Wikipedia:Reference desk/Archives/Science/2008 November 17

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November 17

Water

Is toilet water poisonous? JCI (talk) 00:11, 17 November 2008 (UTC)

Yes and No.

If by toilet water, you meant sewage then yes.

If by toilet water, you meant clean pipe water used to flush the toilet then no. 122.107.203.230 (talk) 00:38, 17 November 2008 (UTC)

Before or after you flush? The water comes from the exact same place as the water that comes out of your kitchen - so initially, it's clean and perfectly drinkable (assuming you live in a place where the mains water supply is clean and perfectly drinkable!) The toilet bowl itself is a lot cleaner than some people suspect because it's a hard surface that's not porous and there isn't much in the way of nutrients or sunlight for bugs to live on - and we typically expend an entirely disproportionate effort into sanitizing it. So this boils down to the issues with human waste - not the toilet itself. If it's your own waste that you're ingesting then whatever you're picking up was in your body before - so in small quantities it's not likely to be radically nasty. If the waste came from someone else - it's a different matter. Obviously, this isn't something you'd want to try if you didn't have to - and (of course) you'd have to be aware of any chemicals such as bleaches and toilet cleansers you might have tossed into the toilet or the cystern in advance - which might be extremely hazardous. I think that in an emergency - if there was no other source of clean water - I'd weigh up the pro's and con's and probably risk it. SteveBaker (talk) 00:43, 17 November 2008 (UTC)

Assuming you have access to the cistern, it contains a tap, just drink the water directly out of the tap and it's exactly like water out of any other tap. --Tango (talk) 01:00, 17 November 2008 (UTC)

And if you mean toilet water, then yes, some of it is fairly poisonous. -Arch dude (talk) 00:52, 17 November 2008 (UTC)

(EC)Depending on the type of toilet water, the high alcohol content and perfume and other ingredients such as liquid waxes or cocoanut oil might be harmful, especially if it were any alcohol but [Ethanol]. Edison (talk) 00:54, 17 November 2008 (UTC)

Ooh! I'd forgotten that meaning of 'toilet water' - yes, that stuff would be horribly bad for you. However, it's been a very long time since I last heard anyone describe perfume as 'toilet water'...for reasons that are fairly obvious! SteveBaker (talk) 01:35, 17 November 2008 (UTC)

Hah! Caught Steve in an area he knows nothing about. Strictly speaking (imagine the French accent, please), Perfume (as in eau de Parfum) is not really the same as eau de toilette - it's much more concentrated. --Stephan Schulz (talk) 07:57, 17 November 2008 (UTC)

People almost never translate "eau de toilette" into English, though. They just use the French. --Tango (talk) 11:36, 17 November 2008 (UTC)

"Both dogs and people occasionally splash toilet water on their faces, but dogs seem to enjoy the scent more." StuRat (talk) 03:09, 17 November 2008 (UTC)

"I've got a headache. I was dabbing some of that fancy toilet water behind my ears just before the show, and the lid came down and hit me on the back of the head." [Little Jimmy Dickens, Grand Old Opry] Edison (talk) 19:52, 17 November 2008 (UTC)

@SteveBaker - Dude, if you ever really do get that desperate, please at least consider going for the water in the tank rather than the water in the bowl... Matt Deres (talk) 00:26, 18 November 2008 (UTC)

Geology

What are the three types of stress force —Preceding unsigned comment added by 65.12.161.166 (talk) 01:01, 17 November 2008 (UTC)

Please do your own homework.

Welcome to Wikipedia. Your question appears to be a homework question. I apologize if this is a misinterpretation, but it is our aim here not to do people's homework for them, but to merely aid them in doing it themselves. Letting someone else do your homework does not help you learn nearly as much as doing it yourself. Please attempt to solve the problem or answer the question yourself first. If you need help with a specific part of your homework, feel free to tell us where you are stuck and ask for help. If you need help grasping the concept of a problem, by all means let us know.

May I suggest Structural geology - I believe the answer you seek is in one of the articles linked from it. Better still - I'm 100% sure that if you crack open the textbook for your course, you'll find the answer listed neatly in the chapter you've just been working on in class. SteveBaker (talk) 01:33, 17 November 2008 (UTC)

Can't we just start giving them wrong answers? The three types of stress are work stress, family stress, and Microsoft-related stress which is the worst stress of all. 216.239.234.196 (talk) 16:41, 17 November 2008 (UTC)

There is an unreferenced article on Stress field, and Shear (geology) is probably useful. Graeme Bartlett (talk) 20:47, 18 November 2008 (UTC)

Home battery recycling

Is there any way to recycle or revive sealed lead acid or lithium batteries at home, for an electric bicycle for example? And are there any batteries that are self-recycling? And what chemical or thermal process would be involved after I wash the chemical out of the battery? Trevor Loughlin (talk) 05:30, 17 November 2008 (UTC)

There is nothing chemical or thermal that a non-specialist can do to fix a battery. "Deep cycling", i.e. charging a rechargeable battery followed by mostly discharging it under steady load and then recharging it again, is an electrical process that can help some rechargeable batteries under some conditions. Though with lithium rechargeables it is important that they never be completely discharged as this will almost certainly tend to shorten their life. Opening a lead acid battery is dangerous. The acid is corrosive and the lead toxic. Lithium batteries are only a little better as lithium will burn skin and the dust should not be inhaled. If the batteries are really dead send then to a professional recycler, don't mess with them yourself. Dragons flight (talk) 07:05, 17 November 2008 (UTC)

What killed the airship?

You know, dirigibles, zeppelins, etc... How did they come to be surpassed by contemporary jumbo jets? Kenjibeast (talk) 06:58, 17 November 2008 (UTC)

The Hindenberg disaster killed public opinion. Plus they are generally impractical. Dirigibles are huge, slow, and hard to operate compared to jumbo jets of the same cargo capacity. They are probably a reasonable solution to aerial surveillance of a fixed location (e.g. Goodyear blimps above sporting events), but they are not competitive as a means of transportation. Dragons flight (talk) 07:14, 17 November 2008 (UTC)

See also Airship#Practical_comparison_with_heavier-than-air_aircraft for a rather lengthy discussion of why airships were abandoned. SDY (talk) 07:48, 17 November 2008 (UTC)

Airships were not "surpassed by contemporary jumbo jets", though. They were abandoned about the time World War II started, and jet aircraft didn't even exist then, let alone jumbo jets, which came along 25 years after the war. But propeller aircraft did, and the war stimulated their development in a big way... and a bomber and an airliner can have many similarities in design. --Anonymous, 06:22 UTC, November 18, 2008.

