Wikipedia:Reference desk/Archives/Science/2009 November 24

= November 24 =

Why are carbon atoms in carbon nanotubes bonded to only 3 other atoms?
Carbons could theoretically have 4 bonds with other carbon atoms, so why must carbon atoms in carbon nanotubes contain only 3 other bonds to other carbon atoms (thus producing the hexagonal shape)? —Preceding unsigned comment added by Bluehark (talk • contribs) 02:08, 24 November 2009 (UTC)
 * Every other bond is a double bond. It is strange that neither our article on carbon nanotube nor the one on fullerene show the double bonds in the diagrams.  Would be nice if a chemist reading this with the right graphic software would produce something for us.  Sp in ni  ng  Spark  02:25, 24 November 2009 (UTC)
 * See, this is what I have a question about. Is every other bond a double bond, or do all have an unbonded pair of electrons facing into the tube? —Preceding unsigned comment added by Bluehark (talk • contribs) 02:28, 24 November 2009 (UTC)
 * Apparently, they're sp2 hybridized; because the bonds are symmetrical the "extra" bond is decentralized and the carbons are essentially planar (with curvature imposed by the overall structure). There are no unbonded electrons.  -- Scray (talk) 03:43, 24 November 2009 (UTC)
 * No, every other bond is not a double bond as all the bonds are equivalent. As Scray said, all the bonds are sp2 hybridized bonds.  J kasd  07:42, 24 November 2009 (UTC)


 * Carbon doesn't hold lone pairs very well. For one, it'd be a carbanion. The concepts of conjugation, resonance (chemistry) and aromaticity may be useful. The large (exploding) number of possible combinations of resonating pi bonds in a carbon nanotube is an analogue to a metallic bond built on top of a framework of sigma covalent bonds, which gives rise to carbon nanotubes' interesting properties. John Riemann Soong (talk) 08:31, 24 November 2009 (UTC)

Blood glucose levels and exercise
Diabetes management says: Other approaches include exercise and other lifestyle changes which impact the glucose cycle. It's not a very helpful article. I have personal evidence that suggests exercise has an near-immediate ability to lower blood-glucose levels. First, is my personal experience generally true, where "immediate" means within 1 to 3 hours post-exercise? If it is true, what exactly is happening to cause the drop? Thanks Bielle (talk) 03:51, 24 November 2009 (UTC)
 * Well, the obvious guess, from my naive and uncredentialed viewpoint, is that you've just burned it up, and that's why it isn't there anymore. Do you have any reason to look for a more complicated explanation than that? --Trovatore (talk) 03:58, 24 November 2009 (UTC)
 * My understanding may be fuzzy, but . . . blood sugar levels above normal can be the result of either insufficient insulin to open the lock-and-key connection that permits the transfer of glucose from blood into body cells or impaired or absent connection points. As far as I know, exercise burns up sugars that are already in the body tissues and not what is in the blood, so, while the body cells may be calling for more glucose, what is it about exercise that "permits" an otherwise impaired system to increase the transfer out of the blood (and thus the lowered blood-glucose number) and into the cells? Bielle (talk) 04:08, 24 November 2009 (UTC)
 * Oh, I see. I don't know, then. --Trovatore (talk) 06:46, 24 November 2009 (UTC)


 * Type 2 diabetes has an explanation but it's not very clear, it has no sources and it seems inconsistent with other articles I checked - someone should look at it. It looks like exercise stimulates a different glucose transporter than insulin. I can't access it, but the third reference at Insulin resistance seems to discuss this. Zain Ebrahim (talk) 10:55, 24 November 2009 (UTC)
 * This is the quote from the article Zain linked: Insulin though, which no longer works effectively in those afflicted with type 2 diabetes, causes GLUT1 to be placed into the membrane. Though they have different structures, they both perform the same function of increasing intake of glucose into the cell from the blood serum [citation needed]. Exercise also allows for the uptake of glucose independently of insulin, ie by adrenaline [citation needed]. It does need cites, certainly, as noted. Is there anything in this assertion anyone can either confirm or can tell me, or direct me, to more? Thanks Bielle (talk) 19:09, 24 November 2009 (UTC)
 * Here are a few that might be helpful:
 * Not a reliable source, but here's an interesting read from WebMD.
 * This is interesting but pretty technical: - I thought the insight about the effect of obesity was interesting, and there is a sizable literature about PGC-1 and glucose metabolism in liver vs muscle - e.g..
 * This one gets more directly at the effect of exercise on blood glucose in type 2 diabetes:.
 * Hope this helps. -- Scray (talk) 05:18, 25 November 2009 (UTC)


