so that it doesn't get deleted, my questions are "why should we expand the article, and with what?" These types of juicy, controversial findings are quick to grab the attention of news agencies (ABC, NY Daily News, Fox as cited in the article) or blogs, but I happen to agree that the subject is not worthy of its own encyclopedic article and should be merged into another existing article or dispensed with entirely until the results have been replicated and better understood. --- Medical geneticist (talk) 11:37, 14 April 2011 (UTC)

Well, afd will be the right place for this discussion. BTW, I was not aware of wp:MEDRS when I created this article. I think since the study is covered by major news organizations, it meets WP:N. So the article can be renamed like Kanai's study of political orientation and brain structure?? --Brain Researcher (talk) 11:43, 14 April 2011 (UTC)

See [8][9][10][11]--Brain Researcher (talk) 11:46, 14 April 2011 (UTC)

This appears to be based on a single small study - hence is likely not-notable ubnder WP guidelines at all. Collect (talk) 11:49, 14 April 2011 (UTC)

Comment: There are previous studies on this topic [12] So we have resolved the single study issue. --Brain Researcher (talk) 11:50, 14 April 2011 (UTC)

And the smallness of the study? Seems conclusively not-notable. Collect (talk) 11:51, 14 April 2011 (UTC)

Please see these links: 1. study published in Nature Neuroscience by New York University and UCLA scientists in 2007 [13], 2. online survey by psychologists in 2009 [14], 3. study in New Scientist in 2008 [15] So we now have multiple studies. And it is not "the study", it "the studies". --Brain Researcher (talk) 11:57, 14 April 2011 (UTC)

AFD commenced. Fifelfoo (talk) 12:00, 14 April 2011 (UTC)

Perhaps this information would be best summarized as a subheading under political psychology (which itself is a pretty mangy article in much need of help). That being said, the main caveats to these studies will remain a small sample size, lack of independent confirmation, and very little insight into causation. --- Medical geneticist (talk) 15:04, 14 April 2011 (UTC)

The people who want this deleted will oppose it no matter what. Debating their issues is pretty much a waste of your time. Something I tried to include earlier, only to run into multiple instant reverters for the faith wherever I put it:^[16]

According to the ASA, IQ data from the "Add Health" survey averaged 106 for adolescents identifying as "very liberal", versus 95 for those calling themselves "very conservative". An unrelated study in 2009 found that among students applying to U.S. universities, conservatism correlated negatively with SAT, Vocabulary, and Analogy test scores. According to a 2004 study by the Pew Research Center, liberals were the most educated ideological demographic and were tied with the conservative sub-group, the "Enterprisers", for the most affluent group. Of those who identified as liberal, 49% were college graduates and 41% had household incomes exceeding $75,000, compared to 27% and 28% as the national average, respectively.

Wnt (talk) 20:31, 14 April 2011 (UTC)

xrays and vitamins

what effect if any would airplane xrays (the ones for checked baggage) have on vitamin supplements and their efficacy? 70.31.58.245 (talk) 11:51, 14 April 2011 (UTC)

The short answer is 'none'. This discussion starts off with a good list of links to sources, though most refer to the smaller, lower-power scanners used for carry-on bags. This post is from a health physicist who measured the dose absorbed by checked luggage on a number of occasions, measuring doses ranging from 35-211 millirem; that's equivalent to between about one and six months' exposure to natural background radiation. TenOfAllTrades(talk) 13:36, 14 April 2011 (UTC)

thank you, that was an awesome answer. much appreciate your time. 70.31.58.245 (talk) 23:09, 14 April 2011 (UTC)

Are there any trends in the half-lifes of isotopes?

If there is, how accurate can we predict an isotope's half-life that is undiscovered?--Inspector (talk) 15:05, 14 April 2011 (UTC)

The island of stability discusses this a bit — theoretical trends make it seem like there might be superheavy elements with relatively long half lives. However it is unclear if this will be true in practice — when you start loading up nuclei to levels that we've never seen before, it's possible that other sorts of effects start to kick in (e.g. deformation of the nucleus, or quantum tunneling) which would affect their stability. My qualitative take away from the article, reading between the lines, is that there are trends, there are theoretical models, but the confidence in these theories being accurate is heavily qualified. Perhaps someone else can give a more informed answer... --Mr.98 (talk) 15:19, 14 April 2011 (UTC)

There are some very general trends. A greater difference in number of neutrons from the that of stable isotopes correlates with shorter half-life. One can see these general trends in graphs such as the one at right. For example, the half-life of undiscovered ¹¹He is likely to be shorter than the 2.7×10⁻²¹ half-life of ¹⁰He (but there is no guarantee). 148.177.1.210 (talk) 15:32, 14 April 2011 (UTC)

But how accurate can we make predictions? I doubt the validity of some isotopes listed in the isotope articles, after I checked out the references below, because it did not cite any other sources. It's like anyone can make a number as long as it looks reasonable. Are there any academic sources discuss about the formula and accuracy of the predictions?--Inspector (talk) 13:26, 15 April 2011 (UTC)

The figure at right links you to its source from its description if you click on it. For another interesting table see File:Table isotopes en.svg. Note especially the cute way that the "magic numbers", including especially 82 and 126 but also 50, sort of "pull in" the alpha decay to a point 2 above them (where emitting an alpha leaves a magic number). I see this huge block of alphas poking over onto the "wrong side" of the graph and feel as if somehow it explains the big gap between the spherical and deformed nuclei, but I don't really know enough about it. Wnt (talk) 02:11, 17 April 2011 (UTC)

But again it did not cite any reference but just saying like "In case no experimental

data is available, trends in the systematics of neighboring nuclides have been used, whenever possible, to derive estimated values"[17]. I am still curious about how they calculate and make the prediction.--Inspector (talk) 11:00, 17 April 2011 (UTC)

shivers down my spine -- are they endorphins?

Sometimes if I'm listening to a piece of good music (or something particularly touching) or make some sort of epiphany, I can feel a wave of relaxation, etc. wash over me. Are they endorphins being released? I'm not sure if it's purely nervous, because the effect lingers well after the initial stimulus. John Riemann Soong (talk) 16:17, 14 April 2011 (UTC)

I don't know, but I think the phenomenon you describe falls under the umbrella of ASMR, "Autonomous Sensory Meridian Response". This term may help you find related information, though it doesn't seem to have much serious scientific study devoted to it. You may be interested in this recent thread on metafilter [18], which gives several audio and video examples that trigger this response. SemanticMantis (talk) 16:51, 14 April 2011 (UTC)

The term "Autonomous Sensory Meridian Response" seems to be purely an internet phenomenon -- it gets zero hits on Google Scholar or Google Books. Shivers down the spine are also known as "chills" or a frisson (French for shiver), but regardless of what they are called, not a great deal is known about their physiology. They are clearly related to "piloerection", i. e. the hair on the back of the neck standing up, and it has been suggested that the response depends on opiates, but that doesn't seem to be proven. This freely available paper summarizes what is known about them, and this paper describes their brain activity correlates and discusses the evidence regarding what causes them. Looie496 (talk) 22:03, 14 April 2011 (UTC)

Looie, for "not a great deal known" that paper you posted certainly has a lot of info. When I was in school studying this stuff, I recall it being considered part of the fight or flight response. Your info is better.OrangeMarlin ^{Talk• Contributions} 22:08, 14 April 2011 (UTC)

Shaking all over deliberately and involuntarily. (videos) Cuddlyable3 (talk) 12:46, 15 April 2011 (UTC)

Breaking neck

Why breacking neck is fatal while breacking other body parts is not?--89.76.224.253 (talk) 17:11, 14 April 2011 (UTC)

Because the neck contains the spinal cord which carries signals from your brain to other parts of your body. If you sever the spinal cord in the wrong place, your brain can no longer send signals to, say, the muscles that make you breathe. That would be contraindicated in for those seeking a long life... --Jayron32 17:21, 14 April 2011 (UTC)

There are rather important things protected by the cervical vertebrae... — Scientizzle 17:22, 14 April 2011 (UTC)

First, breaking your neck is not always fatal. (See Paraplegia and Quadraplegia) Where it is fatal, it is usually because the neck is broken and the spinal cord is severed high up (C1, C2, C3). This cuts the messages from the brain to the body and essential functions, like breathing and heartbeat, are stopped. Bielle (talk) 17:25, 14 April 2011 (UTC) (Sorry to those who answered above. I didn't get an "ec", or I would not have written. Bielle (talk) 17:26, 14 April 2011 (UTC)

Mike the Headless Chicken survived for a while. Cuddlyable3 (talk) 12:28, 15 April 2011 (UTC)

Contrary to the impression one might get from the OP and answers above, it's entirely possible to break the bones of the neck without immediate injury to any critical structure, including the spinal cord. They're just bones, thus breaking can be separate from damage to nearby structures. Examples (this is only scratching the surface): extension teardrop fracture (PMID 21395397) and C3-C4 spondyloptosis without neurological deficit (PMID 20620981). -- Scray (talk) 03:14, 16 April 2011 (UTC)

Yep. In fact I know a woman who broke her neck practicing a swing-dance move. She had to wear one of those metal haloes for, I don't know how long exactly, maybe a year or so. Must have been hell. But she came out of it all right, I think. (To be precise, I don't know for sure that the bones of her neck were actually broken, but that was my impression.) --Trovatore (talk) 05:30, 16 April 2011 (UTC)

sorry for the ignorance. What does 'ec' mean.190.56.107.170 (talk) 20:15, 14 April 2011 (UTC)

It (normally) stands for edit conflict - more information on that there. Grandiose (me, talk, contribs) 20:49, 14 April 2011 (UTC)

"This cuts the messages from the brain to the body and essential functions, like breathing and heartbeat, are stopped."

— Bielle

The heart does not require nerve impulses to beat. Indeed this principle is essential for heart transplantation. Axl ¤ [Talk] 08:59, 18 April 2011 (UTC)

People also do occassionally die from broken bones, or rather health complications that broken bones can cause, such as an embolism or shock. Googlemeister (talk) 19:26, 18 April 2011 (UTC)

Why half-life is more important than total decay?