A bomber and an airliner have some things in common, but the only difference between an airliner and a military cargo airplane is the paint scheme. --Carnildo (talk) 22:43, 18 November 2008 (UTC)

Airships again

What was the operating altitude for the USS Akron and the Hindenberg and other airships from that era? What are the practical considerations for a high-altitude airship (i.e. how much does the lifting power drop as atmospheric pressure decreases)? SDY (talk) 07:48, 17 November 2008 (UTC)

In the airships link above, it states: "The highest flight made by a hydrogen filled passenger airship was 5,500 feet (1,700 m) on the Graf Zeppelin’s around the world flight. The practical limit for rigid airships was about 3,000 feet (900 m), and for pressure airships around 8,000 feet (2,400 m)." And a rigid airship in 1917 "was forced to 24,000 feet", but it crashed as a result. -- MacAddct1984 ^{(talk • contribs)} 18:31, 17 November 2008 (UTC)

The practical operating altitude was "as low as possible": the Graf Zeppelin typically flew within 500 feet of the ground. Since hydrogen airships were typically operated with their lift cells as full as possible, gaining altitude meant venting off hydrogen to keep the lift cells from rupturing from overpressure -- and venting hydrogen means you also need to drop ballast to keep the airship aloft. When you run out of ballast, you either need to start dropping cargo, or you need to land where you are, neither of which is a desirable situation.

Staying low has other benefits, as well. Turbulence is minimized, which is important when you're flying something larger than the typical turbulence cell, and downdrafts are mostly converted into horizontal winds. It also gives the passengers a great view of whatever you're flying over. --Carnildo (talk) 01:04, 18 November 2008 (UTC)

Explain this optical illusion?

I was reading the Wikipedia article on The Fall of the House of Usher. In the "Analysis" section there is an image of a copy of the magazine in which the story was first printed. I had this image at the bottom right of the browser window and was reading the end of the preceding section when I noticed something odd: when, in reading, my eyes move left to the beginning of the next line, the image appears to momentarily take on a distinctly green tinge. Why is this? - 79.79.176.53 (talk) 08:59, 17 November 2008 (UTC)

This can happen particularly if red green and blue images are shown in sequence and one moves ones eyes. Some projector systems in particular suffered from it. I would have thought there wouldn't be too much problem with LCD monitors though. Dmcq (talk) 09:48, 17 November 2008 (UTC)

Seems you could be experiencing the after image phenomenon, due to the red cast of the image in question. Does that fit what you are seeing? --Scray (talk) 11:28, 17 November 2008 (UTC)

Jupiter causes an additional parallax

Stellar distances are measured most directly by parallax, using the fact that Earth's position changes by 3*10⁸ km within 1/2 years. Now of course when planets move around the sun, the sun itself also moves (but of course slower and in a smaller ellipse), and Jupiter causes the Sun's position to change by about 1.5 million km within 6 years. Earth orbits Sun in a close orbit compared to Jupiter, so it can be expected to follow this movement of the Sun (in addition to orbiting it). This should produce an additional parallax of about 7 milliarcseconds at α Centauri - this should be measurable e. g. with Hipparcos. Does this additional parallax have a special name? Maybe Wikipedia's article should mention it.

Additionally, Jupiter causes the velocity of the Sun to change by an amount of more than 20 m/s within 6 years, and the resulting Doppler effect should also be measurable when observing other stars.

Icek (talk) 09:57, 17 November 2008 (UTC)

Smoking and breast milk

Maternal smoking results in exposure to nicotine in breast-fed infants. Smoking mother's breast milk contains nicotine - when this fact was first discovered and who discovered it? Otolemur crassicaudatus (talk) 10:06, 17 November 2008 (UTC)

Who the heck smokes breast milk? Isn't too wet to ignite? I mean, I suppose you could get it into a bong, so that would eliminate the soggy paper problem, but wouldn't you still have problem lighting it? I suppose you could freeze-dry the breast milk, and smoke that, but it seems like a lot of trouble to go through... --Jayron32.talk.contribs 15:32, 17 November 2008 (UTC)

I have asked the breast milk of the mothers who (who denotes mother) smoke cigarette contain nicotine. It not the breast milk which the mother smoke, it is the cigarette which the mother smoke. Now if a mother smokes cigarette during her maternal period, it is observed that her breast milk may contain nicotine. I want to know who first discovered this and when (i.e. relation between maternal cigarette smoking and consequential nicotine concentration in breast milk)? Otolemur crassicaudatus (talk) 16:07, 17 November 2008 (UTC)

No shit, sherlock... I was being funny. You used the phrase "Smoking mother's breast milk" which is an example of a Dangling modifier since it is impossible to determine from the phrase which word "smoking" is intending to modify. Is the mother, the mother's breast, or the mother's breast milk the thing which is smoking. Such imprecise language is often the source of humour; phrases like "Eats, Shoots & Leaves" or "man eating cabbage" or "British Left waffles on Falklands" are other famous examples of imprecise language. Damn it, jokes are not as funny when you have to explain them... --Jayron32.talk.contribs 17:07, 17 November 2008 (UTC)

See also Amphibology. --Jayron32.talk.contribs 17:14, 17 November 2008 (UTC)

To be honest, it wasn't all that funny to start with... ;) If you're going to mock someone's imperfect but completely unambiguous (in context) grammar, it helps to answer the question as well. If you don't know the answer, keep quiet. --Tango (talk) 17:22, 17 November 2008 (UTC)

Alright smarty-pants. I did a google scholar search where the earliest reference I can find is this study done in 1933 by someone named WB Thompson, and appearing in American Journal of Obstetrics and Gynecology. Several other studies cite a 1942 JAMA paper as being fairly authoritative on the subject. Looking through the first 3-4 pages of the Google Scholar search turns up nothing earlier than 1933, but that doesn't necessarily mean there wasn't anything earlier. The online version of the 1933 paper is only an abstract; if you got the original you would probably find at least a cursory literature review, and you could see if there was anything earlier. Going backwards through the papers, you could probably find the seminal study. --Jayron32.talk.contribs 18:33, 17 November 2008 (UTC)

