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October 10

Particle Physics

What is the difference between the Higg's boson and the graviton? They both are hypothesized to explain gravity, right? So how are they different? Ζρς ι'β' ^¡hábleme! 00:44, 10 October 2008 (UTC)

The Higgs boson is the unobserved member of the Standard Model that is supposed to explain inertial mass. The Standard Model does not deal with gravity at all. The graviton is the hypothetical force carrier for gravity within various theories of quantum gravity. Dragons flight (talk) 01:29, 10 October 2008 (UTC)

That's right. Sorry, I got the ideas cross for a second. Higgs deals with mass and the standard model, and graviton deals with gravity and hasn't anything to do with the standard model, really. Thanks, Ζρς ι'β' ^¡hábleme! 02:19, 10 October 2008 (UTC)

Turning off all electronic equipment during take-off and landing

Why are airline passengers instructed to turn off all electronic equipment during take-off and landing, even equipment that does not contain radio transmitters or receivers? I overheard a conversation recently, in which a fellow passenger claimed that it is done to ensure that people pay attention to what is being said over the loudspeakers, in case of emergencies during the most critical parts of a flight. Can anyone confirm this, or suggest other reasons for this requirement? --NorwegianBlue ^talk 11:07, 10 October 2008 (UTC)

I've heard the same reason (on numerous ocassions) as you suggest. LIke you say it ensures people are not distracted if there is a need to make an annoucement/emergency decisions. I have been told to stop reading my book before so I would suggest it is more about paying attention than it is about anything else. 194.221.133.226 (talk) 11:19, 10 October 2008 (UTC)

In the past it could have been do to with interference (even without transmitters any electronic equipment will emit some EM, I believe), but I'm pretty sure all critical systems on planes are shielded these days. As such, it is probably just to make sure people pay attention and, if not, at least don't make too much noise stopping other people from hearing announcements. On a related note, the reason you aren't allowed to use mobile phones in hospitals is simply because it annoys people, it's been a long time since medical equipment was sensitive to such things. --Tango (talk) 11:21, 10 October 2008 (UTC)

In general it's both. EM interference is a legitimate risk (though a much smaller one than when the rules were written in the 60s and 70s), and it is easier to swtich off all electronics than have flight attendents try to figure out which ones actually need to be disabled. At the same time, the FAA also cites the "possibility of missing important safety announcements during these important phases of flight" [1] as an additional reason to turn off electronics during takeoff and landing. Dragons flight (talk) 11:32, 10 October 2008 (UTC)

Note as well that handheld electronics represent dangerous projectiles in the cabin in the event of a crash. Headphone cables can present a tripping hazard. On takeoff and landing, the cabin crew want you to stow everything securely, not just electronics. TenOfAllTrades(talk) 13:30, 10 October 2008 (UTC)

The turning off electronics thing is just to "make sure", but realistically there's no point. If turning on an electronic device could really interfere with the cockpit's electronics, then terrorists would have a field day. 98.221.85.188 (talk) 14:41, 10 October 2008 (UTC)

The initial justification, Crossair Flight 498, was pretty lame since there were other confounding factors involved. That said, I can hear my speakers making odd noises when I point my cell phone at them the right way, and if I were talking to a control tower to avoid smacking into somebody at 400 knots, I think I'd rather the pilot have a clear signal. SDY (talk) 14:51, 10 October 2008 (UTC)

Your speakers (and the cables attached to them) aren't shielded from EM interference, I would hope the flight deck radio is. --Tango (talk) 15:10, 10 October 2008 (UTC)

How does that work with wireless communication, though? Then again, I'd imagine that the cell phone bands are all quite separate from the bands that aircraft use. SDY (talk) 15:18, 10 October 2008 (UTC)

Is anything in planes wireless? The computers they use for duty free transactions might be, but that's hardly a critical system! --Tango (talk) 15:27, 10 October 2008 (UTC)

Many planes have satellite radios, satellite TV, etc. for the passengers. Not to mention all of their telemetry equipment that is used to monitor where the plane is, how it is flying, etc. by flight control. --98.217.8.46 (talk) 15:49, 10 October 2008 (UTC)

The thinking is that if some of the electronic equipment onboard had been stripped of shielding (say, by shoddy maintenance) then your electronics could interfere. Of course, the plane has a high-voltage radio of its own, which would produce a thousand times more interference than your iPod. It is a dumb rule, but lots of these FAA rules are. They are rituals meant to make you feel safe, not actual safety measures. The lifejackets are a great example. How long do they spend teaching you how to put on a lifejacket? "Your life jacket is located under your seat, or under the arm rest between the seats. Pull the life jacket over your head and attach the strap. Infant life jackets will be distributed, if required. Do not inflate your jacket until you leave the aircraft. Pull the strap until the jacket is properly adjusted. If the life jacket does not inflate or needs more air, blow through the rubber tube." It's a nice image, you bobbing safely in the water with a bright yellow life jacket on. How many people have they actually saved? Zero. Meanwhile hundreds of people die from smoke inhalation which can be prevented by a lightweight mask. There is no rhyme or reason. Plasticup ^T/C 16:05, 10 October 2008 (UTC)

Are you sure of that number? I'm aware of several water landings where there were survivors; are you saying that in none of the cases were life vests used? --Carnildo (talk) 22:32, 10 October 2008 (UTC)

They shouldn't have been used if the evacuation went as planned since everyone would be in inflatable life rafts. Of course, if you're making a water landing, things aren't exactly going to plan, so... --Tango (talk) 23:14, 10 October 2008 (UTC)

Carnildo, for my interest, could you point to a water landing where there were survivors? My impression is that no commercial (large) jet passengers have ever survived a water impact. Skidding off runways, yes, but not "crashes". I'd be interested in the details. Franamax (talk) 00:58, 11 October 2008 (UTC)

See Ditching#Survival Rates of Passenger Plane Water Ditchings. From the article this crash] had 52 survivors. - Akamad (talk) 02:19, 11 October 2008 (UTC)

And more specifically, Ethiopian Airlines Flight 961, although I'm under the impression that life jackets actually killed more people than they saved in that particular incident. --antilived^{T | C | G} 05:12, 11 October 2008 (UTC)

Seen another way, improper use of life jackets caused loss of life, because people inflated them prior to exiting the plane, which is directly contrary to standard instruction. Maybe the relatively protracted training reflects the complexity of using these devices properly. Perhaps they should spend more time on when to inflate than how to inflate. --Scray (talk) 15:02, 12 October 2008 (UTC)

They usually say the standard, 'pull one just before you leave the plane, pull the second one after you leave' whenever I've been in a plane, that I recall anyway. Also, I think your summation is more accurate. We don't actually know whether it costs more people their lives then it saved. It's possible many of those who survived would have died without lifejackets and many of those who died would have died anyway. Nil Einne (talk) 13:16, 13 October 2008 (UTC)

coincidentally, yesterday:

Safety investigators will now ask passengers if they were using any electronic equipment at the time of this latest incident. "Certainly in our discussions with passengers that is exactly the sort of question we will be asking - 'Were you using a computer?'," The Courier Mail quoted an Australian Transport Safety Bureau (ATSB) spokesman as saying. The ATSB said the pilots received messages about "some irregularity with the aircraft's elevator control system", before the plane climbed 300 feet and then nosedived. [2] but apparently they've decided laptops were innocent.

that article does contain the following surprising (to me) sentence, though: In July, a passenger clicking on a wireless mouse mid-flight was blamed for causing a Qantas jet to be thrown off course, according to the Australian Transport Safety Bureau's monthly report. Gzuckier (talk) 05:33, 11 October 2008 (UTC)

Thanks, everyone, for your responses! --NorwegianBlue ^talk 12:52, 11 October 2008 (UTC)

This one on the same incident also mentions modems and previous cases [3] Nil Einne (talk) 13:12, 13 October 2008 (UTC)

Now seems that in the specific case that brought all this to light, it wasn't interference [4]

problem sum

a constant retarding force of 50 newtons is applied to a body of mass 20 kilograms moving initially with speed of 15 metres per second. how lomg does the body take to stop —Preceding unsigned comment added by 77.31.137.209 (talk) 16:22, 10 October 2008 (UTC)

Not that we should solve homework problems for you, but consider that a newton is a kilogram meter per second squared (kg*m/s²) and simple factor label cancelling (i.e. do the algebra with the units to figure out how to multiply and divide the numbers) should give you the answer. The article I linked shows the basic framework for solving problems like this. --Jayron32.talk.contribs 16:51, 10 October 2008 (UTC)

While I would probably do the same as you, the more standard approach is the learn the constant acceleration formulae. Pick the appropriate one of them along with F=ma and substitute in the numbers. --Tango (talk) 16:58, 10 October 2008 (UTC)

True, but that requires one to either memorize a list of formlas, or to be able to work the calculus on one formula to derive the rest. The nice thing about the factor-label method is that it requires learning a single method that is broadly applicable accross MANY fields. It will get you the right answer, for example, in any high school or introductory collegiate chemistry and/or physics class for, quite literally, 90% of the homework problems you will get. One method, 90% of the problems. The "learn every formula method" also works, but is, IMHO, more labor intensive and time consuming. --Jayron32.talk.contribs 17:33, 10 October 2008 (UTC)

Couldn't agree more, but it's generally best to help someone get to grips with the method they're being taught (which is almost certainly the memorise formulae method) rather than teaching them a whole new method. --Tango (talk) 19:01, 10 October 2008 (UTC)

You've all forgotten that the dimensional analysis, while certainly very useful, is no substitute for knowing why you're multiplying things in the first place--it's simply a way to check that you haven't combined units in a nonsensical way. For example, for energy stored in a spring, you may be tempted to use U = kx^2, when the formula is actually (1/2)kx^2. If you were to merely use dimensional analysis you would arrive at the wrong answer. Actually, the best way is to learn everything, including the calculus behind it. Then you'll never have any doubt as to whether the formula has a 1/2 or not; just do the integral. --M1ss1ontomars2k4 (talk) 21:03, 11 October 2008 (UTC)

Actually, you don't even need calculus to get the constant acceleration formulae, you can work them out geometrically from distance/time and velocity/time graphs (well, I guess you could say it's calculus because you need to know how to interpret the area under the curve, etc., but you don't actually need to integrate or differentiate anything). But you are correct that the method does mean you are occasionally out by a factor of two (it's always two...), but I generally ignore factors of two, they're rarely important! ;) --Tango (talk) 22:56, 11 October 2008 (UTC)

threshold logic synthesis

can anybody help me to know how to find the false vertices for threshold logic synthesis....... —Preceding unsigned comment added by Sveta rathi (talk • contribs) 19:04, 10 October 2008 (UTC)

Wikipedia has an article on Logic synthesis that also has a long list of referenes and other links at the end. This may be a good place to start. --Jayron32.talk.contribs 19:20, 10 October 2008 (UTC)

"Virgin birth" in a shark

http://ap.google.com/article/ALeqM5gV-UePymWuPU7HFxNgUXRUrakU1wD93NPTM80

How did this exactly happen? Can the same thing happen to humans? --Emyn ned (talk) 20:07, 10 October 2008 (UTC)

The process is called parthenogenesis. (Our article discusses the matter in some detail.) Briefly, there's never been a substantiated case of parthenogenesis in any mammal (including humans) in the wild. Induced parthenogenesis has apparently been demonstrated in rabbits and mice, producing viable offspring. Human parthenogenesis has been demonstrated to the extent of creating human embryonic stem cells from unfertilized eggs, though no human beings have been born via this method. TenOfAllTrades(talk) 20:22, 10 October 2008 (UTC)

it's not too hard to make an egg cell of any animal start to divide, even if not fertilized; it's all caused by a bunch of calcium entering, calcium being a handy ion in organisms for signals like that, it's not too scarce like magnesium and not too abundant like sodium. The chromosomes provided by the sperm actually don't have anything to do with triggering the egg's development, but the whole thing is set up that the arrival of the sperm triggers that calcium influx which starts the division, and the arrival of the chromosomes in the same package is basically a happy accident. but you can trigger the calcium influx via drugs and things in eggs of many species and away they go. once the cell starts the process of dividing and then duplicating chromosomes and dividing again, the fact that it only has one set of chromosomes instead of two gets fixed as that set gets duplicated after a cell division. (the other product of the division has no sets of chromosomes, and just sort of fades away, but that's not a problem; cells early in the division process aren't specialized yet, each one can produce a complete embryo if they're separated, that's where identical twins come from.) so at that point you've got a dividing egg cell with two sets of chromosomes, and you're on your way. the fact that both sets are identical isn't critical, but of course any undesirable recessive genes will pop up.

in sharks? well we're seeing a lot of it now, because we didn't look for it before, so it's likely that some mechanism has evolved which can trigger the egg reasonably frequently without the need for sperm. there are other species which don't have males at all, of course, so this is just a less emphatic version of that. might happen occasionally in other animals too; people for instance. it would be hard to prove, particularly if it was pretty rare. there is this one story about a virgin, a couple of thousand years ago.... Gzuckier (talk) 20:29, 10 October 2008 (UTC)

It could happen in humans, I believe. Unfortunately or fortunately, only females would be produced in such cases, due to the XY sex chromosome thing. Imagine Reason (talk) 04:15, 11 October 2008 (UTC)

i really should know this but

how do volumes add in a liquid solution? i know all about partial pressures, etc. but if 10 ml of alcohol is added to 90 ml of water, is the result 100 ml? how about when dissolving solids in a liquid? thanks. Gzuckier (talk) 20:18, 10 October 2008 (UTC)

Unfortunately, there's not a simple answer to this one. In general, the volume of a solution will not be equal to the sum of the separate volumes of its components. In other words, if you add 10 mL of ethanol to 90 mL of water, the final volume will come out to be slightly less than 100 mL (about 99.5 mL, actually). This discrepancy will depend on the compounds being mixed, and on their proportions. (If you add 40 mL of ethanol to 60 mL of water, the final solution will be a shade less than 98 mL volume.) Dissolving solids in liquids has similar problems.

Conceptually, you can think of the molecules of solute being able to at least partially occupy gaps left between the loosely-packed solvent molecules, but that's an awfully hand-waving description. TenOfAllTrades(talk) 20:44, 10 October 2008 (UTC)

As a more detailed description, consider that there is in the individual pure liquids, the macroscopic "volume" property is determined by a microscopic property we can call "intermolecular distance" that the molecules seperate themselves by. So, there is a water-water intermolecular distance and a ethanol-ethanol intermolecular distance. When you mix the two, you create a new interaction, the ethanol-water interaction, which is a shorter distance than either the ethanol-ethanol or water-water distance. This makes sense if you consider that in order to for two substances be miscable, the molecules of each substance must be more attracted to each other than to themselves.(if the water and ethanol were more attracted to themselves than to each other, then the two would merely aggregate seperately, and would not mix). More attractive force means shorter distance between them. So a solution of two substances should always occupy a smaller volume than the sum of their pre-mixed volumes. --Jayron32.talk.contribs 23:13, 10 October 2008 (UTC)

That's a completely different description. The first one is wrong, and just happens to partially explain a little. — DanielLC 16:22, 11 October 2008 (UTC)

Wow. I mean, really? Come on guys, let's keep our feet on the ground. Yes intermolecular forces in the solution will increase with the presence of a solute (except when combining immiscible solutions), but the resulting change in volume is unnoticeable unless you have spectacular equipment or a tremendous amount of material. When you add salt to water the melting point may drop but the volume does not, even though the packing of molecules in the liquid changes significantly. For all intents and purposes the OP's original intuitions are correct: 10ml EtOH + 90 ml H2O = 100ml. The only real concerns with respect to change in volume when adding liquids is whether or not they'll react, causing product to evolve out of solution or causing the temperature of solution to change. --Shaggorama (talk) 05:02, 13 October 2008 (UTC)

Er no, really really, the OP asked whether volumes add, and gave an example. The answer is no, they almost never exactly add, and in particular it's "close but not quite" for the example given. The why is a different story, but volume of mixing is a real phenomenon (and can be greater or less than the sum of the parts). Mixing a solute into a solvent and looking for change in solution (vs solvent) volume is indeed often a small deviation. But still, that's just a question of temperature whether the solute is solid or liquid, not something about the solution. You can dissolve a heck of a lot of sugar in water and only get a marginal increase in volume, which just proves that volumes often don't add, even approximately. DMacks (talk) 05:11, 13 October 2008 (UTC)

There seems to be a pretty clear consensus here so maybe I should just sit down and shut up, but I've taken chemistry through college level orgo and the phenomenon at hand never reared its ugly head. I maintain that for all intents and purposes it can be ignored. Unless the op is in a high level course (in which case they certainly wouldn't be asking this question) then the phenomenon can certainly be ignored for the purposes of performing ceteris peribus chemistry math on paper. Furthermore, the quantities of solution and necessary significant figures they will be using in lab preclude concerning about it there. I'm not denying that the phenomenon exists, I'm arguing that :

1. it's not even close to as significant/noticeable as has been suggested, and
2. we should therefore be advising the op not to worry about it and do the math intuitively since that's what they'll be observing in the real world.

Dmacks, I don't know where you're going with the sugar example. I introduced the salt example to illustrate that intermolecular forces do not cause significant decrease in volume, as had been suggested earlier. That adding solid solute offers effectively no change to volume, as you pointed out in the sugar case, lends support to my stance. I hadn't suggested that solid + liquid adds the same way as liquid + liquid. Feel free to elaborate if I misunderstood. --Shaggorama (talk) 06:16, 13 October 2008 (UTC)

I think you did understand but maybe are seeing a false dichotomy. There are indeed two issues: does solvent volume change when a solute is added and does the total volume change add when two volumes are mixed. Common experience says "little if any" to the first (salt or sugar in water) and "approximately yes" to the second (alcohol plus water). But wait...those are contradictory positions! If adding solute doesn't much affect the solution volume, the solute acts as if it has no volume of its own. Otherwise, if adding a volume of solute increases the solution volume by its volume, then the whole intermolecular-attraction and fills-in-the-spaces idea is wrong. Now here's where I think you misunderstood. There's no intrinsic difference between "chemicals that are solids" and "chemicals that are liquids", and there's no memory once in solution whether the solute happened to have been a solid or liquid. Solid+liquid vs liquid+liquid is just a matter of whether the experiment is done at a high enough temperature that the solute melts. I picked sugar just as a parallel example to salt, but as something that can be melted easily to ponder whether "physical state" matters. DMacks (talk) 06:44, 13 October 2008 (UTC)

You make a good point and I'm inclined to agree with your reasoning, but that doesn't make the phenomenon itself any stronger. You could never actually add liquid sugar to liquid water because sugar melts above water's boiling temperature. Once you dissolve sugar to add it to pure water as an aqueous solution, you're end result is still mostly water and the volumes will add intuitively. Perhaps I should have qualified my rule-of-thumb for aqueous solutions, but I'm fairly certain it holds true in hydrophobic solutions as well. I'm inclined to agree with you on the "false dichotomy" you pointed out, but in empirical terms solids that dissolve in water do not significantly change the volume of solution, and liquids do (maybe because they are solutions in water). --Shaggorama (talk) 07:16, 13 October 2008 (UTC)

How about trying to mix some liquid water with alcohol at just above  °C and mixing that same amount of water as ice with the same amount of alcohol at just below  °C until they dissolve, then compare the volumes. DMacks (talk) 19:10, 13 October 2008 (UTC)

What is the movement of a submarine called?

Sailing? Driving? —Preceding unsigned comment added by 87.165.220.170 (talk) 20:55, 10 October 2008 (UTC)

'Sailing' appears to be a widely-used, widely-accepted term. (Google submarine sailed or submarine sailing to see many, many examples of usage.) 'Driving' is definitely not. TenOfAllTrades(talk) 23:30, 10 October 2008 (UTC)

It's odd that, for ships, at one time "sailing" was updated to "steaming" but now seems to have reverted to "sailing" even though the technology has gone somewhere else entirely. I guess dieseling, electricking or nuclear reacting just don't roll off the tongue. SpinningSpark 12:41, 11 October 2008 (UTC)

So we sailed up to the sun . . . in our yellow submarine - Lennon-McCartney

Sudden moon

I am writing a story set on a planet that has suddenly acquired a moon. For the purposes of this question, just assume it suddenly appeared and that both the planet and moon are the same size as ours.

I'm trying to work out exactly the nature and scale of the disasters this would cause. All I've got so far are extreme tidal waves and flooding, but would there also be earthquakes? I think it would probably result in massive unbalancing and possibly death among nocturnal species, not to mention the probable extinction of a lot of tidal zone species. What else, though?

While I'm at it, what would a world be like that did not have a moon? It would have very small tides thanks to the sun, and would always be very dark at night... One of my friends claims that it wouldn't have seasons, but I find that dubious. Any thoughts? --Masamage ♫ 21:12, 10 October 2008 (UTC)

I don't think you would get anything more drastic that we get every day, since as the Earth rotates different parts of the Earth are affected by the moon's gravity (you might get some problems immeadiately after the arrival since you would have the effect of 6 hours worth of tidal change in an instant [although the magnitude of the tides would be the same as for the Earth], but that wouldn't last long, although the damage from it might). The fact that life wouldn't be used to the tides would be a problem, certainly, but I think that's about it (and remember, it's just increased tides, not new tides, because of the sun). As for a planet without a moon, it would probably affect the seasons, but it wouldn't preclude having them. Seasons are caused by the rotational axis being tilted with respect to the orbit, the moon may well have affected our axial tilt, but having a moon isn't a requirement to have one. The day would also be shorter, since the same tidal forces which mean the moon always shows the same face to Earth are gradually slowing the Earth's rotation, without the moon that wouldn't have happened so the day would be a few hours shorter (I'm not sure how many, but I believe it's been measured by looking at fossilised coral). I read somewhere that the moon has helped stabilise the Earth's rotational axis, but I'm not sure how, so the seasons may be more variable without a moon (although probably on the scale of centuries at least). --Tango (talk) 21:31, 10 October 2008 (UTC)

Instantaneous appearance? You'd get at least the following:

1. A sudden shock as the planet shifts from following a simple orbital path around its sun to the sine-wave pattern the Earth follows. (The center of gravity of the Earth-Moon system follows an elliptical path around the Sun; the Earth and Moon orbit that center of gravity with a period of one Lunar month).
2. Gradually-increasing tidal heights, with the final tidal range being about three times what it used to be. Timing of the high tides will also change. You won't get tidal waves because the water has a long way to flow to adapt to the new gravity patterns, and it doesn't move very fast. At a guess, it'll take a month or two for the tides to reach their final heights.
3. More earthquakes. They won't be stronger, and they might be weaker, because of increased tidal flexing of the crustal plates.
4. Disruption of activity for many species: some night-active species will have trouble being active during full moons; some day-active species will stay active at night during full moons.
5. Increased predation of day-active prey species. The increased night-time lighting means that camoflage patterns and sleeping habits are no longer adequate for protection. It'll take about five years for the resulting boom-and-bust of night-active predator species to settle out.

Over the long term, you'd see the following:

1. More reliable seasons. Adding a large moon will stabilize the planet's rotation axis, so the strength of the seasons won't change over time (millions to billion of years)
2. An increase in the number of night-active species. More light means it's easier to move around at night. (hundreds to tens of thousands of years)
3. A reduction in meteor impacts: the Moon provides some protection against meteors by variously blocking them, causing them to break up, or throwing them out of Earth-crossing orbits.
4. An increase in volcanism: the increase in tidal flexing will increase the temperature of the planet. (Hundreds of thousands to millions of years)

Hope this helps. --Carnildo (talk) 22:58, 10 October 2008 (UTC)

If you are interested in this subject, and want to see how another author has treated a similar situation (though not exactly the same), may I recommend Jack McDevitt's book Deepsix, it has some interesting descriptions of weird tidal effects caused by two large planets on a collision course. Its part of his "Priscilla Hutchins" series, and is an enjoyable read. --Jayron32.talk.contribs 23:05, 10 October 2008 (UTC)

Why would it take months for the tides to reach their maximum? The water doesn't need to move any faster than it does on Earth and it can go all the way round the Earth in 24 hours (well, individual bits of water don't, but you know what I mean). --Tango (talk) 23:13, 10 October 2008 (UTC)

On Earth, the tides have had billions of years to build up momentum. The Moon's gravity isn't very strong, so the water doesn't accelerate very fast. --Carnildo (talk) 23:29, 10 October 2008 (UTC)

That's utter nonsense.

The water oscillates back and forth twice per day. So the momentum builds up slowly over about six hours then back the other way over the next six. It doesn't "build up" over millions of years. The tides would settle into their regular pattern in about a day or two. I think there could be no earthquakes or anything because the earth too squeezes and stretches in a cycle over 12 hours and we don't see particular problems because of that. I agree though that the SUDDEN arrive of a few gigatons of stuff in orbit would very abruptly jerk the planet in it's orbit - and that would be utterly disasterous - all of the oceans and atmosphere would slosh violently - possibly flying off the planet completely...it's hard to imagine any life surviving that. But if the moon somehow slowly spiralled into position over decades - then I think it would have fairly benign effects (well, crazy weather - tides where they'd never been before - flooding, rivers running backwards...but definitely something you could survive). You'd also have to consider the consequences of the moon suddenly being dumped into the much stronger gravity well of the planet. Since we have no knowledge of the "magic" that makes the moon suddenly teleport into place - we can't guess what forces that entails - but it might well break up, ending up as a truly spectacular ring system...or possibly raining death and destruction onto the surface. SteveBaker (talk) 01:12, 11 October 2008 (UTC)

The change in orbital motion would not cause a "shock"; each planet is in free fall, and would continue falling freely even if in a different direction. The only "sudden shock" would be from tides: expect a lot of earthquakes at first. —Tamfang (talk) 01:39, 14 October 2008 (UTC)

hydrogen reaction

Will a balloon filled with pure hydrogen and pierced with a needle made of palladium explode/combust? —Preceding unsigned comment added by Kaufmann1 (talk • contribs) 21:57, 10 October 2008 (UTC)

Not unless the palladium is particularly hot. Palladium can act as a catalyst for certain reactions involving hydrogen, however as far as I am aware, it does not lower the activation energy of the combustion reaction enough to cause it to become spontaneous. --Jayron32.talk.contribs 22:56, 10 October 2008 (UTC)

Pure hydrogen? What would it react with? --Carnildo (talk) 22:58, 10 October 2008 (UTC)

The oxygen in the atmosphere outside the balloon, presumably. Algebraist 23:05, 10 October 2008 (UTC)

Our article on palladium says it can absorb large amounts of hydrogen. I'm not sure if that reaction releases energy, but I doubt it would do so to the extent of causing an explosion. --Tango (talk) 23:10, 10 October 2008 (UTC)

Where can I get a palladium needle, to try the experiment? Edison (talk) 19:30, 11 October 2008 (UTC)

You would probably have to turn it into a needle yourself, but you could buy a palladium coin here (for about $200, although they're out of stock apparently...). --Tango (talk) 22:51, 11 October 2008 (UTC)

However, a needle or other solid form is just about the worst you can do if you're trying to get a rapid reaction. The reaction between a gas and a metal (or "chemical adsorbed or absorbed onto/into the metal" happens at the metal surface, so the bulk of the solid metal below the surface is useless. Much better to use powdered Pd (or Pd coated on some other powder) or a porous matrix. The large surface area allows much more rapid reaction. I've seen active metals like Pd and Pt supported on powdered charcoal--the form commonly used for lab-scale catalytic hydrogenation reactions--lead to combustion with atmospheric oxygen even without substantial hydrogen present (I'm sure helped by the charcoal being flammable). DMacks (talk) 18:46, 12 October 2008 (UTC)

Mars climate

How does climates on Mars work?Does temperats range by latitudes, seasons or night-and day. Ithouhgt Mars is a very cold planet, often colder than a freezer, and the average planet temp is around minus 67 F. Is that the mid-latitude average surface temp? I thought only tropical zones of Mars or low latitudes get temp range from +10 to +69 F.--Freeway91 22:15, 10 October 2008 (UTC)

Interestingly, we have an article on that: Climate of Mars. --Jayron32.talk.contribs 22:58, 10 October 2008 (UTC)

The variation of temperature with latitude, seasons and day/night don't really depend on the planet so much as how it moves around the sun. Pretty much all of the planets have all of those things (with the sole exception of Mercury which keeps the same face pointing towards the sun all the time - so it doesn't have day/night cycles).

