Wikipedia:Reference desk/Archives/Science/2010 December 14

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

December 14

Native Americans

Where did Native Americans come from? And how far back can they trace their DNA?184.77.224.230 (talk) 06:08, 14 December 2010 (UTC)

Native Americans originally came across the Bering Land Bridge from Asia. The pattern and timing of migration is a matter of debate. See Settlement of the Americas, Paleo-Indians, Pre-Columbian era and Genetic history of indigenous peoples of the Americas. Red Act (talk) 06:34, 14 December 2010 (UTC)

For the Humanities desk-type answer to this, several tribes have origin stories which involve their connection to certain areas in North America and some have actively opposed DNA testing and Siberian migration theories. So "can they trace their DNA", yes, they can but no, they don't. 75.41.110.200 (talk) 13:50, 14 December 2010 (UTC)

And those origin stories have about as much validity as creationism, intelligent design, the flat earth theory, and the flying spaghetti monster "hypothesis". In other words, absolutely none. --140.180.26.37 (talk) 19:45, 14 December 2010 (UTC)

I recently watched a documentary called The Incredible Human Journey which deals with exactly this topic. I'm a bit of a doco buff and I think this one was considerably better then average so i wouldn't hesitate recommending it. The fifth and final episode specifically discusses the peoples of the Americas. Vespine (talk) 23:40, 14 December 2010 (UTC)

There were multiple waves of immigration, some of which came across the Bering Land Bridge, as mentioned above. Others may have come across the Pacific by canoe. If you think about it, the multiple waves are quite obvious, from how different the various Native Americans look. The Inuits, for example, look more Asian, so were likely a relatively recent immigrants from there, while those in South America may have come at a different time and/or via a different route. StuRat (talk) 02:20, 15 December 2010 (UTC)

The Solutrean theory proposes a wave of migration of indigenous North Americans from Western Europe to Atlantic Canada. ~AH1^(TCU) 03:32, 18 December 2010 (UTC)

I suspect the reverse, that some natives from what is now Canada made it at least as far as Iceland, since some of them also look vaguely oriental, like Björk. StuRat (talk) 05:30, 18 December 2010 (UTC)

The Continents of Earth

If all the continents were connected, does that mean that the earth was smaller and where did all the water come from? 184.77.224.230 (talk) 06:22, 14 December 2010 (UTC)

The earth was not smaller, the ocean surrounding the pangea continent was roughly as big as all today's oceans combined. The water was already there. 83.134.145.216 (talk) 06:35, 14 December 2010 (UTC)

It is thought that most of the water in the Earth's oceans originally came from comets and asteroids. See History of the Earth#Origin of the oceans and atmosphere. Red Act (talk) 06:57, 14 December 2010 (UTC)

See also Continental drift and Plate tectonics. WikiDao ☯ (talk) 20:09, 14 December 2010 (UTC)

If all of the land was on one side, the surface area on that side would be higher, which would mean there was more mass on that side. If I glue a coin to the side of a tennis ball, it won't spin well, so did Pangea-era Earth have a lot more wobble in its rotation? —Arctic Gnome (talk • contribs) 23:41, 14 December 2010 (UTC)

The current absolute highest point of the Earth is about 6 miles at Everest, and the deepest is not that much deeper below sea level. The total diameter is roughly 12500 miles. That makes the highest point only 0.05% of the total thickness of the Earth. The total average elevation of land currently on Earth is much less, only 2000-ish ft. That percentage barely registers. Does it make the Earth unbalanced? Yes, but not very much at all. Aaronite (talk) 00:05, 15 December 2010 (UTC)

You can't actually unbalance the earth, instead the center of gravity would move, which would then change the height/position of sea level. So it seems to me the map shown above is wrong - more of the land area would be covered by water. It might not be by much though since water also has mass, so it's not like the low areas are completely empty, they are just less dense. Ariel. (talk) 04:30, 15 December 2010 (UTC)

You can't assume that the density of the Earth is spherically symmetric. It's perfectly possible for all the land to be concentrated on one side, or in other words for one side of the planet to be farther from the center of mass than the other. Rckrone (talk) 18:49, 15 December 2010 (UTC)

sea level reconstruction

The ocean level has risen and fallen over geologic time, but we can expect that the volume has remained similar. The ocean floor tends to sink deeper over millions of years as it cools and shrinks. At some periods the continents seem to have been flooded, eg in Jurassic and Cretaceous Australia was seriously flooded. Australia also had high sea level more recently in Paleocene to Eocene and Late Oligocene to mid Miocene and last high level was in Early Pliocene. I assume this is the case around the rest of the world too. Graeme Bartlett (talk) 03:56, 17 December 2010 (UTC)

The only "unbalancing" that can occur is in the axial tilt, which could shift over a kilometre in certain circumstances. ~AH1^(TCU) 03:14, 18 December 2010 (UTC)

The Eyeball

Who created the human eye? 184.77.224.230 (talk) 06:24, 14 December 2010 (UTC)

No one did 83.134.145.216 (talk) 06:31, 14 December 2010 (UTC)

See evolution of the eye, a fascinating article. Paul (Stansifer) 06:33, 14 December 2010 (UTC)

Some religions believe that their deity or deities did it. Googlemeister (talk) 15:03, 14 December 2010 (UTC)

Humans create human eyes every day. You did it before you were born too, presuming you have human eyes. Vespine (talk) 23:21, 14 December 2010 (UTC)

Highly troubled, self-acclaimed saint of logic seeks epiphany

This is my first refdesk post, let it be known, albeit there is probably some sort of rule prohibiting irrelevant information like that. AAAANNNNYYYYWAYS.... As of about 3 months ago, I started doing research into... well... science I guess, my main fascination would be the universe. Unfortunately, my inability to decipher all of the complex functions that I see on this lovely website has left me with out any concrete opinions about everything... and anything. Just from screwing around with a pen and paper a little bit, I realized that any problem expressed in words (English) could somehow be translated into a more definitive equation, with respect to the arbitrary nature of language as a code. To all of you out there who are equipped with far better CPUs in your brain: I want some answers!

