Wikipedia:Reference desk/Archives/Science/2009 June 29

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June 29

God Delusion question: Infinite regress of multiverses

In The God Delusion, Richard Dawkins suggests that this universe is just one of many in a multiverse, chosen from among them by the anthropic principle. If this is true, don't we need to explain how the multiverse came into existence, and possibly how it became finely tuned to produce universes? Won't this ultimately lead to a multi-multiverse and an infinite regress? And couldn't the same infinite regress also serve to explain the existence of a God, with each god having been created by an older and more complex God? NeonMerlin 02:43, 29 June 2009 (UTC)

That multiverse theory isn't meant to explain the existence of the universe, just the fact that it is so remarkably fine-tuned to support life, so the reason for the existence of the universe/multiverse is still an open question. I'm not sure in what way a multiverse would need to be fine-tuned, though. Fine-tuning refers to the physical constants being just right for life as we know it to evolve. I'm not sure the multiverse would have any such constants - everything can vary from one universe to another. --Tango (talk) 02:48, 29 June 2009 (UTC)

The argument you propose NeonMerlin is an old one. See Cosmological argument. Dawson's book has two flaws; one it ignores the role of pure faith in people's understanding of God. Second, it confuses people's understanding of creation with the creation itself. If we accept God as axiomatic (that is, we take his existance on pure faith) than our changing understanding of creation does not reduce or minimize his role in our lives, as many claim is happening. God is unchanging, creation always happened the same way. All that changes is our more and more finely tuned understanding of it. --Jayron32.talk.contribs 03:01, 29 June 2009 (UTC)

Dawkins' book does indeed address the issue of "pure faith" (I have no idea about "Dawson" however! :-) - you should probably go back and re-read it.

If you insert the god hypothesis as an axiom - then of course it doesn't change the result - which is the universe we can see and measure today. If adding that axiom did make a difference - then we'd have proof that god exists. Since we don't have that proof, inserting that unnecessary axiom is kinda pointless. It's like taking the beauty of euclidean geometry and adding "Banana's are Yellow" as an additional axiom ("All right angles are equal", "You can extend a straight line"..."Bananas are yellow")...it's true - but it's unnecessary. Basing a theory of everything on the circular argument "I believe it because I believe it" (aka "faith") really doesn't help - and the beliefs of some subset of one kind of organism is truly irrelevant compared to the universe as a whole. There are an infinite number of theories like that - but none of them is any better than any other - so we have to fall back on Occams' razor and pick the simplest. If it turns out that we NEED to add some other fundamental thing in order to explain everything - then we're not precluded from doing that (we're adding dark matter and dark energy, for example...we NEED them in order to explain certain observations). But we have no need to add one or more gods in order to explain everything we see...no more than we have a need to add "Bananas are Yellow" into our fundamental laws of geometry in order to understand triangles and circles and such. SteveBaker (talk) 03:34, 29 June 2009 (UTC)

Exactly; which is why we don't really spend much time dealing with God as a scientific construct. He cannot be proven or disproven using the tools of science, and yet the human experience is not all science. Art, music, beauty, and yes, faith, make up a significant portion of the human experience; all of which are really quite untouchable by scientific inquiry. It doesn't make science less powerful, or them less important. Its just the matter of recognizing that people's lives aren't merely made up of a neverending quest to describe the details of the mechanisms of the universe. Certainly, that is an important part of life, but not the totality of it. See Stephen J. Gould, esp. Rocks of Ages, which I found more satisfying that Dawkins... --Jayron32.talk.contribs 02:12, 30 June 2009 (UTC)

You are confusing what humans do with what humans can study using the tools available. I'd certainly agree with the bare statement that: "the human experience is not all science" - after all, most people are not experiencing the practice or findings of science most of the time - sometimes they're vegged-out in front of the TV watching mindless soap-operas for example. But that doesn't mean that I accept what you're trying to say: That human experience cannot be studied and understood scientifically - it most certainly can - there are very few "No Go" areas for science - and those that do exist are of our own discovery (eg you can't know what happens inside the event horizon of a black hole). But we are actually starting to have a pretty good handle on art, music and beauty - and are making inroads in the study of faith too.

