Wikipedia:Reference desk/Archives/Science/2008 December 3

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December 3

Game Over

The title is a documentary by Kasparov chronicling his intrepid series of chess matches against Deep Blue. My understanding is that chess is a game of 100% logical strategy and 0% happenstance. Will there come a time when it is impossible for a human to beat a computer even in a single match?

If true, then I'd like to ask: if chess is a game that can be won in 3 moves, will there come a time when humans struggle to modestly even surpass this lower limit? Sappysap (talk) 00:39, 3 December 2008 (UTC)

To your first question, it's really more the player vs. the programmer rather than against the machine, and the programmers have huge advantages. "Theoretically impossible" (i.e. less chances than winning the lottery) is almost certain to happen, outright "impossible" seems unlikely. For the second, there are very limited situations where early checkmates can happen, and the number of permutations for less than eight or ten moves is pretty easy for a human to know all of the possibilities, and likely all of the "super early" checkmate possibilities are known. That a computer can determine all possibilities 50 moves later is where it has an advantage, a human simply can't juggle all that information. SDY (talk) 00:46, 3 December 2008 (UTC)

From our Deep Blue article "The Deep Blue chess computer which defeated Kasparov in 1997 would typically search to a depth of between six and twelve plies to a maximum of forty plies in some situations." -hydnjo talk 02:03, 3 December 2008 (UTC)

The mathematics seems to suggest that it will be impossible for a computer to ever work out the perfect game, there are just to many combinations (more combinations than there are electrons in the universe - you can prove that just stepping through each combination requires more power than is available in the universe). But certainly PC's could (and I believe they now do) always beat humans, that is within the coming decades a PC should be able to calculate to plies 70-100 which is way more than a human and the length at which most games are played out with, we just may never know the 'perfect' game, nor if one side can force a win.--Dacium (talk) 03:00, 3 December 2008 (UTC)

An unbeatable opponent would be one that had "solved" the game of chess, in the sense that the opponent has laid out all possible moves. For instance in the game Connect Four, the starting player is guaranteed to win if he/she plays perfectly. In checkers, only a tie can be guaranteed from perfect play. A solution for chess is beyond reach today, but all six-piece chess endgames have been solved, so the computer opponent may become "unbeatable" in the endgame phase. Also see Solved game. EverGreg (talk) 10:16, 3 December 2008 (UTC)

Because of the way chess computers are programmed, humans can still defeat even the most powerful by puzzling them with an ingenious innovation that they cannot recognise. However, because chess theory is today so well developed, true innovations are scarce and likely to be flawed. --Dweller (talk) 10:43, 3 December 2008 (UTC)

Something I've wondered: do chess programs have any concept of strategy, or do they always approach each move from scratch? AndrewWTaylor (talk) 13:11, 3 December 2008 (UTC)

Far as I know, the first possible moves in the game are stored in a database of best moves. For later moves it assigns a value to different pieces, so that losing a pawn in taking your tower is "worth it". Finally, it calculates a "tree" of moves and some of these calculations would be identical to what it needs to calculate for the next move, so it may keep on following a path in tree. All this could be called a strategy. EverGreg (talk) 13:35, 3 December 2008 (UTC)

There is a lengthy and interesting explanation of computer chess methods in our computer chess article. Certainly a computer chess program does not approach the game in the same way as a human player - but there is no reason to expect that it would (a plane does not flap its wings to fly). Does a computer chess program have a concept of strategy ? I guess that depends on your definitions of "concept" and "strategy". Gandalf61 (talk) 14:01, 3 December 2008 (UTC)

The truly VAST number of possible games (more than the number of particles in the visible universe) means that it'll NEVER be possible to compute a perfect solution to positions early in the game. Hence although it SEEMS like it's a 100% logical game, you can never play it 100% logically. You simply have to take a leap of faith that a position "looks good" according to some rather vague criteria - then reason about how to get to that position from where you are. So in the end - it's NOT a logical game for a computer with a believable amount of computing power...it might as well have random elements because some positions can't be evaluated using pure logic. However, the human has the same problem - I don't see why a computer shouldn't beat all humans at chess eventually. Heck, a computer can almost beat a grand master player...it can beat an 'ordinary' player very easily. The computer only has to get (let's say) three times as good and it'll win all the time.

It's worth noting that checkers 'masters' are now always beaten by computers. No human can beat a computer at that game anymore. The number of possible games is vast - but no so vast that the computer can't look far enough into the future to annihilate any human player. At the other end of the spectrum, we have 'Go' - which is possibly the simplest game in existance from the point of view of the rules - yet computers have made almost no headway at the game, even a relative beginner can beat the most sophisticated computer players. You only have to look at the number of possible moves that can be played each turn in Go - vastly more than Chess - which in turn is vastly more than Checkers.

SteveBaker (talk) 04:20, 4 December 2008 (UTC)

SteveBaker, thank you for introducing me to [Go http://en.wikipedia.org/wiki/Go_(game)]. No amount of logic could ever account for intuition. A train is about to hit a Jeep stuck on the tracks and yet a human would take precious, frightful moments to scoop up a loved one in the back seat. The logical query would be: Why would anyone risk so much at the stake of ending the game? The intuitive answer: I see the game on much deeper levels than you could imagine. Sappysap (talk) 05:57, 6 December 2008 (UTC)

Do we have the engineering capability to dig a hole all the way thru the Earth?

