Wikipedia:Reference desk/Archives/Science/2008 December 9

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December 9[edit]

Coconut water as an IV[edit]

While perusing of our coconut article, I noticed that it said that coconut water can be used as an intravenous fluid. I'm a little curious about it. Would it be used to help dehydration, or what? bibliomaniac15 00:55, 9 December 2008 (UTC)

It would never be used IV: if you were on a island where you had nothing else to use, you wouldn't have IV tubing and an intravenous catheter; and any place that has IV tubing and an intravenous catheter would have a bag of saline, too. That said, coconut water is hyperosmolar/hypertonic: it is about 500 mOsmol/L in contrast with blood, which is about 290 mOsmol/L. So if infused, the effect would be to increase serum osmolality, resulting in retention of fluid. Since the statement in the article is unsupported by any citation, it needs to go. The one with the citation can stay :) - Nunh-huh 01:08, 9 December 2008 (UTC)
It can be, and has been, used as IV fluid, here is a link to an article discussing it. [1]. DuncanHill (talk) 01:12, 9 December 2008 (UTC)
And here's another [2]. DuncanHill (talk) 01:13, 9 December 2008 (UTC)
And a third [3]. DuncanHill (talk) 01:16, 9 December 2008 (UTC)
And another, [4]. DuncanHill (talk) 01:19, 9 December 2008 (UTC)
Still they keep coming [5]. DuncanHill (talk) 01:20, 9 December 2008 (UTC)
The fact that every time some clown uses it someone writes an article about it is actually pretty good evidence that it's not used except under extraordinary circumstances. - Nunh-huh 02:37, 9 December 2008 (UTC)

(outdent) I think it would be better to drink instead.--Lenticel (talk) 04:32, 9 December 2008 (UTC)

Extracting oxygen from ferrous oxide (FeO)[edit]

Could you? What resource would it drain? Does FeO actually contain O or is such a compound changed for ever? And why, if the moon has as much of this red stuff as mars... is it black and not red? ~ R.T.G 02:35, 9 December 2008 (UTC)

FeO (or iron(II) oxide) does indeed contain oxygen. It is actually a black solid, which would help explain the colour difference. DuncanHill (talk) 02:40, 9 December 2008 (UTC)
But FeO is rust right? And iron is definitely red unless you melt it... ? I thought it was iron that made Mars red and blood red, is ferrite not iron? Whats the difference? ~ R.T.G 02:51, 9 December 2008 (UTC)
FeO is only one form of rust. Iron(III) oxide is the common red rust that you were thinking of. (talk) 03:33, 9 December 2008 (UTC)
The article on Mars surface color is a good place to start. You should read it and follow at least some of the links. Please ask if anything is still unclear. Now, regarding the extraction of oxygen on Mars: as far as I can recall, most projects involved extracting oxygen from CO2 in the Martian atmosphere rather than from iron oxides on the Martian surface; see Mars Surveyor 2001 Lander for example. Extracting oxygen from iron oxides is possible, of course; but probably not as convenient or not as economic. You can do a little research here - this is a good topic for a project. BTW, it is possible to extract oxygen from Al2O3, too. The "by-products" (carbon, iron, or aluminum, respectively) are likely to be of considerable use, as well, so you should take that into account. --Dr Dima (talk) 04:02, 9 December 2008 (UTC)
Another article you should read is In-situ resource utilization. Enjoy, --Dr Dima (talk) 04:18, 9 December 2008 (UTC)
Its a lot easier, in general, to extract the metal from metal oxides (basically by transfering the "oxide" part to another substance, and leaving behind the metal) than it is to extract the "oxide" as oxygen. The reduction potential of the O2 + 4e1- --> 2O2- half-reaction is quite high; to actually oxidize O2- you'd need a rediculously strong oxidizing agent, or to do it electrolyticly you'd need a rediculously huge amount of current. Neither is a particularly economical means of producing oxygen. Free oxygen is such a hard thing to produce, it required a massively complex and convoluted chemical system (photosynthesis) to actually make it on Earth. If we are going to produce free oxygen in situ on another planet we colonize, then its going to come from a biological source rather than from an industrial/chemical one. 04:27, 9 December 2008 (UTC)
It is true that energy demands of restoring a metal oxide to metal and oxygen are relatively high. However, electric energy is pretty much the only thing that will not be lacking on the early stages of Mars or Moon exploration. Bringing and deploying solar panels is very much easier than bringing and sustaining, say, water-tanks with algae. Solar panels have 20-30% efficiency vs 5-6% for photosynthesis, and the working temperature range for the solar panels is much broader. This is of crucial importance on both Moon and Mars, where temeprature changes between day and night are quite extreme. So, on earlier stages of Moon & Mars exploration, the direct electro-thermal process seems the way to go. On the more advanced stages of exploration / colonization / terraforming, the photosynthesis will produce al least some of the breathing oxygen and food for the humans. --Dr Dima (talk) 05:47, 9 December 2008 (UTC)
Agreed. Even though producing industrial amounts of free oxygen on a foreign, uninhabitable planet will probably never be an easy feat, using biological means would probably be even more difficult than using electrical means. Of the photosynthesising organisms we know today, I doubt even one species would survive on Mars for a fair amount of time, let alone being able to produce reasonable quantities of oxygen. Genetic engineering is always an option, of course, but I'm going to go on a limb and say it's probably easier and more economically viable to create a durable, properly catalysed electrochemical oxygen generator than it is to genetically engineer an extremely hardy and efficient photoautotroph. What's more is that using the biological way, a steady and reliable source of liquid water is pretty much a necessity for the organism to even do anything other than just sit there as a planetary ornament. --Link (tcm) 06:12, 9 December 2008 (UTC)
Water tanks and algae may be unworkable, but there may be a promising future in certain forms of archaebacteria and other extremophile life forms which may prove to be useful in this endeavour, especially with a little genetic engineering thrown in. We may find that engineering some little archeon with the ability to extract oxygen from oxides is easier even still than dragging around solar panels. The ability of a wide-range of enzymes and other biological process to turn otherwise impossible or improbable chemical processes into workable systems is mind boggling, and it may simple require putting together the right biological system to make it feasible. 06:02, 9 December 2008 (UTC)
Back to the original question, is there a solvent that can dissolve FeO, and when electrolyzed produces oxygen and Iron metal (rather than hydrogen)? Graeme Bartlett (talk) 10:43, 9 December 2008 (UTC)
And with Graeme Bartletts question, what amount of solvents would current technology want for creating plant supporting atmosphere on the moon including ozone and other nessecary stuff? Would it all float away before it was useful? ~ R.T.G 13:08, 9 December 2008 (UTC)
Iron oxides dissolve in phosphoric acid, see this patent, for example. I never heard of electrolytic extraction of iron, though. Iron is usually produced from oxide in presence of carbon or carbon monoxide in a blast furnace, see Iron#Production of iron from iron ore. I'd venture guessing that the process to be employed on Mars - if iron oxides are to be the source of oxygen there ar all - would be some modification of an induction furnace or an electric arc furnace that would thermally dissociate iron oxides into iron and oxygen. At near-zero pressure the dissociation will go more readily, and there are no consumable chemicals to be brought from Earth - a definite advantage over a chemical process. Regarding your second question (the one about retaining an atmosphere) - Mars has been losing its atmosphere over a few billion years now, and there is still some left; so if humans generate a new Martian atmosphere it will not "float away" any time soon :) . Moon has lower gravity than Mars, though, and is closer to the Sun; and Earth with its magnetosphere does not help either. So I don't know how long a lunar atmosphere may persist once generated. --Dr Dima (talk) 17:46, 9 December 2008 (UTC)

