Wikipedia:Reference desk/Archives/Science/2007 October 8

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October 8

muscular development

if a ten year old child carried a piglet half a mile (or more, how much can a ten year old handle) then would the child be able to continue carrying the pig as it grew into an adult? or would there be a point where the pigs growth outstrips the benefits of the exercise for the child? how would it be after a few years? how about if the kid was a few years older? this has been bugging me for a while, thanks 81.96.164.140 00:20, 8 October 2007 (UTC)

There's too many variables to ever give a reasonable answer here. How big is the child? How big is the piglet? How much development goes on in each? Does the pig wind up as bacon? -- Kesh 00:24, 8 October 2007 (UTC)

ok then: assuming you bought a ten year old boy a normal domestic pig that's one week old for his birthday (his tenth birthday), and then assuming that both he and the pig developed as averagely as possible (aside from the extra development he would gain as a side effect of carrying the pig) would there be a point, say when he's thirteen and the pig is three, that he would be unable to lift the pig? or would he get used to its weight because of the slow speed of its growth and become a freakinishly strong child?

Well, piglet-carrying is like any other form of exercise: it'll build muscles, but only up to a point. Competitive athletes exercise intensively just to stay at their personal limit of muscle strength, but they can't get beyond it -- which is why some of them take drugs to raise the limit. If there are child athletes who at the age of 13 have developed by conventional exercise the strength to carry a 3-year-old pig, then it ought to be possible for the hypothetical piglet-carrier. If there aren't, then probably it's impossible. --Anonymous, 05:03 UTC, October 8, 2007.

This is an old idea - but it depends on a couple of logical flaws:

1. It assumes that a child can increase muscle capacity at a rate that is greater than that a pig can gain weight. I doubt this is true. Since the weight of the pig increases as the cube of it's size yet the kid's muscles (whose power is proportional to the cross-sectional area) only increase as the square of the kid's size. If the kid and the pig were to grow at the same rate, the weight of the pig would rapidly outpace the kid's ability to put on muscle cross-section. That would be true if kids and pigs grew at comparable rates - but they don't. A pig grows to full size in just a couple of years - a kid needs nearly 20 years to do the same thing.
2. It assumes that the kid never has a 'bad day' - if the kid were to get a bad cold - then maybe it would be unable to carry the pig even at it's old weight for several days in a row - the exercise regimene would be broken and it's likely that the kid would never catch up.

SteveBaker 11:52, 8 October 2007 (UTC)

I seem to recall Herakles doing something of the sort with a calf. DuncanHill 11:55, 8 October 2007 (UTC)

That would be a Myth however. Here on the science desk we are generally looking for something more like Reality. SteveBaker 13:00, 8 October 2007 (UTC)

Good grief!! You mean they taught us things in primary school that aren't real? What about that guy who was nailed to a tree and came back to life?? lol! DuncanHill 13:08, 8 October 2007 (UTC)

Nonetheless, it provides proof that "This is an old idea", and is thus useful. Skittle 13:06, 8 October 2007 (UTC)

I seem to remember lifting these things called 'barbels' up and down to make me stronger - which worked until I stopped and all the muscle went floppy - does this have any relevance here?87.102.17.101 13:58, 8 October 2007 (UTC)

No - pigs don't have barbels you're thinking of fish. :-) You'd have gotten further by lifting Barbells.SteveBaker 17:54, 8 October 2007 (UTC)

SB point no 1 about the difference in human and pig growth rates is an important one. Also do note that the vast majority of adults would probably have great difficulty lifting let alone carrying a fully grown pig (from sources 41-120kg). Admitedly most people could perhaps with a large amount of weight training (but why you'd want to I'm not particularly sure). Also if you make your child carry a piglet every day, you may find your local child welfare organisation and/or the police wanting to interview you and perhaps even your local animal welfare organisation Nil Einne 12:57, 9 October 2007 (UTC)

• I have actually performed this experiment with a baby human. In the first few years of its life I could lift it with no problems at all, and did so many times per day. However, I kept feeding it to the point that it became uncomfortable to lift. Now I avoid doing so altogether, to avoid embarrassment to all concerned. --Sean 16:46, 9 October 2007 (UTC)

Just goes to show how anonymity will cause people to admit to the strangest things.87.102.18.10 18:38, 9 October 2007 (UTC)

silicon life forms

Have any silicon based life forms ever been discovered or is it know whether such life forms are possible by comparison of the properties of silicon versus the properties of carbon? Clem 00:21, 8 October 2007 (UTC)

None have been discovered as of yet. Finding one would be a monumental breakthrough in biological science. As to whether they are possible, that's still being debated. -- Kesh 00:28, 8 October 2007 (UTC)

The origins of life (1964) by George Wald had a discussion of issues such as why carbon is used in living organisms, not silicon. --JWSchmidt 01:56, 8 October 2007 (UTC)

The abilities of carbon to form complex molecules exceeds that of silicon, but as biology here on earth sometimes uses materials not suitable for the purpose (from the knowledge of humans), it might possible to create a full new-biochemistry based on silicon (with carbon as minor partner). Silicon in earth biology has only limited use and it is not used to create larger molecules, with the exeption of silicium dioxid shells of diatomeres.--Stone 09:22, 8 October 2007 (UTC)