Not that we'd want to, or need to. Environmental crises withstanding, does any country have this capability? THE WORLD'S MOST CURIOUS MAN (talk) 01:15, 3 December 2008 (UTC)

Have a read about the Earth's Outer core (especially the liquid part) and tell us what you think. -hydnjo talk 01:42, 3 December 2008 (UTC)

It's still an interesting question. Apparently, the refractory material with the highest known melting point is Tantalum hafnium carbide.It melts at below 5000C, but the liquid iron of the outer core is above 6000C. So in addition to all the other trivial little problems, we will need to use active cooling in the walls of our tunnel. We can just put this litle project on our list of things to do after the Singularity. -Arch dude (talk) 02:02, 3 December 2008 (UTC)

Tantalum hafnium carbide would increase its melting point under pressure, but it is probably dissolved by liquid iron. However perhaps all you have to do is cool that iron to make a tube of solid iron! Graeme Bartlett (talk) 02:27, 3 December 2008 (UTC)

Electric arc furnaces use water cooling coils to prevent the crucible itself from melting. Neglecting for a moment the cost and the true impracticality, forced cooling could in principle allow a pipe to exist in an environment above its melting point. Water can be boiled over a flame in a container made of folded paper. Edison (talk) 03:32, 3 December 2008 (UTC)

This is the closest we have come: Kola Superdeep Borehole. 12 kilometers down, 12,730 kilometers to go! --Jayron32.talk.contribs 04:49, 3 December 2008 (UTC)

Then we can jam a giant rocket in there and just tool around the solar system. Make the other planets jealous. Give our planet a wicked paint job; the works. HalfShadow 04:52, 3 December 2008 (UTC)

Thanks for making me laugh (that image is now my visual ear-worm) : )) Julia Rossi (talk) 07:14, 3 December 2008 (UTC)

Distinction to make: the above element is known to melt at 5000C at 1 atm. At lower depths, it might not melt, much like the 5700K solid inner core of the Earth.

Of course, actually digging a hole, rather than just boring through: yeah, that'd be difficult. Given the inner core has a pressure of 3 million atm, it just might be little difficult to keep it from bubbling up to the surface. Magog the Ogre (talk) 10:25, 3 December 2008 (UTC)

Also see David_J._Stevenson#Sending_a_probe_into_the_Earth. A reasonable amount of molten iron poured in to a surface crack will force its way to the center of the earth! Saintrain (talk) 16:54, 3 December 2008 (UTC)

How's about a focused, high-intensity particle beam or laser? Put enough energy into it and it would burn right through and out the other side, wouldn't it? --Kurt Shaped Box (talk) 18:08, 3 December 2008 (UTC)

What it's burning through has to go somewhere - if you vaporise all the rock you will get high pressure rock-vapour coming out the top of the hole which would destroy your laser. --Tango (talk) 00:41, 4 December 2008 (UTC)

Fair point. Put it in geostationary orbit then. You might even be able to get military funding for the experiment. --Kurt Shaped Box (talk) 00:48, 4 December 2008 (UTC)

That would work better, but still not great. There would be nothing to move the rock out the hole other than its own pressure, which means you would still be left with rock-vapour at atmospheric pressure (near the surface - higher lower down). As soon as you turned off the laser (assuming it was able to penetrate the vapour, which would presumably be pretty opaque, in order to get all the way through in the first place) it would start to cool down again and would condense and the lower parts of the hole would fill in with molten rock. --Tango (talk) 00:51, 4 December 2008 (UTC)

The gravitube uses a magnetic containment system to keep the ceramic tube and shuttle melting when passing through the liquid core. Full details can be found in The Gravitube - Tenth Wonder of the World by Vincentt Dott. :) Gwinva (talk) 01:53, 4 December 2008 (UTC)

If we had the technology to send a massive bullet, say the mass of a truck but compacted, @90% of the speed of light into the ground, what would happen? Would we be any closer to digging the completely useless unobtanable hole? Bastard Soap (talk) 23:05, 6 December 2008 (UTC)

chemical reaction of copper with limestone

What is the chemical reaction of copper in the presence of limestone or concrete (a limestone derivative)? I know that copper corrodes, as unshielded copper pipe will do when embedded in crushed limestone under concrete floor slabs or in the floor itself; but what exactly is the reaction? I have asked several chemistry professors without success and can find no help in scientific encyclopedias.JeromeArk (talk) 02:46, 3 December 2008 (UTC)

Copper will react with carbon dioxide and carbonates to form copper carbonate, which is the green crud that forms around weathered copper. Remember that limestone is essentially calcium carbonate... --Jayron32.talk.contribs 04:45, 3 December 2008 (UTC)

You also need oxygen and water to facilitate the reaction. Graeme Bartlett (talk) 09:01, 3 December 2008 (UTC)

Strangely enough, I expect copper water pipes to be rather wet... And there's usually enough dissolved oxygen in the water going through the pipes to do what you need, given enough time... --Jayron32.talk.contribs 17:45, 3 December 2008 (UTC)

Isn't the goal of a pipe to keep the water INSIDE and the limestone OUTSIDE? If your copper pipes are always wet, you might wish to call Joe the Plumber or his colleagues. Edison (talk) 21:44, 3 December 2008 (UTC)

