Wikipedia:Reference desk/Archives/Science/2007 August 24

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August 24

Weak bosons

Can a W⁺ or a W^- emit a Z⁰ I saw this in a list of fundamental interactions but it seems to violate conservation of angular momentum. So how does this work? Thanks, *Max* 01:05, 24 August 2007 (UTC).

Yes, it's possible, and no, it doesn't violate conservation of angular momentum. In order to fully understand how such things work, you must master the Table of Clebsch-Gordan coefficients, no easy task. It's somewhat arcane, but basically this table tells you all the ways that angular momentum vectors can be summed in quantum mechanics. In this case, you want the entry under j₁=1, j₁=1. This means that you have two things that both have angular momentum 1: the W and Z in the final state. Now we need them to add up to a total j=1: the W in the initial state. The entries for m₁, m₂, and m tell you the z component of these three spins. You can ignore the first table there, since it's for j=2. The second and third tables tell you how the state of the final W and Z relate to the initial W. --Reuben 05:41, 24 August 2007 (UTC)

I don't really understand it, but thanks for telling me it's possible. Also, I noticed that my list left out a W decaying into leptons of different generations. Is this just an oversight (they also forgot quarks emitting gluons)? Thank you *Max* 13:31, 24 August 2007 (UTC).

You could also think of the angular momentum as classical. If you put the two final spin vectors along edges of an equilateral triangle, then they add up to the third edge, which has the same length (that's how spin 1 + spin 1 = spin 1). Quantum mechanically the idea is the same, but the mathematical formalism looks very different. There's no simple vertex for W -> leptons of different generations. You can have W -> charged lepton + neutrino, and then the neutrino's flavor oscillates. --Reuben 19:33, 24 August 2007 (UTC)

Wouldn't it be sensible if Nature made us all hermaphrodites?

In a species that reproduces sexually, half of their numbers – the males – do not give birth, but continue to compete with females – who do give birth – for the available food. Wouldn’t a hermaphroditic species have all the benefits of genetic mixing that comes via sexual reproduction, while doubling the number of its members who are capable of becoming pregnant, and thus placing the survival of the species on a firmer footing? And yet no animals more advanced than some lizards are hermaphroditic. Myles325a 04:06, 24 August 2007 (UTC)

And tell us why there does NOT exists any species whose individuals CANNOT impregnate themselves but can impregnate other individuals. 202.168.50.40 04:43, 24 August 2007 (UTC)

(OP myles325 back). Don't understand what you mean. Humans are a species whose members CANNOT impregnate themselves, but who can impregnate others. Maybe you could rephrase your point without the use of double negatives. They can be confusing. Myles325a 05:23, 24 August 2007 (UTC)

When you say 'species' how far are you willing to go? Outside of the animal kingdom, there are a large number of species that have both sexual parts, but cannot impregnate themselves. Think flowers. --Mdwyer 05:12, 24 August 2007 (UTC)

(OP myles325 here). My question was simply why hermaphroditism is not found amongst the "higher" animals, when it is notionally so sensible. I don't understand your point at all. Myles325a 05:23, 24 August 2007 (UTC)

As far as I know, the offsprings produced by mating of different individuals (of the same species) are more robust. Genetically the farther the mating individuals are, the better. -- WikiCheng | Talk 06:13, 24 August 2007 (UTC)

One possible answer, although this is all speculation, is that it provides an easy division of labour. While you think men are competing for food without giving birth, in humans (traditionally anyway) it is the men who are hunting for food while the women raise the children. This system provides a safe environment for child raising and allows men the freedom to hunt. A hermaphrodite species would have to look after a baby while at the same time hunting or gathering, hardly a safe environment for a child. In some species the relationship is more equitable, for example in penguins, the males keep the eggs warm while the females hunt for months, and the men lose much of their weight doing this. The females return, after hatching, take over the job of warming the baby, while the males go off hunting for a long time and this continues. I assume you meant hermaphrodite but not self impregnating, so I don't know if the two sex solution may provide increased competition benefits as well? Cyta 07:17, 24 August 2007 (UTC)

As far as that goes, don't hunter-gatherer societies usually have the women (and children) gathering as well as raising the babies, while the mature men only hunt? So it's not so much of an advantage as you might think. 86.141.89.213 13:23, 29 August 2007 (UTC)

Except that sexual differentiation goes back WAY before humans, way before even division of labor. You can't figure out the origins of sexual differentiation by looking at humans; that's why people like Darwin tried to think about it by looking at animals where the advantages were less obvious to the naked eye (like barnacles and orchids). (And in any case, be aware that speculating on the evolutionary roles of human sexes is a scientific and political minefield. Characterizing men as just "hunters" and women as just "baby raisers" is overly simplistic, and such "naturalistic" explanations often end up enshrining the worst of contemporary social mores and gender roles.) --24.147.86.187 11:35, 24 August 2007 (UTC)

Sorry I didn't intend to offer an evolutionary explanation for gender with my human example, just an example of why it might not be sensible for nature to make us all hermaphrodites, as the original questioner suggested. As for political and scientific minefields, I like to keep the two seperate. And while I appreciate your point on not misusing science to influence politics, I won't avoid what I think is a reasonable "naturalistic" explanation in order to fit in with the "best" of contemporary social mores and gender roles. Cyta 12:59, 24 August 2007 (UTC)

I'm not implying you should embrace political correctness, I'm just implying that if you haven't really taken any serious time to think about gender roles then you should try to avoid speculating wildly on their "natural" origins. I don't claim to know enough about them to sort out the "natural" components or not (and there are surely some there), but I know that I don't know enough to do so with any success at all, and so I avoid speculating. (Put in more religious terms, I am a naturalistic-gender-role agnostic, not an atheist or a true-believer.) --24.147.86.187 00:47, 25 August 2007 (UTC)

OK well I don't consider my speculation wild, although as I admitted in my original post, it is just my speculation. It makes sense to me, that, hunting being a dangerous activity, babies should not be brought along, so someone has to stay home and look after them. Men are on average, faster and stronger and would make better hunters. I can't see any reason why women can't gather as well as men though. And atleast for the first few months of life, there is the obvious advantage that women can breastfeed! None of these things of course apply in the modern world. If I never speculated I'd never answer any RD questions, so I will continue to do so with disclaimers. Cyta 07:02, 27 August 2007 (UTC) ps Simon A's evolutionary answer below seems a much superior one to mine anyway.