1. Is formal logic basically the study of the phenomena I mentioned above? 2. Since there are, from what I gather, three dimensions of space and one of time in this universe we live in. And that time is the rate of change at which space changes, would that make time the first derivative of the universe? I'm probably wrong...

I need a good concise explanation of what I should be trying to study, and maybe a bit of information about the field of study itself. Also, information theory.... it blows my mind for some reason yet, I barely understand it.

An example of a question that wanders into my fetus of a brain would be...

If you were to consider your field of vision a closed system (lets say your eyes disconnected from your brain.. hypothetical yada yada) would the entropy of what you see be all of the possible states being all of the possible combinations of colors, hues, saturations or whatever we measure visual information in (light?) How exactly does this degree of disorder concept play into entropy?

HELP ME INTERNET, I might have potential.. maybe — Preceding unsigned comment added by BloodWasPassion (talk • contribs) 06:34, 14 December 2010 (UTC)

I would advise taking some classes in these topics. Honestly, your speculations are so scattered that it would be impossible to answer them in any way that would be useful. Looie496 (talk) 06:44, 14 December 2010 (UTC)

1. Very often the universe obeys mathematical laws, in other words if you can write a theory as math it often exactly matches what the universe actually does. Why this is/should be so is not known.
2. I would not call time the rate of change (and thus a first derivative) because that's a circular definition - time is how you define rate of change, it can't both define it and be it.
3. I can't answer your vision/entropy question, it's too confusing. Try to first understand entropy by itself (i.e. relating to energy) before trying to understand it in terms of possible states or degrees of freedom.

Wikipedia is not a good way to learn science - it's a good way to understand a new concept, but it's not good as a first course. Get yourself some good books - I especially like getting textbooks. You can also audit classes a local university. MIT (and many others) offer free online classes, you can find a list at OpenCourseWare. Khan Academy is a very prolific youtube teacher who makes hundreds of mini courses in a wide variety of topics - you would probably enjoy watching them. Ariel. (talk) 07:04, 14 December 2010 (UTC)

There's a name for #1, but I'm not sure what it is. Background independence? Cosmological principle? Self-consistent universe? 213.122.3.214 (talk) 08:02, 14 December 2010 (UTC)

I'll just address your question #2 above. Rather than time being the first derivative of something, time instead is commonly a dependent variable with respect to which derivatives are often taken in physics. The Time in physics article may be of interest to you. Beyond that, to see how time is treated mathematically in science, a good place to start would be a class in Newtonian mechanics. But you'll need a class in special relativity to gain a more modern understanding of the nature of time. And then ultimately, you'd need a class in general relativity to understand the connection between gravity and time. Time is a very complicated topic. Red Act (talk) 07:29, 14 December 2010 (UTC)

OP here, the influx of attention has somewhat satiated my previous disdain... I would love to study physics for the rest of my life, but I simply do not think I have the patience to systematically start from the bottom. I think I am doomed to be "scattered" as one of you so kindly put it for eternity. I think i'll just do statistics and manipulate the masses. I do appreciate the last post though (right above this one) for it has given me a good place to start reading into my physics... hobby? even though I said I don't have time to make it an academic pursuit, I do think I will take a look at newtonian mechanics. — Preceding unsigned comment added by BloodWasPassion (talk • contribs) 08:09, 14 December 2010 (UTC)

How about Bayesian statistics which you will need anyway to do physics? It's applicable to any fields where induction or deduction under uncertainty can take place, which includes most of the empirical and applied fields. Also, it is a special case of the formal mathematical logic of deduction for more certain fields including many theoretical fields. It seems like you just want statistics if you don't want to specialize into physics. Ginger Conspiracy (talk) 11:04, 14 December 2010 (UTC)

1. No, formal logic is the application of axiomatic rules within a given framework and not the study of any problem that can be expressed in English. For example, epiphanies are illogical. 2. No, the Universe has 3 observable spatial dimensions and along each dimension the first derivative with respect to time of an object's position is simply its velocity in that direction. You may find Simple Wikipedia's page about Information entropy a useful starting point to study. May your troubles be few. Cuddlyable3 (talk) 15:48, 14 December 2010 (UTC)

As a related aside, for people generally interested in science, in particular but not exclusivley those with a new or renewed interest in it, I recommend Bill Bryson's A short history of nearly everything. I've always liked science but a few years ago I started taking much more interest in it, and even thought probably more then half the book was about stuff I already knew, it was still a great read. Not specifically to "learn" science, but to learn about the history of science and its major discoveries. Vespine (talk) 04:32, 15 December 2010 (UTC)

Perhaps it is already recognized, but I think looking at the appearence of a house is not the same as looking at people inside it, though looking only at the appearence of a house ensures every possibility of the state of the inside of the house untouched. And a good house should, i think, be easy to use for everyone.

Repeat pneumonia

I didn't find the answer to this question in our pneumonia article: Do people have an increased incidence of pneumonia if they're previously had pneumonia? Comet Tuttle (talk) 06:35, 14 December 2010 (UTC)

I think it would be hard to give a single answer because pneumonia is not a single condition. It's the name of a symptom, but it has many causes. Some of those causes would be likely to reoccur, others wouldn't be. Ariel. (talk) 07:17, 14 December 2010 (UTC)

I had it really badly a few years ago, and almost died. Since then, I have to have flu vaccinations, and I have been told by my doctor that the damage to your lungs makes you more susceptible to future attacks.Zzubnik (talk) 09:19, 14 December 2010 (UTC)

I can think of three ways this could be true:

1) As mentioned above, some type of damage could occur the first time, making a recurrence more likely. I can't verify that this is true for pneumonia, however.

2) Perhaps the original case isn't fully cured, but just goes dormant, with the infectious agent remaining in the body. While this happens with other diseases, I've never heard of it for pneumonia.

3) If the person originally contracted the disease because they are at increased risk (say due to a suppressed immune system or walking around in cold rains without rain gear), then, if these additional risk factors are still present, that person will remain at an increased risk, relative the the rest of the population, of contracting it. StuRat (talk) 01:54, 15 December 2010 (UTC)

How many brain cells do gasoline fumes kill?