Isn't it also the case that the corrosion that builds up on the surface of the copper actually keeps out the corrosive agents? So you get a thin layer of surface crud - but the metal beneath stays intact. What kills water pipes embedded in concrete is the vibration. As bubbles flow through the water, they cause vibrations in the pipe - that vibration rubs the copper against concrete and eventually, it simply wears out. SteveBaker (talk) 04:00, 4 December 2008 (UTC)

Making metal

If you were alone on a deserted island and you knew there was iron ore in the ground, would it be possible for you to create metal, and in turn create useful metal tools? Malamockq (talk) 04:24, 3 December 2008 (UTC)

See Smelting. Basically, with most oxide ores, and a source of carbon (such as charcoal) you can extract metal from these oxide ores. So sure, you could do it, assuming you had a source of wood to make charcoal... --Jayron32.talk.contribs 04:40, 3 December 2008 (UTC)

I expect that it would be too labor intensive for a lone worker to extract iron and make useful items from iron ore. In the 18th and early 19th century , it took teams of skilled workers to build the iron making furnace or Bloomery out of large shaped stone blocks, to fell trees and make charcoal by skillfully stacking the wood and covering it with earth to allow the heat of the smoldering wood to change it into charcoal, to dig the ore, then to do the refining, and the hammering of impurities out of the iron while operating bellows. Maybe you could find an iron meteorite and break off pieces. I saw one] that natives in Greenland or some such place used to break off pieces to make useful tools, until European scientists found it and took it to a museum. (Hope they paid the Inuits something for it). Edison (talk) 04:41, 3 December 2008 (UTC)

Maybe you could budget several years to shape the stones and build the furnace, using ramps and block and tackle with wooden pulleys and ropes you make from vines, then build a water wheel on the adjacent stream to power the bellows. Allow a couple of years to dig and haul the ore. Allow a year or 2 to cut and split many cords of wood (using stone tools you create) and make the charcoal. After 10 or 20 years, you might be all set to make the first batch of iron. Edison (talk) 21:42, 3 December 2008 (UTC)

I agree, Iron would be exceedingly difficult. But you could probably smelt some copper, gold, silver...lower melting point metals - assuming you have the ores and a source of timber to make your charcoal and something to build you kiln and bellows with. What you're going to have to go through is all of the 'ages' of mankind - the stone age (you have to learn to make stone cutting tools by napping flint...then the bronze age (you can smelt copper and tin using much lower temperatures and less sophisticated kilns)...and only long after, you'd enter the iron age. But the ancient Egyptians built the pyramids using only bronze and copper tools - so you could go a long way without iron. The critical thing is that you find rock that can keep an edge on your island - if there is no flint - you may be screwed. SteveBaker (talk) 03:56, 4 December 2008 (UTC)

You don't generally need to smelt gold it's so unreactive in can be found in pure form. Silver can as well, sometimes. They're not particularly useful for anything other than looking pretty (or making electrical contacts), though... --Tango (talk) 13:37, 4 December 2008 (UTC)

Escaping a black hole

As we understand physics at this time, nothing can move faster than the speed of light. Thus, since even light can not move fast enough to escape the gravity of a black hole, nothing can escape. Theroetically, IF there were a way to surpass the speed of light would the gravity of a black hole still be too strong to escape from? How much faster than the speed of light would an object need to be going to escape the gravitational forces of a black hole? —Preceding unsigned comment added by 216.154.22.11 (talk • contribs) 04:57, 3 December 2008

Once you're past the event horizon, you're screwed. The gravity of a black hole is effectively infinite. If you pass the event horizon, no force in the universe would enable you to escape. Theoretically, of course. HalfShadow 05:13, 3 December 2008 (UTC)

The original question makes some incorrect assumptions of how things such as "speed" and "light" really work in the universe. Exceeding the speed of light is not a technological problem, its that the way the universe is put together, it is actually a nonsensical concept. The speed of light is an asymptotic condition; any object with a nonzero rest mass may approach it, but cannot ever reach it. Beyond that, as the object approaches that speed, some really bizarre physics starts to occur. Local time inside the object slows to nil, the object's mass increases towards infinity, etc. etc. --Jayron32.talk.contribs 05:28, 3 December 2008 (UTC)

No object can travel faster than the speed of light, but we can still discuss velocities greater than that of light. I remember a freshman physics problem about a ball rolling in a horizontal circle in a hemispherical bowl. If the ball travelled at the speed of light, it would still be circling below the top of the bowl, and one could calculate how much higher it would circle at super-light speeds without ever reaching the top of the bowl. 2xc, 10000xc, and the ball still circles below the top. The questioner might be asking a question of this sort. (theoretically speaking). Edison (talk) 07:23, 3 December 2008 (UTC)

The properties of hypothetical particles that are permanently travelling faster than the speed of light are discussed in our article on tachyons. One property is that they have "imaginary" mass (i.e. m² has a negative value). So it's not clear to me what their gravitational interactions with normal matter would be - maybe they would be completely unaffacted by a black hole. Gandalf61 (talk) 09:43, 3 December 2008 (UTC)

