Wikipedia:Reference desk/Archives/Science/2012 September 18

= September 18 =

how to figure out the habitable zones
I've been told nobody knows where the habitable zone will be in 7.6 billion at the tip of future RGB but with the Habitable zone of foreign stars, it is pretty easy how to calculate where the habitable zones is in on remote stars by luminosity and size of star. The red dwarf star's habitable zone is where Mercury is, and the large blue stars' habitable zone is where 2 AU is. Is figuring out the habitable zones in remote solar systems direct, or is it an estimation. When people use an instruments to look at foreign solar system, they can see all the planets they have in the star, like red dwarf star, they have the rough picture about the habitable planets, and one red dwarf star system is pretty similar to our solar system, it has four rocky planets three gas giants, and two ice dwarfs. Is figuring out the luminosity and the size of star the only way to determine the habitable zone. Can detecting stars involves missing information, I thought when an astronomer look through blue stars through high-tech telescope or spacecraft, they can see all the planets they have, includes gas giants and ice dwarfs they have.--69.226.32.74 (talk) 01:52, 18 September 2012 (UTC)


 * I don't believe they can see extrasolar planets directly. Instead, they find them by measuring how the star wobbles (red-shift/blue-shift changes) or how it's luminosity changes as the planet passes in front of it.  So, yes, it's just an estimation.  So far, they can only detect large planets by these methods, but, of course, life could also exist on a small planet.  StuRat (talk) 02:04, 18 September 2012 (UTC)


 * Believe. :)--Robert Keiden (talk) 04:51, 18 September 2012 (UTC)


 * Interesting. Looks like they've improved the methods of blocking the star's light since last I read up on it. StuRat (talk) 06:04, 18 September 2012 (UTC)


 * I am wondering is it because the small planets like Mercury, Venus, Earth, and Mars are close-packed together, and Jupiter, Saturn, Uranus, and Neptune are far separated apart which leads difficult to predict habitable zones, could that be the case? Did any astronomer try to figure out the habitable zone on far-distant planets at another star? If we have another giant stars which is 100 times bigger than sun they can find out by far distant planets the same distant as Saturn and Uranus, or sometimes when planets are so far from the star, looking at extrasolar planets they cannot see it.--69.226.32.74 (talk) 02:26, 18 September 2012 (UTC)
 * The Sun's luminosity and size are the main factors. If Venus had an Earth-like atmosphere, it would probably be habitable (though it might be a bit warm). Mars, too (but a bit colder).--Robert Keiden (talk) 04:51, 18 September 2012 (UTC)


 * I don't see how the placement of planets affects the habitable zone (only whether those planets are in it). And, yes, astronomers are very much interested in finding extrasolar planets in their star's habitable zones.  However, a few points to consider:


 * 1) Distance from the star and the size and type of star aren't the only factors. A large planet will tend to be hotter at the same location as a smaller planet.  And a planet with a major greenhouse effect (like Venus) can be much warmer than one without it.  Even moons of large planets can be warm, due to tidal heating.


 * 2) The whole concept of a habitable zone is based on the idea that liquid water is needed for life, when other solvents, like liquid methane, might also work, at much lower temperatures. StuRat (talk) 02:33, 18 September 2012 (UTC)


 * The main reason for uncertainty in the Solar System's habitable zone 7.6 Ga (billion years) from now is that we're not sure how much the Sun will expand when it reaches RGB, and exactly how bright it will be. The HZ is likely to start somewhere beyond the asteroid belt, and end somewhere before Neptune, but it could be pretty narrow.  Until we understand the evolution of the Sun better, the best we can do is guess.--Robert Keiden (talk) 04:51, 18 September 2012 (UTC)


 * Robert, what you meant by it can be pretty narrow. It is because Jupiter, Saturn, Uranus, and Neptune are currently vastly far apart, and also star's temperature drop, and planet's orbit expands, is that another key for unknowns/unclear. If HZ happens to Saturn's system can we sequentially predict what will happen for Uranus, or it doesn't necessarily follow the pattern.--69.226.32.74 (talk) 05:06, 18 September 2012 (UTC)
 * You can think of it as a ring around the Sun. Right now, the ring is wide enough that there are 2 or 3 planets inside (whether Venus is just inside or just outside is debatable). In 7.6 Ga the ring will be farther out.  There could be 2 or 3 planets that fit inside it, or there might be 1 or none. Maybe Jupiter, maybe Saturn, maybe Uranus, maybe Neptune, some of the above or none of the above. Mars will be too hot.  Mercury and Venus will be toast.  Earth will be either covered with lava or be toast. By that point, if there are any people still around, they probably won't be living in the Solar System. And they will probably have more interesting things to worry about...--Robert Keiden (talk) 06:06, 18 September 2012 (UTC)