We have discovered that (for example) the perceived beauty of a human face depends on how close it is to the average of all human faces...and that in all likelyhood, the reason for that is that the less 'average' a face is, the more likely it is that the person is somehow sick or possesses some kind of genetic problem that makes them less desirable as a mate. It follows that the experience of beauty is quite possibly a very simple evolved behavior. A beautiful plant is one that's more likely to be useful to us - a butterfly is beautiful but a housefly isn't - because the former is harmless and the latter carries diseases. "Cute" animals have eye-to-head-size ratio's that are closest to human babies. We are discovering LOTS of things about the human experience of "beauty".

These things are not some wonderous mystery that science is somehow locked out of - they are simply harder to study than some other subjects given the tools that we've had at hand throughout most of the history of science. But now that we have things like PET scanners that can see what parts of the brain light up when art/music/beauty/faith are contemplated, you can bet that it won't be long before we start to understand and explain those things. Check out the book: "Why we believe what we believe" by Andrew Newberg for an example of work going on in this area of scientific enquiry. Human brains and thought processes are hard to study - but that doesn't mean we can't do it. SteveBaker (talk) 13:06, 30 June 2009 (UTC)

Well, you are still making the assumption that faith is somehow an invalid or unneccessary aspect of the human experience merely because its effect on human physiology can be described by science. No matter how much detail one can ascribe to a phenomenon, one cannot neccessarily equate that detail with purpose. That we have religious faith, and that we can describe how that religious faith affects the brain does not mean that somehow that religious faith is less "real" or an "invalid" way of experiencing the world. That we can show how ones relationship with God affects the body does not mean that that relationship does not exist. --Jayron32.talk.contribs 14:43, 30 June 2009 (UTC)

Not at all - but I am saying that (perhaps) in a few years time - we might show that a particular brain chemical in a particular place causes faith. Would you be so convinced of the importance of this emotion if we were able to turn it on and off with a little pink pill? You take the pink pill - you are immediately flooded with this profound feeling of religious joy. You take the yellow pill and it goes completely away - god feels about as real and as relevent to you as the tooth fairy. That's a possible result of current studies - would that mean that faith is not something that some supreme deity projects onto us - but instead just the consequence of some unpronouncable protein? If this seems fanciful - check out psilocybin - which produces an effect not dissimilar to the pink pill. SteveBaker (talk) 00:47, 1 July 2009 (UTC)

There are other reasons to consider the multiverse idea - it provides an elegant explanation for some of the wierder aspects of quantum theory (see: Many worlds hypothesis) - but Dawkin's idea is not much more than a means to avoid having to invoke the anthropic principle - which says that the universe isn't the way it is because of the need to support life - but life is here because the universe happens to be the way it is. If it were some other way then there would be no creatures like us to remark on the fact. In most versions of the many-worlds/multiverse hypothesis, they all start at the same instant with the same big-bang and the same exact initial configuration - only becoming different as random quantum events happen differently in each 'copy'. Hence, no special new science would be required to explain the multiverse than to explain a single universe. No god or gods are required in any event. For an interesting alternative way to think about multiverses, I recommend Neil Stephenson's (fictional) book "Anathem". Our article about the book does a poor job of explaining the idea of configuration space/phase space/state space upon which the book ultimately hinges. Basically, he's saying that every possible state of the universe (of which time is a property) simultaneously exists - making our progression through time an essentially illusory property of the instant of time we're in. This includes states that are "unreachable".

At any rate - while most of these ideas allow for the possibility of a god or gods, none of them require such a thing. As such, gods are no more necessary than pink piano-playing aardvarks on the far side of the moon...no more necessary than an infinite number of other things that might be true. Occam's razor tells us to pick the simplest answer - and that says "no gods" - and arguably "no multiverse" either. SteveBaker (talk) 03:17, 29 June 2009 (UTC)

(ec)The logic behind the anthropic principle is that every planet or universe where intelligent life arises must be conducive to intelligent life, so the fact that our universe is just right to support life is a logical necessity and not a sign of God. However, how the fine-tuning was done is not yet known. There are a few possibilities:

1. An all-powerful God did it.
2. Our universe is one of many multiverses.
3. Something else entirely. Perhaps a talking teapot made the universe 200 years ago and erased all evidence of it?

None of these possibilities have any supporting evidence, so scientifically, none of them are more plausible than the others. Philosophically, the second possibility is more satisfying because it proposes a Big-Bang-like beginning for the multiverses, and this beginning has almost no complexity. The first possibility, on the other hand, would require a complicated intelligence to exist at the very beginning of the universe. However, this is philosophy, and philosophy is useless for just about everything. All three possibilities are unproven; until somebody comes up with experimental evidence, all three are rubbish.