Time Travel[edit]

One idea about time travel is that when you exceed the speed of light, everything, relative you you, is going backwards. This will have zero scientific meaning because, as the nice old man with the funny hair tells us, you can't make matter go faster than the speed of light. Even if you are going fast enough to see light stop in its tracks, wouldn't the matter that it's coming from continue to move? You can't measure speed without comparing it to a unit of time, 100 km/hr, 40 ft/second, 3 light-years/minute, so would you bump into the still moving objects because all you would see is the light from 2 min in the past or an hour in the past. If we were an x-ray, which i believe goes faster than the speed of light, would you see the light hitting and bouncing off matter? Say you continue to go the speed of light, which would hurt when, relative you you, air molecules run though you like bullets, could you go to the Sun, and just go through it without getting hurt? Infrared is lower than light so could you run though it like your hand over a candle? Weird stuff, but I think it's interesting. -- (talk) 03:20, 9 December 2008 (UTC)

X-rays don't go "faster than the speed of light". -hydnjo talk 03:32, 9 December 2008 (UTC)
First see speed of light. Many of your assumptions about the speed of electromagnetic waves are simply wrong. -- kainaw 03:33, 9 December 2008 (UTC)
Sorry - all of your basic premises are incorrect - so your conclusions don't work.
  • In your first sentence: This idea that something unknown and interesting happens when you exceed the speed of light completely neglects the indisputable fact that you can't do that. If you plug speeds greater than lightspeed into the equations relating to time, length and mass, they end up producing something like the square root of -1. The square root of -1 is not -1 (which is what you imply by suggesting that time would go backwards)...go ahead and type -1 into your pocket calculator and push the square root button. What you get is "Error". The square root of -1 is not a number that can express a real world property of mass, distance or time. This makes it impossible to ever go faster than ligh - not just some kind of interesting unknown thing...IMPOSSIBLE. That impossibility means that we can't use math or science to speculate on what would happened if you somehow magically did do that. The impossibility lies at the heart of the very mathematics we use here.
  • In your second sentence: Einstein didn't just say you can't go faster than light - he actually said that you can't go as fast as light. So your idea of stopping light in it's tracks by moving alongside it at the same speed would be impossible even in a non-relativistic world. But the distinguishing thing (the utterly WEIRD thing) about light is that it's speed is always the same relative to you no matter how fast you're moving. So even if you are moving away from the Sun at 99.9999999% of the speed of light - if you try to measure the speed of that ray of sunshine, you'll find that it's STILL moving past you at the speed of light...not only does it not stop - it doesn't even slow down to the slightest degree! This is a deeply weird thing - but we've proven it to be true in numerous highly convincing experiments.
  • In your third sentence: You claim that one cannot measure speed without reference to time. In truth - the universe seems to be entirely dominated by this lightspeed thing - and it's arguably the case that we should treat speed and distance as fundamental things and make time be derived from speed and distance. In such a situation, you would indeed measure your speed (as a fraction of lightspeed) without reference to time.
From this point on, your statements pile incorrectness on incorrectness to the point where it's hard to comment on them. But as others have pointed out - infrared light isn't slower than visible light - along with ultraviolet light, radio, microwaves - they all move at exactly the speed of light.
The one thing you that you say which is SO that this stuff is weird but interesting. But you need a better grasp on the underlying science...once you do, things are much weirder than you can possibly imagine.
SteveBaker (talk) 04:09, 9 December 2008 (UTC)
Furthermore, by combining the second law of thermodynamics with the law of special relativity as described by SteveBaker above, you could contruct a completely coherant and consistant system of mechanics and motion with no mention of time at all. By the second law of thermodynamics, the entropy of the universe increases continuously. Thus, if we take the idea of "absolute time" to mean the 0 point is the Big Bang and the end-point of time to be the heat death of the universe; then we could just as well look at the Big Bang as a perfectly ordered universe (0% entropy) and the end of the universe as 100% entropy, and you could deal with temporal measurements merely by saying "event A happened when the universe was at entropy = 50%" and "event B happened when the universe was at entropy = 50.1%" you would have an unambiguous means to order event A and B without resorting to any measurements of time at all. Time is a mathematical convenience we use more easily express the ordering of events, but its not a real physical "quantity" the way that mass and distance and speed are. 04:44, 9 December 2008 (UTC)
Well, I give the OP credit for some original thinking. Perhaps what he says is true in a parallel universe which has its own physics and natural laws. As Shakespeare wrote, "There are more things in heaven and earth than are dreamed of in your philosophy". Even in this universe we may be looking at things in a way that distorts reality, yet which is "proven" by mathematics and physics. Einstein himself showed that the Newtonian way of looking at reality was wrong, even though it was supported by mathematics and physics. Perhaps Einstein, in his turn, will be proven wrong. Conventional wisdom sometimes turns out to be conventional foolishness. Great ideas sometims start as heresy. —Preceding unsigned comment added by (talk) 06:15, 9 December 2008 (UTC)
This demands a little correction. Einstein didn't prove Newton wrong precisely. He amended Newton's laws to account for the strange things that happen close to the speed of light. Newton's laws are stunningly accurate for all 'reasonable' speeds - and over the entire range of conditions for which they had ever previously been tested. Einstein didn't formulate his equations in order to explain some horrible experimental discrepancy that had been found - he was seeking an explanation for the absolute nature of the speed of light and deduced by pure reasoning that this correction to Newton's laws were therefore required. Remember it was only YEARS later when super-careful solar eclipse experiments had been performed specifically to test relativity that we finally had any kind of experimental evidence for the error in Newton's laws. Any amendment to Einsteins laws would have to apply in situations that are stranger still - which have yet somehow evaded our ability to test them. It would also require some kind of new discovery about the nature of the universe - something as stunningly weird as the absolute nature of the speed of light. But since we've tested these laws at all sorts of extremes - and they seem to work just fine - the number of places where a 'correction' to Einstein could possibly be hiding are rapidly vanishing. Certainly any new 'Hawkins law of refined relativity' (or whatever) would have to show Einsteins laws as working just fine over an enormous range of conditions - and any loopholes it provided for potential time-travellers would (by necessity) be impractical in the extreme! Personally - I doubt that'll ever happen. We fixed the bug - and now it's right. SteveBaker (talk) 13:46, 9 December 2008 (UTC)
Such an enquiring mind deserves its own expression in a science fiction novel. Who knows where that would take you? Think on, 70.181... Julia Rossi (talk) 07:09, 9 December 2008 (UTC)
The phrase "time travel" is a double negative. The word time is similar to the word speed and the word motion. It has no size or shape. It is a scale with no measure which looks odd but is spot on. You can traverse a centimeter but not an instant lol. When Einstein says that such speed would slow you down he is refering to the fact you would be squashed so tight nothing could move similar to ice or the Earths core. ~ R.T.G 10:54, 9 December 2008 (UTC)
I respectfully disagree with Steve's comment "We fixed the bug - and now it's right." Einstein's general relativity models gravity and space-time. However it does not model quantum theory. Einstein's theory is a more accurate refinement of Newton's model, but it does not represent every situation. Many scientists have worked to create a more accurate model, and I expect that the scientific community will eventually agree on a new theory that models gravity more accurately than general relativity. Axl ¤ [Talk] 21:46, 9 December 2008 (UTC)
It's perfectly possible that that could happen - but (and here is the crucial thing) whatever this new theory is, it has to agree with relativity rather precisely over the entire range of measurements we've done to date that confirm relativity. So the new theory would pretty much HAVE to prohibit faster-than-light travel. Sure, it could say that gravity doesn't warp space - or that some different set of math applies at the scale of quantum events...but the math has to produce the same results as Einstein over the range of data we have...which is pretty much the entire range of human experience - and higher speeds out to lightspeed and masses up to black holes and down to atoms. SteveBaker (talk) 02:32, 10 December 2008 (UTC)
Indeed, if you want to allow time travel or faster than light travel you need to introduce something which we haven't been able to observe yet. "Exotic matter" is the usual way people construct such theories. --Tango (talk) 14:03, 10 December 2008 (UTC)
Yes...although that's about as meaningful as speculating that the magic time-travelling pixie will come along and tell us how. It's not like there are these mysteriously faster-than-light things that we're trying to explain - there is zero reason to expect or even imagine that exotic matter will do anything interesting whatever in terms of relativity. Of course Newton would have said the same thing if asked about the speed of light (he didn't even know that light HAD a speed) - but the state of experimental science was pretty poor in Newton's day. Apples falling from trees are rather blunt instruments when it comes to probing the secrets of the cosmos...we have cool toys like a computer-controlled telescope the size of a schoolbus in orbit around our planet and something the size of a shoebox that sits on your desk, contains all of human knowledge and can do simple arithmetic about ten billion times faster than Newton could manage. But - as I said in the post that triggered Axl's reply - "Personally - I doubt that'll ever happen." - not "I know for 100% sure it'll never happen." SteveBaker (talk) 21:52, 10 December 2008 (UTC)
Sure, given how much observing we've done, "something we haven't observed yet" means something that probably doesn't exist. It's still interesting to think about, though (at least, it is for me, I'm a mathematician, we rarely let such minor details as whether things exist in reality get in the way of interesting maths). --Tango (talk) 21:59, 10 December 2008 (UTC)
Just to clarify: I do not think that a new widely accepted theory will allow time travel to be possible. Rather I think that there will be a new theory that would be a better model than general relativity. Comment to Tango: I think that the Large Hadron Collider (and later particle accelerators) will indeed show new phenomena that have not yet been observed. Axl ¤ [Talk] 22:19, 10 December 2008 (UTC)
GR does allow for time travel, it just requires you to fudge things a bit (eg. with exotic matter). Finding such matter (or a way to create it) is rather unlikely, but not impossible. The LHC will almost certain show us things we haven't seen yet (that's why it's being built), but they are likely to be things we already know ought to exist, it will just help us fine tune our theories. Observing exotic matter would be a much more significant event than observing the Higg's Boson, say (which would be a pretty big event). --Tango (talk) 22:26, 10 December 2008 (UTC)