The hypothetical tachyons (which would violate causality) always travel on spacelike world lines (never within the light cone). In a Schwarzschild black hole the radial coordinate is timelike at values smaller than the Schwarzschild radius, and the time coordinate becomes spacelike in this region. Therefore, tachyons shouldn't be able to travel along radial trajectories inside the black hole without traveling a longer way along the time coordinate (i. e. without traveling at low speeds in the reference frame of an observer outside the black hole). Somehow that looks like tachyons behave like ordinary particles and vice versa beyond the event horizon. Icek (talk) 11:00, 3 December 2008 (UTC)

You're attaching too much importance to the Schwarzschild coordinates. Nothing that depends on a particular choice of coordinates can ever be physically meaningful. The r and t Schwarzschild coordinates function as time and distance measures respectively inside the hole, but time and space don't "really" change places, only the coordinates do. Something similar happens in Rindler coordinates—there's a coordinate singularity beyond which time "runs backwards", but time isn't really running backwards in that part of spacetime (the spacetime is, after all, just the ordinary flat spacetime of special relativity).

The reason you can't cross back over the horizon of a black hole is that it's moving outward at the speed of light, locally. Globally, of course, the black hole has a fixed size. This sounds strange, but it's not much different from what happens with any other gravitating body. By the equivalence principle, the gravity at Earth's surface (about 10 m/s²) can be correctly understood as a consequence of the ground literally accelerating upward at 10 m/s². The acceleration is caused by the same forces that one normally thinks of as keeping the Earth's size fixed, namely electromagnetism and electron degeneracy pressure. The overall spacetime curvature makes it possible for the Earth to have a fixed overall size while also accelerating outward in all directions. The spacetime curvature at any particular location on the Earth's surface is very small, and is not what accounts for the acceleration of gravity there; that's actually caused by the ground accelerating upward in a special-relativistic sense.

Anyway, in the infinite-acceleration limit of this situation, you get a "surface" moving outward at the speed of light. However, there's no longer anything physically there at the surface—or rather, it makes no difference whether there is, because no interaction is possible with anything that might be there. Again, the curvature of spacetime needn't be large at this surface (it's large for small black holes, small for large ones). It's the fact that the surface is moving at the speed of light, in a special-relativistic sense, that prevents you from crossing back over it.

Since the horizon is "only" moving at the speed of light, faster-than-light particles (classical tachyons) can freely cross "in either direction". That is, a faster-than-light worldline can zigzag across the horizon any number of times, unlike slower-than-light worldlines which can only cross once. The trouble with saying that, though, is that there's no obvious way to distinguish past and future for objects moving faster than light, and so no way to distinguish a tachyon entering the black hole from a tachyon leaving. Was that zigzag worldline really a single tachyon crossing back and forth, or was it a bunch of tachyons being pair-created outside the hole, falling inside, and then pair-annihilating? Or the other way around? Modern physics doesn't suggest any answer to this question. Since no faster-than-light particles have ever been found in reality, most physicists jump to the obvious conclusion (they really don't make sense and really don't exist). -- BenRG (talk) 15:13, 3 December 2008 (UTC)

Further to my original query, I was thinking along the lines of Star Trek (ya, I'm a Trekker!) where there is a way to create a "warp bubble" allowing one to traverse distances at super-light speed without contradicting the known laws of physics.If this were possible, would one still be screwed once past the event horizon?

Classically speaking, escaping from a black hole is the same as winning a race with a light beam that's been given a head start. If your hypothesized warp drive can do that then it can escape a black hole. -- BenRG (talk) 15:13, 3 December 2008 (UTC)

I should qualify that by saying that the event horizon is defined as the boundary of the inescapable region. In a world with faster-than-light travel there would be no event horizon in the first place. There would still be an apparent horizon, which is the radius at which outgoing light rays are stationary. I tend to conflate the two, and I shouldn't. I deleted all occurrences of the word "event" from my reply above, and you should interpret "horizon" as "apparent horizon". Nothing else needs to change because everything I said actually applies to any horizon, i.e. any surface moving toward you at the speed of light, even if it's not associated with a black hole. -- BenRG (talk) 15:32, 3 December 2008 (UTC)

There's also the problem (mentioned by someone somewhere) of the light trapped right inside the event horizon, orbiting and only slowly falling, and obviously unable to escape. You'd be fried. And there's all the hot stuff in the accretion disc outside the event horizon. -- Consumed Crustacean (talk) 20:40, 3 December 2008 (UTC)

The Alcubierre drive is reminiscent of the warp drives in Star Trek, though cannon states that that's not what they are. I doubt you could use one to leave a black hole, but I don't know that much about the subject. I do know that from an outside observer's point of view you never quite fall in. Coming back out would essentially be time travel, and you could rescue yourself from falling in. Of course, faster then light travel lets you go back in time without black holes, so I don't know if that means anything. — DanielLC 05:41, 4 December 2008 (UTC)

I have to correct you that stuff can go faster than the speed of light but not the velocity of light. This correction tells you that you should never consider the speed but instead consider the velocity. This is what Einstein told us in Relativity and this demonstrates that you do not have a proper understanding of Relativity.----The Successor of Physics 14:28, 4 December 2008 (UTC)

What are you talking about? Velocity is just speed with direction - when talking about "faster" and "slower" you are referring to the speed part. --Tango (talk) 16:30, 4 December 2008 (UTC)

