Wikipedia:Reference desk/Archives/Science/2008 October 23

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October 23

Longevity of satellites

With our current quality of satellites, is it possible to build a satellite capable of surviving at least 1,000 years without contact with Earth, and then broadcasting a signal to a specified location? (Also, if possible could you provide a source for me to cite?) --Ye Olde Luke (talk) 01:59, 23 October 2008 (UTC)

no, things like batteries wear out, solar cells degrade, attitude fuel runs out, metal recrystallizes or migrates in the circuits, electrolytic capacitors dry out, cosmic rays damage the small stuff and insulation. It may be possible to build one though! Graeme Bartlett (talk) 02:12, 23 October 2008 (UTC)

But Vanguard 1 is still floating, and they think it'll continue to float for another thousand years. Would there be a way to keep the satellite in sleep mode or something until it comes time to transmit the broadcast? --Ye Olde Luke (talk) 02:25, 23 October 2008 (UTC)

Longevity in a dormant state does not seem to be a factor that has been studied to any great degree. Engineers design things to be economical and to meet the specifications. I have maintained equipment which has functioned in power systems for as long as 80 years, when longevity was not a major objective. I have seen light bulbs which still work after 100 years (not 100 years of being continuously illuminated). I own telegraph relays which work after 110 years, telephones which work after 100 years, and vacuum tubes which work after 75 years. Certainly lubricants can gum up, and copper conductors exposed to oxygen corrode and fail, batteries fail, and insulation can crack and shorts out. If long dormancy and revival after 1000 years (in space) were the goal, I would look to develop suitable technology. I have seen Egyptian glass and ceramics, and implements made of gold and copper. Ceramics can insulate and survive thousands of years. So clearly copper or gold conductors with ceramic insulation on jeweled bearings could function as electromagnets, motors, or relays after a thousand years in space. Vacuum tubes could likely function after a thousand years in space. Ways could likely be found to extend the service life of semiconductors such as solar cells and transistors. This has not generally been an important design goal. Attitude control fuel? Let it twist slowly in the solar wind without control, until it reaches the target solar system, or until sufficient time has passed in our own solar system.. Stored energy? A superconductor can store energy in the form of current without appreciable loss for a thousand years, out where it is cold and no nitrogen flow is needed to maintain the low temperature. Ordinary lead acid storage batteries have an extremely long shelf life when the electrolyte is stored separately, to be thawed and added when the time is right. Solar cells? Drift of dopant might be a problem, leading to degradation. Perhaps solar energy could be used via a heat engine poweredby the sun or some distant star the probe has reached. Chips and microminiaturization of electronic components would seem to lead to early failure, but redundant circuits could be used with the failed ones detected and turned off by devices such as a "deadman switch" circuit. Nuclear fuel would not be a solution with types of fuel assemblies I have read about. Edison (talk) 03:59, 23 October 2008 (UTC)

Space is an environment that's a lot different from what we're used to here on earth. Without oxygen, things can't rust or corrode in the normal way - but substances are subjected to much more intense radiation and more violent temperature changes - which cause stress fractures. I'd want to think in terms of something very crude and unsophisticated. Power held in a big spring - a generator to produce the electrical burst that would be as simple as possible with little reliance on fancy bearings. The 'trigger' mechanism would be an interesting problem. If the timing doesn't have to be too precise, maybe you could design a material to deliberately fail due to some kind of well-understood but slow process...as it fails, the spring does its job - generates a short burst of electricity into the simplest, most chunky radio you could imagine. If the signal doesn't have to be a radio - then perhaps simpler still would be to allow two liquids to mix and generate a chemical laser or something. It's an interesting problem. SteveBaker (talk) 04:44, 23 October 2008 (UTC)

Like a beacon: Break the glass, release chemical which mix and initiate action. Crude and clunky may work better for longevity. I just threw away a 1997 high tech phone which failed, and a 1950's dial phone still works fine. The amount of radiation might depend on where the satellite was. Solar radiation could indeed hit it hard on occasion if it were in Earth orbit for 1000 years. Edison (talk) 04:57, 23 October 2008 (UTC)

I think it probably would be possible and not with too much difficulty, weight is the main problem that makes things flimsy. But not anywhere near the earth with the way it is getting surrounded with space debris. Dmcq (talk) 12:40, 23 October 2008 (UTC)

Haul a small asteroid into earth orbit (we have the technology, but it would be insanely expensive), bore to the core and place your satellite at the core of the asteroid. This will protect it from debris, temperature fluctuations and certain types of radiation. Once the timer activated, have it bore its way out (or leave the original bore unfilled) and transmit. Yes, it would be prohibitively expensive, but it would be possible with today's technology. 152.16.59.190 (talk) 10:32, 24 October 2008 (UTC)

You would still have to be careful that your electronics (and power source) didn't degrade over time. Even just whiskers forming on the contacts would be an issue.

Not to mention time-keeping. How does the satellite know when 1000 years have passed? APL (talk) 12:56, 24 October 2008 (UTC)

That's why "big and chunky" is good. Whiskers grow short distances and are thin and flimsy. Sure, they are enough to take out a teeny tiny chip - but if you had 1" brass bars carrying large voltages and currents - whisker formation would be an irrelevance. If the satellite has to know that 1000 years have passed PRECISELY - then I think this is a tough problem - but you could (for example) use a small nuclear-power source with a half-life of around 1000 years to generate a voltage to hold open a good-old-fashioned solenoid against a big-assed spring. Once the voltage drops below some critical level, the solenoid can't be held open against it's spring and it shoots forward and mechanically smashes the glass vial containing the liquids that combine to make a chemical laser. Perhaps the solenoid also starts a slotted disk spinning in front of the laser that modulates the signal into morse-code...or to send out the first 20 prime numbers in binary or something. You could arrange that it would trip somewhere between maybe 900 years and 1100 years - if that's good enough. The solenoid could be HUGE and chunkily built so it won't fail. Think "steam-punk" here! SteveBaker (talk) 20:05, 24 October 2008 (UTC)

Time to replenish an oil well

Sorry to ask two questions, but how long does it take to replenish an oil well? (I know it takes longer than a lifetime, but does it take less than 1,000 years? If so, how long? And again, if possible, could I get a source?) --Ye Olde Luke (talk) 03:35, 23 October 2008 (UTC)

The article Petroleum says it took geological time to create the material an oil well extracts from ancient organic material. Thousands of thousands of years, in other words. With modern synthetic fuel technology, the creation of hydrocarbon fuels from organic matter might be a fairly quick process. Edison (talk) 04:04, 23 October 2008 (UTC)

We're talking millions of years - certainly not thousands. Petroleum#Formation says "Geologic timescales". The problem is that the formation process requires heat and pressure and an absence of air. So lots and LOTS of dead algae and other ocean-bottom goo has to be layered under hundreds of feet of rock. That's not something that can possibly happen quickly. Then the pressure of all of those rocks compresses and heats the goo - eventually forming oil. The actual oil formation might happen relatively quickly once the conditions are right - but those conditions will take an enormous amount of time to get started - simply because the requirement to have enough pressure means that the goo at the ocean bottom has to accumulate enough layers of sediment to compact into hundreds of feet of heavy rock. But even that's not enough because the oil would tend to form in a very thin layer - which would make it almost impossible to extract. The ground has to fold and crinkle to form natural underground domes into which the oil is squeezed. Only then can we drill down and extract it. Those processes are geological in nature - so "Geologic timescales" is indeed an appropriate term. Mountains don't form in thousands of years. SteveBaker (talk) 04:20, 23 October 2008 (UTC)

Note that "Thousands of thousands" = "millions." Edison (talk) 03:10, 24 October 2008 (UTC)

Plus "an oil well" would never be replenished in the sense of being able to pump oil again. The entire landscape would be utterly transformed, the oil well long long gone. Pfly (talk) 06:08, 23 October 2008 (UTC)

Yeah...oil ain't water. When an oil well runs dry, that's it for that well. Asking when an oil well will be replenished is like asking how long it will take for the sites of archaeological digs to turn up new fossils: once they're gone, they're gone. The well will be long gone before any oil will turn up where the well once was. Try this article out to better to understand where petroleum comes from. --Shaggorama (talk) 08:20, 23 October 2008 (UTC)

Yep - it's wrong to think of those big empty spaces where the oil was gradually filling up again. No - what has to happen is that existing shallow oceans have to have new rivers start depositing sandy silt onto the top of the layers of dead algae. As the silt builds up - it presses down on the stuff beneath - forming sandstones and other rocks. This process alone could take a million years. That stuff sinks downwards and with luck, more layers get built up on top. Maybe a volcano deposits a few feet of lava onto the top of this - adding granite layers on top of the sandstone. Once enough millennia have gone by - the original goo is buried under hundreds of feet of rock - that's probably come from thousands of feet of accumulated river sediment and who-knows-howmany volcanic events.