Containing a super-volcano?[edit]

Could a very large Kevlar bag contain a super-volcano eruption and prevent the consequent mass extinction of mankind? Could any conceivable structure contain the dust and gases?Trevor Loughlin (talk) 07:33, 9 December 2008 (UTC)

Although I'm no expert on the subject, I know supervolcano eruptions are extremely energetic events. Containing the actual explosion would require unobtainium. As for the gas and dust, supervolcanoes eject over 1000km³ of tephra alone - not to mention the enormous volumes of gas that are released. I'd think your options are limited to damage minimisation, luck, and - unlikely but possibly - prevention of eruption. Containment is all but impossible as far as I can imagine. In any case, it would probably be more feasible to construct domes over all the major cities and harness geothermal and nuclear energy to stay alive. You'd also need to create artificial sunlight for greenhouses and the like. --Link (tcm) 08:17, 9 December 2008 (UTC)
Kevlar is seriously weakened by heat, so it stands no chance against lava or a volcanic bomb. Graeme Bartlett (talk) 10:31, 9 December 2008 (UTC)
Perhaps an Operation Plowshare sort of endeavour could relieve the pressure and prevent an explosive eruption. Or at least make an awesome Jerry Bruckheimer movie. --Sean 13:42, 9 December 2008 (UTC)
That might work, yes. On the other hand, it might just set it off early. Which would, kinda, suck. —Ilmari Karonen (talk) 18:15, 10 December 2008 (UTC)

Stellar Classification[edit]

I've read the article, found it a little confusing, but finally think I've got it. However, I wanted to check my understanding....

If a star is rated G1V in its wikibox, it means

  • G - about the same size, temperature and brightness as the sun
  • 1 - a bit hotter than the sun, though, since the sun is G2V
  • V - about the same size as the sun.