• Variation by latitude is because the planet is round and the sun's rays spread out more at the poles than at the equator.
• Variation by season is because most planets are doing their daily rotation about an axis that's tipped over somewhat. This means that the suns rays are more spread out at some times of the year than others. For planets with very elliptical orbits, there is a variation due to distance from the sun too.
• Variation between night and day is because the sun isn't shining on the surface at night.

So all of those things vary on all planets that are round, have an axial tilt and rotate on their axis...and that includes Mars.

SteveBaker (talk) 00:47, 11 October 2008 (UTC)

Actually, Mercury isn't tidally locked (although astronomers did think it was at one time). See Mercury (planet)#Spin–orbit resonance. --Tango (talk) 00:55, 11 October 2008 (UTC)

Seconded. Apparently Steve is stuck in 1964;-) --Stephan Schulz (talk) 01:01, 11 October 2008 (UTC)

In more ways than you can imagine! SteveBaker (talk) 01:20, 11 October 2008 (UTC)

So isn't temperate zone on Mars lattide of 30+ always or often below 0, and lattitude of 50+ alwas colder than Greenland? Generally, Mars I thought is very cold.--Freeway91 01:04, 11 October 2008 (UTC)

Because of its thin atmosphere it doesn't retain heat well, so at night it is going to be extremely cold regardless of your latitude. During the day, it will be warmer the nearer the equator you are (well, not quite the equator due to the axial tilt). I don't know any numbers off the top of my head, but they shouldn't be too difficult to find with a bit of googling. --Tango (talk) 13:53, 11 October 2008 (UTC)

October 11

gas constant?

why should we use a constant for gas equations?where does the universal gas constant come from?i couldn't find any information about history of gas constant(R)? —Preceding unsigned comment added by 88.242.106.180 (talk) 00:57, 11 October 2008 (UTC)

You may want to have a look at gas constant and Boltzmann constant for a more detailed treatment of the topic. Briefly, the gas constant (R) is a proportionality constant which describes how much energy is stored in a mole of (ideal) gas molecules per degree of temperature. (The related Boltzmann constant, k_B, describes the quantity of energy per molecule.) TenOfAllTrades(talk) 01:40, 11 October 2008 (UTC)

A pity nothing is said in the articles about experiments like in de:Universelle_Gaskonstante#Ein Experiment zur Ermittlung einer Näherung der Gaskonstante, or how the constant was measured to this accuracy. --Ayacop (talk) 09:26, 11 October 2008 (UTC)

If you can translate from the german, the English Wikipedia articles could probably benefit from your help. --Jayron32.talk.contribs 12:46, 11 October 2008 (UTC)

Back to the gas constant. The SI system was carefully constructed to in general, avoid these sort of proportionality constants. Many calculations would require them, except that the units are defined to be compatable in ways that generate proprotionality constants of "1". The situation with "R" is because the SI unit for temperature, kelvin, is created not to be compatable with other SI units, but be compatable with the Celsius scale. Since the size of a Celsius unit is arbitary (there's nothing inherently useful about being 1/100th the difference between the sea-level freezing and boiling points of water), the size of the kelvin is arbitrary as well. One could define a temperature scale where 1 degree was equal to the the amount of energy contained by 1 mole of molecules, and under THAT scale, R would be equal to 1. However, for other reasons of convenience and history, we use the Kelvin scale, so we are stuck with a non-unitary R values. --Jayron32.talk.contribs 13:00, 11 October 2008 (UTC)

I'm not entirely sure I'd agree with that. While interconversion among SI units is very straightforward and generally avoids weird proportionality constants, such constants are almost always necessary in calculations which describe physical processes in the real world. (The energy of a photon is equal to its frequency multiplied by 6.626x10^-34: the Planck constant; the gravitational attraction between two bodies is the product of their masses divided by the square of their separation distance, multipied by 6.674x10^-11: the gravitational constant. And so forth.)

The seven base SI units trace their roots to essentially arbitrary roots which don't have any universal scientific or physical significance. (The meter was originally based on a rough measure of the Earth's circumference; the second on arbitrary divisions in the length of Earth's day; the kilgram tied to the density of water.)

To get rid of arbitrary constants of proportionality, physicists will resort to systems of so-called natural units which peg most physical constants to be exactly 1. Under (for example) Planck units, the speed of light, the gravitational constant, the reduced Planck's constant, Boltzmann's constant, and the Coulomb force constant are all set to be 1, and other units defined from there. Such systems can make calculations dramatically 'neater' and eliminate the risk of 'losing' a constant in a complicated expression. The downside of such systems is that they generate base units which aren't convenient for 'everyday' usage. (The base unit of temperature in Planck units is about 10³² kelvin, and the base unit of time is about 10^-44 seconds.) TenOfAllTrades(talk) 14:51, 11 October 2008 (UTC)

Use of Oil

Generally what percentage of a barrel of oil is used strictly for fuels such as gasoline and diesel? How much is used for plastics and other products? I had heard that oil used for fuels was low - around 20% - and the bulk of every oil pumped out of the ground was for other products like plastic. Is this true142.68.216.154 (talk) 02:35, 11 October 2008 (UTC)

You might want to look at this link [5]. Which deals with oils use for energy. Only 20-30% of the energy we use goes to transportation but almost all of that energy comes from oil. I know that doesn't answer you question but it is probably the origin of you mangled statistic. What comes out of a barrel of oil depends on what the oil is like (where it was found) and how you crack it but this link gives you and idea of how an average barrel gets fractioned [6]. The key chunks of plastics are mostly derived from natural gas. The other components are derived from side products in process of refining oil for gasoline/diesel. Transportation fuel is the largest and most powerful market for oil, plastic just removes 4.7% of the barrel of what would other wise be a waste stream to burn for heat/electcity or maybe converted into hydrogen. In addition consumers can afford to pay more for natural gas to heat their homes and produce electricity than chemical producers can afford to pay for natural gas as a feed stock. The price of natural gas in North America has forced many chemical producers to close up shop and move to places with cheaper natural gas like the Middle East and Africa. I think BASF cited this when they closed plants around 2005 among other companies. I hope that helps.--OMCV (talk) 03:28, 11 October 2008 (UTC)

yeah, the demand for gasoline/fuel oil basically requires economically to "crack" as much of the petroleum that can possibly be used into the proper weights. In addition, the advent of fuel injection and the associated in-tank fuel pumps have made it possible to add the lighter petroleum fractions into gasoline which would have created a lot of vapor lock in the carbureted engines with the fuel pump on the engine, and used to be disposed of. In fact, (according to what i read) the vapor pressure on gasoline has risen enough even just in a decade or two to saturate the vapor capture systems on cars from the 80s. basically, any oil that goes into plastics is leftovers that would otherwise be waste. Gzuckier (talk) 05:22, 11 October 2008 (UTC)

Plants with edible stems

Are there plants other than Rhubarb with edible stems?74.50.200.72 (talk) 06:41, 11 October 2008 (UTC)

Cattails Ζρς ι'β' ^¡hábleme! 07:18, 11 October 2008 (UTC)

Leeks and spring onions are commonly eaten in the UK. Axl ¤ [Talk] 07:20, 11 October 2008 (UTC)

The pedia does it again -- try Edible plant stems for a nice list of munchies. (It doesn't mention mushroom stems/stalks which are not notable but edible.) Julia Rossi (talk) 07:25, 11 October 2008 (UTC)

Mushrooms are also not plants. —Ilmari Karonen (talk) 07:33, 11 October 2008 (UTC)

(ec) A lot of herbs are edible in the whole (or at least their above-ground parts are), so I guess they count. At the other end of the scale, pine phloem is edible (if not very nutritious), though the whole trunk isn't. —Ilmari Karonen (talk) 07:31, 11 October 2008 (UTC)

Rhubarb's culinary cousin Celery certainly qualifies, doesn't it?--Jayron32.talk.contribs 12:44, 11 October 2008 (UTC)

Noisy faucet

My kitchen faucet, which works well otherwise, makes a high pitched whine when running hot water through it. Why? Dismas|^(talk) 15:19, 11 October 2008 (UTC)

There is some air in the pipes. As the air flows through the the narrow opening, it makes a sound. Axl ¤ [Talk] 18:50, 11 October 2008 (UTC)

As water flows through your faucet, there may be regions of turbulent flow; there may also be areas of lower pressure created by the flowing water. (See Bernoulli's principle for more details on how that might arise.)

Turbulence and low pressure can generate noise in at least a couple of ways that would be more dramatic with hot water than cold. First, the solubility of air (mostly oxygen and nitrogen) drops with increasing temperatures. In other words, cold water that left the treatment plant or well saturated with air will be supersaturated after being heated in your water heater. The reduction in pressure and increase in turbulence as the water approaches your faucet will encourage that air to come out of solution and form bubbles; turbulent movement of bubbles generates noise.

Even in the absence of dissolved air, you might still see effects due to cavitation. Hot water has a higher vapor pressure than cold, and hot water may actually boil in regions of low pressure within the plumbing. The formation and subsequent collapse of bubbles of water vapor can generate noise as well. TenOfAllTrades(talk) 19:06, 11 October 2008 (UTC)

Quote identification

With regard to the Fermi paradox: "If there are so many alien civilizations, why haven't they visited us? I decided to do an experiment. I wanted lobsters for dinner. I put a plate on my table, sat down, opened the front door, and waited for a lobster to crawl onto my plate. Three hours later, no lobster came. I ended the experiment, concluding there are no lobsters in the world."

This "quote", which is obviously not word-for-word, is from a show that aired on Discovery Channel a few years ago. --99.237.96.81 (talk) 16:34, 11 October 2008 (UTC)

Lobsters are not a highly intelligent species in an advanced technological civilization with a desire to explore the universe. Axl ¤ [Talk] 18:56, 11 October 2008 (UTC)

If they were, is it a given that we would even notice? ;) --Kurt Shaped Box (talk) 02:01, 12 October 2008 (UTC)

A bad analogy is like a pickle playing chess. TenOfAllTrades(talk) 19:12, 11 October 2008 (UTC)

A quick web search indicates that the story is variously attributed to "a SETI offical", and Timothy Ferris (who is not a SETI official). Ferris is a science popularizer, though, so he may be quoting someone else (or he could be the originator - it's hard to tell). I can't find anything that looks like an "original" source. (Most web hits for "lobster Fermi Paradox" are for Accelerando (book).) -- 128.104.112.147 (talk) 19:42, 11 October 2008 (UTC)

Thanks, but I was actually looking for the name of the show I saw the quote on. --99.237.96.81 (talk) 22:42, 12 October 2008 (UTC)

Well, the other issue is that we may be the only advanced civilization in our galaxy, but our galaxy is such an isignificant fraction of the whole universe its hard to say definately we are the only ones. Back to the lobster analogy, imagine putting out your plate and waiting for a lobster to crawl on it from the moon. There universe may be teeming with advanced civilization, but we lack the ability to detect evidence of it because its too far away. --Jayron32.talk.contribs 20:17, 11 October 2008 (UTC)

The Fermi paradox is really a pretty shakey proposition. We are a civilisation - have we visited any alien species? Could we even if we knew which star system thay lived at? Even if they lived on Proxima Centauri (the closest star to the Sun) - we currently have no clue whatever how we could get to them. Why would we expect that other civilisations would have any better ideas than we do?

Even if they are smarter than we are - or have simply been around a lot longer...if travel between the stars is impossible for us right now - maybe it's impossible, period. Worse still - how do they know we're here? Our SETI detectors are unable to detect a signal unless it's either beamed on a narrow-beam directly at us - or a broadcast signal that's VASTLY more powerful than the most powerful signal we've ever sent into space. We don't routinely beam narrow-beam signals at stars - so they would need much more powerful radio receivers than we currently have in order to hear us...and again - if we don't know how to do that, why should we assume that the aliens do?

Also, we've only been transmitting radio signal with any strength out into space for less than a hundred years - so only aliens within 100 light years could possibly know we're here - and only those within 50 light years could possibly have gotten here after hearing us...if it took them a while to plan the mission and get it funded and launched - they might have to be much closer to have gotten here yet. There are only 1000 stars within 50 light years - and only 50 or so within 20 light years. It's perfectly possible that none of those 50 stars have planets suitable for life.

From what we know - even if aliens are REALLY common around our galaxy - and even if they have close to light-speed travel and radio receivers that are vastly more sensitive than ours, it would STILL be quite surprising if they were able to get here to visit us. Far from being a paradox, Fermi's claim is just wrong.

SteveBaker (talk) 01:28, 12 October 2008 (UTC)

That's assuming that they'd even be interested in contacting us. What's to say that they wouldn't view us as savage, warlike, power-hungry carnivorous beasts with just enough brainpower to be a potential threat to *their* peace-loving civilization should an encounter occur - and decide to steer well clear? Either that, or they see that we're just lumps of meat restricted to 3-dimensional space with no subspace hivemind capability and think 'bleh - who cares about that?'. ;) --Kurt Shaped Box (talk) 02:14, 12 October 2008 (UTC)

Perhaps they're preparing an application for a hyperspatial express route? Axl ¤ [Talk] 09:49, 12 October 2008 (UTC)

Or they've seen what we do to the lobsters whenever they venture forth from the ocean in an attempt to engage in peaceful communication with us... --Kurt Shaped Box (talk) 19:13, 12 October 2008 (UTC)

We are very young on an astronomical scale, and we are advancing at a significant rate. For the purposes of the Fermi paradox, we are not advanced. We have never left this solar system, but we currently emit very large amounts of radio waves, and have even done so with the intent of contacting aliens. We are currently quite capable of interstellar travel, as can be seen by Project Daedalus. Unless advanced civilizations stop sending stop sending out signals, there would logically be roughly spherical areas around where each one began where all, or at least many, of the stars are emitting suspiciously large amounts of a small band of electromagnetic waves. — DanielLC 16:07, 12 October 2008 (UTC)

I've got to disagree.

Project Daedalus is a joke - it requires Helium-3 as a fuel. Which they propose to mine from Jupiter over a 20 year period using robotic probes...we are SO far from even being able to start making the robots that would autonomously mine the fuel for the darned thing - we're nowhere CLOSE to being able to do that. The craft itself weighs 50,000 tons...getting that into orbit would require 2,000 shuttle launches! And all of that to get a small number of teeny-tiny robotic probes to one of the nearest stars. Worse still - those probes would shoot past the star at 12% of the speed of light - leaving only a very short period for observation and science! It's also true that this is not just a matter of science. There is also the matter of politics. There is no conceivable way of getting a government to fund a massive 20 program to mine fuel for a 50 year program which would take another 6 years to report back results. Worse still - nobody who was alive at the start of the program would be alive at the end. The cost of launching the components into orbit alone would be 160 times the cost of the ISS! With present funding levels, NASA would be doing nothing else for a thousand years! Politicians will never allocate that amount of funding to achieve a goal that not one of their voters will live to see through to completion. All of this for at most a couple of hours of science data captured at such a high speed that detailed photography would be impossible! A thousand years of funding for a probe that might just fail when it gets there? I don't think so.

No - we REALLY don't know how to do interstellar travel...not in any kind of practical manner. If aliens managed to build a Daedalus - it would pass us by so quickly that we'd never notice it passing.

You say that we're pushing out a lot of radio waves - but not on an interstellar scale. Recall that the very best radio telescopes we have would be unable to detect broadcast signals of the strength we're putting out from a distance of the nearest star.

You say that we're young on an astronomical scale - perhaps we are - but perhaps we're already pushing the outer limits of what's possible? Because we can't know that there are vast improvements in space technology out there - it's perfectly possible that we're already close to hitting the limits. You can't claim that it's paradoxical that we haven't seen any alien visitors - it's perfectly reasonable given what we know. More to the point - I could claim that because we haven't seen any aliens (and the math makes it seem like there must be lots of them out there) then it must be that we're close to the limits of the technologically possible.

SteveBaker (talk) 20:56, 12 October 2008 (UTC)

Isn't there a theory doing the rounds that radio waves of the strength we tend to emit will peter out into the background radiation after a couple of light years? I seem to remember reading about that a while back. --Kurt Shaped Box (talk) 19:09, 12 October 2008 (UTC)

You're assuming that aliens would have to be specifically contacting us. I've always understood the paradox to be that the aliens should have reproduced, or created replicating machines all over the galaxy. Star systems are extremely valuable resources, any intelligent civilization that's billions of years old would probably be using a lot of them. Such a civilization could leave artifacts everywhere, and why haven't we found them?

It would only take one run-away planet-eating Von Neumann probe a long enough time ago to give a long dead civilization a long-lasting legacy.

This, of course, assumes that an intelligent civilization can survive for billions of years, and it assumes a whole bunch of scientific advances are possible but that we simply haven't made yet.

I would like to think that by the time humanity is a billion years old that we've at least sent probes out to a significant segment of the Milky Way, Even if we need to dismantle some planetoids to do so. (Sorry, Pluto.) I think it's that kind of hope that drives the Fermi Paradox. APL (talk) 19:02, 14 October 2008 (UTC)

A point that nobody else raised is that there are many kinds of civilizations that are much more stable than our own. The society in Nineteen Eighty-four is an example--without overpopulation, environmental damage, or global warming, it's much more likely to survive for millions of years than a civilization that's developing quickly.

I also don't believe an advanced species would prefer to use radio waves that spread out spherically. If I had the choice, I would send energy to only the intended destination, not to the boundary of the star system. Laser, or at least directional antennas, are much more energy efficient than ominidirectional radio transmitters. --99.237.96.81 (talk) 22:42, 12 October 2008 (UTC)

That's true - directional transmission makes a heck of a lot more sense. But we aren't talking about aliens talking to us...we're talking about aliens LISTENING to us and then coming to visit. We aren't transmitting to them on nice tight, efficient beams - mostly because we don't know where they are so we don't know where to point the radio beams. So they have to find us based on omnidirectional spherical waves that drop in energy as the square of the distance - and are therefore almost completely indetectable after a lightyear or so of travel.

It would be a different story if we had a powerful ultra-tight-beam transmitter tuned at the "water hole" and undertook a program of transmitting the prime numbers as a series of pulses that were sent at regular intervals to each of the 1,000 nearest stars. That would hopefully catch the attention of any civilisation within ~50 lightyears - and you could start looking for responses from them about 100 years from now.

SteveBaker (talk) 20:15, 13 October 2008 (UTC)

would you freeze in space with nothing on

if i went into outer space without a suit would i freeze instantly? why? is there no oxygen or something?--Majorcolors1 (talk) 17:59, 11 October 2008 (UTC)

You wouldn't freeze very quickly, if at all. In a vacuum (ie. when there's no air) the only way to lose heat it by radiation, which is very slow. You would suffocate long before you froze. We have an article on it: Human adaptation to space#Unprotected effects. --Tango (talk) 19:00, 11 October 2008 (UTC)

Well, it also depends on how you were exposed to the vacuum. If your space suit just suddenly disappeared and all the gas surrounding your body expanded rapidly, the gas would cool so rapidly that the outer layers of your body would be chilled to below freezing. If on the other hand, there was only a slow leak in your space suit until there was no air left, you probably would not freeze, unless your spacesuit was conductive. --M1ss1ontomars2k4 (talk) 20:59, 11 October 2008 (UTC)

Yeah, the gas would cool, but it would be nowhere near your body after a fraction of a second, so how would if affect you? And your spacesuit being conductive won't make any difference since there is nowhere for the heat to go, it still has to be radiated. --Tango (talk) 22:46, 11 October 2008 (UTC)

Well, it depends on the temperature of your spacesuit, I suppose. If it were colder than you (it wouldn't be unless you were in the shadow of something, right?), then you might have a problem. But I'd assume that spacesuits are very insulating, or they'd be conducting heat to/from you all the time. --M1ss1ontomars2k4 (talk) 23:14, 11 October 2008 (UTC)

Your spacesuit is in contact with you and nothing else, so it's almost certainly the same temperature as you. --Tango (talk) 23:25, 11 October 2008 (UTC)

I think the most horrifying thing is that without external pressure your bodily fluids begin to boil, starting with the water on your tongue. Plasticup ^T/C 03:28, 12 October 2008 (UTC)

Your skin is able to provide enough pressure to prevent most bodily fluids from boiling - but your eyes, the interior of your nose, lungs and mouth would certainly have problems with that. For water to boil at body temperature, the pressure has to be down below 100mm of mercury - that's about one eighth of an atmosphere. That's about the pressure at 40,000' - but people have successfully flown unpressurized aircraft at higher altitudes than that. Supermarine_Spitfire#Speed_and_altitude_records - for example, shows a flight up to 51,000' at which air pressure is down to about 76mm of mercury - where the boiling point of water would have dropped to 32 degC - 90 degF. SteveBaker (talk) 03:51, 12 October 2008 (UTC)

Perhaps in those instances the gradual pressure change allowed the liquids to boil off more subtly, but there is no doubt that suddenly being thrust into a near-zero pressure environment makes your tongue boil. It actually happened to one unfortunate gentleman. Plasticup ^T/C 05:48, 12 October 2008 (UTC)

While the plane may not have been pressurised they would almost certainly have been wearing an oxygen mask so the pressure on their mouth and nose would be much greater, and wearing a full face mask wouldn't surprise me. They would probably also have had a pressure suit to apply pressure to the rest of their body (although that wouldn't be vital, since skin can do the job in a pinch, as you say). --Tango (talk) 11:43, 12 October 2008 (UTC)

You would certainly freeze, Tango, although not before you suffocated. Heat loss by radiation is given by the Stefan-Boltzmann law: $P=\sigma (T^{4}-T_{0}^{4})A$

where

σ is the Stefan-Boltzmann constant, about 5.7e-8 W/m2K4

T is the body temperature, normally about 310 K

$T_{0}$ is the cosmic background temperature, about 3 K

A is the body surface area, about 1.7 m2

(I'm ignoring the emissivity of skin which is, to my surprise, close to unity. [7])

The result is about P = 879 watts, dropping to about 528 watts at freezing point. That is a significant rate of heat loss. Let's see how quickly you would freeze.

Energy to cool a 75 kg body from 310 K to 273 K: 75 kg x (310 K - 273 K) x 4000 J/kg.K = 11.1 MJ

Energy to freeze a 75 kg body at 273 K: 75 kg x 333 kJ/kg = 25.0 MJ

At an average 700 watts rate of cooling, it would take (11.1 MJ + 25.0 MJ) / 700 W = 14 hours to freeze you solid. But I imagine that, if you were losing heat at 879 W, you would start getting frostbite quite soon after exposure.

--Heron (talk) 15:47, 12 October 2008 (UTC)

That 3K figure is for deep space away from any heat source. If you are in Earth orbit and not in the shadow of the Earth you are more likely to burn than freeze (the average daytime temperature on the moon is 107°C according to our article and that's pretty much the same as being in space at the same distance from the sun). Space suits have sophisticated refrigeration units in them. You would get very cold in the shadow of the Earth, though, so in LEO you would be going from over 100 degrees above to over 100 degrees below every hour and a half or so. Of course, you lose conciousness in about 15 seconds from hypoxia, so it doesn't really matter. --Tango (talk) 17:09, 12 October 2008 (UTC)

Damn Interesting has a great article on exposure in space here

In the absence of atmospheric pressure water will spontaneously convert into vapor, which would cause the moisture in a victim's mouth and eyes to quickly boil away. The same effect would cause water in the muscles and soft tissues of the body to evaporate, prompting some parts of the body to swell to twice their usual size after a few moments. This bloating may result in some superficial bruising due to broken capillaries, but it would not be sufficient to break the skin. -- Within seconds the reduced pressure would cause the nitrogen which is dissolved in the blood to form gaseous bubbles, a painful condition known to divers as "the bends." Direct exposure to the sun's ultraviolet radiation would also cause a severe sunburn to any unprotected skin. Heat does not transfer out of the body very rapidly in the absence of a medium such as air or water, so freezing to death is not an immediate risk in outer space despite the extreme cold. -- For about ten full seconds– a long time to be loitering in space without protection– an average human would be rather uncomfortable, but they would still have their wits about them. Depending on the nature of the decompression, this may give a victim sufficient time to take measures to save their own life. But this period of "useful consciousness" would wane as the effects of brain asphyxiation begin to set in. In the absence of air pressure the gas exchange of the lungs works in reverse, dumping oxygen out of the blood and accelerating the oxygen-starved state known as hypoxia. After about ten seconds a victim will experience loss of vision and impaired judgement, and the cooling effect of evaporation will lower the temperature in the victim's mouth and nose to near-freezing. Unconsciousness and convulsions would follow several seconds later, and a blue discoloration of the skin called cyanosis would become evident.

-- MacAddct1984 ^{(talk • contribs)} 16:08, 12 October 2008 (UTC)

I don't believe you'll get the bends - and I don't believe that your blood would boil. You are making the mistake of assuming that the pressure inside your body drops to zero. It doesn't because your skin is able to exert a force to keep your innards under pressure (to some degree at least). So pressure inside your body will remain at some fraction of an atmosphere. As I explained before - for water at body temperature to boil, you need the pressure to be below one eighth of an atmosphere - and I'd certainly expect your skin to be able to do that...at least for short periods...in the longer term, you're dead anyway. The liquid on the surface of your eyes, inside your mouth and near other orifices will boil because they WILL fall to zero pressure - but not your blood.

As for getting the bends - I'm not sure what the threshold for getting the bends is - but remember that your body is pressurised to one atmosphere when you are just 32 feet underwater - you can happily snorkel to that depth and come up quickly without getting the bends - and that's the same pressure differential as going from normal air pressure into a vacuum. Note also that astronauts have their space suits pressurised at only half an atmosphere anyway (to keep them flexible apparently) - so the drop is more like coming up from 16 feet to the surface...which I can do in any decent swimming pool with a diving board. How many people get the bends in a swimming pool?