The major problem with silicon based life forms is that they would breath out SiO2(as we do CO2), SiO2 is sand, and would not be a nice thing to have in ones lungs :DShniken1 13:49, 9 October 2007 (UTC)

This one made me fall off my chair. --Ouro (blah blah) 14:44, 9 October 2007 (UTC)

Afterthought: ain't so sure, I mean, I don't think simple substitution of C with Si cuts it. A silicon-based life form would surely have different biochemistry all over, and this'd include breathing probably. I think. --Ouro (blah blah) 14:47, 9 October 2007 (UTC)

Friction in Trains

Hello all. I'm having some trouble finding information for my school poster. The topic is "Friction in Trains." I tried looking for information here and on google but I couldn't find it. If anyone could help me here it would be greatly appreciated. P.S I'm looking for information relevant to a year 11 level (Upper High School level). Lots of thanks in advance. Cuban Cigar 05:11, 8 October 2007 (UTC)

A web search is unlikely to reveal much unless your project is more clearly defined. Assuming you mean kinetic friction as it applies to railway transport (see friction), take a look at our articles on rolling resistance and drag.--Shantavira|^{feed me} 09:42, 8 October 2007 (UTC)

With specific application to trains and railways, we have articles on rail adhesion, sandbox (railways) and slippery rail. Gandalf61 10:39, 8 October 2007 (UTC)

I know this might sound old fashioned, but you might better be served by visiting your local library, and speaking with your librarian about the subject. You should learn to research a subject using multiple sources, not just the internet. It might give you some places to start, but Wikipedia, like other encyclopedias, should not be cited as a source of a reference. -- JSBillings 10:41, 8 October 2007 (UTC)

As a way to approach this problem, you might do well to consider all of the things that move in trains and try to find some analyses of those moving things. For example, the wheels move on the rails but the wheel axles also turn in bearings of some kind. The air moves against the train but also flows through any internal combustion engine in the train. And so on...

Atlant 12:42, 8 October 2007 (UTC)

I think you should think about: Friction of the wheels against the track (you need some friction or the wheels will just spin and the train would stay still) - friction in the wheel bearings (which is bad because it slows the train down and requires more energy - fuel - to overcome it) - friction inside the engine(s) (also bad - same reason). Friction is also desirable in other places - the couplings between the train carriages for example. If they were super-slippery, they might come undone. The brakes need to use friction to slow the train down. Friction inside the train also matters - you don't want really slippery floors or table-tops if passengers are to be comfortable. There are lots of things to think about in this topic. SteveBaker 17:50, 8 October 2007 (UTC)

• There's also a pretty good article at Howstuffworks called "How Diesel Locomotives Work". Some non-obvious sources of friction to ponder: friction among the engine parts (very much like in an automobile, with substances very much like an auto's motor oil to reduce it) and friction in braking (where the friction is how the brakes work). --M@rēino 03:37, 9 October 2007 (UTC)

This is all very good thanks for the help.Cuban Cigar 08:02, 9 October 2007 (UTC)

materials&metallurgy

which steel is used for railway tracks?203.94.231.74 11:19, 8 October 2007 (UTC)

Pearlitic steel see pearlite See http://www.chiark.greenend.org.uk/~cneal/rails.html but also http://www.msm.cam.ac.uk/phase-trans/parliament.html — Preceding unsigned comment added by 87.102.17.101 (talk) 12:08, 8 October 2007 (UTC)

Switch rails may be special steels. — Preceding unsigned comment added by 87.102.17.101 (talk) 12:09, 8 October 2007 (UTC)

here's some info on american steels http://findarticles.com/p/articles/mi_m1215/is_n3_v198/ai_19239923

You could search the web for 'rail steel' — Preceding unsigned comment added by 87.102.17.101 (talk) 12:51, 8 October 2007 (UTC)

• Bonus points -- in addition to steel, thermite is used for repairs. --M@rēino 03:39, 9 October 2007 (UTC)

Human Horns

Do you have any information on abnormal bone structure among humans that presents like two mini horns on the top of a human head? — Preceding unsigned comment added by 87.232.1.88 (talk) 11:32, 8 October 2007 (UTC)

Never heard of such a thing, but if this about the old, old myth that Jews have horns, see this section of our article on Moses --Dweller 12:43, 8 October 2007 (UTC)

I've heard of it. Here are a couple of sites that may be of interest - [1] and [2]. -- JackofOz 14:07, 8 October 2007 (UTC)

Interesting stuff! Thanks for a better answer than just sending the poster to watch "Spanish Fry". DMacks 18:38, 8 October 2007 (UTC)

I recall that some adherents of the body modification subculture have metal balls or lumps of coral inserted underneath the skin on their head so that they resemble horns. Exxolon —Preceding signed but undated comment was added at 21:00, 8 October 2007 (UTC)

I remember reading something about human horns related to Shope papilloma virus 71.226.56.79 05:33, 9 October 2007 (UTC)

Oxidant, oxidising agent, oxidation...

Is "oxidant" the same as "oxidising agent"? And does an "oxidant" oxidise or reduce? Thanks. Oidia (talk) 12:23, 8 October 2007 (UTC)

An oxidant is the same as an oxidising agent. The linked article will explain what they do much better than I can! DuncanHill 12:48, 8 October 2007 (UTC)

How was precession of the Earth's axis explained in Geocentric models of the solar system?