Or neuronal pathways, along with that?

You see, a fuel line froze so I had to go to a Dara's convenience store to get a gas canister, unleaded, and a fuel-line antifreeze.

Now from the time I filled up the 1 gallon, 4 oz. canister (some spilled onto the outside of the plastic canister itself), to the time I had to fill it up into my car, the fumes were overpowering.

I tried my best to only breathe through my t-shirt and sweater, but I've still been influenced by it.

Therefore, how much of my brain would the fumes kill? I already feel like I have a reduced mental capacity now. (It might be psychosomatic, or not, but I would hope it is!!) How do I undo that damage?

(I have an Accounting final to take tomorrow, plus some more finals, odds and ends to finish up until Friday night, so I really, really hope it doesn't damage my academic prospects here.) --70.179.178.5 (talk) 07:03, 14 December 2010 (UTC)

Breathing through a shirt wouldn't help anything. I'm not seeing anything about gasoline damaging nerves, just that it's a carcinogen (not sure that's exactly good news), but anyway, even if it did damage nerves, the body is very good at healing. There is a massive difference between a single exposure and chronic exposure. After a single exposure the body starts to heal, and if you let it finish you'll be ok. Chronic exposure damages things before they have a chance to fully heal causing far more severe problems. Look at Second-impact syndrome for an example of this. I would avoid gasoline for a while, but not worry about the single exposure. And BTW it's not really possible to actually feel reduced mental capacity, the reason is that along with the reduction comes a reduction in ability to detect the reduction. In other words stupid people can't tell they are stupid (Illusory superiority, Dunning–Kruger effect). So I'm quite sure what you are feeling is psychosomatic. Ariel. (talk) 07:13, 14 December 2010 (UTC)

Edit: This lists the symptoms of exposure, but be aware they are frequently talking about much higher exposures than what (I assume) you were exposed to. Scroll also to the bottom near "Are any future health effects likely to occur?" Ariel. (talk) 07:27, 14 December 2010 (UTC)

This does border on medical advice. Consulting a doctor about this would be better. --Chemicalinterest (talk) 12:02, 14 December 2010 (UTC)

The idea that minor toxins such as alcohol and fumes kill brain cells is a myth. Research indicates that the great majority of intoxicants don't kill significant numbers of neurons until very high dosages are reached, doses approaching the level needed to kill a person directly. They can however make you feel bad in a variety of ways that don't involve killing brain cells. Looie496 (talk) 16:44, 14 December 2010 (UTC)

No offence, but imho the above post crosses the line about medical advice, it could pretty much be construed as saying that "sniffing petrol isn't as bad as people make it out to be" and "you practically need to kill yourself doing it for it to do any harm". Whether it actually "kills" neurons or not, or what it does to you neurologically, the effect is what I'd colloquially call "turns your brain to mush", other's even more colloquially call it f**cking your brain up. Have you met people who have sniffed petrol chronically? It is really horrible. Yes, that level of damage requires chronic exposure, but your definition of chronic is "nearly enough to kill you". Not a significant proportion of people kill them selves sniffing petrol unless they pass out with a bag on their head. Saying it can "make you feel bad" is like saying chopping your hand off "might hurt a little bit". To recap, I agree you don't need to worry about getting the occasional whiff at the petrol station, it'll be diluted with the air even if it smells strong and your body will easily recover from such a tiny exposure, but sticking your face into a can or bag of gas and deliberately inhaling the concentrated fumes is a very very bad idea not just because it will make you feel bad. Vespine (talk) 03:47, 15 December 2010 (UTC)

Chronic means "repeated" not "nearly enough to kill you", I don't know where you found a different definition. Also the criteria for medical advice is mainly is it a diagnosis. It's perfectly fine to talk about if something is dangerous, and how dangerous - as long as we are not talking about a specific person, but rather the item in general. Ariel. (talk) 11:10, 15 December 2010 (UTC)

Yes I know what chronic means, "repeated" and "nearly enough to kill you" are not mutually exclusive. My point was that chronic use IS extremely harmful even if it does NOT nearly kill you. Unlike Looie who imho sounded like he was suggesting that sniffing petrol is not so bad UNLESS you nearly kill yourself. As for "it's perfectly fine to talk about if something is dangerous", yes but not when the "talk" suggests something is not dangerous when it really is. Maybe it's not specifically "medical advice" in this case, but the principle is exactly the same: random person on the internet gives "advice" about something to do with health that could result in someone reading it and doing something really stupid and dangerous. Clear enough? Vespine (talk) 22:41, 16 December 2010 (UTC)

Without being medical advice, unintended brief exposure to fumes from volatile substances in everyday life can make you feel strange, or affect your mental experience temporarily, but "feeling strange" is not a synonym of "brain cells dying". Oxygen levels and very short-term chemistry changes are more likely. They could in principle have some eventual secondary effect given enough time, that's all. Exposure that is deliberately more intense may cause harm but this could happen in many different ways, not just the one the poster suggests. If this is a concern see a doctor. FT2 ^{(Talk | email)} 01:11, 21 December 2010 (UTC)

crude oil, a part of earths design

Is crude oil a layer around the earths core.