SteveBaker (talk) 20:11, 12 October 2008 (UTC)

The above sounds kind of like what was posited in one sci-fi book I read once (set in 2017, astronauts thought they were in space, trapped underground, to get out had to get through this place w/no pressure & properly fitting suit caused some nasty bulging/bruising; someone might know what I mean). But, I always thought that the lack of pressure in space was so huge that one would literally "pop" instantly. I'll have to read that article on exposure to space when i have more time. I guess it wouldn't be as instnat as I thought.Somebody or his brother (talk) 17:00, 12 October 2008 (UTC)

The classic scene is the one in 2001 (movie) when Bowman is forced to cross from the 'pod' into the main spacecraft without a helmet. SteveBaker (talk) 20:11, 12 October 2008 (UTC)

There's also that scene in Event Horizon where Baby Bear gets locked outside of the airlock. IIRC, he bled from his eyes and his veins began to bulge. Mind you, the ship went to hell and back, so anything's possible... -- MacAddct1984 ^{(talk • contribs)} 22:54, 12 October 2008 (UTC)

That's more or less what happened in Total Recall too...it didn't seem very convincing. SteveBaker (talk) 23:46, 12 October 2008 (UTC)

Robotics - what is static stability?

I find definition of "static stability" as it relates to missiles and whatnot, but not as it relates to robotics. It sounds like it means just the concept that when a robot is at rest it should be stable, but I don't know for sure so I decided to query the WP community. Smaug 18:01, 11 October 2008 (UTC)

Ack nevermind. Just found the answer: "A statically stable robot can stand still without falling over." So I was right. Smaug 18:02, 11 October 2008 (UTC)

Stability is a slightly more subtle thing. With very great care, you can balance a coin on it's edge - but it's not stable - the slightest knock or jolt and it'll fall over. When you leave the coin lying on it's side - then it's very stable - it takes a HUGE jolt to make it flip over. That's "static stability". A statically stable robot would not only be able to stand still - but it would be able to do that with the power turned off - and it wouldn't fall over if you knocked it hard. SteveBaker (talk) 01:05, 12 October 2008 (UTC)

There is also a strange condition between stable and unstable called astable, where the system is in an unstable state, but if disturbed merely goes to another similarly unstable state. Our article redirects to multivibrator which is certainly an example of a device in an astable condition, but not the most informative one. A ball lying on a flat surface is in astable equilibrium, the slightest force on it will change its state, but only to another one exactly the same. A cone has all three types of stabilty: stable if on its base, unstable if on its apex, and astable if lying on its side. In terms of robotics, walking is a challenge to the designer because it requires astable equilibrium. A walker is continually falling, but never does so as he/she immediately moves to another falling state on the other leg. The mechanical equilibrium article appears only to cover static equilibrium. SpinningSpark 12:01, 12 October 2008 (UTC)

Jobs in the private spaceflight industry

It seems that private-sector spaceflight is really taking off (pun not intended) these days. I'm really excited about what's happening with it lately, and I really want to be a part of it all. I'm preparing to go into college starting next semester and I still haven't made up my mind on what I want to specialize in. My question is, what sort of degrees would be useful to the private spaceflight industry? My goal is to collect skills that would make me indispensable to a company in this field. I'm not particularly good at anything as it is. I have some very basic computer programming skills (I could get better, though) and I'm extremely bad at math (I'm aware that this is a huge drawback for what I seek). Does anyone have any suggestions for the career I should choose and what I should learn about in school? Thanks. 63.245.144.77 (talk) 20:11, 11 October 2008 (UTC)

My goal is to collect skills shows you are very wise, that is exactly what will make you indispensable in any field. I'm literally doing the same thing right now. I'm already "competing" against future neurologists(m.d.) who are still in their undergrad. Just think of the bell curve. You have to compete to be in the top 5, in whatever you genuinely want to excel at. The problem is you don't know who the other top four are. You have to be extremely motivated, and (possibly even more importantly) you have to know where to direct your efforts. Its just that (if you live in U.S.A.) most teachers who are great at teaching math, all conspire to make sure that they aren't your math teacher. Math is a dealbreaker, and you need to be an expert at quantitative reasoning. Specific advice: study rigorously and take the LSAT (its a puzzles test mainly), make yourself better at math (ask questions on the math ref desk anytime--always glad to help aspiring rocket scientists), and become a master of metacognition as that's the only way to change your brain's wiring about motivation. Sentriclecub (talk) 21:05, 11 October 2008 (UTC)

There are certain jobs that exist in any industry - personnel (aka human resources), accounts, etc., which you could go for. Jobs specifically related to space flight would be physics and engineering related, most likely, with some mathematicians as well. All of those involve quite a lot of maths, unfortunately... They will certainly need programmers to do simulations and things, but you would need the maths and physics knowledge in order to know what to program. I think, in short, you can't be a rocket scientist without maths! If you're interested in the space tourism side of the industry, you could try studying hospitality and tourism. While you would be learning about land based hotels rather than space hotels, there would be transferable skills. There will be lots of new legal issues with the new sector opening up, so I'm sure they'll need lots of lawyers - working out what jurisdiction a space hotel or moon base falls under could be quite interesting, as would extraterrestrial real estate. Really, they're going to need people from all disciplines, so just pick something that sounds interesting as a degree and then apply for whatever jobs you're suitable for (a lot of jobs just require a degree and it doesn't matter what it's in). --Tango (talk) 20:52, 11 October 2008 (UTC)

Learn Mandarin and business. If by "private spaceflight" you mean space tourism, it's likely many of the punters will be the Chinese nouveau riche showing off their wealth. If you mean it to include privately launched spacecraft in general (including satellites) then a lot of that business will be Chinese entrepreneurs blanketing the middle kingdom with cheap video messaging services and such. -- Finlay McWalter | Talk 21:21, 11 October 2008 (UTC)

There are really a vast range of skills that are going to be needed when private spaceflight really takes off - I would start with a solid grounding in math and science - probably physics, electronics and computer science would be good places to concentrate your efforts. But if you can learn as much breadth of science as possible - and enjoy doing it - then I think your speciality can be almost any science-related subject and you'll find jobs are available. But that wide knowledge base is critical. No small rocketry company can afford to have an extreme specialist in a very narrow field on their staff - they need generalists. SteveBaker (talk) 00:57, 12 October 2008 (UTC)

Obviously you'll want to master all of the intellectual disciplines enumerated by my venerable RefDesk colleagues, but you shouldn't neglect your physical health. Competition for the jobs of first generation space pilots will be nothing short of astronomical, and you will need to be in peak physical condition to remain in contention. Plasticup ^T/C 05:42, 12 October 2008 (UTC)

You're assuming "job in private space travel" means being a pilot - the vast majority of the jobs will be ground based. I didn't even discuss becoming a pilot because the competition is so great it's barely worth considering - you would need to already be an experienced aeroplane pilot, it's not a job you can get straight out of college. --Tango (talk) 11:46, 12 October 2008 (UTC)

Oh - sure. Forget being a pilot. They won't need many pilots and EVERYONE who ever dreamed of being Buck Rogers is going to be after that job. Supply and demand means that that's going to become an increasingly low-grade job. These space-planes are going to be automated to death and you won't need any more skills than (say) an airline pilot needs to fly one. I'm assuming that the interesting, high-dollar jobs are on the ground. Design, test, construction, launch. SteveBaker (talk) 15:10, 12 October 2008 (UTC)

I'd expect the spaceship pilots themselves to be recruited exclusively from the pool of experienced military test pilots anyway... --Kurt Shaped Box (talk) 19:07, 12 October 2008 (UTC)

I think Virgin Galactic are recruiting experienced commercial pilots, not just military. You need a lot of experience, though. While SteveBaker is right about the automation, that only applies to routine flights - if something goes wrong you need to be able to take manual control and know what to do. While lots of people will want the job, there won't be many people qualified, so the supply is actually very low and I would expect them to be extremely well paid (there will be equally well paid jobs on the ground and probably a few better paid jobs, though). --Tango (talk) 20:20, 12 October 2008 (UTC)

Commercial spaceflight is going to be all about weight. For the early passenger flights, they'll be able to charge a small fortune for each seat - filling one of those seats with a non-paying pilot is a costly thing to do. There is really no practical reason why you couldn't fly the spaceplane from the ground and use automation for the majority of the flight. The "when something goes wrong" argument is really untrue. In modern commercial aviation, pilot-induced errors by far exceed pilot-corrected mechanical faults. (Don't consider situations where the pilot lands the plane with one engine out - that could have been done from the ground - I'm talking about situations where the plane would have crashed had the pilot not been physically aboard the plane to fix something.) We could drop the pilot anytime if it were not for the legal ramifications and the fact that people might be a tad nervous about flying in a plane with no pilot. But in a 500 seat 747, adding a handful of crew makes almost no difference to your revenues and keeping passengers happy is more important. But in a 5 seat space-plane, losing 20% of your revenue is a tough business decision. NASA puts human pilots on board the space shuttle - but those people would need to be there to carry out the mission anyway - so the cost of having them there to fly the shuttle is $0. Remember the Russian Buran space shuttle did it's one and only flight entirely under automation. So whether there will be many space-plane pilots in the future ends up being more a matter of how secure the passengers can be made to feel than any actual NEED for a pilot to be physically present in the cockpit.

SteveBaker (talk) 23:02, 12 October 2008 (UTC)

As someone who works in the airplane business (specifically, avionics) I don't think the situation is quite as clear-cut as that; our avionics are not yet good enough (and, importantly, robust enough) to permit pilotless teleoperation on a large scale. In a few years, maybe. Although I will agree that the decision to have a pilot on the first suborbital ships will be partially a technical one and partially a financial one (the non-paying-passenger argument you made).

Oh no, I have contradicted Steve!! :) — QuantumEleven 14:11, 13 October 2008 (UTC)

And what do you do when the radio antenna falls off during re-entry? Even if the radio control works perfectly, I would imagine (I'm not a pilot) it's far easier to fly a plane when you can feel what it's doing that when you can just see lots of numbers on a computer screen. You get genuine feedback from the controls as opposed to simulated feedback that will be inevitably delayed, you can feel the turbulence as it affects the plane rather than just seeing the results on the screen a split second later. Having an actual pilot is very important. Unfortunately, getting accurate statistics on the matter is rather difficult - the failure rate of unmanned spacecraft is much higher, I believe, than manned (there are certainly far more accidents, although there are far more launches so the ratio may not be so different), but they are much more careful with manned craft so that's to be expected. --Tango (talk) 14:31, 13 October 2008 (UTC)

(unindent) I don't agree with ANY of the things you just said!

• What you do if an antenna falls off is what you do if the tailplane falls off. The trick is to design it so that doesn't happen. This is really very easy with stuff like electronics. You can easily have three or four of everything.
• Flight simulators (which I used to design) have hydraulically actuated haptic feedback devices on the controls that have real "feel" to simulate the effects you'd feel in a real plane. They work very well. It would be entirely trivial to measure the forces on the flight surfaces and provide feedback to a pilot on the ground. However, most modern planes don't provide that feedback anyway. An F16 fighter (for example) has a rock-solid steel bar for a joystick that provides no feedback whatever - it doesn't even move! It operates by measuring the force you apply to it. Several modern airliners have little joysticks like on videogames with no feedback whatever. So this is neither necessary - nor difficult to provide if it were necessary.
• The delay in getting feedback isn't going to be critical for space planes. Things just don't happen that quickly until you are about to touchdown on the runway - and at that point you are so close to the transmitter that the speed-of-light delays are irrelevent. Things that need human-response-time rates but not human intelligence can be handled by computers. Things that don't need that response rate but which do need human intelligence can be done from the ground. The only problematic things are things where human response rates AND human intelligence are required - and if you have a system that's designed that way then you have a disaster just waiting to happen because humans are highly fallible when pushed to perform quickly.
• The US military fly planes (called UAV's - Unmanned Aerial Vehicles) by telepresence and computer control all the time. Their pilots mostly sit in the Pentagon building - flying the planes from halfway around the planet via satellite links. This gives them speed-of-light response rates that are about the same as the worst case for an unmanned spaceplane. The technology is extremely well established and there are WAY more UAV's over the skies of Iraq than there will ever be spaceplanes in orbit at any given time. This is a solved problem. The Soviet Buran space shuttle flew an entire mission including launch and landing under remote control...and that was with soviet era hardware from 20 years ago.
• The failure rate of unmanned spacecraft is high because they can save money by cutting back on the safety systems. They don't have anything like the amount of redundant systems when launching a cheap telecomms satellite as they do on the shuttle (for example). But note that shuttle launches are not exactly reliable - having the pilots on board hasn't helped them at all - I don't think there has been a single case where the crew were able to do something to save the spacecraft that couldn't have been done without them.

SteveBaker (talk) 20:03, 13 October 2008 (UTC)

• • I'm not going to comment on the spaceflight angle so this is slightly OT but while I agree one of the reasons why airplanes have pilots is because not having pilots make the people nervous I would disagree that if it can be done by remote control then you don't need the pilot. I find it hard to believe, especially in the current security environment, that there will be much support for having commercial planes being operatable by remote control due to security concerns. Even though if you develop it right, the risk of an unapproved person being able to take control of the plane by hacking or breaking the system is probably lower then a hijacker, this won't necessarily allay the concerns of a lot of people including I suspect many politicians. Plus there is still the physical aspect/risk of having many planes controllable from a single point. So in other words, for commercial flight, if you need it to be done by remote control then you need a pilot since remote control is not likely to be acceptable. Also I should point out that while I have no doubt UAVs are resonably successful, it's unlikely we will have complete statistics on how many of these have crashed in the near future given this is likely to be consider sensitive information to the US military Nil Einne (talk) 10:07, 15 October 2008 (UTC)

Organisms living inside crude oil

Just out of curiosity, are there any organisms that live in oil deposits in the ground? Surely there's at least some kind of bacteria that have taken advantage of the energy in the oil. 63.245.144.77 (talk) 20:14, 11 October 2008 (UTC)

Check out entropy, oil has less usable energy than the stuff it started out as. Then again, evolution is more a model to fit past data, and it really doesn't hold any prediction ability. (The evolution sentence was a joke. -sorry) If that dream organism existed, it sure would have a monopoly and would propogate very quickly. I'm guessing that biology doesn't work that deep below ground, its sequestered by too much rock. Any organism fit for glycolysis surely would have a field day down there! All those C-H bonds, maybe cockroaches could live down there? Good question, I am very curious myself and hope someone can explain this better. Sentriclecub (talk) 20:46, 11 October 2008 (UTC)

You are incorrect. Evolution is a testable theory that has significant prediction ability. Organisms that are fit for glycolysis are essentially all organisms (yes, including humans). Oil is not sugar. It doesn't matter how good we are at glycolysis; we will in no way be able to digest oil. Cockroaches can't live down there because there's no oxygen. Evolution theory essentially tells us that if there were a way for life forms to get down there and adapt, they would (organisms will adapt to fill open niches). However, they'd have to pass through the intermediate layers of rock, which do not support any life whatsoever. Obviously things cannot live in an area that supports no life, so it's pretty much impossible for any organisms to end up down there. Entropy is also not related to any of this, because entropy has little to do with how much chemical potential energy something has. The amount of useful work that can be done with a given amount of enthalpy is decreased by the temperature times the change in entropy (see Gibbs free energy). Oil has less usable energy (per unit mass, probably) than the organic matter it started out as due to inefficiencies in converting organic material to oil. --M1ss1ontomars2k4 (talk) 20:57, 11 October 2008 (UTC)

Endoliths have been found 3 km down in rock (ref). It seems the only limit on how deep these guys can go is increasing temperature, so it's possible they go down a lot deeper (this article claims maybe 7 km). -- Finlay McWalter | Talk 21:11, 11 October 2008 (UTC)

And there are places where oil literally oozes from the surface of the earth at sea level. No - the remoteness of oil from bacteria isn't a reason they might not have evolved to use oil as an energy source. SteveBaker (talk) 00:52, 12 October 2008 (UTC)

It's hard to find a niche on Earth that doesn't have some kind of life living in it, so I wouldn't be at all surprised if there is something living in oil deposits underground. I know nothing about it, though. --Tango (talk) 20:54, 11 October 2008 (UTC)

Note there are (a rather small minority of) oil geologists who subscribe to the abiogenic petroleum origin theory, wherein oil deposits are not only inhabited by microorganisms (particularly thermophiles, both bacteria and archaea), but are actually made by them. -- Finlay McWalter | Talk 21:03, 11 October 2008 (UTC)

Read Ananda Mohan Chakrabarty to learn about one scientist who created and patented organisms which eat oil. Not sure about the "in the ground" part. It might be undesirable to release bacteria which consumed all the oil under the ground. Edison (talk) 00:03, 12 October 2008 (UTC)

In order to extract usable energy from oil (which is essentially hydrocarbons), one would need be able to create compounds with lower internal energy (enthalpy, or H) than the hydrocarbons. This is generally accomplished via oxidation. However, in order to oxidize these compounds, a source of some usable oxidizing agent needs be present. The most likely source of this is oxygen itself, and underground oil has no access to this. From a purely chemical point of view, that oil underground is safe from nearly any biological organism that might be able to "eat it". There may be some that exist that can consume oil at the surface, but that is because of the availibility of free oxygen. --Jayron32.talk.contribs 11:48, 12 October 2008 (UTC)

The fact that oil has "bugs" is well known although I can't find a good that talks about it in specifics. There is more chemistry that life than preform than photosynthesis and standard respiration, take a look at extremophiles. Even without oxygen life goes on. One of methods that eventually get used on every oil field is water injection (oil production). Its a standard part of enhanced oil recovery. According to Matthew Simmons book this process has been in effect for sometime within the Ghawar Field. But that is important for other reasons. Our concern here is that if oil producers flood wells with water containing dissolved oxygen life flourishes in the oil field eventually complicating or preventing oil recovery. It standard practice to use aquifers of sterile brine from strata above the oil fields for the purposes of water injection. This brine is for all intensive purposes free of oxygen and life. In leu of a brine aquifers, water form the surface needs to have the oxygen removed and life killed prior to injection. Regardless check out the water injection (oil production) I think its the only place on wikipedia that covers life in oil. As far as the science goes I don't know how much is well known publically besides methods to kill the "bugs" described in Society of Petroleum Engineers publications. Oil companies would rather people not know that they are exterminating rare forms of life in the process of bringing them their gasoline.--OMCV (talk) 03:39, 13 October 2008 (UTC)

Part of what inspired me to write this question was the memory of a ninth grade biology experiment we did on the first day of school where we put some water and some vegetable oil in an empty water bottle and then shook it up creating little shperical globs of oil, which are essentially the same structures in cellular membranes. Anyway, I explained this experiment to a friend of mine who wasn't in that class and I just said "oil" not being specific, so he made his own version...with motor oil. Nevertheless, it still worked the same even though it wasn't transparent. Anyway, a few weeks later, I noticed long strings of bacteria or mold or something growing in my experiment, which I stupidly set in a window sill in my room (source of energy). Coincidentally, My friend had set his in a window too and...lo and behold, there were strings of bacteria in the motor oil too. I know from personal experience that life can survive in oil if there's a source of energy, but can it survive under the ground? I'd be extremely surprised it it couldn't, actually. I recently found out that there's huge slimy colonies of bacteria in the cracks between rocks in gold mines in South Africa three miles below the surface. Scientists think that cells living at such extreme depths were the cells that repopulated the surface after huge meteorite impacts destroyed all surface life billions of years ago. So bacteria can definitely get that deep. If bacteria can live off of rocks using chemosynthesis as a source of energy, they can live off of oil in a similar way.

I guess I just answered my own question, but I'm still curious as to the nature of things living in oil. I'm surprised I can't find any info on it on google.63.245.144.77 (talk) 05:29, 14 October 2008 (UTC)

From a quick search of Nature (journal):

• Biodegradation of oil in uplifted basins prevented by deep-burial sterilization - "Biodegradation of crude oil by bacterial activity - which has occurred in the majority of the Earth's oil reserves..." (28Jun01)
• Biological activity in the deep subsurface and the origin of heavy oil - "At temperatures up to about 80 °C, petroleum in subsurface reservoirs is often biologically degraded, over geological timescales, by microorganisms that destroy hydrocarbons" (20Nov03)
• Crude-oil biodegradation via methanogenesis in subsurface petroleum reservoirs - "has been attributed to aerobic bacterial hydrocarbon degradation..." (10Jan08)

Bacteria in crude oil? Early and often. And as you note, bacteria in deep rocks unrelated to petroleum are known and may be the progenesis of current life on earth. Sign up for an account and I can email you copies of those papers and many more. Franamax (talk) 09:15, 15 October 2008 (UTC)

Oh yes, here in Canada we're talking about harnessing those bacteria - though I'm not too enthused about injecting little lifeforms into the second-largest store of petroleum on the planet, seems to me one or two things could go wrong in that process and we could, umm, come to regret the decision. Franamax (talk) 09:26, 15 October 2008 (UTC)

Strange thermodynamics question

Say we have some ideal gas. It undergoes an adiabatic expansion from 1 Liter to 2 Liters and does no work. What are ΔU and ΔH for this process? I already know ΔU (ΔU = ΔQ + ΔW, all of which are zero), but I don't quite get ΔH. So far, we have that dH = dU + PdV + VdP. dU is zero, PdV is zero (no work done). But what's VdP? Since no work is done, can we say that the external pressure is zero and constant, and thus VdP is zero? --M1ss1ontomars2k4 (talk) 20:30, 11 October 2008 (UTC)

Your question is self-contradictory, I'm afraid. If you let the ideal (or any) gas expand adiabatically from V₁ = 1 L to V₂ = 2 L, it will perform work equal to integral of PdV from V₁ to V₂. On the other hand, if you put external pressure to zero, the gas will not do any work, but the expansion will not be adiabatic. The only way to stay adiabatic AND to have zero pressure is to have initial pressure = 0. That implies either an ideal gas at initial T=0, or ideal gas with zero particles in the volume considered. Hope this helps. --Dr Dima (talk) 03:58, 12 October 2008 (UTC)

Why would it not be adiabatic, if external pressure were zero? Reversible adiabatic processes are isentropic but this is not really reversible, if the external pressure were zero. --M1ss1ontomars2k4 (talk) 04:04, 12 October 2008 (UTC)

Sorry, I misunderstood your question. I thought you are referring to reversible (isentropic) adiabatic expansion process. If you are referring to non-isentropic adiabatic expansion with zero work performed, the enthalpy H should stay constant. indeed, H = U + PV. In your process (non-isentropic adiabatic expansion with zero work performed) U does not change, and PV is zero all the time so it cannot change (both PdV and VdP are zero). Thus, ΔH = 0. For an ideal gas that means that you stay on an isotherm. Indeed, U = DNT/2 where D is number of degrees of freedom per particle, N is total number of particles, and T is temperature. As long as U stays constant, so does T. Hope this answers your question. For clarity, it is important to realize that the initial state for your process is out of the equilibrium: pressure is zero but NT/V is not zero. That happens when you suddenly remove a wall separating gas in volume V₁ from the void in the rest of the volume V₂, where V₂ > V₁. And a final note: many physicists, including myself, normally use the words "adiabatic process" only when they are talking about reversible adiabatic ( = isentropic ) process. A process in which ΔQ = 0 and ΔN = 0 but entropy increases is simply referred to as "irreversible process". Keep that in mind and you'll be fine ;) --Dr Dima (talk) 01:17, 13 October 2008 (UTC)

Intelligent Life in the Universe/Voyager Golden Record

I have been interested in the Golden Record that is on Voyager 1 and 2. I learned about how it is there in case Voyager encounters intelligent extraterrestrial life on its journey. If other intelligent extraterrestrial life created something similar and it went through our solar system, would we have any way of knowing? —Preceding unsigned comment added by 75.169.21.144 (talk) 21:28, 11 October 2008 (UTC)

It would probably be difficult to spot unless it passed very close to Earth. I expect any radio transmissions would be pointed back towards where it's come from, if there even are any (the Voyager craft will stop transmitting millennia before they reach other stars). Because they operate so far from the sun, they use nuclear power rather than solar panels, which means they don't have a particularly large reflective area so would be very bright. You would probably only see one if it passed close to Earth and you happened to point a large telescope in the right direction at the right time. --Tango (talk) 22:39, 11 October 2008 (UTC)

if such a device entered the solar system, it might have a circuit to trigger a beacon which would send radio sugnals to get our attention. When Voyager was launched, we did not know how to build a device which would "wake up" and send out signals after tens of thousands of years. Edison (talk) 23:56, 11 October 2008 (UTC)

It's probably safe to say that we still don't know how to build such a device. We have no idea what happens to our spacecraft after tens of thousands of years, since we've only had most of the supporting technology and advanced materials for less than a century. We could design a system to be "very reliable" and develop some system (software?) to wake it up in a few millenia, but there is no way we could test the reliability of it over thousands of years. HALT testing only goes so far in estimating certain types of failure. Nimur (talk) 00:37, 12 October 2008 (UTC)

Most of it doesn't need to be operational for 10,000 years, it just needs to sit there, so there isn't a whole lot that can go wrong (you would want some good shielding from radiation, etc, but that's about it). I think the real problem isn't the time, it's the cold, electronics break pretty quickly if they get too cold and the power requirements of keeping the probe warm for 10,000 years are most likely beyond us at the moment. --Tango (talk) 11:51, 12 October 2008 (UTC)

The point is that once Voyager gets away from the Oort cloud, there is no reason why it shouldn't keep moving off into the galaxy for millions or even billions of years. Over all that time - it is perhaps possible that some alien species would find it. It seems unlikely that they'd be able to decypher it though. The plaque and record are really poorly designed IMHO. SteveBaker (talk) 03:30, 12 October 2008 (UTC)

I think the likelihood of anything finding it is probably less than the likelihood of making any sense of it. Assuming something beyond dumb and impossible luck, any species that had the technology to locate that particular need in the interstellar haystack should be able to figure out the technology without too much difficulty, I'd imagine. --98.217.8.46 (talk) 03:33, 12 October 2008 (UTC)

That doesn't diminish how undeniably cool it is. We recorded the fundamentals of our species in a (hopefully) universal format and sent it careening into the depths of space. That has an intrinsic value to our species, even if it never facilitates communication with another. Plasticup ^T/C 05:23, 12 October 2008 (UTC)

I agree that it's an interesting statement, one that says more about the act of creating it than it does about its potential discovery. But it's worth noting that the selection of content says more about the people who created it than it does about the human species. Not all members of our species would agree on what the fundamentals were. For example, from what I can tell via Voyager Golden Record, there were no religious texts included whatsoever. No doubt Sagan may have thought that "Johnnie B. Goode" was more fundamental to understanding US culture than the Bible, but I'm sure there would be those who would vehemently disagree. ;-) --98.217.8.46 (talk) 13:33, 12 October 2008 (UTC)

It's about putting our best foot forward, I suppose. Plasticup ^T/C 16:14, 12 October 2008 (UTC)

There don't seem to have been any texts included at all, religious or otherwise. It looks like among the vocal music there was none with a religious text, but it's not as though an extraterrestrial could tell what the words meant anyway. -- BenRG (talk) 19:15, 12 October 2008 (UTC)

Well if we were really a space-faring society, i.e. one with personal and commercial inter-planetary travel, then I suspect that Space Traffic Control would monitor every rock much bigger than a ping-pong ball and fairly quickly notice a new metallic object entering the solar system. Obviously that makes assumptions about what the distant future of space travel might be like, but there is no reason to assume that ET will be as primitive as us. Dragons flight (talk) 06:03, 12 October 2008 (UTC)

If Voyager I ever travels through a planetary system similar to our solar system then it will be moving very fast indeed by the time it reaches the vicinity of an Earth-like planet's orbit. At the moment it is about 100 AU from the Sun and is travelling at about 17 km/s. If it fell into the gravity well of a star similar in mass to the Sun then at 1 AU from that star it would be travelling 10 times as fast, so 170 km/s. At this speed it covers a distance equal to the diameter of the Earth's orbit in about 20 days. So not much time to detect it, and quite difficult to catch it if it is detected. Gandalf61 (talk) 10:31, 12 October 2008 (UTC)

Ummm, your numbers are off. Falling into the sun's gravity well would only give you ~42 km/s at Earth's orbit. Dragons flight (talk) 16:51, 12 October 2008 (UTC)

42 km/s is escape velocity from the solar system starting from the Earth's orbit. But Voyager I is going much faster than escape velocity, mainly due to gravity assists from Jupiter and Saturn on its way out of the solar system. In the absence of interactions with planets, velocity of a free-falling spacecraft is inversely proportional to the square root of distance from the Sun (by conservation of energy), so 17 km/s at a distance of 100 AU becomes 170 km/s at a distance of 1 AU. Gandalf61 (talk) 20:19, 12 October 2008 (UTC)

I don't follow your calculation. Falling adds to the velocity, it doesn't multiply it by something (what it adds is dependant on initial velocity, but I can't see how you end up that result). --Tango (talk) 20:38, 12 October 2008 (UTC)

No, 17 km/s approximately goes to ${\sqrt {17^{2}+42^{2}}}\approx 45$. The energies, which are proportional to velocity squared, will add not multiply. You seem to just multiplying by 10 since that is the sqrt of 100, which is wildly wrong. Dragons flight (talk) 21:15, 12 October 2008 (UTC)

Yes, you are right. Escape velocity is inversely proportional to the square root of distance from the Sun, not velocity of spacecraft. Total cock-up on my part. Gandalf61 (talk) 10:11, 13 October 2008 (UTC)

Even if we spotted an Alien Voyager probe, we'd have no way of retrieving it to read the alien golden record. We'd have to just hope that it settles into a stable orbit until we were ready to go after it.