 * Thank you, Scray. It will take me a while to work my way through the PMIDs. I hope my medical dictionary is up to the challenge. Bielle (talk) 06:30, 25 November 2009 (UTC)

cancer
hello, my dad has colon cancer.. he went through an operation 20 days back, 124 cms of his large intestine a removed.. now doctor s started chemeotherapy.. may b 4 lymph node s infected.. wat diet should he have now and wat al care to be taken?? will he get well completely??? pls do reply.. —Preceding unsigned comment added by Shilpa.upadhya (talk • contribs) 05:36, 24 November 2009 (UTC)
 * Hi Shilpa! I hope you understand that we have a serious rule here against responding to requests for medical advice.  It doesn't mean we're heartless, and I'm sure everyone here wishes the best for your father. --Trovatore (talk) 09:20, 24 November 2009 (UTC)
 * Shilpa, I am sorry to hear about your father. The best people to ask about how to care for him are his doctors, and I am sure they will take your concerns seriously. All the best. --TammyMoet (talk) 10:32, 24 November 2009 (UTC)

Diving support vessel
2 men RCC is an equipent wich is using in diving support vessel.RCC stands for? —Preceding unsigned comment added by Akhilsvnair (talk • contribs) 05:41, 24 November 2009 (UTC)
 * Recompression chamber. Deor (talk) 11:09, 24 November 2009 (UTC)

Human Anatomy
What is the reason for men having nipples? What purpose do they serve? —Preceding unsigned comment added by NirocFX (talk • contribs) 05:46, 24 November 2009 (UTC)
 * See Nipple DMacks (talk) 06:14, 24 November 2009 (UTC)
 * The basic reason is simplicity.
 * Although the human body is constantly changing, overwhelmingly the most concentrated period is during fetal development, with a secondary node at puberty. As Nipple mentions, individuals are first formed on a unisex basis. (IMO, the assertion that this is a "female template" is sexist nonsense, based on the notion that without obvious male genitalia, the individual is "merely" female, even without obvious female genitalia.) In any event, at 14 weeks in a second spurt of development, the urogenital systems differentiate into male or female. As these systems must be in place by birth, clearly the physical development must occur within the womb.
 * On the other hand, functioning nipples are only needed after puberty. There are three sensible schemes for getting this to happen:
 * (1) Have nipples develop only in females during fetal development,
 * (2) Have nipples develop ab initio only in females during puberty, or
 * (3) Have nipples develop on all individuals, but have them "turned on" only in females during puberty.
 * The first scenario puts extra strain on the development of the fetus. With all the other changes occuring, why add yet another item to the list of things to be accomplished - and accomplished correctly - for something that will not be needed for another dozen years?
 * While the second scenario delays the action to a more appropriate time, it demands that females grow an entirely new organ, years after everything else is in place.
 * The third choice is what actually happens. The potential which all mammals have is activated only in females.
 * The trade-off is simple to understand when we consider the consequences. Males get non-functioning nipples which cause them no harm. Under either of the other plans, something might go wrong and a female would not grow nipples. Thus what actually happens is safer, in terms of the odds of it coming out right, because it's simpler.
 * B00P (talk) 09:51, 24 November 2009 (UTC)
 * What's important to realize is that in addition to the excellent answer above, it must be noted that it isn't this way because it's simple, or because it's safer. Because it implies it was planned out that way.  It is this way because out of all the ways it could be done, this way turned out to be most likely to survive and reproduce, therefore it is what exists.  While it is technically that way because it's safer, it's not as if it was picked, only tested out. Chris M. (talk) 12:20, 24 November 2009 (UTC)
 * Agree with Chris on this one -- see Occam's razor. It's not so much that this is simpler and therefor it happens, but that it happens, and we thus see that it's simpler.  It's all nice and good for us to say what is biologically simpler, but until it happens, we don't really know.  DRosenbach  ( Talk 13:11, 24 November 2009 (UTC)
 * Also, be sure to realize that neither "simple is better" and "better is what we have" are accurate statements, or at least both of them aren't necessarily true in all cases. I mean, look at the conjoined airway/foodway we have.  You could argue that's "simpler" then two, or you could say it's more complex.  But it seems almost certain it isn't "better" in any reasonable way, due to how frequently we die from misusing it (choking). Chris M. (talk) 18:02, 24 November 2009 (UTC)
 * Until we've directly compared with an alternative, I wouldn't be so sure. Subtle benefits may escape notice when things are running smoothly.  For example, the esophagus is a convenient waste bin for our respiratory system; a great deal of nasty stuff from our upper and lower airways is eliminated by the digestive system.  Where would that go if they weren't connected?  That's just one obvious example; there may be other more subtle benefits (e.g. immunologic).  -- Scray (talk) 23:18, 24 November 2009 (UTC)
 * Chris M. is quite right; I certainly didn't mean to imply anything else. B00P (talk) 04:06, 25 November 2009 (UTC)