Coffee

It is my understanding that coffee is a diuretic, but that drinking coffee will still increase hydration levels (just not as much as water). Is that correct, and is it possible to quantify the "hydration effect" for a given type/strength of coffee (assuming that water is 100%)? Thanks WAYB (talk) 12:40, 3 December 2008 (UTC)

Yes coffee will hydrate you. I recall having this discussion with a friend who didn't believe it counted in his amount of water intake a day. Here's a link http://www.positivelycoffee.org/topic_hydration_overview.aspx 194.221.133.226 (talk) 13:25, 3 December 2008 (UTC)

If coffee wasn't going to have at least some hydrating effect, it would have to make you pee at least the same volume of water you'd consumed in the coffee, in addition to your normal output. I think you'd notice! Eve Hall (talk) 13:37, 3 December 2008 (UTC)

Could I extend onto this question: If you were stranded on a boat in the middle of the ocean, and all you had was brewed coffee, it seems you'd be made better off by drinking it. What if all you had was beer? Wine? 40% hard alcohol? 80% alcohol? Sea Water?NByz (talk) 20:39, 3 December 2008 (UTC)

Protein Structure

Hi, I could use some help here, please. I'm trying to gain some understanding of protein structures, necessary background info for a project I'm involved with. THe thing is, the paragraph on tertiary structures is much more complex than the parts before it, therefore I would be really grateful if someone could translate the following section into something a bit more understandable:

• Similarly, the formation of molten globules and tertiary structure is driven mainly by structurally non-specific interactions, such as the rough propensities of the amino acids and hydrophobic interactions. However, the tertiary structure is fixed only when the parts of a protein domain are locked into place by structurally specific interactions, such as ionic interactions (salt bridges), hydrogen bonds and the tight packing of side chains. The tertiary structure of extracellular proteins can also be stabilized by disulfide bonds, which reduce the entropy of the unfolded state; disulfide bonds are extremely rare in cytosolic proteins, since the cytosol is generally a reducing environment.

Thank you--128.243.21.225 (talk) 14:48, 3 December 2008 (UTC)

Read a bit further, specifically the Tertiary Structure of Proteins subsection, and you might find your answer. - Draeco (talk) 15:39, 3 December 2008 (UTC)

Looking back in time through space

I recently read that light emitted by the sun takes approximately 8 minutes to reach earth. Nothing remarkable in that you may think, but it then got me pondering the possibility of sending a satellite into space to then peer back at earth and look back in time. So, assuming that we had the technology, we could send our super-satellite 670,616,629.40 miles into the universe for every hour that we wish to look back in time. However the speed at which we can send our satellite into space is capped at the speed of light so there is by this method there is no way to look back at earth before the point at which our satellite was launched. Is there a solution to this problem, so that we one day might be able to peer back at earth to the time of Jesus and beyond to the point at which the earth formed? Or will we have to hope that our alien friends have beaten us to it and have had us under CCTV surveillance for the past 4.54bn years? --79.67.171.134 (talk) 14:50, 3 December 2008 (UTC)

According to the present understanding of physics, there is no way to get a craft out there fast enough to catch up with and observe light that left the earth 2000 years ago (or even 20 years ago.)

Suppose for sake of discussion that we already had a space craft with a telescope out there 2000 light years away. Getting images good enough to see what was happening on earth is another big hurdle.

It would take another 2000 years to send the images back to earth. But that's an interesting idea.

Good try though. CBHA (talk) 15:14, 3 December 2008 (UTC)

So am i right in thinking that there is no way to even send data over distances at a speed faster than the speed of light?? 79.67.171.134 (talk) 15:45, 3 December 2008 (UTC)

You just have to look at the light sent back to us from going closely enough round a black hole. So we don't have to go anywhere. There are a few little practical problems but yes there very possibly is a quantum or two of light from the death of Christ or whatever. Now all I need is for all true believers to give me loads of money and I'll promise it in full technicolour though it may take some time :) Dmcq (talk) 16:04, 3 December 2008 (UTC)

This is a novice's insight, but don't the effects of gravity 'transmit' instantly through space? Could a gravity-based communications system transmit data FTL?NByz (talk) 18:33, 3 December 2008 (UTC)

No. Gravitational effects propagate at light speed. — Lomn 19:19, 3 December 2008 (UTC)

Placing a mirror (simplistically) a long way from the earth would let you use a telescope to look back in time - sure. But not (of course) before the moment the mirror was launched. However, quicker, easier and MUCH cheaper would be to set up some cameras in orbit with video recorders on board. Years later, you could "look back in time" by commanding the satellite to replay the video. Suddenly, this doesn't seem so amazing as shooting a mirror out there a few light years...but functionally, it's the same thing. You can easily "look back into the past" by picking up a DVD and watching it...now it's even less glamorous - but it's the same thing. Using the long distances of deep space to "store" video isn't all that much different from storing the video in some memory or on a disk someplace. SteveBaker (talk) 03:43, 4 December 2008 (UTC)

Don't physical effects propogated via quantum entanglement effectively travel faster than the speed of light? Might this be useful? —Preceding unsigned comment added by 194.63.116.72 (talk) 11:11, 4 December 2008 (UTC)

As I understand it, no. Two people a large distance apart can get the same random information at the same time, but they can't transfer information from one person to the other. Getting the same random information could have uses in cryptography, but that's about it. --Tango (talk) 11:44, 4 December 2008 (UTC)

Smelling your own B.O.