Then when the temperature and pressures are just perfect, the goo undergoes a couple of stages of chemical change and turns into a THIN layer of oil - this might happen quickly once the conditions are right. Perhaps (and I'm guessing here) a 10 foot layer of dead algal ooze might form a layer of oil-soaked sandy rock maybe just a few inches thick. That's impossible to extract economically with current drilling or mining technology - so it's useless to us like that. But we see "oil shales" and stuff like that all around the world - so we know it exists.

If a continental plate happens to bump into the edge of the continent where our oily layer formed then the rocks will crumple under the lateral pressure. Maybe a major earthquake makes the rock layers tilt at an angle. Some parts of our thin oily layer get pushed deeper underground where the pressures are higher - some get pushed upwards into mountains. The oil in the layers that went deeper is now under even more pressure - but the areas that were pushed up are under less pressure - the oil is slowly squeezed out from the deep areas to the shallower areas. Sometimes, the oil is squished all the way to the surface where it gradually gets washed away - but in a few lucky areas, the underground rock formation forms a dome - like an up-side-down bowl - and the oil collects there.

If we're even more lucky, the rock on the upper-side of the 'dome' is impermiable to oil so the oil collects there. With luck, there are no underground streams to wash it all away again. If we're yet luckier still - that bowl doesn't get eroded from above to form a 'tar pit' which dries out and becomes useless as "oil" because all of the interesting volatile chemicals have evaporated. If we're lucky, the entire bowl doesn't get 'subducted' down under another continental plate and be pushed towards the core of the earth where we can't reach it anymore. Hopefully it doesn't end up under ocean that's too deep or too stormy to drill there. If absolutely everything works out just right (which is surprisingly rarely) then eventually - there is a reservoir - perhaps hundreds of feet deep and a few miles wide that's completely full with millions of barrels of crude oil. Now if we can find that dome - we can drill down into it and pump out the oil - but once it's empty - that's that. There is no more algae there to form sediments and to be squished - so the dome will eventually either collapse or fill up with water or something. Either way - that's it...no more oil will ever come out of it. "New" oil is indeed gradually forming somewhere where the bottoms of shallow oceans were long ago covered over by newer layers - but it'll be millions of years before we can get at it - new mountains are formed more rapidly than new oil! We're extracting oil tens of thousands (perhaps millions) of times faster than it's being formed - so once we've used it all - we'll have to wait for millions of years before we can do that again.

SteveBaker (talk) 14:12, 23 October 2008 (UTC)

Guinea worm extinction

If the attempts to eradicate dracunculiasis succeed, is there any way to keep the worm itself from going extinct? I understand that ending the disease will improvbe people's lives, and I support it -- but could the species be saved, too? Unlike smallpox, it's not just a germ, but a complex animal - and we saved samples of smallpox anyway. It seems like there's a non-negligible amount of genetic information and, well, biological uniqueness in this creature, more than in germs which evolve new species in mere years. Could they be somehow kept alive in some sort of human-substitute chemical bath for that phase of their life cycle? It seems like that might be the only possibility, as finding human volunteers to host it would be nearly impossible and counterproductive anyway.

Even if not, has someone sequenced the DNA so that information, at least, survives? 128.194.161.154 (talk) 03:54, 23 October 2008 (UTC)

Dozens of minor species go extinct every day. Extinction says that experts expect half of the species on earth today to be gone by 2100. Species says that we estimate that there are between 2 and 100 million species on earth right now. So over 100 years - between 10,000 and 500,000 species disappear each year. that's between 30 and 1500 species lost every single day. More importantly - it's believed that the "natural" rate of extinction (ie without us humans messing things up) is 100 to 1000 times less than this rate. So between one species every couple of years to 15 species per day is the NATURAL rate of extinction. So this one species disappearing isn't really a big deal. There are better ways to spend our conservation efforts. If it goes extinct...big deal...it's a drop in a bucket. SteveBaker (talk) 04:34, 23 October 2008 (UTC)

Although we like to generally treat the concept of species with the attitude of "the more the merrier," the fact is that there are a few around that we'd just as well be happier to do without. You raised the example of smallpox: we held onto that one just in case it pops up again (or something close comes along). If we're going to fight to keep a species around, the question needs to be asked: why? Conservation is an investment and we can't build reserves for every inconsequential species on the verge of disappearing. The reason ecologists and biologists generally fight extinction is to retain genetic diversity in the wild; most endangered species we hear about are fought for by the general population because they're cute, quite frankly, and are used to spearhead efforts to garner support for the conservationist movement in general (the panda is a great example).

Given our impact on the planet we like to act as curators of nature to try and minimize the negative effects our lifestyle has on the planet, but protecting nature will always be done in a manner that is beneficial to humanity as well. No sympathy well ever be felt for parasites and diseases, and if any samples are retained after their extinction in the wild it will only be for the sake of their potential for designing future cures, as was (presumably) the case with smallpox. --Shaggorama (talk) 08:08, 23 October 2008 (UTC)

We (as responsible beings and 'custodians' of the planet) have a duty not to go around destroying species at a rate of a thousand species per day...but the loss of at least a few species per year is completely natural - and indeed a necessary part of evolution. As a few individuals of a species get mutated into new forms (new species) - they will naturally start to out-perform the members of their former species - and when that happens, the old species will become extinct. This is how creatures adapt to changing conditions. A part of that change is the rise of humanity...the unfortunate part is that we're wiping out species who can't compete with us for land because they have yet to invent defences against the bulldozer - or who can't tolerate the toxins we put out or the climate changes we're causing. Given enough time - they certainly would evolve to handle that - but evolution can only creep along fairly slowly and the rate at which we're changing things is causing the system to fail. This kind of 'mass extinction' has happened in the past - when the dinosaurs were wiped out, for example. One day there are dinosaurs - and a few years later...no dinosaurs - suddenly, all of the species who relied upon dinosaurs for their livelyhood went extinct - but other species suddenly found there were large tracts of land with no large carnivores - and they thrived. The earth did recover - and it will this time too. The problem is whether humanity will be one of the species who can't adapt fast enough to the changes that we, ourselves are causing. If our crops fail due to global warming and we over-fish the oceans - then there won't be enough food and we'll be quite likely to die out. Other species will survive - evolve and repopulate the planet...but it will be a very different planet afterwards - just as it was after the dinosaurs vanished.

In a sense, the Guinea worm and the smallpox virus simply failed to mutate fast enough. They needed to evolve into a form that either survives all the efforts of humanity to eradicate them (the HIV virus is managing to do that - but smallpox couldn't) - or they had to evolve to attack other creatures so as not to cause humans to want to kill them (there are plenty of viruses that don't hurt humans at all - and we're not really not trying to eradicate them). There is an old science fiction story (I think maybe by Isaac Asimov) in which all of the creatures of earth have evolved to not harm humans - because in some future world, that's the only way to avoid extinction. So humans can walk safely through the middle of a pride of wild lions because the lions have evolved a mechanism to avoid killing people - and thus avoid people killing them. It makes perfect sense that this should happen - indeed it's been argued that animals such as dogs have "evolved" to be good with human children because the vicious baby-killers don't survive to reproduce. We think of this as humans breeding gentle dogs - but we're just another evolutionary pressure on the canine genome. The guinea worm failed to do that - and it's about to pay the price.