Okay, another way to look at it: The sequence is predictable, but we don't know how far it will go. Maybe something like this: --Robert Keiden (talk) 06:06, 18 September 2012 (UTC)
 * 2 Ga ago - Venus, Earth, Mars
 * Present - Venus(marginal), Earth, Mars
 * 1 Ga from now - Earth(marginal), Mars
 * 4 Ga from now - Mars(marginal)
 * 6 Ga from now - Jupiter(??), Saturn(??)
 * 7 Ga from now - Jupiter(???), Saturn(???), Uranus(???)
 * 8 Ga from now - Jupiter(????), Saturn(????), Uranus(????), Neptune(????)
 * 11.5 Ga from now - Venus (which no longer exists), Earth (if it still exists will be crispy fried)
 * 12.0 Ga from now - Mercury, Venus (which no longer exist)
 * 13.0 Ga from now - Mercury (which got eaten by the Sun around 7-8Ga)
 * 14.0 Ga and after - none
 * You oversimplified a little bit on Venus, Venus may still be around, just less likely than Earth.--69.226.32.74 (talk) 06:26, 18 September 2012 (UTC)
 * The changes in the Red Giant phase are quite rapid when compared to main sequence stars, though. If it starts in 6 Ga, it will probably be over in another ~0.2 Ga.
 * 6 Ga from now: Red Giant phase begins. Jupiter, Saturn
 * RGP+0.1Ga: Jupiter(?), Saturn, Uranus.
 * RGP+0.2Ga: Saturn(?), Uranus, Neptune, and some trans-neptunic minor bodies. End of Red Giant phase. If Earth survives, it'll have an iron-nickel atmosphere by then.
 * RGP+0.3Ga: Earth(if still around), Mars?
 * RGP+0.4Ga: Venus if it's still around (although Red giant says it won't)
 * The main problem is that scientists cannot "watch" anything that slow. In 0.2 Ga we'll be able to predict with much greater accuracy how big the sun will be in its Red Giant phase, and how long it will stay a giant. - ¡Ouch! (hurt me / more pain) 11:51, 18 September 2012 (UTC)

Newtonian two-body problem
In the Newtonian two-body problem, the masses are assumed to be point masses. What if the size of one or both objects is not negligible compared to the distance between them (say a moon of Jupiter). Is the solution still the same as if they are point masses? Bubba73 You talkin' to me? 02:20, 18 September 2012 (UTC)


 * Not exactly the same, as you get tidal effects, which cause the orbit to decay (very slowly). Although, I think if the body was absolutely rigid and uniform at each depth, then, by the shell theorem, it would behave exactly as a point. StuRat (talk) 02:23, 18 September 2012 (UTC)


 * Just a little quibble. The orbit might decay but it might also rise. In fact, that's what's happening with our moon which is actually slowly moving away from the Earth. Dauto (talk) 14:48, 19 September 2012 (UTC)


 * I was under the impression that the term "orbital decay" included both cases, but our article seems to agree with you. Do you know of a term for an orbit of ever increasing altitude and a term encompassing both ? StuRat (talk) 21:16, 19 September 2012 (UTC)


 * Gravitational force is what is known as a central force - that is, it appears to come from a point located at the object's centre of gravity. StuRat's shell theorem is a special case of this, applying to spherical objects. So, yes, neglecting tidal damping, the solution is the same, once you have the location of the centres of gravity in each object. Distance does not matter. See wiki article on central force. Wickwack121.215.23.108 (talk) 02:40, 18 September 2012 (UTC)


 * Thank you both. Bubba73 You talkin' to me? 02:51, 18 September 2012 (UTC)


 * You're quite welcome. StuRat (talk) 04:31, 18 September 2012 (UTC)