Of course, who knows? Maybe one day our own space travel will advance to the point where Voyager 1&2 will wind up in the Smithsonian one day. (Or at least the CD-Roms on Mars.) APL (talk) 12:54, 14 October 2008 (UTC)

What does Radioactive Waste look like?

I read the article on radioactive waste, but I'm still not sure what the final "stuff" looks like. In popular culture, it's usually depicted as this glowing green stuff, but I have a feeling that's not really what it looks like. I guess in other words, what does the radioactive waste inside of those containers look like? ScienceApe (talk) 22:37, 11 October 2008 (UTC)

Radioactive waste can be unprocessed, in which case it's just raw fuel rods (containing fuel pellets). So that's just thin shiny cylinders filled with little metal cylinders the size of short stacks of coins. For reprocessed waste, high-level waste can be encapsulated in a number of ways; one is in glass blocks (or disks). -- Finlay McWalter | Talk 22:48, 11 October 2008 (UTC)

Radioactive waste (low level) can be clothing, rags, mops, cardboard, bottles, and many other materials which could become contaminated with radioactive materisl, as when there is a fluid leak in a power plant which releases radioactive materials that must be cleaned up. It goes in drums and gets stored. Edison (talk) 23:54, 11 October 2008 (UTC)

What's the fluid usually? ScienceApe (talk) 01:13, 12 October 2008 (UTC)

My understanding is that most high-level radioactive waste is produced in reprocessing plants—acids and washes used to separate out plutonium from other fission products and things like that. Probably just looks like sludge. If you google "hanford waste tanks" you can find images of a lot of liquid waste—nothing very interesting. Certainly not glowing green goo. --98.217.8.46 (talk) 03:16, 12 October 2008 (UTC)

So it would look like just some thick brown fluid? ScienceApe (talk) 14:42, 12 October 2008 (UTC)

For the record, the Cerenkov radiation in nuclear reactors causes them to glow blue, not green. Radioactive waste stored in water could also glow blue if there was enough of it, but more likely it would be broken up into small enough portions that there would not be a human perceptible glow. Dragons flight (talk) 04:13, 12 October 2008 (UTC)

Another form of nuclear waste is the power plant after decommissioning. Especially the material that contained the reactor core. So that would look like construction material, I suppose. Metal plates and such? Amrad (talk) 07:01, 13 October 2008 (UTC)

And concrete.

Note that when it comes to disposal, sludge is not favoured, because if the container were damaged it could leak into groundwater. I believe, the British Nuclear Decommissioning Authority favours "microencapsulation", where liquid wastes are immobilised inside containers with a grout. AlmostReadytoFly (talk) 10:06, 13 October 2008 (UTC)

October 12

Image licensing

HI,I AM DOING THIS PROJECT ABOUT NORTH AND SOUTH POLE AND I JUST WANT TO ASK YOU THAT IF I CAN PRINT SOME PICUTER THANKYOU VERY MUCH FROM MEENAKSHI —Preceding unsigned comment added by 68.183.31.96 (talk) 00:18, 12 October 2008 (UTC)

Yes

SpinningSpark 11:23, 12 October 2008 (UTC)

Smallprint for lawyers to read

Almost every photo on Wikipedia is freely licensed. This means that you may re-use or modify the photos (including printed copies). For any specific image, check its license information, which will provide details on what the image owner requires regarding re-use. Also see Wikipedia:Image copyright tags for general information. In general, if you are using these photos for a school project, that would be permissible under most of the image licenses on Wikipedia. Nimur (talk) 00:32, 12 October 2008 (UTC)

I have no idea what cutting pie has to do with the North and South poles....--el Aprel (^facta-_facienda) 00:36, 12 October 2008 (UTC)

Hi! It's OK to print most pictures that are on Wikipedia - but there are a few exceptions. All of the photos at our South pole, Antarctica, North pole and Arctic are OK to copy. You can also go to our sister site "WikiCommons" - and type "North pole" or "South pole" into the search box...you'll find also that there are "categories" of photos: Category:South_Pole and Category:North_Pole. There is also a bunch of photos of the Amundsen-Scott south pole station. All of those photos are OK to print.

If you need to know about other pictures on Wikipedia, what you need to do is to click on the photo you are interested in and when the image's own page pops up, it should look a bit like this one: HERE. Now you need to scroll down and look where it says either: "Licensing" or "Permission (Reusing this image)" - if it says something about "Fair use" then it's not OK.

SteveBaker (talk) 00:47, 12 October 2008 (UTC)

Though honestly if you are using it in an elementary school assignment I don't think anybody cares about the copyright status. --98.217.8.46 (talk) 03:29, 12 October 2008 (UTC)

You mean ANY school project? Who's going to sue you because you used, say, Coca-Cola's logo in a school assignment? That would just make the copyright owner look bad. --M1ss1ontomars2k4 (talk) 04:06, 12 October 2008 (UTC)

Well, I left out "any" because I could imagine some school projects in some scenarios where stuff like that could matter. (A dissertation is a "school project", in a sense, and you have to be mindful of copyrights with those.) But yeah. Really not worth worrying about for run-of-the-mill assignments. Falls under fair use pretty solidly. --98.217.8.46 (talk) 13:25, 12 October 2008 (UTC)

It is important to teach a respect for the copyright law. If kids get the idea that they can copy anything anytime - they are going to get into a lot of trouble in later life. Copyright laws are annoying and a big pain in the butt - but they are laws - and it's important that kids realise that. The idea that copyright holders don't "care" about little things like school projects is likely true - but that's not true of trademark law - where if you don't actively pursue infringements you can lose your ownership of them. Hence, CocaCola may well be forced to pursue even "irrelevant" infringement at the level of a high school project. SteveBaker (talk) 14:58, 12 October 2008 (UTC)

Oh yeah, sorry, I was forgetting about all those CocaCola billboards at the North Pole and the pictures of them in Wikipedia to catch out the unwary. Context! please. SpinningSpark 18:24, 12 October 2008 (UTC)

Large corporations will most certainly sue schools over misues of their trademarks: Disney has done it to day care centers and most other companies will as well. They will also always win, and it isn't only because they have lots of high powered lawyers. Under intellectual property law, there is a concept known as "trademark dilution"; once a trademark (be it a word, logo, or character, basically any symbol of your company) has entered the common lexicon, you can no longer use it as a trademark. Basically, if Disney did NOT aggressively defend its trademark, and was shown to allow, say, a day care center in Florida to use Mickey Mouse in their logos without proper permission, then it would set a precedent for anyone to use it. Disney cannot be selective in allowing infringements of its trademarks; it either has to expressly require that all uses are licenced, or it has to allow all uses by anyone for any purpose. As a result, large corporations can and do pursue these cases... --Jayron32.talk.contribs 18:35, 12 October 2008 (UTC)

Jayron is exactly right. Consider for example a school student project which then becomes entered in the state science fair and wins, subsequent to which prominent newspapers publicize the event c/w pictures. The way copyright law works is that you have to pursue any violations that come to your attention, otherwise you fall foul of the equitable doctrine of laches and your trademark becomes public domain. Aspirin and kleenex are examples of former trademarks that became common names. Companies don't want to pursue daycares, they have to. Franamax (talk) 04:56, 14 October 2008 (UTC)

What colour would you say best describes the upper mandible of a male Eclectus?

Question as topic. A user has suggested that 'candy-corn-coloured' (as stated in the article at present) is less than ideal. I'm inclined to agree.

Any suggestions? I'm thinking 'saffron' - though I'll readily admit that colour naming is not my strong point... --Kurt Shaped Box (talk) 02:52, 12 October 2008 (UTC)

It looks like scarlet (or orange) with a bright yellow tip, though I see what the phrase "candy-corn-coloured" means when I look at the photograph of the parrot. Just "candy corn", without the "coloured", might work for those who have seen candy corn (and for those who haven't, click here [8]) but candy corn has a white tip. ៛ Bielle (talk) 03:09, 12 October 2008 (UTC)

I agree. When writing for Wikipedia, one should strive to keep specific cultural references like "candy-corn" out of articles like that. We are read in dozens of countries around the world - most of whom will never have seen or heard of candy-corn. Most people in the USA know what it is - and what color it typically is - but I doubt whether people from other countries would know. Sure, you can provide a link to the article candy corn - but it would be much better to use a proper description of the color rather than to send people off on hunts for obscure references like that. Better still - just put a nice color picture in there. SteveBaker (talk) 03:26, 12 October 2008 (UTC)

People who don't know candy corn? My God, man! I don't believe it. I won't believe it! Plasticup ^T/C 05:15, 12 October 2008 (UTC)

Well, I've never heard of it. But I wouldn't want to interfere with your deeply held beliefs. Algebraist 09:08, 12 October 2008 (UTC)

Looks orange-yellow to me. [By the way, I have no idea what "candy-corn" is. ;-) ] Axl ¤ [Talk] 11:04, 12 October 2008 (UTC)

Candy corn is little multi-colored globs of sugar, usually served at Halloween in the U.S. I've never had a taste for it... --Jayron32.talk.contribs 13:00, 12 October 2008 (UTC)

Nobody has tasted it. None have been produced since 1934. The entire supply at that time has simply been recycled each year. -- kainaw™ 17:08, 12 October 2008 (UTC)

Yeah, every year the entire supply is melted down to make Circus peanuts. Interestingly, every year the entire suply of Circus peanuts is melted down to make candy corns, resulting in a never ending cycle of recycling inedible "candy". --Jayron32.talk.contribs 18:01, 12 October 2008 (UTC)

I think you've all forgotten that the sole purpose of candy corn is to insert two of them - pointy-end-down - between teeth and upper lip for the purpose of scaring little sisters into thinking you have turned into a vampire on all-hallows evening. Subsequent consumption of these objects can only be accidental. SteveBaker (talk) 19:46, 12 October 2008 (UTC)

I wonder if Eclecti will eat candy corn, if offered? --Kurt Shaped Box (talk) 22:41, 13 October 2008 (UTC)

For what little it's worth, I rather like the stuff. —Tamfang (talk) 01:31, 14 October 2008 (UTC)

I'd never seen, nor heard of 'candy corn' until yesterday. When I saw the term used in the article, I was imagining something like toffee popcorn - or maybe candyfloss. --Kurt Shaped Box (talk) 19:28, 12 October 2008 (UTC)

...which is PRECISELY why we shouldn't use it. SteveBaker (talk) 19:48, 12 October 2008 (UTC)

Be better to pick from shades of yellow and link to the chosen shade. Bazza (talk) 14:21, 13 October 2008 (UTC)

Copper(II) Sulfate Crystal

Hello. Are there any catalysts or fancy methods to make a solution of CuSO₄ • 5H₂O and water crystallize faster, clearer, and with clean cuts? Thanks in advance. --Mayfare (talk) 04:08, 12 October 2008 (UTC)

The problem is that speed and quality are exactly competing factors in crystalization. Any method used to make crystals quickly (such as rapidly dropping solution temperature, or "scratching", or adding seed crystals) will cause LOTS of small, imperfect crystals to form. If you want faster, then create a hot supersaturated solution of CuSO₄, and let it cool to below the precipitation temperature. Drop a small "seed crystal" of CuSO₄ • 5H₂O into the mixture, and viola, you'll get crystals, but they will likely be small and imperfect. If you want high quality crystals, you should aim for making them AS SLOW as possible. You should start with the same hot, supersaturated solution (this is generally made by boiling a saturated solution of CuSO₄ until the volume reduces, but there are ABSOLUTELY NO crystals in the solution) and then place it in some insulation, and let it cool VERY SLOWLY. After several days, crystals should form, and they should be nice and big and well defined. --Jayron32.talk.contribs 11:38, 12 October 2008 (UTC)

1876 Supplement to Harper's Bazar, No.13 and No. 25

I recently discovered two tapestry patterns from 1876 each are double sided on one side clothing patterns on the other side maybe embordry prints/designs. The patterns and instructions are printed on old newspaper and folded in half twice. The paper is very fragile to handle or measure without causing damage. I want to know more about these documents and how to share them? —Preceding unsigned comment added by Yma99 (talk • contribs) 09:35, 12 October 2008 (UTC)

I copied this question from the new users page as how to handle old newspapers is bit beyond a question on how to use Wikipedia. SpinningSpark 09:47, 12 October 2008 (UTC)

Perhaps call a museum in your nearest large city? Or go to the local library and ask? Either of these will have people who can direct you to specialist advice. You might check though whether these are already scanned in a web archive somewhere. Franamax (talk) 04:42, 14 October 2008 (UTC)

photographic chemicals

Up to the 1940's photographers knew various chemical formula for making black & white negatives and prints. Where can I find this chemistry? —Preceding unsigned comment added by 122.111.64.194 (talk) 09:58, 12 October 2008 (UTC)

A good place to start looking is History of photography and follow the links there. Timeline of photography technology may also link to useful articles. SpinningSpark 11:06, 12 October 2008 (UTC)

Which formula do you want? I have books listing many. Edison (talk) 23:21, 12 October 2008 (UTC)

electron configuration of Barium

Hi is the following electron configuration for I have come up with for the element barium correct?

1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2. Thanks. —Preceding unsigned comment added by 139.222.240.110 (talk) 12:43, 12 October 2008 (UTC)

Looks right to me. Barium is in period 6, group IIA, which should have the configuration "...6s2" and it doesn't look like you missed any core orbitals either. --Jayron32.talk.contribs 12:57, 12 October 2008 (UTC)

Yeah, that's right. Source: Clicky —Cyclonenim (talk · contribs · email) 13:58, 12 October 2008 (UTC)

thanks :) —Preceding unsigned comment added by 139.222.240.66 (talk) 17:50, 12 October 2008 (UTC)

Using nuclear weapons as a propulsion system for spacecrafts

I'm reading Neal Stephenson's new book Anathem and in it he describes a rather unusual propulsion system for spacetravel (this isn't a big spoiler at all, feel free to read on even if you haven't read the book yet).

The idea is this: a spaceship would have one side on it that is covered by a so-called "pusher plate", which acts as a big shield, capable of withstanding a nuclear blast. A nuclear weapon is deployed on the other side of it and detonated, and thus the spaceship would fly off with enourmous velocity (essentially rocket jumping, but with nuke instead of a rocket and a spaceship instead of a player).

I've thought a little bit about this, and it seems to me that this wouldn't work. The reason a nuclear weapon will blow everything around it to smithereens (like that famous exploding house that we've all seen), is that it has an enourmous shockwave. But space is essentially a vacuum, there's no medium for a shockwave to propagate through. So it wouldn't impart basically any momentum to anything near it. The only thing that would happen (I imagine) is that it releases lots and lots of energy through electromagnetic radiation, which would barbeque any organic material nearby, but it wouldn't actually have a shockwave. I don't know if electromagnetic radiation departs any momentum on the things it hits, but even if it does, it's not all that much, is it?

Look at the sun: the sun is basically a mindnumbingly big nuclear reaction, much much bigger than any nuclear weapon, yet it doesn't "propel" it's satellites to enourmous speeds. The earth isn't flying off into space because of the sun. So why would this system work? 195.58.125.56 (talk) 17:51, 12 October 2008 (UTC)

See Project Orion (nuclear propulsion). Its "performance" section explains how they intended to design special bombs such that they'd maximise the kinetic yield of the nuclear explosive, which they'd then impart to the spacecraft itself by collision. -- Finlay McWalter | Talk 17:56, 12 October 2008 (UTC)

(e/c) Neal stephenson is just one in a long line of science fiction authors who have used the idea proposed by Stanislaw Ulam in or about the late 1950s. See Nuclear pulse propulsion.--Fuhghettaboutit (talk) 17:58, 12 October 2008 (UTC)

Yep - project Orion is famous in Sci.Fi. circles - lots of books have used it. I'd argue that the rather subtle manouvering that's implied would be impossible for such a craft - you've only got an all-or-nothing thrust mechanism. You can't do a "three second orbital injection burn" with a motor that either kicks you up the backside with 20 megatons or does nothing at all. But with such a large craft - you'd need something pretty powerful. SteveBaker (talk) 19:39, 12 October 2008 (UTC)

If I were building such a craft I would include a conventional rocket engine as well for the subtle stuff. Just use the nukes for simple acceleration. You need to be able to get a safe distance from anything you don't want to blow up/irradiate anyway, which requires some kind of propulsion. --Tango (talk) 20:40, 12 October 2008 (UTC)

If you don't mind wasting a bit of ΔV, you can dial down the thrust by delaying the explosions by various amounts, to detonate the bombs further from your ship. --Stephan Schulz (talk) 22:45, 12 October 2008 (UTC)

Nah, you only use nukes for intersteller travel. For manuvering you use conventional muntions. "Three grenades to starboard. Aye, Captain!".  ;-) Dragons flight (talk) 22:49, 12 October 2008 (UTC)

At least that will improve chances for peaceful first contact with the Minbari. --Stephan Schulz (talk) 22:52, 12 October 2008 (UTC)

Just to address the main question in it: it's not the shockwave that pushes the ship. You put in some plastic (basically) and the heat/radiation of the bomb turns it into a very dense plasma which expands/explodes and that pushes things. Basically. --98.217.8.46 (talk) 02:14, 13 October 2008 (UTC)

Also interesting is Nuclear salt-water rocket. Essentially a continuously exploding nuclear pulse propulsion rocket. ScienceApe (talk) 00:13, 13 October 2008 (UTC)

Wow! That's a cool idea. I like it! SteveBaker (talk) 01:37, 13 October 2008 (UTC)

What good an anal probe?

I've just thinking about all those personal accounts of (supposed) abduction and experimentation upon humans by aliens. How much useful data would one actually be able to collect on a human subject by probing its anus? Can anyone think of what it is that the prober might actually be trying to discover about the probee by doing this?

The taking of skin, blood, sperm and tooth samples at least kinda makes sense from a 'research into the species' viewpoint. --Kurt Shaped Box (talk) 19:24, 12 October 2008 (UTC)

It's a particularly unpleasant and degrading experience which elicits sympathy from those the abductee tells about it. --Tango (talk) 19:35, 12 October 2008 (UTC)

Apparently aliens are fascinated by cows (e.g. cattle mutilation). Perhaps they are looking for evidence of beef consumption? Dragons flight (talk) 19:50, 12 October 2008 (UTC)

Temperature and eating habits come to mind. —Cyclonenim (talk · contribs · email) 20:53, 12 October 2008 (UTC)

As does inspiring the fear of invasion. Julia Rossi (talk) 21:44, 12 October 2008 (UTC)

I think they are looking for our brains - they must be in an out-of-the-way place as we only occassionaly use them. SpinningSpark 22:20, 12 October 2008 (UTC)

If this were truly happening - an alien wanting to do a "non-invasive" investigation would of course start off by checking and sampling material from every obvious external orifice. SteveBaker (talk) 22:28, 12 October 2008 (UTC)

Though can cross the galaxy but somehow they haven't invented x-rays, cat scans, or MRIs? Dragons flight (talk) 22:44, 12 October 2008 (UTC)

Sampling...extracting fluids and solids. SteveBaker (talk) 23:50, 12 October 2008 (UTC)

They have. But they have a huge co-pay. - Nunh-huh 22:57, 12 October 2008 (UTC)

You know, I would consider someone sticking something up my rear end to quite invasive... --Tango (talk) 23:01, 12 October 2008 (UTC)

Fair point, Steve - but I don't recall reading many (any?) accounts of oral probing in the abduction accounts. --Kurt Shaped Box (talk) 23:33, 12 October 2008 (UTC)

Observer bias. The people who were asked nicely to say "Ahhhh" and got a lollipop at the end of the probing didn't complain as much as the ones who suffered less dignified forms of testing.  :-) SteveBaker (talk) 23:50, 12 October 2008 (UTC)

I forget the poet and the poem, but it was on the lines of "Aliens came from another planet/and studied humans/and decided they were a means/for the production/of shit". Any outside observer studying our hygiene habits, and the attention paid by humans to the emanations of dogs (picking up in bags and carrying it around fer gawdz sake), would surely conclude that there must be something very important up there and feel the need to investigate. Franamax (talk) 04:35, 14 October 2008 (UTC)

the whole anal probe thing is a front, they only do it to distract the abductee from what they're really doing, and make stories of their experiences sound even more ridiculous when they're returned to Earth. What they really do is something much, much more sinister. --86.135.181.146 (talk) 14:42, 16 October 2008 (UTC)

how much gas?

How much gas would an average human be able to pass in his or her lifetime? ("Would" because normally we don't try to maximize this. I mean if they were to eat a lot of beans all their life -- nothing chemical/artifical). —Preceding unsigned comment added by 82.120.232.170 (talk) 21:41, 12 October 2008 (UTC)

Well, the Mythbusters measured between 3 and 10 'gas passing incidents' per day on a normal diet - with a typical volume of around 13ml per 'incident'. Let's pick 5 per day as an average. Over a 70 year lifespan - that's 70x365x5x13ml = 1600 liters - which you could visualize as being about the volume of a good-sized house. On a 'bean-intensive diet, the Mythbusters registered 22 incidents per day - with a peak volume of 170ml in one hour - so we should say that about five times the 'normal' amount is probably about the maximum. But there are HUGE error bars on those numbers. I'd believe 5 times more or 5 times less than that 1600l number. SteveBaker (talk) 22:46, 12 October 2008 (UTC)

1 cubic meter is exactly 1000 liters, so 1600 liters is 1.6 cubic meters. That's about the volume of a 1.2 m x 1.2 m x 1.2 cube. --99.237.96.81 (talk) 22:56, 12 October 2008 (UTC)

Er - yeah. Sorry - I slipped a zero or three there! Wow...that's *NOTHING*. SteveBaker (talk) 23:52, 12 October 2008 (UTC)

Steve, we're allowed to screw up like that - you're not! ;) hydnjo talk 00:59, 13 October 2008 (UTC)

According to Britannica, a lactase deficient person will produce (or rather, the persons gut bacteria will produce) 500ml to 1000ml of gas from one glass of milk. So if you really wanted to go for it and do record breaking stuff, ten glasses per day would not be too challenging and would yield (for Steve's 70 years) 70x365x10x750ml = 191,625 litres. Which is a bit more house sized. SpinningSpark 23:39, 12 October 2008 (UTC)

October 13

Is our solar system flat ?

In all models and illustrations of our solar system that I have seen, the planets appear to be traveling in one plane. This seems strange to me. Don't the planets actually revolve in different orbital planes, and if so, is there some way that the distance between planets varies with time, maybe to the point of possible collision between two planets? —Preceding unsigned comment added by 58.167.231.238 (talk) 00:11, 13 October 2008 (UTC)

Solar system says: Most large objects in orbit around the Sun lie near the plane of Earth's orbit, known as the ecliptic. The planets are very close to the ecliptic while comets and Kuiper belt objects are usually at significantly greater angles to it., so yes, they're all basically on the same plane. This came about because the planets all formed from a spinning disk of stuff. As for the second question, no the planets are too far away from each other to ever collide. --Sean 00:18, 13 October 2008 (UTC)

Actually, if you ignore the now disgraced Pluto, they do all revolve in roughly the same orbital plane. Our articles on the solar system are actually some of the best at Wikipedia, most are featured or good articles. See Solar system and Planet for some broad overviews. As far as planetary inclination, which is the term for deviation from the mean orbital plane of the solar system, the largest is Mercury at 7^o off center. All other planets are less than 3.5^o off center. Now, lots of other objects do orbit at distinctly greater angles outside of the orbital plane, but none of the main planets do. See List of spherical astronomical bodies in the Solar System for a full list of planets and their stats. The planets are all in fairly stable orbits, and stand no real chance of coliding with one another (even Pluto and Neptune, which swap place in terms of distance from the Sun, do not actually physically cross orbits, and would never collide). Objects in the Solar System do colide all the time, but this usually occurs because some of the smaller objectes, with more eccentric orbits, will collide with a planet. There is no chance for two planet-sized objects to collide. --Jayron32.talk.contribs 00:25, 13 October 2008 (UTC)

Pluto IS a planet, dammit. 67.184.14.87 (talk) 20:30, 13 October 2008 (UTC)

The distances between planets varies dramatically because they all orbit the sun at different rates. Mars (for example) goes around the Sun once every 1.9 earth-years. So if Earth and Mars were as close together as they ever can be - then about a year later, they'll be on opposite sides of the Sun...and about as far apart as they can ever get. But I presume that you are asking whether the radius of the orbits changes. Well, things are a bit more complicated. The planetary orbits are not circles - but ellipses - so the distance of the each planet from the sun varies slightly through the planetary-year. Those ellipses are also slowly rotating - so each planet's path through the solar system looks a bit like a flowery spyrograph pattern. While this pattern seems very stable and is unlikely to change much in the future, the solar system is an "n-body problem" - which is an unsolved mathematical problem - and is believed to exhibit chaotic properties. That means that we can't reliably predict what will happen over the very long term - and it's possible that some strange combination of conditions could perturb the stability of the solar system. While the planets seem to know where they're going - that's not true of moons. It is known (for example) that our Moon is gradually spiralling away from the Earth and will eventually disappear off into space - it's unclear what the consequences will be when that happens. One of Mars' moons is going to break up in the next million years and form an amazing ring system around that planet. Pluto's orbit is thought to be somewhat unstable. So things are not as stable and clear-cut as they seem. SteveBaker (talk) 01:33, 13 October 2008 (UTC)

The moon is backing away from the Earth because it is increasing its orbital angular momentum by stealing from the Earth's rotational angular momentum via tidal drag. Given a long enough time the Earth rotation would slow to match the orbital period of the Moon, and the system would be doubly tidally locked (like Pluto and Charon are). Once that happens the Moon will no longer recede from the Earth. The mechanisms responsible for its recession don't allow the Moon to escape. A back of the envelope calculation suggests that the orbit of the moon can grow to about 5 times it's present size before the Earth's angular momentum is entirely depleted, so that sets an upper limit on the ultimate size of the orbit. Dragons flight (talk) 07:24, 13 October 2008 (UTC)

Actually, if it expanded to 5 times its current distance I think it would outside the Earth's Hill sphere (our article says the Earth's Hill sphere is about 1.5 million km and the Moon's orbital radius 0.384 million km, and 5*0.384=1.92>1.5), so it would be perturbed by the Sun and would eventually enter a direct solar orbit. --Tango (talk) 11:11, 13 October 2008 (UTC)

squid blood

I was watching a tv show about colossal squid. The narrator said that the squid's blood was blue. I have read through the articals on squid, giant squid and colossal squid but can't find any information as to why the blood is blue. Why is this? Also, are there any other animals that do not have red blood?