If we're going to expend effort to save species - it makes more sense for us to try to preserve the ones that are harmless - or even beneficial to humans. That will place evolutionary pressure on the ecosystem to be more friendly to us. Evolution is relentless - and if we can avoid wiping ourselves off the planet - the planet will eventually bounce back.

SteveBaker (talk) 13:44, 23 October 2008 (UTC)

This rings of Social Darwinism. Besides the OP asked HOW could dracunculiasis be preserved, not whether it should. Does anybody know an answer to the question? --S.dedalus (talk) 04:13, 24 October 2008 (UTC)

It has nothing whatsoever to do with Social Darwinism, as Guinea worms have no society. As for the original question: the guinea worm is a parasite, but humans are not its only host. So it would be possible, for example, for a dedicated staff of personnel to preserve the worm after the disease's eradication by inflicting it upon successive generations of captive dogs, horses, cows, wolves, leopards, monkeys or baboons. But it would probably be more humane to simply sequence its genome and let it go extinct. - Nunh-huh 04:26, 24 October 2008 (UTC) P.S. Actually, now I wonder if a "behavioral" eradication program would really result in the eradication of the organism, as there would seem to be pockets (dogs, horses, cows, etc.) that wouldn't be affected by such manipulations. The program might be aimed at minimizing human disease, and may not actually wipe out the organism in animals. - Nunh-huh 05:48, 24 October 2008 (UTC)

I disagree. This is reminiscing of social Darwinism in that the latter ethical theory is based on a “might makes right” philosophy. The idea that because this creature is harmful to us, and because many species go extinct without our help, it is morally acceptable for us to exterminate the Guinea worm is suspect in my mind. --S.dedalus (talk) 05:42, 25 October 2008 (UTC)

You misunderstand Social Darwinism, which is about the evolution of human society, not shorthand for "might makes right" (which is in itself a gross mischaracterization of Darwinism). - Nunh-huh 06:15, 25 October 2008 (UTC)

No, I don’t think I’ve misunderstood. “Might makes right” is the characterization used by my professor of ethics. I agree that it is a bit of an oversimplification when it comes to the theories of contemporary philosophers, but it’s actually quite accurate when describing the ways in which the theory was applied (by Andrew Carnegie for instance). Remember that social Darwinism is NOT the same as evolutionary ethics. --S.dedalus (talk) 21:08, 25 October 2008 (UTC)

Well, you can keep misusing the term Social Darwinism if you like, but it's not "might makes right", and you can't count on everyone sharing the same misunderstanding of the term that you share with your ethics professor. - Nunh-huh 02:10, 26 October 2008 (UTC)

We have to agree to disagree then. --S.dedalus (talk) 07:30, 26 October 2008 (UTC)

Humans are the only hosts for the adult stage of the worm, at least according to our article and [this] cite. It's kind of the entire point of the eradication campaign and the OP's question. Where did you get your list of "captive dogs, horses, cows, wolves, leopards, monkeys or baboons" from? Matt Deres (talk) 10:47, 24 October 2008 (UTC)

It would seem our article and the cartercenter.org site are definitely wrong, as the medical literature definitely contains case studies of dog dracunculiasis as well as other species which can be affected. [1][2][3][4]. I don't recall the exact source of the list I used, but if you google "Dracunculiasis" with the various species you'll find similar lists, as at [5], [6] The Carter Center could perhaps make its statement true by sticking in a "significant": "Humans are a Guinea worm's only significant host": They seem to have simplified for didactic or polemic reasons. - Nunh-huh 19:04, 24 October 2008 (UTC)

Can we get rid of ticks and mosquitos too? I mean, I know we're supposed to value all species equally.. but I definitely don't! --98.217.8.46 (talk) 15:40, 24 October 2008 (UTC)

I would say that would be nearly impossible, beyond perhaps some sort of super virus or perhaps nanobot, which IMHO would be too risky to try. (Eradicting a parasite which needs a host is a far easier goal) Nil Einne (talk) 15:13, 25 October 2008 (UTC)

Animal search.

Its a very small microbe kind of organism which lives in waters, mainly rain forests. and lighten when any disturbance created in the water they are in. I don't know its name, but it starts with "Noctal---". I would be glad if i could get any article based on this organism. Thanking you.

Dishant Kamble —Preceding unsigned comment added by Dishant kamble (talk • contribs) 04:10, 23 October 2008 (UTC)

Hmm...sounds to me like you're looking for dinoflagellates. They like to collect in calm, warm water, I think bays especially, and glow when disturbed. You may also want to read Bioluminescence. PS: in the future, sign your posts by ending with "~~~~" to generate a signature with a timestamp like this one: --Shaggorama (talk) 07:53, 23 October 2008 (UTC)

the Noctilucales or the species Noctiluca scintillans? They're dinoflagelates. However, they're Noctil- and not Noctal-. --Lenticel ^(talk) 07:58, 23 October 2008 (UTC)

"Universe" clusters; matter/energy beyond our own universe

Since I was a child, I was taught that time started with the Big Bang, and that all existence is contained within this universe. And yet I rarely if ever hear anything about the possibility of matter/energy clusters well outside the range of the localized Big Bang. I am preciously interested in reading about this, yet little to no information appears to be present on Wikipedia or elsewhere on the net.

In case my wording is not clear, let me give another explanation. What exists beyond the current universe? In all likelihood, it is empty space (it clearly was before, or the universe would not have been able to expand). What if there is matter or even other "universes" there, even if really far away? Is there any way whatsoever to detect matter coming from outside, and/or is anyone else theorizing about this? The more I think about the theory, the more likely it seems (i.e., providing explanations of our own universe; perhaps matter did not come from the Big Bang, but the Big Bang sucked in energy until it exploded under its own weight). Magog the Ogre (talk) 08:17, 23 October 2008 (UTC)

See Multiverse. There are lots of theories about other universes in various senses. I don't think any of them allow information to travel from one universe to another, though, since that rather goes against the definition of "universe". The universe is, by definition, everything in some sense. What we often mean when we say "the universe" is "the observable universe" which is everywhere from which light has had time to reach us. Anything outside that can't possibly have had any effect on us (given our understanding of the laws of physics, at least). That means that discussion of other universes isn't really scientific (it's not "falsifiable", it's more in the realms of philosophy. --Tango (talk) 09:35, 23 October 2008 (UTC)

Whether there is anything "beyond the current universe" depends on how you define "beyond", "current" and "universe". Here are a few possible answers:

• There are, almost certainly, regions of space-time that originated in the Big Bang but lie beyond our current observable universe - we might be able to interact with these regions of space-time at some distant point in our future.
• It is fairly likely that there are regions of space-time that originated in the Big Bang but will always lie beyond our observable universe - we will never be ale to interact with these regions of space-time unless we develop some form of faster than light communication.
• It is fairly likely that there is some stuff that originated in the Big Bang, is present all around us, but has no interaction with the rest of the universe apart from a gravitational effect.
• It is possible that there are other dimensions beyond space-time that originated in the Big Bang. Although regions of these other dimensions may be technically within the observable universe, it will probably be very difficult for us to interact in any direct sense with them (otherwise we would have done so before now).
• It is possible (although very speculative) that there are separate quantum timelines that originated in the Big Bang but which we will never be able to interact with because they split off from our current timeline at some point in our joint past.
• It is possible (although very, very speculative) that there are regions of space-time or some different dimensional structure that did not originate in the Big Bang - that may indeed have existed "before" or "outside of" the Big Bang, if such terms can have any possible meaning in an entirely different set of dimensions. It is very, very unlikely that we will ever be able to interact with these separate universes. Gandalf61 (talk) 10:39, 23 October 2008 (UTC)

I just want to note that you've made a critical error in your description of the Big Bang. It did not expand into empty space. The Big Bang was the creation of empty space, along with everything else. It did not expand "into" anything. --98.217.8.46 (talk) 12:28, 23 October 2008 (UTC)

Yeah - it's a very common misconception to think of the big bang as if there was this infinite empty vacuum of space - and a gigantic explosion goes off, spewing matter into that space...we think of it in our mind's eye as if we're a few miles away from the explosion and something goes "bang" like a stick of dynamite going off with bits of matter flying outwards from that point. But that's a totally wrong idea. That's not at all like how it actually happened.