This study: [1] seems to cite the 1933 Thompson study, and its title "The Excretion of Drugs in Human Milk—A Review" would seem to indicate that it would be a great place to start if looking for that first study... --Jayron32.talk.contribs 18:35, 17 November 2008 (UTC)

Here's one from 1927: [2], and IT cites studies from as early as 1908. Again, I would start somewhere like this one, and work backwards until I got to the earliest study to mention it. It may take time; however access to a university library would make it possible to work it out. here's one from 1911 that talks a bit about the mechanisms of milk secretion, and the action of certain drugs thereupon. --Jayron32.talk.contribs 18:44, 17 November 2008 (UTC)

toilet seats

Assuming it is used normally, is it actually possible to catch any disease from a toilet seat? Reading transmission (medicine) suggests that it is not.--Shantavira|^{feed me} 10:11, 17 November 2008 (UTC)

Per this, toilet seats are relatively germ-free; an average toilet seat contains approximately 49 microbes per square inch compared with a keyboard, which may contain 25,127 microbes per square inch. Toilet seats are not common transmission channels of infectious diseases. To infect someone, the bacteria must have to enter his body through mouth, anus or urethra. But the bacteria cannot jump from the toilet, so someone using the toilet in usual manner is basically safe. But, yes there are possibility of skin diseases like scabies, herpes. Regarding Gonorrhea, a study in 1979 titled The gonococcus and the toilet seat claimed "nonsexual transmission from toilet seats is not impossible, just very unlikely". Here is an interesting reference which will help you a lot. Otolemur crassicaudatus (talk) 10:47, 17 November 2008 (UTC)

You really ought to be more worried about door-handles than toilet seats, especially in public bathrooms. Think about it, thousands of people touch those things, and many probably don't was their hands properly (if at all). You get it on your hand, and then you eat a popcorn or something, and bam!, you're infected. Much bigger hazard than toilet-seats. 83.250.202.208 (talk) 11:53, 17 November 2008 (UTC)

I wonder if there's a greater transmission problem with the widespread use of auto-flush toilets? I find they tend to perform quite a few, er, premature evacuations. On the one hand, the extra flushing presumably helps whisk away any residual nasties in the water; on the other hand, it tends to deposit a fine coating of "toilet dew" on one's nether regions, thus overcoming the bacterial obstacle of migrating from bowl to anus. Matt Deres (talk) 00:34, 18 November 2008 (UTC)

Keep in mind also that germs can't magically go through the skin, at least the vast majority can't. In order for any surface to be a vector of infection, you need a cut, abrasion, ect. In my opinion, the vast majority of concerns about germs from toilet seats are hysteria induced by overprotective parents, typical in women. The theoretical transmission of some skin-contact viruses supposes they got there in the first place, which would require blood contact (or mucus membrane) in the first place. Now an airborne virus might get deposited, as might microbes from, say, vomit, but even then the microbe would have to A) get on the sear B) survive long enough to be around when you get there, some germs will be dead in 15 minutes (IE HIV) some might last a week or more (IE Hepatitis), but it will reduce numbers C) you'd have to have an means for the virus to get into your bloodstream, such as a cut. In general I think that it could be said that your risk of exposure is the same as from any skin/surface contact that isn't your hands, hands being a greater vector because you often expose them to your internals by touching your eyes, mouth, food, ect. 69.210.56.62 (talk) 09:25, 22 November 2008 (UTC)

Red / Blue Shift

Apparently astronomers can determine the distance to a star or galaxy by its red shift or blue shift. Do we have any concrete proof, such as from experiments that can be replicated in a laboratory, that we are correctly measuring the distance to these celestial bodies, ie the red / blue shift measurement is accurate? Or is it all based upon theories and resulting formulae? —Preceding unsigned comment added by 75.67.217.220 (talk) 10:41, 17 November 2008 (UTC)

Ummm, well all science is based on a combination of evidence, experimentation, and theories, so I'm not sure what you are really asking. However, as discussed at cosmic distance ladder, a wide variety of techniques are used to validate measurements of cosmological distances and the agreements between different types of measurements can be seen as evidence that astronomers know what they are doing. Dragons flight (talk) 11:20, 17 November 2008 (UTC)

You don't measure distance with redshifting or blueshifting, you measure if something is moving towards you (blueshifting) or moving away from you (redshifting). As for concrete proof or a laboratory experiment confirming this effect, we absolutely have it! In fact, you can observe it for yourself! The principle behind it is something called the Doppler effect, and it happens with all sorts of waves, including sound-waves. Next time you're stuck in traffic, and hear an ambulance or a police-car rushing at great speed near you, think about how the pitch of the siren changes as the ambulance (or police) passes by you. It will be at a much higher pitch when approching you, and then as it passes you, it will suddenly have a much lower pitch. This is exactly what happens to light when they are emmited from stars that are travelling away from you. Instead of having a lower pitch, it will be slightly shifted to red side of the color-spectrum. 83.250.202.208 (talk) 11:50, 17 November 2008 (UTC)

"You don't measure distance with redshifting"? Doesn't Hubble's Law say that "the redshift in light coming from distant galaxies is proportional to their distance"?--Shantavira|^{feed me}

Yes, for sufficiently distant galaxies, redshift gives you an pretty good approximation of their distance, but only by comparing them to closer galaxies that you can measure the distance to via different methods (see the article Dragons flight linked to). --Tango (talk) 13:29, 17 November 2008 (UTC)

Yes, I should've been clearer about that point. I just meant that that wasn't what you were measuring directly, and without a reference it doesn't work. 195.58.125.52 (talk) 13:55, 17 November 2008 (UTC)

Thanks - put simply, the question was, when a distance is provided to another star or galaxy, how do we know the distance is accurate? If we are using a set of assumptions, means or formulae, can we use the same to measure a distance on earth and therefore prove that the assumptions, means or formulae produce correct results, thus giving creedence that the distance to the star or galaxy is accurate (or at least in the ballpark)? Sorry if I am not sufficently clear . . . I think the cosmic distance ladder probably answers the question, but I was wondering if you could explain it in a simple manner for us "common folk"? Thanks again

Tricks by Nikola Tesla in the movie "The Prestige"

I just rewatched the brilliant film The Prestige, and had some questions regarding some of the science-tricks that Nikola Tesla performed.