Although I may be wrong.--89.76.224.253 (talk) 17:14, 14 April 2011 (UTC)

I'm not sure I follow the question. Can you explain what you mean by "more important" and in what context you are asking? --Jayron32 17:19, 14 April 2011 (UTC)

Maybe you're wondering why we measure the time for half of a sample to decay, rather than the time for the full sample to decay (the "full-life")? This is because atoms decay exponentially, which means that the rate of decay slows down in such a way that the "full-life" would mathematically be infinite. So the only thing which can be meaningfully measured is the time until some chosen proportion decays, and 1/2 seems like a natural choice for a proportion to measure. (I'd assumed that half-life would explain this, but it doesn't seem to address the question specifically.) Staecker (talk) 18:18, 14 April 2011 (UTC)

The half-life article may be a little confusing because it seems not to contain a graph. this graph may make it easier to understand. If the half-life is one year, then it takes one year for it to decay by half, and then another year for what's left to decay by half again, and another year for what's left to decay by half again... So in two years, you will approximately a quarter of the original substance left, and in three years you will have an eighth of the original substance left. In ten years you will have 0.0009% of the substance remaining, and there may still be a tiny bit of stuff remaining after 100 years. This is why the "full" decay isn't something you can really measure. Note that this isn't some special property of radioactive decay, it's a property of statistics. If everyone flips coins and you discard all the tails, then half will be discarded after one flip, then half of what's left will be discarded after the second flip, etc... — Sam 63.138.152.135 (talk) 18:59, 14 April 2011 (UTC)

What is special about radioactive decay is that it is probabilistic, unlike e.g. Newtonian mechanics. In the coin example, it is not exactly half the coins that come up tails, that is merely the expected value. In a given toss of 100 coins, we may only see 10 tails. Half-life works well for macroscopic samples due to the law of large numbers, so the chance of seeing significant deviations from the expected 1/2 decay is vanishingly small. SemanticMantis (talk) 19:50, 14 April 2011 (UTC)

Sam, I think you meant 0.098% after ten years (rounded to 2 s.f.). After 20 years it would be 0.000095% left. The total amount of radioactivity is the only important factor to someone exposed for a short time. See our article on Ionizing radiation for details. They wouldn't care about half-life unless they ingested of absorbed some of the radioactive material. We use half-life as a measure of how long the danger from the material will last. Dbfirs 07:27, 16 April 2011 (UTC)

Ionization of d-block elements

In the d-block of the periodic table I've read that when atoms of elements in there ionize becoming cations, the electrons are pulled from the highest s-orbital with principal quantum number n where n is the row of the periodic table in which the element is found, instead of from the d-orbital which, though it has a lower principal quantum number by one, has more energy than the s-orbital. Why aren't the first electrons to go the ones with the most energy? 20.137.216.64 (talk) 18:10, 14 April 2011 (UTC)

The energies are all negative so by most you actually mean least and by more you actually mean less. Dauto (talk) 18:39, 14 April 2011 (UTC)

The reason is that the organization of the resultant ion is going to be different than the organization of the neutral atom. Don't think of it as "removing an electron", as though you come and pluck a little ball from its orbit outside of the atom, and the rest of the electrons keep going as though nothing happened. The electrons and nucleus system is always interacting, and any change at all to the system affects the whole system. Compare the following configurations:

• Fe⁰: [Ar] 3d⁶ 4s²
• Fe²⁺: [Ar] 3d⁶

At first it looks like what was done was that the 2 4s electrons were removed from the iron atom. However, it doesn't work that way. Electrons a) don't stay put and b) are indistinguishible from one another. Two electrons are removed. That is all we can say. The way that the *Fe²⁺'s configuration is derived is exactly the same way that the *Fe⁰'s configuration is derived: The configuration comes from the lowest energy solution to the Schrödinger equation for Fe²⁺. Pedagogically (that is, to teach this stuff to students) there are derived certain heuristics or mnemonics or "rules" to describe how to write the configuration correctly, i.e. the Aufbau principle, the diagonal rule, the periodic table method, etc. etc. These rules are merely descriptive of the end result of the Schrödinger equation for any particular system; they are not the real reason why the configuration is as it is. That's why there's all of the exceptions (like copper and chromium) that we have to create new, more convoluted rules. Solving the Schrodinger equation for any system has mathematics that is beyond the average first year chemistry student (indeed, at this point in my life, 15 years from when I learned this stuff, it's beyond MY ability as well), which is why all of the rules are taught to students. --Jayron32 20:48, 14 April 2011 (UTC)

Lugol's iodine

is "true" Lugol's iodine 2 % or 5 % is this it? http://www.amazon.com/J-Crows-Lugols-Iodine-Solution-2/dp/B001AEFM9Y — Preceding unsigned comment added by Wdk789 (talk • contribs) 19:56, 14 April 2011 (UTC)

You deleted my answer here: [19]. I don't know why you did that. To restate it again, you can find the answer for the composition of Lugol's Iodine at the wikipedia article titled Lugol's Iodine. It has a recipe in the article, so you can answer the question yourself. --Jayron32 02:58, 15 April 2011 (UTC)

Magnetism

What creates magnetism I always believed it was the circular movement of the electrons that gave magnetism but I am not entirely sure. Also if magnetic monopoles do exist not if they don't why cannot we detect them why don't we see evidence them in everyday life if they do exist.—Preceding unsigned comment added by 82.38.96.241 (talk) 22:20, 14 April 2011

Magnetic fields are always associated with electric current, the effect can be described in a number of different ways such as Ampère's circuital law. A loop of current will give rise to a magnetic dipole, that is, a pair of magnetic poles. The motion of an orbiting electron amounts to a current loop, and even more strongly, the spin of electrons generates a magnetic field. Materials where these spins align in the same direction are ferromagnetic.

It is not possible to create a single magnetic pole, a monopole, with current loops. However, there is nothing in the laws of physics that forbids them from existing but no one has yet discovered any. Some versions of grand unified theory (GUT) require them to exist but no GUT has yet been generally accepted - it is still possible magnetic monopoles simply do not exist, and this is the reason that they have not been discovered. SpinningSpark 22:47, 14 April 2011 (UTC)

April 15

Why is DC voltage used in public transportation

Help my boyfriend sleep better at night. He's currently tormented by the idea that today's worldwide subway, tramway, and electric train system use brutally inefficient DC Voltage rails to power motors. Since voltage must be supplied over a long distance (a whole rail, or at least have a long cable going up to the rail in question) there would be a lot of energy lost even when there is no train going on the rail (leaking capacitor).

So why does subway, maglev, tramways, and train use DC third rail exclusively? Esurnir (talk) 02:40, 15 April 2011 (UTC)

Electric motors operating on direct current (DC) are readily controlled to vary the speed. This allows the vehicle driver to choose the speed at which the vehicle is traveling. Electric motors operating on alternating current (AC) rotate at synchronous speed, or some fraction of synchronous speed, such as 3600 revolutions per minute (or 3000 or 1800 or 1500 rpm etc.) It would be feasible to have the distribution system supplying alternating current, and for each vehicle to have an AC motor coupled to a DC generator, and then have one or more DC motors driving the traction wheels, but that would double the cost, double the weight, and double the electrical losses.

Variable-speed AC motors are now available, but in the past they were not, and they are more temperamental than DC motors. Very-long-range power distribution is often done with direct current because of lower losses. Dolphin (t) 02:51, 15 April 2011 (UTC)

(ec) DC power lines are "leaky capacitors"; AC power lines are "giant antennas"; both suffer losses due to physical limitations. But, it's rarely a good idea to try to apply "first principles" physics to complicated, sophisticated engineering projects; estimating the losses requires detailed analysis of specific technologies and parameters for any particular project. While AC power has certain theoretical advantages, it also has certain practical disadvantages. In today's technology, high-voltage DC is probably more efficient than AC for long-distance power transmission, though in any particular instance, specific engineering details may sway the balance one way or the other. DC systems are usually supplied by AC from a power plant, so there is a conversion loss to worry about; but you never have to worry about phase matching, nor radiative losses. We have numerous articles on electric train topics; the most helpful will be Railway electrification system, which discusses AC and DC systems. Nimur (talk) 02:53, 15 April 2011 (UTC)

I don't get it - if HVDC is so efficient, why has everyone been drilled into thinking that long-range transmission requires AC? Wnt (talk) 05:09, 15 April 2011 (UTC)

High-voltage AC is easy to convert to low-voltage AC. It's harder with DC. --Trovatore (talk) 05:18, 15 April 2011 (UTC)

Yes, in a word transformers. These are only available for AC (except in network theory books). High voltage (sometimes as high as 400 kV) gives less loss over long distances but is unsuitably high for most power stations to generate directly (around 25kV is normal for anything with a turbine) and is way too high to be safe in a factory or a home. SpinningSpark 11:30, 15 April 2011 (UTC)

The AC vs. DC dispute is old, see War of Currents. Cuddlyable3 (talk) 12:18, 15 April 2011 (UTC)

The article link that Nimur provided in his comment provides a good discussion, but briefly, HVDC transmission makes economic sense only for long runs with few 'taps' off them. First, there is a small loss incurred each time current is converted from AC to DC or back again, so the line has to be long enough that the increased efficiency on the line more than makes up for the bigger losses in AC/DC conversions at the ends. Our article puts the break-even distance as about 50 km for undersea cables and 600-800 km for overhead cables, but it doesn't have a supporting reference. Second, each tap off the HVDC line needs to have an installed high-voltage inverter (to convert DC to AC) before the transformer, this increases the cost of each tap. TenOfAllTrades(talk) 16:33, 15 April 2011 (UTC)

Diagnosing an electrical problem

In my house all the lights on the even circuits are blinking, computers are rebooting on their own, etc., while the odd circuit numbers are fine. There are two "phases" coming into the house, one which feeds the even circuits, and one which feeds the odd circuits. So:

A) This indicates to me that the source of the problem is external to the house. Is this correct ? In this case, how can I convince the power company it's their problem ? (The power company is Detroit Edison.)

B) Is there any danger to continuing to use the even circuits until it's fixed ? (I installed an uninterruptable power supply for the computer, to stop it from rebooting when the voltage drops.) The other approach is to use extension cords from the odd circuits, but I doubt if the whole house can be run on half power like that, especially if this isn't fixed by the time we hit A/C weather (we use window air conditioner units). StuRat (talk) 03:59, 15 April 2011 (UTC)

No, the problem can be at the transformer, or it can be in the house. If you have a high-resistance arcing connection in the panel, disconnect or meter socket, you could have a fire. This should be checked out immediately. If you run any 240V equipment, it won't work efficiently, and if it's a 240V motor, like a heat pump or high-output air conditioner, you'll burn out the unit. Intermittent loss of one leg (it's technically not a phase) is often a sign of a failing circuit breaker - in this case, the main breaker. Have it checked as soon as possible by an electrician. Acroterion (talk) 04:17, 15 April 2011 (UTC)

There's no sound or smell of arcing, so it doesn't seem likely that's happening within the house. Nothing is running 240 in the house (we have gas heat, water heater, and dryer, and small window A/C units). StuRat (talk) 05:59, 15 April 2011 (UTC)

If the problem is at a transformer, neighboring homes will also be affected (unless yours is the only one on that transformer.) We had a situation years ago where some circuits were fine; others had no power. They had to replace the transformer to fix that.

I get the impression this situation has gone on for some time. If the power company won't check the situation, perhaps the only way to get their attention is to have an electrician tell them the fault is in their equipment. I'm quite sure our power company would be out quickly to check the transformer if I reported such a problem.