The big bang created the space itself - as well as all of the stuff inside that space. There also isn't a "before" the big bang because it created time as well as space. At the literal beginning of time the universe was a dot - something with zero size - and because time is also crunched up, the idea of time passing is meaningless too. At the instant of creation - that infinitely dense point expands rapidly - time starts running forwards and space gets bigger. It's hard to imagine a nothingness in which there isn't even any vacuum and the concept of distance and time don't exist - but that's what we have to envisage. When the big bang happens, space and time are formed - and rapidly expand - and they are already full of matter. It's not that the matter gets hurled outwards into empty space - it's that space itself expands outwards - remaining full of matter all the time it does that. And it's still happening. When we talk about the universe expanding and all of the galaxies receding from us - we're emphatically NOT saying that the galaxies are moving though space away from us - we're saying that space itself is stretching outwards and carrying the galaxies along with it. It's possible for very distant objects to recede from us at faster than the speed of light - but nothing can travel faster than light...what's going on is that the object is staying pretty much stationary and space itself is stretching away from us at that phenomenal speed. So asking whether there was something else 'outside' of the big bang is meaningless because there was no 'elsewhere' or 'outside' for anything else to exist in.

This is really almost impossible to get your head around - but that's what we're talking about here. I like to think of space as a sheet of graph-paper - printed on an amazingly stretchy rubber sheet. Matter is 'glued' to the graph paper. At the moment of the big bang, all of the matter is there - but the graph paper is squished into a teeny-tiny point. The 'explosion' corresponds to the rubber sheet rapidly stretching outwards - all of the grid lines on the sheet stretch out too and get further and further apart - moving the matter that's glued to it outwards too. The 'speed' of the matter across the grid lines is zero because it's all pretty much glued down - but they still get further apart because the grid itself is stretching. Now - the tricky part is that the universe might actually be infinite...so the sheet of graph paper has an infinite number of lines on it and it's infinitely "large" even at the instant of the big bang when the lines are squashed together until the are all touching each other. So something that is infinite is also zero in size...but since time doesn't exist when that happens - we don't have to think about it. In the first picosecond of time - the zero-yet-infinite sized thing becomes truly infinitely big - but the grid-lines are still insanely close together - the grid lines shoot away from each other as the early universe grows explosively.

The grid lines are still moving apart even now - and science has not yet decided whether they'll continue to move apart - or whether they'll gradually slow down and stop - or eventually reverse and shrink back to a big-crunch - like the big-bang played backwards...the smart money is saying that not only is the 'grid' still expanding - but it's actually expanding faster and faster! SteveBaker (talk) 13:17, 23 October 2008 (UTC)

I wouldn't say the universe "pre-big bang" was infinite and zero sized, it was infinite and infinitely dense. Therefore, any finite amount of matter (for example, the matter which makes up our observable universe today) would be in a zero sized region of it. (This is all very imprecise and involves lots of hand-waving, if you want to do things properly you need to wait until around a Planck time after the big bang, then the laws of physics start making a bit of sense.) --Tango (talk) 17:52, 23 October 2008 (UTC)

I think talking about expanding grid lines can be helpful, but it emphatically IS the same as saying that the galaxies are moving away from us in the usual sense. General relativity doesn't distinguish the two situations. See this old thread. -- BenRG (talk) 17:58, 23 October 2008 (UTC)

There really is no information to be had on this subject, just a lot of speculation. Until we can test the possibilities against each other—which may never happen—the speculation is more science fiction than science. It's entirely possible that the uniform expanding cosmos we see doesn't extend forever, and that beyond it are other regions with very different characteristics. Unfortunately in these models the different regions are causally disconnected, i.e. nothing (moving at the speed of light or less) can get from one to another because they're expanding too fast. In other words, these models all but predict their own untestability. Being untestable is not at all the same as being wrong, but testability is profoundly important. There's a quote on this subject that I like a lot:

"About 500 years ago man's curiosity took a special turn toward detailed experimentation with matter. It was the beginning of science as we know it today. Instead of reaching directly at the whole truth, at an explanation for the entire universe, its creation and present form, science tried to acquire partial truths in small measure, about some definable and reasonably separable groups of phenomena. Science developed only when men began to restrain themselves not to ask general questions, such as: What is matter made of? How was the Universe created? What is the essence of life? They asked limited questions, such as: How does an object fall? How does water flow in a tube? etc. Instead of asking general questions and receiving limited answers, they asked limited questions and found general answers."

— Victor Weisskopf (as quoted in "Nature's Greatest Puzzles" by Chris Quigg, hep-ph/0502070)

That's why, like Peter Woit, I'm more interested in electroweak symmetry breaking than eternal inflation and brane worlds: because there's a real chance that we'll learn something new about electroweak symmetry breaking within my lifetime (in fact, within the next decade, from the LHC). We've gotta stick with questions we know how to answer. -- BenRG (talk) 17:58, 23 October 2008 (UTC)

I find staggering the degree of confidence that comes through in some of this discussion of the big bang, and especially of the conditions prior to it.

For example, "The big bang created the space itself - as well as all of the stuff inside that space. There also isn't a "before" the big bang because it created time as well as space. At the literal beginning of time the universe was a dot - something with zero size - and because time is also crunched up, the idea of time passing is meaningless too. At the instant of creation - that infinitely dense point expands rapidly - time starts running forwards and space gets bigger."

Wanderer57 (talk) 18:50, 23 October 2008 (UTC)

Well, the "According to our current understanding of physics" bit is implied in any such answer. Is that what you mean? --Tango (talk) 19:53, 23 October 2008 (UTC)

It seems to me the certitude with which the statements are made is, shall we say, very bold. I accept the implied qualification "according to our current understanding of physics". However, with our current understanding of physics, we can't accurately predict the weather a month from now. This is not meant to be critical; just to express an element of disbelief. Wanderer57 (talk) 02:11, 24 October 2008 (UTC)

Thank you, Wanderer (no offense, Tango!) - the answer simply failed to understand that I was looking beyond those assumptions. I am operating under the quite possible assumption that space is of indefinite or indiscernibly large size. However, all of the matter in the local universe was in a very small area pre-big bang within this space (as a note, I find explanations that the area was "infinitely small" also to be presumptive, given our lack knowledge of quantum physics).

BenRG: the question is infinitely relevant to me, because it involves the nature of the universe. It may be that observable universe will eventually expand to the point of no return for life (this would be unavoidable under current theories). Would it all be over forever, or might another mass of energy form elsewhere from the remnants of other big bangs, gathering mass until it also explodes.

However, most importantly, I believe that matter/energy from other localized big bangs (or whatever other systems) may indeed be detectable, especially were it approaching us. I doubt any such research has been done; it would be enormously diffucult to establish a way to detect.

But: does anyone know of any literature on this? Magog the Ogre (talk) 04:49, 24 October 2008 (UTC)

I think what you're describing are called "bubble universes" and there has certainly been theoretical research done on them. I don't think there has been any real attempt to detect them since the theory says that's impossible. Remember, matter doesn't move outwards after a big bang, space just expands and the matter goes along for the ride (from the inside, it looks the same, of course), so another universe wouldn't be expanding towards us, it would be expanding within itself and would always be outside our observable universe. --Tango (talk) 09:41, 24 October 2008 (UTC)

No, I am decidedly not talking about those. I am talking about very distant big bang clusters in the same space-time continuum with the same physical constants as our own. If hope if you read my posts carefully, you will see that. Just like another galaxy is relatively far away to our own galaxy, perhaps there are other big bang thingies really far away from our own. Before, the idea that there were other galaxies was completely out of the paradigm of science; now, the idea of multiple big bangs at far distances is outside its paradigm.