1. In one scene, Andy Serkis (Tesla's Igor, basically) takes Hugh Jackman out to a huge snowy field, with hundreds of lamps that are just sitting in the snow. Hugh Jackman asks "But where are the wires?". Andy Serkis replies "Exactly." (this particular scene is illustrated in the article, under the production heading). What is going on here? Has Tesla somhow electrified the snow? If so, why would the electricity pass through the light-bulbs, instead of going straight into the ground? The only plausible thing I can think of is that he has an enourmous electro-magnet nearby that generates a fluctuating magnetic field and there are some sort of generator in every one of the lamps (I haven't studied these things since high school, so I'm completely just guessing here). But Hugh Jackman lifts one of the lamps off the snow and then it turns off, but when he puts it back, the lamp turns on again. If anyone could explain that scene to me, I'd be mighty grateful.
2. In another scene (also helpfully illustrated in the article, wikipedians are apparently obsessed with Tesla) the great engineer walks underneath a Tesla Coil that's shooting bolts like crazy, apparently completely unharmed (the man knows how to make an entrance). I understand the principle here, that Tesla is wearing insulating shoes and so the electricity doesn't pass through him, but this is still got to be hugely dangerous, right? I mean, the air in that chamber where he walks has to be extremely hot from all the electricity, and what if a bolt passes through him and jumps through the air from his ankles down to the floor (the floor is definitely conductive, you see sparks hitting it all the time). I mean, this is not something a sane person would do, right?
3. After he has made his glorious entrance through the storm of lightning-bolts, he walks up to Hugh Jackman and grabs his hand, and hands him a lightbulb. Still clasping hands, Jackman picks it up with his other hand, and lo!, the bulb lights up (seriously, now he's just showing off). Asking where the electricity comes from, David Bowie in his best Serbian accent says "Ze body is a most excellent conductor!". Again, what's going on here? Has Tesla become so charged by walking through the lightning-bolts that he can keep a lightbulb on for several seconds, even after the electricity has passed through two bodies? And wouldn't the charge pass through Jackman's body straight into the ground (wouldn't that be the path of least resistance?), completely skipping the light-bulb?

I realize that this is a film with science-fiction elements in it, but I would expect the scenes introducing Tesla to be somwhat grounded in reality (as he was a really cool guy who could do really cool tricks with electricity, so why would you go the sci-fi route?). Can anyone explain this to me? 83.250.202.208 (talk) 11:41, 17 November 2008 (UTC)

Let me try to answer these the best I can...

1. He used a Tesla coil to power them. (wonder where THAT name comes from... hm...) A Tesla coil generates a strong electric field around it. Basically, a Tesla coil is a really freaking powerful broad spectrum radio antenna. Radio works by inducing an electric current in your reciever, but the current is small; it needs to be "amplified" by an external current in order to have enough energy to drive the speakers. If you drive enough static charge into the atmosphere, you can induce a current in the same way in just about any metal availible.

   You can do the experiment yourself relatively simply. If you have an AM radio tower anywhere nearby, take a simple hand-held transistor radio and get right underneath the radio tower. You will hear the broadcast from the tower without any batteries in your radio at all. At this distance, the power of the antenna is strong enough to power the circuit without amplification.

   The same principle works in a tesla coil; it will provide enough electrical potential in the air itself to power lightbulbs just inside the field, without any wires. Tesla had some pretty wild ideas about using these for civilian power generation. Basically, you'd build on in the town square, and everyone in town got free electricity. The downside is that these things have a nasty habit of discharging into anyone that gets too close, so it basically acted like a giant bug zapper that takes down birds, pets, wandering drunks, etc. etc.

2. Is likely bullshit, but only slightly. He could wear a "conductive suit" like linemen wear when working on high-tension wires, they act like a personal faraday cage, directing current away from themselves into the ground.
3. Is more likely total bullshit. I can't imagine that his body would act as a good enough capacitor to hold a charge long enough to do that. --Jayron32.talk.contribs 14:02, 17 November 2008 (UTC)

But here's my question about 1. Hugh Jackman picked up the lightbulb from the snow, and it turned off. Then he put it down again, and it turned on. I.e. it didn't work when it was in the air, it only worked when it sat in the snow. Wouldn't your Tesla coil electric field also work when the lightbulb was in the air? Or is the electric field somehow confined to the ground? 195.58.125.52 (talk) 15:37, 17 November 2008 (UTC)

Ah, I see the problem. No, then, that part is bullshit too... --Jayron32.talk.contribs 18:22, 17 November 2008 (UTC)

2) There is a very famous photograph of Tesla sitting under the coils in his laboratory. It's fake (double exposure), but most people don't realize that. (or don't care.) Virtually every portrayal or parody of Tesla recreates this photo somehow. 72.10.110.109 (talk) 14:27, 17 November 2008 (UTC)

Tesla demonstrated in the 1890's that if you set up a strong enough AC field in a room, specially built light bulbs would light without wires connected. This works for glow tubes like neon lights or Geissler discharge tubes, and even for fluorescent tubes. This was back before they worried about the effects of EMF on living things. Back then, they did not even know that X-Rays were harmful. Edison (talk) 19:47, 17 November 2008 (UTC)

Of course User:Edison would play up the danger of Tesla's research. 72.10.110.109 (talk) 20:23, 17 November 2008 (UTC)

Note that User:Tesla has made no contributions.Edison (talk) 00:57, 18 November 2008 (UTC)

There was an art installation in the UK by artist Richard Box back in 2004. The installation, called Field, placed more than a thousand fluorescent tubes on end under some long-distance high-voltage transmission lines. The electric field (and electric field gradient) below the wires was sufficient to light the tubes. Have a look: [3]. TenOfAllTrades(talk) 20:50, 17 November 2008 (UTC)

Box "discovered" this in 2004? It was demonstrated by opponents of overhead high voltage lines back in the 1970's, and had been demonstrated by Tesla and others back in the 1890's. There is a danger if the tubes are raised too high in the air, since they conduct electricity and if brought too near an energized conductor they could electrocute the person holding them. The conductors are elevated for a reason. Edison (talk) 00:51, 18 November 2008 (UTC)

Earth-like planet forming in the absence of life

In 2006, someone asked an interesting question on the talk page for the terraforming article:

http://en.wikipedia.org/wiki/Talk:Terraforming#Earth-like_planet

The question hasn't gotten much attention there and I'm very interested in it, so I'm asking it here: is there a way for a planet with conditions that could support human life (oxygen/nitrogen atmosphere, liquid water, appropriate gravity and atmospheric pressure etc) to form in the absence of life? It might be really unlikely, far-fetched and rare, but it's a huge galaxy and an even huger universe, so surely it's happened somewhere.