So precession of the axis was discovered way back during the heyday of Greek astronomy, and apparently even heavyweights like Ptolemy studied the topic, so it must've been addressed in some way - but the article on geocentrism doesn't mention how it explained the apparent movement of the stars (obviously they wouldn't have thought of it as a movement of the Earth but of the stars), and some more searching turns up Trepidation which seems to be close but not the same thing. So how did they account for this phenomenon? --Gwern (contribs) 15:26 8 October 2007 (GMT)

They couldn't explain it in scientific terms, but then they probably didn't feel any need to do so. They didn't have the sort of mechanical understanding of the universe that we have today. They assumed the Earth was fixed, so precession must therefore just be another motion of the heavens. If it hadn't been for questions such as this (and retrograde and direct motion) it might have been many more centuries before we finally figured out what was going on.--Shantavira|^{feed me} 17:20, 8 October 2007 (UTC)

They certainly could explain it in scientific terms. To assume that pre-Copernican astronomers were devoid of mathematical understanding is simply incorrect. Retrograde motion was not too hard for them to explain either, given enough epicycles. Bigger threats were things like comets which totally screwed up the model of perfect spheres of the heavens, much less something like the phases of Venus which was totally incompatible with a Ptolemaic system. (James Lattis' Between Copernicus and Galileo is an excellent study of the work of Christoph Clavius, probably the last major geocentric astronomer in Europe of any real mettle.) --24.147.86.187 19:29, 8 October 2007 (UTC)

What they were doing was to consider each object in the sky as being attached to a wheel - or a wheel mounted on another wheel - possibly on another wheel. Wheels could be different diameters and rotate at different rates. In effect, they were turning all motion into cycloids. Or to put it another way, they were summing a bunch of sine waves of varying amplitude, frequency and phase. This technique is something we use all the time in Fourier analysis/synthesis - and we know that ANY mathematical function can be broken down into the sum of some number of sine waves. So it was inevitable - that with enough wheels of the correct size ("amplitude") and frequency - they could reproduce exactly the motion of all of the heavenly bodies. Of course Fourier analysis hadn't been invented back then - so they thought it miraculous that their idea of how the universe worked fitted so well with reality - but that was because they'd inadvertently stumbled on something that could be used to describe ANY motion. Of course they rarely used enough wheels to get the motion down with 100% accuracy - but whenever they noticed a discrepancy and analysed it carefully enough - they'd discover that just adding one more teeny-tiny wheel would 'fix' the problem. It's all kinda elegant in a way. SteveBaker 17:36, 8 October 2007 (UTC)

Well, they were specifically spheres, not wheel or disks. This is important — the spheres didn't have to rotate exactly on a single axis, which could explain a lot of things. Additionally, in Ptolemy's system the spheres did not necessarily rotate around their center — they could "wobble" (see equant). Kuhn's The Copernican Revolution is an excellent and readable overview of the pre-Copernican approaches to astronomy. --24.147.86.187 19:29, 8 October 2007 (UTC)

Yeah - there were all sorts of elaborations on the basic idea - especially as more exacting measurements caused ridiculous amounts of additional complexity in the system and efforts had to be made to prop it up. But in the end, it's a sum of sine-waves (possibly in two or three dimensions) - which explains why such a wildly "wrong" system could produce results that actually worked out pretty well in practice. It's quite impressive that they cobbled this together from raw measurements - with no theory of WHY all this worked the way it seemed - and a total lack of understanding about what they were doing mathematically (Fourier series weren't known until the early 1800's - by which time Copernicus's ideas were totally accepted). The fact that it enabled astrologers to do a reasonable job of predicting where planets would be at some time in the future is pretty amazing given that they'd missed the critical simplifying idea of putting the sun in the middle. SteveBaker 19:47, 8 October 2007 (UTC)

Well, my understanding was that their physics and observations didn't really let them accept a heliocentric model and that it wasn't until sometime after Galileo that it actually made better predictions (drawing on some fuzzy memories of Feyerabend's writings). But is this the answer? That they had no problem introducing another epicycle for the celestial sphere itself? --Gwern (contribs) 20:27 8 October 2007 (GMT)

I'm reasonably sure the celestrial sphere did not have its own epicycles, if that is what you are asking in the end there; if I recall correctly from Kuhn, it was simply given the ability to have its orbit "wobble" a bit (imagine a sphere which rotated in more than one direction and at somewhat different speeds). And the Copernican system as put forward by Copernicus was still filled with epicycles (and also lacked the more nuanced understanding of ellipical orbits that would be Kepler's major contribution). In any case the Ptolemaic model pretty much died with Galileo's work, though Galileo's work did not exclude other geocentric models (like the Tychonic system), which is observationally identical for all intents and purposes to the Copenican model within a certain range of observation. --24.147.86.187 21:37, 8 October 2007 (UTC)

For 'ANY mathematical function' read 'any function that is even slightly pleasant, including all arising in nature'</pure mathematician's pedantry> Algebraist 19:11, 8 October 2007 (UTC)

Yes - absolutely. I was trying to minimise the amount of clutter around an already-too-complicated explanation! You need a repeating function without nasty discontinuities and such - but the motion of all of the planets and moons and orbital 'stuff' fulfills those requirements (so long as nothing collides with anything else!) - so in this context, we're OK. Thanks for the correction. SteveBaker 19:33, 8 October 2007 (UTC)

Sorry about that; no real place in this discussion, I'm just too much of a pure mathematician to ignore a false statement, however justified. Algebraist 23:19, 8 October 2007 (UTC)

Geology of the Balearics (Mallorca)

Im writing a report on the geology of Masllorca. But I have some problems finding litterature on the subject. Im studying to become at teacher in the Dansih school. Im not a geologist or anything. I know that the islands in the mediterrian sea, where formed due to the collision of the african and the eurasian plate, but after what I have read so far it seem to me, that its a bit more complicated than that. I hope someone can help me!!!