 * Think of nipples as more than just a milk transference device. They are also good for detecting subtle things. They're like a couple of navigational sensors on the Enterprise, if you are familiar with Star Trek. Vranak (talk) 16:59, 24 November 2009 (UTC)
 * ... are you implying that you can navigate with your nipples? Or use them to avoid incoming asteroids?APL (talk) 17:13, 24 November 2009 (UTC)
 * Yes, yes I am. Seriously though, you can detect local weather phenomenon with your nipples. They can also be a gateway to intimacy for sex partners. Vranak (talk) 18:07, 24 November 2009 (UTC)


 * I can agree with that. I always find my nipples are indispensible for getting through a dense forest at night during a snow-storm. --  KageTora - SPQW - (影虎)  ( talk )  02:25, 25 November 2009 (UTC)
 * Oh yeah - it's easy - you go up to the nearest hunter and say "Show me the way out of this nasty forest and I'll show you my tits!" SteveBaker (talk) 04:54, 25 November 2009 (UTC)

mind altering drugs
What mind altering drugs were used or known in Ancient Civilization such as THC from hemp and hashish? 71.100.11.112 (talk) 06:57, 24 November 2009 (UTC)


 * I'd say "see Psychoactive drug", but it isn't very useful. How about Entheogen? Some examples of ancient mind altering drugs listed (but not all understood well today) include: Kykeon, Soma, Peyote, and Ayahuasca. Other possibilities include Amanita muscaria, Psilocybe, Atropa belladonna, Nymphaea caerulea, Datura, Opium, others. Pfly (talk) 09:34, 24 November 2009 (UTC)
 * I would guess that the oldest one in systematic use is plain old ethanol. But I don't really know that, and of course it does require more preparation than just picking a leaf or berry or something.  Can anyone do better than guess? --Trovatore (talk) 09:52, 24 November 2009 (UTC)
 * You'd have to define the terms "oldest" and "systematic use" for the question to have a well-defined answer, but I think you're basically right. Sumer is the oldest known civilization, and they had beer.  See Ninkasi.  Ethanol has a disadvantage of requiring more preparation than just picking a mushroom or a berry, but it has the advantage of being able to be produced from a wide variety of plants, including whatever grain is a dietary staple in whatever region, instead of being tied to a plant species that only grows in certain locations.  Red Act (talk) 11:25, 24 November 2009 (UTC)
 * Additionally, beer has some properties that other psychoactive drugs do not have—e.g., it can be used as a potable water source as it resists going bad. That's a pretty big advantage in many cultures! --Mr.98 (talk) 21:53, 24 November 2009 (UTC)
 * Beer was known to the Ancient Egyptians and Mesopotamians. --TammyMoet (talk) 10:29, 24 November 2009 (UTC)
 * As well as cocaine and tobacco, apparently. --  KageTora - SPQW - (影虎)  ( talk )  17:29, 24 November 2009 (UTC)
 * Err, that seems very unlikely. That particular source would not count as "reliable" on here (a second-hand account of a caption of a photo in a French magazine—no peer review, no source, no follow-up, after over 10 years). Since tobacco and cocaine are both "new world" products, it would imply some significant cross-oceanic trading long before that is known to have happened. I would file that as "dubious"/"unlikely"/"bullshit"; certainly, a "needs to display some evidence." --Mr.98 (talk) 21:50, 24 November 2009 (UTC)