Hmm. I mentioned 'size' twice. Maybe that's ok. Have I got this right? mike40033 (talk) 07:58, 9 December 2008 (UTC)

The classifications are explained in Stellar classification. G will be the Harvard spectral classification. I think the number (in this case 1) relates to the absolute magnitude and V is the Yerkes spectral classification, all of which are explained in the article I cited. Jdrewitt (talk) 15:43, 9 December 2008 (UTC)
Yes, that's the article I mentioned, that I read, and found confusing, and wanted to check my understanding. Have I got it right? mike40033 (talk) 00:35, 10 December 2008 (UTC)
Hello, well the Harvard classification indicates the temperature of the star's atmosphere, so strictly speaking G will stand for a star which has a comparable temperature to the sun. I think though since the sun is a main sequence star, you can infer the size and other properties from the temperature (This would not be the case for a red giant though). The number relates to the luminosity of the star, so 1 will stand for a star that is simply brighter than the sun, not necessarily hotter though. Then the Yerkes sectral classification relates the luminosity to the size of the star, so V will indeed represent a star about the same size as the sun. That's my interpretation of the article anyway. Jdrewitt (talk) 15:45, 10 December 2008 (UTC)
You are wrong about the arabic number. As the article says: "The spectral classes O through M are subdivided by Arabic numerals (0–9)." Hence, the spectral type of the star is G1 as opposed to the sun's G2. This means that the star is a little hotter and therefore has a spectrum closer to type F than the sun. This agrees with what the original poster stated. Indeed, the designation G1V has two parts (not three as one might suspect), in agreement with the Hertzsprung-Russell Diagram being a two-dimensional representation of properties. The spectral type is essentially given by temperature, the luminosity class (as indicated by the Roman numeral) by luminosity, although the boundaries between the luminosity classes are different for hot O type stars than for cool M type stars. The variation of size and mass can also be traced on the Hertzsprung-Russell diagram, but that is a little more complicated. --Wrongfilter (talk) 18:40, 10 December 2008 (UTC)
Thanks for pointing that out, it is not clear from the article by any means. Yeh, that makes sense now. Jdrewitt (talk) 10:46, 11 December 2008 (UTC)

Energy crisis[edit]

HI pple, I wanted to know whether its feasible to convert IR radiation to electricity..and use it ,say, for mobile charging ... If so, can you just tell me how.. —Preceding unsigned comment added by (talk) 08:36, 9 December 2008 (UTC)

Well, for starters you can use IR radiation to heat things, so if you had enough of it you could use it to run a boiler to power a steam generator, but I'm almost certain there would be more efficient ways to do it. Gunrun (talk) 10:06, 9 December 2008 (UTC)

Possible? Definitely. Feasible? Apparently, not quite yet. --Link (tcm) 12:06, 9 December 2008 (UTC)
The boiler/steam generator concept has been implemented here, although it's not exactly a mobile solution, and the power it generates is currently still more expensive than conventional methods. Gandalf61 (talk) 13:27, 9 December 2008 (UTC)
There is research work going on in the field of infra-red 'solar panels' that would collect radiant heat and convert it to electricity. There are all sorts of interesting applications for them. However, if they exist at all - they are lab experiments - not something you can go out and buy. SteveBaker (talk) 13:30, 9 December 2008 (UTC)

Speed and mass[edit]

I remember reading somewhere that the faster an object goes the more mass it has. Is this right? Assuming it is does this mean that if you could accelerate a 9mm bullet to massive speeds (possibly using magnets?) you could demolish a house with it? Also would it be possible to accelerate an object to such speeds that its mass would be more than its atomic structure could withstand causing it to collapse in on itsself and form a black hole? Is this the reason nothing can move as fast as light? Gunrun (talk) 10:01, 9 December 2008 (UTC)

This is right, mass increases with speed. But no, a thing cannot be made to collapse into a black hole this way. See our article on mass and relativity. As for destroying a house with a single bullet, to get any really noticeable increase in mass, you would have to accelerate the 9 mm bullet to such a velocity that it would not hold together for an instant flying through the atmosphere. If the house were in a vacuum, however, then you could do a lot of damage with a single bullet, although it wouldn’t require a relativistic velocity, just plain very, very fast would do. This sort of thing is a problem for stuff in outer space in general, and especially for delicate instruments and space vehicles in orbit; we’ve managed to pile up quite a lot of junk up there in the past fifty years.--Rallette (talk) 10:49, 9 December 2008 (UTC)