Is Crude oil a part of the earths design? Is coal,old plant source deposits absorbed by crude? 184.77.224.230 (talk) 07:25, 14 December 2010 (UTC)

No. And I am sceptical about a question that starts off with "Isn't..." Makes it instantly rhetorical, as if you believe you already know the answer. If so, are you trying to convert us? HiLo48 (talk) 07:29, 14 December 2010 (UTC)

Crude oil formed from the preserved remains of prehistoric zooplankton and algae. See Petroleum#Formation. Crude oil on Earth did not predate life on Earth. Red Act (talk) 07:55, 14 December 2010 (UTC)

We do have an extensive article on Abiogenic petroleum origin. It is a bit wishy-washy, but the gist is that it was a proposed theory that had some support, but the current position is that nearly all crude oil is biogenic and that abiogenic contributions are insignificant. One very strong argument for this is the isotopic composition of oil (biogenic material is depleted in ¹³C compared to the normal abundance, because many primary producers (i.e. plants) slightly prefer ¹²C). There certainly is no layer of crude oil around Earth core. --Stephan Schulz (talk) 10:04, 14 December 2010 (UTC)

No one designed the earth, therefore nothing is part of the earth's design. --Lgriot (talk) 11:09, 14 December 2010 (UTC)

On the Science reference desk no one designed the Earth. On the Humanities reference desk the idea that the Earth was created by God can be entertained. Bus stop (talk) 17:19, 14 December 2010 (UTC)

Does that mean it could also go on the entertainment desk? Vespine (talk) 23:17, 14 December 2010 (UTC)

Oil and gas exploration have not been done around the outer core. ~AH1^(TCU) 03:07, 18 December 2010 (UTC)

More seriously,

1. Oil forms due to various processes in a body of biological debris. Such bodies of biomass form as a result of local geology. Being fluid they rise, fall and move around under pressure until blocked. There's no evidence of a formal "layer" existing and given movement within the earth it seems unlikely a stable layer exists.
2. If creationism was considered here (which it isn't) then even so they are no more a part of earth's design than any other feature we know about (ice at poles, curents in water, weathering). They form where appropriate physical conditions exist geologically, nothing more. Even if a "designer" existed there's no way to tell if this was a deliberate decision, a lucky chance, or pure hapstance.

FT2 ^{(Talk | email)} 01:00, 21 December 2010 (UTC)

Anodes, salts, and cathodes for water electrolysis

Which anode, conduction salt, and cathode combination is the most cost-effective for recovering hydrogen and oxygen by electrolyzing water? Is the main problem oxidation of the anode? I am told that ruthenium-iron alloys might be very useful, but I'm interested in the most cost-effective solution. Ginger Conspiracy (talk) 10:28, 14 December 2010 (UTC)

Our electrolysis of water article states that platinum electrodes are used, which are the default electrodes for most chemistry as platinum is very unreactive. The electrolyte is normally sulfuric acid as the sulfate ion is very hard to decompose. Failing this, potassium hydroxide or sodium hydroxide can be used. CS Miller (talk) 10:31, 14 December 2010 (UTC)

Hydrogen and oxygen aren't usually produced by the electrolysis of water, so cost-effectiveness doesn't really come into it. Physchim62 (talk) 10:49, 14 December 2010 (UTC)

Is the sulfur-iodine cycle with electric heat more cost effective? Ginger Conspiracy (talk) 10:55, 14 December 2010 (UTC)

Oxygen is usually produced by fractional distillation of liquid air. Hydrogen is sometimes produced electrolytically, as in the chloralkali process (where it is a by-product), but is usually produced industrially by reacting steam with coke to produce syngas:

C + H₂O → CO + H₂

steam with methane (natural gas) will also work, although the temperature needed is a little higher (1100 °C):

CH₄ + H₂O → CO + 3 H₂

Just checking that in Greenwood, Norman N.; Earnshaw, Alan (1984). Chemistry of the Elements. Oxford: Pergamon Press. p. 44. ISBN 978-0-08-022057-4. does give one other answer to your question. Apparently, electrolysis of barium hydroxide solution with nickel electrodes is used to produce high purity hydrogen: the process is "expensive but becomes economical on an industrial scale when integrated with the chloralkali industry." Physchim62 (talk) 11:12, 14 December 2010 (UTC)

That process is called the steam reforming process. Zeolites are also used to separate oxygen from air. It really depends on how pure the oxygen and hydrogen streams must be. CS Miller (talk) 11:25, 14 December 2010 (UTC)

Also on how much you want to make. Steam reforming and fractional distillation are the bulk-scale processes; the zeolite fractionation of air (the process does have a proper name, but I can't remember it for the moment) is cost-effective on smaller scales. Methanol cracking is also used for the small-scale production of hydrogen:

CH₃OH → CO + 2 H₂

This patent has some more details about the industrial electrolysis of water to produce hydrogen. Physchim62 (talk) 11:54, 14 December 2010 (UTC)

I'm interested in the economics of production of hydrogen from non-fossil sources in large quantities to estimate the cost of reducing carbon dioxide into methane. Ginger Conspiracy (talk) 13:33, 14 December 2010 (UTC)

You'd need to provided at least the enthalpy of combustion of methane in order to convert water + carbon dioxide into methane + oxygen. I have to question the wisdom of this, as methane is a more potent greenhouse gas than carbon dioxide is, and all you are doing is reversing the combustion of fossil fuels. Until such time as all of the world's power comes from non-fossil fuel sources, you are on a losing proposition. CS Miller (talk) 13:52, 14 December 2010 (UTC)

See the Sabatier process and the Fischer-Tropsch process for details of how it is done. Theoretically, once we stop using fossil fuels, these processes could be used to create fuel for aircraft etc, where there is no other practical energy storage mechanism. CS Miller (talk) 13:59, 14 December 2010 (UTC)

Thanks! The people at http://windfuels.com think they can do it for $45/barrel petroleum equivalent cost from excess overnight wind power. Ginger Conspiracy (talk) 11:31, 15 December 2010 (UTC)

To reduce our carbon footprint, you'd be better to invest in grid energy storage projects, rather than converting CO₂ into methane. CS Miller (talk) 12:19, 16 December 2010 (UTC)

Methane ("natural" gas) synthesis might be a very cost-effective form of storage. Ginger Conspiracy (talk) 07:07, 17 December 2010 (UTC)

pure rotational spectra

why pure rotational spectra is absorptive in nature ? — Preceding unsigned comment added by Pikesh pal (talk • contribs) 12:01, 14 December 2010 (UTC)

There are rotational emission spectra; see Rotational spectroscopy. I'm not sure what you mean by "pure". Ginger Conspiracy (talk) 13:40, 14 December 2010 (UTC)

Absorbance spectra are generally more useful in many applications than emission spectra. This is because when you fire a beam of light at a sample, the incoming light comes in one straight beam, so you can just build a detector opposite your emitter, and measure how much light is lost. Emmission spectra are non-directional, so while the substance you are testing should emit the same wavelength it absorbs, it will emit in all directions in three dimmensions making detecting such emissions difficult. Genrally, emission spectra are used where the source of exciting energy is non-directional, such as flame ionization spectroscopy and nuclear magnetic resonance. --Jayron32 14:20, 14 December 2010 (UTC)

Are mad people always mad at something?