Jayron: Does Dawkins ignore the role of faith? I would have thought that the whole book's point is to address the stupidity of believing in God with no evidence whatsoever. --Bowlhover (talk) 03:47, 29 June 2009 (UTC)

So the problem is - why do the values for certain fundamental constants appear to have exactly the values that are needed for life to exist - if they had different values, then there would be no life. Well, there are lots of possibilities:

• That there is a true, underlying reason why those numbers have to be like that - a reason we have yet to discover.
• That all possible values for these constants show up in an infinity of universes - allowing the weak anthropic principle to explain why we are living in the good universe.
• That the values were randomly determined at the instant of the big bang - and we just got lucky.
• That we are incorrect in assuming that no life is possible with other values for these constants. Do we really understand ALL of the implications for a 10% larger charge on the electron? We haven't studied that scenario in any great detail - there are a few brief dismissals of the possibility of atoms forming - but maybe something else forms instead - and life appears from the something else? Is it possible that life of other kinds are possible in these very strange universes? If so, it might mean that intelligent life (although not "as we know it") appears in almost all configurations of the universe - and no "coincidence" is required.
• ...Or some supernatural entity made the universe especially for us.

The last of these is unsatisfying on many levels: How did the creator get created? Why does the place where the creator exists have exactly the right parameters for the creator to exist? This isn't any kind of an answer at all - it's just regressing the question back one more step for no particularly good reason. SteveBaker (talk) 04:28, 29 June 2009 (UTC)

There are different types of multiverse theory. The many-worlds interpretation of quantum mechanics is independent of the kind of multiverse Dawkins is talking about. You may want to read up on the distinction between the strong and weak anthropic principles. Multiverse theory allows us to do away with the strong version (which is very difficult to justify) and means we can just use the weak one (which doesn't need justifying at all, common sense is sufficient). --Tango (talk) 04:05, 29 June 2009 (UTC)

Seashells (Clam/Giant Clam) that have morphed

I live on a Pacific island and make jewelry from things that I find on the beach: shells, coral, sea glass etc. (no live animals taken). I have found whole, half and pieces of bi-valves that seem to have morphed into what looks like Marble. They are beautiful and the pieces that have rolled around in the surf are absolutely stunning! My theory is that the shells have been buried under extreme pressure in the sea bed and have morphed into Marble. If this is indeed correct I would like to share it with my customers who buy my creations but I don't have any proof. Can anyone provide me with the answer?Billyabston (talk) 02:52, 29 June 2009 (UTC)

I don't think that's how they are formed - shells under extreme pressure turn into limestone - and under even more extreme circumstances, limestone turns into marble - so the chemical composition of marble may not be all that different from your shells - which may explain the similarities in appearance that you're seeing. But after all of those extreme circumstances, there would be nothing left of the original shape of the material - it wouldn't look like a shell fragment anymore. SteveBaker (talk) 03:40, 29 June 2009 (UTC)

To go from the original aragonite of the mollusc shell to calcite doesn't take much burial but to completely recrystallise the calcite to make a marble requires quite high temperatures (rather than pressure) and by then it's going to be part of a rock. Although the original fossil shapes can be preserved in a marble, they normally get destroyed by ductile deformation, as calcite is a relatively weak mineral at elevated temperatures. As to what the OP found, I'm with Dauto below. Mikenorton (talk) 07:30, 30 June 2009 (UTC)

Are you talking about mother of pearl? Dauto (talk) 06:15, 29 June 2009 (UTC)

The shape of the mollusk survives. The walls of the shells have thickened and the weight has increased ten fold. The now morphed material has layers ranging from stark white to light gray. We have giant clam shells that have not changed into this material that I am speaking about and they are much lighter weight and have not thickened. Not Mother of Pearl either. Billyabston 20;57 30 June 2009 —Preceding unsigned comment added by Billyabston (talk • contribs) 09:00, 30 June 2009 (UTC)

Effects of higher gravity

Some works of fiction have adopted a theory that a human body forced to develop under greater weight will be much stronger than average if returned to a normal Earth environment. This is accomplished either by the use of weighted clothing (e.g. weight belts, wrist bands, leg weights, etc.), or by allowing the person to develop on planets with intrinsically higher gravity. Quite contrary to the fictional stories, I've heard comments that the prolonged use of external weights can actually damage ligaments and things, but I don't know how reliable those reports are.