 * Fair enough, Mr98, apologies for the poor link, but I doubt it that Colorado State University thinks it's 'bullshit', as you call it, considering they have written a paper here about whether it's true or not and basically agreed that it is. Again, apologies, it was just the first link I found after looking for something I had been hearing about for years. When I post links in future, I'll be a bit more careful. --  KageTora - SPQW - (影虎)  ( talk )  02:19, 25 November 2009 (UTC)


 * No KageTora...bad KageTora - check that article again. (HINT: It's a good idea to actually read the stuff you post as links!) Your Colorado State University paper CLEARLY says at the top left corner (in red ink no less!): "For teaching purposes only, do not review, quote or abstract"...so don't!  It's possible that this paper is used in some course in which students are required to debunk a clearly bogus paper or something - who knows?  At any rate - it's certainly not authoritative - if anything, it's further evidence that this is bogus.  They ask you NOT to use it as a reference.  You really should respect that and not associate their good name with a clearly bogus theory when they specifically ask you not to do that!  So I'm with Mr.98 - "dubious/unlikely/bullshit"...we still don't have any evidence.  The theory that the Egyptians and the pre-Colombians had met (mostly on the grounds that they both built pyramids) - is pseudoscience (or is that "pseudohistory"?)  SteveBaker (talk) 04:50, 25 November 2009 (UTC)


 * Well, in that case, maybe the Wikipedia article on Egyptian mummies needs to be adjusted, as it was through there that I found that article linked to in my last post. The link in the Wikipedia article leads to the wrong page, but it said 'Colorado State University' and a Google search on that plus cocaine plus Egyptian mummies led me to the page. --  KageTora - SPQW - (影虎)  ( talk )  17:06, 25 November 2009 (UTC)


 * Coca leaf has been chewed by people who live near it for a long time, but more as a mild stimulant than a mind-altering stay up all night party drug. --Sean 13:44, 24 November 2009 (UTC)
 * It's quite possible that psychoactive drug use predates humanity, although I'm not aware of any actual evidence for this. The book Food of the Gods by Terrence McKenna -- which, I note, is generally considered pseudoscience -- puts forth the so-called "stoned ape theory of human evolution".  In any case, given the omnivorous diet of hunter-gatherers, it's almost impossible that they could have avoided eating psychoactive plants now and then. Looie496 (talk) 18:36, 24 November 2009 (UTC)
 * And some animal species have been observed to become drunk after consuming naturally fermented fruit. Googlemeister (talk) 19:22, 24 November 2009 (UTC)
 * Cats and catnip too! SteveBaker (talk) 04:35, 25 November 2009 (UTC)

rise in temperature
To get an idea of just how much energy is contained by a single neutron or in the alternative how much energy is released by the fusion of two hydrogen atoms how many degrees would the temperature of one pound of liquid water rise if a neutron were converted entirely to thermal energy or the fusion of two atoms of hydrogen occurred and the energy released expressed as temperature rise of water? I know this is a dumb question and no its not homework. Thanks in advance. 71.100.11.112 (talk) 18:06, 24 November 2009 (UTC)


 * The neutron mass can be found in the linked article to be approximately mM~940 000 000 eV. Using the convertion factor we get mM~0.000 000 000 15 J. That's the same as mM~0.000 000 000 036cal. That means that 1 neutron will lead to a change of 0.000 000 000 036 oC for a mass of 1 gram. 1 pound has about 454 grams so 1 neutron worth of energy would cause a change of 0.000 000 000 000 079 oC on a pound of water Dauto (talk) 19:06, 24 November 2009 (UTC)


 * As for the fusion of two protons, according to Proton–proton chain reaction, that reaction yields about 420 000 eV (about 1/2000 the rest energy of the neutron) so the temperature change would be about 0.000 000 000 000 000 035 °C. Rckrone (talk) 20:05, 24 November 2009 (UTC)


 * ...which is not very useful for visualization purposes. A better way would be to figure out how many neutrons or proton-proton reactions are needed to cause a temperature change of 1 degree.   --99.237.234.104 (talk) 23:10, 24 November 2009 (UTC)


 * That would be given by the inverse of the number I calculated above Number of neutrons ~ 1/(0.000 000 000 000 079) ~ 12 600 000 000 000. Dauto (talk) 00:30, 25 November 2009 (UTC)
 * To get back to measurable(ish) units, that's about 2x10–14 grams of neutrons. DMacks (talk) 02:52, 25 November 2009 (UTC)
 * Or to put it another way, one gram of hydrogen atoms fusing would boil an incredible amount of water, something like a billion liters or something... Vespine (talk) 05:45, 25 November 2009 (UTC)