The ameteur geologist Martin —Preceding unsigned comment added by Martinchristiansen (talk • contribs) 18:10, 8 October 2007 (UTC)

I recently had to teach myself Geology 101, so to speak, and I found this to be a good overview of the science of physical geography. It helped me understand the other more specific material I found. --Milkbreath 20:36, 8 October 2007 (UTC)

There is probably an in-country journal for this sort of local detail. Also there may be geological maps available, with accompanying notes - but they could all be in Spanish. Are you going to write the wikipedia article for this too? Graeme Bartlett 03:21, 10 October 2007 (UTC)

No...I don´t really feel that i´m a qaulifyed writer for that kind info. I just resently visited Mallorca with fellow students and we had to write a paper on the subject of Mallorcan geology. I was just looking for some info on the subject.

I have a French article that mentions Balearics a little, but chances may be better if we look elsewhere. The geology is in the same style as the north coast of Africa and the south east coast of Spain. Also if you are interested I could give you a list of names of Spanish Geological journals. Your question has triggered me producing a Geology of Spain article. THough its not uploaded yet. Graeme Bartlett 02:50, 12 October 2007 (UTC)

Atomic Composition of Animals

Could someone direct me to a site that would have the atomic percent composition (by mass) of animals (specifically mosquitos). Would the composition be very close to the same among say, mosquitos and humans or any other animal. 64.230.97.20 18:15, 8 October 2007 (UTC)

Pretty much, yes. Being that we are all carbon-based life, we are largely carbon, oxygen, hydrogen, and nitrogen. I imagine that a big difference is that something with an exoskeleton is not going to have the calcium that goes into an internal skeleton made of bone. --24.147.86.187 19:23, 8 October 2007 (UTC)

Mushrooms

Are mushrooms considered more animal than plant? --WonderFran 18:57, 8 October 2007 (UTC)

Mushrooms are a type of fungus. Fungi were once considered plants, but now are generally considered to be a separate kingdom of their own. Algebraist 19:04, 8 October 2007 (UTC)

They aren't more animal than plant - but they aren't "plant" either. These days, we consider fungi to be a completely different thing from either plants or animals. SteveBaker 19:29, 8 October 2007 (UTC)

Then again, animals and fungi are both in the group of opisthokonts, while plants are not, so some biologists must think they're more closely related. —Keenan Pepper 19:36, 8 October 2007 (UTC)

I was just reading in Richard Dawkin's The Ancestor's Tale about how animals and fungi are more closely related to each other than either is to plants. It made me wonder though -- How come both plants and animals are thoroughly abundant on land and in the sea while fungi are limited to the land? Is there something about fungi that makes them utterly unable to colonize the sea? And.. wouldn't the common ancestor split between fungi and animals have been way back when all life was in the sea? Was there once sea fungi? Is there still? Pfly 04:56, 9 October 2007 (UTC)

The Fungi article says "Most fungi grow in terrestrial environments, but several species occur only in aquatic habitats." So your premise isn't entirely correct. It could be that there may be few aquatic species, but that those few proliferate and thus still have a considerable biomass. Does the book say anything on that? DirkvdM 08:41, 9 October 2007 (UTC)

It could be that the Mycorrhizal symbiosis with plants that got fungus a big start on land -- without it, plants probably wouldn't have been that effective on land. -- JSBillings 10:29, 9 October 2007 (UTC)

This hypothesis is supported by some sources, e.g. see [3], [4],[5] & [6]. [7] is about animal colonisation but briefly mentions the current state of knowledge at the time vis-a-vis fungi colonisation and is full text. Nil Einne 12:45, 9 October 2007 (UTC)

Locations of virtual image charges versus optical images

The electric field produced by a point charge and a conducting plane is the same as would be produced by the point charge and a second, opposite point charge on the other side of the plane, called an image charge. This image charge is at the same place an optical image would be if the plane were a mirror. It seems to me this must be the case, because if the charge were vibrating at optical frequencies, it would radiate light, and the reflected light had better appear to come from the same position behind the reflecting plane as the image charge.

However, for a spherical conductor, the image charge is at a different location from the optical image in a spherical mirror. If the radius of the conductor is r and the distance from the center of the conductor to the charge is x, then the distance from the center to the image charge is $r^{2}/x$. If the conductor were a mirror, on the other hand, the distance from the center to the image would be $xr/(2x-r)$. These do not agree except in the limit $x\rightarrow r$. It's as if the "focal length" for the electrostatic case is equal to the radius r, whereas we all know the optical focal length of a sphere is r/2.

How can this be? Why is the image in one location for electrostatics, and a different location for electrodynamics (optics)? —Keenan Pepper 19:32, 8 October 2007 (UTC)

The flat mirror is only a special case and there's no a-priori reason to suspect that optics and electrostatics should be linked like you suggest. You may imagine a large conducting flat mirror where a slab of it is replaced with plastics or removed. In optics, this wouldn't affect the reflections in other parts of the mirror, while I believe the "image charge" would get distorted by this.