And, again, you have given a confident assertion that empty space is tied to the big bang, a completely unproven and frankly presumptuous theory (if you have proof otherwise, I will listen). Magog the Ogre (talk) 03:44, 25 October 2008 (UTC)

In what way would they be a different universe if they are part of the same space-time continuum and have the same physical laws and constants? They're just distant parts of the same universe. That the big bang involves expansion of space and not just matter within space is a critical part of the theory, it doesn't make sense without it (for example, the speed of light limit doesn't apply to the expansion because the matter isn't actually moving, in your version it would apply and the universe wouldn't be able to expand as fast as it has done). --Tango (talk) 13:26, 27 October 2008 (UTC)

diabesity

what is the current status of diabesity in India? —Preceding unsigned comment added by 123.252.166.228 (talk) 11:51, 23 October 2008 (UTC)

Are you asking about "metabolic syndrome"? See this article. Axl ¤ [Talk] 12:38, 23 October 2008 (UTC)

I think the OP may have been referring to diabetes mellitus type 2, along with the related obesity. —Cyclonenim (talk · contribs · email) 17:29, 23 October 2008 (UTC)

Sugar bowl

In a nutshell ... and in lay terms that are not too scientific ... why exactly does sugar "clump" together when in a sugar bowl? And why do you get several little clumps mixed in among some non-clumped sugar? In other words, why does only some of the sugar clump together (while some does not), so that you don't get just one big massive clump? Thanks. (Joseph A. Spadaro (talk) 13:39, 23 October 2008 (UTC))

And, by the way ... is "crystallize" a correct term to describe the above situation? Or is that word inappropriate for some (scientific) reason? Thanks. (Joseph A. Spadaro (talk) 13:49, 23 October 2008 (UTC))

pockets of dampness? 194.221.133.226 (talk) 14:07, 23 October 2008 (UTC)

Yeah, dampness. And no, clumping is not the same as crystallization, though sugar is generally a crystal. — Lomn 16:47, 23 October 2008 (UTC)

I assumed something to do with dampness. What about dampness, though? If you have a sugar bowl in a cupboard, is one section of the cupboard significantly more/less damp than a section of the cupboard that is less than an inch away? A sugar bowl is perhaps 5 inches or so in diameter. In the kitchen cupboard, how much difference can the levels of dampness possibly be within that tiny amount of space contained by the sugar bowl? Thanks. (Joseph A. Spadaro (talk) 17:03, 23 October 2008 (UTC))

I don't know that it has to be significantly more damp; I would expect that simple variation is likely enough to start the process. Once begun, some mechanic (I'd guess something akin to surface tension) causes a preference for more water to accumulate on the clumps. So long as there's a positive feedback mechanic, you don't need much starting moisture, either absolutely or relatively, to get the end result. — Lomn 17:59, 23 October 2008 (UTC)

If you don't disturb the hardening sugar, you will end up with a crust or hardened grains. Putting in the spoon will break up that surface crust into lumps. Graeme Bartlett (talk) 20:38, 23 October 2008 (UTC)

Sugar is incredibly hygroscopic; that is, it attracts water very strongly. This is part of the reason why jams, etc. can preserve without becoming mouldy - no water is left available for the mold to use. In lay terms, the clumping occurs as a result of that hygroscopy as well as the purity of the sugar in your bowl. Unlike most things in your kitchen, sugar is a very pure substance; something like 99.9% sucrose is the estimate I've heard. We don't seem to have an article on it, but some cooking application actually require you to add a different sugar (such as corn syrup), to prevent that clumping. So you've got a material that draws moisture from the air, that bonds easily with water, and that is very pure so that nothing can get in the way of the creation of clumps. Matt Deres (talk) 15:34, 24 October 2008 (UTC)

Wow! That's interesting. I had not realised that lack of available free water was the reason why jam doesn't go bad. However, our OP's question is not so much "Why does it absorb water and stick together?" - it's "Why are there clumps?" - after all, a bowl of uniform, granular, dry sugar seems like it would absorb water evenly throughout the mass and end up with either a crust on the top or as one solid mass. What explains the clumps? It seems like there must be some kind of mechanism that causes sugar that's already glued together a couple of grains to preferentially cause water to be absorbed on the boundaries of the growing clump rather than elsewhere in the still-unclumped bowl. That seems kinda counter-intuitive to me - which is what makes this a difficult question. SteveBaker (talk) 15:45, 24 October 2008 (UTC)

I'm just speculating, but my guess is that it has to do with the way water is attractive to itself. A random molecule of H₂O might be more attracted to an already "damp" bit of sucrose than the surrounding dry sugar. That could create a situation where a bit of sugar that starts to become "damp" would have a tendency to attract more water rather than allowing the water to distribute itself evenly, which would create a crust.

The bit about sugar drying out jam and preserves is true, but not the entire story (which is why I said "partly" :-). A better example would have been for me to say that was true of honey, since it cannot go rancid (millennia-old honey is still "good") and the effect is, so far as I know entirely due to the hygroscopy of the sugar therein. Jams are "preserved" because they're cooked into jars in such a way that there should be no living mold or bacteria inside it; the sugar comes into play after the jar has been opened. When you think about it, jam should be a mold and bacterial heaven - a jellied material filled to the brim with nutrients and sugars. An opened jar of jam kept in the fridge should turn green long before the bread and fruit would, but it doesn't and that (so far as is my understanding) is due to the dryness. Matt Deres (talk) 17:22, 24 October 2008 (UTC)

Thanks for all of the above replies and input ... it was very helpful and informative. Thank you. (Joseph A. Spadaro (talk) 12:52, 25 October 2008 (UTC))

nature

why oxygen is combustible? —Preceding unsigned comment added by 121.247.248.185 (talk) 14:00, 23 October 2008 (UTC)

It isn't. Algebraist 14:07, 23 October 2008 (UTC)

To expand on Algebraist's answer, oxygen itself isn't combustible, only fuels are. However, fuels require oxygen to burn. —Cyclonenim (talk · contribs · email) 16:34, 23 October 2008 (UTC)

And to expand on that, the key oxygen-related processes are redox reactions. Our combustion article may also be of interest. — Lomn 16:43, 23 October 2008 (UTC)

What's going on is that the chemical bonds that hold two oxygen atoms together to make an O₂ molecule and the chemical bonds that hold whatever the fuel molecules start off as - contain more energy than when oxygen is combined in the same molecule as the fuel. So (to pick an easy one) the energy bound up in two H₂ hydrogen molecules plus the energy bound up in an O₂ oxygen molecule is much greater than the energy found in two H₂O molecules. So when you mix hydrogen and oxygen - the molecules try very hard to get into that lower energy state. If you can just supply a tiny spark to get the first few hydrogen and oxygen molucules to rearrange themselves - then the left-over energy when all you have left is water is enough to start more molecules reacting. This kind of chain reaction pumps out massive amounts of 'left over' energy. Oxygen is good at doing this because there is a fair amount of energy bound up in the oxygen molecule - and the nature of the bonds that oxygen can form with other elements means that the reactions generally go rather easily and produce lots of left-over energy. SteveBaker (talk) 00:58, 24 October 2008 (UTC)

what happens if we give AC excitation to alternator

what happens if we give AC excitation to alternator instead of DC excitation ? —Preceding unsigned comment added by Sai krshn (talk • contribs) 15:40, 23 October 2008 (UTC)

The answer might depend on the polarity and phasing of the AC field comparede to the rotor position. Do you mean AC excitation which is not rectified to DC? "AC excitation" in books sometimes refers to rectified AC [7]. Variable frequency AC excitation might be useful for wind or hydro generators [8]. Edison (talk) 03:07, 24 October 2008 (UTC)

Oil Creation

(relating to the earlier question on oil well replenishment)

Not to suggest for an instant that I think this is practical, but suppose hypothetically that we had a system for collecting "dead algae" from the present oceans, as well as a quick process for converting it to oil.