The critical thing here would be the generation of oxygen. Oxygen has to be constantly replenished on Earth because it reacts so well with many other elements and so gets locked up in rocks, but perhaps there could be some complex geological process that generates large amounts of oxygen. If the oxygen is too far fetched, what about a planet with otherwise Earth like temperature and pressure conditions but no oxygen so that it would be possible to go outside with only a tank of oxygen? Sure, it'd be limiting, but it's a start. 63.245.144.68 (talk) 13:11, 17 November 2008 (UTC)

I agree, oxygen is the critical thing. Without the oxygen requirement, it's easy - the Earth during the Archean period fits your description quite well (there was some primitive life, but I don't think it had had time to change the planet much - I may be wrong). --Tango (talk) 13:36, 17 November 2008 (UTC)

Only if you aren't too picky about pressure, speculation generally puts Archean atmospheric pressure at 3-10 times modern. Though one could almost certainly come up with inorganic ways to make a pressure closer to modern, so that probably isn't an impediment to the question being asked. Dragons flight (talk) 14:11, 17 November 2008 (UTC)

I've moved your edit conflict message to your own comment - I didn't conflict with myself! ;) A human could survive in 3 atm pressure with no problem, and probably 10 atm too (moving between that and 1 atm requires some care, of course). I think the OP is just looking for habitable planets for colonisation, so that qualifies. --Tango (talk) 14:36, 17 November 2008 (UTC)

That's not my EC note. It was already there before I got here. Dragons flight (talk) 15:07, 17 November 2008 (UTC)

Ah, it was Jayron's, my bad! I'll move it again! --Tango (talk) 15:45, 17 November 2008 (UTC)

(EC with tango) From a purely chemical/thermodynamic perspective the presense of free oxygen is an impossibility in any system which does not compensate in some way. If you look at almost any system with the following equilibrium:

$X+O_{2}<->XO$

The numbers skew SO FAR to the right for most elements that it is an impossibility for any element to exist in the presence of oxygen WITHOUT producing its oxide. The half-dozen or so elements it doesn't work for (copper, silver, gold, platinum, maybe one or two more) are not going to exist in significant amounts in any plantary system. The reaction is always spontaneous and highly exothermic. There's usually a high activation energy to this reaction, but that really only effects the rate of reaction. Given earth-like temperatures, and given a substantially long-enough time frame (say measured in the thousands of years) free oxygen will just stop existing. In fact, I can't come up with any spontaneous chemical process that will generate free oxygen from something that does NOT involve life in some way... --Jayron32.talk.contribs 13:41, 17 November 2008 (UTC)

It may actually be possible to have abiotic free oxygen production; this is a major issue for extra-solar planet spectroscopy missions like TPF and Darwin. For example, in (Selsis, F, Despois, D & Parisot, JP 2002, "Signature of life on exoplanets: Can Darwin produce false positive detections?", Astronomy & Astrophysics, vol. 388, no. 3, pp. 985-1003), it is estimated that a maximum equilibrium concentration of about 5% of $O_{2}$ can be maintained through photochemical processes. The actual photochemical equations (mainly revolving around photo-disassociation of $CO_{2}$ and $H_{2}O$) are apparently quite complicated (the source listed above includes about 150 in their model). I don't think they considered surface processes since these are potentially very variable; there are huge differences between a water-rich planet covered entirely by ocean and a water-poor planet with lots of geological activity (recycling the surface often). 58.96.70.254 (talk) 15:59, 17 November 2008 (UTC)

So if we were to find a planet with otherwise habitable conditions but with no oxygen, how difficult would it be to add the amount of oxygen necessary to support animal life? Industry on Earth is putting out massive amounts of gases into the atmosphere and is demonstrably changing the composition of it, so wouldn't it be possible to do the same on another planet by perhaps separating oxygen from oxide compounds in the crust and releasing it into the atmosphere? 63.245.144.68 (talk) 20:30, 17 November 2008 (UTC)

No, the amount of energy required to generate an oxygen atmosphere directly is ridiculously large. Completely unapproachable by technological means. The global microbial biosphere powered by the sun was able to do it, and any terraforming project is likely to have to rely on the same kind of process. Dragons flight (talk) 22:04, 17 November 2008 (UTC)

If a society has access to trans-stellar travel would likely have access to virtually unlimited energy, the amount it would require to put a workable colony into another star system is ridiculous in and of itself (talking, say, 500 colonists, microfactories, survival gear, trans-stellar communications gear, shelter, ect.) I agree that microbes (or even larger plants) are probably the way to go, but if you have access to that much energy you might be able to crack CO2 or water into usable oxygen. Cracking water has the benefit of producing useful hydrogen gas and the fact you can tap off some of the O2 production into stored LOX for use in a metal/oxygen rocket or fuel cells. As to getting that much energy. Solar satellites beaming power to the surface? Fusion? Geothermal? 69.210.56.62 (talk) 09:39, 22 November 2008 (UTC)

I think there are two separate issues here:

1. Do all planets with the right chemical and thermodynamic environment to produce life necessarily do so in a reasonable time-frame?
2. Do all planets which DO produce life inevitably see it evolve to produce intelligent civilisations?

Neither question is very well understood.

Sadly, science hasn't quite figured out the precise step that lead from "lifeless" chemicals to replicating and evolving lifeforms. Personally - I feel that the oceans are so enormous - and the amount of time involved is so immense that sheer statistics means that sooner or later a replicating molecule would appear - and from that point onwards, evolution takes hold and you have lots of life forms. But the precise chemistry of the situation might mean that this spontaneous formation of a small replicating molecule could take (on average) a trillion years of random chemistry - in which case we are an amazing flook that may have happened only once in the observable universe...or perhaps the statistics works out such that these molecules form within a matter of months - and absolutely every planet that's remotely capable of supporting life must therefore be crawling with the stuff. Which of these things is the truth is hard to know because we don't really know how simple life can be and still cause evolutionary change. The folks who are working on creating completely synthetic life-forms may well have an answer to that within a very few years...and they we'll have a better answer for this one.

If life is everywhere and evolution is in top gear - will there necessarily be intelligent civilisations? I kinda doubt it. The dinosaurs were around for a vastly longer time than the mammals have ruled the place - and they didn't manage to evolve this ability...presumably because there was no advantage to them in having it. So again - it might take a highly unlikely set of environmental pressures to make intelligence worth the price you have to pay for it in reproductive terms.