Chemistry change
What do you call the irreversable process which occurs when molucular compounds such as ScH3 condense from the gas phase into a non-stoichiometric interstitial alloy (ScH2.9), eliminating trace hydrogen in the process? I don't think that it is polymerisation. Plasmic Physics (talk) 03:07, 18 September 2012 (UTC)
 * Adsorption? -- Jayron  32  03:55, 18 September 2012 (UTC)
 * That doesn't seem correct, because the initial molecule does not retain its identity. An actual chemical reaction is taking place, adsorption could be the initial stage, but there's more to it. Plasmic Physics (talk) 04:06, 18 September 2012 (UTC)
 * That sounds like chemical precipitation or an analog of it. μηδείς (talk) 04:21, 18 September 2012 (UTC)
 * Does trawling papers describing this behaviour of ScH3 (or analogous compounds) not reveal an appropriate term? Brammers (talk/c) 22:10, 18 September 2012 (UTC)
 * No. Plasmic Physics (talk) 02:22, 19 September 2012 (UTC)

glass in thistles/nettles
I can't remember which it was, nettles or thistles, but one of them, our biology teacher told us 30ish years ago, is equipped with prickles made of a form of sugar glass - the former seems more likely, considering the nettle's trichomes, which are brittle and snap on contact to release toxins...

Is there any truth to this at all? Do plants produce glass?

Thanks Adambrowne666 (talk) 04:25, 18 September 2012 (UTC)


 * Yes, it is true. Nettles have microsized silica based spines. Plasmic Physics (talk) 04:31, 18 September 2012 (UTC)


 * Sorry, but silica crystals are not glass, especially not candy glass. μηδείς (talk) 05:27, 18 September 2012 (UTC)


 * I didn't say that it was glass, I said "yes" to "is there some truth to this". Plasmic Physics (talk) 05:49, 18 September 2012 (UTC)


 * You probably would have been better off with a "not exactly" than a "yes"; but I only indented to show temporal sequence, my post was not a criticism of yours. The OP is the one who asked about glass and candy glass. μηδείς (talk) 06:00, 18 September 2012 (UTC)


 * Would temporal sequence be unclear if your entry were below PP's but on the same level? —Tamfang (talk) 22:01, 18 September 2012 (UTC)


 * OK, lets not make the whole conversation about indentations. We should settle that while there is a prescribed Wikipedia indentology, Medeis was simply unaware of it: Indentation. I made the same mistake before I changed to the prescribed one. Now let us leave it at that. Plasmic Physics (talk) 22:10, 18 September 2012 (UTC)


 * You will find most people simply indent one from the post above no matter what. I tend not to indent at all specifically when I want to make it clear I am not responding to any response above mine.  But I don't like when people use the same indentation as the person above them without an asterisk, as it sometimes makes it look as if the second party's post is a continuation of the one he didn't indent from.  I have even had a lunatic tell me I couldn't place my post below his no matter how I did or did not indent it.  Oh well. Back to the question, back in the day before Alvarez I remember reading the dinosaurs went extinct due to the rise of the grasses, which had a high silica content, grinding their teeth down and starving the plant eaters. μηδείς (talk) 01:29, 19 September 2012 (UTC)


 * Doesn't sound like much of a theory to me. Dinosaurs would have evolved harder teeth, more frequent replacement of teeth, eating things other than grass, etc., in response. StuRat (talk) 02:01, 19 September 2012 (UTC)


 * The OP might like to read a in-depth explanation of how biomineralization with silica forms the nettle hairs. See: Advances in inorganic chemistry, Volume 36 As edited by A. G. Sykes On pages 147 & 175.]--Aspro (talk) 09:22, 19 September 2012 (UTC)


 * Thanks, all - just what I needed - thanks for the link too, Aspro Adambrowne666 (talk) 09:43, 19 September 2012 (UTC)

Highest railway gradient in England
What is the highest gradient stretch of railway in England between two stations ? — Preceding unsigned comment added by Tarka4 (talk • contribs) 07:25, 18 September 2012 (UTC)
 * If by "highest gradient" you mean "steepest", then Lickey Incline could be what you're looking for. - Ka renjc 08:21, 18 September 2012 (UTC)
 * I concur with the Lickey Incline, but only if you mean (a) still in use and (b) standard gauge railway. We have a List of steepest gradients on adhesion railways which gives others. --TammyMoet (talk) 08:24, 18 September 2012 (UTC)