The above is just speculation. As Acroterion says, Have it checked as soon as possible by an electrician. Wanderer57 (talk) 05:28, 15 April 2011 (UTC)

You can have high-resistance connections and arcing without sounds or smells. My money would be on either a transformer fault or a breaker fault (I had a similar issue with a 50A 240V breaker for a range - the oven wouldn't heat all the way and half the burners didn't work - replacing the breaker fixed it), but the possibility of a faulty connection is sufficiently dangerous to warrant immediate investigation and action. An electrician can provide ammunition if it's the power company's fault; I got my power company to add a transformer for my house and my neighbors after convincing them that six houses on a transformer was too many - we had serious voltage drops every time somebody turned on a load. Get it checked out immediately: it's potentially dangerous. Acroterion (talk) 13:06, 15 April 2011 (UTC)

Thanks so far. How would an electrician determine if it's the main breaker or the transformer ? StuRat (talk) 18:06, 15 April 2011 (UTC)

Measure the voltage before the breaker with a graphing multimeter. You could probably do it yourself if you like to take risks, the wires are accessible in the box. You could probably attach a light before the breaker, and one after and watch them. It's risky though - you have no protection against shorts while working on it. Also, ask your neighbors, if it's only you it's your breaker, or meter, or wires, or junctions. Ariel. (talk) 19:33, 15 April 2011 (UTC)

What Ariel said; the main feed lugs are normally shielded, but can be accessed by a very careful person, ideally one who is used to doing this. Since it's intermittent, some time will be needed, which are further grounds for leaving to an electrician, who will have the right clamps. If there's a load on the leg and the problem is internal, there may be visible damage or heat somewhere in the panel - the main breaker may be hot.. Bear in mind that conductive tools inside a live panel can be dangerous for the uninitiated; an arc flash (vaporized copper) in your face can blind you. Acroterion (talk) 19:41, 15 April 2011 (UTC)

Damn Detroit Edison! Perhaps they should never have been granted a franchise. Better to have a DC generating plant every mile or so. Edison (talk) 03:51, 16 April 2011 (UTC)

Relativistic mass

Hello. Mass in special relativity#Controversy explains that some researchers have rejected the concept of "relativistic mass", but apart from saying that it is "a troublesome and dubious concept", the article doesn't go into any depth regarding why they reject relativistic mass. Could someone please tell me what is fundamentally wrong with this concept? Thank you. Leptictidium (mt) 06:17, 15 April 2011 (UTC)

It just seems like a fudge factor to me. That is, when the numbers didn't add up, they just decided to say that the mass was changing. Imagine if your tax accountant could do that: "well, the balance sheet doesn't balance, so I will say that this is 'dynamic cash' and changes quantity as needed to make everything balance". StuRat (talk) 06:40, 15 April 2011 (UTC)

Isn't this just what the central banks do all over the world? 95.112.143.65 (talk) 09:02, 15 April 2011 (UTC)

It's not a fudge factor and it is a occasionally useful concept. For instance, if you put a block on a scale to measure its mass, then you heat it up to a higher temperature increasing its internal energy, its relativistic mass also increases and that should be measurable by the scale in principle (In practice the effect is too small to be measured). The problem is that the concept causes more confusion than it's worth and the modern convention is to reserve the word mass for the rest mass as BenRG points out below. Dauto (talk) 15:08, 15 April 2011 (UTC)

What's troublesome and dubious is thinking that you can plug relativistic mass into equations that have an m in them, such as F=ma, and get something that makes sense. Generally, you can't. To the extent that relativistic mass is just energy divided by c², it's a well-defined concept, but there's no point having two names (energy and relativistic mass) for the same thing. The modern convention is to call it energy, and reserve the word "mass" for rest mass (which is often written in units of energy as well). -- BenRG (talk) 09:23, 15 April 2011 (UTC)

I think it's quite the opposite - if you don't include relativistic energy in equations such as f=ma you will get incorrect results. This energy has inertia and momentum and causes gravity. Which is why I prefer to call it mass. But the hard part is that the mass of an object is relative, it's not fixed. This can make calculations all but impossible. For example, what is the mass of a magnet? If I turn on an electromagnet on the other side of the planet, the magnet in my hand is now heavier (relative to that electromagnet anyway). Ariel. (talk) 19:30, 15 April 2011 (UTC)

If you use the proper form $F={\dot {p}}$ with the three-momentum $p=\gamma mv$, you can easily dispense with "relativistic mass". Here's a quote from a book by Taylor and Wheeler: "Our viewpoint ... is that mass is an invariant, the same for all free-float observers... In relativity, invariants are diamonds. Do not throw away diamonds!" Modern physics understands relativity as a geometrical theory, a theory of the structure of space-time, not as a dynamical theory as suggested by the concept of relativistic mass. In relativity, energy and mass remain distinct physical quantities; "relativistic mass" obfuscates that distinction. Having said that, if the energy is in internal degrees of freedom of a composite body (not center-of-mass motion), then this energy does indeed show up in the effective mass of that body. That's where the mass deficit of, say, the helium nucleus comes from. --Wrongfilter (talk) 20:38, 15 April 2011 (UTC)

Ariel, the point BenRG was making is not that The formula F=ma is correct if you use the rest mass. The point is that even if you use the relativistic mass the formula is still wrong which seems to have gone right over your head. Dauto (talk) 03:15, 16 April 2011 (UTC)

Triplet v.s. Singlet Oxygen

According to the formula for calculating the bond order for diatomic molecular species, both triplet and singlet oxygen species have bond orders of 2. This does not make sense to me - triplet oxygen cannot have a double bond and concurrently be a diradical. I think the reason for this is that the formula ignores electron spin direction. Is this true, and does triplet oxygen have a bond order of one? Or, do I have it wrong? Plasmic Physics (talk) 08:17, 15 April 2011 (UTC)

Sure it can. You cannot draw a proper lewis structure for O₂ with a bond order of two and still have it be a diradical, but that's just a limitation of lewis structures. The molecular orbital diagram at the lower right corner of triplet oxygen shows how it works. The diradical occurs in the two degenerate π* antibonding orbitals. The bond order is calculated as: (bonding electrons - antibonding electrons)/2, which (8-4)/2 = 4/2 = 2. The reason that the Lewis Structure doesn't work out is that the geometry of the molecular orbitals does not work easily in a 2D representation, and lewis structures ignore the whole "antibonding" thing all together. --Jayron32 12:17, 15 April 2011 (UTC)

I was not using the Lewis model approach. Each oxygen has 6 valence electrons, if it has a bond order of two, that means that each atoms makes a net contribution of two electrons to the bonding orbital. This means that each oxygen has four remaining valence electrons. If triplet dioxygen is a diradical which I believe it is, then each atom has only one electron pair and two unpaired elecrons, not just one (according to a two bond order system).

I used the MO diagram for my argument, from it I used two factors - the total number of valence electrons, and the total number of unpaired electrons. Plasmic Physics (talk) 12:50, 15 April 2011 (UTC)

You can't consider the electrons of each atom separately when you're looking at their arrangement in the combined molecule. Electrons that are unpaired for the independent atoms are not required to remain unpaired in the final molecule. Do you understand how the orbitals are filled in the MO diagram at triplet oxygen, and how to calculate bond order based on filling of bonding and antibonding orbitals? TenOfAllTrades(talk) 13:51, 15 April 2011 (UTC)

@ Plasma Physics: To expand on what TOAT said above, when considering the organization of the electrons in the O₂ molecule, you cannot consider each atom as retaining any individual characteristic. The whole thing with Molecular orbital theory is that you treat the entire molecule as a single entity, and calculate the quantum states of the electrons based on that presumption. The system cannot be accurately modeled (for these purposes) as individual atoms which are merely sharing a few electrons (which is how both valence bond theory and hybridization theory model bonding). Molecular orbital theory models the O₂ molecule as a 16-electron system with two nuclear charges of 8+, and calculates the shapes and populations of the various orbitals that way. For convenience, the molecular orbital diagram referenced above only looks at the valence electrons, but the actual calculations are based on all of the electrons. Its the organization and shapes of these molecular orbitals that gives rise to the particular properties of triplet oxygen, that being that it has a second order bond (or "double bond") and is diradical. You can easily arrange all of the electrons in orbitals to get this result; in the case of triplet oxygen you have a total of 8 valence orbitals: five of them have 2 electrons in them, two have one electron each, and the last one is empty. That's 8 orbitals, a double bond, and a diradical. This is empircally confirmed by things like the bond strength and length of the O=O bond in O₂ (compare the bond lengths of O=O with the average peroxide bond length of O-O here, which gives O=O a bond length of 121 picometers, and O-O a bond length of 148 picometers. This is on par with the 20 picometer difference between C-C and C=C), and with the magnetic properties of ground state(triplet) O₂, which is experimentally confirmed to be paramagnetic, as would be expected of a diradical. To sum up; the experimental evidence indicates that oxygen is BOTH second bond order (double bond) and a diradical. Molecular orbital theory predicts both facts about oxygen (again, check the MOT diagram at triplet oxygen), so it is the model which is perhaps best in describe the organization of the oxygen electron cloud. There's actually even MORE evidence that confirms this model of triplet oxygen (vis-a-vis chemical reactivity and spectroscopy), which I'll not go into in the interest of not extending this discussion to the TLDR point. If you are using a model that leads you to a structure which contradicts the empirical, observed properties of oxygen, then simply put, the model is inadequate and needs to be discarded for this purpose. --Jayron32 14:33, 15 April 2011 (UTC)

Well, it's just that the molecular modelling program I'm using does not like the idea of a double bonded dioxygen diradical. It seems to have the least problems when the unpaired electrons are on the same atom. Yes, I have to specify where the unpaired electrons are. One more thing, why do I find lewis structures of single bonded triplet oxygen on google images? Plasmic Physics (talk) 20:47, 15 April 2011 (UTC)

The usual skeletal diagram notation doesn't work so well for complex MO situations. The line between two atoms represents a covalent bond, which means a shared pair of electrons. But the diradical isn't a shared pair making one bond--that's impossible if they have the same spin. Instead (again, exactly as the MO diagram illustrates) it's two shared lone electrons each in separate orbitals that are orthogonal to each other. The limitation is in your modelling program and meaning implied by the diagram style (or at least in the the modelling program's interpretation of the diagram style). Drawing it as a single-bond with a single electron on each atom at least gets the idea of "electrons are not paired, and therefore easily have same spin" correct, at the cost of error in the estimated bond-length. Drawing it as a double bond would imply (to those that don't know the details) that ³O₂ would undergo reactions characteristic of other pi bonds, which is not true. DMacks (talk) 21:03, 15 April 2011 (UTC)

OK, helpful. What do you think, should there be two bond order formulae, one for calculating the total net bond order, and one for calculating spin matched bond order? In the spin matched bond order, only electrons of the same spin cancel, this kind of formula can distinguish between a true bond, and a quasi-bond, which is really what triplet oxygen has. Triplet oxygen has an effective bond order of one and two halves. Plasmic Physics (talk) 21:34, 15 April 2011 (UTC)

"One and two halves" is a pretty good description! One way might be to have the "second" bond written as two dots (but in the bonding position) rather than as an actual connecting line (like the sigma bond is)? The minimum technical notation is to include a superscript "3" to the left of the whole diagram to indicate the spin (see my last sentence in my previous comment), just like you can write the net charge of a structure as a superscript to the right.^† I would like a more detailed way (analogous to "formal charge" on atoms vs "net charge" on a structure) to indicate where the unpaired spins are rather than just the fact that there are two of them, but I don't know a notation for that. But using the "individual dots" vs whole bonds comes close perhaps. A more technical way is to write the spin at each electron (up/down vector), not just its location (dot) or bonded/nonbonded state. DMacks (talk) 15:31, 16 April 2011 (UTC)