So I've gotta conclude that a planet with the perfect conditions for forming life might not ever do so - and even if it did, it's not obvious that it wouldn't be locked into a particular evolutionary path that does not favor intelligence. It's not certain that this is a true statement - but there is currently zero evidence that it's not true.

SteveBaker (talk) 22:18, 17 November 2008 (UTC)

While those are two interesting questions, I don't think either of them are what the OP is asking. I think the OP is talking about finding planets suitable for colonisation, not finding extraterrestrial life. --Tango (talk) 00:55, 18 November 2008 (UTC)

It's worth considering IMHO that whatever the case given the long travel distances, you're probably better off just terraforming planets that don't have the conditions suitable for life but could if you terraform them. Yes terraforming them may take thousands of years but I would say there's a good chance so would finding and reaching an already habitable planet without life. Indeed I would go so far to say that there's a fair chance we will terraform some planet or moon in this solar system even those the challenges are numerous before we reach an already habitable extra-solar planet. Nil Einne (talk) 08:11, 19 November 2008 (UTC)

information on the temperature and precipitation in the BOREAL SHEILD ecozone

information on the temperature and precipitation in the BOREAL SHIELD ecozone doesn't exist can someone add this info soon? —Preceding unsigned comment added by Shadow56121 (talk • contribs) 14:27, 17 November 2008 (UTC)

Neolithic period and a Young Earth

Without wanting this to turn into a religious debate, do those who adopt a Young Earth ignore the wealth of archeological evidence from the Neolithic period? While I know YECs are hesitant to accept radiometric dating, surely there must be enough archeological evidence to construct a fairly accurate timeline? -- MacAddct1984 ^{(talk &#149; contribs)} 17:27, 17 November 2008 (UTC)

You might have more luck on the Humanities page, as the beliefs of creationists have no basis in science. StuRat (talk) 18:08, 17 November 2008 (UTC)

On the contrary, there is no desire of adherants to any form of creationism to attempt to construct a coherant theory from evidence. Evidence is either modified or discarded as needed to fit the pre-existing theory; its a "cart-before-the-horse" method of "science" which is why no one with any real understanding of how science works takes it seriously. They don't derive the age of the earth from availible evidence, and modify that age as new evidence arises; they START with the date in mind, and bend the interpretations of the evidence to fit that date. --Jayron32.talk.contribs 18:20, 17 November 2008 (UTC)

I guess what I'm actually asking is: is there significant archeological evidence of the Neolithic period where a timeline can be formulated without having to resort to radiometric (carbon) dating? Which, as StuRat said, may be more of a question for the humanities page. -- MacAddct1984 ^{(talk &#149; contribs)} 18:28, 17 November 2008 (UTC)

I'd imagine that some evidence from dendrochronology could be used for events that are that recent (i.e. <10kya), though preserved wood construction from the neolithic is either very limited or virtually nonexistent. SDY (talk) 18:37, 17 November 2008 (UTC)

Proponents of the Young Earth theory like to ignore radiocarbon dating evidence not because of anything inherently wrong with the methodology of radiocarbon dating, but because it provides evidence that is in conflict with their pre-conceived date as to the birth of the Earth. If you were to present to them any other method which arrived at the same results as radiocarbon dating, they would dismiss it as a flawed method because it arrives at a different date than the exact one that they have in mind. You cannot use reason to talk someone out of a conclusion they did not use reason to arrive at in the first place! --Jayron32.talk.contribs 18:51, 17 November 2008 (UTC)

Indeed. While YECs come up with all kinds of complicated explanations for why carbon dating, etc. get the "wrong" results, those explanations are purely intended for us non-believers, they aren't the reasons the YECs believe what they do. The believe what they do because that's what they believe (probably because that's what they were told to believe by their parents and they never questioned it until it was too late and it was already so deeply ingrained in their psyche that they can't believe anything else), not because they have been convinced by the arguments they try to convince us with. --Tango (talk) 19:41, 17 November 2008 (UTC)

They seem to blame any archeological evidence that doesn't mesh with YEC as an artifact of (or 'proof' of) the Great Flood. They often don't call it the great flood, though. They come up with adorably pseudo-scientific ways of describing a giant, world-covering 40 day flood without actually sounding like they're talking about a biblical event. 72.10.110.109 (talk) 20:20, 17 November 2008 (UTC)

How much water would it take to flood the entire Earth? Assuming all the clouds rained until there were no clouds, would that be enough water? 216.239.234.196 (talk) 21:13, 17 November 2008 (UTC)

Not even remotely. To flood the earth, you would need about 8500 meters of water. 10 meters of water is about one atmosphere of pressure. Hence, for that much water to be suspended in the air, whether as clouds or as vapor, would cause about 850 atmospheres worth of extra pressure. In other words, it would require a major miracle... --Stephan Schulz (talk) 21:20, 17 November 2008 (UTC)

At any one time, the atmosphere collectively only holds enough water to raise sea level a few centimeters. You would need some totally different source of water to flood the Earth. Dragons flight (talk) 21:21, 17 November 2008 (UTC)

Out of curiosity, how much depth of water is currently on the earth that is not in liquid form? In short, if you melted all of the ice caps and glaciers and took the atmoshpere as well, could you get the 8500 meters necessary to cover Everest? SDY (talk) 21:53, 17 November 2008 (UTC)

According to freshwater, about 2% of the earth's water is ice. According to ocean, that means melting all the ice would give you about 25 million cubic kilometres. That's enough to raise the sea level by about 70m; a pretty significant increase, but a long, long, way from the top of Everest. The atmosphere gives you almost nothing. Algebraist 22:01, 17 November 2008 (UTC)

Well - let's be a little bit careful. Sure, there isn't enough water vapor in the air to do that. But we believe that if all of the ice and snow in the world melts - the oceans could rise 20 meters. Because water gets less dense as it gets warmer, if the climate heated up a lot - the water would expand and get quite a bit deeper than that. As the continents get inundated, the downward force of all of that water pushes the continents downwards - and that makes for still less visible land. It's not THAT unreasonable to assume that so much of the land would be underwater that a family with a fricking ENORMOUS boat and a lot of very fractious animals might imagine there was no land left anywhere! But that's OK - every other aspect of that story is ridiculous. SteveBaker (talk) 21:57, 17 November 2008 (UTC)