 * Surprisingly, the above article doesn't mention the Docklands Light Railway where the entrance to the tunnel from the original London and Blackwall railway viaduct to the tunnel to Bank has the steepest gradient on any British railway at 1 in 17 (5.88%) (according to this article).--Shantavira|feed me 08:48, 18 September 2012 (UTC)


 * There is also the short section on the line that links Exeter Central with Exeter St Davids (sometimes called the 'Exeter Incline' I think), which is variously claimed to be 1 in 31, 33, 36, 37 or 39, from what I've been able to find, but it's definitely steep. Mikenorton (talk) 18:09, 18 September 2012 (UTC)

Are black holes point particles?
Are black holes point particles?165.212.189.187 (talk) 15:40, 18 September 2012 (UTC)


 * Perhaps the singularity can be considered as such, but not the event horizon. StuRat (talk) 16:00, 18 September 2012 (UTC)


 * (ec) No. And maybe yes.  The event horizon is a useful, usable physical concept that has dimensionality.  On the other hand, the gravitational singularity is at least potentially a point particle (in a non-rotating black hole), though there's a good chance that's an artifact of the math rather than the true physical representation. &mdash; Lomn 16:03, 18 September 2012 (UTC)

Lets say for argument sake it is an artifact. What is being done to address the artifact?165.212.189.187 (talk) 16:33, 18 September 2012 (UTC)


 * You may be interested in reading the Cosmic censorship hypothesis and the Black hole information paradox, which is one way of addressing it. In this case, it amounts to throwing up your hands and saying "fucked if I know", but with lots of equations instead of words to say that.  -- Jayron  32  16:36, 18 September 2012 (UTC)


 * See Fuzzball (string theory). Wnt (talk) 16:53, 18 September 2012 (UTC)

OK, let me rephrase my second Q: Lets assume that its an artifact, ie. it is not a point particle but in fact a very volumious "black star." now knowing that the math is returning the artifact of a point cant we learn how the math is wrong? THe math must be "using" space-time as an inherent part of how we measure not only that black star but everything else also, in other words taking the space-time for granted?165.212.189.187 (talk) 14:12, 19 September 2012 (UTC)


 * The short answer is that there isn't any verified theory of quantum gravity. With black hole singularities you're trying to calculate the effect of something very small (normally the purview of quantum mechanics) with a theory worked out for the very large and very heavy (general relativity). The two, as currently formulated, are incompatible, which explains why you end up with "nonsensical" results like singularities. I believe the general impression is that once a workable theory of quantum gravity is developed, infinite density singularities will "disappear" in more the complete calculations. (The same sort of thing has happened before in quantum mechanics - see renormalization). -- 205.175.124.30 (talk) 01:12, 20 September 2012 (UTC)


 * Another way to look at it: A singularity means (by necessity) an object of zero volume, and thus of infinite density. Infinity is math's way of telling you you screwed up somewhere.  Or less colloquially, any model contains some approximation of reality.  Sometimes, the nature or source of the approximation is unknown, but the fact that some calculation gives you "infinity" for any measurable quantity is usually a remind that you're still working with a model.  -- Jayron  32  04:55, 20 September 2012 (UTC)


 * Well, there do seem to be some physical phenomena which are indeed "infinite". Superconductivity means infinite conductivity, for example.  A Bose–Einstein condensate is another example. StuRat (talk) 05:12, 20 September 2012 (UTC)


 * Well, kind of. Superconductivity is a physical zero, not a physical infinity.  The key property is resistance, and in a superconductor, the resistance drops to zero.  Saying that the conductivity is infinite is just a mathamatical restatement, since conductivity is the mathematical inverse of resistance.  But the physical property itself is resistance, and physical properties can measure zero.  They just can't be infinite.  You can't, for example, have a truly infinite resistance: any real material will conduct an electric current given a sufficiently large voltage.  There are Superinsulators, but these probably don't have truly infinite resistance (despite what our article says), merely very large resistance jumps (5-6 orders of magnitude) when cooled to very low temperatures.this paper for example, contests that the resistance is trule "infinite".  In a singularity, the density (the physical property) would be actually infinite, which is a physical impossibility.  See Gravitational singularity, where it explains quite well: "Many theories in physics have mathematical singularities of one kind or another. Equations for these physical theories predict that the ball of mass of some quantity becomes infinite or increases without limit. This is generally a sign for a missing piece in the theory, as in the ultraviolet catastrophe, renormalization, and instability of a hydrogen atom predicted by the Larmor formula." -- Jayron  32  05:45, 20 September 2012 (UTC)