People talking alone seem rarely engaged in amenable conversations and mentally ill person seem rarely to be happy beings. Does being mentally ill mean that you'll be mad at something? Could it be that that's (feeling offended, pissed off, ...) a part or mental illness? 212.169.191.200 (talk) 13:05, 14 December 2010 (UTC)

Some mentally ill people are euphoric or maniac, which is no better position than the above, but still something different. Quest09 (talk) 13:15, 14 December 2010 (UTC)

(edit conflict) Mental illness covers a VERY wide range of conditions and behaviors. Its impossible to say that people who are mentally ill are always angry. --Jayron32 13:16, 14 December 2010 (UTC)

(edit conflict):Very, very generalised question (and the section header isn't entirely P.C.). Anyways - the term "mental illness" cover a wide range of different disorders, people suffering from depression or bi-polar disorders are likely to spend a significant amount of time feeling depressed, but to ask the question with reference to such a broad generalisation increases the chances that you will have unsatisfactory answers/replies. Can I suggest that you refine your question, I'm sure that will lead to you getting some decent responses on here (you may want to read Mental Illness#management) Darigan (talk) 13:21, 14 December 2010 (UTC)

As an aside, have you considered sampling bias? Perhaps you're not noticing the mentally ill people who are having quiet conversations with themselves. (They look too much like the self-absorbed-but-still-technically-sane people who are inseparable from their hands-free Bluetooth earpieces.) TenOfAllTrades(talk) 13:45, 14 December 2010 (UTC)

mad a. 1. an offensive way for describing someone who is mentally ill 2. angry 3. very silly or stupid. Now, what was the question again? Cuddlyable3 (talk) 15:15, 14 December 2010 (UTC)

The OP's parenthetical clarification makes it clear he is using the American understanding of mad=angry rather than the British understanding of mad=crazy. --Jayron32 15:46, 14 December 2010 (UTC)

There are forms of mental illness that bring more positive emotional states. For example, I heard on NPR that some people who 'hear voices' hear voices that tell them nice things- and thus, they are less likely to seek treatment. -FisherQueen (talk · contribs) 15:50, 14 December 2010 (UTC)

Perhaps the satisfaction in life comes from talking with other people rather than with oneself. It could be frustrating to carry on a conversation with oneself as you are rarely likely to surprise yourself. So, I think the OP is likely correct—that most people talking alone are not having such a good time. Bus stop (talk) 16:00, 14 December 2010 (UTC)

I find it difficult to distinguish mentally ill people having solitary conversations from people with a little phone stuck in their ear presumably talking to someone at the other end of the phone conversation. Someone years ago suggested giving your old broken cell phone to a crazy street person, so people would assume they were arguing with their broker rather than the voices in their head. Edison (talk) 16:14, 14 December 2010 (UTC)

Consider selection bias. Hearing voices is only one manifestation of mental illness, but it is likely to be the explanation for a person wandering down the street having a one-sided conversation without benefit of a handset or bluetooth receiver. A person who hears voices, understands what is happening and is in control of their symptoms, or one who is hearing a benign voice whispering pleasantries, is unlikely to appear obviously agitated and distracted. The person hearing taunts, threats, orders or frightening nonsense, unable to get away from the voice or get a calm perspective on what is happening to them, is very likely to exhibit behaviour bizarre enough to attract attention. They are the ones you notice. Karenjc 21:26, 14 December 2010 (UTC)

People with certain mental illnesses that make it hard to communicate may find misunderstandings of what there saying frustrating. Albacore (talk) 21:35, 14 December 2010 (UTC)

Rage and mental illness are not necessarily the same thing. Depression is basically anger turned inwards. ~AH1^(TCU) 03:03, 18 December 2010 (UTC)

• "Mad people" is a very slipshod expression for people with mental health issues. Mental health is a tremendously complicated topic (some would argue most if not all of the human race has some mental issues, just of a socially accepted and manageable level). So you'd have to classify what kind of "mad" you meant.
• "Mad (angry/rage) feelings" are a possible, but not universal, result of mental health issues.
• Anthing except trivial truths related to "what humans do/don't do" is very likely to have an answer of "sometimes yes and sometimes now". So you need to specify what "mad" you mean? How much of a person's life should be spent "mad" to count as "yes"?

In its broadest terms the best answer I can think of is:

Many people have mental health issues some or the time, and it has been argued almost all of us do (to a subclinical level). Anger and rage are one possible reaction to the world not conforming to expectations or delivering what was desired (see denial). However they are very common reactions to the same type of event by people who are not classified as "mentally ill" and are not universal among mentally ill people. So "no".

FT2 ^{(Talk | email)} 00:50, 21 December 2010 (UTC)

Would terraforming the Moon have any effects on Earth ?

So I was thinking - if you'd cover Moon with lush green grass, it would probably make its surface less reflective, thus making full moon nights darker on Earth. If so would it have any adverse effect (i.e. some people believe Moon phase have great impact on life on Earth, not that I agree with this, but maybe it still could make a difference for animals, for example) and could anything else done to terraform Moon have any effect on Earth ? 84.237.191.120 (talk) 14:02, 14 December 2010 (UTC)

The moon's main effects are gravity and light. I would imagine that many nocturnal species may find their life cycles, which depend on the cycles of shifting moonlight, altered. It would have little to no effect on things like tides. --Jayron32 14:16, 14 December 2010 (UTC)

Actually, the Moon's albedo is fairly low, lower than Earth's. If it could be terraformed and possessed an atmosphere and clouds, it would be more reflective, not less. That said, I concur with Jayron's analysis. — Lomn 14:40, 14 December 2010 (UTC)

Just to explore theory - how about it not being completely terraformed and having thin atmosphere (I assume that grass needs less atmosphere than human, if not grass then perhaps something like fungi, small scale, but still causing discoloration) 84.237.191.120 (talk) 14:49, 14 December 2010 (UTC)