Ah, ah, ah! Your calculations are based on the earth being a spheroid. I think you'll find things work out just fine when you correct it to the proper shape. Look at all that extra water there; just imagine where it must end up. Matt Deres (talk) 00:45, 18 November 2008 (UTC)

It ends up...on....the.....back......of......the turtle! OH OF COURSE! Now it's all so clear. SteveBaker (talk) 05:17, 18 November 2008 (UTC)

The problem with creationists is that they know full well that if they spell out their beliefs carefully enough - they'll become testable and falsifiable. That's something they don't like to risk - so they have to keep it vague or science will crush their puny belief system under a large pile of rock-solid reasoning. So long as you keep saying "God did it" - then it's hard for science to pin it down. The conversation generally goes something like: "Why are there fossils of damned great dinosaurs - but no sign of any actual dinosaurs on earth right now?"..."God did it". "How come we can trace a clear history of human and proto-human ancestry back through the fossil record and back to the common ancestor of chimpanzees and man?"..."God did it". "Why does the cosmic background radiation appear so smooth - indicating a common point of origin for all of the universe?"..."God did that too". "Why the heck did God do such bizarre and unnecessarily annoying things?"..."To test our faith in him". QED. Where it gets tricky for them is when they want to get this doctrine taught in US schools in defiance of the constitutional separation of church and state - so instead we get "creationism-lite" - or "intelligent design" - where they say all the exact same things - but instead of "God" they say "some intelligent designer" (except when they slip up and say "God" by mistake). Sadly, this eliminates the "to test our faith in him" defense - so there have to start being some actual reasons - and that's where things start to get messy. SteveBaker (talk) 21:57, 17 November 2008 (UTC)

I've always wondered about those Young Earth Creationists you see occasionally who have real degrees from respectable schools. What do those people really believe? Assuming they're sincere, they must experience enormous mental dissonance every time some new fact comes out from the various fields they believe to be arrayed against them (biology, geology, astronomy, paleontology, archaeology, etc.). How do they reconcile that almost all natural evidence seems to point them away from something they believe? --Sean 13:19, 18 November 2008 (UTC)

I know of one case of a quite senior scientist from a very different field of science. He looks at very narrow bits of evidence and picks them apart until he can find a torturous interpretation that is in principle compatible with YEC. He ignores all the other evidence and the interconnections that make a mature field of science so resilient. If you read his texts on the topic, you get the feeling that he consciously and painfully avoids thinking one step beyond his immediate goal of dissecting just one single bit of evidence. --Stephan Schulz (talk) 13:40, 18 November 2008 (UTC)

On the other hand, people like that are quite rare. Most scientists, even the evangelical christian ones, have little problem working both thought systems into their world view. I know that I don't... --Jayron32.talk.contribs 17:13, 18 November 2008 (UTC)

The Laws of proportioning aggregates for concrete

Could anybody hep me find article by Fuller, W.B. and S.E. Thompson. The Laws of Proportioning Concrete. Journal of Transportation Division, American Society of Civil Engineers, Vol. 59, 1907. Thank you. —Preceding unsigned comment added by 202.70.74.132 (talk) 17:45, 17 November 2008 (UTC)

It sounds like you've found it! An article written in 1907 is not likely to be online - you'll probably have to take a trip to the library and get a copy on interlibrary loan. SteveBaker (talk) 21:37, 17 November 2008 (UTC)

comparative world livestock populations

Do we have a world list of livestock by quantity? i.e. how many domesticated pigs, goats, sheep, cattle, Bactrian camels, Arabian camels, donkeys, yak, horses, llamas, etc. are alive in the world today?--206.248.172.247 (talk) 17:57, 17 November 2008 (UTC)

This list provides information on cattle population by country, however it is not complete list. Otolemur crassicaudatus (talk) 18:06, 17 November 2008 (UTC)

Here is a good reference [4]. Click the arrow button to navigate to the other pages for information on other animals. Otolemur crassicaudatus (talk) 18:14, 17 November 2008 (UTC)

Compost pile

What happens if you put diseased plants into a compost pile? —Preceding unsigned comment added by 189.58.24.177 (talk) 20:27, 17 November 2008 (UTC)

That would depend on the disease. Some diseases might be specific to that type of plant or might be destroyed by the decomposition process, while others could possibly infect other plants which have the resulting compost spread around them. StuRat (talk) 20:34, 17 November 2008 (UTC)

If the compost gets "hot enough" during the decomposition process, it can kill disease organisms. However it is hard to be sure if your compost gets "hot enough". The cautious approach is not to put diseased plants into your compost system. CBHA (talk) 21:08, 17 November 2008 (UTC)

Math and physics podcasts

I've already found Mathgrad, Math mutation, Math factor, and Discrete Mathematics, but I'm having a harder time finding good physics podcasts. Could anyone please recommend podcasts about Math and Physics, not necessarily aimed at experts or professionals but maybe enlightened amateurs. Thank you. 190.220.104.35 (talk) 20:44, 17 November 2008 (UTC)

Well, Physics podcasts I don't know of, but usberkeley on youtube has physics lectures from 2007. I hope that helps 66.216.163.92 (talk) 23:39, 17 November 2008 (UTC)

type of screen

Does anyone know what technology is used for these station displays [5], [6]? They don't look like the traditional LED or plasma displays. And if possible can a link also be provided to the wikipedia article which explains the technology. Thanks in advance. Clover345 (talk) 20:54, 17 November 2008 (UTC)

I would guess they are digital rear projection screens utilizing DLP technology. They are large and bright and relatively cheap, but do have the disadvantages of being energy hogs, getting hot, and burning through bulbs. StuRat (talk) 03:50, 18 November 2008 (UTC)

Buoyancy

What causes the buoyancy force? The article doesn't really explain the origin of the force, just the equations used. —Preceding unsigned comment added by 76.69.241.185 (talk) 23:32, 17 November 2008 (UTC)

The medium (usually liquid) pushes on the object from all sides, but presses slightly less on the top than on the bottom because the bottom in this case is at higher pressure. If you push less on the top than on the bottom, the net force is up. SDY (talk) 00:11, 18 November 2008 (UTC)