^†(later/expanded comment on this point). That's actually the standard way for quantum modelling programs: you declare the spin of the system not of specific electrons or parts of the model. The whole Lewis/skeletal-diagram idea of covalent bonds as specific pairs of electrons at specific atom-pair locations is of a bunch of crap (to use the scientific terminology) at that level anyway. So ³[O=O] vs ¹[O=O] would be fairly accurate for bond-lengths, bond-order, and spin, at the cost of the less important (for many readers) idea that one of those lines is "two half-bonds" rather than a normal covalent pair. But it also leads the reader to think the only difference is one of an overall or hidden detail, even though it really is a major difference in the whole nature of the bonding and physical and chemical properties. DMacks (talk) 18:27, 16 April 2011 (UTC)

While I'm on topic, while I studied the consequences of particle spin at Univeristy, I have no idead what spin actually is. All I know about it, is that it is some kind of description of a particle's kinetics. Does an electron cycle around an actual locus? If it does, what are the constraints? Does the locus describe a point, line, or a surface? Does the locus lie within the electron? Plasmic Physics (talk) 00:07, 16 April 2011 (UTC)

If a charged particle (such as an electron) were to spin, that would cause it to have a magnetic moment and other magnetic effects. These particles do have the properties that result from spinning, therefore they are described as having "spin". But it's an intrinsic property itself, not quite that the particle really "spins". To my mind, since a quantum particle doesn't have a definite position, I can't see how that would be consistent with it having a definite physical rotation as the actual underlying property. See spin (physics) for the gory details. DMacks (talk) 15:31, 16 April 2011 (UTC)

Period food

Are there any studies into what foods women particularly crave on their periods? I know sugary food is pretty common, and iron-rich food, as well as the more specific chocolate, but I'm interested in if anything has looked in more detail or more broadly. I don't have access to most of the paid-for literature at the moment, so public-domain or summaries would be appreciated. 86.164.75.102 (talk) 09:48, 15 April 2011 (UTC) Brain-fart, I meant freely available, not actually released into the public domain. I think. 86.164.75.102 (talk) 15:22, 15 April 2011 (UTC)

Binge eating occurs in a minority of menstruating women. This may be due to fluctuation in beta-endorphin levels. Source: Price WA, Giannini AJ (November 1983). "Binge eating during menstruation". J Clin Psychiatry 44 (11): 431. PMID 6580290. See also Premenstrual dysphoric disorder.

Thanks, that's an interesting start, although I cannot read the paper (even its summary). The Wikipedia article is an interesting read, as the more recent findings on variable response to hormones fits with some of the stuff I've been reading about different women's responses to different versions of the pill, suggesting years more profitable research to be done. So thanks. For this question, I suppose I'm looking more for research into food cravings experienced by women in the 'normal' range, rather than eating associated with various interesting disorders. 86.164.75.102 (talk) 15:22, 15 April 2011 (UTC)

Pinion?

what is racken pinion —Preceding unsigned comment added by 175.157.66.79 (talk) 14:09, 15 April 2011 (UTC)

Did you mean to start a new question? (I've reformatted this, because I think you did..) Are you perhaps thinking of Rack and pinion steering in an automobile? SemanticMantis (talk) 14:54, 15 April 2011 (UTC)

See also rack railway.--Shantavira|^{feed me} 16:57, 15 April 2011 (UTC)

Design pattern: both for software and art

Is there a design pattern which can be applied both to works of art and software? Quest09 (talk) 15:40, 15 April 2011 (UTC)

You may be interested to read the works of Lawrence Lessig et al. The so-called "free culture movement" inherited its philosophical inspiration from the free software movement. Nimur (talk) 17:18, 15 April 2011 (UTC)

I'm not sure that I necessarily understand your question correctly but you may also be interested in Carlos Amorales' modular "Liquid Archive" approach to making his art. Sean.hoyland - talk 17:46, 15 April 2011 (UTC)

I also am not sure what your question means. could you be thinking of fractal geometry? as in the Mandelbrot set.190.148.136.166 (talk) 19:32, 15 April 2011 (UTC)

Software is often created by iterating the cycle Run-Crash-Debug. Most artists and composers follow a similar cycle of successive improvement e.g. Compose-Listen-Make better. Cuddlyable3 (talk) 12:19, 16 April 2011 (UTC)

Cuddlyable3 has the precise answer: something that can be applied both by an artist and by a software developer. The rest is also interesting, in a more broad context.Quest09 (talk) 12:34, 16 April 2011 (UTC)

Live vs. recorded sound

Why do they sound so different? Quest09 (talk) 15:42, 15 April 2011 (UTC)

You mean Acoustic music vs. electronically recorded music played back through electronic amplifiers and loudspeakers? Pfly (talk) 15:50, 15 April 2011 (UTC)

Live sound reaches your ears as each sound source sends out waves which bounce around rooms and off surfaces and arrive at your ears. Recorded sound can only approximate all of these relationships, and generally (unless you are an audiophile with a shitload of cash and time) most people listen to recorded sound from a set of earphones/headphones or speakers which are at a fixed location, and so do not accurately model the actual source sounds. They do a passable job for most people who just want to listen to the latest Lady Gaga song, but there is a noticable difference in the sound of hearing her come from the speakers on the stereo in your living room, and hearing her sing in your living room. --Jayron32 16:01, 15 April 2011 (UTC)

Also, consider a piano, for example, vs. a recording of a piano played back through loudspeakers. There's a huge difference between what is making the sound. Loudspeakers are nothing like pianos. A piano's sound board alone is a resonating surface far larger and different in design and function than a loudspeaker. The amazing thing is that loudspeakers can even come close to sounding like so many different things, from pianos to people singing to cymbals and so on. Still, loudspeakers do a poor job of reproducing the experience of sitting close to the front of an orchestra, or listening to a powerful pipe organ playing full bore. Pfly (talk) 16:14, 15 April 2011 (UTC)

But if the question is about live, as in performed in "real time" vs. recorded, as in created in a studio, then the answer is something to do with live performance vs. the process of building something slowly and in pieces. Something like theater vs. film. Pfly (talk) 16:12, 15 April 2011 (UTC)

No, I asked in the sense that you pointed to at your first reply. But, what's the difference in the wave that hits my ears when coming from a recording or coming directly from an instrument? Which properties are different? Quest09 (talk) 16:33, 15 April 2011 (UTC)

The waveform is different; and to be strictly accurate, the only real reason is because the wave field is different. It is difficult (but not impossible) to completely re-synthesize the entire wavefield; instead, electronic recording only resynthesizes a sampled waveform. For most purposes, your human ears are a stationary set of two single points that sample the pressure level of a multidimensional acoustic wave field; a more complete description of the total wavefield must account for its extent in 3 spatial dimensions, plus the pressure, velocity, and other non-linear acoustic properties of sound waves in air. Most electronically recorded sound waveforms only seek to sample the pressure as a function of time at one (or maybe two or more locations). (They accomplish this by recording pressure fields, placing a microphone as a pressure transducer at one or more fixed locations). For most purposes, this totally replicates the "99th-percentile" of the audible experience; but it is a known fact that the perception of sound waveforms is actually more complicated. A good friend of mine worked on a project to synthesize a multidimensional surround-sound experience; you can read "artistic" and technical descriptions at the technical specifications page. Nimur (talk) 17:27, 15 April 2011 (UTC)

From the list of sound wave properties, frequency, wavelength, and wavenumber are basically the same in this context, as are amplitude, sound pressure, and sound intensity. "Speed of sound" doesn't seem relevant in this context. So that leaves three basic properties, frequency, amplitude, and direction (Nimur addressed wave shape issues above I see, which curiously isn't included in that properties list). A few quick comments:

• Frequency: typical consumer-grade loudspeakers have trouble with very low and very high frequencies. Not uncommonly they drop off below 40-60 Hz and fall off somewhere around 15,000 Hz or perhaps around 20,000 Hz, depending on quality. Subwoofers can handle very low frequencies, but typical consumer-grade, not-super-expensive subwoofers are not very good at producing strong stable pitches, tending more toward booms and rumbles. Compare pipe organs, which can produce extremely low pitches--sometimes so low you feel them more than hear them. No subwoofer can make a sound like a big 32' pipe on a pipe organ. I was lucky enough to get to watch this pipe organ being installed. The sound of the 32' pipes was intense. If I recall right, that beast can accurately and loudly produce pitches down to 8 Hz or so. There's further issues regarding the recording medium, which limit and distort the frequencies in various ways (see Sound recording and reproduction).
• Amplitude: With electronic amplification you can make acoustic instruments much much louder than they could ever be themselves. It is common, I think, to listen to recorded music at louder volumes than would be normal for acoustic instruments (at least the quieter ones like guitar). Plus, when music is put together in a studio it is typical to mix the amplitudes of different instruments in "unnatural" ways--a quiet singer overpowering a drum kit, for example. In olden times you needed a operatic voice to overpower loud instruments. Today on a recording a whisper can overpower a marching band, if desired.
• Direction: The sound from stereo loudspeakers comes from two relatively small, usually non-moving places. Surround sound systems up that to five or so. Compare a live modern orchestra, where the sound comes from well over 100 sources. Even a single acoustic instrument, say a piano, produces sound from multiple sources—the strings, the sound board, etc. Pfly (talk) 18:05, 15 April 2011 (UTC)

To clarify: if you are only modeling the sound pressure level, you are only modeling p wave; this is the straightforward "acoustic wave equation" that is suitable for describing sound in a gas (like air). But in reality, air is not ideal; it has some viscous properties; and you should use a suitable elastic wave equation, such that the velocity of any individual particle is not equal to the velocity of the wavefront. It is unlikely that most human ears can perceive this difference, but we absolutely can measure this phenomenon using sophisticated equipment. A typical condenser microphone only responds to pressure, not to velocity; but a scientific-grade acoustic transducer will be able to record pressure and at least one component of the 3-dimensional acoustic velocity vector. Sampling and recording this information would be critical to a total and exact re-synthesis of the wavefield. And as always, I will re-emphasize the caveat; the goal is to mathematically model the physical effect to some specified level of accuracy/detail. We can always make a more complicated model to account for the 99.999999...th percent effects. Most human ears only "hear" or perceive stereo sound (i.e., two pressure-waveforms) sampled at 40 kHz, so it's not necessary to record more data. Nimur (talk) 18:12, 15 April 2011 (UTC)

Nimur, your technical understanding is way beyond mine. This brings up a question I've wondered about. Human hearing range doesn't normally reach much beyond 20 kHz (if that), and one often hears how it is therefore unnecessary to record or reproduce frequencies above 20 kHz or so. But I wonder--is it possible, or even common, for frequencies above 20 kHz bouncing around a room after, say, a gong is struck, to interact with other waves bouncing around, with the room itself, etc, such that lower, audible frequencies are produced and heard? Something akin to a resultant tone (or better, combination tone), but at the high end? I've long wondered if this is possible and if so, how common it is. And if so, whether it would have an effect on music with lots of very high overtones/harmonics--making it sounding richer live, with all those ultrasonic waves existing and bouncing around, than recorded, with no ultrasonic frequencies in the first place. ? Pfly (talk) 18:55, 15 April 2011 (UTC)