Hello. Is perceiving your own bad body odor as difficult as perceiving your own bad breath because of habituation? Kreachure (talk) 14:58, 3 December 2008 (UTC)

No. At least not certain parts of it. Lift your arm and have a smell at your armpit. If it stinks, you'll smell it. The same goes for stinking feet. The difference with breath is that you do not smell your armpit or feet continually, and therefore do not habituate. Unless you have smelled terribly for days, I suppose.Lova Falk (talk) 20:32, 3 December 2008 (UTC)

Indeed, it's only if you've smelt like that for some time that you'll habituate to it. You hear lots of stories about people coming back to civilisation after being isolated in a small group for a while (my uncle tells it about when he was in a research team in Antarctica) and none of the group have been particularly careful about personal hygiene. Because they've all been together the whole time smelling it constantly they don't notice but when they first meet other people they get told how much they stink. --Tango (talk) 22:32, 3 December 2008 (UTC)

Measurement of the speed of light

Is there a way to measure the speed of light with everyday household products? --Emyn ned (talk) 15:01, 3 December 2008 (UTC)

If a telescope that can resolve the moons of Jupiter and a clock that is accurate to within one or two seconds per day count as everyday household products then, yes, you can use Ole Rømer's method. Gandalf61 (talk) 15:16, 3 December 2008 (UTC)

Sure, all you need is a microwave oven and some chocolate chips. --Sean 15:19, 3 December 2008 (UTC)

If you are being serious Sean, how does that measure the speed of light?--Emyn ned (talk) 15:21, 3 December 2008 (UTC)

Well, part of the "measurement" involves turning the microwave around and reading the frequency in the back. You measure the wavelength using buttered toast (or, I suppose, chocolate chips), and then apply c=f*lambda. See this The Naked Scientists experiment for the details. --Stephan Schulz (talk) 15:51, 3 December 2008 (UTC)

OK, so that part's cheating a bit. You could also recreate the Fizeau experiment, which got to within 5% of the right answer with very primitive equipment. You could set it up with just a flashlight, a bathroom mirror, a pane of glass, and an upside-down bicycle. --Sean 16:03, 3 December 2008 (UTC)

A flashlight won't be visible at a great enough distance unless you use optics that most people won't have in their households... but a laser pointer ought to do the job.

Using no equipment but your home phone, you could place a call to someone whose country code indicates an Inmarsat satellite phone. You then ask them to speak in synchrony with you as you count to 20. As they match your cadence, you will hear their voice about 1/4 second behind you. Knowing the altitude of a satellite in geostationary orbit, compute the speed for light (well, radio waves) to travel twice that distance in 1/4 second. (Okay, I have not used an Inmarsat phone myself. But around 1980 it was common for ordinary overseas phone calls to be carried by satellite, before the phone companies switched back to cables when optical-digital ones came into use, and I heard the same delay effect with those satellite calls. I imagine there are still some satellite connections on ordinary calls today.)

Of course, this version of the experiment does involve a bit of equipment that's not in your household, even if you never see it! And you have to know how it works, too, i.e. the number of satellites involved.

--Anonymous, 02:27 UTC, December 4, 2008.

Is that the time between when a traffic light turns green and the "clock" hits the horn in the car behind you? Julia Rossi (talk) 04:35, 4 December 2008 (UTC)

No, what you have just described, is based on reaction time and the speed of sound, the speed of light having a negligible effect. --131.188.3.21 (talk) 16:41, 7 December 2008 (UTC)

• I saw a method on Stupid Science that involved a microwave oven and a plate of cheese. The scientist, heated teh cheese and found two bands of molten cheese. He measured the distance between the two, combined it with the wavelength of the oven and made a pretty good approximation of c. - 131.211.211.5 (talk) 08:23, 4 December 2008 (UTC)

Yes - we already discussed that (chocolate chips work better than cheese IMHO) - but the problem is that you need to know the frequency of the microwave oven - which is just as hard to measure as the speed of light! Generally, it's printed somewhere on the oven - but some of us regard that as 'cheating'. It's like doing an "experiment" to find the speed of light that involves looking it up in a textbook! SteveBaker (talk) 03:46, 5 December 2008 (UTC)

Rare as hen's teeth

What are the tooth-like structures on the roof of the bird on the left's mouth? Thanks. —Preceding unsigned comment added by TotoBaggins (talk • contribs)

Egg tooth. --Jayron32.talk.contribs 17:39, 3 December 2008 (UTC)

No, an egg tooth is a sharp nub on the top of a critter's beak used to break through an eggshell, which obviously would be tough if they're on the roof of the mouth. The pics in our article aren't too good; these are better: [1], [2], [3] --Sean 17:50, 3 December 2008 (UTC)

(after edit conflict)Na. The egg tooth would be a little bump on the end of the beak - those serrated structures are something else. I'm not 100% sure (my memory might be playing tricks on me, as it was quite a few years ago now) but I think that the young gull I raised had them in the roof of her mouth too. No idea what they're called - but if I had to guess, I'd say that they are an anatomical feature 'designed' to grip the food and thus aid swallowing. No idea if my budgies have them or not - they never open their mouths wide enough for me to take a look inside. --Kurt Shaped Box (talk) 18:00, 3 December 2008 (UTC)

If you double-click the OP's photo to enlarge it, the structures in the throat become much plainer.