I'm curious, have there been any studies (either theoretical or practical) on how terrestrial physiology would respond to a higher gravity environment? And would that response impart heightened strength and other benefits to a person then returned to normal gravity as imagined in those fictional works? My initial guess is that human physiology, having known only life on Earth, would be largely maladaptive under high gravity.

I also have this fanciful imaginary image of a rodent colony forced to live their entire lives in a 2g centrifuge. Has anyone ever done any real experiments like that? Dragons flight (talk) 07:26, 29 June 2009 (UTC)

There is a centrifuge being advertised for experimenters, and there was a centrifuge experiment in 1995 concentrating on the effect on rat temperature and mating. Many other experiments have been to determine changes in muscles, the liver, membrane integrity etc. Centrifuge experiments were also conducted on rats on the Russian satellites Cosmos 936 and Cosmos 1129. Our articles on these flights are single sentences which barely qualify even as stubs. - KoolerStill (talk) 12:00, 29 June 2009 (UTC)

I have seen archeologists report in National Geographic Magazine skeletons whose bones show enlarged muscle attachment points that they think are caused by the occupational stresses on galley slaves and bowmen. Sorry no references. Cuddlyable3 (talk) 13:23, 29 June 2009 (UTC)

Cool! My crazy rat experiment really gets done in real life. Dragons flight (talk) 02:08, 30 June 2009 (UTC)

Masturbation

How much calorie is lost during male masturbation (if the total time including erection and ejaculation is 6 min)? KnowledgeAbound (talk) 12:23, 29 June 2009 (UTC)

While you will burn calories, just as you would by sleeping, the amount you burn is negligible. A calorie is a big unit. For reference, there is a chart in the rehab room at our hospital that shows calorie burn per exercise. An average person doing a vigorous workout on the treadmill for 10 minutes will burn around 100 calories. So, compare that to about half the time while exerting far less effort. -- kainaw™ 12:33, 29 June 2009 (UTC)

If you did it with weights attatched to your wrist, what do you reckon about building up large muscles....Alaphent (talk) 12:36, 29 June 2009 (UTC)

You can do it while running on a treadmill. The question is limited to masturbation. It is not "What can I do while masturbating to maximize calorie burn?" -- kainaw™ 12:53, 29 June 2009 (UTC)

I was just interested after reading this in the possibility of masturbation as a form of excersise. Not interested in it as anything more than a curiosity though, mind Alaphent (talk) 13:05, 29 June 2009 (UTC)

Swimming consumes calories. Sperm swim. There are lots of sperm. Has anyone a figure for the calories ejaculated? Cuddlyable3 (talk) 13:08, 29 June 2009 (UTC)

According to Cecil Adams it's pretty small figure. [1] APL (talk) 15:45, 29 June 2009 (UTC)

It really depends on how you engage in it. Some people move a lot during masturbation, using their back, leg, and gluteal muscles, raising their heart rate, and breathing heavily. Others lie relatively still and mainly move just their hand. Some people may find it helpful that masturbation tends to cause the rapid release of endorphins, which reduces perception of muscle pain (this is why people often notice a sudden muscle soreness after sex). The ultimate limiting factor though is the duration - even running for 6 minutes just won't burn a lot of calories. You'd have to get the duration up to have a more significant effect (which you can do - masturbation for extended periods is possible). Even if you did this, though, it would make uneven use of your muscle groups, so it would be an incomplete workout for muscular strength, and it would be difficult to maintain an intensity suitable for cardiovascular exercise. Dcoetzee 04:22, 30 June 2009 (UTC)

Surely there's energy needed to produce sperm? And surely new sperm must be produced after masturbating? —Preceding unsigned comment added by 81.11.170.162 (talk) 09:05, 30 June 2009 (UTC)

Not particularly, no. First of all, sperm constitute only a very tiny percentage of the volume of semen - mostly it's water. Also, sperm are continuously produced and reabsorbed. They don't really live long enough to just hang around waiting forever. Dcoetzee 20:05, 30 June 2009 (UTC)

Esterification Mechanism

In an esterification reaction between a carboxylic acid and an alcohol (I know they are normally carried out with acyl chlorides) the mechanism I have shows an electron pair moving from the carboxylic acid OH to the carbonyl carbon, and then an electron pair from the carbonyl double bond (NOT the O) moving to generate a bond with a H⁺ catalyst. This protonation forms a more reactive electrophile for the alcohol to attack. It looks like a carboxylic acid group with a H attatched to a positivly charged O. I am fine with this, however my question is why doesn't the carbonyl O use a lone pair to form a bond with the H⁺? As this would give exactly the same intermediate. This movement is possible, and is neccessary for the acid catalysed formation of hydrates/acetals/hemiacetals etc....basically any nucleophilic carbonyl reaction that requires a stronger carbon electrophile. Alaphent (talk) 12:35, 29 June 2009 (UTC)