Certainly I feel that way, but my preference is actually for the recording. The clash of real cymbals in the highest frequencies is just so painfully loud that it cuts up the rest of the song. Wnt (talk) 23:37, 15 April 2011 (UTC)

Regarding technical understanding... Anyone can understand mathematical descriptions of physical phenomena if they spend enough time analyzing them. I have spent, and continue to spend, a lot of time thinking quantitatively about daily mundane things. It also helps to have academic or formal training in physics or mathematics. Anyway - regarding wave mixing. It is a fundamental assumption of linear system theory that frequencies are preserved by systems. In other words, the simplest model forbids a high frequency from "reflecting" and producing a lower frequency. On the other hand, a nonlinear wave model (such as the elastic wave model) does permit nonlinear, frequency-altering interactions. For most purposes, the amplitude of such an effect is very small, so we safely ignore it for day to day ordinary sound waves. I can think of at least one case where we cannot ignore these effects! A broken loudspeaker results in a nasty rattle that is nothing like the intended waveform; what is happening is that energy is coupling nonlinearly into the torn paper cone of the speaker, which is then buzzing and sounding awful! Nonlinear acoustics are therefore not merely a theoretical concoction of bored physicists! Nimur (talk) 02:25, 16 April 2011 (UTC)

I question the premise that they sound different, if the sound is recorded and reproduced by high-fidelity media. If they are all that different, then perhaps you need to buy better microphones, recorders, amplifiers, or speakers. Edison (talk) 03:46, 16 April 2011 (UTC)

They certainly aren't exactly the same. The question is if they are enough different that you can tell. StuRat (talk) 03:49, 16 April 2011 (UTC)

And that's the entire premise behind sampled audio and lossy sound compression technology - when recorded properly, essentially no human can perceive the difference between the live and the recorded sound. Nimur (talk) 05:59, 16 April 2011 (UTC)

...except for those blessed with one or more Golden ears, such as everyone who writes in an Audiophile magazine. Years ago a loudspeaker amnufacturer (was it Quad Electroacoustics?) gave a stage demonstration showing a string quartet. Midway through a music piece the musicians got up and left the stage, leaving only the loudspeaker that had really been producing the music all the time. Cuddlyable3 (talk) 12:13, 16 April 2011 (UTC)

The "live vs recorded" demo would be more impressive were it not for the fact that Thomas Edison did the same thing with acoustically recorded "Diamond Disc" records and his phonograph 1915-1925. It was reported that the audience could not tell when the musician was performing and when the phonograph was playing[20], [21]. The repertoire was generally limited to solo voice or solo instrument, so there was no need to reproduce the high sound pressure level of a brass band or orchestra, and the soloists may have avoided loud sounds. For an overview of "live vs recorded" tests over the years, see [22]. Edison (talk) 19:50, 16 April 2011 (UTC)

My impression is that a lot of people who think/claim they have golden ears don't, they just don't ever actually test their alleged ability to hear differences properly (e.g. with an ABX) but often still make the claim they can hear these differences. I can't say if this applies to audiophile magazine writers in particular, but again my impression is a lot of the magazines don't publish or use ABX or other more scientific testing methods and are willing to promote things like Monster cables usually with questionable technical advantages (worse of course are those that promote cables and other things that are supposed to provide better output despite the fact both are capable of providing the exact same digital signal). I'm not of course denying there are people who can hear differences that many others can't and there are of course audiophiles who do approach their hobby/whatever from a more scientific viewpoint, e.g. those at Hydrogenaudio Nil Einne (talk) 21:40, 16 April 2011 (UTC)

A string quartet plays quite low frequency sound - only a few sorts of things go over 20,000 Hz. One thing about very high pitched sound is that it's almost line of sight. Back in the 1980s it was easy for people to tell because all the TVs and monitors and videocameras consistently made a lot of this sound when on (sometimes uncomfortably loud in the case of "hidden" anti shoplifting cameras) - I don't think they do this nowadays, though I'm not sure because I'm also losing high-pitched hearing with age. See ultrasound. Wnt (talk) 04:08, 17 April 2011 (UTC)

two questions about electromagnetic waves

1.I have no imagination of photons as particles. I mean we can think of electrons as particles moving (or present) in regions called orbitals. do photons have a certain measurable "area of influence" or something like that?

2.In the emission or absorbtion spectrum of different elements,there are lines that show different transitions in energy levels.well, according to the formalae, each kinds of transition must produce a single kind of electromagnetive wave(E(n2)-E(n1)=hf). but when we look at the spectrums there are neighbours of wavelengths, not "exactly one" wavelength.I mean although the neighbourhood may be small, but it is still a neighborhood, otherwise we couldn't see it.

It's REALY hard for me to ask such questions in English, so I'm sorry and I hope you understand what I mean.Thanks! —Preceding unsigned comment added by 178.63.158.171 (talk) 16:55, 15 April 2011 (UTC)

For question #1, a single photon's "area of influence" is probably best thought of by defining a particular fall-off in the electric field intensity (or, for one single photon, the probability of measuring an electric-field at a particular intensity). There's going to be a "soft edge" for the photon; for any radius r from the photon's "center location," there's going to be a lower probability that the photon can interact with anything. This is described mathematically as a wave packet, which has finite extent in space and time. (We also have wellenpaket in German).

For question #2, see hyperfine structure (also available in German at Hyperfeinstruktur). Nimur (talk) 17:57, 15 April 2011 (UTC)

(EC) The answers to both of your questions involve the Heisenberg uncertainty principle.

Similar to how you can't say with certainty exactly where within an orbital an electron is, there is also a "fuzziness" as to where exactly a photon is. For example, if you shine a monochromatic light on a circular aperture, the light intensity behind the aperture will form a diffraction pattern known as an Airy disk, rather than a solid circle as one would expect if each photon traveled along an infinitely thin line.

Spectral lines not having zero width is due in part to excited states having a finite lifetime, which causes an uncertainty in the emitted photon's energy, as explained in Uncertainty principle#Energy-time uncertainty principle. Red Act (talk) 18:18, 15 April 2011 (UTC)

The German articles on the topics I mentioned are Heisenbergsche Unschärferelation, Beugung (Physik), Beugungsscheibchen, Spektrallinie and Linienbreite. Red Act (talk) 18:34, 15 April 2011 (UTC)

An other reason for widening of spectral lines is the Doppler effect due to the relative motion of the atoms that emit the photons due to thermal motion. Dauto (talk) 03:24, 16 April 2011 (UTC)

Discovery of rimantadine and references

In the past few days a history section was added to the rimantadine article. An anon-IP editor has added several references to verify the claims, but I am having difficulties verifying the claims, mainly of two reasons: 1) Chemistry is not something I am familiar with. 2) English is not my native language. Can someone with knowledge in chemistry please have a look at the references, and explain whether the references really verifies the claims or not, and perhaps explain why – since I, as a layman am not able to understand the references given at first sight. Thanks in advance. ^Talk/♥фĩłдωəß♥\^Work 18:02, 15 April 2011 (UTC)

Head rotation

Is it theoretically possible by surgical means to make the human neck safely rotate the head at 360 degrees or so (bearing in mind that it's not fatal in some birds)?--89.76.224.253 (talk) 18:16, 15 April 2011 (UTC)

No, this is not possible. The structure of our spine and neck is different from birds. Nimur (talk) 18:20, 15 April 2011 (UTC)

I'm pretty sure birds don't rotate 360 - they probably do 180. Ariel. (talk) 19:23, 15 April 2011 (UTC)

OP, what birds are you referring to? The usual example of a bird rotating their head to an extreme is the owl. And according to our article on the owl, "Owls can rotate their heads and necks as much as 270 degrees in either direction". Or do you mean 360 from one extreme to the other? Dismas|^(talk) 19:41, 15 April 2011 (UTC)

Screen-width Problem in computer

The ratio of width-to-height in new laptops is considerably different than traditional desktops. Does that mean that everything will appear deformed i.e. stretched along horizontal axis ? —Preceding unsigned comment added by 124.253.130.232 (talk) 21:52, 15 April 2011 (UTC)

Please don't ask the same question on multiple ref desks, especially when it has already been answered on one of them (Computing). Looie496 (talk) 22:16, 15 April 2011 (UTC)

Seafloor river bed in Toyama Bay, Honshu from Google Earth

Hi. On Google Earth, a long river valley appears carved onto the seafloor leading out from Toyama Bay in Japan, extending toward the bottom of the Sea of Japan. It is most likely not volcanic or tectonic in origin, and also does not extend from the mouth of the Shinano River, which lies closer to Niigata farther northeast. It appears to wind itself around the eastern edge of some continental shelf and steadily drops off in elevation on the seafloor, tracing a path from a reverse-delta toward the north. In fact, the main undersea channel appears to be a merger of the Shō River and the Jinzū River. The channel appears to have a lower sea bottom elevation on Google Earth than its surroundings and stretches for about 590 km before ending at the edge of a deep basin, at which point it is closer to Sapporo than to Tokyo. At the point equidistant between the two cities, the elevation at the bottom of the channel is about 2800 metres below sea level, It is noticeably longer than any other apparent seafloor river channel in the area and may be one of the longest in the world. Also, the channel appears to bypass the edges of a few underwater volcanoes, suggesting that sea levels were lower or the river has enough power to carve this deep channel even when underwater. At various points, the channel itself lies an average of 145 metres lower than the surrounding ocean floor. Any information on what was responsible for creating this channel, whether it was an ice age event or a phenomenon similar to the conditions today, and how this particular locale compares to any similar channels worldwide? Thanks. ~AH1 ^(discuss!) 22:59, 15 April 2011 (UTC)

Apparently it's called the Toyama Deep-Sea Channel.^[23] Wnt (talk) 00:02, 16 April 2011 (UTC)

I don't know about that one specifically, but our article on submarine canyons give information (or at least speculation) about how such things form. Looie496 (talk) 00:05, 16 April 2011 (UTC)

"Submarine canyons are well developed around the Japanese Islands. Three major large-scale submarine canyons are the Kushiro Canyon, the Toyama Deep-sea Channel, and the Boso Canyon. The Kushiro Canyon greatly encroached on the continental shelf and deeply eroded the continental slope. This characteristic is markedly different from other canyons. The Toyama Deep-Sea Channel is characterized by the length of over 500 km, considerably meandering, a vast submarine fan, and well-developed submarine natural levees. The Boso Canyon has significantly incised meander 100 km in length."^[24] Looks like 3.6 million articles just aren't nearly enough. ;) Wnt (talk) 00:10, 16 April 2011 (UTC)

April 16

Question about gravity and absolute zero temperature?