Don't worry about it. The idea that men and women were not designed for different purposes (either by God or at random, thank you Darwin!) is scientifically nonsensical. The key idea to keep in mind is that there is no evidence we are confined to operating within these purposes (besides the obvious ones, of course, until some truly sadistic biologist finds a way to allow men to bear children). Someguy1221 07:12, 27 August 2007 (UTC)

I'm not worried at all, I have confidence in my opinions! I have to say I'd be happy to stay home and look after my future kids if necessary, but I am eternally grateful I will never have to go through the pain of childbirth! Cyta 08:23, 28 August 2007 (UTC)

[Edit conflict]

Myles, first of all: Beware of group selectionism. It is the not that uncommon fallacy in thinking about Darwinian evolution to assume that a species will thrive if its characteristics is of benefit for the species. Evolutionary selection only acts on the level of individual organisms (or even of single selfish genes). Now, I'll try to speculate a bit on the reason: Imagine a higher hermaphroditic species and assume that one individual has, due to some mutation, lost the functionality of its female reproductive apparatus. (Let's say the the organ simply got too small and does not work properly.) The individual hence does what it (or now rather: he) can do best, namely impregnate other animals. Given that it costs much more time to grow an egg or even allow an fetus to develop in a womb than to simply inject some semen, our mutated animal uses its time quite productively to spread it genes and the new male-only form will flood the species's gene pool. This results in over-abundance of male mating partners, which requires those of the hermaphrodites who choose to act as females to choose their partner carefully in order to not waste time on bad gene material (which would cause their gene-line to die out, see sexual selection). This renders being female a full-time job, where producing male genitalia is only a waste of energy, and so, a dimorphic species arises. In lower organisms, it seems to me, the disparity in the energy costs of producing eggs and semen is not that large yet, and hence, the advantage of this division of labor does not yet outweight the opportunity cost of not having the flexibility to perform both roles, and hence hermaphrodites occur. (Note, by the way, that many fish retain this flexibility: they can change their sex when needed. Also, observe that unisexuality and bisexuality seem to be quite on equal footings in plant sexuality) You may also like our article on evolution of sex. Simon A. 07:28, 24 August 2007 (UTC)

Sharks have been known to reproduce asexually, but why this is rare is explained in the article. Bendž|Ť 08:14, 24 August 2007 (UTC)

I presume that this is why (in higher species where the cost of child bearing is greatest) the females have evolved to demand often ridiculous adaptations in males. A male bower-bird doesn't have to suffer the 'cost' of producing gigantic eggs and keeping track of the young - which would suggest that the males would out-compete the females for food and such. To counter that, the females have evolved a strategy which requires the males to collect all sorts of junk - carefully arrange it into a bower and do complicated (but ultimately meaningless) dances to attract them. This disadvantages the male to level the playing field when it comes to hunting for food. Many male animals have to produce brightly coloured plumage/fur/scales in order to attract females. This puts them at a terrible disadvantage when it comes to hunting or hiding from predators - but it's the price of doing business...so they bear it. In humans, there is good evidence that females prefer the 'reliable type' of men who are going to stick around and share the cost of child rearing - rather than running off with other women. Females who make this demand are more likely to produce viable young that live to reproduce - so from the male's perspective, it's worth the price. This balances out the disparity of energy costs to the point where the advantage of being a male reduces enough that there is a reasonable population balance. SteveBaker 15:16, 24 August 2007 (UTC)

I've always thought the most enlightening example of gender distinction in animals to be the rotifer. The males can't eat or swim like their female counterparts, and merely twirl around trying to reproduce until they starve to death. Make your own conclusions as to what that means about us guys ;-) Someguy1221 20:56, 24 August 2007 (UTC)

Hermaphrodites have the problem of self-fertilisation which can be disadvantegous in some circumstances. Yes there are other ways to avoid self-fertilisation but seperating your sexes is one of them. I'm not saying this is the reason simply pointing it out as a possibility. Also note that while seperate sexes allows the division of labour it doesn't mean it necessarily has to be genetic or have a strong biology basis. The very existance of seperate sexes allows a division of labour and there could be only a minor genetic and biological basis amplfied by other factors. Finally note on the politics, it's highly questionable whether the existance of a biological and/or genetic basis for the division of labour implies it must be preserved. There is likely a biological and genetic basis for violence particularly among competing males but it doesn't mean it's okay for men to beat each other silly in the opinions of most people Nil Einne 23:16, 27 August 2007 (UTC)

Don't get caught up on the division of labor angle, people...our ancestors (going from early homonids to waaay back to the first mammals) didn't have high levels of hermaphrodism, and widely variable divisions of labor. The simple answer (as to why we're not all hermaphrodites) is that modes of reproduction are inherited down the tree of life and only drastically change if some selective pressure can act on available mutant phenotypes. That is, there would have to be some level of hermaphrodism in a species, and that would have to be selected for to establish itself, allowing such a shift to occur. There's no evidence that hermaphidism would be an "improvement" that would be selected for (in fact, they often have fertility problems) and there are some distinct advantages to regular ol' sexual reproduction that might be "bad" to lose.

Finally, remember that evolution is not (no matter how much Michael Behe wants) subject to external design, and doesn't create a mythical perfectly-adapted species design but rather a currently-most-well-adapted-to-the-present-niche-requirements-given-the-history-of-genetic-diversity-within-the-species-and-an-element-of-randomness design. — Scientizzle 23:29, 27 August 2007 (UTC)

It's important to keep in mind that evolution only builds on what came before. The most primitive organisms that reproduce sexually (and presumably the earliest ones as well) had no gender distinctions. It likely came about that sperm and egg, or the most primitive version thereof, was more advantageous for some ancient ancestor of ours than identical reproductive cells. Now look at human hermaphrodites for a moment. They are rare primarily because testicles and ovaries are derived from the same base organ in devoloping embryos, but those few that exist have never been documented to have functional ovaries and testicles. This is largely because the differing sets of gene activity necessary for bringing each set of sexual organs to maturity are incompatible with each other. It's possible that for some ancient ancestor of ours, it was simply easier for the oganisms devolopment to seperate processes of creating distinct reproductive cells between different organisms, and thus the creation of genders. Now, as to where division of labor actually came from, it's important to realize that there are a great many organisms that reproduce sexually for which there is no division of labor, and those for which there exists no form of society within which to divide the labor. It's possible that any division of labor was an emergent property of human genetics, not directly coded for by our genes. It may have been advantageous for early humans for men to do anything dangerous, not because they're better at it, but because they're pregnant and breastfeading somewhat less often, and an individual man is less significant to the survival of a small group than an individual woman. But it is the nature of division of labor as an emergent property (at least in the absence of any convincing evidence otherwise) that should give us pause when we begin thinking in terms of what gender roles are "supposed to be." Someguy1221 01:09, 28 August 2007 (UTC)

Geometry of complex

I want to know the geometry of potassium trioxalato aluminium trihydride complex?