EDIT - The wikipedia on Fischer-Speier esterification shows the second mechanism I proposed. Now I am really confused....Alaphent (talk) 12:43, 29 June 2009 (UTC)

A carboxylic acid group is stabilized by resonance: "an electron pair moving from the carboxylic acid OH to the carbonyl carbon" (and back again, switching between those two forms) happens at all times whether or not H+ (or anything else) is present. Well technically, it doesn't actually happen at all, "reality" is some single average/intermediate structure looking sort-of like both cases:) Because both forms are already present, you can draw either one as the reactant in the protonation step. In one sense, it's more likely the O- form that reacts ("the most negative thing is most likely to be protonated" and "less stable/charged form more likely to react than totally neutral form"). But the neutral form is more stable and a better representation of the starting structure, so some prefer to use that as the reacting form directly or via explicit resonance. And it totally doesn't matter which mechanism you use, because the result is the same. The protonated form is also involved in resonance via the same first step you described. DMacks (talk) 17:01, 29 June 2009 (UTC)

The lewis-electron-pushing-arrows mechanism does not really capture how the electrons flow , but rather show a sort of "shortest path" from the starting and ending state. In reality, the electron density probably moves from between the carbon-oxygen atoms to between the oxygen-hydrogen atoms as described, but rather than attacking from that location, the electrons probably flow around the oxygen atom to form the new bond to hydrogen. If you could find an electron-density-flow animation of some sort, it would make more sense than the simple lewis arrow diagrams, which are an approximation of reality meant to simplfy stuff for people working with pencils and paper to model the processes, and not the sort of advanced computer modeling we can do today... --Jayron32.talk.contribs 02:07, 30 June 2009 (UTC)

Cities on the Moon

Assume in the future there are large cities on the moon (approximately the population and size of the Eastern Seabord of the US). During a new moon (also assume these cities are on the side facing us) would a person be able to see city lights with an unaided eye?

Also, how small of a lightsource could it be before you wouldn't be able to see it? Assuming cities there are similar to those on Earth (in terms of density, light output per capita)what population size would be required before you could see it?

Finally, what about Mars (I imagine you'd need a telescope but even than what would it take to be visible)? TheFutureAwaits (talk) 15:04, 29 June 2009 (UTC)

A city on the moon would be several arcseconds in angular diameter from Earth, so would appear as a point source of light with the naked eye (you could probably resolve a few details with decent binoculars). Unfortunately, I can't find any details about the amount the minimum brightness required to be visible to the naked eye (it's about magnitude 6, but I can't find a way to convert that to luminosity - anyone?). As for Mars, I don't think you would be able to see much. Since Mars is further away from the Sun than us it doesn't have phases, the side facing us is always lit. There might be a dark bit on one edge depending on the relative positions of the Earth and Mars, so I guess with a decent telescope you might be able to see some lights there, but they would only be visible for a short amount of time. Just like Venus is only visible from Earth for either a short time after sunset or a short time before sunrise, the same is true of Earth from Mars, and it's only during that time that you would be able to see the light from a given Martian city. --Tango (talk) 15:52, 29 June 2009 (UTC)

While hardly definitive, The Straight Dope quotes Apollo 12 astronaut Alan Bean as saying:

"The only thing you can see from the moon is a beautiful sphere, mostly white [clouds], some blue [ocean], patches of yellow [deserts], and every once in a while some green vegetation. No man-made object is visible on this scale. In fact, when first leaving earth's orbit and only a few thousand miles away, no man-made object is visible at that point either."

— Alan Bean

I'm assuming that we'd have similar luck, or lack thereof, resolving lunar human details from Earth. If nothing else, there's a good chance that Earthshine will wash out detail. As our article notes, it's at its strongest near the new moon, counterbalancing much of the benefit of a generally darker moon. I don't see a specific reference for the equivalent magnitude, but it's certainly higher than mag 6, since it's easily visible in my generally urban area. This photo provides a good comparison and this paper suggests that its magnitude may be on par with the brightest stars in the sky. — Lomn 18:03, 29 June 2009 (UTC)

At new moon, the Sun, Moon, and Earth are almost in a perfect line. It's absolutely impossible to see cities on the Moon at this time; in fact, the Moon itself is impossible to see since it would be within a few degrees of the Sun. The "newest" moon that has been sighted was 12 hours old [2], but that sighting was only possible with a telescope and lots of amateur astronomy experience. For the few days following or preceding new moon, the Moon can be seen but it stays close to the Sun; seeking out dim lights on the dark side would be very difficult.