As both [Einstein’s and Newtonian] models of gravity are independent of temperature therefore “Does gravity cease and clocks stop or slow down at Absolute zero temperature?” Also this might help: http://www.jupiterscientific.org/sciinfo… 68.147.41.231 (talk) 02:47, 16 April 2011 (UTC)Eclectic Eccentric Khattak#1

Seeing that we've gotten much closer to absolute zero than we have to the speed of light, with no strange things happening (EDIT: with gravity and time; some other strange things happen, for example see superconductor), I think it's safe to say "no". 72.128.95.0 (talk) 02:52, 16 April 2011 (UTC)

Your link is broken, but I'm guessing you might be indirectly referring to a Big Freeze, which is one form of a heat death of the universe scenario. In any form of a heat death of the universe scenario, there will no longer exist any kind of astronomical objects, or even any macroscopic objects, that would produce anything significantly different from a constant curvature of spacetime, so you could kind of in a limited sense say that gravity at that point has ceased. And in any heat death of the universe scenario, entropy comes arbitrarily close to its asymptotic limit (in particular, a temperature of absolute zero is approached in a Big Freeze scenario), so at that point there will be essentially no thermodynamic arrow of time, so you could kind of in a limited sense say that at that point "time has ceased". But the same laws of physics will still apply, it's just that there won't happen to be any astronomical objects around for gravity to be meaningful anymore except for describing the universe as a whole, and there will no longer be any physical processes going on such that "forward in time" looks noticeably different from "backwards in time" locally, so the second law of thermodynamics will lose its significance.

At any rate, it's not like a temperature of absolute zero causes gravity to become insignificant. If you managed to create a macroscopic object with a temperature of absolute zero, it would still produce a gravitational attraction, to use the Newtonian description. Basically, any nonzero component of the stress-energy tensor causes a curvature in spacetime, to use the general relativity description, and thermal energy is in general only a minor contributor to the stress-energy tensor, so zero thermal energy does not at all imply a zero curvature of spacetime.

And a constant temperature of absolute zero doesn't really cause time to cease, either, even if there is no longer a thermodynamic arrow of time, and even though a clock can't actually function at a temperature of absolute zero. At the very least, even in a Big Freeze scenario, there will still exist a cosmological arrow of time. Red Act (talk) 06:28, 16 April 2011 (UTC)

Here is the link "http://news.harvard.edu/gazette/1999/02.18/light.html" Sorry about the broken one.

Help! I have some questions about Venus, Uranus and the moon

1. "Does the planet Uranus get hit by earthquakes? I read this off of a website: "In the course of a study of tidal effects on earthquakes2, the astronomical positions of the planets have also been taken into account and a remarkable correlation between the positions of Uranus and the moment of great earthquakes has been established for a certain period. Gutenberg and Richter's data of all earthquakes equal or greater than magnitude 7; have been used." Could someone explain this to me?

2. A long-standing mystery of Venus observations is the so-called 'ashen light', an apparent weak illumination of the dark side of the planet, seen when the planet is in the crescent phase. The first claimed observation of ashen light was made as long ago as 1643, but the existence of the illumination has never been reliably confirmed. Observers have speculated that it may result from electrical activity in the Venusian atmosphere, but it may be illusory, resulting from the physiological effect of observing a very bright crescent-shaped object." In astronomy, Venus has been called the twin sister of Earth. Both planets are about the same size. If another planet could support life, it was once thought to be Venus (of course, now it's realized that the heat and sulfur make that impossible). What association do the Moon and Venus have in common in astronomy?

3. Does the planet Venus get hit by meteor showers? I read this information of a website: Venus is a Crescent V when it is most visible twice a day and for a long period. Also during this time it becomes much easier to monitor the ever going meteor storms ranging around and into Venus. Venus is known well for being the planet most hit by Meteor Showers. Go outside before sunrise, around 5:30 a.m. is best, and look East. The brightest object in that direction is the planet Venus. It looks like a star going supernova. Above Venus lies Saturn, and below, near the horizon, is Jupiter. Every 10 minutes or so you'll see a meteor streak among these planets. The meteors are pieces of Halley's Comet.

"Every year around this time Earth glides through a cloud of dusty debris from Halley's Comet," explains Bill Cooke of the NASA Marshall Space Flight Center. "Bits of dust, most no larger than grains of sand, disintegrate in Earth's atmosphere and become shooting stars."

"It's not an intense shower," he says, "but it is a pretty one."

Astronomers call it the "Orionid meteor shower," because the meteors appear to stream out of a point (called "the radiant") in the constellation Orion. The radiant is near Orion's left shoulder. But don't stare at that spot, advises Cooke. Meteors near the radiant seem short and stubby, a result of foreshortening. Instead, look toward any dark region of the sky about 90 degrees away. The vicinity of Venus or Jupiter is good. You'll see just as many Orionids there, but they will seem longer and more dramatic." Please give me more information. Neptunekh2 (talk)

While we wait for experts to answer your first two questions (and give a better answer to the last), I can answer the bit about meteor showers on Venus. Yes, all the planets get hit by meteor showers, but we can't see these from Earth, or at least not with the naked eye. The shooting stars mentioned are meteors in Earth's atmosphere that just happen to be highly visible near to the horizon where Venus can often be seen most clearly. There is no connection between the planet Venus and the Orionids except this visibility factor. I would like to see some evidence for the correlation that you mention between the position of Uranus and the time of earthquakes. I can think of no logical reason for any causality here. Dbfirs 07:02, 16 April 2011 (UTC)

1) If they are talking about the position of Uranus causing quakes on Earth, that's absurd. At that distance there's no way it could have an effect. The Moon could contribute to quakes, due to it's proximity, and possibly the Sun, due to it's size. StuRat (talk) 08:48, 16 April 2011 (UTC)

2. The OP mentioned but didn't ask about the Ashen light of Venus. An early astronomer believed that it was from the fires from celebration of a new Venusian emperor. This purports to be a picture of it] but I can't make out the emperor nor even his clothes. Cuddlyable3 (talk) 11:57, 16 April 2011 (UTC)

To me the "ashen light" looks pretty clear there - I can quite easily see the dark side of Venus, if that's what it is, against the background. If it's due to electrical activity it must be something pretty homogeneous throughout the dark side. But Earth has all sorts of weird upper atmosphere activity that people are discovering around all the time - and Venus has more sun and more atmosphere. Wnt (talk) 01:44, 17 April 2011 (UTC)

The OP will be aware that Venus has no moon for moonshine on the surface, though one was announced in 1686 and the object 2002 VE68 is in a 1:1 orbital resonance with Venus, so is considered a quasi-moon, but only for the next 500 years or so. Dbfirs 12:04, 16 April 2011 (UTC)

As for question 3, all planets are hit by meteorites, but the OP seems to be confused as to how meteors are observed. They are strictly atmospheric phenonomea and the ones the OP has seen are certainly in the Earth's atmosphere. The apparent streaking among the planets is merely the coincidence of alignment. Astronaut (talk) 12:44, 16 April 2011 (UTC)

This is the letter you're quoting: R. Tomaschek. "Great Earthquakes and the Astronomical Positions of Uranus." Nature 184:177-178 (18 July 1959). (To see more than the abstract, one needs an appropriate subscription.) The author found a fairly strong correlation between the location (the right ascension, actually) of Uranus in the sky and the occurrence of earthquakes of magnitude 7.75 and greater, during the years 1904-1906. It is not explained why he chose that particular cutoff for earthquake strength. The author fails to discuss in any detail the rest of the earthquake record; the source he was working from contained data up to at least 1950, but all we hear is that the correlation after 1906 "becomes less significant". Hm.

Among other issues, his significance testing fails to account for the effect of multiple comparisons. If one takes a three-year window and slides it across five or six decades' worth of the earthquake record, one will find clusters of earthquakes that correlate with other totally irrelevant measures purely by coincidence. Besides cherry-picking the six or seven percent of the earthquake dataset which best fits his thesis, we also don't have any information about what other phenomena were examined. (Did he look at the right ascension of a bunch of other astronomical objects and find no correlations? Weather conditions: rainfall, snow, temperature? The stock market?) The larger the set of data he was trying to match the earthquakes against, the greater the likelihood that such a match will occur somewhere by coincidence. If we don't know how many such comparisons were made, then we can't appropriately account for this source of false significance. There is, as always, an appropriate xkcd: [25]. TenOfAllTrades(talk) 14:35, 16 April 2011 (UTC)

This response to some criticism suggests that it is the hour angle of Uranus, not the right ascension that correlated with earthquakes (with an orbital period of 84 years for Uranus, RA doesn't change very much over the course of two or three years). Which doesn't change the fact that this was bull from the start... --Wrongfilter (talk) 16:00, 16 April 2011 (UTC)

I'd say that the immediately preceding letter (a response by a legitimate mathematician to the original paper, and which Tomaschek poorly and incompletely attempts to rebut in the abstract you've linked) is probably the most illuminating comment: Burr, E.J. "Earthquakes and Uranus: Misuse of a Statistical Test of Significance" Nature 186:336-337 (23 April 1960). He makes essentially the same points that I do, but does so much more eloquently. (This isn't the first time I've been scooped at the Ref Desk, but it may be the first time I've been fifty years late.)

I will note that Tomaschek's rebuttal is silent on the most important question—that is, how many different sets of astronomical or other data did he examine in searching for correlations with earthquakes?

Tomaschek's rebuttal also asserts – in defence of his silly claim – that the apparent effect of Uranus is significant (though smaller) when the entire fifty-year earthquake record is considered. This is unsurprising, since we already know that a portion of that record contains a small region with a (likely spuriously) high correlation. Tomaschek errs in including the 1904-1906 data when he asserts that his correlation exists across all of the data; you can't reuse data when you're trying to confirm a correlation. If one only looks at the remaining data covering the years 1907-1952(?), then one finds 111 earthquakes, 24 of which occurred within one hour of Uranus being in the desired location. The expected value is 1/6 of 111, or 18.5, so there were slightly more quakes than the mean we would expect by chance. If we assume that earthquakes are instead randomly distributed in time (and follow a Poisson distribution), that expectation value carries with it a standard deviation of 4.3. Our measurement is a trifling 1.28 standard deviations from the mean, something that we would expect to occur by chance about 20% of the time.