Thanks. —Preceding unsigned comment added by 216.154.17.55 (talk) 03:30, 13 October 2008 (UTC)

It's bluish. All your questions are answered in hemolymph and hemocyanin articles. --Dr Dima (talk) 03:46, 13 October 2008 (UTC)

short answer: it uses copper instead of iron to grab the oxygen. rust is red, but copper oxide is green. see articles mentioned above for details.Gzuckier (talk) 00:23, 14 October 2008 (UTC)

to know mechanism

please give me satisfactory mechanism of how blood cells come out from the bone marrow? which mechanism do they follow to come out?

i also want to know that through which respiration method RBC respire?

please send me answers of all this questions. i am a biology teacher.

thanking you. —Preceding unsigned comment added by 117.196.0.122 (talk) 04:59, 13 October 2008 (UTC)

For the record, you sound like a biology student. I'd suggest consulting your teachers manual and colleagues for answers. If you can't find them there, read Red blood cell and Bone marrow. In reponse to your second question in particular, consider the following: What enzymes or cellular machinery does a cell require to perform aerobic or anaerobic metabolism? What do RBCs have/lack? --Shaggorama (talk) 07:28, 13 October 2008 (UTC)

Orthogonal translation

Wikipedia doesn't have an article for this. What is it? --M1ss1ontomars2k4 (talk) 05:50, 13 October 2008 (UTC)

Some context would be useful here. Is this phrase just the "plain-English" sum of its parts, i.e., approximately "Orthogonal translation--motion at a right angle to some other direction"? DMacks (talk) 05:57, 13 October 2008 (UTC)

I agree, context is needed to answer this question properly, but orthogonal transformation might be meant if this is a mathematical concept, and the Maths desk might be able to help more]] SpinningSpark 07:08, 13 October 2008 (UTC)

My bad; I intended this question to be in the biological sense. "Orthogonal translation" is noted in several places in my lecture slides but no definition is given. --M1ss1ontomars2k4 (talk) 16:43, 14 October 2008 (UTC)

Alright, so it's translation (biology), and "orthogonal" meaning "completely different of or independent from each other". Consider doi:10.1038/nchembio789:

"Notably, each module is mutually orthogonal with the other modules such that there is little unintentional cross-talk. For example, the lac repressor acts on promoters containing the lac operator sequence but does not repress transcription from the tet or the cI operator sequence; a similar relation exists among other repressors and promoters."

So you either have orthogonal conrols over translation of a certain gene or different pieces of the transcription machinery that only act on certain pieces of genetic code (instead of a single all-purpose ribosome, for example). DMacks (talk) 13:40, 15 October 2008 (UTC)

quantum mechanics

de broglie predicts that matter is a wave, and hence has a wavelength, right? when my teachers explained this, they usually used a baseball or something to show that the effects were small for large objects. well, let's say that plancks constant was large, like 1 J*second. would the baseball have a discernable wavelength? well, the equations of quantum mechanics say that λ=h/p, and so, since the baseball has momentum, it would have a wavelength. but the baseball is just a myriad of electrons, protons, and neutrons. so wouldn't it be those particles which have the large wavelength, rather than the baseball. this question can also be generalized to other concepts like the uncertainty principle: are analogies with macroscopic objects valid? —Preceding unsigned comment added by 65.92.231.82 (talk) 09:32, 13 October 2008 (UTC)

Both the baseball and each constituent would have a wavelength. An experiment has been done with a very small balls, in fact with buckyballs of 60 atoms (see Quantum Mechanics in that article), and the complete balls produce a diffracton pattern just like electrons. Dmcq (talk) 10:04, 13 October 2008 (UTC)

The de Broglie wavelength of any object is given by the simple equation:

$\lambda ={\frac {h}{p}}$

where h is Planck's constant and p is the object's momentum. Since momentum is directly proportional to mass, then the wavelength is inversely proportional to mass; i.e. the more massive an object is, the shorter the wavelength. For any significantly large object, the wavelength of its DeBroglie wave will be so small as to be meaningless, like wavelengths smaller than the diameter of a proton. --Jayron32.talk.contribs 18:13, 13 October 2008 (UTC)

Clockwise or Anti-Clockwise

I know our solar system travels around the our galaxy the milky way. But I do not know if it travels clockwise around the core of the galaxy or Anti-clockwise. By that I mean if the direction pointed by the north pole of the Earth is defined as up, are we traveling around the core, in a clockwise manner or anti-clockwise manner? 122.107.229.49 (talk) 09:40, 13 October 2008 (UTC)

For that matter, I don't even know if the Earth travels clockwise or anti-clockwise around our Sun. —Preceding unsigned comment added by 122.107.229.49 (talk) 09:42, 13 October 2008 (UTC)

Using the Right-hand rule with north in the direction of the thumb, the earth rotates counterclockwise as can be seen from the sun rising in the east. We go around the sun anticlockwise as well, but that axis is tilted by 23 degrees relative to the north pole. (Warning: Tilting causes seasons)

According to [9] the sun rotates around the galactic centre with an axis that's tilted 117 degrees relative to the earth's north. So we're basically going clockwise around the galaxy. According to the sun article, that's at 220 km/s so it takes the sun 8 days to move a distance equal to the distance between us and the sun. Adding the speed of the milky way with respect to the rest of the universe, we're going at a comfortable 370 km/s.

Sundial shadow

The milky way you can see in the sky are simply stars along the galactic plane, which gives you a bearing on where we are. You can see the 117 degree tilting in that the milky way is never aligned exactly east-west in the sky. (If it had been tilted 90 degrees, it would have run north-south and east-west if by 0 degrees) EverGreg (talk) 10:37, 13 October 2008 (UTC)

As an aside, the shadow on a sundial travels "clockwise" (in the northern hemisphere). Clock hands just copy the motion of the shadow. Saintrain (talk) 16:50, 13 October 2008 (UTC)

FISH

In fluorescent in situ hybridisation, how many fluorescent entities must converge on a point to make it visible? How small a point is it likely to be for a typical probe and its unique recognition sequence?

I don't have an answer to your question, but we do have a page on the technique: Fluorescent in situ hybridization (U.S. English spelling) --Scray (talk) 11:01, 13 October 2008 (UTC)

I've created a redirect. --Tango (talk) 11:14, 13 October 2008 (UTC)

I consulted the article before coming here. It was not helpful in this case. :( ----Seans Potato Business 15:25, 13 October 2008 (UTC)

I can't speak to what is typical for the FISH technique, but there is no reason why with the right probe and a sufficiently sensitive sensor that the answer couldn't be one. In general it helps both for visibility and background rejection to have a brighter signal, so FISH may be designed to operate with a greater abundance, but from a technical perspective detecting an isolated fluorescent tag is certainly possible. Dragons flight (talk) 16:52, 13 October 2008 (UTC)

Yup, all you need is one. In FISH, a filter is used on the microscope to exclude all light that isn't within the range emitted by the flourescent tag, so it is an extremely sensitive technique. It is often used to locate individual binding sites on a chromosome, which are tiny! Poke around google for some images. --Shaggorama (talk) 18:13, 13 October 2008 (UTC)

The article is actually a pretty good description of how FISH works. Since the technique is based on hybridization of a unique probe sequence to the target chromosome, only one "fluorescent entity" can be present at a single point on the chromosome. Usually this is a large (50-300 kb) piece of DNA (a bacterial artificial chromosome or fosmid which can be propagated in bacterial culture and purified in large quantities) that is labeled with fluorescent nucleotides so that multiple fluorophores are incorporated into the probe. The size of the probe largely determines the sequence specificity (i.e. whether the probe binds to only one position in the genome), and the sensitivity (brightness) of the fluorescent signal. There will almost always be some background non-specific hybridization that comes from repeated sequences within the probe or low complexity sequences in the genome that are just "sticky", which requires optimization for each given probe. The spatial resolution will depend highly on the conformation of the chromosomes you are using -- the highly condensed mitotic chromosomes will give much lower spatial resolution than interphase ones or the stretched out "fiber FISH" technique (which can supposedly give a resolution of around 1 kb). From a theoretical perspective, one might be able to identify a 16-20 base pair sequence that is present only 1x in the genome of interest, label an oligonucleotide probe and use some fancy tricks to amplify a fluorescent signal so that it could be detected by a highly sensitive microscope. The smallest reported probe is around 50 bp (see this), but from a practical standpoint it isn't done this way very much. —Preceding unsigned comment added by Medical geneticist (talk • contribs) 20:35, 13 October 2008 (UTC)

Questions about massive sqid

1. Is there a theoretical maximum possible size for squid?

2. Would it be possible to capture a giant/colossal squid alive to place on display in an aquarium? —Preceding unsigned comment added by 84.71.115.30 (talk) 12:10, 13 October 2008 (UTC)

Tthere are some theories on how large an animal can get. A predator for instance, may be limited by the size of its prey [10]. But according to Deep-sea gigantism, there may be advantages to being big in the deep ocean. But noone has calculated an exact maximum size. In [11] it is speculated that an unusually large squid had messed-up hormones so in any case there'd always be giant freaks that didn't fit into the theories. As for the second question, it's probably easier to catch a young one and raise it to adulthood in captivity. EverGreg (talk) 12:33, 13 October 2008 (UTC)

Squid belonging to the 'large' species decompress and die if you haul them up from the deep to the surface, don't they? --Kurt Shaped Box (talk) 22:36, 13 October 2008 (UTC)

I get this, ...with the extreme change in pressure, and environment in general, these creatures can't survive for very long, if at all, on the surface. from the article Deep sea creature. Julia Rossi (talk) 09:51, 15 October 2008 (UTC)

composite aircraft

Good Day,I would like to know how many composite (carbonfiber/fiberglass) Federal Aviation Administration certified aircraft were built every year from 1998 to the present.Please if possible list by manufacturer. I would also like to know if any projections are made by the manufacturers or the F.A.A. for the future of composite aircraft.65.15.124.92 (talk) 18:44, 13 October 2008 (UTC)

O-ring and G-ring

I'm confused by the term O-ring; it seems to have one or two additional meanings beside the one found here, referring to metal rings. Is there a 2nd meaning to the term "O-ring" that means the kind of double-looped steel ring that is commonly used as a keyring? I found this meaning e.g. here. My theory is that people don't know how this type of ring is properly called and make an analogy to the related G-ring - "it's like a G-ring but in the shape of an O". Is that right, or is "O-ring" a proper name for this thing? The 3rd possible meaning of the term "O-ring" can be found in items of jewellery such as necklaces and earrings. If my interpretation of the pictures I found via Google is correct, here the term means something like "a bigger decorative circular ring sideways attached" - is that right?--84.155.219.241 (talk) 19:22, 13 October 2008 (UTC)

I have always only heard O-ring to mean a big rubber gasket or washer of some sort. Though it certainly may have other uses. --Jayron32.talk.contribs 19:27, 13 October 2008 (UTC)

Sorry, I need to rephrase the 2nd part of my question. I'm also wondering whether there is a 2nd meaning to the term G-ring, found in items of jewellery such as necklaces and earrings. If my interpretation of the pictures I found via Google is correct, here the term means something like "a bigger decorative circular ring sideways attached" - is that right? 84.155.219.241 (talk) 19:30, 13 October 2008 (UTC)

Sounds to me like in jewellery, an O-ring would be a solid ring such as one found at one end of a necklace; and a G-ring would be an O-ring with that little opener thing (i.e. a clasp) that you pull back to fasten the necklace. By my interpretation, when you pulled open the little clasp-thingie, it would look exactly like a "G". Franamax (talk) 05:07, 16 October 2008 (UTC)

How does NASA calculate trajectories?

When NASA calculates the trajectory of an interplanetary space probe, do they use Newton's formula's (classical physics) or Einstein's (relativity)? 67.184.14.87 (talk) 23:07, 13 October 2008 (UTC)

Newton is plenty good enough for trajectories. The systems that provide the thrust and measure the position/velocity aren't accurate enough to show the consequences of relativity at the speeds that current spacecraft move. SteveBaker (talk) 23:53, 13 October 2008 (UTC)

It's true that the probe will usually get close enough to its target without relativity, but to take the question literally, "they" (JPL) do actually "use ... relativity" in the detailed calculations. According to this blog, the Messenger's voyage to Mercury requires relativistic corrections. --Heron (talk) 18:14, 14 October 2008 (UTC)

I wonder if that's for all space probes or just Mercury. I've read that Newton's equations don't accurately predict the orbit of Mercury. 67.184.14.87 (talk) 17:12, 15 October 2008 (UTC)

The precession of Mercury's orbit is greater than Newtonian physics would predict and requires GR to get it right. I'm not sure how big a difference that would make over the length of time required for the probe's journey, but it might be enough to warrant including in the calculations. Missions to Mercury will probably require more relativistic corrections that elsewhere in the solar system, since you're closer to the Sun, but I don't know if you just need less for other missions or none at all. --Tango (talk) 17:33, 15 October 2008 (UTC)

The extra 43"/century is about .5 km/day, so significant. Saintrain (talk) 18:33, 15 October 2008 (UTC)

Yes, there are effects like that - but they are negligable compared to the errors due to the inaccuracy of the rocket burn power and duration - and the inability to point the rocket with enough precision. Hence course corrections are needed - and those unpredicatble corrections totally swamp the magnitude of any relativistic effects. In the case of Mercury - you may need relativity to figure out where it will be in 10 years time when your rocket is intended to get there - but the path the rocket takes to get to that point at that time is an entirely Newtonian calculation. The errors due to the speed of the spacecraft causing time & space dilation is nothing compared to the unpredictability of photon pressure from the sun, inaccuracy in your initial launch, etc, etc. It's negligable.

What is the theoretical wavelength upper limit for electro-magnetic waves?

Extremely low frequency waves have a wavelength of ~ 10,000km - 100,000km. Is there an upper limit? The size of the Universe?, or as the Universe is unbounded is the upper limit infinite? Jooler (talk) 23:04, 13 October 2008 (UTC)

There is no natural limit, though the size of the antenna one can operate and other factors do impose many practical limits. Dragons flight (talk) 17:43, 15 October 2008 (UTC)

(ec (who cares about ec's anyway? :-)) It appears that there is no theoretical upper limit to wavelength. From Planck constant (and a little rearranging) $\lambda =hc/E$, where $\lambda$ is wavelength, $h$ is Planck's constant, $c$ is the speed of light and $E$ is the energy of the photon. Since there's no lower limit to E, there's no upper limit to $\lambda$. There is probably a minimum actual energy (steps between electron energy bands, say) that puts a practical limit on the wavelength of a photon that can be emitted. Saintrain (talk) 17:52, 15 October 2008 (UTC)

The expansion of the universe has stretched the wavelength of light in a (so far as we know) continous manner. The microwave background radiation for instance, started out with shorter wavelengths. And if Planck's law is to be taken literally, black-body radiation contain photons of arbitrarily long wavelengths, since the wavelength distribution has no cutoff for large wavelengths. In that case, name a wavelength and it's all around us, though in small amounts.

But with analogy to the quantum well which enforces a maximum wavelength, you can probably find a cutoff invoking the size of the visible universe and inflation theory. If I recall correctly, there's also some low-frequency waves reflected in the upper atmosphere, that have their wavelengths limited and quantized by the circumference of the earth. EverGreg (talk) 08:54, 16 October 2008 (UTC)

What triggers a missile to explode?

What, exactly, is it that causes a missile, specifically a surface-to-air missile, to explode? Does it have guidance built in so that when it reaches a specific point in space, it goes "I have now reached my target; I shall explode now", or does it have sensors to detect that, or a mechanical trigger which goes off on impact? (Could you theoretically grab a missile (gently) out of the air and hold it without setting it off?) What happens if the conditions for exploding are not met and the missile gets lost or starts running out of fuel to keep seeking the target? Does it explode, or become inert/safe? SamSim (talk) 23:11, 13 October 2008 (UTC)

We'd tell you but then, well you know...  ;) hydnjo talk 23:30, 13 October 2008 (UTC)

Well, that scuppers my plans for stealing SAM's and asking on Wikipedia how to set them off. I guess I won't post my question on how to launch them either. Anyone know a good place to sell unused surface-to-air missiles? eBay? Franamax (talk) 04:08, 14 October 2008 (UTC)

Its called a # Fuse_(explosives), If missile goes wrong and is heading back to you, there is a thing called a Break up system that, well, breaks up the missile without detonating the warhead.

--GreenSpigot (talk) 01:04, 14 October 2008 (UTC)

Clearly one could build a missile to explode due to the passage of time, due to altitude, due to impact, or due to proximity to a possible target, as well as due to triggering by the party who launched it. Edison (talk) 05:17, 14 October 2008 (UTC)

For guided missiles, the same system that's doing the guidance is likely to be the trigger. A radar-guided missile (for example) can use the radar returns to set itself off when very close to the target. SteveBaker (talk) 09:43, 14 October 2008 (UTC)

No, sorry. Guidance system and fuzing are completely separate parts of a missile: the fuze is in the warhead. If our articles combine them, they're wrong to do so.--GreenSpigot (talk) 02:44, 15 October 2008 (UTC)

Maybe I'm nuts, but I've always had the impression that most missles were actually designed to physically impact their targets, and hence would generally be expected to have fairly dumb impact driven triggers. That's different from same a cluster bomb or area-effect artillery that simply wants to get close and then detonate in the air. Dragons flight (talk) 10:24, 14 October 2008 (UTC)

For manouvering air targets the chance of a direct impact is relatively small, so relying solely on an impact fuse would not be a wise thing. Also I'm not sure if using the main guidance is generally done. I always thought most *-to-air missiles had a seperate proximity fuze, because the explosion (see continuous-rod warhead) is most effective to the side (where the main guidance system cannot scan, though it could possibly estimate). To answer the second part of your question: the K-13 and Sidewinder articles have a nice paragraph about your theoretical situation. Ever since then, air-to-air missiles self destruct if they miss their target. I'm not sure if it's also true for surface-to-air missiles, but something tells me they do, after all, you don't want your own missile coming down on your troops. - Dammit (talk) 10:44, 14 October 2008 (UTC)

Correct. Physical impact is not required as proximity fuzes of one type or another are almost always used. In fact I think achieving physical contact would be rather difficult in the case of a missile trying to shoot down another missile.--GreenSpigot (talk) 02:44, 15 October 2008 (UTC)

Actually, the Aegis Ballistic Missile Defense System is a direct impact missile to missile system. The impactor is a "kinetic kill vehicle" (see kinetic projectile) and has no explosive at all. This works, in part, because ICBMs are largely unpowered during their sub-orbital arc, and hence don't dodge. Dragons flight (talk) 17:55, 15 October 2008 (UTC)

Why can pulse be normally abnormal?

I'm a little confused, after reading the article on the pulse as it relates to the body. I understand it's not always the same as heart rate - so is that it? Because, I'd been under the assumption one would just check for 10 seconds or so and multiply by 6, or at least 15 and multiply by 4. Does this mean that pulse rate can have a few little skips, and if so, why? Is it slight movements - the hand moving a bit while trying to measure at the wrist? is it the different things that cause the waves in the heart's normal sinus rhythm? Or, what? —Preceding unsigned comment added by 209.244.187.155 (talk) 23:44, 13 October 2008 (UTC)

Pulse rate and heart rate are identical under most circumstances (the exceptions mainly occurring when the heart is pumping abnormally). But neither is as regular as, say, a CPU. It's not a clock. It speeds up, it slows down, based on a variety of variables: exertion, rest, drugs, stress, emotion, vagal nerve stimulation, etc. So 10 seconds is too short a time for a reliable estimate of heart rate. Count for 30 seconds and multiply by 2, or for a full 60 seconds. And you should expect the pulse to fall within the normal range (60-100) rather than to be the same each time you take it. - Nunh-huh 23:57, 13 October 2008 (UTC)

Perhaps the OP is asking about regularly irregular pulse, e.g. second degree AV block. These rhythms are irregular, but beat patterns can be grouped in a way that can be described as regularly irregular. In particular, for these rhythms one should count for a few cycles of the beat group, or about a minute, before estimating the heart rate. --Scray (talk) 02:34, 14 October 2008 (UTC)

To rephrase, they are irregular at regular intervals. They follow a clear pattern, but the pattern is an irregular. --Shaggorama (talk) 16:39, 15 October 2008 (UTC)

October 14

Plutos' core

Is Pluto's core generally hot or cold? From this image, it said the center is made of alloy, iron-nickel, and the mantle is rock and ice. I thouhgt Pluto's core would not be hotter than the surface of Venus, but may still be warm enough for water to become a steam? Since Pluto's atmosp is only 1/1000 of Earth's fraction, the globe colour would be gray perhaps yellow-tan or orange-yellow tinge add to the gray.--Freeway19 00:50, 14 October 2008 (UTC)

Do we have answer to is Pluto's center hot or cold. Some scientist beieve it is made of ieon nickel with alloys stuff. Will It put pluto's center to at least 100 C. I know it is unlikely to be 500 C or 1000 C. --Freeway19 02:30, 14 October 2008 (UTC)

Probably over 1000 C. Hundreds of kilometers of rock and ice is a very good insulator; it holds in heat. If there is a liquid ocean, people think it starts only ~250 km down. [12] Dragons flight (talk) 03:54, 14 October 2008 (UTC)

Except that everything in the solar system is roughly formed at the same time, so roughly exposed to the same conditions. As Pluto is smaller than the moon, and the moon can demonstratably be shown to have a cold center, Pluto is likely to also have a cold center. --Jayron32.talk.contribs 10:38, 14 October 2008 (UTC)

Well, if the moon formed from a collision with the Earth, then it could lack some of the heavier elements and those are often the radioactive ones. That would mean there would be more radioactivity in Pluto's core than the moon's, but I'm not sure it would be enough. --Tango (talk) 10:46, 14 October 2008 (UTC)

The moon's core may be as high as 1400 C [13]. That's "cold" only from the point of view that iron is not molten (needs 1600 C). Dragons flight (talk) 10:51, 14 October 2008 (UTC)

I'd have to do some research to be sure, but my guess would be that Pluto's core is ice cold. How much heat it could have retained from the formation of the solar system is dependant on size and Pluto is tiny, so it likely has very little retained heat. The sun is obviously too weak at that distance to heat it up. There could be some heat from radioactivity, but that's about it (there won't be any tidal heating since it is tidally locked with its only large moon - I doubt Nix and Hydra are large enough or close enough to do much). Radioactivity could keep it warm, but I would guess not to above freezing. If I get a chance, I'll research it later. --Tango (talk) 10:46, 14 October 2008 (UTC)

I already provided a reference to a scientific paper predicting liquid water on Pluto at only 250 km, i.e. 1/5th of Pluto's radius. Dragons flight (talk) 11:03, 14 October 2008 (UTC)

Here's another one [14]. Pluto goes above the freezing point of water at only 180 to 300 km depth. That leaves another 1000 km of temperature rise to get to the core. Radioactive heating is efficient when you are planetary size and can't easily dissipate heat. Dragons flight (talk) 11:14, 14 October 2008 (UTC)

Light Concentration

What exactly is a Light Concentration diagram? I have failed to find one on Google, or anywhere for that matter. And if someone can answer that, could you tell me where I could find one for Lake Baikal (in Russia), or what one would look like?72.65.101.51 (talk) 00:53, 14 October 2008 (UTC)

Could you mean light intensity? A diagram or graph would show the intensity dropping with depth. Graeme Bartlett (talk) 03:07, 14 October 2008 (UTC)

Some mathematical physics expression

$\displaystyle {D_{x}^{I}\rho _{I}V_{I}T_{I}\ {\overline {B_{xy}^{(I\,II)}}}}$
This is an expression I saw in a picture written on a blackboard behind Niels Bohr. Could someone please tell me what it pertains to and means and what articles would have more information about whatever it is? Thanks in advance, Ζρς ι'β' ^¡hábleme! 02:14, 14 October 2008 (UTC)

I don't think you are going to get a definite answer from just that. It might help to know how old Bohr was in the photos since physics evolved a lot in his lifetime. Off hand, I'd guess some form of quantum mechanics expression, with ρ a density, V a volume, T a temperature, D_x a differential operator in x, and the I and II denoting two kinds of material. If you assume he's dropping constants (as theorists often do) then it looks like a derivative operator in x acting on an energy times some interaction function B. What B is, I haven't a clue. Often "B" denotes a magnetic field, but you'd be unlikely to sub and superscript it that way if that were the case.

Also, I could be totally wrong. Dragons flight (talk) 04:53, 14 October 2008 (UTC)

He was older in the photos, perhaps 60-65. Ζρς ι'β' ^¡hábleme! 23:19, 14 October 2008 (UTC)

Looks like Einstein notation to me, but not sure. EverGreg (talk) 09:06, 16 October 2008 (UTC)

Is Heisenburg's Uncertainty Principle really universal?

Perhaps it's just personal, but I find this Principle to be a fraud. Surely, though, I'm not right and everyone else is wrong. It states that by locating a particle you make its momentum uncertain and vice versa. But a Principle of physics should accurately describe matter and the universe, not our ineptitude as observers. For example, if we were omnipotent gods, and could 'see' these particles, Heisenburg's Principle surely would not make sense. If really small aliens possessing intelligence and observational powers were the same size of these particles, surely THEY could determine the position AND momentum for any given unit of time.