How much oil could be produced per annum, just based on the amount of raw material that is created per year? Wanderer57 (talk) 17:17, 23 October 2008 (UTC)

If we removed all the dead algae we would probably destroy the ecosystem. We could only take the dead algae that reached the bottom of the ocean and wasn't going to be eaten by anything, and that's going to be a very small amount over short time spans. --Tango (talk) 17:32, 23 October 2008 (UTC)

If one assumes that you only remove organics that would otherwise be stored in rock, and avoid more aggressive action at the risk of damaging the ecosystem, then you would be limited annually to about 1/500th the amount of carbon humans release through fossil fuel burning. Dragons flight (talk) 19:06, 23 October 2008 (UTC)

It's not exactly a silly idea. There are companies out there looking to farm algae on industrial scales (see Algae fuel). There are certainly ways for us to turn almost any plant material (algae are plants) into biodiesel or ethanol that could be used in place of oil in many applications. What they are doing is effectively using the plants as little machines to capture sunlight and turn it into carbohydrates - and from carbohydrates to hydrocarbons is not such a huge step. So farming algae as a means to trap sunlight and turn it into fuel is not so silly. However, digging up algal deposits from the ocean bottoms isn't going to be particularly effective. Remember - the process I described in mind-numbing detail earlier today is all about concentrating the oil from large areas of ocean bottom - over millions of years - into convenient puddles. The actual oil formation step is not conceptually very difficult. You might have to dredge thousands of square miles of ocean bottom (with the obvious horrific environmental consequences) just to make a relatively small amount of oil - and once you've done that - it's going to take a long time to replenish.

What makes oil so potent and useful as a fuel is that it's the result of a LOT of sunlight being absorbed by a HELL OF A LOT of algae - and then squished down to a tiny fraction of it's original volume by all that pressure. Oil is (in effect) highly concentrated sunlight (it's the same with coal and natural gas). But to concentrate it to that degree - you have to start off with an insane amount of the stuff. The oil we have burned in just a couple of hundred years is all of the oil formed by all of the ocean bottoms over millions of years. There just isn't that much naturally occurring algae out there.

SteveBaker (talk) 00:51, 24 October 2008 (UTC)

Confusion with organoselenium compound toxicity

It was my understanding that it is the electrons in an atom which account for its chemical properties. In this case, selenium should interact very similarly to oxygen, which is does by forming C-Se organoselenium bonds in compounds such as selenols (alcohols with SeH functional groups rather than OH). Why would the equivelent of usually non-toxic alcohols, but where the OH is replaced with SeH, be toxic if chemically these compounds should act the same? I hope this makes sense. Thanks.

—Cyclonenim (talk · contribs · email) 17:34, 23 October 2008 (UTC)

Life is very finely balanced, even the slightest change can make a big difference. Alcohols are toxic, we just have enzymes that can deal with them (in small quantities). Those same enzymes, which are highly optimised, aren't going to work as well (if at all) for selenols, so they have a greater effect. There's probably nothing stopping there being enzymes to deal with selenols, but the fact that we very rarely ingest them means there has been no evolutionary pressure to create them. --Tango (talk) 17:48, 23 October 2008 (UTC)

(ec) Careful: "similar" is not the same as "same". It's only similar, and electrons only account for some properties. "The s and p valence electrons" might look similar for Se vs O, but they are further from the nucleus and there are lots of other electronic differences. There's a whole paragraph in the organoselenium chemistry introduction talking about patterns of differences within that column on the periodic table. Bond strengths are different, so anything that relies on the C-(Se/O) bond breaking or (not-breaking) during a reaction is susceptible to that difference. The atoms are different sizes and have different covalent radii (related to bond-length to C), so anything that relies on the part of a molecule having a certain physical shape or atomic position may be affected. The two elements have different electronegativities (stability regarding charge), so anything that relies on the ionic form having a certain reactivity may be affected. The atoms have different masses, so anything that relies on the atoms moving may be affected (although it's only a slight difference here). DMacks (talk) 17:54, 23 October 2008 (UTC)

Thanks, that pretty much solves my query :) —Cyclonenim (talk · contribs · email) 19:11, 23 October 2008 (UTC)

Question involving special relativity

Hi! If I sent a friend at a little more than half the speed of light and I ,myself, went in the opposite direction at the same speed, and looked back, what would I see? How much heavier will the friend seem?? —Preceding unsigned comment added by 116.68.77.65 (talk) 17:56, 23 October 2008 (UTC)

You would see your friend redshifted by a factor of ${\tfrac {1+(v/c)}{1-(v/c)}}$, where $v/c$ is your speed as a fraction of $c$ (i.e. a little over 1/2). There's no natural answer to the "how much heavier" question, since your friend is far away and getting farther all the time; you can't put him/her on a scale. You'd have to carefully define what you mean by "weight" before this question could be answered. I think you're thinking that the two speeds of a little over $c/2$ would "add up" to a speed of a little over $c$, but it doesn't work that way. You're both traveling at a little over $c/2$ with respect to the reference frame you chose when you specified the speeds. With respect to a reference frame moving with one of you, the other is moving at a little over $4c/5$. -- BenRG (talk) 18:03, 23 October 2008 (UTC)

There is an important thing here. Your friend is moving at half the speed of light away from the starting point - and you are moving the other way at half the speed of light...BUT...that nice Mr Einstein pointed out that you cannot move away from your friend (not he from you) at the speed of light. That's not allowed because (a) all motion is relative so the starting point isn't in any way special and (b) you can't move faster (or even as fast) as light. So the odd things you're suspecting you might see because the light from him to you can't catch you up won't possibly happen and (aside from some time/space/mass distortions due to your high speeds) - nothing particularly odd happens. There would be some significant red-shift in the light coming from your buddy. SteveBaker (talk) 00:37, 24 October 2008 (UTC)

Physics Exhibition

Please suggest me a working model for Physics Exhibition in my schhol of class XIth standard. —Preceding unsigned comment added by 117.199.176.59 (talk) 19:02, 23 October 2008 (UTC)

What areas of physics interest you? It's a very broad subject. --Tango (talk) 19:54, 23 October 2008 (UTC)

Perhaps you could do something with polarized light. a piece of stressed transparent plastic between crossed polarizing filters looks great. Or perhaps you could make something to measure the speed of light, or speed of transmission down a cable. For this have an oscillator that sends a pulse down a "long" cable and then regenerates it and sends it again. Then you can have a counter to measure the frequency. Graeme Bartlett (talk) 23:14, 23 October 2008 (UTC)

My son made a Lego machine that counts the number of licks it takes to get to the center of a tootsie-pop (the company advertising always used to say that "nobody will ever know" because people have to crunch through the coating to get to the center before they've licked it enough. So he built a totally dispassionate robot that would lick the pops and be totally incapable of crunching them! Silly though this sounds - it was very successful. He came first out of a couple of hundred projects in his school - got a special award from the science staff (who said it was the best science fair project they'd ever seen!) and it got him a plaque from the company that makes tootsie-pops after someone wrote to them to tell them what the answer was. Photos of the "lick-o-matic" can be found here. The answer (my son claims) is (on average) 332 licks - with a surprisingly narrow standard deviation. But I think we'd be hard-pressed to justify that claim in terms of human licking! He did a fairly detailed analysis of the statistics of his results - comparing different flavors of pop and different brands. Interestingly, there was a very solid statistical difference between tootsie pops of different flavors - cherry and orange tootsie pops stood up to a lot more licking than grape or chocolate.