[K⁺]₃ [Al(C₂O₄)₃]^3- Potassium trioxalatoaluminium complex has 6 coordinate aluminium with oxygens bonded to Al (can be chiral)

I can't see how the 3 hydrogens can be incorporated - have you missed a bit of the name - or can you give more details (eg its synthesis)...87.102.79.29 13:21, 24 August 2007 (UTC)

This link http://classes.uleth.ca/200401/chem2810a/lecture_15.pdf page 91, first set of diagrams, last (rightmost) diagram shows Iron (III) trioxalato complex which has the same structure as the aluminium complex.87.102.79.29 13:27, 24 August 2007 (UTC)

Colour question (related to one above)

How many colours should I be able to distinguish on a monitor - eg what's the 'bit equivalent' of the eye - and is 24bit colour beyond what the eye can percieve in terms of hue..87.102.79.29 13:51, 24 August 2007 (UTC)

This is another question that comes up a lot...and once again, a clear, simple answer is impossible because our eyes simply don't work like a digital camera:

• The eye is very sensitive to brightness variation - but much less sensitive to colour. Our eyes work in Red+Green+Blue+Brightness, not Red+Green+Blue like a TV set, a computer or a digital camera. Interestingly, there is a lot of work out there on RGB+Brightness displays (they are called 'RGBS' or 'RGBE' depending on who you read). Many modern computer games work in RGBE and convert to RGB at the last moment inside the graphics card (I do this stuff for a living!).
• In a computer monitor, the voltage sent to the monitor is directly proportional to the number used to represent it - so 8 bits per colour gives you 256 equally spaced voltages - however TV and LCD monitors aren't very linear - so equal changes of voltage do not produce equal brightness changes. In order to correct for this, computers and such have to perform a trick called 'gamma correction' which re-maps the numbers from a linear-voltage to a linear-brightness. This process causes a loss of precision over some of the brightness range - so the 8 bits you thought you were getting is more like 6 bits over the mid-range brightnesses. Cameras do similar tricks. Our eyes are also non-linear. We can tell the brightness differences between dark things much more easily than between bright things - so you can't directly compare bits-of-computer-colour-resolution to bits-of-human-eye-resolution...it's just not an apples-for-apples comparison.
• The eye is vastly more sensitive to green (and to a lesser extent, red) than it is to blue. However, in computer graphics, we tend to use the same number of bits for all three colours. We can easily see MUCH more than 256 brightnesses of (say) green - so 8+8+8=24 bits is simultaneously more bits of blue than we really need - and not enough green bits. The choice of 8 bits per component for computer graphics, etc is more because of the limitations of the display than of our eyes.
• Our eyes have all sorts of sneaky tricks for grabbing more light - by adjusting the amount of light let into the eye through the iris - and by releasing chemicals that sensitize the retina after you've been in the dark for maybe 20 to 30 minutes. So in a dark place - with dark-adapted eyes, you can see very dim things indeed - but you can't simultaneously see very bright things because as soon as a bright objects enters your line of sight, it erases your dark-adaptation and you don't get it back for another 20 to 30 minutes. So whilst 'instantaneously', 8 bits might be enough - over the entire range of your vision from something as bright as the sun down to something as dim as a candle a couple of miles away, you'd need maybe 24 bits for each of red, green and blue!
• Our 'resolution' is better in terms of brightness than in terms of colour - so for very small objects, colour doesn't work very well. You could imagine using fewer bits of colour for drawing text than for (say) cartoons.
• We are very good at spotting changes in colour - but less good at absolute colours. If you take two swatches of colour and place them a couple of inches apart on a grey background, you can only distinguish differences in the colours when they differ by maybe one or two percent. But if you place the two colours next to each other, then under the right circumstances (muted room lighting - brightly lit colour swatches, etc), you can see a change between the two of maybe 0.02%
• Our brains are designed to recognise the shapes of objects from subtle differences in shading. This is how you can tell the difference between a sphere and a flat circle. But we're pretty astoundingly good at that. Using subtle differences in lighting, we can look at a cylinder (which is just a shaded rectangle on our two-dimensional retinas) and tell whether it has a circular cross-section or a slightly oval cross-section. Remarkably, we can do this using shading cues that have less brightness difference than the smallest brightness differences we can recognise when comparing side-by-side colour swatches. This suggests that our eyes produce 'better' quality images than our brains actually need so that much of that precision is lost when performing unimportant tasks like comparing colour swatches - but which is fully utilised when deciding on the shape of a roughly cylindrical object. This makes sense from an evolutionary standpoint because telling which of two apples is the ripest to a precision of one part in a thousand is definitely overkill - but estimating the cross-sectional area (and hence the strength) of a branch whilst swinging through the trees might well be a life-or-death kind of a thing.