The little white things do not show up in diagrams of bird skulls, so perhaps they are not really as solid as they look, and not anchored like mammal teeth are in the mandible. The appear to surround what is in some birds the "maxillo-palatine process." See also [4]. Could these protrusions be part of the vomer, which [5] says is a plate connected to the maxillary processes, which may be "notched, lobed, clubbed, etc.? (I claim no familiarity with bird anatomy). Edison (talk)

Mercury's extra day

I remember reading something (I think it was in Stephen Hawking's a brief history of time) about Mercury being so close to the sun that the time distortion allows it to experience an extra day each year or something like that (not sure if it was a mercury day/mercury year or ours or a combination). Also not sure if it was extra time or missing time or if you'd have to be on the planet or if it could be observed from earth... just trying to remember what the fact was. I read it Tests_of_general_relativity that mercury experiences an extra 43 arc-seconds a century under relativity versus newtonian laws, but not sure how that translates into what I'm trying to understand about Mercury. If anyone knows what I'm talking about, please fill in any details I am missing. Anythingapplied (talk) 17:45, 3 December 2008 (UTC)

Well, 43 arc-seconds relates to precession and units of angle, not units of time. It's true that gravitational time dilation exists, but it certainly doesn't operate on an order of magnitude such as "a whole extra day per year" (particularly not a Mercurian day, which is 2/3 of a year). A quick read of the math presented suggests that a clock on Mercury moves at approximately 99.99999997% the speed of a clock stationary at Mercury's average distance from the sun. That would be a difference of less than a second per Earth year. — Lomn 19:15, 3 December 2008 (UTC)

Thanks! One last question: You said "a clock on Mercury moves at approximately 99.99999997% the speed of a clock stationary at Mercury's average distance from the sun." What about a clock on Mercury compared to a clock on earth? or is this what you meant to say? Anythingapplied (talk) 19:58, 3 December 2008 (UTC)

Well, it looks like I need to clarify. The stationary clock actually appears to be the ideal one outside the sun's gravitational field entirely. Earth's time dilation would be about 37% of Mercury's, as dilation has an approximately linear relationship with distance from the massive object's Schwarzschild Radius. — Lomn 20:58, 3 December 2008 (UTC)

I think the "extra day" thing is nothing to do with relativity, but refers to the difference between the sidereal day and the solar day. If a planet rotates around its axis in the same direction that it revolves around the Sun, its year includes exactly one more sidereal day than the number of solar days. This is true for any planet, simply because of the geometrical facts of rotation. For example, the Earth has about 365¼ solar days in a year and about 366¼ sidereal days, so the sidereal day is shorter by 1 part in 366¼ or about 4 minutes -- not exactly a huge difference.

For Mercury, on the other hand, its position close to the Sun produces a large tidal drag that has greately slowed its rotation until it has only 1½ sidereal days in a year. (That's exactly 1½, a situation what has developed instead of tidal locking due to its high orbital eccentricity.) So it has just 1/2 a solar day in a year, which is a huge difference from 1½ days. As seen from a typical point on Mercury's surface, the Sun rises only once every 2 years. (Mercurian years, that is -- about 88 Earth days each.)

Oh, and another thing. Like any planet, Mercury rotates at a constant rate, but its motion around its orbit is faster during the part of the year when it is closer to the Sun. I've read that because its rotation is so slow, this variation actually causes the Sun to appear to reverse temporarily in its apparent motion. So from some places on Mercury, the Sun rises twice during the 2 years that one day lasts. In between the two risings, it sets again in the same place where it rose. That might be considered an "extra day".

--Anonymous, 02:48 UTC, Earth date December 4, 2008.

Indeed - that retrograde motion is discussed in Mercury (planet)#Orbit and rotation. --Tango (talk) 11:42, 4 December 2008 (UTC)

Will wind farms, solar power,and ocean wave power destroy the Earth?

Will using wind farms to generate electricity change the weather pattern for areas downwind? If solar panel collectors are collecting the Sun's heat, instead of warming the Earth's surface layer, what will happen because of this temperature change in future generations21:09, 3 December 2008 (UTC)Will harnessing the power of ocean waves end up destroying the biology of the oceans72.90.86.171 (talk) 21:09, 3 December 2008 (UTC)

No, although there are some knock-on effects of all kinds of renewable energy. "Solar panel collectors" - whether you mean photovoltaics or solar water heaters - are not going to cover a very large surface of the earth in the foreseeable future. Like other surfaces they absorb heat while reflecting some of the radiation back into Space. We can harness far, far more of the wave power than we do at the moment without having any measurable effect on ocean systems. Having said that, renewable energy projects certainly can have negative environmental impacts in the short term. Wind farms can detract from the amenity of rural areas and can cause noise pollution. Hydroelectric dams on rivers can drastically alter ecosystems and destroy communities. Tidal power schemes can transform estuary ecosystems. On balance, if deployed carefully, renewables are just that, renewable and with much less environmental cost than fossil-fuel-based energies. Itsmejudith (talk) 21:21, 3 December 2008 (UTC)