Another project that my kid got awards for was a study of which brands of paper kitchen wipes were strongest when wet and when dry. He used a long vertical plastic tube with holes cut into the side every 5cm and dropped a ball bearing through each hole in turn (starting at the lowest) until it could tear through a single sheet of the test material (which was held across the bottom of the tube with an elastic band). He tested a dozen brands - ten tests each both wet and dry - and also tested some other kinds of paper product for comparison purposes. Interestingly - his conclusion was that in almost every case "you get what you pay for" and the cost of the paper (per sheet) was almost exactly proportional to it's strength in terms of the kinetic energy of a ball bearing that could just tear through the sheet. At the actual science fair, he used the same apparatus to measure toilet tissue in a 'live' demonstration of his technique. He got awards for that one too.

The message is that you can do well with an amazingly silly or highly trivial topic - if you do the science properly. That means using proper controls (where appropriate), double-blind testing if humans are involved - analysing the results from a reasonable number of trials, showing your data, relating your results to other researchers, stating a clear conclusion...all of those good things are what you score points on...not on the 'gravitas' or 'appropriateness' of your subject.

SteveBaker (talk) 00:23, 24 October 2008 (UTC)

That that lego lollipop licker is impressive. From your description I had assumed he used Mindstorms. He took no such new-fangled short-cuts. I am impressed. APL (talk) 01:01, 24 October 2008 (UTC)

Yeah - we have a couple of LEGO Mindstorms sets and it would have been a lot easier to count the revolutions of the 'licker' using the RCX computer and a rotation sensor. But because the machine was going to be on show, and needed to be visually attractive - Oliver decided to build the gearing stages to make a device like a car odometer to do the lick counting. Lego gears come in 40, 20, 16 and 8 tooth varieties so it wasn't too tough to get the 10:1 gearing you need to build an odometer-style counter.

Another hard part was finding the right amount of water to get into the sponge 'tongue' so that it would slide over the surface without sticking to it if everything dried out - and yet wouldn't splatter water everywhere as it whirred around. The level of the water in the plastic container is very critical to operations - and because it gets kinda sugary after licking through half a dozen tootsie pops - the water had to be replaced and carefully filled to the right level after every few runs. The machine does about two licks per second - so it takes about two minutes to get to the oh-so-delicious center of the tootsie-pop - which is just about right as a crowd-pleaser. In the end we used that dense black electrically-conductive foam because it seemed to best match the rate of 'erosion' that we were getting by licking the tootsie-pops the old-fashioned way...but that's definitely the weak spot in the experiment.

I was helping him with one part of the design because he originally wanted to automatically detect when we got to the center of the tootsie-pop - perhaps by drilling a hole through to the center from the opposite side of the 'pop and pushing the drill-bit through the soft center until it hit the underside of the hard candy shell. The idea was that we should be able to measure the electrical conductivity between the tongue and the metal rod and see a voltage spike at the same point in every revolution when we got to the soft center - but with water everywhere and the foam tongue not being as conductive as we thought - we never did get that part to work reliably - and on the night before the presentation, we yanked that part of the gizmo and ran without it. So in the end, we just stopped the machine manually when we could see the soft-center showing through. Fortunately, nobody seemed to mind!

SteveBaker (talk) 05:27, 24 October 2008 (UTC)

While not for a science fair and not physics, you may be interested in [9] & [10] Nil Einne (talk) 15:38, 27 October 2008 (UTC)

• Wow, that is some impressive science. :) I have no doubt your son will become a great scientist if he wants to (and probably a good wikipedian too). - 131.211.211.25 (talk) 07:18, 24 October 2008 (UTC)

Pulsejet afterburner?

Could you put an afterburner on a pulsejet if the injectors were timed perfectly? Would it work or does it only work on other types of jet? Thanks. 92.5.107.9 (talk) 20:44, 23 October 2008 (UTC)

Perhaps. The afterburner's job is to burn up any unburned fuel or carbon monoxide in the outflow from the main engine. Doubtless pulsejets leave just as much unburned fuel and CO as conventional jets - so presumably more energy could yet be extracted. However, the mechanisms that make these wierd machines operate make unusual demands on the shape of various chambers in the engine and it may well be that obstructing the outgoing jet would somehow stop them from working. SteveBaker (talk) 00:11, 24 October 2008 (UTC)

Thanks, but the afterburner doesn't just burn up unburnt fuel but it injects fuel in the exhaust flow which then gets ignited, so you could put the injectors in the exhaust section. Would that work? 92.0.49.113 (talk) 00:25, 24 October 2008 (UTC)

Indeed according to the article the efficiency is reduced because your adding more fuel but there is already not much oxygen Nil Einne (talk) 15:43, 27 October 2008 (UTC)

Unknown firstborn vaccination

While on my trip to Brazil I noticed that most native Brazilians have a small circular scar on one of their upper arms. I havent seen anyone with this type of scar in the US, where I live. I presume this scar is from a vaccination taken as an infant, and seeing as Brazil is a third world country with many endemic diseases the US has long eradicated, I wonder if this is a vaccination for some kind of tropical disease or a disease that hasnt been eradicated yet. —Preceding unsigned comment added by 189.58.26.29 (talk) 21:01, 23 October 2008 (UTC)

Lots of people in the UK have a very similar scar from the BCG vaccination against Tuberculosis. --Tango (talk) 21:09, 23 October 2008 (UTC)

Probably a Smallpox vaccine scar. You see them in the USA too. Mostly in people over 40. APL (talk) 21:10, 23 October 2008 (UTC)

I live in the UK and my dad has that scar, I think from the BCG. I have had all the vaccines I need to have (that includes the BCG), but I don't have that scar and nor does any other young person I know. I hated the BCG though, 9 injections in one go - torture.

Also, I didn't have it as an infant, I had it in school at twelve or thirteen and so did all the other people in school. Or maybe I did have it as an infant and the one I had in school was a top-up vaccination...I dunno. 92.5.107.9 (talk) 21:50, 23 October 2008 (UTC)

In the US, vaccinations for smallpox and tuberculosis have not been routinely given for thirty years or so. In the case of smallpox this led to a number of concerns, a couple years back, that the US would be particularly susceptible to bioterrorist attacks from smallpox. --98.217.8.46 (talk) 22:12, 23 October 2008 (UTC)

Here's a nice PowerPoint file showing how to tell a BCG scar from a smallpox vaccine scar: [[11]] --Scray (talk) 01:31, 24 October 2008 (UTC)

Data point: I was born in Brazil in the 1970s, and have a BCG scar as shown in those slides, but on my right arm, while they say it's usually on the left. --Sean 15:11, 24 October 2008 (UTC)

I once noticed a model from the UK on a non-nude porn site I used to go to had a scar on her arm and I wondered why she had a smallpox vaccination but she was so young. —Preceding unsigned comment added by 63.245.144.77 (talk) 07:17, 24 October 2008 (UTC)

The BCG is a single injection. The "nine injections in one go" are probably the Heaf test: six needles at once. The Heaf test is now obsolete in the UK. Axl ¤ [Talk] 16:58, 24 October 2008 (UTC)

I had the Heaf test (probably one of the last that did) and it's not very unpleasant at all. It's about the same as the finger prick tests they do for blood sugar or iron levels, just 6 of them. However, I was Grade II, so didn't have the BCG. According to friends that did have it, that wasn't pleasant at all. While it's one needle, it's one pretty big needle. --Tango (talk) 17:07, 24 October 2008 (UTC)

I can't remember the needle but the swelling post injection is rather painful and it takes quite a while to go down (depending on the person). Incidentally, in some countries (including Malaysia) the BCG is given more then once (usually at birthas a baby and ~12 years old) so is more then one injection (albeit not at the same time). And AFAIK, the BCG in Malaysia is usually given to the left arm Nil Einne (talk) 15:06, 25 October 2008 (UTC)

Burj Dubai

How deep do the foundations need to be for the Burj Dubai? Thanks 92.5.107.9 (talk) 21:45, 23 October 2008 (UTC)