So, the disappointing bottom line is the same as for your last question...we don't really have a way to come up with a good number. The number that's used most often is 12 bits of green, 11 bits of red and 9 bits of blue...but that's by no means a "correct" answer. SteveBaker 15:03, 24 August 2007 (UTC)

Thanks - that was a long and good answer87.102.75.201 15:21, 24 August 2007 (UTC) (I didn't ask the previous question - just to be clear and prevent any confusion)87.102.75.201 15:51, 24 August 2007 (UTC)

Oops! My bad! SteveBaker 16:42, 24 August 2007 (UTC)

Thanks from me, too. I raised the question on the Computing desk (someone else copied it here) because I created an image containing all 2**24 colors (see the top entries here) and found that I cannot distinguish some adjacent colors no matter how much I blow it up. —Tamfang 21:15, 24 August 2007 (UTC)

True - I've tried similar things with long bands of colour varying by one unit. I couldn't see the join - it looked continuous- but I didn't look at every combination; specifically the green colours which I now know I should have been checking..87.102.6.217 22:11, 24 August 2007 (UTC)

But read what I wrote above. Unless your monitor gamma is set up perfectly - and even if it is - and room lighting conditions and that your eye is more sensitive over some of the bit range than others...it's inevitable that there will be some regions and some sets of conditions where you can't see single steps. The best region to see single bit variations is with a properly gamma-corrected monitor in a dark room - looking at only dark shades of colour. That (wonderful!) 4kx4k fractal with all 2²⁴ colours is great - but it puts light colours next to dark ones so it's hard to get a total screenful of dark colours. When I worked in flight simulation, we'd draw a night sky as a subtle blend from some kind of soft glow at the horizon to total black at zenith. In a darkened flight simulator cockpit, it was easy to see single bit steps in brightness - and it was impossible to fix with 8+8+8 bit graphics - so I know for sure that 8 bits isn't enough under all conditions. But this isn't a simple thing - eyesight is very complicated with lots of interacting phenomena. Even under controlled conditions, the amount of time you spend in darkness or how tired you are - all of those things interact. SteveBaker 20:47, 25 August 2007 (UTC)

Scary Movie

Hi, I've recently watched a scary movie about vampires n that sort of stuff... yeah, i know I shouldn have done so , but what's done is done... the problem is that I'm really scared now I know this may sound stupid, but is there a way to stop being scared? I've tried pushin it out of my mind but in vain... Thanks.

Maybe watching Buffy the Vampire Slayer would help?87.102.75.201 15:55, 24 August 2007 (UTC)

Or a humorous webcomic like Scary Go Round or Chopping Block. -- BenRG 01:42, 28 August 2007 (UTC)

I remember getting really scared after watching "The Ring" alone. I tried watching spongebob to counter the effect. :D

Yes, read the How to be saved instructable. That should do the trick. Either that or make it worse. Clem 17:05, 24 August 2007 (UTC)

I've always found that reciting the Litany against fear helped.  :) -- JSBillings 18:04, 24 August 2007 (UTC)

Just remind yourself it's a movie. Maybe after watching a scary movie, watch Scary Movie (a parody of scary movies). Juanita Hodges 18:08, 24 August 2007 (UTC)

I've done the same thing numerous times. The thing to remember is that the vast majority of the time you are afraid of what you don't know. For instance, you are afraid of a dark room because you don't know what is there (i.e. a vampire or werewolf). You could also be afraid of water because you don't know what's under you (i.e. a hungry shark). Of course, your assumption is that these creatures' intentions are to kill you or otherwise commit unspeakable harm to you. The point is that you don't know, which is what you really fear. It's not a huge help, but it gives me some comfort to put it in perspective. --204.23.231.181 18:35, 24 August 2007 (UTC)

Don't be scared. I mean, if the vampires are going to get you, you're not going to be able to do much to stop them. ;-)

Personally I find scary things less scary once I know how they work. Look up how they did the special effects for the movie. Once you see a few "behind the scenes" photos of the actor looking like a doofus it'll be easier to think of it as a staged production. After I saw The Ring (I don't watch very many scary movies) I took some time to look up all of the "scary" death scenes, which are really scary because they are flashed really quickly on the screen in the movie. Once I got a good long look at them and how the special effects were done I didn't worry so much anymore. --24.147.86.187 00:53, 25 August 2007 (UTC)

I still can't bear to look at any shots from The Ring. What did help is that I saw the movie Underworld right afterwards; it is another horror movie, but one where the protagonists have more direct abilities to confront their enemies. That might help. Eran of Arcadia 18:56, 27 August 2007 (UTC)

Next time listen to what mummy and daddy say and don't watch a movie you're too young to watch :-P Nil Einne 14:06, 25 August 2007 (UTC)

If rational reasons don't work, think irrationally. Scared vampires will get you in the night? It's okay; vampires can't enter your house unless you invite them in. Vampires can't go near any sort of cross. Vampires fear books and so can't go within 20 m of one! Decide the rules, then use them in your favour. Skittle 13:10, 29 August 2007 (UTC)

Salt in processed foods

Is it possible that there might be so much salt in a processed food that if you ate it without having any water to delude the salt that the salt content would actually be enough to kill you? Clem 17:01, 24 August 2007 (UTC)

Well LD50 of table salt is about 3g/kg body weight - so if you weigh 50-100kg you'd need 150g to 300g of salt to give you a 50/50 chance of survival.

That's about 10kilograms of corned beef.. (22lb) That said you could make yourself pretty sick by just eating a lot less .

You'd probably gag first before you eat enough.87.102.75.201 17:32, 24 August 2007 (UTC)

Since 1kg of seawater contains 35g of salt - if you weighed 50kg, your LD50 is 150g of salt - you'd only have to drink 5 liters of seawater. That's still an awful lot - but it seems like you could maybe do it. But processed food isn't ever even close to being that salty. SteveBaker 20:12, 24 August 2007 (UTC)

(OH! ...and of course, the LD50 dose is the dose at which half of the subjects die - at good proportion of people would drop dead with a lot less than the LD5- amount.) SteveBaker 20:14, 24 August 2007 (UTC)

I dont know how true this is but i thought the thing that killed you was that you drunk too much water after consuming too much salt? Tiddly-Tom 00:24, 25 August 2007 (UTC)

Per the point several people have made, the LD₅₀ is the median lethal dose. Of more interest perhaps is the LD_Lo which according to [1] is 1000mg/kg in humans. I.E. 50g of salt may be enough to kill a 50kg human. Nil Einne 11:50, 25 August 2007 (UTC)

Could try Dead Sea water. bibliomaniac15 Prepare to be deleted! 01:23, 27 August 2007 (UTC)

So one could die just by drinking 2 glasses from the dead sea ? Interesting --81.67.15.32 18:43, 28 August 2007 (UTC)