There are a few things to note here:
  1. The mass of the bullet is no different from the perspective of the bullet. It's only heavier for outside observers. But since the house is an outside observer - the bullet would indeed seem heavier.
  2. The bullet's energy is kinetic energy - which is given by 1/2 M v2 - so when you double the speed, you quadruple the amount of energy. So even without the relativistic effect, a bullet moving close to the speed of light would do an insane amount of damage.
  3. However, the bullet won't collapse or break apart or anything - as far as it is concerned, it's just sitting there minding it's own business, being the same mass it always was. So providing it's moving through a good, hard, vacuum - it'll be just fine. Of course in air there would be severe problems - the heating due to friction would evaporate the bullet at just a few thousand miles per hour - LONG before it got remotely close to gaining mass noticably!
  4. Note that the energy it would take to get something as big as a bullet moving that fast would be horrendous.
  5. When we're talking about relativistic effects, there is an ENORMOUS difference between going at (say) 99.999% of the speed of light and going at 99.9999% - adding that extra '9' causes enormous differences in the mass we'd perceive the bullet to have attained - and spectacular increases in the damage it could cause.
  6. You can work out the change in mass quite easily. Take the mass of the bullet and multiply it by (where v is it's velocity and c is the velocity of light) - then, you can calculate the energy by multiplying that mass by v2 and dividing by two.
So if we take a 6 gram 9mm/17 Browning round and push it up to 99.9999% of lightspeed, we have a mass of 6g / sqrt ( 1-(99.9999x99.9999)/(100x100) ) which is 4242g - about 4 kilograms. At 99.9999% of 299,792,458 meters per second (light speed) that bullet would release 1,900,000,000,000,000,000 joules - which is about 500 megatonnes of TNT. About ten times more than the biggest nuclear bomb ever detonated! The bullet wouldn't just destroy the house - or the city that the house was in - it would stand a good chance of destroying an entire european country. That's at 99.9999% of light speed. Make that 99.999999% (six nines after the decimal point) and the amount of energy goes up by another factor of ten and most of the planet would be at risk from your 9mm bullet!
Of course the amount of energy you'd need to get the bullet up to that speed in the first place would be...exactly the to get your bullet up to 99.9999% of the speed of light - the propellant would have to be something with about the power of ten decent size hydrogen bombs.
SteveBaker (talk) 13:24, 9 December 2008 (UTC)
Actually, the city would probably be fine, in fact the house would probably survive. In order to do any damage that energy would have to be absorbed somehow, I would expect the bullet to just go straight through barely slowing down. --Tango (talk) 13:59, 9 December 2008 (UTC)
So it seems it would actually do less damage to humans as an ordinary 9mm bullet does. Yes, it will make a hole, but not turn and/or deform. -- (talk) 14:42, 9 December 2008 (UTC)
I think it depends on how it impacts. If it came in at an angle and hit the ground - I don't see how it could keep going for long. You'd have a large crater and an enormous amount of material ejected into the atmosphere - nuclear winter...all of that stuff. If it came in horizontally - then maybe it's a different picture.
Let's consider your "pristine bullet" scenario. The tip of the bullet touches the wall at 99.9999% of c. The molecules of brick immediately in front of the tip do...what?
  • Suppose the tip of the bullet is a shallow cone. The molecules of the brick either have to move out of the way laterally (which means accellerating to maybe a tenth the speed of light from a standing start - and then continuing at that speed through the brick above, below and to the sides of the bullet - with maybe 50 Megatonnes of energy between them.
  • ...or the molecules have to accellerate to 99.9999% of the speed of light to stay in front of the bullet and fly out of the 'exit wound' on the far side. The force required to do either of those things has to be imparted by the bullet it has to apply a SPECTACULAR amount of force to the material of the brick...there is no way for it to do that without shedding a lot of energy (and in truth - evaporating into a cloud of relativistic particles.
  • More likely is that the atoms of the bullet act like particles in the large hadron collider and convert the material they impact into who-knows-what exotic particles - which in turn shoot off at relativistic speeds...but we're not talking about a small cloud of a few dozen protons at near light speed - we're talking about an avagadro's number (or so) of protons doing that! The amount and energy of the resulting sub-atomic debris would vaporize a problem.
So, no - I don't see how the bullet can go right through without releasing an enormous amount of energy. If you think it can - tell me in detail what happens to the cylinder of material immediately in front of the bullet - it can't just "go away" - and it can't gently move to one side because it doesn't have enough time. So it either accellerates to near lightspeed itself (causing secondary, tertiary, etc damage in the multi-megatonne range) or it's converted to other particles - which form a VAST amount of hard radiation with similar consequences as it's absorbed by surrounding materials.
Nope - I'm pretty sure we get our big satisfying explosion...not just a neatly drilled hole. SteveBaker (talk) 15:03, 9 December 2008 (UTC)
I'm not sure exactly what would happen, but let's consider the possibility of the cylinder of matter just being pushed forward ahead of the bullet and see what happens. That requires a spectacular amount of force, certainly, but we have that. Let's assume we have a perfectly inelastic collision, what we need to work out is the energy lost in that collision because that's the energy that's going to go into destroying things (the bullet and cylinder of brick will head of into space if they don't hit anything else first (we'll assume there is just one house and nothing but desert to the horizon), so that energy doesn't go anywhere interesting). We have 4 (relativistic) kg of bullet colliding with a thin cylinder of brick (we'll ignore the bonds between that cylinder and the rest of the house because I'm a mathematician and that's what we do - the energy to break them is probably trivial compared to the energy of the bullet anyway). Most of the house is air, so we'll ignore that, let's say we have two external walls and an internal wall to get through, we'll say that's 2 metres of brick (it's something of that order). According to Brick, the density of brick is about 2000kg/m3. The diameter for the bullet is 9mm, so that's a volume of 9mm*2m=0.018m3, so a mass of 36kg. Now we get to calculating the energy lost in a relativistic completely inelastic collision, and I'm not entirely sure I've done it right, but this is what I got: The bullet and brick are now moving at 0.11c (much slower than I expected, brick is heavier than I thought!), so you have an object of rest mass 36kg moving at 0.11c, that's an energy of, well, 1/2 mv2 (0.11c isn't very relativistic), so 2*1016J, or 5 megatonnes of TNT, so we have 495 megatonnes left to destroy the world, so ok, that's pretty nasty. Out of interest, I did the same sums for your even faster bullet and got that the bullet and brick after the collision are now going at 0.74c, giving an energy of (using relativistic formulae this time) 1.6*1018 or about half a gigatonne of TNT, leaving 4.5 gigatonnes left. So, the moral of the story is not to shoot houses with relativistic bullets (and that Steve has a better intuition about relativistic physics than me)! --Tango (talk) 16:49, 9 December 2008 (UTC)
I can't calculate the volume of a cylinder... hang on while I revise all that... --Tango (talk) 17:32, 9 December 2008 (UTC)
Ok, it's 1kg of brick (I thought 36kg was a bit much!), so the final speed is 0.97c (far closer to what I was expecting), which corresponds to an energy of 2.8*1017J, or 67 Mt, leaving 433 Mt left. So, still a massive bang. For the faster case we have a final speed of 0.9997c, and an energy of 3.6*1018J or 0.86 Gt, leaving 4.14 Gt, so again, still a massive bang. Oh well, the final conclusion is the same, but not by quite as much as I my first calculations showed. --Tango (talk) 17:44, 9 December 2008 (UTC)
Since the proportion of energy left is decreasing as speed increases, I've done it again for 99.9999999999% c to see what happens. This gives a final speed of 0.99999997c and an energy of 3.6*1020J, or 86 Gt, from an initial energy of 500 Gt, leaving 414 Gt left, exactly the same proportion as last time, perhaps this is an asymptotic thing? 0.86 is about , could that be the limit? --Tango (talk) 17:52, 9 December 2008 (UTC)
No, that would be stupid, while the brick weighs a nice round number the bullet doesn't, so we wouldn't expect a nice answer. It's probably coincidence. --Tango (talk) 17:54, 9 December 2008 (UTC)
The problem with the bullet pushing a neat cylinder of brick out of the wall is that the particles of brick have to accellerate from zero to 99.9999% of the speed of light (minus a little bit) in the time it takes the bullet to travel maybe a couple of millimeters at most. At lightspeed, a nanosecond is a foot - 300mm - so the brick molecules would have to accellerate to a significant fraction of lightspeed in just a few picoseconds - it's a very, very VERY short period of time. Classically F=ma - and for the relatively small mass of the brick, and an accelleration of zero to lightspeed in a few picoseconds...that's a PHENOMENAL amount of force that the bullet has to apply to the brick. Worse still - the brick cylinder is being accellerated to relativistic speeds - so the energy it needs is pretty much the same as the amount of energy it took to get the bullet up to that speed in the first place. So the energy of the bullet would have to be divided roughly equally between brick and bullet post-collision. So the brick accellerates from zero to maybe half the speed of light in maybe 3 picoseconds - and the bullet slows down by about the same amount just as quickly. Just think of the g-forces on the bullet! We're talking g forces comparable to a neutron star. How can a lump of lead or brick suffer that much force without being utterly annihilated? It's just inconceivable that this can end in anything much short of two thousand quadrillion joules(!) of spectacularly high energy gamma rays...which will cook everything out to the horizon and to a depth of a few kilometers into the ground. A few thousand square miles of everything would simply vanish - the resulting debris would likely be thrown up into the upper atmosphere and would probably shut out the sun for a few years - maybe plantlife dies - then animal life dies - then it's game over for humanity. SteveBaker (talk) 02:23, 10 December 2008 (UTC)
It doesn't matter if the bullet and brick are completely annihilated, as long as the remnants continue to travel on at relativistic speeds and take a large chunk of the energy isn't space with them. However, my calculations show that it wouldn't be a large enough chunk and we would still be looking at an explosion big enough to wipe out all life on Earth. (Although, I've realised I still can't calculate the volume of a cylinder, I used the diameter instead of the radius, so it's actually 0.25kg of brick. That doesn't seem to make a significant difference to the end result though.) --Tango (talk) 13:58, 10 December 2008 (UTC)
You might be interested in the Oh my god particle, a relativistically-fast micro-bullet From Beyond! --Sean 13:46, 9 December 2008 (UTC)