Several days before or after, it would be possible to see the Moon when the Sun is well below the horizon, but ask an amateur astronomer and they'd tell you dim stars are easily washed out by the Moon if the Moon is anywhere in the sky at all. Since the cities to be looked for are on the dark portion of the moon, and that's less than half a degree from the lit portion, the limiting magnitude would probably be very low; based on personal experience, I'd be surprised if it were higher than 2 without optical aid. With a 6-inch telescope, though, even 8th magnitude shouldn't be a problem.

For something on the Moon to appear to be 6th magnitude, it'd have to put out 15 GW (back of the envelope calculation)--about 70 times higher than the total wattage of artificial light that the entire UK sends skywards. Even 8th mag would require 2 GW, which is lower but still much too high. Add to this the fact that electrical power on the Moon will presumably be scarce, so the lunar colonizers will make sure they don't waste as much energy sending light upwards as Earthlings do light polluting their skies, and you get an idea of how dim lunar cities will be.

So sadly, it probably won't be possible to see city lights on the moon without a very powerful telescope; they're just too dim. However, if a large portion of the lunar landscape is reworked--"large" meaning more than a few arcseconds--and the reworked area is much more colorful, reflective, or otherwise distinctive than the asphalt-like moon rock, it might be possible to see this area using a telescope while it's on the lit portion of the moon. --Bowlhover (talk) 20:22, 29 June 2009 (UTC)

I have changed your ref-tag into an external link since we do not have a References Section on the Science Desk. Nimur (talk) 13:18, 30 June 2009 (UTC)

Thanks Bowlhover, that was a very interesting read! Quick question, do you know how this would work in reverse (ie can you see the cities on Earth from the Moon?) TheFutureAwaits (talk) 20:42, 29 June 2009 (UTC)

Yes, that shouldn't be a problem. The interesting thing about the Moon is that it's tidally locked to the Earth, so to an observer on the Moon, the Earth would always be in the same position. While the Sun and the other stars move slowly across the sky due to the Moon's rotation, Earth would go through its phases once a month but always remain at the same altitude and azimuth. That's great for lunar telescope users because the telescopes don't have to be tracked; they can remain absolutely stationary and still never lose sight of Earth. This is actually not absolutely true due to libration, but unless someone is planning to stare at Earth for days on end, it's a good enough approximation.

The Moon also doesn't have an atmosphere, which means there is no scattering of sunlight or Earthlight. As a result, no matter where the Sun happens to be, the surrounding sky is always pitch black. As long as the Sun, the Earth's lit portion, and any objects illuminated by them are kept out of your eyes' field of view, your eyes will eventually dark adapt to the point of being able to see dim stars.

Based on the figures for U.K. light pollution, a city like Las Vegas should be magnitude 11-12 at nighttime. Since cities are typically several arcseconds across when viewed from the Moon, Las Vegas's size and brightness would be similar to that of a dim galaxy. A 6-inch telescope could probably pick up downtown, and with larger telescopes it would be possible to see some of the suburbs. Very little detail is visible with objects this dim, however, and seeing color would certainly be impossible because the cone cells require a lot of light to activate. Las Vegas would look like a dim, virtually featureless patch of light that's barely distinguishable from the surroundings.

Viewing Earth's cities is a bit easier if those cities are in daylight. In that case, they would stand out as grey patches in the surrounding green forests or blue lakes/oceans. Because you'd be looking through Earth's atmosphere, astronomical seeing is just as much of a concern as it is for astronomers on Earth, and seeing typically limits a telescope's resolution to 2 arcseconds. That corresponds to 3 km on Earth's surface. To get an idea of what Earth would look like, see these Blue Marble images. Click on an 8 km/pixel image and zoom in on your browser. Do the same for an 2 km/pixel image. The size and detail of what you see approximately matches the size and detail a lunar observer can expect with an amateur telescope and 140x magnification. --Bowlhover (talk) 10:10, 30 June 2009 (UTC)

The perfect viewing time would be a total eclipse of the moon during midnight. —Preceding unsigned comment added by 84.187.70.226 (talk) 20:44, 29 June 2009 (UTC)