Editing Wikipedia telekinetically

I think I read about a kind of advanced, artificial limb that just came out that is designed such that the user can move his/her fake arm just by thinking about it. I think this is prety cool (does someone have a link to that an article about this, btw?). I'm wondering what other types of machines we'll eventually be able to operate just by thinking about their use... Are there other examples of this technology? In the future, could I, for example, edit Wikipedia articles just by thinking about the edits I'd like to make?--The Fat Man Who Never Came Back 18:07, 24 August 2007 (UTC)

You may be thinking of technology similar to this. This company (article) claims to have developed technology which allows players to control video games with their mind. I've read news articles about similar technology in the past but I can't find any of them - sorry — Matt Eason ^{(Talk • Contribs)} 18:14, 24 August 2007 (UTC)

There have recently been a lot of studies about brain waves which have produced experiments using these brain waves to control mouse movement, prosthetic movement, etc. I would suggest you do a google search on brainwave experiments, brainwave studies, or brainwave control. I'm sure you will get many sites on it. To be clear, these experiments use a "cap" of sorts that fits on your head and it connected to whatever device you want to move, it isn't telepathy as we think of it in science fiction. --204.23.231.181 18:46, 24 August 2007 (UTC)

Yes, this stuff exists - but it's not at the level of you thinking "I really wish such-and-such would happen" - and it magically happens - you either have to make a peripheral nerve do something (eg by trying to move an amputated arm) - or in some implementations, you concentrate on modifying your alpha brain waves, which is something you have to learn to do with biofeedback techniques. Either way, we're a long way from being able to think words and have them appear on the page. These are at best fairly slow one or two bit binary inputs. There is plenty of scope for improvement on this though. I suspect the worst part will be in getting electrodes that can be worn comfortably and easily and which don't have to be positioned too precisely. Failing that, we need implantable technology and medical ethics being what it is, I don't think doctors will be routinely implanting brain probes into perfectly healthy individuals. It's possible that in the future, you'll have to take a trip to some country with less medical ethics than in (for example) the USA in order to get your bio-implant widget implanted. The real problem then will be getting it upgraded every few years as the technology improves. SteveBaker 19:22, 24 August 2007 (UTC)

For the sensors to be precisely positioned, they do not need to be implanted in the brain. In the skull would also do the trick and would be a much less tricky operation. Actually, the sensors need only be 'anchored' this way and don't have to be in the skull. All the electronics can then be at the surface. Maybe that would require shaving the head and maybe wearing a whig, but that's hardly a medical issue and I'd be willing to do this if it really gave me direct mind control over electronics. DirkvdM 08:03, 25 August 2007 (UTC)

Some early work on this was done by Miguel Nicolelis, who gave a monkey the ability to control a computer game. An extremely simple one, but it proves the principle. Given that it's a fairly unobtrusive experiment, I wonder why he didn't use a human (such as himself).

Similar work is also done with pilots controlling planes through thought. DirkvdM 08:03, 25 August 2007 (UTC)

Unobtrusive? Did you read the article you linked to "He and his colleagues implanted electrode arrays into a monkey's brain that were able to detect the monkey's motor intent and thus able to control reaching and grasping movements performed by a robotic arm". If you consider that unobtrusive I guess you can volunteer for the next human trials but I'm guessing Miguel himself didn't. BTW, this sort of thing has actually been done in humans [2] [3], not surprisingly in people who had a good reason for being willing to take the risk. Oh and I just found we have a surprisingly detailed article Brain-computer interface Nil Einne 14:05, 25 August 2007 (UTC)

Running On Water

I am aware that there are several species that are able to traverse the surface of water. Plumed basilisk seem to be able to do with speed that counteracts their low weight, while water striders rely on the hydrophobic nature of their legs to beat surface tension. My question, however, is not a biological one, but more in the realm of physics. How fast would a human being need to run to run on water? If you know of some forumlae that can provide the answer, you need but provide it - I am capable of plugging in numbers. If you choose to run the numbers yourself, choose any arbitrary variables that please you (for instance: mass, weight, surface area of foot, etc) as long as you state what variables you assumed at what value, and that they are within human norms. I am fully aware that it is not possible, and that there are likely a number of complicating factors. Let them trouble you not. :) Thanks. -- Sapph42 18:25, 24 August 2007 (UTC)

You can barefoot ski at ~35 mph, according to the article. --Reuben 18:34, 24 August 2007 (UTC)

I'm assuming this takes advantage of hydroplaning, which is hydrodynamically very different than running on the surface. Its a good start, though. Thanks. -- 69.255.155.141 18:57, 24 August 2007 (UTC)

Well, let's think about this. As you push one foot into the water, you are displacing water out to the sides. That requires a force to be applied to the water - which will operate to counteract your weight. The ikky snag is that as you pull your foot out of the water, you have to suck back enough water around the sides to fill in the hole you left. At first thought (and I confess I've spent about 20 second on this one so far!) I suspect those forces are about equal - meaning that you could obviously push yourself up out of the water by stamping down very hard - but in pulling your foot up for the next 'stamp', you'd pull yourself back down into the water to the same degree. So I think a simplistic "running very fast" kind of thing can't work. But maybe with some kind of extreme speed (now purely hypothetical) - you could be trying to make the water move faster than the speed of sound in water - and then maybe something interesting and non-linear might happen. Hmmm - tough. The Plumed basilisk can only do this for a relatively short distance - it's possible that it's feet sink slightly deeper into the water with each step - which is about what you'd expect to happen - but the shape of it's feet maybe minimise the losses so it can stay up for much longer than we might expect. If it could run on water indefinitely (or at least until it got tired) then maybe we'd have to say there was a way for humans to walk (or run!) on water. Hydrodynamics is a tricky subject though - I could easily be way off base on this one. SteveBaker 19:32, 24 August 2007 (UTC)

My initial thought is that the only way this could work and avoid the force/counterforce problem you outline is if the surface is never breached. Is there a minimum response time for surface tension, below which no contact will break it? If so, a sufficiently fast stride could circumvent your objection. Further, in the case of the Plumed basilisk, if it could move twice as fast, would it be able to travel twice is far? If so, regardless of non-linear affects, could a supersonic basilisk travel miles? -- Sapph42 20:24, 24 August 2007 (UTC)