This whole bullet scenario is pretty silly. You're applying a physical model which is designed for elementary-particles to macroscopic objects. There are so many problems - like, bullets would not remain in solid-form when their individual particles attain kinetic energy many orders of magnitude above their intermolecular binding energies. Once again, when you pose a ridiculous physical scenario, there's no good scientific-model to apply, so throwing equations at it will not conclusively answer anything. Maybe we should move this question to the Science Speculation Desk For Crackpot Theories Applying Quantum Mechanics and Special Relativity to Unlikely Scenarios. I don't think it does a service to the "uninitiated" readers who are unfamiliar with advanced physics when we use inapplicable theories on non-physical situations. It's bad physics, even if the math is flawless. Nimur (talk) 16:17, 10 December 2008 (UTC)
But the bullet's kinetic energy is zero in the only reference frame that tells you anything about what state of matter the bullet is in. --Tango (talk) 16:56, 10 December 2008 (UTC)
It's hard to say where to begin in shooting down Nimur's post! Firstly, the 'physical model' is Einsteins special relativity theory - which most certainly does apply to macroscopic objects. The bullet is PERFECTLY able to retain it's solid form (so long as we're in a vacuum) precisely BECAUSE relativity says that the laws of physics are the same for all inertial frames of reference - so the bullet is able to consider itself to be stationary - and if it's stationary in a vacuum then it's certainly not going to fall apart due to some mysterious binding energy issue. The same is true for the building...and in fact, this is just as much a question of what happens when a building that's moving at 99.9999% of lightspeed hits a completely stationary bullet...because that's the EXACT same question. Bullets don't usually spontaneously disintegrate just before something hits them! Until bullet and building actually meet, neither of them is in the slightest bit inconvenienced. If you don't know this (and given what you just said - it's hard to see how you do) then you should sit back and read some of the things posted here rather than complaining about them because there is a strong possibility that you'll actually learn something. The equations I was throwing at the problem are all perfectly acceptable for this kind of situation. It's hardly "advanced physics" - the equations have been around for 80-some years. Lorentz, F=ma, E=1/2 mv2 are all taught in any good high school - and those are the only equations I've used. This is a perfectly legitimate way to discuss the question as asked. If you're going to start whining about the nature of the questions that are asked here - then you are on a slippery slope. SteveBaker (talk) 21:37, 10 December 2008 (UTC)
You were taught special relativity in high school? I didn't get taught about Lorentz factors until Uni. (I'd read about them in books before then, of course, but that's just because I'm a geek.) --Tango (talk) 21:56, 10 December 2008 (UTC)
Again, I won't contest your equations, I don't doubt relativity. When anyone can show me an experimental setup which tests bullets at relativistic speeds, (or stationary bullets and relativistic brick walls), I'll start worrying about the details. In the meantime it's an irrelevant gedankenexperiment - you apply relativity to something which has never been observed in a relativistic context... you may as well start throwing the Theory of Evolution at the brick wall (again, a perfectly sound and scientific theory - but only applicable to the correct context!) My only point is that you can't take a scientific model and expect it to be universally applicable, no matter how rigorously verified it is in a specific context... Science must be based on experiment first and foremost. No relativistic bullet/brick-wall experiments exist, so you are blindly speculating that these equations which have only been verified for muons (and their ilk) hold for walls and buildings. You are "pretending" without any scientific evidence that Relativity is the Grand Unified Theory, and you're implanting that idea into other people who don't yet have enough training to decide for themselves. Nimur (talk) 14:47, 12 December 2008 (UTC)

Sequence line-ups[edit]

I am starting a project involving the use of computer programs (BLAST, ClustelW, AlignX) to line-up the genes of different clades of the same enzyme in two species of flatworm. I don't know where to begin, however, as I have no experience in this area. Can anyone guide me where to go to find information about how such a project may be undertaken or a link to a paper or two that have used the same method before? (talk) 11:35, 9 December 2008 (UTC)

This paper covers a lot of relevant tools: [6]. Another resource is CDD. TreeFam seems relevant: [7]. Some of these I found Googling "alignment orthologs flatworm", etc. BioEdit is a nice, free (Windows) sequence editor that has plenty of built-in tools. HTH --Scray (talk) 11:54, 9 December 2008 (UTC)
You might also want to consider using Psi-BLAST, and it has a nice tutorial. --Scray (talk) 11:57, 9 December 2008 (UTC)
I also find ClustalX much friendlier than ClustalW. --Scray (talk) 11:59, 9 December 2008 (UTC)
There are several pretty decent Wikipedia references that you might want to read through. If you already have your sequences in hand, you can assemble them into FASTA format and run them through Clustal (use version ClustalX as suggested above, since it's a graphical user interface) to generate your multiple sequence alignment. ClustalX can also export the alignment file as in a format that can be used to generate a phylogenetic tree or dendrogram (which is what I assume you are trying to do). As mentioned above, Bioedit is very useful for modifying/annotating your alignment file from ClustalX into a form that can be published.
If you don't already have sequences in hand, then you need to use BLAST ([8]) to find all of the sequences that are significantly similar to each other in the sequence database. To do this, take your known enzyme sequence and blast against a particular flatworm genome. There are a few variations that you need to be aware of:
1) BLASTN - nucleotide blast, searches a nucleotide database using a nucleotide sequence query
2) BLASTP - protein blast, searches a protein database using a protein sequence query
3) TBLASTN - translated blast, searches a translated nucleotide database using a protein sequence query
Any given enzyme will probably have fairly high identity at the protein level between closely related species, but the nucleotide conservation will be much lower. For that reason, I would recommend starting from a protein sequence and searching your different species using BLASTP to pull out the homologous enzymes. Note that this will only identify annotated protein sequences (or in some cases predicted protein sequences). You can extend your search using TBLASTN against the whole genomic sequences to find unannoted nucleotide sequences that could encode the enzyme you're interested in. If you find a piece of genomic sequence that seems to contain a protein-coding gene, you can run it through a gene prediction program. It can get a little complicated sifting through genome data, but it's a good exercise to see if you can find intron/exon junctions, etc. Have fun! Medical geneticist (talk) 20:14, 9 December 2008 (UTC)

Why does light refract upward at cold temps?[edit]

Was out snow shoeing earlier, have always wondered why at colder temperatures (<-25C) light refracts upward way into the sky? The only info I could find about this was instead for forming ice plates and cooler temps, when its real cold the ice crystals for a more vertical shape? Does air density have to do with this as well? —Preceding unsigned comment added by Oilsandsfj (talkcontribs) 12:50, 9 December 2008 (UTC) This should help you I think. Gunrun (talk) 14:01, 9 December 2008 (UTC)

Cheese and intestinal blockage.[edit]