In electrostatics, there's no "reflection" of the field lines, only the requirement that they intersect the conducting plane at a 90 degree angle, so as not to have a current running. In optics, there's no case of a part of the mirror affecting the light at anoter, while in the electrostatic problem this is how an equilibrium with no current running is set up. EverGreg 09:08, 9 October 2007 (UTC)

Actually, it's not true to say that removal of a part of a mirror does not affect the rest of the image. There is a kooky little effect that happens very close to the edge of a mirror (argh - I can't recall the name) - too close for you to ever really notice. It's explained very nicely in Feynman's book on quantum electrodynamics and it requires bizarro quantum effects to explain it. It had been noticed long before quantum effects were known and had been a mystery for some hundred or more years. Darn! I wish I could remember the name of it. SteveBaker 15:42, 9 October 2007 (UTC)

Dialysis bag permeable to sucrose?

Disclaimer: This is a homework question in some measures. In any case, I could have sworn my instructor said that dialysis tubing is not permeable to sucrose, but when doing the literature search for this lab, I wanted a reliable source to cite. surprisingly it seems like Dialysis tubing should be permeable to sucrose: this site says that sucrose has a molecular weight of about 340 Daltons, and this site says that dialysis tubing usually has cut-offs in the tens of thousands of daltons. Can anyone confirm or deny what I'm seeing? With a reliable source of course. --Ybbor^Talk 19:41, 8 October 2007 (UTC)

Sucrose is indeed 340ish Da. I don't know the specifics of the Dialysis tubing you are using, but a disaccharide such as sucrose might well pass through. Look at the google hits for sucrose "dialysis tubing" to get a sense of what is likely. DMacks 19:49, 8 October 2007 (UTC)

You could help us by giving details of the particular protocol being used, but it is not uncommon for people to use dialysis tubing and sucrose to concentrate dilute solutions. The first Google hit I found with an example (go down to day 5). In general, the sucrose can cross the tubing (although some dialysis membranes claim 0.1 kD cut-offs) that is used, but the point is, if there is a high concentration of sucrose outside, then water will quickly leave the solution that is inside the tubing. --JWSchmidt 20:24, 8 October 2007 (UTC)

Sorry, can't give you much details of the specific type of tubing being used :( Okay, so sucrose will move across the tubing, just not nearly as fast as water, and not significant enough to offset the movement in water. Is that understanding correct? Thanks for your help :) --Ybbor^Talk 20:47, 8 October 2007 (UTC)

Wormhole creation

If wormholes are permissable by General Relativity, is their creation permissable? I didn't see anything in the article on any hypothetical formation mechanisms for wormholes; I don't see how you could imagine them actually being formed while still being within the bounds of GR. And if there was no real permissable route for creating them, then they probably don't exist, theoretically valid or not. Any thoughts? No maths please if possible. ;-) --24.147.86.187 21:31, 8 October 2007 (UTC)

Check out casimir effect for stabilization theories at least. --Cody Pope 22:59, 8 October 2007 (UTC), Nasa's got stuff on wormholes too. --Cody Pope 23:17, 8 October 2007 (UTC)

The latter seems to be about artificially created wormholes, which is interesting though it doesn't sound like a feasible technical problem. I'm interested in natural wormholes in particular. And the Casimir effect page wasn't exactly in terms that I could make real sense of... --24.147.86.187 00:23, 9 October 2007 (UTC)

Quantum foam could be permeating space and could be full of tiny wormholes, ready to expand to macroscopic size. Graeme Bartlett 00:27, 9 October 2007 (UTC)

The worry about wormholes is, as you probably know, that they seem to allow for time travel, which violates causality due to the grandfather paradox. As a paradox usually hints at a flaw in the theory, the possibility of wormholes is usually interpreted as meaning one of the following three things: (i) There is some flaw in the theory of general relativity because a sound theory should not allow for paradoxes. (ii) There is some flaw in the reasoning that general relativity allows for wormholes; closer investigation will show that it actually does not. (iii) There is some flaw in the argument that a wormhole causes a paradox.

What you are heading at is the possibility (ii): Maybe it will turn out that physics does not allow the creation of wormholes and so avoids the paradox. This is actually the principal reason why physicists like Kip Thorne and Paul Davies investigate whether the creation of a wormhole is feasible in principle. Their ideas are so wild that it seems ridiculous to assume that one could actually build them. But whether this impossibility is just a technical infeasibility or an impossibility in principle is an important question to judge whether our fundamental theories harbour a flaw or not. And if one identifies a way to build a wormhole in principle, this may help to pinpoint the flaw. 85.127.183.143 00:28, 9 October 2007 (UTC)

You are forgetting (iv) that paradoxes are not impossible. In a many-worlds view of the universe, going back in time and killing your grandfather is not a problem since the version of the universe you came from will simply not be the version of the universe in which your grandfather is dead. Time travel devices come in two distinct varieties: The kind which allow you to travel back in time only back to the point where the device was created (as is the case with wormhole-based time machines) - or the "H.G.Wells" devices where you can travel back to before the time the machine was created. The latter type can be responsible for all kinds of wierdnesses - but the former type are less problematic. For example, we can answer the question "If time machines exist, how come we havn't seen any time travellers yet?" - because we don't have a wormhole yet. SteveBaker 15:35, 9 October 2007 (UTC)

just applying logic to the question (as I am not a physicist) I would say that if something exists, then its creation must have been possible. —Preceding unsigned comment added by 88.109.198.32 (talk) 00:42, 9 October 2007 (UTC)