Surface tension is far too weak to have a measurable effect on something the size of a human. It's not a matter of speed. I've had some revised thoughts about this. As your foot strikes the water, the space it wants to occupy is full of water - so if your feet sink into the water (say) an inch - then a volume of water equal to the area of your sole times one inch deep has to be moved out to the sides. In so doing, it accellerates from a standstill to some speed that's determined by how fast your foot comes down. Since force equals mass times accelleration, in order to get a force that's enough to support your weight under gravity - you'd have to move the water out of the way with an accelleration that's proportional to your weight divided by the mass of the water you are displacing. If you displaced (say) 1 liter and you weigh 100kg - then you're going to have to push the water out the way with an accelleration of about 100g's! That's very fast...but in principle you could do it. So for as long as you are pushing your foot deeper and deeper into the water, you are not sinking. But there comes a point where that foot is down as far as it will reach - so you have to stamp with your other foot WHILST PULLING THE FIRST FOOT OUT! But to get your foot out of the "hole" it made, the water has to flow back in beneath it - and if your two feet are moving at the same speed, it seems likely that the upward force required to pull the water back in would be pretty similar to the downward force you get by stamping down on the water. I guess the saving grace here is that when you push down, you are trying to raise the depth of the water slightly - so you are also lifting water upwards vertically. Gravity opposes that so you can apply a bit more force to overcome it. When you pull your foot back out, gravity is helping the water to flow back underneath again - so maybe you have more water resistance in the foot that's going down than you do on the one that's moving up. That tiny amount of difference might be enough for a very light creature with proportionately large feet. Those basilisk guys are small - and skinny with big feet. Since the weight a creature has to support increases as the cube of it's height and the area of it's feet as only the square of the height - the amount of water displacement - as a fraction of weight gets worse the bigger you are. Perhaps that explains how the basilisk does so well at this? SteveBaker 20:54, 24 August 2007 (UTC)

Bored physicists to the rescue. From The Physics of Superheroes by James Kakalios: "The density of water is much greater than that of air - water molecules are in contact with one another, while there are large open spaces between air molecules. . . . [F]or the Flash, when running in top of the water's surface, this is a good thing. Just as someone is able to water-ski if he or she is towed at high speed, the Flash is able to run faster than the response time of water molecules. As his foot strikes the water's surface at speeds greater than 100mph, the water is not able to move out from underneath his boot fast enough and instead forms a shock front, similar to the shock front that forms in front of a supersonic airplane." -- Sapph42 22:33, 24 August 2007 (UTC)

I think that's an unnecessarily exotic explanation. I just point my -- um, that is, the Flash, yeah, that's the ticket -- just points his feet. He leans forward and pushes against the water at an angle with his forward foot. He slides the back foot backwards out of the hole in the water; this requires very little force because he doesn't have to move any water out of the way, except what sticks to the foot. --Trovatore 06:50, 25 August 2007 (UTC)

It's an easy question to answer; the only variable you need to control is the temperature. Just get the water down to around -20C for a while and it should be solid enough to walk, run, and skate on. Matt Deres 14:48, 26 August 2007 (UTC)

Space-time continium

Hi, im writing a science fiction story which involves a device that is able to look back in time, problem is i can't describe how it works because i don't know. I think it would be something to do with the space-time continium, but i'm not sure, i've already checked wikipedia for information, so i was hoping you could give me some info on how such a device could work. Thanks for taking the time to read this. (I would also like to thank everybody who has taken the time to provide answers for my question).

Best regards Sci-fiGOD2k7 18:51, 24 August 2007 (UTC) Sci-fiGOD2K7

A popular idea I've seen in a lot of science fiction is to take advantage of the Multiverse theory, and to view an alternative universe that is identical to our own, only that it is 20 years younger (or whatever time you want to look at). -- JSBillings 18:54, 24 August 2007 (UTC)

Look at info on pages like black hole and event horizon. Looking back in time is what we do all the time. What you see is not happening right now. It took time for light particles to bounce off stuff and then hit your eye. So, seeing far into the past simply means having some old light particles around to catch a peek at. -- Kainaw^(what?) 18:55, 24 August 2007 (UTC)

Or if something less scientific appeals to you, perhaps this device could access the Akashic records.--Shantavira|^{feed me} 19:17, 24 August 2007 (UTC)

Merely looking back seems maybe possible. Firstly, all the information about what was happening back then may not have been lost (talking about a scifi plot rather than reality here). Suppose a book slid across that table an hour ago. The energy of it's motion got turned into heat - perhaps some amazing scifi gizmo could examine the energy present in the world now - and track that backwards in time to someplace in the past. Not possible in reality for all sorts of thermodynamic and heisenburg-ish reasons - but maybe a good writer could make it seem plausible! Alternatively - if we don't have to look back into time before the creation of the technology, it could merely be recording where things in the world are right now - and replaying them later. In a sense, a VCR does what you ask. It's a spooky device that lets you watch TV from the past! A camera and a VCR lets you see into the past. So a device that recorded MUCH more information than a camera and a VCR could record EVERYTHING that happened. Maybe a ubiquitous array of sensors made out of nanotechnological 'dust' and sprayed from the air over everything and everyone - recording in massively complex nanotech memory and replayed via some kind of holistic network which allows you to broadcast a command for any mote of dust that was around 10 years ago at this location to please return data to me. But that limits you to not seeing further into the past than the invention of the machine. Most of the hypothetical relativistic/black-hole/wormhole time-machine contraptions that people come up with would have the same restrictions - but my way is a lot more do-able in reality. To actually see far into the past - before the invention of a machine to do it is exceedingly dubious. Parallel universes (as far as we know) are undetectable and cannot communicate information to us - so they don't really help - although if you are prepared to bend science enough, you could argue for it.