 * I'm not seeing the difference. A black hole singularity has zero volume, and thus infinity density, just like a superconductor has zero resistance, and thus infinite conductivity.  And what makes resistance the fundamental property, and not conductance ? StuRat (talk) 16:42, 20 September 2012 (UTC)


 * There is a fundemental difference. If I have zero money in my pocket, I can say that I am infinitely broke.  That is mathematically true, but the difference is the absence of the money in my pocket.  That's a physical zero that I can call an infinity by performing some math on it (taking the inverse).  But just as it is actually impossible to have an infinite amount of cash, but not to be infinitely broke, it is impossible to have an infinite resistance, but not an infinite conductance.  For any inversely related pair of named properties, you're always going to have one of which relates to a physical quantity or property that ultimately ties to the physical components of the system.  The difference is the difference between Intrinsic and extrinsic properties.  Anything which requires the intrinsic properties of the material to be infinite is a physical impossibility.  In a material, the intrinsic property is resistivity (resistance is dependent on the amount and shape of the material as well as the resistivity.  Consider what causes conductivity: a substance conducts electricity if you can get its electrons to move into the "conduction band" as explained by Electronic band structure.  Now, here's the thing: the distance between the conduction band and the valence band is never infinite, that would require an electron to take an infinite amount of energy to be able to promote to a higher energy level: that doesn't happen.  You can have zero resistance if the conductance and valence bands become degenerate (that's what a superconductor is), but there is no physical way to have an electron which can take an infinite input of energy and stay put.  So resistivity is the intrinsic property, because it starts counting at zero and goes up from there.  Conductivity can never be zero.  -- Jayron  32  18:12, 20 September 2012 (UTC)


 * Aren't the mass and volume of the singularity also the intrinsic properties, with density being merely a derived value ? StuRat (talk) 17:04, 21 September 2012 (UTC)

Again: OK, let me rephrase my second Q: Lets assume that its an artifact, ie. it is not a point particle but in fact a very volumious "black star." now knowing that the math is returning the artifact of a point cant we learn how the math is wrong?165.212.189.187 (talk) 12:38, 20 September 2012 (UTC)


 * Per the first answer to your last rephrase: no, not yet. What theories we currently possess yield a singularity, and no theory that resolves the singularity has yet gained anything approaching widespread acceptance.  So no, right now, we can't, though we're trying.  Perhaps someday we will be able to resolve the matter (although direct experimental verification of phenomena within an event horizon is unlikely to ever happen). &mdash; Lomn 13:18, 20 September 2012 (UTC)


 * Addendum: bear in mind that the solution to "learn how the math is wrong" isn't "get rid of the singularity", it's "get rid of the singularity with a theory that is at least as accurate as current theory in all other regards". The former is trivial, but also meaningless. &mdash; Lomn 13:21, 20 September 2012 (UTC)


 * Hear, hear. ;-) --Modocc (talk) 13:58, 20 September 2012 (UTC)

Observer effect
Who first came up with the theory that the act of observation materially affects that which is being observed? Our article doesn't say. --TammyMoet (talk) 17:58, 18 September 2012 (UTC)
 * Which Observer effect are you asking about? There are several unrelated concepts known by that name, so before we can nail down where the particular usage originated, we need to know which usage you are asking about.  -- Jayron  32  18:27, 18 September 2012 (UTC)
 * Did I not make it clear? Someone once said that if you observe a situation (particle, wave...) then the act of observation affects that thing that is being observed. The Observer effect (physics) article is not one of our best, and only says that it is often confused with Heisenberg's uncertainty principle - but doesn't say who first come up with the Observer effect. --TammyMoet (talk) 19:11, 18 September 2012 (UTC)
 * Actually, you didn't in your question make any mention of the physics effect, compared to the other observer effects, such as the one from psychology. In that case, the concept of the "obersver effect" is very closely related to the Copenhagen interpretation and other similar interpretations of quantum mechanics.  I don't know if we can narrow down exactly which physicist invented the specific word formulation "observer effect" to describe it, but as a concept the idea that the observer fundementally changes a quantum system (as opposed to merely recording what was indetermined before their observation) is, as far as I know, very closely tied to the Copenhagen interpretation.  Other interpretations don't necessarily hold it to be true, except in the trivial sense that photons striking things causes them to change.  -- Jayron  32  19:18, 18 September 2012 (UTC)
 * A bit more: The observer effect in physics is predicated, by the Copenhagen Interpretation, on Wave function collapse, which as a concept was devised by John von Neumann to deal with what was known as the Measurement problem. So there's a lead for tracking down the concept.  -- Jayron  32  19:21, 18 September 2012 (UTC)