Well, if you terraform the moon so it has some similarities to earth, you will probably get some nice reflective clouds which will alleviate the slightly darker water and grass that the moon now has. Googlemeister (talk) 14:58, 14 December 2010 (UTC)

An ability to put colour on the surface of the Moon could be turned to useful advertising. Cuddlyable3 (talk) 15:09, 14 December 2010 (UTC)

Re: "darker water and grass": as noted, the Moon's albedo is really low. Clouds are particularly reflective, but grass is also more reflective than the moon, and water generally so. — Lomn 15:26, 14 December 2010 (UTC)

That's a very old joke Cubblyable3 Cuddlyable3 :) I acctualy was considering asking what effect painting moon red would have. Okay so, I gather that anything done on moon would rather improve reflectivity - still, any effects on Earth ? Perhaps no nights at all ? 84.237.191.120 (talk) 15:39, 14 December 2010 (UTC)

I corrected the spelling of my name and don't care what you think about it, since you're only a number to me. Cuddlyable3 (talk) 13:14, 16 December 2010 (UTC)

Terraforming, painting, or even completely eliminating the moon would do nothing to stop the earth from rotating on its axis. We would still have day and night on earth. Googlemeister (talk) 15:49, 14 December 2010 (UTC)

Don't be a wise-ass - no one ever mentioned it having impact on Earth's rotation, when someone is talking about very bright moonlight, you probably should be able to put 2 and 2 together to realize that if it was as bright as in day you wouldn't call that a night 84.237.191.120 (talk) 16:31, 14 December 2010 (UTC)

You can make that differentiation, but White nights disagree with your choice of terminology. Googlemeister (talk) 16:44, 14 December 2010 (UTC)

I was asking what the light conditions would be not what people would call it. And term "as bright as a day" somehow happens to be common for referring to summer nights, that still are darker than days and can even be darker than current full moon nights 84.237.191.120 (talk) 17:39, 14 December 2010 (UTC)

Since the prototypical definition of night is when the sun is below the horizon, then it would not matter if you somehow made the moon reflect light to be equally bright, it would still be night time. If you would like to change the definition of night and day to validate your point of view, then don't let me stop you. Googlemeister (talk) 19:26, 14 December 2010 (UTC)

Gosh, take a wikibreak - the rest of the world dosen't function according to definitions and what you think someone's POV is. Even the article on Midnight sun dosen't follow your logic (note that it is where polar day redirects). Note that I merely was talking about how bright moonlight is, explained that to you twice and you're still going on about what words mean when this is about physics and astronomy 84.237.191.120 (talk) 21:16, 14 December 2010 (UTC)

Please be civil, or if you can't be civil be funny. The World is watching. Cuddlyable3 (talk) 13:14, 16 December 2010 (UTC)

Great song (and amusing video): morcheeba - world looking in WikiDao ☯ (talk) 19:02, 16 December 2010 (UTC)

(Edit Conflict) Don't forget that the Moon's monthly phases and positional movements (relative to the Sun) would still operate as before, so you'd still have dark nights when the Moon was a crescent, set, or up during the day (overlapping cases, of course). Nights in the weeks either side of full moon would be noticeably lighter than previously experienced, such that you could probably read by moonlight (in fact, from personal experience one can already do so at full moon with a clear sky and several minutes' dark adaptation), but we generally underestimate the tremendous ranges of illumination we (and other creatures) already take in our stride; I'd suggest that effects on the natural world in general would be measurable and interesting, but minor in the overall scheme of things [/handwaving]. 87.81.230.195 (talk) 15:56, 14 December 2010 (UTC)

While there is no wikipedia article about it, some plants that exhibit "selenotropism" might suffer if the brightness of the moon changed. -- JSBillings 21:07, 14 December 2010 (UTC)

Thanks. Can someone tell how bright moonlight would be in conditions when there was no massive change in lunar atmosphere, but Moon's surface color was different ? (either from something similar to primitive plant cover or someone painting the moon, your choice) 84.237.191.120 (talk) 21:21, 14 December 2010 (UTC)

It depends entirely on what you cover the Moon with. Since the Moon reflects about 11% of sunlight, there's an approximate upper bound of 9 times brighter than it actually is. That's an apparent magnitude of about -16, still around 1000 times dimmer than the sun as seen from Earth. — Lomn 02:41, 15 December 2010 (UTC)

I think you assume a diffuse reflecting surface. Given a shaped mirror surface the Moon could appear brighter than the Sun as seen from some point on Earth. (A Fresnel-type reflector could conform to the hemispherical surface and act as a parabolic concave mirror.) Cuddlyable3 (talk) 13:14, 16 December 2010 (UTC)

What kind of atmosphere could the Moon hold? I thought that was the reason that it couldn't be terraformed. Ginger Conspiracy (talk) 11:37, 15 December 2010 (UTC)

Well, you'd surely have to top it up every so often, but I'd expect it to stay breathable for at least decades without that. I'm sure I read a treatment of this somewhere. I'd be delighted for someone to reference something that either agreed or disagreed with this. 86.161.208.185 (talk) 15:11, 15 December 2010 (UTC)

According to article on Moon even now it has very thin atmosphere, I am not an expert but I figure that if enough atmosphere would have been created it would hold for some time. Anyway, I acctualy wanted to learn about effects changing surface would have, I didn`t consider atmosphere, so as far as I am concerned it could have lush grass and no atmosphere at all (OP) 89.235.213.243 (talk) 00:06, 16 December 2010 (UTC)

When astronomers (and geologists) talk of short timespans, they're usually speaking of millions or tens of millions of years. For example, the half-life of an Earth-like atmosphere on the Moon is a few million years. Just a blink of the eye in the evolution of the Solar System, but plenty long enough to terraform the place. --Carnildo (talk) 03:09, 16 December 2010 (UTC)

blue light/energy from gummed envelope

I was opening an envelope in the dark a few nights ago. Being a useless envelope opener, I tore the gummed flap away in untidy sections. I noticed that each time I lifted a section, there was a bright blue light created at the point where the peeling away occurred, sort of "in" the glue. Fascinated, I pressed it all down again and re-peeled—I saw blue light again, but much fainter. What exactly was this? What was responsible for creating the energy? Chemical? Friction? Does it always happen and we don't notice because we don't normally open post in the dark? Phantasten (talk) 14:27, 14 December 2010 (UTC)

Triboluminescence will answer all of your questions. --Jayron32 14:29, 14 December 2010 (UTC)

Perfect, thanks! It even mentions envelopes. (I have a feeling I should have known about this already...) Phantasten (talk) 14:35, 14 December 2010 (UTC)

What does nothing look like?