Flat-nose feature of the actor in Twilight
Does that feature have a technical name? 20.137.18.50 (talk) 20:06, 24 November 2009 (UTC)

beetleguese supernova
Given what we know about the star Beetleguese (sp?) if it was to go supernova (or rather had gone supernova a long time ago and now the light is just reaching earth), would the result be a celestial object visible during the day, or would it not be bright enough? Googlemeister (talk) 20:11, 24 November 2009 (UTC)
 * SN 1054 was visible in the day, and it was ten times further away than Betelgeuse, so I expect yes. Algebraist 20:18, 24 November 2009 (UTC)
 * When it goes, it will be bright enough to read a newpaper by its light, there will be no missing it. See Betelgeuse.  Sp in ni  ng  Spark  23:24, 24 November 2009 (UTC)

Eye color changing mammal
Is there such a mammal that can change the color of its iris, maybe according to mood or food or whatever? --Reticuli88 (talk) 21:13, 24 November 2009 (UTC)
 * FWIW eye colour in humans changes, particularly between the age of birth and about two years old. Very few Caucasian babies are born with dark brown eyes, the tendency is to lose blue in favour of gaining green to brown. --BozMo talk 21:38, 24 November 2009 (UTC)

I mean besides humans - --Reticuli88 (talk) 21:42, 24 November 2009 (UTC)
 * FYI kittens eyes also start off as blue and change colour as they mature  . I suspect eyes changing colour from birth to maturity is fairly common in mammals actually. I'm not really sure if that's what you're thinking of on the other hand you did say simply 'besides humans' in response to BozMo's post so it seemed it may be relevant `Nil Einne (talk)
 * Prostaglandin and its analogs such as latanoprost can darken irises in people and animals.. Irises can change colour after death, as shown in this experiment with pig eyes:. As a tangent, pigmented cornea in dogs can mean "dry eye" or Keratoconjunctivitis sicca. Fences  &amp;  Windows  18:58, 25 November 2009 (UTC)

Max. temperature
What is the maximum temperature (climate) that a human body can survive in? --AlexSuricata (talk) 21:40, 24 November 2009 (UTC)


 * For how long? Googlemeister (talk) 21:43, 24 November 2009 (UTC)
 * I think the word "climate" is intended to imply indefinitely long. Red Act (talk) 22:27, 24 November 2009 (UTC)


 * I would guess a lightning strike produces the hottest temperatures that a human can survive, but that doesn't really count as climate. Ks0stm (T•C•G) 22:22, 24 November 2009 (UTC)

What I mean is, that I read that in some countries the temperature can reach into the 50sº (even up to mid-50sº) - therefore, if I were a God and slowly started to turn the temperature up, what is the temperature at which most people would start to die? --AlexSuricata (talk) 22:35, 24 November 2009 (UTC)
 * Are you now changing your question to refer to something like MaxTemp50?  DRosenbach  ( Talk 01:22, 25 November 2009 (UTC)
 * There are many other factors to consider. Humidity, for one. And the prevalence of shelter and/or shade - does it still have to be 55 degrees in the shade, in buildings? Vimescarrot (talk) 22:48, 24 November 2009 (UTC)


 * Hottest survivable climate is hard to answer...there is Al 'Aziziyah, where the hottest temperature on earth was recorded, however we do not have an article on the town with the hottest climate. There is also the temporary Heat burst. Ks0stm (T•C•G) 22:51, 24 November 2009 (UTC)


 * Humans have been experimentally exposed to very high temperatures for short periods without harm in dry heat. This paper, for instance, went as high as 90°C for ten minutes.  I am certain I have read of a military experiment going to an even higher temperature but cannot locate the paper right now.  Sp in ni  ng  Spark  23:14, 24 November 2009 (UTC)


 * Doesn't answer the question, but see Extremes on Earth. Fences  &amp;  Windows  18:41, 25 November 2009 (UTC)

Shape of a black hole
This is something that's never been very clear to me. In terms of the space it takes up in, erm space, is a black hole actually spherical, or is it more like a conical depression/whirlpool with the singularity at the bottom? --84.69.185.215 (talk) 21:51, 24 November 2009 (UTC)