Our buoyancy article does explain this in more or less those exact words. Because pressure increases with depth - the upward pressure on the underside of the object must be more than the pressure pushing down on the upper side because of the thickness of the object. Since the total upward facing area must equal the total downward facing area (measured at right angles to the gravitational field) - there must be a net upward force. The math falls out pretty simply from there. I suppose if you want the ULTIMATE source of the force - it's pressure - which is molecules in the fluid bouncing off of the object, imparting little bits of kinetic energy. But they bounce because of the electromagnetic repulsion between the outer electrons of the molecules - so that's a layer of explanation below that. SteveBaker (talk) 00:32, 18 November 2008 (UTC)

The explanations above do not explain why a stone doesn't float. And if an object does float in water, why doesn't it go on rising above the water, up into the air to the stratosphere, for the reasons given. (Air pressure on the bottom of the object is greater than air pressure on the top.) In fact, a submerged object that floats to the surface would leap into the air when the top of it leaves the water. (Directly below the surface, water pressure will not be greatly more than air pressure on the surface. But parts of the object that are deeper down will experience a rapidly increasing pressure with increasing depth because of the weight of the water around it. The pressure on the bottom of the object will be very much greater than the pressure on the top of the object, so it will leap out of the water, then continue to rise.) Actually, there will be an upward surge when the object breaks the surface, but it will not continue to rise into the stratosphere. Not many people can say "gotcha" to SteveBaker. —Preceding unsigned comment added by 98.16.67.220 (talk) 02:11, 18 November 2008 (UTC)

Well, that's because the difference in pressure in air is smaller than the difference in pressure in water, because water is denser than air...but I agree that the explanation doesn't make sense (in my mind, at least :)). See, wouldn't your explanation require that the shape of the object be significant. If the object was a sheet of something slightly denser than water with the same dimentions as a piece of paper, then in one orientation (long side perpendicular to the surface of the water) it might float because the bottom is much deeper than the bottom, while if rotated 90 degrees (so the long side is parallel to the surface) then it might sink for exactly the opposite reason. —Preceding unsigned comment added by 76.69.241.185 (talk) 02:21, 18 November 2008 (UTC)

Well, technically you have to think of it as billions of little molecules bouncing off the object. A sloped surface will transfer some down and some "right." In a cone, for example, all the "right" would be canceled by "left" and you'd get a net force that's either up or down. With an irregular object, it'll tumble as it rises or sinks. If you add up all of the vectors, though, you get a "down" force that's less than the "up" force. The main "enemy" is gravity (always "down" more or less by definition): if the net "up" force doesn't exceed that, the object sinks. Much easier to explain with a drawing, really. SDY (talk) 02:53, 18 November 2008 (UTC)

The reason a stone doesn't float - and most things don't float in air (although some clearly do) - is because the difference in pressure between the top and bottom doesn't exceed the weight of the object...so it still sinks (albeit a bit slower than it otherwise would have). My explanation makes it sound like a cone or something might behave wierdly - but you do have to read EXACTLY what I wrote. I said "Since the total upward facing area must equal the total downward facing area (measured at right angles to the gravitational field) - there must be a net upward force." - note the boldface here. A cone has the same area on the pointy end as the flat end when you measure the area at right angles to the gravitational field. As for your concern about a flat object and a flat object on its side: The surface area (at right angles to the gravitational field) of (say) a thin, flat, HORIZONTAL sheet of metal is large - but the pressure differential over it's skinny thickness is small. That small pressure differential multiplied by the large surface area (at right angles to the gravitational field) gives you the value for the buoyancy force. Turn the plate on it's side and the cross-sectional area (at right angles to the gravitational field) becomes very small indeed - but now it's much greater "height" increases the pressure differential between the 'top' and the 'bottom' edges of the plate. Crunch the math and you discover that the buoyancy of the plate remains the same no matter how you turn it around. In fact - it depends on the volume of the object - which is why we can neglect all of the complicated shape stuff and concentrate on the density of the object alone. Why an object breaking the surface doesn't leap up into the air is because the pressure on the bottom of the object depends on the depth of the water - which is now less than the thickness of the object - so even though the downward pressure has gone to more or less zero - the upward pressure is less than it was when the object was completely submerged - so as a floating object breaks the surface, the upward force gradually drops in strength until it exactly supports the weight of the object. SteveBaker (talk) 05:13, 18 November 2008 (UTC)

Ah, thank you for clearing that up. But I have another question: why does pressure increase with depth? I can understand why it would happen for a gas (the weight of the atmosphere above compresses the gas, increasing pressure), but why would the same happen for a non-compressable liquid? Thanks for your patience btw :) —Preceding unsigned comment added by 76.69.241.185 (talk) 23:50, 18 November 2008 (UTC)

The pressure is due to the weight of all the water above you...nothing complicated about that! Steel doesn't compress much either - but if I drop a one ton safe on you (OK - if I very gently LOWER a one ton safe onto you) - the pressure is still pretty significant!

Would you mind going into more detail? I see why there would be a greater force pushing down, but why would this force be distributed everywhere. —Preceding unsigned comment added by 76.69.241.185 (talk) 03:39, 20 November 2008 (UTC)

If you take a cube of jello and push down on the top of it hard with your thumb - what happens? It squishes out sideways - right? So the downward pressure of your thumb was translated into lateral pressure of the jello moving sideways. It's the same deal with the water. This has nothing to do with compressibility or incompressibility though. SteveBaker (talk) 20:14, 20 November 2008 (UTC)

I see why this would produce downward and lateral pressure, but how would upward pressure exist? —Preceding unsigned comment added by 76.69.241.185 (talk) 23:42, 20 November 2008 (UTC)

Here's another way to look at it. For simplicity, assume a flat-topped object is rising upward in water due to buoyancy. When the flat top is just a tiny bit below the water surface, the pressure on the top of the object is just a tiny bit less than pressure due to air pressure on the water surface. So when the object breaks the surface, there is no sudden decrease of pressure on top of it, so there will be no upward surge due to any sudden decrease of pressure on top. Of course, momentum will cause a surge, and breaking through the surface tension of the water will slightly slow the rate of upward motion. —Preceding unsigned comment added by 98.16.67.220 (talk) 15:35, 18 November 2008 (UTC)

Another factor is the viscosity of water. When the flat topped object breaks through the water surface, a little time will be needed for water to roll off the top of it. After the roll off, a film of water will remain, weighing the object down until the film of water evaporates. —Preceding unsigned comment added by 98.16.67.220 (talk) 22:52, 18 November 2008 (UTC)