I find it like cave men trying to understand tigers, only the tiger eats them when they come near him. They only way they can study him is to throw spears at him until he's dead. Would these perhaps thoughtful cavemen have a Tiger's Uncertainty Principle, and state "Well a living Tiger is just UNKNOWABLE" because they lack the proper tools to analyze the Tiger?

I feel that Heisenburg's Uncertainty should not be presented as a Principle, a 'rule,' or really any part of Physics other than a statement along the lines of "We suck as observers and can only 'detect' these particles by shooting high energy particles AT it, thereby ruining our original setup."

Why is this not presented in this way, or has noone made these objections? Am I missing something?

Ehryk (talk) 05:41, 14 October 2008 (UTC)Ehryk

No the point, and I agree it is spooky, is that a particle cannot have both a precise position and precise location at the same time. It is not simply that they are unknowable, but rather non-existent, even to God, aliens, or whoever else might claim to be able to see them. The double slit experiments, Bell inequalities and related results demonstrate empirically that our conception of matter having fixed position and momentum simply isn't how the universe works on a small scale.

At a fine scale, quantum mechanics tells us that everthing is smeared out in a fuzzy way. Even a single particle doesn't have one precise position but rather a whole distribution of positions, and with them a whole distribution of momentums. Things at the subatomic scale simply don't exist at only one place and time. The more we try to confine them to only a single position, the more they will necessarily widen their range of momentums. Your view that there should be some hidden and singular true position/momentum visible to God is known as local hidden variable theory and the most obvious forms of that have been shown experimentally to be false. Dragons flight (talk) 06:19, 14 October 2008 (UTC)

Heisenburg isn't talking about our ability to measure - he's talking about the fundamental nature of the particles themselves. It is literally true that if you try to limit the momentum of a particle it literally becomes a fuzzier thing so that its position is an increasingly vague thing. If you try to confine it into a small space to nail it's position more accurately - then it's momentum will become more 'blurry'. So you can take the "Us" and "observers" out of the debate here. Even omnipotent gods and teeny-tiny aliens would see the position of a particle as a statistical 'cloud' and its momentum as an indeterminable thing. Quantum mechanics is something that we humans are not equipped to comprehend because at our 'scale' of existence, the effects are generally negligable - but they are strange and oddly beautiful. But without them, the computer you're sitting at right now wouldn't work. The statistical weirdness of the position and momentum of a particle is what makes 'quantum tunneling' work - and without that, you wouldn't have any flash memory for your BIOS, your MP3 player or your memory sticks. So Heisenburg isn't just a means to describe the limits of our abilities - it's describing how the universe operates at a fundamental level. SteveBaker (talk) 09:41, 14 October 2008 (UTC)

As SteveBaker points out, the UP is not just about our limits as observers. Another way to think about it, a more elegant way than the "we move a particle to detect it", is as a wave function. Every complex wave can be considered a series of waves added together. You could, hypothetically, layer more and more wave functions together and they would cancel each other out leaving one big wave in the middle. Now imagine doing that for a very small particle. You'd layer wave after wave after wave, trying to get one little spike in the center. Well, when you get down to the scales where the UP takes effect, it requires an infinite number of waves to make that final tiny wave. Or something along those lines. This formulation of the UP is identical to the more classical ones—except it has nothing to do with measurement. --98.217.8.46 (talk) 11:31, 14 October 2008 (UTC)

The uncertainty principle is a mathematical theorem that holds for any kind of wave, not just quantum mechanical wave functions. If you force a classical light wave (Maxwell's equations) or a classical water wave through a narrow opening it will spread out in all directions on the other side, because by confining its position you've left its momentum very uncertain. Musical notes are subject to a pitch-time uncertainty relation: a note of brief duration has uncertain pitch. Piano tuners listen for beats between a note made by the piano and a reference tone; as the two pitches approach each other the frequency of the beats approaches zero, so it takes arbitrarily long to tune a piano arbitrarily well. That's the uncertainty principle. Waves of any kind behave more and more like particles as the frequency increases. That's why geometric optics works so well for visible light. Classical physics is (in a mathematically precise sense) the geometric-optics version of quantum physics. It works well at ordinary scales because Planck's constant is small. -- BenRG (talk) 11:57, 14 October 2008 (UTC)

The first thing you must know is that Heisenburg's Uncertainty Principle is a mathematical property and NOT a physical property. By that I mean it occur because of mathematics and not because Physicist discovered it in the real world. Human beings are not designed to think in terms of wave like behavior which is why you have such a hard time understanding it. If you imagine taking a picture with a SLR camera, you can increase the sharpness of the picture by reducing the aperture but doing so you would need to increase the shutter time. So you can say the aperture (size) * the shutter time is a constant. The uncertainty principle is just like that. 122.107.229.49 (talk) 13:09, 14 October 2008 (UTC)

Einstein thought that the randomness of the uncertainty principle is a reflection of mankind's ignorance of some fundamental property of reality, leading to Einstein's famous quote, "God does not play dice with the universe".

I read that the Bell test experiments put to rest Einstein's objections although I cannot see how any test can possibly prove this if this test was conducted by a human. To rule out human ignorance, you would need a higher life form.

Scientists have for decades tried to reconcile quantum mechanics and general relativity in a single unified theory, which implies that one or both theories might be wrong or at least incomplete.

I agree with the original poster that the Heisenberg Uncertainty Principle is flawed. According to quantum mechanics, the Moon does not exist unless there is someone to observe it.

Given that everything else in the universe is deterministic - everything from the boiling point of water to the timing of the next solar eclipse, I find it hard to believe that subatomic particles would behave any differently. I still think it is more likely that our inability to make deterministic quantum predictions is due to a lack of understanding than a lack of determinism.

It should be pointed out that scientific consensus can and does change over time. Ptolemy's model of the universe was the consensus for over a thousand years, until it was supplanted by Copernicus' model, which lasted over 300 years until it too was supplanted. Yes, quantum mechanics is the current scientific consensus. But for how long?

Fortunately, science is a self-correcting process. As long as human intelligence is great enough to figure it out, it's only a matter of time before it's disproved.

It would be nice, however, if in my lifetime, this issue is resolved. 12.10.248.51 (talk) 14:06, 14 October 2008 (UTC)

The issue has already been "resolved" - many times over - and to the utter (eventual) satisfaction of great minds like Einstein. The Uncertainty principle is as real as Newtons laws of motion. It is literally true that the computer you are sitting in front of when you read my words would not function if it were not for the truth of the UP at the physical level. This is not something you should be doubting! SteveBaker (talk) 23:04, 14 October 2008 (UTC)

Actually, the HUP says nothing about observations of macroscopic objects like the moon. Your senses and reason are perfectly adequate to make statements of objective reality about objects like the moon, because the act of observing the moon does not change the moon. This is VERY different for fundemental particles. When you look at the moon, you do not need to change it; you can passively observe it. For something like an negatively charged electron, in order to observe it, you need to set up a detector with some sort of charge of its own, and measure the deflection of your detector. The problem is, and this is a basic "classical" mechanics situation, any deflection on your detector will result in an equal and opposite deflection on the electron. Thus, by the very act of observing the electron, you must change it. The HUP is a generalization of this phenomenon, and it patently does NOT apply to large objects whose observation does not depend on changing them in some fundemental way. The moon really is there if no one looks at it. --Jayron32.talk.contribs 16:42, 14 October 2008 (UTC)

Personally, I do believe that the moon exists when no one is looking at it, but that's not what David Mermin, Professor of Theoretical Physics of Cornell University claims:

"Pauli and Einstein were both wrong. The questions with which Einstein attacked the quantum theory do have answers; but they are not the answers Einstein expected them to have. We now know that the moon is demonstrably not there when nobody looks."

http://www.jstor.org/pss/2026482 —Preceding unsigned comment added by 12.10.248.51 (talk) 17:20, 14 October 2008 (UTC)

That's SO bogus. "Looking" is not the same as "observing". Even if the moon were subject to quantum effects (which - for all practical purposes - it's not). What "demonstration" can be done to show that the moon isn't there when you're not "looking"? I can be on the other side of the planet from the moon - and notice that the tide is going in and out. Which is indirect proof that the moon is still there. To have any hope of proving such a patently false hypothesis - you'd have to exclude all kinds of observation. So you'd have to say that the moon isn't there when nobody is looking at it AND nobody is noticing the tides AND nobody is noticing it's effect on the progress of the earth's orbit around the sun AND...so on. Since every atom from here to the next star over is feeling SOME gravitational tug from the moon - how can there ever be a situation when it's not be observed in some sense. This SO bogus. I have two pieces of advice here: (1) Philosophers are a waste of space...unless they are actually IN SPACE - then they're a waste of perfectly useful vacuum. Not one thing they've ever come up with has been worth the effort of reading. (2) If you attempt to learn about quantum theory and what the likes of Einstein and Pauli were REALLY talking about - "The Journal of Philosophy" should not be your first (or last) stop! SteveBaker (talk) 23:04, 14 October 2008 (UTC)

(edit conflict) Err, you really do have to read the whole article to make sense of what he means. He's not talking about the literal moon. He's talking about the EPR paradox and how the Bell tests appear to have resolved it. In a very very simplistic version of the EPR argument: if you know UP means you can't know position/momentum at the same time, what if you do some sort of process which theoretically spits out two identical particles at the identical velocities in exactly opposite directions. Couldn't you measure the momentum of one, jot that down, and at the same time measure the position of the other? Wouldn't that tell you two impossible-to-know things about the particle which you measured the position of? That's basically the EPR argument (except that spin and something else was the entangled property, if I recall)—that UP would limit you physically from measuring things but didn't limit the possibility of measurement of entangled properties. Einstein said, "you can know everything despite UP," Bohr said, "well really you're just wrong", and Pauli said it was just a philosophical debate—like asking about the moon. But decades later a smart dude named Bell came along and actually came up with an experimental setup that could distinguish between the two points of view. That's what the Bell tests are about. They are not that easy to explain (the Mermin article does a pretty good job of it but I was still pretty baffled) but the gist of it is if you do a bunch of statistical tests you'll find that when you "look" at the properties you see different things than if you hadn't looked. Very weird stuff but experimentally it seems to work out. --140.247.11.9 (talk) 23:09, 14 October 2008 (UTC)

You people are talking about Werner Heisenberg, right? I wouldn't trust that Heisenburg guy for a second. Franamax (talk) 08:32, 15 October 2008 (UTC)

If Mermin meant that as a metaphor, then it's not quite that bad, but still wrong. Not being able to measure an electron's position and velocity at the same time is not the same thing as saying that the electron has no position or velocity until it is measured. 67.184.14.87 (talk) 14:49, 15 October 2008 (UTC)

hmm. i'm not satisfied with anybody's answer thus far, so i have to throw in my $.000000002 worth. the uncertainty principle is based on the principle that all particles are actually waves. as such, fooling around with fourier analysis or just a little insight will tell you that a wave of a specific frequency extends infinitely; in order to put boundaries on it, you have to smear the frequencies out a little so that they are finally out of phase where you want the wave to end. in the ultimate opposite case from having a defined frequency with infinite dimensions, you have a pulse with a single defined position; but this requires a mix of an infinite number of frequencies. that's absolutely true for waves, nobody has any disagreements or doubts. well, if all particles are actually waves, then it must be absolutely true for them as well; the more defined they are in "location space", the less defined they are in "frequency space" and vice versa. how it works out in reality, and perception, etc. are all just derived from that basic property. Gzuckier (talk) 15:11, 15 October 2008 (UTC)

Why did bacteria evolved?

What is the need for more complex forms of life above bacteria? Aren't bacteria not fit enough everywhere on Earth? Mr.K. (talk) 09:48, 14 October 2008 (UTC)

Because multi-cellular life didn't die out. One can speculate about what advantages multicellular life might have had (greater mobility, greater ability to regulate intracellular conditions, greater longevity, intelligence, dashing good looks, etc.) but ultimately the only real "reason" behind complex life is that life tried it out and didn't die. Evolution doesn't have some overarching plan or some predesigned number of niches to fill, it is simply the persistent accumulation of whatever genes happened to have worked. Dragons flight (talk) 10:00, 14 October 2008 (UTC)

(Repeating Dragons Flight because this cannot be repeated enough...) Evolution is not intelligent and, therefore, doesn't decide when to evolve and not to evolve. Evolution is a term for a process in which DNA slowly changes over long periods of time. So, you cannot ask "Why did bacteria evolve?" You can ask "How did bacteria evolve?" It evolved by a slow process of DNA mutation, survival of the fittest, and replication of rare qualities until they became common qualities. -- kainaw™ 13:29, 14 October 2008 (UTC)

Of course you can ask why a living organism evolved. The answer would be that some living organisms were not fit for their new environment. That makes specific mutations become stable in a population. The problem with bacteria is that they seem to be the fittest form in any environment on Earth and apparently even outside it. Mr.K. (talk) 15:53, 14 October 2008 (UTC)

Hardly. Archaea are much fitter. --Ayacop (talk) 16:03, 14 October 2008 (UTC)

Well, there's a tautology here, and a valid one, that we are ignoring. When you judge fitness on a set of arbitrary conditions, like "hey, this stuff grows in lots of weird places, so it must be the best form of life EVER", well, that isn't really a measure of fitness. The true measure of fitness is survival. Many organisms are quite fit in their own ways, and if they were somehow less fit than others, the others would have crowded them out by now. --Jayron32.talk.contribs 16:33, 14 October 2008 (UTC)

To Kainaw: Yes, DNA is a big part of the picture, but there's also evolution of the epigenome and siRNA's that are not strictly heritable only through DNA, they seem to be a meta-system inherited with the DNA. In other words, DNA comes with the pre-formed elements that shape the use of the DNA. Just my impression, but it's all quite fascinating. Franamax (talk) 08:24, 15 October 2008 (UTC)

bottom line; there were some environments which bacteria hadn't thoroughly exploited successfully, so there were niches for other organisms to evolve into. (the inside of a refrigerator, for one example....) bear in mind, though, that for billions of years bacteria and their cousins blue green algae were the only critters on earth, so they did a pretty good job. on the other hand, as soon as eukaryotic cells evolved, there has been this burst of complexity in a relatively short time, so that was apparently the area prokaryotes couldn't evolve into. Gzuckier (talk) 15:28, 15 October 2008 (UTC)

A) Blue gree algae are bacteria. B) Bacteria shared the early Earth with archaea. C) Prokaryotes did evolve into those niches... by way of becoming eukaryotes. D) Single-celled eukaryotes arose at least 500 million years before they evolved into large complex forms, and perhaps more than 1.5 billion years (i.e. no rush to complexity). Dragons flight (talk) 17:32, 15 October 2008 (UTC)

I see that my knowledge of the evolutionary dates of eukaryotes is sadly out of date. Gzuckier (talk) 21:24, 15 October 2008 (UTC)

Medical condition relating to films

I once heared about a medical condition where the sufferer could not follow films (or tv shows) because if a different camera angle was used in a scene they could not comprehend that it was the same scene. Does anybody know what this condition is? Thanks Mark Model (talk) 11:17, 14 October 2008 (UTC)

This doesn't sound like it's necessarily a medical condition: our capacity to understand the narrative shown to us in filmic media is a trained skill. One common convention we take for granted is the match on action: shot 1 john points to his left, shot 2 we see a car accident. If it we hadn't seen so many movies and TV already, we wouldn't necessarily make the connection that john was pointing at the car accident. I remember hearing that when motion pictures were still young, there was a film that showed a train coming towards the viewer (maybe man with a movie camera?). The audience fled in terror. You may find culture-bound syndrome interesting. If what you describe is a real 'condition,' it may be an agnosia. --Shaggorama (talk) 16:35, 15 October 2008 (UTC)

Some people on 4chan say that their parents get dizzy or sick while watching them play 3d video games. What's this about?Avnas Ishtaroth _{drop me a line} 01:31, 16 October 2008 (UTC)

pwnitis, perhaps. --Shaggorama (talk) 07:33, 16 October 2008 (UTC)

This is the same phenomena as Sim-sickness.

I certainly get dizzy/sick when watching other people play some kinds of 3D game - and (very rarely) a movie will cause it (the one that comes to mind is Cloverfield). (Which - since my job is writing software for computer games - can be a pain to deal with!) For what it's worth, I can generally pin the problem down to poorly written camera motion software - especially if the field-of-view is set out unrealistically wide (which is almost always the case with 1st person games). When the virtual camera ("eyepoint") is moving at high speeds but not leaning into the corners or being thrown out sideways realistically - then I get sick. The effect is much worse when the frame rate is poor and it's worse when someone else is playing than when I'm playing (but it's still there when I play alone for a large amount of time) - and it's much MUCH worse on large TV's or projection systems. The error between physical reality and what the computer does can be fairly subtle. My "gut feel" (in an all-to-literal-sense!) for bad camera motion has become legendary in some places I've worked. My belief is that when you play the game yourself, your control over the camera gives you some kind of feedback for why it's doing what it's doing. The large screen TV issue is because the more of your visual field is filled by the bad camera action - the more your brain starts to think you're "in the game" rather than "outside the game". The sensation itself is identical to sea-sickness - and drugs like dramamine do help. In the flight simulation world, this is called "Sim-sickness" and an amazing amount of government dollars have been put into fighting it for military flight simulation. SteveBaker (talk) 13:30, 16 October 2008 (UTC)

Cola as a spermicide?

Is this true? Why do so many people still drink it then? Which amounts are they talking about for it to work? --217.227.77.18 (talk) 11:20, 14 October 2008 (UTC)

They mean if you directly immerse your sperm in cola they might swell up and die (2008 Ignobel Prize). This is not generally claimed to be an effective contraceptive under any normal circumstances, and merely drinking lots of cola is not claimed to have any effect at all. Dragons flight (talk) 11:29, 14 October 2008 (UTC)

Yes, although it is probably a weak spermicide. "The Spermicidal Potency of Coca-Cola and Pepsi-Cola," C.Y. Hong, C.C. Shieh, P. Wu, and B.N. Chiang, Human Toxicology, vol. 6, no. 5, September 1987, pp. 395-6. Pubmed. Ingesting a liquid is entirely different than applying the liquid to your sperm. Your digestive system breaks down liquids before they are circulated through the body so it isn't as though pure coke is being pumped into your testes.--droptone (talk) 16:05, 14 October 2008 (UTC)

Just to be absolutely clear, Droptone is not suggesting anyone inject cola into their testes as a contraceptive! ;) My guess is that it would be very effective and very permanent... --Tango (talk) 12:21, 14 October 2008 (UTC)

That sounds like an excellent recipe for a Darwin Award. Dragons flight (talk) 13:21, 14 October 2008 (UTC)

No - it's DEFINITELY not true. The Mythbusters busted this theory. Also Snopes says "No" - and they cite a half dozen impressive scientific studies in reputable journals. SteveBaker (talk) 22:42, 14 October 2008 (UTC)

Actually... the exploration of the "Effect of 'Coke' on sperm motility" (in the NEJM, no less) that showed it was effective, and the followup that refuted the claims were joint winners of a 2008 Ig Nobel Prize! :) — Scientizzle 22:53, 14 October 2008 (UTC)

Name of Phobia

Is there a name for a phobia of seeing a swarm of the same thing? For instance, I panic and run if I see a swarm of ants. It skeeves me out. But if I see one ant walking around, its fine. Same for worms, bees, ladybugs, etc. And one time, I saw a cartoon of a swarm of catepillars (with happy faces) in a coloring book. I couldn't even look at it without feeling like I was gonna dry heave. Is there a name for this phobia? --Emyn ned (talk) 13:32, 14 October 2008 (UTC)

It may simply be a mild insect/worm/creepy crawly phobia. One is not too much for you to handle, but several at once is too many.CalamusFortis 15:28, 14 October 2008 (UTC)

(ec) Most person-specific phobias aren't medically recognized and named. You could call it swarmophobia if you'd like. -- MacAddct1984 ^{(talk • contribs)} 15:34, 14 October 2008 (UTC)

err..says who? The APA has made a point of classifying every human neurosis and eccentricity imaginable! In fact, I'm of the opinion that they've gone somewhat overboard and are blurring the lines between personality trait and condition in a growing number of instances. --Shaggorama (talk) 17:33, 14 October 2008 (UTC)

See specific phobia (DSM-IV 300.29). The only phobia I can find specifically mentioned is agoraphobia (300.21, 300.22). -- MacAddct1984 ^{(talk • contribs)} 17:47, 14 October 2008 (UTC)

Since it's up for speculation, let's try plethoraphobia because it seems to be a fear of an excess of something, or more precisely, aggregatophobia from aggregare for "herded together" or "a flock". Julia Rossi (talk) 09:46, 15 October 2008 (UTC)

Computer program to visualise biomolecular pathways/interactions

The network of interactions occurring between different proteins in different cellular contexts is terribly confusing. Is there are computer program that aims to help process and visualise the interactions and their effects, using the many databases that exist on the Internet? I'm thinking along the lines of those complicated posters of signalling pathways except that using a computer program, the display could be more simple (not displaying necessary information), dynamic (adding or removing complexity while one studies) and always up-to-date. Does such a program exist?

Such data is manually gathered and presented at http://www.reactome.org

You can't automatize this. Even UniProt has an automatized partition (TrEMBL) and an edited part. --Ayacop (talk) 15:58, 14 October 2008 (UTC)

That website is pretty cool, thanks for sharing! --Shaggorama (talk) 17:22, 14 October 2008 (UTC)

McCain's arm

I have observed that McCain's arm is somehow too stiff. Does he has any known medical condition?Mr.K. (talk) 15:55, 14 October 2008 (UTC)

Yes. Due to injuries sustained while a POW, McCain cannot fully raise his arms. Likely this extends to general stiffness. — Lomn 16:06, 14 October 2008 (UTC)

He's also a septegenarian. Most people to reach his age have some form of arthritis, or stiffening of the joints. Its a general symptom of being old. --Jayron32.talk.contribs 16:28, 14 October 2008 (UTC)

That makes a difference. Is his conditions degenerative? Should we vote for Obama? Mr.K. (talk) 16:37, 14 October 2008 (UTC)

It shouldn't make any difference, we have had very successful presidents who have had crippling mobility issues far worse than McCain has. McCain's arthritis and former injuries should not be a reason to make a decision over his ability to lead. His fitness to lead should be judged on his past actions and on his plans for the country. On those facts alone, we should judge him entirely unfit to lead, but not on any perceived health issues. --Jayron32.talk.contribs 16:46, 14 October 2008 (UTC)

It's worth noting, however, that FDR did die in office. According to our article, his medical condition affected his (and his party's) choice of running mate in the 1944 election—serious consideration was given to the issue of who his successor would be as President if he were to be elected and die. Honestly, John McCain is getting on in years, and it would be foolish to pretend that he isn't. Asking if his running mate capable of running the country in the event of his death is not an unreasonable question.

To be fair, it's a question that should be asked regarding all Presidential tickets. According to our list of United States Presidents who died in office, eight of the United States' 43 Presidents have died on the job (four by assassination), and we've lost at least one other to resignation. Historically, there's a better than one in five chance that the guy elected in November isn't going to make it all the way through his Presidency. TenOfAllTrades(talk) 22:02, 14 October 2008 (UTC)

If not for the incumbent advantage, the relevant question would be how likely he is to get through one term. That would make the odds look better. —Tamfang (talk) 03:26, 15 October 2008 (UTC)

True, but we'd be breaking new statistical ground with McCain. Only three past Presidents first took office after age 65, and none after age 70. (McCain is now 72.) For white males in their mid-seventies in the United States, the average mortality (all causes) is about 3.5% per year—roughly a one in seven shot that McCain wouldn't survive his first four-year term. That doesn't account for the appreciably-better-than-average medical care a President is likely to get, nor does it include the extra stress the Presidency would apply relative to the average 72-year-old's lifestyle. It also doesn't include the risk of an elderly President suffering a non-fatal but incapacitating medical event (most likely a heart attack or stroke) that renders him temporarily or permanently unable to carry out his duties. (Figure the odds of a serious but non-fatal cardiovascular event are going to be another 1% or so per year.)