Burj Dubai#Construction says there are piles buried more than 50m. --Tango (talk) 22:29, 23 October 2008 (UTC)

Thanks, I must have missed that. 92.5.107.9 (talk) 22:39, 23 October 2008 (UTC)

Lactose Intolerance

Why does consuming lactose if lactose intolerant result in diarrhoea ? —Preceding unsigned comment added by 80.5.198.130 (talk) 21:56, 23 October 2008 (UTC)

See lactose intolerance. Basically, since a lactose intolerant can't process lactose, any lactose consumed will reach the large intestine intact. When it does, the bacteria that reside there go on a feeding frenzy and their waste products prove very unpleasant for the host. Someguy1221 (talk) 22:04, 23 October 2008 (UTC)

The fascinating thing about lactose intolerance is that it's not some kind of unfortunate mutation or disease. Almost all mammals are lactose intolerant. Animals who drink their mother's milk when they are babies have to be weaned off onto regular food at some point. Most mammals (and also humans) have evolved to lose the ability to digest milk once they get past the age when they should be on solid food. This makes the process of weaning off of the mother's milk happen automatically when the young animal gradually finds that milk makes them feel sick. This is a good thing for most mammals because it means that the next set of babies don't have to fight with older siblings for their share of the mother's milk supply - and the mother doesn't have to eat as much to keep the supply going. For non-human mammals, there is no down-side to this because once they are weaned, they have no way to get milk products anyway. Humans are the sole exception - and it seems that even we have been 'naturally' lactose intolerant and we are literally in the process of evolving the ability to continue to digest milk into adulthood. But humanity hasn't finished that evolutionary step yet - so some of us have a specific gene mutation on chromosome 2 that prevents the "normal" shutting down of the lactose-digestion pathways when we are a couple of years old - and that allows those freakishly lactose-tolerant mutants to pull off this highly unusual trick! Meanwhile the 'normal', un-mutated humans can't cope with milk products once they are more than a few years old.

Since this evolutionary change can only possibly have started when we first started farming and domesticating other mammals - perhaps as little as 10,000 years ago - this is an interesting take on how fast evolution can operate. The ability to consume the milk of other animals into adulthood has probably been only a fairly small benefit - and in more civilised countries where there are plenty of alternatives to milk products, the evolutionary advantage must be close to zero - so humans will probably end up only patchily lactose tolerant off into the indefinite future. Those societies that have been domesticating cattle for the longest time (basically, Europeans) are the most lactose tolerant - those that never did get around to doing that are still mostly lacking this handy little mutation.

According to our article on lactose intolerance the problems for intolerant adults arise because the bacteria that naturally live in our gut take advantage of all of this undigested food passing into the intestines - and they go into overdrive. That causes much gas production. Gas in the intestine prevents it from working efficiently - so water is not absorbed well and the excess liquid winds up in the fecal material along with the gas. This easily explains the symptoms of bloating, flatulence and runny poop.

Fortunately - I'm one of the freakish mutants - which really makes me fancy a piece of ripe brie right now. Thank god for that little 'oopsie' on chromosome 2! SteveBaker (talk) 23:57, 23 October 2008 (UTC)

Would the genetic mutation be the only reason why some people can eat dairy or is there also an environmental effect. If you ate dairy products regularly, would there be no sign of lactose intolerance even though the child does not carry the mutation? As a "weaned" (as in old enough to eat normal food) Chinese person, I can still drink milk with no ill effects (although I can't say that about my parents). 96.242.34.226 (talk) 01:19, 24 October 2008 (UTC)

Steve, I'm pretty sure that lactose-intolerant people can eat brie, too. It's a low-lactose cheese. --Scray (talk) 01:27, 24 October 2008 (UTC)

The Lactose intolerant page has an error I think, the table has messed up data, correct me if I'm wrong. What happened there? 96.242.34.226 (talk) 01:44, 24 October 2008 (UTC)

To ansawer 96.242.34.226, whilst there are genetic differences (hence more of problem in Far East and less in Europe), can also be acquired due to bowel inflammation affecting lactase production: temporarily after childhood episodes of gastroenteristis is common (may last upto 12 weeks), and sometimes perminantly so (especially after a bout of giardiasis). David Ruben ^Talk 01:59, 24 October 2008 (UTC)

Sure - there are diseases that make even tiny babies (who should NOT be lactose intolerant through genetics) incapable of digesting milk...which (since that's all they eat) is a pretty serious matter. But the vast majority of people who are lactose intolerant are 100% "normal" - and those of use who have lactose tolerance even into adulthood are mutants. (It's less exciting than on X-men...trust me!) SteveBaker (talk) 05:01, 24 October 2008 (UTC)

According to this source (and many others), for example, over 90% of Asian-Americans are lactose-intolerant. ~AH1^(TCU) 13:17, 24 October 2008 (UTC)

But can you be lactose tolerant without the mutation? Which was what I was saying before. 96.242.34.226 (talk) 00:28, 25 October 2008 (UTC)

I don't see how. If you have lactose-intolerant genetics, you simply don't have the mechanism to make the lactose-digesting enzymes. It's hard to imagine any kind of disease that would somehow restore that ability. SteveBaker (talk) 22:14, 25 October 2008 (UTC)

Apologies if this is too repetitive of SteveBaker's points, but I don't see it put quite this way on a cursory glance above. In most cases of what people call "lactose intolerance", the genetics is as follows: "Normal" humans are born with the ability to digest lactose: that is, they produce lactase in amounts adequate for digestion throughout their childhood. But they also normally lose that ability when they mature. It's people who have persistence of lactose tolerance into adulthood who have a mutation, located on chromosome 21, that causes lactase persistence. "Lactase persistence is a heritable autosomal dominant condition that results in a sustained ability to digest the milk sugar lactose throughout adulthood." - Nunh-huh 00:35, 26 October 2008 (UTC)

I thought I'd already posted this but must have previewed or something. Anyway I believe people who regularly consume milk (well lactose), particularly those who consume it from childhood and don't stop tend to have a higher tolerance for lactose (in other words they can drink a great amount without symptoms) even if they lack the lactase persistence mutation. I suspect they'd still usually be called lactose intolerant however. This isn't that surprising since as mentioned by Nunh-huh, humans do have the ability to digest lactose, they just lose it over childhood. Most of our regulatory and development systems are quite complex so it's not unlikely there will be some feedback mechanism that comes in from the continual consumption of lactose. This is partially supported in our article which says "Some cultures, such as that of Japan, where dairy consumption has been on the increase, demonstrate a lower prevalence of lactose intolerance in spite of a genetic predisposition" (well okay this supports the idea that people who are genetically lactose intolerant can in fact be lactose tolerant but it suggests to me there is resonable chance what I'm suggesting is true). It also describes how lactose intolerance arises. It's not a simple process and in some people it develops over many years. And the levels of lactose intolerance in a population increases with age. Nil Einne (talk) 13:40, 27 October 2008 (UTC)

Trees in Mongolia

Why do trees only grow on the north side of mountains in Mongolia?70.88.40.1 (talk) 23:40, 23 October 2008 (UTC)

What makes you think that's true? I just surfed over to Google maps - and typed in Ulaanbaatar - and it looks to me like there are trees on the southern slopes too. But if it is true (and to the extent that it's true) - I would imagine it's because the northern slopes are retaining rainwater better because they get a little less sunlight and any wind blowing onto them would have to come from the North - where it's presumably cooler. It's also possible that winds blowing from the North carry lots of water which is dumped onto the hillsides as the air is forced upward into the cooler altitudes...where the wind from the south comes over the desert steppes and therefore contains no water to dump onto the southern slopes. Most of Mongolia is pretty arid (think "The Gobi Desert"!) - and on a steep mountainside - what little rain does fall would run downhill pretty fast...so avoiding evaporation would be a good thing. This is just an educated guess though - I don't know for sure. SteveBaker (talk) 00:07, 24 October 2008 (UTC)