I know that. They don't know if they exist—they have never observed one (or evidence of one). My point is that if the creation is not possible, then they won't exist. --24.147.86.187 14:30, 9 October 2007 (UTC)

Well, yes - but remember that we didn't know for sure that black holes existed until we found one just four years ago. Between the time someone first though up the idea (John Michell in 1783) until the first one was actually discovered (Maillard, Paumard, Stolovy and Rigaut in August 2003) was 220 years! Discovery of these weird things often lags the theory that they could possibly exist by decades...or even centuries. So wormholes might exist - but it could easily take hundreds of years of searching with exotic instruments like orbiting telescopes for us to find one. SteveBaker 14:48, 10 October 2007 (UTC)

General relativity relates the local geometry of spacetime to the local distribution of energy and momentum. Wormholes are inherently global, so general relativity doesn't say anything about them. It's consistent with them, but that's not saying much, because it's consistent with anything. The field equations don't constrain the geometry, they just tell you the energy-momentum distribution of any given geometry. So the first question is whether there's any traversable-wormhole geometry whose energy-momentum distribution resembles any known form of matter, and the answer to that is no. (I think there's a theorem to that effect.) Even if it were yes, it doesn't follow that you can construct a wormhole by deploying matter in the required configuration, because GR doesn't tell you whether the two ends connect up, and I have trouble even imagining a post-GR dynamics that would allow for such a thing. -- BenRG 11:45, 9 October 2007 (UTC)

Tetrachromatic, ultraviolet, etc

I've been reading up on colorblindeness and tetrachromatic vision. In a book I have on psychology, there is a diagram of four pictures, three with different types of color removed, and if any of them look the same then it means you are colorblind (I apparently passed the test and am not colorblind). However, a while back I was talking to a physics major and a biology major, who say that there are similar diagrams for people who may be tetrachromatic, or even tests for ultraviolet vision, where a "normal color" picture is lined up with a tetrachromatic or ultraviolet one. Do any of these diagrams exist of the internet? I can't find any, but perhaps an optometrist could be of help. 130.126.67.144 22:26, 8 October 2007 (UTC)

Given that monitors work on a trichromatic RGB system, I'm not sure anything you pull off of the internet would work. GeeJo ^(t)⁄_(c) • 22:33, 8 October 2007 (UTC)

Is there a cheap and easy way to test a person IRL for trichromaticism? 130.126.67.144 22:48, 8 October 2007 (UTC)

Indeed due to colour calibration, reproduction accuracy and other issues, many sites testing for colour blindness warn that you really should see a professional or at least use a book designed for the purpose Nil Einne 12:14, 9 October 2007 (UTC)

If you mean "an easy test to determine if someone can see ultraviolet" you could use window glass. It dosn't let through UV, which is why you can't get a tan indoors on a sunny day. So the outdoors should look quite different through glass. There are also certain flowers that have patterns that's only visible in ultraviolet light. EverGreg 09:15, 9 October 2007 (UTC)

the Tetrachromacy has some links and a google search on "test for Tetrachromacy" bring up papers that might point to test for the condition of extra sensitivity somewhere between green and red. EverGreg 11:25, 9 October 2007 (UTC)

Bear in mind if you aren't female the chances of you being a tetrachromat are probably very very slim (although this is still AFAIK still not a very well researched area from our current knowledge this is the case) Nil Einne 12:10, 9 October 2007 (UTC)

I thought that if you were female, your chances are very slim (like one in 20 million) - if you are a male, it's utterly impossible to be a tetrachromat. SteveBaker 14:00, 9 October 2007 (UTC)

People who have lost the lenses from their eyes (due to cataract surgery perhaps) can see a little further into the UV than the rest of us. Computer displays only produce 'pure' red, green and blue light - nothing else. So it's impossible to generate a UV test on a computer.

Tetrachromats see two hues of green (yellowish green and 'pure' green) as 'different' colours. Tetrachromats find synthetic pictures of all kinds (books, computers, TV, movies) unrealistic because they don't reproduce both kinds of green correctly and they can tell (we can't). So all you need to test for tetrachromacy is to show a 'spectrum' of colour on the monitor - and have the person compare that to a spectrum spread from sunlight using a prism - if the two look pretty similar, you're a 'normal' person - if the spectrum on the computer is missing a bunch of colours around green - then you're a tetrachromat. But this is kinda like testing for colourblindness by showing a monochrome photo and asking whether it looks real...not a really conclusive test since it requires a judgement call from the viewer. The standard tests require you to see a number or shape in a bunch of coloured dots - and it's really an all-or-nothing, definite answer kind of thing.

However, tetrachromats are used to the very unrealistic colouration of computers, TV's movies, books, etc and they may find this 'normal' for them because they know that these devices are horribly unrealistic. You can't print a tetrachromacy test with normal cyan/magenta/yellow/black (CMYK) printing techniques - although a specialised test for tetrachromats could be printed on a printing press that can use more colours. I suppose you could also do a test for UV vision using specialised UV inks...but again, this isn't something that is routinely easy to do.