Do me a favor though. If you write this story - think about this: If you have a machine that can see back in time, it also has to be able to see different locations in space too - the earth is orbiting the sun - if you look back at the spot you are at right now, but 6 months ago - all you'll see is vacuum - because the earth was a long way away back then! So your device has to be able to look at any place as well as any time. If it lets you look back (say) 1 millisecond ago - but anywhere in space - then it's able to spy on anyone right now! It would be a tremendously useful instrument because we could (presumably) use it to explore the bottoms of the oceans - or the innermost parts of the earth's core. If the device were cheap enough so that (for example) a major newspaper publisher could afford one, you just know that nobody would have ANY privacy anymore. Forget being able to see into the past! Seeing any place here in the present would be an earth-shattering thing. SteveBaker 19:54, 24 August 2007 (UTC)

This is the plot for an old Isaac Asimov story. The government suppresses the technology because it allows someone to spy on anybody. Delmlsfan 02:31, 25 August 2007 (UTC)

I thought it measured the trajectory of neutrinos.. it's a pretty stupid idea. Based off of "if you know every particle's location and trajectory then you know the future".. of course it's impossible to define exactly where a particle is at quantum size, and it makes even less sense to try to pull off that calculation with only a miniscule data set --froth^t 04:05, 25 August 2007 (UTC)

There's a fairly famous old story on this premise, "E for Effort" by T. L. Sherred. Damon Knight revisited it, in a mellower key, in "I See You" (1976?), which i think assumed a sort of slow light. —Tamfang 21:56, 24 August 2007 (UTC)

I want to thank people for helping me with this matter, as its driving me nuts. My original idea was that it was a system of satellites all hooked up to a quantum computer, and the satellites were somehow able to look back in time, but i'm not sure how this would work. Thanks again, Sci-fiGOD2k7 22:30, 24 August 2007 (UTC)

I'm a big fan of this kind of 'hard-core' scifi - and in my view, I'll allow any story writer ONE ridiculously impossible invention providing that:

• It's self-consistant (like with what I said about it being able to see any PLACE as well as any TIME) - if there is a glaring inconsistancy - it'll bother me through the entire book!
• That all of the implications of the thing are properly explored.
• That it's actually necessary for the plot.

What I hate is when some device is postulated - and I find myself saying "But if you had a thing like that - why wouldn't you use it like this?!?" - or "Why did the author need to invent such a thing when the story would have been just the same with more reasonable technology". So I'd be happy to read a story where you handwave the details of why some quantum effect in a satellite allows you to look into another place at another time - so long as you tell me about the consequences of using it for spying on your boss one second in the past (or whatever). (I'm also trying to remember another story based around the "machine that looks into the past"...something to do with investigating the history of Christopher Columbus...I don't recall. SteveBaker 01:05, 25 August 2007 (UTC)

A looking-back-in-time machine

At right is a real-world device that once looked 13 billion years back in time. --Sean 01:10, 25 August 2007 (UTC)

I remember an Isaac Asimov short story had such a device. I can't remember if it had much explaination. Basically someone came up with the theory. The device was invented and under the control of the world government science ministry. They controlled the information about the device that was release. They did regularly release 'discoveries' from the past. Then a history professor got annoyed when his proposal to study something never received any attention and enlisted a student to help him (illegally) make a device. The student accepted but after a while realised that the government had been bullshitting as the device couldn't look back that far as it got more blurry the further back you go. The professor's wife found out about the device and was very interested. The professor himself lost interest because 1) It couldn't study what he wanted to 2) His wife wanted to look at their dead daughter which was bad because a) It was unlikely to be beneficial for her well being to keep look at her dead daughter b) He was a smoker and was afraid he may have been responsible for the fire that killed his daughter. The government meanwhile found out and was watching the involved parties with their version of the device. They professor intervened and tried to get the student to stop making the device. The government joined in and pointed out the reason they'd been protecting the device was because it completely destroy society as it would destroy privacy; as the past is basically the present. Unfortunately it was too late as the student had already given his research to his uncle who had then given it to the press and the government had not noticed the uncle's involvement so had not watched him. Anyway the point of my retelling here was to concur with SB. If you want to include such a device you have to think of the implications it will have. I mean there's already enough of Britney and Paris in the media without "watch Britney drinks a glass of water" or "watch Paris try out 3 dresses before deciding just to go naked (everyone's already seen her naked anyway)". Unless you take the easy way out and do the opposite Asimov's device, it can't look into the near past but only the far past. But this makes far less sense to me... Nil Einne 12:55, 25 August 2007 (UTC)

In fact, on the theme of implications, doesn't the story conclude that the whole reason for the interfering government and broken, fragmented academic system was to prevent this machine being built? The 'evil' government was just trying to protect everyone from the implications of progress. Completely unlike the Philip K. Dick (I think) short story where the man creates a time/space-viewing-portal thing in order to pass the exams that only robots have previously passed and get a job in government... But I digress. Going only far back in time is more like 'The Ugly Little Boy' (or whatever it's called, also by Asimov) isn't it? It could work. Personally, I wouldn't try to explain it properly; just have your characters accept that it works, and keep it consistent. Skittle 22:54, 28 August 2007 (UTC)

Yes I think it was the reason for the intefering government (or it may have just been to stop this machine and whatever else that may come along with similarly very nasty implications in some regards). Definitely the government person said something about how people like you always think about how bad the interfering government but fail to consider perhaps what they're doing is necessary and good. As for the Ugly Little Boy, was that one a physical limitation? Or was because they weren't just looking back but actually intefering and things tend to balance out in the end over time but if you go to close (or steal a famous person or whatever) they might not. Nil Einne 21:51, 30 August 2007 (UTC)

I have thought of what i want the device to be, a series of satellites linked to a powerful earth based quntum computer. The device can look a far distance back in time and as its a system of satellites it can look any where on earth. But i have a problem, as im not sure how i could get it to look back in time, does anyone have any ideas to how it could look backwards through time, because personaly i'm no good with the whole spacetime thing, but i was thinking it could use a series of light cones to look through a closed time like curve, but im not sure how it would do this and if it would work (in a fictional stand point). So if anyone has any ideas of how this would work i would love to hear them. Thanks for all answers past and future

Sincerly Sci-fiGOD2k7 16:29, 25 August 2007 (UTC)

A large mirror placed 2 light-years away - coupled with a really powerful telescope - would allow you to see exactly four years into the past. But as with all such devices, even if you launched it at some insane speed, close to the speed of light, it would take more than two years to get to the right place and by the time the light reflected from it got back to our telescope, it would be another two years - so the machine would only be able to look back to points in time AFTER its initial creation. This does seem to be a fundamental limitation of all such contraptions. SteveBaker 22:06, 25 August 2007 (UTC)

Also, the diffraction limit implies that you wouldn't be able to see very much. At visible wavelengths, with a mirror and telescope both as large as the entire Earth, you wouldn't be able to resolve any feature smaller than about a kilometer. You can get much better resolution much more economically by taking some photographs locally and looking at them four years later. -- BenRG 22:07, 30 August 2007 (UTC)