A more subtle point is that the earthquake events listed aren't actually all independent. In Tomascheck's Table I, there are several quakes that appear to be clustered in time and space and which I would expect are quakes followed by aftershocks. Between June 25 and June 27, 1904, there are three earthquakes at (nearly) the same location in Russia; the initial temblor and first aftershock falling outside Tomaschek's Uranus rule, and only the second aftershock fitting within. Similarly, there are a pair of earthquakes in or near Mongolia in July of 1905; the first quake fails the Uranus test but the aftershock squeaks in. Should initial quakes and aftershocks be treated the same way? It's just sloppy analysis and wishful thinking. TenOfAllTrades(talk) 19:05, 16 April 2011 (UTC)

Old Balls

This came up in a question on the Miscellaneous Desk. Someone found what is probably an American Civil War cannon ball which has a diameter of 3 inches and is covered in rust. Using a table found on Field artillery in the American Civil War, it ought to weigh 9lb 8oz. My thought was that oxidation would make it a bit lighter now; was I right or just talking balls? Alansplodge (talk) 08:18, 16 April 2011 (UTC)

The rust ought to make it heavier, not lighter. Rust is iron + oxygen + water, so it's heavier than just iron. None of the original iron atoms have escaped unless the rust has flaked off. On the other hand, if by 'lighter' you meant less dense, then you would be right - rust is probably less dense than iron. --Heron (talk) 10:23, 16 April 2011 (UTC)

A common high-school or freshman-college chemistry experiment is to take a piece of metal of known mass and oxidize it. From the mass increase, students then determine how much oxygen was added, and from that, various details about the metal and its oxididation properties. DMacks (talk) 14:58, 16 April 2011 (UTC)

The rust might make it heavier if it were all there, but for an iron ball that has been sitting around in the rain since the Civil War, a good bit of rust is likely to have flaked off and washed away. Looie496 (talk) 16:22, 16 April 2011 (UTC)

I suppose that was my chain of thought, but there wasn't much scientific enquiry behind it. Thank you for your answers all. Alansplodge (talk) 16:59, 16 April 2011 (UTC)

Translational acceleration

I am looking for a definition of translational acceleration, preferably one that is easy to understand. Lova Falk talk 09:09, 16 April 2011 (UTC)

It means acceleration (getting faster) in a straight line, as opposed to rotational acceleration, which means acceleration in a circle. See Translation (physics). --Heron (talk) 10:26, 16 April 2011 (UTC)

I think the exact meaning may depend on context. In Newton–Euler equations, "translational acceleration" is used to mean the instantaneous acceleration of the centre of mass of a body. In rotation around a fixed axis it is used to mean the tangential component of the acceleration of a general element of a body. Gandalf61 (talk) 10:42, 16 April 2011 (UTC)

Thank you! Something that confuses me is that the Thesaurus in the free dictionnary says that translational is: "of or relating to uniform movement without rotation". As far as I understand, uniform movement is the same as constant movement, and in that case there cannot be any acceleration. Lova Falk talk 11:11, 16 April 2011 (UTC)

A thesaurus is a reference work that lists words grouped together according to similarity of meaning (containing synonyms and sometimes antonyms), in contrast to a dictionary, which contains definitions and pronunciations. Never rely on a thesaurus for definitions! Cuddlyable3 (talk) 11:43, 16 April 2011 (UTC)

Always nice to learn more than I asked for. Thank you! But to return to my original question, is translational acceleration basically the same thing as linear acceleration? Lova Falk talk 14:02, 16 April 2011 (UTC)

Gandalf61's answer was better than mine, so the answer to your question is no. Linear acceleration is a special case of translational acceleration in which the object follows a straight line while its speed varies. If the path is not a straight line then the acceleration is still translational but not linear. --Heron (talk) 17:15, 16 April 2011 (UTC)

Strange archive search message

Whenever I search the reference desk archives I am told You may create the page "Your search terms prefix:Wikipedia:Reference desk/Archives", but consider checking the search results below to see whether it is already covered. Surely I may not do this; maybe someone could tweak the appropriate template.--Shantavira|^{feed me} 09:42, 16 April 2011 (UTC)

You used the Search box at top right of the page, which is for searching ARTICLES. When you want to want to search the ref. desk archives, use the Search archives button (in the header on this page). Cuddlyable3 (talk) 11:37, 16 April 2011 (UTC)

But I did use the search archives box. Try it. (I meant to put this question on the Help page but never mind.)--Shantavira|^{feed me} 12:43, 16 April 2011 (UTC)

I will echo this. This is the current response from the "search archives" box at the top of the page. I'm not familiar with the reference desk, but Cuddlyable3's answer suggests that what we're seeing is not what's intended. As Shantavira points out, we should not be offered the ability to create a page called Fred prefix:Wikipedia:Reference desk/Archives (which is what is presented in response to a search for 'Fred'). -- EdJogg (talk) 14:52, 16 April 2011 (UTC)

Yes, this seems to be a bug in the archive search engine. Fortunately it still gives sensible search results. I struck out my incorrect assumption above. Cuddlyable3 (talk) 22:47, 16 April 2011 (UTC)

An archive search box is just a convenient way to produce a search with a prefix operator you could have entered manually in the normal search box. bugzilla:21102 is: "don't propose to create the page when using prefix:, intitle: or +incategory:". PrimeHunter (talk) 01:15, 17 April 2011 (UTC)

Sensations and the vocabulary to describe them

In elementary school, children are taught that humans have five senses (sight, hearing, taste, smell, and touch.) These senses convert physical stimuli into signals that go through multiple layers of processing before they eventually reach consciousness. There are other signals (feelings? sensations?) processed by the brain that are not linked to simulation of the five traditional senses, at least not clearly so. Some examples:

• hunger
• nausea
• vertigo
• the feedback that you get about the tension in a muscle
• the feeling that you experience when you are in a free fall
• the feeling that you experience when you exercise at a level that your body cannot comfortable handle
• the feeling of disgust when you think of something unpleasant

These examples are not all of the same nature, especially the last one. However, at some level they are "signals" that rise to the level of consciousness.

Is there is systematic categorization of these "signals"? If so, where can I find a categorized list of terms for referring to the different signals/feelings/sensations? —Preceding unsigned comment added by 173.49.79.68 (talk) 12:36, 16 April 2011 (UTC)

Not very systematic, but our sense article lists quite a few more than the "traditional" senses, plus a few more in the see-also list. Part of the problem is that many of these senses do not have specific names.--Shantavira|^{feed me} 14:15, 16 April 2011 (UTC)

Proprioception! Lova Falk talk 14:17, 16 April 2011 (UTC)

What do glucocorticoids do?

My 9-year old son has an Intelliquest Quiz Book "Gross and Yucky Human Body". The Intelliquest system uses an electronic wand to check the answers of a series of multiple choice questions. For the question What do glucocorticoids do? (no 156 in the book) the correct answer is (apparently):

D) Prevent you doing your homework

My son wanted to know why this was the correct answer (the others being: Prevent bleeding, Prevent infection, Prevent swelling.)

We did have a look at the glucocorticoid article, but not being degree level chemists we could not work out an answer for ourselves. Hence we come here to consult the collective wisdom of the reference desk! -- EdJogg (talk) 14:45, 16 April 2011 (UTC)

Judging by this line in the article, "glucocorticoid turns immune activity (inflammation) down", I'd say "prevent swelling" is a better answer. SemanticMantis (talk) 15:13, 16 April 2011 (UTC)

Our article on glucocorticoids is pretty sucky when it comes to conveying useful information. I think the information the question was trying to evoke is that glucocorticoids, especially cortisol, are activated by stress, especially chronic stress, and if elevated for a long time can have a variety of negative effects on brain function. Looie496 (talk) 16:18, 16 April 2011 (UTC)

I think glucocorticoids also have a vasoconstrictive effect that may counter bleeding, but their use on a bleeding animal is apparently debatable.^[26] But I think any book entitled "Gross and Yucky Human Body" aimed at kids should not be asking such a question unless it gives the answer somewhere inside! Wnt (talk) 20:18, 16 April 2011 (UTC)

To answer Wnt, it is a rather curious way of learning. The book contains a series of multiple choice questions, and the wand (which is pre-programmed with the book number, and hence the answers) keeps track of how many the child gets right. I think the idea is that through repeated attempts to get all the questions right, the facts are memorised. One reason for giving all the book details was on the off-chance someone knew if the answers were on-line!

I would guess that Looie496's answer is the most likely (assuming that the wand has been programmed correctly!) but it is a surprising question to find in a kid's book. Thank you all for your help. -- EdJogg (talk) 22:13, 16 April 2011 (UTC)

A dumb kid would get the answer faster, but even a genius should eventually figure out the right place to tell the author to stick that wand... =) Wnt (talk) 01:47, 17 April 2011 (UTC)

Infinite re-reflection

I remember a ,probably, childhood experience about mirrors. If you stand between two mirrors and position yourself so that you can see your rear reflection reflected in the mirror in front of you, and you look closer you will see that the same reflection back and forth, smaller each time is repeated apparently ad infinitum. Not something I ever worried about very much, but I did cogitate a bit about the reflections continuing down to the micro limits of light particles/waves, and wondered if this had anything to do with infinity. Recently I saw something on a N.Geo. documentary about 'fractal geometry'. This triggered the mirror memory, and I've tried several guesses at artical headings but can't find anything that mentions the mirror thing or anything about a connection with infiniy or fractal geometry. Am I seeing something that's not there? Layman. No advanced math please.Phalcor (talk) 18:51, 16 April 2011 (UTC)

Some thoughts:

1) The reflection isn't really infinite, since mirrors don't reflect 100% of the light that hits them, so get darker each time, eventually fading to black. I wonder what the maximum number of reflections ever recorded is ?

2) I see what you mean about the fractal nature of the reflections, each being the same as the original but slightly smaller (depending on the curvature of the mirror, of course).

3) Light has a dual wave/particle nature. It's an interesting thought problem to consider when the reflection stops, under both the wave and particle models. In the case of waves, there's no reason they can't continue to reduce in magnitude infinitely, although at some point they become indistinguishable from "noise". (Think of ocean waves below a certain size being impossible to tell apart from the random splashes and ripples on the surface.) But, as for the particle nature of light, each photon either is or isn't reflected, so there should be a precise time when the last photon fails to reflect, but instead turns into heat, I suppose. StuRat (talk) 19:01, 16 April 2011 (UTC)

Essentially I think you are talking about recursion. I remember Douglas Hofstadter's book Gödel, Escher, Bach has some pictures showing and discussing the effect you describe (except using cameras and monitors) to illustrate the various optical feedback strangeness that can occur. The "In science" section of the optical feedback article is likely to be of interest to you. Sean.hoyland - talk 19:45, 16 April 2011 (UTC)

I'm not sure if an infinite regress of mirrors is a fractal - I think a fractal branches at each increasing level of detail (like tree branches or snowflakes, but infinite). Anyone want to venture an opinion on the Hausdorff dimension of the image? Wnt (talk) 20:09, 16 April 2011 (UTC)

Relevant is our short Perfect mirror article. Comet Tuttle (talk) 20:21, 16 April 2011 (UTC)

Brain scan lie detection

I was recently fascinated to read this paper about modern lie detection (available here temporarily) from the U.K. Is there a review of this technology that talks about accuracy rates for incarcerated convicts, captured belligerents, and whether it is possible to discern subjects' answers to questions when they refuse to speak? How much more accurate are these techniques compared to a typical polygraph? 99.39.5.103 (talk) 19:09, 16 April 2011 (UTC)

I suspect it would have the same shortcomings as regular lie detectors:

1) People are different, and can react differently when lying or telling the truth. Hopefully each person reacts consistently when either lying or telling the truth, but there's no guarantee.

2) Probably wouldn't work on people who don't know what the truth is, like those with mental diseases.

3) Still sounds like it has the same problem as the current test, that the results are highly subjective, and different experts may read the results differently (possibly depending on who is paying them).

4) Not very good info for a jury to base decisions on. That is, even if a certain portion of the brain "glowing" absolutely meant they were lying, this isn't obvious to the jury, they just have to take the word of an "expert". For juries that distrust so-called experts, this doesn't work.