SteveBaker 14:00, 9 October 2007 (UTC)

This helps me—but are you saying that tetrachromats only see green differently, and not other colors? I read of supposed tetrachromats picking out differences between reds and dark purples that are supposed to be black. —Preceding unsigned comment added by 130.126.67.144 (talk) 20:37, 9 October 2007 (UTC)

I don't know where you read that - or why we keep talking about human tetrachromats in the plural. So far, only ONE human is known to be a tetrachromat. It takes a really rare combinations of circumstances that make this happen - it requires a woman with a particular set of colour-blindness symptoms in all four grandparents - and a lot of luck as the genetic dice are rolled.

The lady in the UK who has been shown to have this quirky genetic makeup has two sets of green sensors that are sensitive to different frequencies near green. That's the only form of tetrachromacy that's possible.

HOWEVER, you make the rash assumption that her brain lets her see two very similar colours for the two greens. That's not the case. Those two greens are as different to her as red and blue are to you and me. We really only see the three primaries (red, green and blue), plus mixtures of two of those (yellow, cyan, magenta), plus all three together (white) - at different saturations and intensities. She sees four primaries (red, green, splot, and blue - I'm calling her 'other' green sensor by the nonsense word "splot" because we don't have a name for it and I want to emphasise how different it is) - plus six secondary colours that are mixtures of two colours (yellow, green/splot, splot/blue, magenta, red/splot, and cyan) - plus four tertiary colours that are mixtures of three of her primaries (red/green/splot, red/green/blue (not white because it has no splot in it), red/splot/blue, green/splot/blue) plus all four primaries at once (which I presume she'd call 'white').

We have seven basic combinations that look like different colours, she has fifteen colours that are likely to be as different to her as red, yellow, green, cyan, blue, magenta and white are to us! It's WAY more than just a little more subtle ability...it's and ENTIRELY different perceptual system. We simply cannot comprehend what the world looks like to her...there is no way to comprehend that. She has a good idea what the world looks like to us - because that's how TV, movies, books and computer screens look to her (these things don't produce splot - so they can't produce eight of the fifteen colours she can see).

SteveBaker 03:02, 10 October 2007 (UTC)

Do normal humans lack the mental ability to comprehend such colors, or is it just a matter of physical eye characteristics? I mean, I remember reading an article in Vanity Fair about a blind man with a primitive vision device resembling sunglasses wired to his brain who was able to see very basic light/dark differences--if the passage of time allowed such a device to be built which had a tetrachromatic spectrum, would our minds be able to deal with that? Would they be able to deal with something even wider in range, such as infrared or ultraviolet information?

And by the way, I would like to thank you for all of the time and patience you have taken here too.

We do lack the ability to comprehend things we havn't learned to see - but the brain is amazingly adaptable - so I think we would be able to learn to see with extra colours. People who are cured of blindness - or deafness do eventually learn to use their new senses. The lady who was born a tetrachromat has evidently learned to use her extra colours. I read someplace that she had worked for a while in a knitting yarn shop and had realised that her sense of colour matching was vastly better than that of her customers.

There is an interesting perceptual problem that perhaps 5% of people suffer from. Lots of babies are born with cross-eyed eyes. Usually, this problem corrects itself within just a few days of birth - but for some babies it takes months. Sadly, that period is when the brain learns to use the different images from your two eyes to estimate 3D depth - so kids with this problem NEVER learn to see in true 3D over much of the range of vision. As I said, as many as 5% of adults have this problem! I was reading about a lady who had this problem who managed to teach herself to see in 3D and 'educated her brain' to start seeing in 3D correctly. It's interesting to note that quite a few of the people reading this posting are suffering from this problem and don't even know it!

People who have cataracts removed and can see a little into the ultraviolet are a different case though. They don't see any 'new' colours - it's just that things that formerly had a UV component to their colour now look to have more blue in them. Things like flowers (which are often patterned with UV spots and stripes) would have new patterns on them that 'normal' people can't see - but those spots and stripes would appear as a perfectly normal blue tint.

SteveBaker 13:51, 10 October 2007 (UTC)

Those don't go together! =(

Would Nuclear devices dropped and detonated in volcanoes would cause an unbelievable amount of destruction? In cartoons and sci-fi stories the results vary but still, is there any evidence to support this? The most logical things I could think of would be something like this:

Option 1: The Nuclear device detonates, causing both the volcano and nuclear bomb to explode. (Worst case scenario)

Option 2: The Nuclear device detonates, causing the volcano to explode and send tons of ash, dust, rocks, sulfur and, now radioactive, debris into the air causing widespread radiation poisoning and (ergo) death. (Worse-than-Worse Case Scenario)

Option 3: The Nuclear device detonates, causing the volcano to collapse on itself. (O.K. Scenario)

Option 4: The Nuclear device detonates, does NOT cause an eruption and due to the extreme heat, melts the inside surface on the volcano and "glasses" it. (Best Case Scenario)

Option 5: The Nuclear bomb detonates, and the volcano is destroyed in a manner that would ensure that it could not erupt again (like, if the volcano shattered, and due to the extreme heat, melted over again) (Best-than-Best Case scenario)

Which would be the most likely outcome of an event like this? The yield and size of the bomb and volcano may vary but in general....