 * The conical depression is just a way to visualize the gravity well—it doesn't mean that is actually how it occupies three dimensional space. (No more than the Sun actually exists in a little depression as shown in some visualizations of gravity). That being said, my understanding is that the equations come out spherical, but you can have things like relativistic jets that give it a definitely non-spherical appearance. This has to do with the fact that though it is a sphere, it is rotating along an axis, or something along those lines. Someone who knows more, please feel free to correct me. --Mr.98 (talk) 22:13, 24 November 2009 (UTC)


 * As I recall, the black hole itself is an infinitely small point. I may be wrong however, so I'll let other people verify that answer... Ks0stm (T•C•G) 22:20, 24 November 2009 (UTC)


 * Logic would dictate that an infinitely small point with a gravitational pull all around it (i.e. 360°) should be considered to be spherical, or at least, the pull should be. --  KageTora - SPQW - (影虎)  ( talk )  23:36, 24 November 2009 (UTC)
 * A non-rotating black hole has a spherical event horizon. Rotating black holes are a little weirder - they also have a spherical event horizon, but in addition to that they have an oblate spheroidal ergosphere. --Tango (talk) 23:44, 24 November 2009 (UTC)


 * Strong gravitational fields distort the shape of space. A solid sphere is a subset of 3-dimensional flat Euclidean space, but the space around a black hole is not shaped like 3-dimensional Euclidean space.  The problem is that our minds aren't really designed to visualize this distortion.  What's often done to illustrate what's happening is that the picture is simplified to 2 space dimensions, so that space is like a big flat sheet.  Here we can picture distortions in the sheet caused by gravity since we have an extra dimension in our imagination we aren't using.  It's in this representation where a black hole causes that cone shaped sink.  If you try to imagine the same sort of departure from flat 3D space you will have a great deal of trouble. Rckrone (talk) 00:06, 25 November 2009 (UTC)

How does the Transit of Venus allow calculation of the distance from the earth to the sun?
From a diagram on the Transit Of Venus page, I can see how its transit could be used to estimate part of the geometry required to estimate the diameter of the sun, and hence its distance away. But this geometric calculation appears to be subject to knowing the proportional position of Venus between the sun and earth. How was this obtained, in Captain Cook's day? 92.24.170.160 (talk) 22:04, 24 November 2009 (UTC)
 * That proportion could be found using Kepler's laws of planetary motion since the orbital periods of Earth and Venus were known. Rckrone (talk) 22:21, 24 November 2009 (UTC)
 * The proportional distance is easily calculated from the maximum angle between Venus and the Sun, as viewed from Earth. Looie496 (talk) 00:05, 25 November 2009 (UTC)

On second thoughts I'm not sure I do understand the transit method - would anyone like to explain it more please, step by step? It seems to me that you would need to know the distance from the earth to Venus to start with - I presume that was not known. 78.146.176.198 (talk) 23:12, 25 November 2009 (UTC)


 * The transit would have to be measured from different points on the earth. The exact time that it starts or stops can then give a difference in the angle to Venus as observed by the two observatories, then triangulation can be used to measure the distance to Venus. Graeme Bartlett (talk) 06:26, 26 November 2009 (UTC)

OK, although provided you could see Venus, then couldn't you do that at any time without requiring a transit? 78.146.237.244 (talk) 09:38, 26 November 2009 (UTC)

Speed Of Light
If humanity had not developed senses that could detect light, what would Einstein's idea about it being impossible to travel at or over the speed of light have become? This sounds like a hypothetical question, but what I mean is, is there anything stopping us, besides the existence of light? --  KageTora - SPQW - (影虎)  ( talk )  23:31, 24 November 2009 (UTC)


 * I think there are a range of answers, one of which might be that humans might have invented sensors that measure light, much as they've invented sensors that measure other things humans cannot sense but which are measured by humans using those sensors. It's the law that stops us, not the light, so although the existance of light has to do with the law, it is not the existence of light which is the barrier. --Tagishsimon (talk) 23:38, 24 November 2009 (UTC)


 * The speed of light is also the speed of radio - the speed of microwaves - the speed of heat (when it's radiating). If (for example) we'd still have been able to discover radio - then I think we'd have made radio telescopes and the question might have arisen that radio waves from far distant quasars or whatever always arrived at the same speed.  So presuming that we'd still somehow have been able to develop science and technology at all - then I don't see why we couldn't figure out relativity based on other frequencies of electromagnetic radiation. SteveBaker (talk) 00:04, 25 November 2009 (UTC)
 * The speed of light appears as a parameter in Maxwell's equations for electromagnetic fields. So if we understood electricity and magnetism, we would know about the speed of light regardless of our senses. Looie496 (talk) 00:10, 25 November 2009 (UTC)
 * Indeed, it was the puzzling appearance of c as a constant in those equations that lead Einstein to formulate relativity. Algebraist 00:14, 25 November 2009 (UTC)