 * Hmm, this is an interesting question. I have always thought of this as being derived from Complementarity, but I've never really tried to zero in on the specific origins of the observer effect before. I'll dig through some of my books on this subject tomorrow if I get the chance... I suspect that one of Max Jammer's many books holds the answer, here. --Mr.98 (talk) 02:39, 19 September 2012 (UTC)


 * Heisenberg was the first to do analysis of measurements, the accuracy they would provide and the disturbance they would cause, as a function of the wavelength and thereby the energy of the photon. That's what he expressed in his uncertainty relations (or relation, if using the vector form). Bohr and Heisenberg concluded that statistical distributions only existed potentially, and the potentiality is made effective by the measurement itself. Einstein pointed out an observer effect at the Solvay conference (not saying he called it that), that a negative measurement could also collapse the probability wave. The Copenhagen School holds that the description given by the wave function of the interaction is optimal. When the observer reads the result, the knowledge changes the probabilities. But since the Copenhagen school holds that our description was optimal before we read the result, the reading itself has changed the system. Schrodinger objected, with his cat paradox. von Neumann disagreed with Schrodingers conclusion that the observer in effect killed the cat, according to the copenhagen interpretation. Neumann extended the system to include the observer, as made up of atoms etc. The change in the observers consciousness by registering the result changes the total wave function. Einstein, Podolsky and Rosen came up with another paradox, and so on... Ssscienccce (talk) 15:36, 19 September 2012 (UTC)

gas-filled fiber for space elevator cable

 * I, somewhat before, acquainted with (acqired?) an idea about "space elevator"(cf.Space elevator).
 * I am now obtaining infornation mainly from newspaper, television, radio in Japan. And from as far as information I have tells me, as material for fiber, two of "strong" ones possible, recently developed, are "carbon nanotube" and "carbon graphite"(which I read in newspaper article, as I remember, maybe not for space elevator).
 * I am now wondering, is it possible to have something like "gas-filled fiber", a fiber in which gas is, and hopefully supporting it and/or light (lighter than the atmosphere)?
 * Like sushi (talk) 21:18, 18 September 2012 (UTC)


 * A space elevator goes all the way through the atmosphere; at higher altitudes there isn't much outside air, so to be buoyant there would have to be even less gas (by mass) inside such a structure. There isn't such a magical flying-gas. Science fiction authors have toyed with the idea of producing a nano-tech vacuum aerostat, where the carbon nanotubey-thing is evacuated, but is so strong that it keeps a larger size and holds up against external air pressure. But that's even more science fiction than a space elevator. -- Finlay McWalterჷTalk 21:32, 18 September 2012 (UTC)


 * Ah. In non-buoyant(?) atmosphere, how about hydrogen, helium... And how about charging them to make it with more pressure?
 * Like sushi (talk) 01:55, 19 September 2012 (UTC)


 * Retyping, with Mr. or Ms. (?) A8875 commenting below,
 * it should have been something like:
 * Ah. To be buoyant in the atmosphere, how about hydrogen, helium... And how about charging it for more pressure?


 * And I noticed, hydrogen can be dangerous, by itself, and helium is difficult to charge, as I learned.
 * So, how about mixed gas of two instead?
 * Like sushi (talk) 03:06, 19 September 2012 (UTC)


 * At the the diagram on the Space elevator nicely demonstrates, the vast majority of the structure is in space, where there is nothing to be buoyant against. Atmospheric density falls to essentially 0 at 40km above Earth, while the space elevator must go to 35,800km. The part of the elevator within the buoyant atmosphere is less than 0.1% of the overall structure. A8875 (talk) 21:49, 18 September 2012 (UTC)


 * So, in buoyant(?) space, it can be, at default, vacuus inside?
 * Like sushi (talk) 01:55, 19 September 2012 (UTC)