Thanks for your time on my bizarre question!

♥ECH3LON♥ 23:50, 8 October 2007 (UTC)

My bet would be a combination of options 2 and 3. You'd probably get a lot of ash and fallout from the bomb, but it would probably cause the volcano's top to destabilize and fall in on itself. Now of course you've left out the option where the heat of the volcano just melts the bomb into an un-usable state... -24.147.86.187 00:28, 9 October 2007 (UTC)

To start, a couple of questions for you. What kind of (Active, dormant) and type (stratovolcano, caldera, etc.) volcano are you picturing? Anynobody 00:46, 9 October 2007 (UTC)

In general, I don't see much reason to put it at anything significantly beyond the otherwise-imminent eruption and/or nuke, as appropriate. A nuke won't make an inactive volcano erupt. While a nuke might trigger an eruption prematurely, it's unlikely to change the scale of the eruption -- even nukes aren't that powerful. And while yes, there will be radioactive dust, a single nuke isn't world-shattering -- particularly if people know that it's a nuclear explosion, precautions can be taken. Dust is relatively easy to filter, and by the time you're talking about the high-altitude world-circling dust from the eruption, the radioactivity should be diffuse enough to be a relatively minor concern. In short, there's not much synergy. — Lomn 01:47, 9 October 2007 (UTC)

I think you're very misunderstood about the fallout risks that would be in place from a ground-level nuke in a rocky environment. It would produce a lot of nasty heavy bits that, with a bad gust of wind, would contaminate a large area, making it quite difficult to live in, much less raise crops in, etc. It wouldn't be good. That being said, it's not terribly different from setting off a nuke next to a mountain in any situation; it being a volcano doesn't change much in that respect. --24.147.86.187 05:14, 9 October 2007 (UTC)

Would that be worse than a volcanic eruption? DirkvdM 08:49, 9 October 2007 (UTC)

I dont know how to qualify "worse" in this case, but it would be different. If we are assuming a worst-case volcano eruption (immediate, massive, followed by massive lava floes and mud slides) then maybe not. If we are assuming an eruption where you could get warning out and evacuate, then definitely. The fallout would make the land far more uninhabitable as a health risk in the long term than the eruption (which is to say, it's not that people would immediately die if they went on the last—of course not—but if they stayed on it and ate from it and etc. they would develop much higher risks of cancer, birth defects, etc.). --24.147.86.187 14:03, 9 October 2007 (UTC)

Does this somehow pertain to scientology doctrine about H-bombs and volcanoes? 130.126.67.144 04:39, 9 October 2007 (UTC)

Would anyone care (irrespective of what it is)? DirkvdM 08:49, 9 October 2007 (UTC)

Just a little too much of a coincidence. See Operating_Thetan#OT_III:_The_Wall_of_Fire and Xenu#Summary. Snicker. No word yet on why you'd need wings in space. --froth^t 04:01, 10 October 2007 (UTC)

A grown-up Bart Simpson would love this question. I'm picturing a Doomsday H-bomb of 100 megatons lowered into the pipe as far as it will go and then set off. I don't suppose it would alter the appearance of the average volcano very much; volcanoes are pretty big. But it might sort of blow the top off if it were set off shallow in a steep cone like Fuji. I'd expect to see a jet of nightmare isotopes shoot out the top and plume out downwind as fallout, ruining the lives of anything living there. What the volcano would do would depend upon what state it had been in at the time. If you had done that to Mount St. Helens one day before it blew, I suppose the nuke would have made it go then. You see estimates of around 35 megatons equivalent explosive yield for the eruption itself, so 100 megatons of bomb is not insignificant and would have actually punched it up a notch or two.

If you look at pictures from the underground A-tests in the US West, you see a spherical cavern of fused rock that has collapsed on itself somewhat. In a volcano, the blast would have someplace to go, up, and the chief effect would probably be melting. If the volcano was dormant at the time was because of a plug, the nuke just might dislodge or damage it enough to cause an eruption, I guess. (This is what you want, right? Idle surmise? I'm no vulcanologist nor nukeologist neither.)

So, option one: Sure, under the right conditions. Two: Same thing. Three: Most likely, I think. Four: Not much different from three. Five: Can't see that happening, because the forces at work have time on their side, and add up to more power than our little firecrackers have. --Milkbreath 11:36, 9 October 2007 (UTC)

Our articles notes Mt. St. Helens eruption as 350 Mt equivlent (not 35 Mt) while the largest bomb ever built was only 50 Mt. (Tsar Bomb) Rmhermen 18:17, 9 October 2007 (UTC)

I was under the impression that the Tsar Bomb was the largest bomb ever [i]detonated[/i], not necessarily the largest ever built. Though I may be wrong --Teacosythesecond 21:07, 25 September 2008 (GMT)

A megaton here, a megaton there, pretty soon you're talking real destruction. I just had 100 in my head for that Ruskie bomb at Novaya Zemlaya that time. It was only a piddling 50? What the hell were we boomers so worried about? And a quick google on "saint helens eruption megatons" gives figures much lower than 350. OK, but still, 50/350 is a chunk. --Milkbreath 19:07, 9 October 2007 (UTC)

The Tsar Bomba was originally designed as 100Mt, but they decided it would be a good idea to scale it back a bit. Algebraist 19:40, 10 October 2007 (UTC)