You can't really look back in time. All you can do is make inferences about the past based on surviving relics, like old light or old neutrinos or old manuscripts. We can only see the cosmic microwave background because it's right here, right now; if it weren't, we couldn't see the early universe no matter how hard we looked. Your device can only work if there's some hitherto unknown phenomenon that records information about the past in some locally recoverable way. -- BenRG 22:07, 30 August 2007 (UTC)

Okay, so what if somebody traveled to the past would there be any way for the device to lock onto them from the present? Sci-fiGOD2k7 18:30, 31 August 2007 (UTC)

I suppose it depends on what mechanism you've introduced to allow time travel. In general, if people can time travel somehow, I suppose a mechanical probing device could also travel back and forth in time relaying messages. -- BenRG 14:19, 1 September 2007 (UTC)

user knowledge

I have developed an indicator circuit to display the status of a Hall sensor. A friend says the user of the device it is in will not buy it because it is diagnostic tool only a technician would find of any value. I contradict saying that knowing is far better than not knowing regardless of whether the knowledge is useless of over your head. Who is right? Clem 20:54, 24 August 2007 (UTC)

I'd say you and your friend are right, whereas the user is wrong, and you might want to adapt to the user. As you say, for a completely rational person, more knowledge is always good. Your user, however, might find it intimidating or something, because he does not understand it. I did a similar thing at the supermarket the other day. I was going to buy ham, but there was too much to choose from so I ended up buying nothing! Stupid of me, but that's what I did. —Bromskloss 21:38, 24 August 2007 (UTC)

Perhaps a compromise is in order. I agree that displaying something all the time which the typical user won't understand would be annoying to them. Instead you could have them hold some combination of buttons down to get the status of the Hall sensor. That way, the user won't be annoyed by it, but techies can still get the info if they want it. StuRat 03:42, 25 August 2007 (UTC)

Good idea. An on/off switch. Clem 22:45, 26 August 2007 (UTC)

Maglev technology & Meissner Effect/Flux trapping

I know about the Japanese maglev system that uses superconducting coils for efficiency in its EDS system, but why has no-one tried using the Meissner and flux-trapping effects demonstrated by super-conductors (below their critical temperature) to create a stable maglev platform? The technique has been demonstrated on 'toy' maglev trains, videos of which can be found on YouTube ie. http://uk.youtube.com/watch?v=rfUWDYm0ewI

Would such a design not be favourable over both electrodynamic (EDS) and electromagnetic (EMS - eg. Transrapid) suspension, EDS requiring the movement of the train to create the levitating force, and EMS being naturally unstable and requiring a computer control system?

Or are there technical limitations that I am unaware of? For example can this method carry the weight of a laden train?

Thanks, Jonaboff_talk

22:41, 24 August 2007 (UTC)

Just an idea. I believe the superconducting property vanishes in the precense of too strong a magnetic field (right?). Carrying a full-size train would require a stronger magnetic field than carrying a toy. Perhaps it would be too strong. —Bromskloss 23:01, 24 August 2007 (UTC)

It would be a matter of price. A superconducting coil in the train is one thing, but making hundreds of kilometers of superconducting track would exceed the budget of the train company. The material costs on the order of $100 per gram, or $100,000,000 per ton. Graeme Bartlett 23:16, 24 August 2007 (UTC)

A minor note—the toy shown uses conventional (albeit fairly powerful) magnets in the track. The only superconductor in the toy is aboard the train. Of course, sufficiently powerful permanent magnets for such an application would also be quite costly. I'm not prepared to comment on whether it would even be possible to scale up such a system to operate at hundreds of kilometers per hour and with cars weighing tens of tons. TenOfAllTrades(talk) 13:09, 25 August 2007 (UTC)

I'd say Graeme is right. No chance to make such a large installation superconducting. The largest device build so far to my knowledge is the Large Hadron Collider: The 30 kilometre circumference ring is kept at liquid helium temperature to be able to use superconducting magnets. Simon A. 08:39, 25 August 2007 (UTC)

It there any reason why you have to use low temperature superconductors? Most maglev systems in development using superconductors are using 'high' temperatures ones cooled by liquid nitrogen Nil Einne 12:58, 25 August 2007 (UTC)

As Ten said, only the bogeys of the train would be superconducting, the track would be ferromagnetic. Do the superconductor effects only work with permanent magnets, or could electromagnets be used?

I also have a feeling that the $100 per gram estimate is a little high, that puts it at around £50, right? I can buy a kit like the one shown in the video for little more than £100, and the superconductor block weighs much more than 1 gram.

Thanks, Jonaboff_talk

14:05, 25 August 2007 (UTC)

I'm not 100% sure if I understand the difference between what you're proposing and what's be done but, are you sure this has never been attempted? What about the Southwest Jiaotong University, China test (see Maglev train). Our article has limited information but there is more information in various journal articles. Nil Einne 14:46, 25 August 2007 (UTC)

The Southwest Jiaotong University, China maglev is actually exactly what I meant by the sounds of the article, I'm not sure why I haven't noticed that in the article? I'll check the history, see how recently the section was added. Thanks anyway. My point still stands, that it seems strange to me that this approach isn't more popular, when it eliminates the problems of stability, power failure, does not require wheels etc.

On a side note, does anyone know if electromagnets can be used in such a system, or can only ferromagnetism achieve these effects? Is there a physical difference between electromagnetism and ferromagnetism besides the source?

Thanks, Jonaboff_talk

15:45, 25 August 2007 (UTC)

It's actually been there for quite a while (unless it was removed and re-added). I researched maglevs a bit a while back and it was there then. Check out the talk page for comments I made, it was there when I made them. However I don't and didn't have access to the journals which talk about it so I couldn't update the article (and it's probably over my head anyway). There is actually surprising little information I could find in more general publications other then an occasional PR from the China side which doesn't generally provide much useful information. I do recall that there is some controversy in Germany recently over whether some of China's recent work on maglev trains may have been 'borrowed' from the Shanghai maglev but the 2000 thing is I presume mostly home grown (well as homegrown as anything in China is). Nil Einne 21:55, 30 August 2007 (UTC)