It might have the advantage of stopping one method of fooling the test, by causing pain (say by stepping on a tack), to produce stress on truthful answers. Presumably the pain area of the brain would be distinct. However, a brain scan that involves swallowing a radioactive tracer sounds like it might violate the "first, do no harm" law. Doing that to diagnose a medical problem is one thing, but doing that for no medical benefit whatsoever sounds like iffy medical ethics. StuRat (talk) 19:26, 16 April 2011 (UTC)

I have to wonder if you read the paper. It was about (2) entirely. 99.39.5.103 (talk) 22:09, 16 April 2011 (UTC)

The use of fMRI for lie detection is still in early stages of being developed, and the technique has not been validated for use in a court of law, at least in the US. (Some strange things have happened in India, as I recall.) Our article on lie detection gives a brief description of it, with references. In my view this is not likely to become a widely used technique even if it can be validated, because it is very expensive, and because the procedure is pretty unpleasant, especially for people who are claustrophobic. (You're crammed into a narrow tube surrounded on every side by a huge mass of metal, and while the scan is running the machine makes a hell of a racket.) Looie496 (talk) 19:55, 16 April 2011 (UTC)

Thanks! I was amazed to read in the article that there are already two commercial vendors and a Mythbusters segment where 1 out of 3 were able to fool the test. 99.39.5.103 (talk) 22:09, 16 April 2011 (UTC)

(ec) I would be wary of assuming all such techniques will go away. See P300 or "brain fingerprinting", which sounds intimidating - but which is aimed specifically at recognition. I can think of very sinister uses.

The data here sounds significant-ish, but it's not entirely clear to me what data that Student's t-test was done on, and p<0.05 studies come up fairly often (someone posted a cartoon about that recently...) That 74% +- 17.5% consistency (50% baseline) sounds like something to watch.

I find myself suspicious of an ulterior motive with this study. It says the sample group included one murderer and one rapist, and I can't get over the feeling that somebody was interested in some single particular truth in the study. I also wonder if their conclusion - that schizophrenics make an active effort to lie, involving "executive decision" might potentially be used to make an argument that they know what they're doing is wrong, and hence are not legally insane. I'm likely wrong about where or what, but I smell something funny here. Wnt (talk) 19:59, 16 April 2011 (UTC)

Nationwide ground stop effect

After the September 11 attacks, a nationwide ground stop was ordered at all US airports, which lasted for several days. Our article about this is at Security Control of Air Traffic and Air Navigation Aids. At one point, I read that after a couple of days of no commercial (nor GA) air traffic, there had been a small average temperature increase that was attributed to the nationwide ground stop.

Has anyone compiled other studies or analyses, of atmospheric effects or any other effects, of the nationwide ground stop? Comet Tuttle (talk) 19:32, 16 April 2011 (UTC)

There is often a temptation to wrongly infer causation from correlation. Edison (talk) 19:39, 16 April 2011 (UTC)

Sounds like the sample size might be too small to determine if there is even a real correlation. StuRat (talk) 19:43, 16 April 2011 (UTC)

Christ, you guys, I wasn't born yesterday. I'm under the impression the claimants of the above weren't, either, though I could be wrong and it could be some news reporters speculating or something. But I seem to remember that atmospheric scientists were said to be excited about getting data from this event that would be unlikely to ever recur, and a definite temperature increase attributable to the stop was said to be one of the findings. Comet Tuttle (talk) 20:19, 16 April 2011 (UTC)

I heard that they were interested in how jet exhaust contributed to cloud formation, and a few days without jets gave them a nice "control", which they lacked before. But extrapolating from that to it having an effect on the global temperature is new to me. StuRat (talk) 02:50, 17 April 2011 (UTC)

You are looking for this or this. There may be other papers too, but that was what I found first. People have definitely looked at this issue. Dragons flight (talk) 21:05, 16 April 2011 (UTC)

I'd go with the 2nd paper, which says that it's difficult to draw conclusions over such a short time period, since local weather patterns have far more effect. StuRat (talk) 03:11, 17 April 2011 (UTC)

Antarctic ice sheet

Hi. What are the values of pressure, temperature and ice density over the rock of Antarctica beneath the ice, assuming 2.2 km of ice depth and bedrock elevation of 150 metres above sea level? Thanks. ~AH1 ^(discuss!) 20:41, 16 April 2011 (UTC)

Roughly 0.92 g / cm³ and 20 MPa (200 atm). Temperature will depend strongly on local conditions (e.g. surface temperature, geothermal flux, ice convection), but somewhere between -30 C and 0 C typically. Dragons flight (talk) 22:29, 16 April 2011 (UTC)

3 science questions

What is the bond that holds salt molecules together with water molecules and what is the most efficient way to break these bonds leaving the water by itself? Would bombarding the nucleus with alpha particles move the element up the table of elements and would high voltage electricity have a effect on this? Could waste materials be heated up to a high enough temperature leaving all the elements of the waste by themselves then could these be filtered by their density? —Preceding unsigned comment added by 82.38.96.241 (talk) 21:39, 16 April 2011 (UTC)

I'm thinking that moving up the table would involve cold fusion. No?190.56.105.59 (talk) 23:51, 16 April 2011 (UTC)

I believe that sodium chloride has an ionic bond, but I guess that's not what you were asking. As for how to separate water and salt, heat the water until it evaporates, using the Sun, leaving behind the salt. Of course, if it's the water you're after, then other desalinization methods work better. StuRat (talk) 02:40, 17 April 2011 (UTC)

For the first question, see solvation. In the case of polar solvents (like water) dissolving charged particles (like salt), the ion-water bonding is ofter thought about in terms of dipole moments and electrostatic interactions (like the above mentioned ionic bond, but much weaker). More detailed treatment would also consider the covalent nature of the solvent-ion bond.

For your second question: One typical way to remove charged particles is through ion exchange. Distillation is another, which requires not just breaking the water-salt bonds, but also the water-water bonds. Finally, in reverse osmosis, a pressure gradient across a semipermeable membrane is used to remove dissolved substances. Distillation (particularly Multi-stage flash distillation) is currently the most used method in the desalination of water, with reverse osmosis the second preferred method. Both methods require large amounts of energy to purify water: distillation takes about 23-27 kWh/m³ of water [27], while reverse osmosis systems are probably only somewhat more energy efficient. Buddy431 (talk) 03:56, 17 April 2011 (UTC)

If this article on reverse osmosis is to believed (and the calculations at least look plausible) the theoretical maximum efficiency in getting pure water from sea water through reverse osmosis is less than 1 kWh/m³, considerably more efficient than the 23-27 used in flash distillation. However, real reverse osmosis desalinization plants apparently operate at close to 2-4 kWh/m³ [28] [29]. These values are still much more energy efficient than the distillation plants, though I think distillation plants are easier to scale up to large sizes (the total volume of desalinated water from distillation is greater than from reverse osmosis, even though there are more reverse osmosis plants, if our article is to be believed). Buddy431 (talk) 04:15, 17 April 2011 (UTC)

Freedom of navigation in the Earth's outer core

Is there any way to predict whether the Earth's outer core is free of strands of solid material? In particular, the Earth's inner core may rotate at 1 revolution per 400 years. Is there any chance that some "mountain" poking out from the inner core might ram into some crystalline strand poking in from the mantle and suddenly the whole inner core is stopped or pushed off center? If so, would this have noticeable effects for those on the surface? Wnt (talk) 22:58, 16 April 2011 (UTC)

Not sure about the Earth's core, but there is some evidence that giant impacts may have perturbed the Earth's interior, causing giant mantle plume eruptions on the opposite side of the impact point, see e.g. here.

Hmmm, the formation of antipodal craters involves the coalescence of waves travelling along the surface of the Earth which comes together. But do these also affect the deep mantle? Wnt (talk) 01:04, 17 April 2011 (UTC)

Also if this actually occurs then it could cause not only plume erruptions but also magnetic reversals. Phalcor (talk) 23:34, 16 April 2011 (UTC)

Any body remember any periodicity info on magnetic reversals.Phalcor (talk) 23:42, 16 April 2011 (UTC)

Our article magnetic reversal talks about the frequency and timing of them. DMacks (talk) 23:48, 16 April 2011 (UTC)

I think there is persuasive modeling of magnetic reversals with a simple liquid outer core model - though the disruption I'm asking about, if plausible, could cause all sorts of weird phenomena. Wnt (talk) 01:01, 17 April 2011 (UTC)

Sounds like you're concerned about navigation. Are you planning to take a magma proof submarine down there? A little early I think caus. nobody knows yet.190.148.132.157 (talk) 03:49, 17 April 2011 (UTC)

April 17

Does FRET work on IGE?

Does Förster resonance energy transfer work on induced gamma emission? Specifically, for purposes of sci-fi, I'd like to rely on "metatope batteries" in which covalent or ionic compounds of elements with nuclear isomers are used to break up the energy from one into another in diminishing steps until fissionable energy is broken down to a usable chemical scale. (I think that the range, which varies by the sixth power of distance, is a function of the virtual photons, rather than the size of the emitting/receiving particles, but I'm not 100% sure) Wnt (talk) 03:27, 17 April 2011 (UTC)

How to cheat reading eye chart?

I'll start with lenghtly explenation, if you don't want to read it all just cut to the question in the end :) I have nystagmus, I did some research on it and noticed that many people with it can't drive just because they need to be able to read number plate from 20 meters away. Now I don't intend to get drivers licence any time soon, but I don't think my vision is so bad that I wouldn't be able to drive. I also believe that eye charts are crapy way to test visual acuity. So I did some research - in my country you need acuity if no less than 0.5 to be able to drive, pretty sure they use eye chart for testing. I recently got myself contact lenses (I also got astigmatic myopia), so I developed a theory on how I could cheat the eye test. I imagine nobody would ask to check the power of my contact lenses and you can buy any contact lenses you want online. The big idea is that using viciously owerpowered lenses for duration of the test would turn my eyes into binoculars. The problem, besides widely known tale that wrong glasses can make you ill, is that I noticed that my current contact lenses make things look slightly smaler, I'm not sure if it is from blurrines reduced or because of lenses themselves - you know how things look smaler when you look trough magnifying glass from distance - which is making me question my theory - maybe overpowered lenses would instead make chart appear mycroscopic. The question - is there any way to shortly improve vision for sole purpose of reading as much of the eye chart as possible? —Preceding unsigned comment added by 46.109.116.140 (talk) 03:23, 17 April 2011 (UTC)

Overpowered lenses will give you blurry vision, not zoomed in vision. Lenses adjust where the focus of light is inside your eye. For most people, it does not fall directly on the retina. Your prescription will be the focus in or out to place the focus directly on the retina. If you increase the power of your lens, you will move the focus too far and end up with blurry vision. -- kainaw™ 03:26, 17 April 2011 (UTC)

Wikipedia has an article about pathologic nystagmus that describes actual therapies - I'd say I hope you've explored those, but actually, I suppose it would be better if you haven't since then you have an obvious alternative to cheating the test. Best to be able to read the speed limit signs, road construction, etc. I don't know if there are specific stimuli that trigger the vibration for you - might there be some alteration to the test environment you might be able to request, so that you can pass the test that way? Wnt (talk) 03:36, 17 April 2011 (UTC)

Oh, one example of a tech to pass the test is a toric lens for astigmatism - too thick and unpleasant IMHO for long-term use, but bearable for a few hours. Or eyeglasses, of course. Have you tested how well you do at distant reading with vision fully corrected? Wnt (talk) 03:44, 17 April 2011 (UTC)

Hear's an idea. Why don't you take a real pair of binoculas with you to the eye test. probably nobody would notice.190.148.132.157 (talk) 04:10, 17 April 2011 (UTC) `