Here's a suggestion. Underwater ocean turbines driving underwater electrical generators would cause minimal interference with natural processes. They would be placed in ocean currents. The Gulf Stream would be a good place for some of these generators. The turbines would have blades like a windmill but designed for moving water. Perhaps ships' propeller-design techniques would be suitable. Air pressurization of the generator housing would prevent minor water leaks; an excessive drop in air pressure would indicate the need for repair. Flotation tanks receiving pumped air from the surface would bring a generator to the surface for servicing. If necessary, it would be towed into a harbor for repairs. The turbo-generators would be placed deep enough, or close enough to shore, that they would not interfere with shipping. They would be completely out of sight, and there would be no noise nuisance. Cables would bring the electrical power to shore. Perhaps the ocean itself could be used as one conductor, unless that would cause problems for marine life. Teflon coating of the generators and cables would prevent or minimize marine growths.

The article on Wind power compares the energy in the wind with the global energy requirements: there is 72 TW available compared with current energy consumption (from all sources) of 15 TW (terawatts). Using nearly 20% of the earth's wind would have serious effects on the earth's winds. In contrast, the earth's surface receives 89,000 TW from the sun (see Solar energy) - wind energy is derived from solar heating, as is hydroelectricity, biomass power stations, energy human/animal labour, etc - so taking what we need from the sun should have little effect. Note that most energy that reaches the earth is eventually converted to heat (except the portion lost into space and the amount used to manufacture biomass) so whether we let solar energy warm the air and ground, or collect it and have it do work which via friction warms the air and ground, the only difference will be the distribution of the heat, not the total amount. --Maltelauridsbrigge (talk) 13:04, 4 December 2008 (UTC)

Actually, according to this article, building a large wind farm across North America may change weather patterns. ~AH1^(TCU) 00:14, 5 December 2008 (UTC)

Or may not. The article makes it clear that no-one knows, and besides there is no plan to create such a large wind farm. Itsmejudith (talk) 11:03, 5 December 2008 (UTC)

Parrot - how cold is too cold for her?

Now, I've always believed that parrots are very hardy birds and tolerant of low temperatures by virtue of being far better insulated than I am. Just had a disagreement today with someone who believes that I should be keeping the heating in my house on full blast at night in winter for the sake of my Hyacinth macaw. I'm convinced that she doesn't care about the chilly weather in the slightest. I've owned her for more than 20 years and for all that time, she's been doing what comes naturally and turning into a big blue puffball when she needs to keep warm and never seemed any the worse for it.

I have some heating but I never keep my house hot. That's the way it's always been. If I'm feeling cold, I prefer to put a jumper on instead of turning the radiators up. We're having a cold spell in England at the moment but it's not like the temp. ever drops below zero in my home.

So my question, do you think I'm doing the wrong thing by my birdy? I know that macaws are supposed to be tropical birds but I don't know for sure if this bird has even seen the rainforest on TV, let alone been there.—Preceding unsigned comment added by 84.71.248.149 (talk • contribs) 23:21, 3 December 2008

Surprisingly, parrots, which are tropical birds, seem to survive in temperate climates when they are released in the wild. I believe there's a wild population in San Francisco which is thriving, for example. However, note that surviving doesn't mean they are comfortable. I don't know the recommended temp range for your bird, but suggest that giving them access to different temps will allow them to choose which temp is the most comfortable. If the bird has the run of the house, it will naturally cuddle up to a radiator when it gets cold. If it's in a cage, you may want to put the cage near a radiator, so they can get closer if they crave heat and farther when they get hot. This would obviously be more effective with a larger cage. You could also provide an alternate source of heat for the bird, like a small infrared light shining on one side of the cage. StuRat (talk) 03:03, 4 December 2008 (UTC)

Puffball=putting on a jumper; and 20 years=acclimatised (in my book). Doesn't seem bothered, ill or suffering=healthy bird. Julia Rossi (talk) 04:30, 4 December 2008 (UTC)

Careful in putting the cage next to the radiator! They are meant to heat a whole room. She could overheat if she can't get away. Consider a blanket/cover for the cage instead to insulate and to eliminate drafts. Saintrain (talk) 18:33, 4 December 2008 (UTC)

Well, me I'm comfortable down to about minus 25 Celsius. I was caught on videotape once after a prolonged squawk in a cold environment, but otherwise there's certainly no lack of movement, and that remark about 4 million volts was totally uncalled for. --NorwegianBlue ^talk 20:55, 4 December 2008 (UTC)

I know nothing about parrots, so this is a theoretical analysis. Your parrot has a sophisticated thermoregulatory system: she can vary her insulation by puffing up, like other birds. There is a limit to how much insulation she can add in this way. As long as she has not reached the limit, she is warm enough. This means that if she is not currently as puffed up as she can possibly get, then she is warm enough. If you can tell by experience how much she can puff up, and if she is not at max, then she is OK. -Arch dude (talk) 02:38, 5 December 2008 (UTC)

However, preventing death using that method doesn't mean it's comfortable, just as when we shiver to keep warm, that doesn't mean we're comfortable. StuRat (talk) 11:30, 5 December 2008 (UTC)

You should really ask an animal doctor or expert if you are concerned about your bird. I wouldn't trust a pet's well-being to opinions from our reference desk. cheers, 10draftsdeep (talk) 14:42, 5 December 2008 (UTC)