Well, this is what I'm getting at. 'C' may be a constant, but why does it have to be light? Before the 'discovery' of light, in our hypothetical universe where humans don't perceive light directly, what would have been the constant? I suppose radio waves would answer that question, as said above, but radio comes in waves, whereas light behaves both as a particle and as a wave (or has that puzzle been sorted out yet?). In either case, there are particles which have been found to travel faster than the speed of light, or at least appear to. When we sort that question out, will they become the new 'constant'? The question I am asking really, is why is light so special? --  KageTora - SPQW - (影虎)  ( talk )  02:03, 25 November 2009 (UTC)
 * To attempt to answer your questions in order: human-like beings smart enough to have discovered relativity will probably have discovered electromagnetic radiation already (whether or not they are able to directly perceive it), and will recognize the maximum speed prescribed by relativity as the speed of electromagnetic rays. If not, then the maximum speed in relativity will just be a new fundamental constant they'll have to think of a name for. Radio and light are essentially the same thing: they're both electromagnetic radiation, just of different wavelength/frequency/energy. Electromagnetic radiation comes in neither waves nor particles; both of these notions are just imperfect models which are sometimes useful in studying them. There are no particles which go faster than light, or which appear to do so. On your last question, you seem to be thinking the wrong way round: the unfortunately named speed of light is first and foremost the maximum speed anything can go at, and secondarily the speed at which light happens to go (when in a perfect vacuum). Light moves at c because it is massless, and all massless things move at the same speed, so light isn't particularly special in this regard. Algebraist 02:20, 25 November 2009 (UTC)
 * Likewise, "light" in the strictest sense, that is visible light, is a narrow range of wavelengths between about 400-800 nanometers. There is absolutely nothing at all special about it compared to other parts of the electromagnetic spectrum except that human eyes are "tuned" to detect radiation in that very narrow range.  The speed is more properly called "the speed of electromagetic waves"; there is nothing all that special about "light" compared to any other parts of the spectrum, except that humans are predisposed to paying more attention to it due to our special biology.  Indeed, the attention we give to that narrow band of wavelengths is all out of proportion with the part of the spectrum that band represents.  -- Jayron  32  02:30, 25 November 2009 (UTC)
 * Notably, our OP seems to think that light and radio waves are somehow "different" - but they aren't. Both exhibit the "wave-particle duality" thing - both travel at the same speed and obey the exact same laws.  As you go through the colors of the spectrum from blue down through green, yellow, orange and red - you reach infra-red, then millimeter-wave radio, then regular radio waves - it's a continuous thing.  The only thing that changes is our eyes' ability to see them and our ability to pick them up with an antenna. SteveBaker (talk) 03:35, 25 November 2009 (UTC)


 * In terms of causality, the main thing that distinguishes "light" from other wavelengths of electromagnetic radiation is that solar irradiance of the Earth's surface peaks within the wavelength range we call "light". That wavelength range also being the range we can see is just due to it being in our evolutionary environment:  We have evolved to be able to see that range, because that's the range for which there was the greatest evolutionary pressure to be able to see.  Red Act (talk) 08:06, 26 November 2009 (UTC)

Let me try to address the question in a different way. Einstein did not start out by assuming that the speed of light is constant -- this was a consequence of his theory, not an assumption. What he really cared about was Maxwell's equations for electromagnetism. According to Newtonian physics, Maxwell's equations could only be valid in one frame of motion (called the "ether"). This violated Einstein's intuitions: he thought that Maxwell's equations should remain valid even in moving reference frames, and worked out a set of rules that would make that happen. The constancy of the speed of light was a consequence of those rules. Looie496 (talk) 18:02, 25 November 2009 (UTC)

KageTora, the Universe has a speed limit and light happens to travel at that speed limit (because light particles are massless) so it is convient to call that speed limit the speed of light. You could also call it the speed of gravity which also travels at the speed limit. Dauto (talk) 19:28, 25 November 2009 (UTC)