In the interest of completeness, it should be noted that all of these risks apply to Obama as well, but at age 47 the probabilities are about an order of magnitude smaller. There's also nothing to preclude him being the victim of an assassination attempt, a car accident, or just a bad fall down the stairs. While it is much more likely that McCain's health will fail him in office, voters will certainly want to evaluate both candidates' running mates. TenOfAllTrades(talk) 05:51, 16 October 2008 (UTC)

@Jayron32 - re: "His fitness to lead should be judged on his past actions and on his plans for the country. On those facts alone, we should judge him entirely unfit to lead, but not on any perceived health issues" - this isn't the place to be advocating for or against any candidate on political questions. It's the Science reference desk. -- JackofOz (talk) 04:04, 15 October 2008 (UTC)

He released his medical records to try and convince people that he was healthy enough for the job and there was nothing in there that suggested it would be a real problem. Of course, at his age new problems can develop quickly. If you think McCain would be a better president that Obama but are worried about his health, you need to decide how bad it would be if did fall ill (based on you opinion of Palin, among other things) and how likely that is to happen and compare that to how bad you think it would be to have Obama as president and vote accordingly. --Tango (talk) 16:59, 14 October 2008 (UTC)

He didn't "release" them, he let a bunch of reporters look through the ~1200 (I've heard 1173) pages for three hours, without taking any copies or such. Among the findings seem to have been four bouts of melanoma, several precancerous colon polyps and a bunch of other worrying things. -- Aeluwas (talk) 17:15, 14 October 2008 (UTC)

And, you must consider the health of Obama, who has not released his medical records. He could easily have extreme hypertension and hypercholesterolemia without showing any outward signs of illness. Then, after a couple stressful months in office, he could have a heart attack. If you are basing your vote on something as silly as possible health risks, why not go for the silliest? If you are simply trying to validate your vote on some silly factor, why not base it on something sillier, such as refusing to vote for anyone who has ever been a pilot? -- kainaw™ 17:19, 14 October 2008 (UTC)

Obama did release a partial medical history that claimed he was in "excellent health".[15] Although the article states that his blood pressure was 90 over 60, which is a bit low for a systolic pressure... -- MacAddct1984 ^{(talk • contribs)} 17:31, 14 October 2008 (UTC)

People never seem to worry about low blood pressure... I'm not sure why not since, as far as I know, it can be just as dangerous as high blood pressure. --Tango (talk) 18:19, 14 October 2008 (UTC)

That depends on how you define "high" and "low" blood pressure. High blood pressure is a modifiable risk factor for cardiovascular disease, and it's more common than low blood pressure. See "Blood pressure". Axl ¤ [Talk] 18:37, 14 October 2008 (UTC)

Oh my! If we are speculating about future ailments, we can toss in a possibility of Addison's disease with a blood pressure as low as 90/60. Can we trust a man with the faint possibility of Addison's to make reliable decisions? -- kainaw™ 18:51, 14 October 2008 (UTC)

You mean like JFK? ;) -- Aeluwas (talk) 18:59, 14 October 2008 (UTC)

Even worse! Now there is historical evidence that electing a President with Addison's leads to an assassination! How many more idiotic reasons can we find to back a superficial preference for one candidate over the other? -- kainaw™ 20:28, 14 October 2008 (UTC)

7812819, give or take 42. --Stephan Schulz (talk) 22:50, 14 October 2008 (UTC)

I plan on voting for whoever is taller. APL (talk) 23:21, 14 October 2008 (UTC)

Au contraire, your the one who is being idiotic. Are you seriously suggesting that it's not valid to consider the health of a candidate or that age and known existing or previous medical conditions are a factor in considering the health of a person; in an election where you are electing that person for a fixed term? Personally, I would say McCains health, while of concern, is probably not enough to warrant people not voting for him solely for that reason. But his health is clearly of far greater concern then it is for Obama. And while if I were an American I would never vote for him anyway, if I was in the position of deciding between the two I would definitely factor his health into the equation and the possibility of Sarah Palin taking over as President I would consider far more likely then Biden. Nil Einne (talk) 08:43, 15 October 2008 (UTC)

I disagree with your premise. Given the nature of the US electoral system, you're basically stuck with the vice-president until 2012 if something were to happen to the president to make him or her unfit for office (including death). Therefore, it's perfectly resonable to consider whether ill-health is likely to make this happen. While obviously this applies to all candidates there is intriscly significantly greater reason to have concern when the candidate is 72 years old with some relatively serious health concerns then there is when the candidate is 47 years olf with no known health concerns. Obviously you can't predict precisely what will happen but this doesn't mean you shouldn't make a decision based on the evidence at hand. After all, for all we know McCain or Obama might go nuts and decide to nuke China and Russia one day because they're bored. In both cases I would say the evidence suggests this is unlikely but clearly if one of the candidates did have a tendency to do reckless things which seriously endanger others when they were bored, d it's perfectly resonable for a person to consider it more likely that this candidate would do something to endanger the security of the US and to let this affect their vote. In other words, just because it's theoretically possible that all candidates would do the same thing or worse doesn't mean it's ludicrious to consider the likelihood of something happening based on the evidence at hand. Nil Einne (talk) 08:31, 15 October 2008 (UTC)

The story now seems to be that his arms were injured when he was tortured as a prisoner of war, but in January 1968 interview with a French reporter [16], he said his arms and a thigh were broken when he ejected from his plane. In the propaganda tape he recorded under duress for the North Vietnamese which was broadcast by Radio Hanoi to U.S. forces in South Vietnam on June 2, 1969, McCain said "“I was a U.S. airman engaged in the crimes against the Vietnamese country and people. I had bombed their cities, towns, and villages and caused more injury even death for the people of Vietnam. After I was captured I was taken from a hospital in (?Da Nang) where I received very good medical treatment. I was given an operation on my leg, which allowed me to walk again, and a cast for my right arm which was badly broken in three rpt three places. The doctors were very good and they knew a great deal about the practice of medicine. I remained in the hospital for some time, I regained much of my health and strength.” In a propaganda interview with a Cuban official 14 days after being shot down, McCain said that when he bailed out he collided with the remains of his plane and fractured both arms, one in three places, and his right leg at the knee. See also [17] which has reports of the McCain interviews while he was a POW and [18]. Edison (talk) 05:01, 15 October 2008 (UTC)

@Jack – so it is! (the science desk). In that case I find Jayron32's comment observational and objective. And personally am enjoying the role of Mccain's arm as punctum.;) Julia Rossi (talk) 09:36, 15 October 2008 (UTC)

Clearly he might have sustained additional injuries "while a POW," as Lomn stated, but his injuries while ejecting from his plane 'before' he was a POW are sufficient to explain his present limited range of motion in his arms. Edison (talk) 14:52, 15 October 2008 (UTC)

what is this plant?

I've been given this plant as a gift, however it has no provided information about species/care instructions etc. I'm fairly sure it's quite a commonly owned house plant but I have no idea what it might be. Here is an image of it: [19] —Preceding unsigned comment added by 86.135.81.194 (talk) 17:53, 14 October 2008 (UTC)

I don't remember what it is called either, but I owned a very similar, if not the same species, of plant. I am fairly certain it is a variety of succulent, but I can't remember anything more specific than that. --Jayron32.talk.contribs 17:57, 14 October 2008 (UTC)

It's either Holiday cactus or some closely related species.CalamusFortis 18:04, 14 October 2008 (UTC)

Thanks, that looks about right :) --86.135.81.194 (talk) 18:09, 14 October 2008 (UTC)

Yes, it is. I've got one. Axl ¤ [Talk] 18:41, 14 October 2008 (UTC)

i have heard the term "Clopathia" applied to similar plants. Edison (talk) 05:37, 15 October 2008 (UTC)

Getting contact lenses in

Hehe, I'm extremely impatient and I can't get the hang of it. Is there any quick tip or something? A putter-inner from eBay for 9.99? --217.227.103.178 (talk) 19:35, 14 October 2008 (UTC)

The first time i got contacts, it took me an hour to get them in by myself. I have now worn contacts for 18+ years. Give it time and practice. Like anything else, you are training your body something new, and it just takes practice. Your body has a natural reflex to prevent bad stuff from getting into your eye. You simply have to retrain your body against this reflex. It's well worth it, I find that my vision is much better with my contacts than with the same prescription of glasses, and once you get used to it, you don't even notice it. --Jayron32.talk.contribs 19:47, 14 October 2008 (UTC)

I'm rather new at it myself. When I have trouble getting them in, I set up a mirror; it helps my aim and also, by giving me something to look at beyond my finger, helps me resist the reflex. —Tamfang (talk) 03:21, 15 October 2008 (UTC)

Frequency guard bands in OFDM

Can anybody explain why the lower and higher frequency subcarriers are left unused in OFDM systems? For example, 802.16 uses a 256-point FFT, however, the 28 lowest subcarriers and the 27 highest are not used. This is also true for the DC subcarrier. What's the reason of this? 85.243.50.175 (talk) 20:42, 14 October 2008 (UTC)

The transmission and reception has to pass through a band pass filter to stop spurious transmission and remove adjacent interference. At the high and low frequency ends there is a roll off in the passband, that will reduce sensitivity and result in noise if signal was used. There is also phase shift in these parts of the passband, so it is best not to use it. The frequency allocations are already overlapped in these sort of systems, so there is no wastage of spectrum. Graeme Bartlett (talk) 21:04, 14 October 2008 (UTC)

Thanks a lot! It has to do with filtering, just as I thought. The frequencies are overlapped indeed, but leaving some slots unused will still make the system sub-optimal. However, that could only be solved by an ideal filter. 85.243.50.175 (talk) 21:37, 14 October 2008 (UTC)

Identify this tree

An unidentified tree, presumably taken near Agumbe.

Same image, retouched to look less foggy.

I recently spotted this image on IfD. I think it could be worth keeping, but it's not very useful if we don't know what it shows. So, can anyone identify the tree with red flowers in this photo? Based on the name and the description page, the picture was presumably taken somewhere near Agumbe, Karnataka, India. In case it helps, I've also uploaded a version I tweaked to make it look somewhat less foggy. Thanks in advance for any help. —Ilmari Karonen (talk) 21:37, 14 October 2008 (UTC)

Royal poinciana or Delonix regia is found in India, or it may be another kind of flame tree. The Indian coral tree is known as Erythrina variegata found throughout southern Asia. Both are suited to tropical areas. Julia Rossi (talk) 09:24, 15 October 2008 (UTC)

Hmm... it does look remarkably like some of our pictures of E. variegata, particularly this image. The timing is a bit suspicious, since all the sources I've found suggest that E. variegata should flower around March, while the Agumbe photo has an Exif timestamp in July, but I suspect the timestamp may simply be bogus — not everyone sets their camera clock correctly. Anyway, thanks! —Ilmari Karonen (talk) 10:36, 15 October 2008 (UTC)

You're welcome, Julia Rossi (talk) 22:20, 15 October 2008 (UTC)

Ethidium Bromide

I was doing PCR analysis today, and touched the ethidium bromide stained agarose gel with my hands when i - instinctively, and without thinking - took it when someone handed it to me. Later i touched the gel again with gloves and then when removing the gloves touched my hand with the glove that i had just used to move the gel. I guess i'm probably not going to die, and after googling i'm almost content in the knowledge that i wont likely be getting cancer any time soon either, but one of my fellow students told me that - if i was concidering it - it would be a bad idea to get pregnant, and that that was a general safety precuation. So for how long should i not be getting pregnant? The next week? Year? Does this mean that my future children will have genetic defects or am i just being paranoid? Thank you 87.60.70.3 (talk) 22:01, 14 October 2008 (UTC)

The Wikipedia Reference Desk is not allowed to give personal medical advice. You are welcome to read Ethidium Bromide (which doesn't really answer your question either), but for concrete advice you should speak to a doctor or poison control specialist. Dragons flight (talk) 22:38, 14 October 2008 (UTC)

(Trying to tiptoe around possibly medical question) I have never personally worked with the stuff, however some background information. MSDS's (JTBaker and Fisher, as well as my LCSS list it only as "possible" teratogen, with more study being needed. I guess it depends on the half-life of it in your system, as teratogens normally only act on a developing fetus. It also depends on how much you came into contact with.

All that said, I'm guessing you are doing this research at a university or school. If you are at all worried, contact your Environmental, Health, and Safety department (or something similar), even to just put your mind at ease. They will possibly have more information, and you are able to give them more information on medical history and under what circumstances it happened, as well as how much and if you followed safety precautions (throughly rinse for 15 minutes or so with water?). It is also likely very confidential. In other words, get information from professionals, not other students.

And being slightly paranoid is good when it comes to your health. This is the only body you get (probably) :) --Bennybp (talk) 22:53, 14 October 2008 (UTC)

[Edit conflict] I don't think that a doctor or poisons service could give you any more helpful information. I searched Pubmed and didn't find any relevant articles. I'll try to look at ToxBase later. From our Wikipedia article, I didn't know that ethidium bromide is used to trypanosomiasis in cattle. Axl ¤ [Talk] 23:01, 14 October 2008 (UTC)

Here is an interesting article, although I can't vouch for the reliability/accuracy of the website. Axl ¤ [Talk] 23:30, 14 October 2008 (UTC)

Also [20] Nil Einne (talk) 07:31, 15 October 2008 (UTC)

That is a SPECTACULAR article Nil. Good find, thanks for sharing. --Shaggorama (talk) 07:45, 15 October 2008 (UTC)

Ironically, it was originally in the Ethidium bromide article until I removed it (it appears to be well written but as the personal blog of an unknown scientist I don't think it can be classified as a reliable source), although I didn't find it from there (I found it from Google). Nil Einne (talk) 09:35, 15 October 2008 (UTC)

It is directly linked from the "bitesizebio" article. Axl ¤ [Talk] 10:27, 15 October 2008 (UTC)

Doesn't help for your question, but I recall talking to a researcher who was complaining about other people who were completely paranoid about any exposure to EtBr, but cavalierly stared into the UV lightbox unprotected. (Ignoring the possibility of getting cataracts or skin cancer from the UV exposure.) My experience has been that most labs have a "bogeyman" which everyone gets irrationally paranoid about, while completely ignoring the 20 other items around them which are as bad or worse. Of course, the MSDS's which recommend full protective gear for water, and labels which claim "this product has not been completely investigated" for compounds which are FDA approved drugs doesn't help things. (Both examples have been seen personally.) Back on point, don't trust medical advise from Wikipedia, but also don't trust medical advise from paranoid labmates. -- 128.104.112.147 (talk) 21:41, 15 October 2008 (UTC)

Tropospheric gas giants

After the tropophere have those gas giants have a surface prior to the fliud interior or not. I know Jupiter and Saturn's sky starts at the upper level to be blue, then at lower level is it the tropos it's sky is like orange, brown, yellow (gold or tan). For Uranus and Neptune the sky must start to be blue as a gatorade, then at lower level it's paler blue. Anyways what part of atmosp layers is tropos on gas giants? And what's beenath the troposhper? Normal people say Jupiter, Saturn Uranus and Neptune contains no surface.--Freeway19 23:06, 14 October 2008 (UTC)

As far as I know, your assertions as to the color of the sky from within whatever planet's atmosphere remain entirely unsourced. I'm not sure why you keep repeating them. Anyway, there's not generally an expectation of a solid surface prior to liquified gases around the core. Per atmosphere of Jupiter, the troposphere's lower boundary is the liquid interior. — Lomn 23:49, 14 October 2008 (UTC)

Image:Structure of Jovian atmosphere.png This image is tough to understand. Jupiter's sky will not be black becasue it have an atmosp perhaps the upper level is blue or blue-purple. About Jupiter's center I know it's 5 to 6 times hotter than surface of sun, is the interior bright and hot or black and hot. Thi s is what the book said, I guess the interior is white-hot.--Freeway19 00:00, 15 October 2008 (UTC)

[21][22] [23] [24] This is the source. The trace above the globe glows tinge of blue on Saturn and Uranus. For Jupiter when Galileo pass t's atmos, I belive is thermo, it's tropo must be orange or orange-scarlet, hoever at upper layer jupiter's sky appears blue or indigo. Lomn, you said no source how you explin those.--Freeway19 01:41, 15 October 2008 (UTC)

I don't mean to be insulting, but you do realize that none of those images are real, right? They're just artwork. APL (talk) 03:54, 15 October 2008 (UTC)

Additionally, the first link (the only one that could be used as an actual reference) doesn't appear to be discussing color. I see no reason to assume that the colors present are anything but a visual aid. — Lomn 13:09, 15 October 2008 (UTC)

Artist interpretations generally make use of artistic license. Plasticup ^T/C 15:54, 15 October 2008 (UTC)

• On those planets I saw the diagram. They don't have a solid surface between. Hydrogen or methane haze will possibly make those sky on stratos blue, but at tropos, is the place of varying cloud layers. At that level the sky may be brown or orange, that's for Jupiter and Saturn, however because of the methan haze of Uranus and Npetune, their sky must start to be deeper blue at top layer, and at lower layer, the sky must be lighter blue. After tropos, it will be liquid interior bound. I wonder will it be light / dark at liquid interior. --Freeway8 22:22, 15 October 2008 (UTC)

  I wouldn't expect any sunlight to penetrate the atmosphere of a gas giant (I haven't researched it, though). It could be hot enough to be radiating in visible light itself, though. I don't know where you're getting all this stuff about colours, it sounds like guess work to me... --Tango (talk) 22:30, 15 October 2008 (UTC)

• Titan's also get very little or no sunlight. it's light is only 1/3000 to Earth, but it's sky appears to be light orange or tangerine colour because of it's haze, Cassini have been able to land on Titan.--Freeway8 00:10, 16 October 2008 (UTC)

• Some source says jupiter, Saturn and Uranus have hazes. hazes is judge to be blue.--Freeway8 01:12, 16 October 2008 (UTC)

  It's pretty dark on Titan due to the distance and thick atmosphere, but yes, there is sunlight on the surface. However, it doesn't have anything like as thick an atmosphere as a gas giant - the thicker the atmosphere the less light can penetrate to the surface. The gas giants certainly have hazes and clouds and their atmospheres will scatter different wavelengths of sunlight differently, so as long as you're not far enough down that sunlight is blocked the sky will have a colour, but I don't know where you are getting these ideas about what that colour would be. Who judges hazes to be blue? --Tango (talk) 15:34, 16 October 2008 (UTC)

• I thouht Uranus is mostly coverwith haze, this is why the sky is blue all the time. Those gas giant's sky stay the same all the time, same as Neptune and Saturn. Saturn is much cover with haze too is thicker than Jupiter and neptune's.For uranus and neptune the sky color should be darker blue on top and get lighter on bottom. At the lowest layer must be light blue. Saturn is also much a blue planet I thouhgt, so it's sky much start out blue on haze, but at lower layer must vary to yellow, brown, and orange. Jupiter's have haze, but the disc is rainbow or opal-like color, so the sky on top is specualte to be blue, but not define. At the tropo level juptier may vary white, orange, brown. For Venus, the sky stay the same much all the time I thought. At the cloud levels, it appears to be yellow, but beenath the cloud could be orange mix, becasue of the terrible greenhouse effect, Venus' sky may look scarlet seen from surface. I am not certain what's the color above the top clouds of Venus, becasue it is on the bound to outer space, so I guess it's black.--Freeway8 20:01, 16 October 2008 (UTC)

October 15

physics

why the electric field inside the conductor is zero?if the electric field inside the conductor is zero then how can current flow through it. —Preceding unsigned comment added by 221.120.210.41 (talk) 06:20, 15 October 2008 (UTC)

• You're totally right. The eletric field inside a conductor in only zero in static situations, i.e., if no current flows. baszoetekouw (talk) 08:54, 15 October 2008 (UTC)
  • But if it is a perfect conductor there is no electric field. Current can still flow, but because there is no resistance there is no electric field. Also the current has to flow on the surface of a perfect conductor, the magnetic field lines cannot penetrate. See superconductor Even in an imperfect conductor such as sea water the magnetic field is slow to penetrate and therefore alternating currents cannot go deep into the sea. see skin depth. Graeme Bartlett (talk) 11:29, 15 October 2008 (UTC)

Practical conductors, even a copper bus bar of 100 sq cm cross section, have resistance and have a measurable and significant voltage drop when carrying rated current. A superconductor may be different story. Edison (talk) 14:55, 15 October 2008 (UTC)

The OP was talking about the electric field inside a conductor (not between its ends) being zero. see this [25]--GreenSpigot (talk) 15:10, 15 October 2008 (UTC)

The "sides" of a conductor and the "ends " of the conductor are all "inside" the conductor. It is relevant to the discussion that in a practical conductor, there is a measurable voltage gradient throughout the substance when it carries substantial current. The OP referred to current flowing, and your example shows a conductor in equilibrium, with no current flowing. Edison (talk) 15:53, 15 October 2008 (UTC)

Baszoetekouw is right. Superconductors have zero resistance at DC, but non-zero reactance and even losses (see here under "Resistance") at AC. This means that a changing E field (e.g. a step function) can penetrate the material and thus set up a current. When the E field stops changing, the current keeps flowing (assuming you have a closed circuit) until you stop it by applying a reverse field. --Heron (talk) 19:00, 15 October 2008 (UTC)

Hückel's rule

I am having difficulties grasping the concept of how the aromaticity of a compound is determined in cases such as that of furan. The oxygen atom has two lone pairs, yet just one of the pairs is counted while counting the no. of pi electrons in the cyclic ring (whereby the no. of pi electrons comes to 6, satisfying the condition for huckel's rule). I read about the relation between the hybridization concept and huckel's rule on the furan article page but could not understand it very well. What exactly is the state of hybridization on the oxygen atom in furan? Additionally, how are we supposed to count the pi electrons in a ring in such cases where multiple lone pairs occur? Leif edling (talk) 06:41, 15 October 2008 (UTC)

It's been awhile but here's how I remember how this one works: 3 of the oxygen's electron pairs are sp2 hybridized, and the third pair is unhybridized in the pi orbital. The pi electrons contribute to to aromaiticity. the sp2 hybridized electrons all lie in the plane of the ring: 2 pairs make up the sigma bonds with the neighboring carbon atoms, and the third electron pair is a lone pair. When counting electrons for huckels rule, use whatever electrons are available to you that are committed to pi orbitals, or in this case CAN BE committed to pi orbitals in the correct plane. The lewis structure shows you 2 pairs of pi bonding electrons already in the ring and 2 more available pairs on the oxygen. One pair contributes to the aromaticity, the other becomes a sp2 hybridized lone pair pointing straight out from the molecule (normally it would be sp3 because there are 4 pairs of electrons associated iwth the oxygen right? BUT we lose one p orbital to that pair of electrons stolen for aromaticity, so instead of sp3 we're downgraded to sp2! It looks just like the hybridzation on the carbon atoms in benzene). The combination of aromaticity and significant resonance causes the lone pair to be very tightly bound: loss of the lone pair would destroy the aromaticity, so the molecule is much 'happier' (more stable/lower energy) with the electrons bound. --Shaggorama (talk) 07:23, 15 October 2008 (UTC)

As far as Huckel's rule or hybridization goes, lone pairs can either be part of the hybridization scheme or part of the pi-system as needed. Because lone-pairs are not "tied up" in a specific location, they are free to "shift" to produce whatever geometry will result in the lowest-energy configuration. All other things being equal, oxygen which is singly bonded (as in, say, dimethyl ether,) will assume an sp3 hybridization. However, in furan, the presence of unhybridized p-orbitals on neighboring atoms makes it so that one of the lone-pairs in the oxygen will assume an unhybridized p-orbital state as well, because of a property called conjugation. Basically, p-orbitals in conjugation (aka "delocalized pi-system) are at a lower energy state than the sp2-sp3-sp2 system which would exist if the singly-bonded oxygen maintained its expected geometry. Again, this is all because the lone pairs on oxygen are "mobile" in a way that bonding pairs are not. Analysis of furan shows that it is, indeed a planar molecule, unlike the similar Cyclopentadiene, where the two hydrogens on the lone sp3 carbon lie out of the plane. --Jayron32.talk.contribs 17:52, 15 October 2008 (UTC)

Gem quality Epidote mineral

I was wondering, and looked everywhere for that matter, the odds of finding gem quality Epidote in the united states. The only things i have read have stated Brazil as the main occurence for gem quality. Also i have read that people buy gem oddities such as this, i was wondering what a gem quality would catch per carat. Thanks to anyone that can find, or knows more information then me. —Preceding unsigned comment added by 216.52.133.15 (talk) 07:43, 15 October 2008 (UTC)

'Landing on Jupiter'

We were discussing in physics class yesterday about the gravitational field strength of Jupiter. We then got onto the subject of what happens if you genuinely do try to land on it. I'd love to know what would happen assuming that whatever we 'land' with is able to cope with the high pressures and the pummelling it'd get on the way down. Can anyone talk me through it? Would there eventually be a rocky, or icy, core because of the high pressure or would it still remain gasous all the way through?

Thanks, —Cyclonenim (talk · contribs · email) 07:51, 15 October 2008 (UTC)

• See Jupiter#Internal_structure baszoetekouw (talk) 08:52, 15 October 2008 (UTC)

• Also note that it's been done, insofar as it's possible. --Sean 13:15, 15 October 2008 (UTC)

It sounds like at some level of the Jovian atmosphere conditions are such as to allow a balloon, or a more solid probe with a degree of bouyancy, to float for an extended period. The article about the Galileo probe indicates that it lasted down to a pressure of 23 atmospheres and 150 Celsius, but a probe with a gas bag or a bouyancy chamber filled with gas or liquid could be deployed to float at a higher and cooler level of the atmosphere, or it could ascend or descend like a submarine. Like the bathyscaphe, it could have a large flotation chamber which was not shielded from ambient pressure and a small instrument chamber which was braced to keep lower pressure inside. It could also have a cooling system to keep the instrument chamber cooler than the ambient temperature, with a refrigerant system which transferred heat from the instrument chamber to the flotation fluid or gas in its larger chamber, which would in turn reject heat to the atmosphere. The pressure of 23 atmospheres was not all that high. The manned Bathyscaphe in 1960 descended deeper than 10,000 meters in the Challenger Deep on Earth, where the pressure should have been about 1000 atmospheres, 43 times the pressure the probe was able to endure. Modern submarines are tested to a depth equivalent to 50 atmospheres, and are estimated to be able to survive over 70 atmospheres. Edison (talk) 15:18, 15 October 2008 (UTC)

Have you seen Floating city (science fiction)? It's a similar idea, although not going so deep. --Tango (talk) 16:01, 15 October 2008 (UTC)

You really sould be thinking about a balloon, not a submarine. 50 atmospheres of gas still only has about 5% of the density of water, and hence only ~5% the bouyant force. I don't think anything that looked like submarine could sustain high pressures with so little mass. You could probably design a balloon-like system to be bouyant at a few atmospheres of pressure though. Dragons flight (talk) 16:39, 15 October 2008 (UTC)

You might be interested in the article Comet Shoemaker-Levy 9. --Shaggorama (talk) 16:09, 15 October 2008 (UTC)

The density question was not clearly adressed in the article about the Jupiter probe of a few years ago. I recall a sci-fi story of many years ago about a metal craft which dropped down into the Jovian atmosphere until it reached the layer where its density allowed it to float. With today's technology a Blimp might be a better model than a bathyscaphe, to stay at a higher and cooler level. Lightning and tumultuous wind would be a challenge. I wonder how far down into the atmosphere sunlight penetrates before it is as dark as a cloudy moonless night on earth? Edison (talk) 22:39, 15 October 2008 (UTC)

It seems like it depends on wavelength - see the image caption on the right hand side here. --Tango (talk) 22:54, 15 October 2008 (UTC)

Another interesting feature is that Jupiter's clouds are generally thought to give way to an essentially transparent Hydrogen/Helium sky within 100km or so. So if you could float a blimp there, you could get to look up at the swirling clouds from below. Dragons flight (talk) 01:11, 16 October 2008 (UTC)

Arthur C. Clarke wrote about balloon travel in the atmosphere of Jupiter in his 1971 novella A Meeting with Medusa. Gandalf61 (talk) 13:30, 16 October 2008 (UTC)

orchestra

why doesn't the sound emitted by the instruments of an orchestra interefere with each other? on an unrelated note, are the different instruments arranged in any particular order? thanks —Preceding unsigned comment added by 65.92.231.82 (talk) 08:25, 15 October 2008 (UTC)

Q.2. Yes, they are usually, although various conductors have experimented with alternative layouts. I'm surprised we don't seem to have an article with the traditional orchestral seating plan. Anyone? -- JackofOz (talk) 08:42, 15 October 2008 (UTC)

This is the usual arrangement. -- JackofOz (talk) 21:15, 15 October 2008 (UTC)

Q.1: They do; however, most composers work to make that interference pleasant to the listener. The concept of acoustic beats may also be of interest (tuning the orchestra is used to prevent this) — Lomn 13:05, 15 October 2008 (UTC)

A band or orchestra has the sounds of the instruments combine in various harmonies and dissonances, intended or unintended. "Tuning" is an exercise musical ensembles go through to get all instruments on the same pitch, and if two or more are not tuned exactly the same, audible "beats" are heard, which sound like the volume increasing and decreasing by a number of times per second equal to the difference in the frequencies of the two instruments. String tensions are adjusted, brass instrument tuning slides are pushed in or out, and woodwind mouthpieces are pushed in or out to alter the physical characteristics of the instrument. Edison (talk) 15:24, 15 October 2008 (UTC)

As the preceding responders have stated, the sounds certainly interfere with each other. Each instrument produces a complex wave, and the waves from each instrument add up, producing a very complex signal indeed. The amazing thing is that your brain more often than not is capable of doing the reverse transformation, i.e. to decompose the composite wave into its constituent parts, to allow you to distinguish the oboe from the violin. The article psychoacoustics might be of interest to you, as well as some of the articles it links to, notably missing fundamental and auditory masking. --NorwegianBlue ^talk 21:21, 15 October 2008 (UTC)

Just to make sure i understood what was said, when the orchestra is 'practicing', they're also making sure that there isn't much unwanted interference? Also, for my second question, yes I do know that the orchestra has a certain, fixed arrangement. I was wondering if there was any reason (acoustically) for, say, the violin's being closer to the centre than the cello's etc. THanks

This is one of those ikky things where pure, simple Physics-101 doesn't really cover the bases.