 * Please refer to buoyancy. I think you have the (extremely common) misconception that some gasses, like hydrogen and helium, are "light" and thus will float up no matter what. In reality, it's the difference in density that makes things float. Since vacuum has a density of 0, nothing can have buoyancy in a vacuum. A8875 (talk) 02:10, 19 September 2012 (UTC)


 * Perhaps something with negative mass, although physicist haven't found such a thing yet. StuRat (talk) 02:19, 19 September 2012 (UTC)


 * Part of the point is that a space elevator does not NEED to be buoyant! It connects the surface of the earth to a geostationary satelite, the satelite is what hold the cable up. Sort of how the chain on a hammer throw is kept taught by the rotation of the ball at the end. The only complication is that the cable would drag a regular geo-stationary satellite out of geo-stationary orbit so you just put the satellite further out, so that with the cable the satelite will be geo-stationary. Vespine (talk) 02:32, 19 September 2012 (UTC)


 * The forces on the cable from gravity pulling it down at one end and the satellite pulling it up at the other end might be enough to snap the cable, though. This problem could be eliminated if the cable was neutrally buoyant at all points.  However, for the large portion beyond the atmosphere, this would require that it have zero net mass. StuRat (talk) 03:12, 19 September 2012 (UTC)


 * Sorry. I took, without reference, "buoyant" may mean something similar to "vacuus".
 * Retyping:
 * So, in space where there is no need to be "buoyant", it can be, at default, vacuus inside?
 * Like sushi (talk) 03:06, 19 September 2012 (UTC)


 * If structure can include space with less heavy gas than the atmosphere, more structures are possible, with a little bit of additional "float", I think.
 * Like sushi (talk) 03:06, 19 September 2012 (UTC)


 * I doubt this is what the original poster meant, but I notice he used the word "charged". Is it possible, in space, to build a very long, highly charged fiber and keep it charged by connecting it to a power supply (with reasonable losses) - and if so, is there any way that this might improve the fiber's tensile strength?  (True, you'd think charges would push away from each other and make things worse, but though I don't know anything about materials science I know it's not all that simple) Wnt (talk) 04:09, 19 September 2012 (UTC)


 * It is not a, perhaps, usually conceieved "power supply", but does cosmic ray help?
 * Like sushi (talk) 06:25, 19 September 2012 (UTC)


 * And maybe to be added, being light, by itself, may alliviate burden.
 * Like sushi (talk) 06:32, 19 September 2012 (UTC)


 * Slight escaping of gas, if there is, may "support" some form of material.
 * Like sushi (talk) 07:01, 19 September 2012 (UTC)


 * As I recognize myself, I am not good at probability, but fiber, usually not spherical, and probably positioned longer vertically, would be, lighter gas inside and heavier gas outside, if pressure is probabilistically neutralised, very slightly "expanding" horizontally, for outside gas needs to be pressured more.
 * Like sushi (talk) 07:21, 19 September 2012 (UTC)


 * With gas, probably vertically longer fiber slightly expanding horizontally, would additionally "pull" a little, though atomic bond would be more burdened.
 * Like sushi (talk) 20:03, 19 September 2012 (UTC)


 * Would, charging cable, positive, negative, positive, negative, ...in turn, improve "tensile strength"?
 * For positive-positive, negative-negative shortest distance being twice positive-negative, negative-positive shortest distance,
 * coulomb force for nearest positive-positive and negative-negative pair would be, without other effects,
 * one-forth of coulomb force for nearest positive-negative and negative-positive pair,
 * next nearest such being addtionally, but not so differently distanced,
 * and if number of postively charged parts and negatively charged parts are the same,
 * positive-negative and negative-positive pairs would be more than positive-positive and negative-negative pairs.
 * Like sushi (talk) 13:57, 19 September 2012 (UTC)
 * Salts are like that, but I don't know of any that are strong. Even after some consideration, I don't actually know why ionic bonds are weaker than covalent bonds, though if I had to guess, it would be because you can separate the participants in an ionic bond and both retain octets, whereas one or both members of the covalent bond would lose them.
 * Another idea would be if you had something with alternately charged side groups, but usually I'd think that just building another covalent chain there would be stronger. Still, I don't actually know it couldn't strengthen a structure in the right situation... and looking up Kevlar, I see that indeed, its separated partial charges (-O- and N+-H in the enol resonance structure) contribute to its structural strength. Wnt (talk) 03:43, 20 September 2012 (UTC)