Ok so lets say I take a clear glass bottle, and suck all the air out of it, creating a vacuum. There is no matter in the bottle, so you can just see through both sides of the clear glass as if it was full of air.

Now lets say I take a clear glass bottle, but this time I (somehow) physically destroy the space inside of the bottle. This time there isn't simply an absense of matter, but the space itself inside the bottle has ceased to exist. What would the bottle look like?--178.167.224.118 (talk) 17:25, 14 December 2010 (UTC)

A solid piece of glass? --Jayron32 17:34, 14 December 2010 (UTC)

I think it would still look clear, although if the area was devoid of matter and fields I'm not sure light would still exist. Forgive me if I'm totally off, as I quite plainly suck at physics. Crimsonraptor (talk) 17:37, 14 December 2010 (UTC)

I don't think space can be destroyed. Bus stop (talk) 17:47, 14 December 2010 (UTC)

But it could be designed away on the Humanities reference desk. Sean.hoyland - talk 17:55, 14 December 2010 (UTC)

It would depend on what you do with the boundary of the space that you removed. You could glue the "ripped edges" of space together in various ways that might change the way that light is bent when it goes through the deleted part. Perhaps you could glue it "straight" and see through the jar, or maybe glue it "with a twist" like a mobius band, and see things on the other side upside-down. Maybe you don't glue it together at all? Then you'd be looking at an edge of the universe. Then I guess it would be black, since no light would be coming out of it. (Unless there is light coming out of it.) As far as I know there are no "edges" of the universe for us to observe, so nobody knows what it would look like. Staecker (talk) 17:57, 14 December 2010 (UTC)

If the space itself is removed, than the one side of the bottle will be in contact with the other side. Actually, what is more likely to happen is that the bottle will shatter into pieces. The various sides of the bottle would be put under great stress, certainly enough to break it. So ammending my prior conclusion: What it would look like is "a pile of broken glass". --Jayron32 17:58, 14 December 2010 (UTC)

(e/c 2x) I think Jayron32 is right. WikiDao ☯ (talk) 17:59, 14 December 2010 (UTC)

It would shatter if a vacuum was created, but that's the first scenario. Removing the space means the inside of the glass now touches at the center of the removed space. But, of course, it can get bogged down in semantic issues... WikiDao ☯ (talk) 18:02, 14 December 2010 (UTC)

Exactly. How do you take the opposite sides of a glass bottle and make them touch without breaking the bottle? The exact method you use to cause the insides to touch is irrelevent here. --Jayron32 18:05, 14 December 2010 (UTC)

It's a question of whether there would be a "stretch" or a "pull" on the matter in the space on the boundary of what is removed. A vacuum -- no matter but still space -- will shatter the glass if the external pressure on it is great enough, and the material weak enough. It's not clear what would happen when it is the space itself which is removed. The answer is not known, but I suppose it can be speculated about here... WikiDao ☯ (talk) 18:09, 14 December 2010 (UTC)

One answer that's as valid as any other is that such a bottle would appear to be purple with pink polka dots. There never has been, nor will there ever be, a bottle which has a nonzero interior surface area, but within which space has ceased to exist, which has an appearance different from purple with pink polka dots. You can say pretty much anything you want to about the nature of the elements in the empty set, without your statement being provably false. Red Act (talk) 18:14, 14 December 2010 (UTC)

Yes to this. The problem here is not just physical, but also logical. Just to elaborate, if P is false, any statement of the form P->Q is TRUE, for ANY Q. Thus "If my name is Joe, then this ref desk is staffed by unicorns." is a true statement, because my name is not Joe. SemanticMantis (talk) 20:17, 14 December 2010 (UTC)

Logic, of course, ignores relevence. There are an infinite number of true, but irrelevent, statements. OTOH, there are a finite number of true and relevent statements. --Jayron32 20:37, 14 December 2010 (UTC)

Yes, the responses seem to indicate that any answer of the form "the bottle with interior space removed would look like X" are all true, but irrelevant. SemanticMantis (talk) 20:43, 14 December 2010 (UTC)

The question is really unanswerable. The behavior of light is predicted from the structure of space using the equations of general relativity, but there is no way to simply remove some space without causing the equations to be violated at the boundary. Physics, therefore, can give no prediction of what would happen. Looie496 (talk) 18:44, 14 December 2010 (UTC)

Yeah, I don't think there can be a "nothing" that humans can began to comprehend since the presence of space is already a something. The limits of a mammalian brain evolved from this planet I guess. -- Sjschen (talk) 19:05, 14 December 2010 (UTC)

And yet, if difficult-to-conceive thought experiments were never done, where would Science be? WikiDao ☯ (talk) 21:01, 14 December 2010 (UTC)

What does it mean to, "(somehow) physically destroy the space inside of the bottle"? Science has a concept of space, or more than one concept of space—but does science have a concept of the absence of space? Bus stop (talk) 19:24, 14 December 2010 (UTC)