When we think of interference, we're thinking of nice, simple sine-waves that go on for a long time so that when two waves are mixed together, they add together to produce extra large peaks and troughs when the peaks and troughs of the two waves happen to line up - and they cancel out when the peaks of one wave line up with the troughs of another. This is all very wonderful - and you can have it happen before your very eyes in a wave tank or with electronic systems that produce perfectly pure sine wave audio.

But in reality, the waveform produced by a musical instrument is a mixture of an insane number of sine waves - all of different frequencies. Each part of the instrument is vibrating and resonating - each part producing different harmonics and noise. Each sine wave is starting and ending - or changing amplitude or frequency as the note progresses. Look at almost any instrument on an oscilloscope or a spectrum analyser and it's a total mess to look at. The waves within a single instrument are continually interfering with each other for short periods - those effects shift around millisecond by millisecond as the note builds up and dies away.

When you add more instruments, it just gets more and more complicated. Certainly the instruments are interfering with each other periodically. But consider why two seemingly identically tuned violins playing the same note at the same time sound completely different from one violin played at twice the volume. The two violins will never completely cancel each other out and never completely add together because they are subtly different - their dimensions are not the same, the wood they are made from has different thickness and flexibility because they have aged differently and have different amounts of humidity inside and varnish on the surface. The wood grain density is a little different. The bows have different amounts of rosin on them - and the horse-hair the bows are made from came from horses of different genetic makeup giving them different frictional characteristics. The two musicians are applying different amounts of force to bow and string for different durations throughout the note. The instruments are not identically or perfectly in tune and the position of the musician's fingers on the fingerboard are not identical. The distance of each violin from the walls and ceiling of the room are different - and since the musicians are not perfectly still (compared to a wavelength of sound at least), that distance is changing throughout the note. The audience has variable refractive indices depending on how they are dressed - this bends the sound around in yet more complex ways.

The result is that even with two seemingly identical instruments, those interference patterns are totally chaotic - changing so fast throughout the note that it would be utterly impossible for the two instruments to perfectly add or perfectly cancel each other out for more than a tiny fraction of the time. The result (to our ears) is that we hear two separate instruments...which is an amazing feat of calculation in our brains!

Two perfectly tuned electronic music synthesizers - playing the same, simple waveform through really high quality amplifiers and speakers in a large anechoic room WOULD interfere...but we are never in that situation with a real source of live music.

SteveBaker (talk) 13:14, 16 October 2008 (UTC)

Molecular Formula of Gasoline

What is the molecular formula of gasoline(petrol)? —Preceding unsigned comment added by PunarvasuOMEGA (talk • contribs) 08:26, 15 October 2008 (UTC)

Gasoline is not a pure substance, so it doesn't have a single molecular formula; it is a mixture of different hydrocarbons. Our article says "typical gasoline consists of hydrocarbons with between 5 and 12 carbon atoms per molecule ... benzene (up to 5% by volume), toluene (up to 35% by volume), naphthalene (up to 1% by volume), trimethylbenzene (up to 7% by volume), MTBE (up to 18% by volume) and about ten others". Gandalf61 (talk) 09:34, 15 October 2008 (UTC)

Would a car run well on a single carefully selected hydrocarbon, for instance if someone found a way to add hydrogen molecules to carbon dioxide with the addition of energy from solar or nuclear to create a synfuel? In other words would some single compound like octane serve as auto fuel, or is a blend necessary to achieve proper combustion? Edison (talk) 15:45, 15 October 2008 (UTC)

Propane is used as a fuel, and so is natural gas which is mostly methane so I don't think a blend is necessary. I believe gasoline is a blend because the energy it would take to separate it doesn't actually give you a benefit.-- Mad031683 (talk) 16:23, 15 October 2008 (UTC)

I suspect one could almost certainly find pure substances that a normal car would happily run on. It's less obvious whether a pure substance would outperform a mixture when it comes to variables like efficiency of combustion and pollution control. Some of the things in gasoline are explicitly added to improve performance, and I suspect that even synfuels are likely to be blended for best performance. Dragons flight (talk) 16:28, 15 October 2008 (UTC)

(ec) With minimal modifications, most cars today can be easily adapted to run on pure propane and natural gas (primarily methane). Brazilian flex-fuel vehicles can run on pure ethanol, while flex-fuel vehicles in other jurisdictions are often able to handle up to 85% ethanol (E85 gasoline). I would expect that an unmodified car today could run quite comfortably on pure iso-octane (2,2,4-trimethylpentane), as such a fuel would by definition have an octane rating of 100. TenOfAllTrades(talk) 16:31, 15 October 2008 (UTC)

Orthogonality in OFDM

Why does the fact that the subcarriers used in a OFDM system are equally spaced mean that they are orthogonal? Can anyone provide a clear and simple demonstration of the subcarriers' orthogonality in OFDM? 85.243.50.175 (talk) 15:32, 15 October 2008 (UTC)

Have you read Orthogonality#Radio_communications? --Shaggorama (talk) 16:12, 15 October 2008 (UTC)

Yes, sure. I'm just looking for a couple of explanations from other people in order to formulate a more comprehensive view on the issue. —Preceding unsigned comment added by 85.243.50.175 (talk) 16:33, 15 October 2008 (UTC)

If you build a perfect coherent detector for any one of those carriers it will not respond to any of the other carriers. To demonstrate this integrate over one symbol time the product of one carrier, with another one. When you multiply sine functions you will get a sum frequency and a difference frequency. If this difference frequency is the same as the symbol rate, the integral will be zero. Graeme Bartlett (talk) 20:41, 15 October 2008 (UTC)

Mining collapse question?

What is it called when the surface ground (way above where mining took place) suddenly sinks a few metres because of shifting of the earth or collapsing in mines underground? Or if a deep hole/shaft suddenly opens up like a pothole on the surface due to collapsing hollowness and mining underneath? Are there terms for these changes to the surface's geology?--Sonjaaa (talk) 17:55, 15 October 2008 (UTC)

"Subsidence". Axl ¤ [Talk] 18:15, 15 October 2008 (UTC)

"Subsidence" refers to the process, but does not necessarily imply that it reaches the surface; it could be entirely underground. If a hole forms in the surface, it is called a sinkhole. But both terms could apply to wholly natural effects as well as the consequences of mining. You need to use additional words if you want to limit it to that cause, I think. --Anonymous, 21:40 UTC, October 15, 2008.

"Sinkhole" explicitly refers to subsidence caused by the action of water. It is not a consequence of mining, but may be due to artificial alteration of water courses. Axl ¤ [Talk] 22:14, 15 October 2008 (UTC)

Well, the "sinkhole" article says "Sinkholes also form from human activity, such as the ... collapse of abandoned mines..."; perhaps there are conflicting definitions in use. --Anon, 04:05 UTC, October 16, 2008.

From Sinkholes: "Many ground collapses are labelled sinkholes when they actually belong to a more general category: subsidence." Axl ¤ [Talk] 09:09, 16 October 2008 (UTC)

Acorn

Are all varieties of Acorns edible?--76.28.73.16 (talk) 20:18, 15 October 2008 (UTC)

According to our article Acorn all are, with the exception of toxicity to horses. Some have higher tannin content which takes some processes to deal with whether you're a wildlife creature or a human. Is all there under "Nutrition". Cheers, Julia Rossi (talk) 22:24, 15 October 2008 (UTC)

Other sources say acorns are poisonous, unless specially treated:[26] , [27] , [28] . Edison (talk) 22:33, 15 October 2008 (UTC)

October 16

Manhole question

why is that a person going in a manhole had met with accident and blood came out of his body —Preceding unsigned comment added by 117.197.116.74 (talk) 05:04, 16 October 2008 (UTC)

Why did they go into the manhole? To chase an alligator, perhaps? If so, that would be a clue. --Scray (talk) 05:35, 16 October 2008 (UTC)

Are you sure it's not a hole in a man, that would leak blood. Graeme Bartlett (talk) 05:39, 16 October 2008 (UTC)

Didn't you two read the question? It's not how the person met with a bloody accident, it's why. If you are a religious fundmentalist, the answer is probably because he/she pissed off God. If you are an atheist, it's because he/she was not fit for going into manholes due to genetics. :-P

Right. For the latter, the genetic non-fitness was that he was too stupid to stop traffic before working in a manhole in the middle of the highway:) DMacks (talk) 18:25, 16 October 2008 (UTC)

Thank you to the contributors

Hi everyone. I used to contribute to this reference desk occasionally, but that has fallen off. Nonetheless, I wanted to start a section to thank the contributors of the Science Reference Desk. Not only do you help people everyday in their pursuit of knowledge, you make for some darn good reading. I could put this on the talk page, but you all deserve a slightly more public recognition. Cheers! Eric (EWS23) 09:59, 16 October 2008 (UTC)

I too would like to thank everyone for their contributions. Some of the discussions going on here are quite interesting and often shed a lot of light on subjects that the Wikipedia articles themselves fail to do. 12.10.248.51 (talk) 13:13, 16 October 2008 (UTC)

Heat effects

You know sometimes you get sun shining through a window onto a wall, and if it is a hot day you get sort of wavy shadows in the sunlight hitting the wall? What is this called, and is it linked to the effect you get when heated air distorts what is behind it. What is this effect called as well? I'm sure I have the word somewhere in my head but I can't recall it right now. 88.211.96.3 (talk) 10:45, 16 October 2008 (UTC)

Heat wave? The shadow is simply the same thing as the shadow is just cause by light. 194.221.133.226 (talk) 11:00, 16 October 2008 (UTC)

No that doesn't look right, that seems to be an article about exceptional large area high temperatures. 88.211.96.3 (talk) 11:44, 16 October 2008 (UTC)

It's hard to guess the word you are thinking of - so let's toss in some gratuitous explanation and maybe we'll hit the right word by luck!

So the effect you are thinking of is caused by the air temperature variations causing subtle shifts in refractive index. Glass is a better conductor of heat than air - so the air nearest to the window is likely to be at a different temperature than the air in the remainder of the room. As convection causes warmer air to rise and cooler air to sink, there is likely to be a certain amount of turbulence - although laminar flow is also possible, this would not cause the effect you are seeing. A bubble of turbulent air that is at a different temperature to its surroundings (and hence has a different refractive index) acts like a lens - focussing or dispersing the sunlight that is cast onto the wall - increasing the light intensity in some areas at the cost of decreasing it in others. The areas of decreased light intensity look like shadows and the turbulence makes tham wave around. Hence "wavy shadows".

Words to describe this phenomena would be "heat haze" (a term I've never been very happy with), or perhaps "shimmer". It's possible that you are also thinking of a mirage. But that's a different effect - although it's also caused by temperature variations in the air and consequent changes in refractive index. A shimmer due to turbulance will be more obvious in the case of a mirage. You might also be thinking of the scintillation of stars (more commonly called "twinkling") - or perhaps the word you are after is "dispersion". The pattern of light on the wall might also be called a "caustic" - although that term is more commonly used for things like the pattern of light on the bottom of a swimming pool. The root cause of caustics in a swimming pool is the same as with the shimmering air though - regions of different refractive index (hot and cold air - or air and water) are moving relative to each other and focussing the light in peculiar ways. A plot of the light concentrations in an idealised caustic takes the form of a nephroid.

SteveBaker (talk) 12:31, 16 October 2008 (UTC)

Thanks! I still wonder if wikipedia has an article on the effect. I just thought of another example of what I am (well was, it is raining now, bloody weather) seeing. You know when you have a large fire, and you get distortion. I am sure this is the same effect as what causes the shadows on the wall, and what you describe, but surely it has an actual name? I'd call it heat distortion or something. 88.211.96.3 (talk) 12:46, 16 October 2008 (UTC)

It's the same thing - the heat from the fire is now the source of the temperature variation - and the convection and refractive index changes that result from that are exactly the same as in the case of the window. SteveBaker (talk) 12:49, 16 October 2008 (UTC)

Yes but does it have a name? If it does someone should maybe write a wikipedia article on it, and I may even have a pop at it. 88.211.96.3 (talk) 12:52, 16 October 2008 (UTC)

Schlieren effect. DMacks (talk) 15:01, 16 October 2008 (UTC)

Stability of carbon

I came across the following passage: "The rarest carbon isotope is carbon-14, with eight neutrons. Unlike the other two isotopes, carbon-14 is unsta- ble". Is ¹³C stable? Why is C-14 unstable?Mr.K. (talk) 12:17, 16 October 2008 (UTC)

For smaller elements, the general trend is that elements that deviate greatly from a 1:1 proton-to-neutron ratio are generally less stable. The "stability line" generally trends more towards the neutron side as elements get larger; the actual stability line has a somewhat parabolic character. There are also some trends over the stability of "even-even" proton-neutron nuclei as well. See Isotope#Nuclear properties and stability and Stable isotope for more information on this. The general understanding is that the balance between the three forces which work to hold the nucleus together, which are the nuclear force, strong interactions, and weak interactions, require a certain balance of neutrons to protons (this relationship is not necessarily linear, however). Carbon-14 is "out of balance" with regard to this relationship, and so is unstable. The other two carbon isotopes, C-13 and C-12 are stable. --Jayron32.talk.contribs 12:29, 16 October 2008 (UTC)

The nuclear force is the same thing as the strong interaction. The relevant forces are electromagnetism and the strong nuclear force (the weak force may be involved as well, but as the name suggests, it quite weak!). --Tango (talk) 18:33, 16 October 2008 (UTC)

HIV and hemodialysis

Could a HIV virus load be removed through some sort of hemodialysis ? Mr.K. (talk) 12:23, 16 October 2008 (UTC)

No - dialysis is able to remove certain undesirable substances from the blood by physical and chemical means - but these are typically simple chemical byproducts. The complex biochemistry of a virus makes it hard or perhaps impossible to distinguish and remove by such a simple process. Being a virus also means that HIV has insinuated itself inside the cells of the host's body. Some of those (white blood cells, for example) could perhaps be removed by some hypothetical dialysis process - but there is a limit to the number of white blood cells you can remove and still remain protected against all of the other infectious agents in the environment. But HIV invades all sorts of other cells that are not a part of your blood - so even in theory, with some amazingly high-tech science-fiction blood cleaning machine, you couldn't remove more than some percentage of the HIV load. Viruses (not just HIV - but viruses in general) invade the inside of functioning cells and actually insert their DNA into your DNA. This makes them very hard to eradicate. Viruses replicate by having your own body make new copies - and even if you remove every single independent "virus" from your body - their DNA will still be tucked away inside your DNA waiting for your own cells to produce new viruses the next time the cell replicates. SteveBaker (talk) 12:48, 16 October 2008 (UTC)

Steve is (as always) right on the money - just thought I'd add a fascinating reference to a study of plasmapheresis for HIV and Hepatitis C virus: [[29]]. As Steve said, even removing a large percentage of a virus from the blood still leaves more than enough inside and outside the cells to maintain the infection. --Scray (talk) 12:58, 16 October 2008 (UTC)

Steve's answer is a good one, but a minor clarification would be good here. While many types of virus will make use of some of their host's DNA/RNA processing equipment, most viruses don't insert their DNA into the genomic DNA of the host. Group VI reverse transcribing viruses – including HIV – are the key ones that do; in addition to AIDS, these viruses can also be responsible for an assortment of other unpleasant diseases, including some cancers.

Interestingly, some of these viruses have become permanently incorporated into our genome, and may serve a host of useful purposes. See endogenous retrovirus for more details. TenOfAllTrades(talk) 14:29, 16 October 2008 (UTC)

Effects of masturbation

I am too embarrassed to ask anyone this question face to face, so I thought this might be a good place find an answer. I just wanted to know what the effects of masturbation are in teenage boys. --203.81.223.178 (talk) 15:41, 16 October 2008 (UTC)

Ejaculation, usually. A feeling of guilt maybe, if you grew up in a culture that still treats masturbation as some vile evil practice that makes your hair fall out. Certainly there are no serious negative health effetcs -- Ferkelparade π 15:47, 16 October 2008 (UTC)

...unless you do it often enough to get raw ;-). Seriously, it's good exercise, may decrease the risk of getting prostate cancer, will have no obvious side-effects, and everybody does it. --Stephan Schulz (talk) 15:55, 16 October 2008 (UTC)

Indeed - the general advice "if it hurts, stop" applies to masturbation just as to anything else. If you're doing it right, it won't hurt! --Tango (talk) 16:00, 16 October 2008 (UTC)

In fact there are possibly some benefits. It won't give you hairy palms, you can rest assured there. If you want more detailed advice, however, you really do need to speak to a doctor (don't be embarrassed, it's a perfectly normal thing to be curious about and doctors will keep your question entirely confidential, you can generally ask specifically to see a male doctor if that would make you more comfortable), we can't give medical advice. I'll give you some general advice, though: People in the playground generally don't have the faintest idea what they're talking about! Ignore any advice you get from a unreliable source, it's probably worse than useless. --Tango (talk) 16:00, 16 October 2008 (UTC)

There is an addiction side-effect. Addiction is often overlooked as a health problem, but it is a problem. Just noticed that orgasm makes no reference of any kind to endorphin. I was going to point out that becoming addicted to an opioid compound is not difficult. -- kainaw™ 16:01, 16 October 2008 (UTC)

Now, be careful. See Chuck Negron. While our article (perhaps rightfully) doesn't cover it, Mr. Negron's penis exploded due to massive overuse of said organ. [30] He reports the incident in gory detail in his own autobiography Three Dog Nightmare (the phrase "split open like a hot dog" appears in the book). He had been warned by his doctor that his level of sexual activity was damaging his L'il Chuck, but he unwisely ignored the advise of medical professionals, and continued to have sex like if he stopped for 10 minutes he might die. He reports an incident that led him to an Emergency Room in Oklahoma; the incident involved an audible tearing sound, lots of blood, and a groupie who will likely be in serious, intensive therapy for the rest of her life. Gives new meaning to the song Mama Told Me Not to Come, now don't it? Moderate levels of any sexual activity is perfectly safe (and some medical studies indicate that a regularly emptied scrotum is vital to helping prevent prostate cancer: [31]), but as with anything, you CAN overdo it. The above does not constitute medical advice in any way. --Jayron32.talk.contribs 16:03, 16 October 2008 (UTC)

Is it just me or "masturbation in teenage boys" is ambiguous? Indeed, it can be quite destructive to the personality of teenage boys. Mr.K. (talk) 16:11, 16 October 2008 (UTC)

I don't see an ambiguity and it's only likely to destroy someone's personality if they become addicted, which is unlikely. --Tango (talk) 16:38, 16 October 2008 (UTC)

I think Mr K. is playing on the word in there. As in, "The sixty year old felon who performs masturbation in teenage boys...". Personally, I think the terms masturbation and teenage boys are pretty much redundant. Matt Deres (talk) 17:33, 16 October 2008 (UTC)

Are you suggesting that adults and girls don't masturbate? I think the statistics would disagree with you there... --Tango (talk) 17:38, 16 October 2008 (UTC)

It's a superset/subset, not equivalency. He didn't say which term is redundant (and could be omitted without changing meaning) vs which term is the more limited in scope. Given "a hot fire", consider "a fire" vs "something hot" (assuming you have more experience with flames than with chicken-chokin' and...whatever the comparable female slang would be:). DMacks (talk) 18:16, 16 October 2008 (UTC)

Ok, I suppose that makes sense - since said both were redundant I assumed he meant they were mutually redundant (ie. equivalent), it makes more sense if he only meant one of them was redundant given the other. --Tango (talk) 18:27, 16 October 2008 (UTC)

Why does pressure increase with depth

If pressure is caused by experiencing the sum total of elastic collisions of fluid molecules against an arbitrary plane (my words as I'm writing them)...

but given my current definition for studying fluid mechanics, this doesn't explain why the collisions are "stronger" at deeper depths because the density is the same and the temperature is the same.

If water molecules are crashing into the vertical wall of a dam then why should forces coming from above affect the frequency or impulse of collisions? If the impulse was greater, that would imply greater kinetic energy in the fluid molecules, which means they have more energy.

Take a 100 meter high dam, the horizontal collisions near the bottom should not depend on molecules above them, which act in a perpendicular direction, right? Water has the same density, and lets stipulate that the fluid is iso-thermic

How does defining pressure this way not explain why at greater depths, pressure is higher? I think it is because pressure exists in all directions right? So the upward force = the horizontal force. Right? So does that mean that the collision frequency is higher? or that the impulse per collision, greater? Or am I just completely wrong. Sentriclecub (talk) 17:49, 16 October 2008 (UTC)

I'll take a stab at it (though admitedly by stat-mech/thermo is a bit rusty… Pressure really does exert "in all directions" as you suggest. Molecules don't just bounce "up and down or side to side", but at all other angles as well. So vertical pressure (weight of what's above, or the effect of vertical collisions each pushing down upon the next) can exert a non-vertical force if any molecule has a non-zero horizontal component to its motion. DMacks (talk) 18:08, 16 October 2008 (UTC)

Additionally, I've spent 5 days studying the topic, and know it can be explained by Pascal's law, but I want to know why it can't be explained or deduced from the method of looking at pressure as ultimately a result of elastic collisions on an arbitrary surface. There's only two ways to increase the average force of a series of impulses... either increase the frequency, or increase the impulse per collision. How does the random translational motion increase with depth, if density and thermal energy and temperature stay the same? I've already asked on yahoo answers, and got a starred question award, and 2 wrongs answers ("because density increases") and the other answers are not helpful, and they use weasel words "well could be..." Sentriclecub (talk) 18:13, 16 October 2008 (UTC)

DMACKs, Yes I understand they exert a force downward onto other molecules, but the bottom line is that somehow there is a resultant increase in collision frequency or an increase in impulse magnitude. I fully understand Pascal's law, but my book doesn't answer my specific question, nor the related wikipedia articles. Sentriclecub (talk) 18:18, 16 October 2008 (UTC)

So far the best answer from the other website is...You asked a very good question. You can't quite compare gas and fluid but for simplicity, I will. Water is NOT incompressible. As you go deeper, its density increases with pressure. Before you go down, there is very little room between the molecules. But you go down 30 m, there is now even less room. This means that the number of collisions will go up dramatically. So the pressure increases. The water, however, keeps the same kinetic energy and temperature. BTW: The reality is a little different. The water molecules vibibrate against each other, but they also impinge on each other's electron clouds. Kinda of a spring effect, so it is not quite so straight-forward.

My next guess is through statistics and a normal distribution. Maybe if the layer of water molecules on the bottom of the fluid can only bounce between 0 and 180 degrees, then the second layer has an extremely small chance of colliding straight down because of the concentrated upward range of the the molecules directly below it. In other words, near the bottom, the statistical distribution of all possible collisions that can occur in 3d space isn't equally probable. Molecules on the bottom have zero probability of being able to return from a collision against the ground with a downward momentum. That is a majority of molecules near the very bottom can only have an upward momentum at any given time. This "fact" must be balanced by the second layer of water molecules who must pass the "fact" along, and give this problem to the layer higher up, who must eventually "resolve" the fact, by being basically free to have zero net momentum as observed in the top layer. This is just a educated guess, based on creativity, not science. Sentriclecub (talk) 18:46, 16 October 2008 (UTC)

To put in better terms, 100% of molecules on the bottom layer must have a upward momentum immediately after a collision. 50% of molecules on the bottom layer have an upward momentum before a collision. Thus the net momentum of the bottom layer is 75% upward, if a reasonable assumption is that all the bottom layer fluid molecules are returning from a collision, and fixing to collide again. A net downward force would need to act on the bottom layer to counteract the upward momentum as suggested by the 50%/100% theory. Still this is all a guess, but I have been unable to finish writing my notes because I hate the feeling of a lingering doubt on pressure. Sentriclecub (talk) 18:52, 16 October 2008 (UTC)

Just a teaser, and I plan to write a long response this afternoon when I get a chance. However, some of the confusion stems from drawing a false analogy between pressure in gases (mediated primarily by kinetic energy) and pressure in liquids/solids (mediated primarily by bond energy). Dragons flight (talk) 18:58, 16 October 2008 (UTC)

I think I'll take a wild guess. How about gravity? Looking at a free water particle outside of a gravitational field, any of the 360 degrees are equally possible. Within Earth's gravity, however, it becomes more probable that the particle has some "downward" component to its velocity vector. These add up the deeper you go, resulting in higher pressure. The interesting question would be: If you had a jug of water (maybe a large pool-sized jug) in space, would the pressure change the "deeper" (more towards the center) you go? I don't really have an answer to that. --Bennybp (talk) 19:50, 16 October 2008 (UTC)

Actually I didn't really answer the question (why it would be omni-directional, and not just downwards). It's probably a pretty flimsy theory, but - Due to the pressure from the molecules coming from the top, the molecules at the bottom would be given more side-to-side velocity, since 1.) They have the same average speed (same temperature), and 2.) There's a limit on their direction of motion ("up" is no longer available, so all others become more probable). Man, I think I'm just digging myself a nice hole. I eagerly await Dragons' answer :) --Bennybp (talk) 20:03, 16 October 2008 (UTC)

The false analogy here is that the treatment of "pressure" for the gas phase is the same as for "condensed" phases. It isn't. For gases, there is roughly a linear relationship between pressure and density; double the pressure, double the density (I say roughly; its exact under the Ideal gas law; the Van der Waals corrections alter this slightly). That is because, for gases, the intermolecular distance is roughly 1000x greater than the molecular radii, meaning that gases are compressable (you can simply "push" the gases molecules together). The entire question by the OP assumes this compressable model of pressure; it works fairly well for gases. However, liquids and solids are condensed phases; for all intents and purposes the intermolecular distance between them is essentially nil. (they can be compressed slightly; water at 100 m below the surface is slightly more dense than the water at the surface). In the case of condensed phases, pressure is determined by weight of the bulk material above you. That's it. Pressure is only force per unit area, and weight is only a force. With a gas, the force is primarily determined by collisions, since the gas molecules don't remain in contact with the surface for any meaningful length of time. With condensed phases, the surface is essentially in constant contact with the molecules (and for a liquid, the exact molecules shift places because it is a fluid, but in bulk, essentially the entire surface where the pressure is measured is totally covered with the molecules). Consider two thought experiments:

1. Imagine burying someone under a 100 m tall pile of sand. What happens? We say they are crushed to death because of the weight of the sand on top of them But this is merely convention. The weight is a force, and it crushes them by pressing in on the surface of their body? What is a force distributed over a surface? Pressure... Now, replace "pile of sand" with "depth of water". Its the exact same problem.
2. Imagine the same person, with appropriate breathing apparatus, encased in a cube of water 100 m on a side, but the person and the water are in a zero-g situation, like floating in space. What happens? Nothing. They survive fine, because the water doesn't press them because there is no gravity to force the water in any one direction. Even if they swim to one side or the other of the cube, there is no net pressure effect, because there is no gravitational force. No force equals no pressure.

Does that make sense to everyone, the OP's question is in error because it makes assumptions about pressure which are incorrect to the situation; liquids are fundementally different than gases WRT molecular organization, and that fundemental difference affects the way that the molecules exert a "force" on their surroundings. --Jayron32.talk.contribs 20:26, 16 October 2008 (UTC)