Ah, crap, I didn't know that. The atmosphere refracts too much light around the earth. —Preceding unsigned comment added by 84.187.70.226 (talk) 20:51, 29 June 2009 (UTC)

No, you're correct -- a total lunar eclipse is the best time to see this sort of phenomenon. It's just that even then it's still a long shot (the paper above estimates that the lunar surface remains roughly magnitude 0; only 4 stars in the night sky are brighter. — Lomn 21:03, 29 June 2009 (UTC)

Hmm. On one hand, the Moon is much brighter during a lunar eclipse than the dark, Earthshine-lit portion of the Moon is during other phases. On the other hand, during an eclipse there is no bright sunlit Moon to light-pollute the sky. I don't know which effect dominates, but if I had to guess I'd a lunar eclipse would indeed be the best time to see lunar cities.

Some food for thought: maybe a solar eclipse would work as well? --Bowlhover (talk) 10:10, 30 June 2009 (UTC)

No, the moon is darker during a lunar eclipse than is the Earthshine portion normally. A solar eclipse would still be dominated by solar phenomena. — Lomn 12:14, 30 June 2009 (UTC)

Not in my experience. Lunar eclipses vary widely depending on atmospheric conditions, but most I've seen have been pretty bright. Earthshine is very dim indeed. --Tango (talk) 03:02, 1 July 2009 (UTC)

Quoting from the source linked above, "...indicates that earthshine on the Moon is several times brighter than the totally eclipsed Moon and should easily be visible except for the fact that it may be overwhelmed by the brightness of the sunlit Moon", which noted earlier in the source, is some 100 times brighter. — Lomn 13:02, 1 July 2009 (UTC)

Ah, that's a good point - a totally eclipsed moon will be in a dark sky, an Earth-lit moon is always right next to a Sun-lit moon. That probably explains why my naked eye observations differ from the actual numbers. --Tango (talk) 01:52, 2 July 2009 (UTC)

Interesting. I have photos of two lunar eclipses, along with the EXIF data and the camera I took them with, so I'll try photographing earthshine with the same settings and see what I get. --Bowlhover (talk) 03:37, 2 July 2009 (UTC)

wind turbine numbers

How many wind turbines have been installed in the US in the past year that are 1MW or larger? 65.121.141.34 (talk) 15:41, 29 June 2009 (UTC)

[3] (page 14) shows the number of windmills installed in 2008 and the total MW for each windmill producer. But it doesn't breakdown which ones are more than 1 MW. 5105 windmills larger than 100kW were installed last year for 8554 MW total, or 1.69 MW average. Rmhermen (talk) 19:01, 29 June 2009 (UTC)

Page 19 of that document has a graph of installed sizes but you can't get exact numbers from it either. Rmhermen (talk) 19:35, 29 June 2009 (UTC)

Ethanol molecule structure

There is a picture in Ethanol article that shows the hydrogen bonding: File:Ethanol-xtal-1976-3D-balls.png. It can be seen that in some molecules the hydrogen atom near the oxygen is located symmetrically, and in others it is rotated. Does it mean that these are different isomeres of ethanol? Or may be this angle isn't strictly defined and the hydrogen atom can rotate rather freely around the oxygen? Btw, on Wikimedia Commons there is an entire category with ethanol molecule representations, which also locate that hydrogen atom differently.--Ring0 (talk) 21:21, 29 June 2009 (UTC)

All of the bonds in an ethanol molecule can freely rotate. See: conformational isomers. --Mark PEA (talk) 22:14, 29 June 2009 (UTC)

Punching completely through someone

In various comics I've perused over the years, sometimes obstensibly human characters have literally punched straight through human opponents. While this obviously isn't supposed to be realistic, what sort of level of force would be required to do this? Is it feasible for even the strongest human to punch clean through someone else?