Is there anything in cheese that makes it cause constipation? I've noticed with myself and friends, whenever we eat a meal with quantities of cheese, our bowels get blocked up. I've eaten tons of dairy and lots of fatty foods in meals without any similar problems. But what is there about cheese that seems to act like intestinal concrete? -- (talk) 14:31, 9 December 2008 (UTC)

The bigger issue is that when you are eating cheese, you are NOT getting as much dietary fiber as when you eat other foods. Try the experiment and see if eating some high-fiber foods alongside cheese doesn't improve the situation for you... 16:51, 9 December 2008 (UTC)
Or get your fiber in your cheese, with caraway cheese: [9]. (Actually, this is low on fiber, so you'll still need other sources.) StuRat (talk) 05:01, 11 December 2008 (UTC)
What, no article ? Now I'm really cheesed off ! StuRat (talk) 05:03, 11 December 2008 (UTC)

Road salt[edit]

Will road salt kill grass? Grsz11 16:49, 9 December 2008 (UTC)

It can yes, if too much of it gets on grass it can burn it, the same way over fertilizing it can. -Djsasso (talk) 16:51, 9 December 2008 (UTC)
Oh well, I rent. Thanks, Grsz11 17:13, 9 December 2008 (UTC)
See Salting the earth... --Dr Dima (talk) 17:15, 9 December 2008 (UTC)
Instead of sodium chloride, potassium chloride is sometimes used to melt road ice. Would potassium chloride be less harmful to grass and to the metal parts of cars? —Preceding unsigned comment added by (talk) 14:37, 10 December 2008 (UTC)
A very good question. Googling for KCl NaCl plant toxicity returns plenty of fascinating stuff, including a great 1908 paper on wheat root growth in solutions of several metal chlorides at various concentrations. Skimming conclusions from a few sources, the somewhat surprising answer is: KCl is not necessarily less toxic than NaCl for grasses. So please don't salt your garden! That is, unless Menelaus is calling ;) . --Dr Dima (talk) 18:47, 10 December 2008 (UTC)

How do you use microwaves to find out if there's foil inside butter tubs?[edit]

I've just started a new project with school and Dale Farm that we have to detect the foil inside butter tubs without taking the lid off. Microwaves work at finding out if there's metal there or not but I can't work out how to make a circuit that will tell me without looking at every current coming out. Anyone know of any useful websites? —Preceding unsigned comment added by C ocean (talkcontribs) 17:39, 9 December 2008 (UTC)

Puting metal in a microwave is contraindicated (don't do it!) for several good reasons. First, the potential for fire or other hazards is quite great, and secondly the presence of metal could damage the magnetron (the working bit) of the microwave as well. It would actually be quite easy to, using stuff lying around the house or availible at the local SuperMegaHardware Store, create a rudimentary Metal detector. this google search turns up literally hundreds of sites which show how you can do this. Good luck! 18:01, 9 December 2008 (UTC)
It sounds like what you want is a radar setup. I agree, though, a metal detector is much more practical for the typical school project (unless this is a particularly unusual sort of school). (talk) 19:08, 9 December 2008 (UTC)
Butter+foil+microwave oven=fire, don't do this combination. Graeme Bartlett (talk) 20:21, 9 December 2008 (UTC)
Although the flaming result would certainly reveal the foil. Fire extinguisher recommended. --—— Gadget850 (Ed) talk - 20:47, 9 December 2008 (UTC)
I don't see the word "oven" anywhere in the original question; C ocean, can you clarify what you are trying to do? Beyond that, I have seen microwave ovens with metal racks, so clearly the whole "never use metal in a microwave!!!111" meme is overwrought. --LarryMac | Talk 20:47, 9 December 2008 (UTC)
You can use metal in a microwave oven— such as a rack —under certain circumstances. You get some electric current induced into any metal, but pointed edges cause arcing and heating. A spoon would not arc, but a fork would. I suspect the the edge of the foil cover would arc, and melted butter is flammable. This would occur in a standard microwave oven or if it was just focused microwaves such as from radar. --—— Gadget850 (Ed) talk - 21:00, 9 December 2008 (UTC)
I've seen microwaves specifically designed to be safe with metal, but only one piece of metal and it needs to be pretty flat (eg, a piece of foil covering a bowl would be fine). If you have two pieces, of one piece that bends, then you can get arcs from one bit of metal to another, but if you only have one bit there is nowhere for the arc to go. I think the way they do it is to not have any metal around the edge of the oven so nothing can spark from a bit of metal inside to the edge. --Tango (talk) 22:10, 9 December 2008 (UTC)
Wait, wait, wait...are we over-thinking this? Are they talking about some foil contaminant buried deep inside the butter (seems unlikely) - or are they simply asking whether the foil that is SUPPOSED to be sealing the butter under the lid has somehow not been put there or perhaps was subsequently removed? If THAT is the question our OP has to answer then perhaps it's as simple as rotating the lid and seeing how stiff it is? Or tapping on the top of the lid and listening to the sound it makes (or having your computer listen to it)? Or weighing it? ...or...lots of REALLY simple tests! SteveBaker (talk) 01:51, 10 December 2008 (UTC)
The OP indicated some aspect of the project involved circuitry, so I assume that an electronic device is supposed to be built which will detect the presence of metal. Rudimentary metal detectors, involving simple inductor circuits, can easily be built using household materials, so I still think that's the easiest way to go. 03:32, 10 December 2008 (UTC)
Or do a biopsy stick in a needle and take out a sample, too bad about the little hole though. Graeme Bartlett (talk) 03:46, 10 December 2008 (UTC)
This sounds VERY much like a common electronics class lab (sometimes used in physics as well). The point of the lab is to build two variable oscillator coils. Put one in the middle of the other and get them on the same frequency. Connect a tiny speaker between them. Everything should be fine until something interferes with the magnetic waves (not microwaves - magnetic waves). Then, the frequencies get messed up and get out of sync - causing an audible signal over the speaker (the beep that metal detectors make). I've seen it printed up many times for many different schools. The test is always "detect (some metal object) inside (some opaque container)". -- kainaw 03:51, 10 December 2008 (UTC)

cosmic string[edit]

If a cosmic string passed through the Earth, what would happen? Assuming they exist. -- (talk) 19:10, 9 December 2008 (UTC)