To "does science have a concept of the absence of space?" I'd answer "yes, currently." I think a mixture of Staecker's and Red Act's answers is the closest to the stock response you'd get from the average cosmologist or particle physicist these days. Modern particle physics is based on quantum field theory, in which the (quantum) field is the basic object of study. Particles are vibrations of the field. If there are no particles, the field isn't vibrating, but it's still there. In GR you have a similar situation: it's easier to think of spacetime as an entity in its own right. It's pretty easy to envision taking away the field, leaving literally nothing behind. However, you have to be specific about the boundary conditions. The rules of the Standard Model and GR work "in the bulk" (the region where every point is surrounded by points in all directions) but not on a boundary (where there are no nearby points in "half of the directions"). You can either identify different points on the "boundary" in such a way that there actually isn't a boundary (as Staecker suggested) or you can specify a different set of physical laws for the boundary, in the form of differential equations in one fewer spacetime dimensions. Generally physicists don't bother with this because there are gazillions of theories of this type and no evidence to suggest that the universe uses any of them (which I think was Red Act's point). One exception, though, is AdS/CFT, where the bulk laws (AdS) imply the boundary laws (CFT) and vice versa. Black hole event horizons can also be treated as boundaries of spacetime in a similar fashion. -- BenRG (talk) 22:16, 14 December 2010 (UTC)

So is it a good bet that it would look like a black hole? "No perturbation of the field" suggests light "entering" it does not propagate further, so it would look very black through the glass? Without the gravitational lensing effects around a black hole's event horizon. Can the energy "of" that volume of spacetime be calculated according to accepted theory at this point? WikiDao ☯ (talk) 22:27, 14 December 2010 (UTC)

It depends on the boundary conditions. You could certainly put a black hole inside a glass jar, if the glass was strong enough to resist imploding. The black hole would have to be spherical because they all are, and this would have to be in outer space because on Earth the black hole would just fall through the bottom of the jar (and the floor). Another example of a wave "vacuum" with a hole in it is a pillar in the middle of a lake. Surface waves are partially absorbed by it and partially carried around, I think. Another example is an ordinary opaque object inside the jar! You can treat different propagation media as though they were different vacuums (that's largely what condensed matter physics is about). A medium that doesn't transmit visible light at all is like a missing piece of vacuum, for the purposes of visible light. As for calculating energy, you would have to come up with a new notion of energy to go with your boundary physics, whatever it is. If it's a black hole, then there isn't really a well-defined energy aside from the usual black hole mass. The nature of energy in general relativity is actually not understood very well. -- BenRG (talk) 23:56, 14 December 2010 (UTC)

Depending on how you destroy the space, you could get a black hole, a wormhole or a Klein bottle. ~AH1^(TCU) 02:59, 18 December 2010 (UTC)

Can inaudible "noise" cause physical damage to people?

I was wondering whether a radio frequency that was too high—or too low—to be heard by the human ear could cause hearing damage (or some other physical problem) when broadcast at 150 db or higher.

Even if it cannot be "heard", can it still cause problems? Pine (talk) 22:34, 14 December 2010 (UTC)

are you rambling 'referring' on about infrasound?--Aspro (talk) 22:37, 14 December 2010 (UTC)

Didn't the KLF explode a cow using infrasound? If it can be done to a cow, it can be done to a man! DuncanHill (talk) 22:48, 14 December 2010 (UTC)

No, that's just a rumor. Their percussion experiments startled and may have induced labor in a pregnant cow resulting in a stillborn calf and a very angry farmer. It's unlikely that the sound was the cause of the stillbirth. Ginger Conspiracy (talk) 18:15, 15 December 2010 (UTC)

Did you really mean to write radio, and broadcast?? Because that's an utterly different thing from the sound a human ear can hear. Ariel. (talk) 23:25, 14 December 2010 (UTC)

Our ultrasound article may be slightly more relevant (there's more there than at infrasound, though the principles are the same). We note that exposure to ultrasound in excess of 120 dB may result in hearing loss. — Lomn 02:37, 15 December 2010 (UTC)

Infrasound can definitely kill people. I doubt ultrasound can. Greglocock (talk) 01:02, 16 December 2010 (UTC)

From Ultrasound#Safety: Occupational exposure to ultrasound in excess of 120 dB may lead to hearing loss. Exposure in excess of 155 dB may produce heating effects that are harmful to the human body, and it has been calculated that exposures above 180 dB may lead to death. Cuddlyable3 (talk) 10:32, 16 December 2010 (UTC)

See noise pollution, brown note and acoustic resonance. ~AH1^(TCU) 02:56, 18 December 2010 (UTC)

Noble gas compounds

Which noble gas compound is the most stable at room temperature? --70.134.49.69 (talk) 23:00, 14 December 2010 (UTC)

Lots of noble gas compounds are perfectly stable at room conditions. Xenon hexafluoride is one, but by no means the only one. A sample of Xenon hexafluoride will remain Xenon hexafluoride indefinitely if kept dry and clean. Lots of other noble gas compounds will be as well. --Jayron32 23:05, 14 December 2010 (UTC)

Are there any noble gas compounds that don't have to be kept dry? --70.134.49.69 (talk) 23:24, 14 December 2010 (UTC)

That depends a bit on what you mean by a "compound". Things like xenon hexafluoride need to be kept dry because there is an easy and exothermic decomsition route with water, that produces hydrogen fluoride (a very stable molecule) along with xenon and oxygen gas. However, if you take xenon clathrates, for example, or conjugates of protein molecules with xenon atoms lodged in hydrophobic clefts, then these can be stable in the presence of water. The difference is the type of bonding. Physchim62 (talk) 23:55, 14 December 2010 (UTC)

There is, of course, some question about whether a clathrate is a compound or its own class of substances. It shares somethings in common with solutions, for example, which are not normally counted as "compounds". --Jayron32 23:59, 14 December 2010 (UTC)

I'm not disputing that at all ;) as I said, all depends on your definition of a compound! If you take the definition of a chemical compound to be a substance of fixed stoichiometry, then it it is clear that xenon forms compounds that are stable in the presence of water. However, these are molecular species held together by London dispersion forces, not Lewis-type covalent bonds, and for this reason many chemists are hesitant to call them real compounds... Physchim62 (talk) 00:48, 15 December 2010 (UTC)

Are there any fully covalent noble gas compounds that don't have to be kept dry? ----J4\/4 <talk> 13:38, 15 December 2010 (UTC)

[1] Xenic acid and its salts are stable in water.--Stone (talk) 14:23, 15 December 2010 (UTC)