I'd imagine part of the issue would relate to where the punch was aimed (easier to punch through soft abdominal tissues than the sternum or skull) and the physical condition/size of the punchee (smaller/weaker target easier to punch through)

We have the additional problem of whether if such a punch due to Newton's third law would cause serious injury to the puncher. Any ideas anyone? Exxolon (talk) 22:41, 29 June 2009 (UTC)

Sorry. I remove my comment. (In response to below.) Bus stop (talk) 00:19, 30 June 2009 (UTC)

I'm not sure if that answer belongs on this page, it was neither helpful or humorous. This person clearly has a reasonable level of understanding of physics, and your answer just takes the mickey to be honest. Alaphent (talk) 23:24, 29 June 2009 (UTC)

No worries mate, I'll leave the above to stand though if that's ok? Alaphent (talk) 00:33, 30 June 2009 (UTC)

Sounds OK to me, mate. Bus stop (talk) 00:39, 30 June 2009 (UTC)

There would have to be something holding the person being punched still, otherwise they would just be thrown backwards. --Tango (talk) 00:27, 30 June 2009 (UTC)

I seem to remember reading somewhere (no source, sorry - may have been here) that human flesh takes on similar characteristics to rubber when struck hard and fast. I'd say that trying to punch straight through a person would be much like trying to punch straight through one of those thick rubber gym mats. I have seen football (soccer) injuries where someone's foot has been driven straight through someone else's leg (not just at the joint either), leaving the thing dangling there by a thread - but that's a rather different situation. --Kurt Shaped Box (talk) 00:32, 30 June 2009 (UTC)

I guess that's more ripping off than ripping through, so is quite different. --Tango (talk) 00:48, 30 June 2009 (UTC)

Expansion - I imagine part to the fundamental physics is that it's much easier to push a small, hard and sharp object through someone that a large, soft and blunt one. The concentration of force at a point is the key. For instance a moderately strong person could lunge with a rapier and pierce completly through a human body, assuming they missed the bones - the question is can it be done with the fist, a much larger, softer (relatively) and blunter instrument? Exxolon (talk) 00:56, 30 June 2009 (UTC)

I don't think that even the strongest punch could go completely through someone, because the force is not strong enough and because it's spread over the area of the puncher's fist. A karate kick, though, might go through soft tissue or even through bone, provided that the entire force is concentrated at the kicker's heel and applied at a right angle to the target (I've seen someone in my team get his head busted open in just this way -- OUCH!), but that's a whole different situation too. 76.21.37.87 (talk) 01:57, 30 June 2009 (UTC)

If it's just a matter of pressure - then we can look at the cross-sectional area of a rapier (maybe 20mm²?) and the cross section of a fist (maybe 5000mm²) and say that it takes 250 times as much force? But I strongly suspect that's an under-estimate. The rapier can slide off and slip between bones - the fist really can't do that. It's clearly impossible. But even if some super muscle-bound freak could apply that much force - you'd have to expect the damage to his fist and arm to be comparable to that of the victim. SteveBaker (talk) 02:03, 30 June 2009 (UTC)

I have this mental image of the MythBusters, their chicken gun, and the inevitable pig carcass... 62.78.198.48 (talk) 04:03, 30 June 2009 (UTC)

So that raises the obvious question: if a mere human could not punch through a person without significant harm to themselves, what about a Terminator-style humanoid made entirely out of steel or some other hard metal? Could they pull it off, or would some other unexpected result occur? Dcoetzee 04:13, 30 June 2009 (UTC)

Mythbusters shot canon balls through human analogs at 300 or 400 mph. The canon ball was probably of similar size to a fist, so if you could get a metal fist going that fast, I'm sure it is possible. Engineering a robot capable of getting that much power in it's punch would be very challenging though, and the fist would need to be quite solid to avoid also breaking it in the process. Dragons flight (talk) 06:54, 30 June 2009 (UTC)

If a barracuda 4 feet long can impale a human, and a 13 year old can impale himself on the bicycle handlebar under his own power, without a fall from a height or a car crash then a human should be able to impale a human. I think it is plausible that extended fingers might penetrate the front of an unmuscular abdomen if there was a full force strike. Sharp fingernails would doubtless aid the initial penetration. It would be hard to make it all the way out the back. The striking area would be far smaller than the typical cannonball so the force of the blow would be more concentrated. There would certainly be a chance of finger breakage. Google news archive has a horrible collection of impalement stories. Typically someone falls onto a fence or is thrown against a post, pipe, or railing in a train, car, or horse riding accident. (Iron spiked fences have caused countless unnecessary deaths.) If someone in the 1930's in Germany had fallen from an airplane and landed on Hitler's upraised arm, how far would the penetration be? Edison (talk) 23:20, 30 June 2009 (UTC)

I have been informed that the first person to refer to Hitler in a debate, loses, so I concede. As a consolation prize, I imagine it to be Hermann Göring that falls out of the airplane. Coincidentally, one of the Google News archive results for "impalement" was "BULLFIGHTER RECOVERING FROM GORING. Edison (talk) 05:41, 1 July 2009 (UTC)