For a long cosmic string (kilometres or bigger), I expect the Earth would be destroyed by tidal forces before it got too close, so it wouldn't be able to pass through the Earth. For a very short one (smaller than an atom) it would be much like a micro-blackhole and would pass straight through with little effect. I'm not sure about ones inbetween. --Tango (talk) 19:48, 9 December 2008 (UTC)
How to destroy the Earth: Whipped by a cosmic stringDanielLC 01:52, 10 December 2008 (UTC)
Theoretically we can calculate many results, but one thing should be noted the concept of cosmic string is still in a hypothetical stage. Otolemur crassicaudatus (talk) 10:35, 10 December 2008 (UTC)
The interesting thing about cosmic strings is that they have no gravitational field at all! At least, straight sections of them don't. The metric of a straight cosmic string can be written ds² = dr² + r² dθ² + dz² - dt², which is exactly the same as the metric of Minkowski space in cylindrical coordinates (r,θ,z,t). The only difference is that the range of the angle θ is smaller than 360°. To put it another way, you get the cosmic string metric by starting with Minkowski space, deleting a wedge-shaped region from it, and gluing the two sides of the wedge together. There are no tidal forces and not even any gravitational attraction—you can hover at any fixed distance from a cosmic string without firing your engines at all. But two comoving objects that pass a cosmic string on opposite sides will end up moving towards each other at an angle equal to the angle of the wedge you removed (the defect angle). The deflection is the same regardless of the speed of the objects and the distance from the string.
I can't remember reading anything about the effect of a cosmic string passing through an object, so what follows is just idle speculation—but I suppose it would be like slicing the object into two pieces and sending them crashing into each other at a relative velocity that depends on the defect angle and the speed of the string through the object. With a small defect angle and a low speed you would get compression waves radiating outward from the collision plane, like an earthquake. With a large enough defect angle and/or a high enough speed I suppose the object could be compressed enough to form a black hole. In intermediate situations there would be massive devastation of some kind. But nothing will get "sucked in" to the cosmic string; it has no gravity at all. -- BenRG (talk) 06:41, 13 December 2008 (UTC)

Native Americans and Atlantis[edit]

How plausible is the information in the link here? --Emyn ned (talk) 19:20, 9 December 2008 (UTC)

"Genetic researchers determined that 96% of Native Americans fell into one of the four A-D haplogroups and while these mtDNA types were also found in Asia they are not present in Europe or Africa. This too indicates that Asia was the ancestral region of most Native American tribes. Then in 1997 another lineage was discovered, which geneticists dubbed X. This discovery ignited a storm of controversy that has not died down to this day. The X haplogroup needs careful,thoughtful, and deep historical analysis because this group may well hold one of the most important keys to unlocking the secrets of our collective past. ......

Moreover, the vast majority of tribes contained no X members. In fact, it was not found in any native tribes in Central or South America. Again, what did these patterns mean? Independent researchers associated with the Edgar Cayce Association (A.R.E.) quickly pointed out that the data supported some of the material found in the Atlantis readings that the 'sleeping prophet' had given in the 1930s. Cayce noted that some Atlantis refugees had immigrated to the northeastern region of the United States and later formed the Iroquois nation. It was in those tribes that the highest concentration of the X haplogroup was found." --Emyn ned (talk) 19:25, 9 December 2008 (UTC)

No comment on the genetics, I'm just amused by the concept of a mass migration from the Mediterranean to New England. I wonder how many Atlantians survived their first winter. APL (talk) 20:17, 9 December 2008 (UTC)
There are certain persistant cultural traditions and artifacts among Native American peoples which raise some questions as to how "isolated" they were. The Quetzalcoatl/Kukulkan myth in Central America has some depictions of the "feathered serpent god" as a bearded, pale-skinned man; neither traits were common among native American peoples, leading to speculation that the myth had European connections. Additionally, certain artistic traditions of the Olmec people show subjects with decidedly African (and not really Central American) features, suggesting contact there. Beyond that, there is the Vinland settlements circa 1000 AD, speculation over Chinese exploration of the N. American west coast, and other evidence of possible pre-Columbian contact between the hemispheres. While the celebrated, the well funded "expeditions" had the benefit of being ventures supported and historically recorded by the power elite, and so show up in the historical record. There may well have been fisherman plying the coasts of North America and other, less celebrated contacts, between the hemispheres that disappeared from the formal historical record. There are many, simpler, Occam's razor-compliant explanations for genetic anomalies among Native American populations than "Mega continent disappears without a trace, and leaves no evidence except genes among the Native Americans". 22:18, 9 December 2008 (UTC)
Is anyone willing to comment on how this ties in with the reported descent of Native Americans from the lost tribes of Israel? CBHA (talk) 22:37, 9 December 2008 (UTC)
Sure. There is no such descent, at least as the Mormons or Atlantismaniacs tell it. See Human mitochondrial DNA haplogroup for a map of the travels of the peoples bearing Haplogroup X. - Nunh-huh 00:21, 10 December 2008 (UTC)
To be precise, Mormons (more correctly known as Latter-day Saints) do not claim that Native Americans descend from the "Lost Tribes" of Israel. Lehi in the Book of Mormon was a descendant of Manasseh (Alma 10:3). Thanks to other references such as Alma 46:23-24, it is traditionally inferred that Ishmael, who joined Lehi's group with his family, was a descendant of Ephraim.
But that's probably not what you're referring to. A good answer to the assertion that it's *impossible* that Native Americans descend from Middle-Eastern heritage can be found [here[10]]. I probably would have worded it "There is no *proven* descent...." Kingsfold (talk) 14:01, 20 October 2009 (UTC)

Does lemon juice damage your teeth?[edit]

All over the internet it is suggested that it does; but one can't always believe the internet. Nothing about the matter on Wikipedia, as far as I can see. I've recently taken to drinking green tea with lemon, which is very refreshing; and I suppose I'm going through about the juice of one small lemon a day. But if I'm damaging my tooth enamel, I'd better stop. (talk) 23:16, 9 December 2008 (UTC)

Lemon juice is somewhat acidic, and the acid could damage your teeth, but the final pH of the liquid is what matters. Even highly acidic drinks like orange juice or pop don't really make much difference, the enamel damage comes from sugar that feeds bacteria that stay on the teeth, not the acid that just passes right by into your already acidic stomach. These bacteria produce acid that remains in contact with the enamel for a long time and can cause real damage. You might theoretically be damaging your teeth, but chewing on a piece of bread is probably worse. SDY (talk) 23:42, 9 December 2008 (UTC)
Here is a good reference. Otolemur crassicaudatus (talk) 00:05, 10 December 2008 (UTC)
Can't get access to the full article. I assume they were soaking the teeth in the liquid? Again, the final pH of "tea with lemon" is probably in the 4-5ish range at best unless it's "do you want some coffee with your sugar?" amounts of lemon juice. SDY (talk) 00:10, 10 December 2008 (UTC)
This is another interesting article (although orange rather than lemon). Axl ¤ [Talk] 22:51, 10 December 2008 (UTC)
Thanks for your help, everyone. I'm still confused a bit, though. Sure, orange juice, on the scale that people drink it, is bad for your teeth; but I was hoping that the juice of one lemon a day would not be a problem. Quite a few internet sites claim that even lemon water may be bad for the teeth. Anyway, I'm reducing to the teeniest squeeze of lemon per cup of tea. (talk) 22:23, 12 December 2008 (UTC)