Wikipedia:Reference desk/Archives/Science/2010 May 18

= May 18 =

CO2
Why does a can of pressurized carbon dioxide (in a liquid state) down so much when it is released (in a gaseous state)? Thanks. 173.179.59.66 (talk) 03:44, 18 May 2010 (UTC)
 * If by "down" you mean "get cold"; when a liquid evaporates into a gas it goes through a phase transition which involves Enthalpy of vaporization. In short, it takes energy to change a liquid into a gas, the energy is the heat in and around the canister which is absorbed by the carbon dioxide as it evaporates into a gas. The reason this might seem "strange" is because the boiling point of carbon dioxide is 57 degrees Celsius below freezing, we think 0 degrees C is some special "low" energy point, but it's actually 273 degrees Kelvin so still has a lot of energy for something like carbon dioxide. Vespine (talk) 04:19, 18 May 2010 (UTC)


 * The process by which a liquid or gas is allowed to expand freely is called throttling.   During throttling the temperature changes and this is called the Joule–Thomson effect.  Whether the temperature increases or decreases during throttling depends on the gas’s Joule-Thomson coefficient and its inversion temperature.  Hydrogen and helium at room temperature warm as they are throttled to a lower pressure.  Carbon dioxide, nitrogen and oxygen at room temperature cool as they are throttled to a lower pressure.  Dolphin  ( t ) 05:10, 18 May 2010 (UTC)
 * Are you saying that if you had a gas bottle with liquid helium in it and you released it, the gas bottle would not get cold? That doesn't sound right. I've never heard of Joule-Thomson effect (which isn't saying much) but looking at it, it seems to specifically refer to the temperature of the gas in situations where there is no heat exchange with the environment, which is certainly not the case when you just let gas out of a gas bottle, or a can. Vespine (talk) 06:34, 18 May 2010 (UTC)
 * A gas or liquid can be allowed to change from a higher pressure to a lower pressure in a variety of ways. The change can take place with no heat transfer to/from the surroundings (adiabatic), or it can take place with heat transfer.  The change can be reversible, such as when it accompanies the raising of a weight and takes place slowly; or it can be irreversible, such as when it is allowed to "explode" out of its container.  A reversible, adiabatic change takes place at constant entropy and the resulting temperature can be determined accurately by knowing that the entropy of the gas doesn't change.  See isentropic process.  An irreversible, adiabatic change is called throttling and takes place at constant enthalpy.  See isenthalpic process.  The resulting temperature can be determined accurately by knowing that the enthalpy of the gas doesn't change; also this resulting temperature will be significantly different to the isentropic process.  The Joule-Thomson effect is the change in temperature during the isenthalpic process, not the isentropic process.  The original question does not specify precisely what process is intended, but it talks about a can of liquid CO2 being discharged to the gaseous state.  The idealized process which best represents this process is the throttling process, even though the isenthalpic process involves no heat transfer whereas discharging a can of CO2 will involve a small amount of heat transfer in the brief period of time that the discharge takes place.  Dolphin  ( t ) 12:48, 18 May 2010 (UTC)
 * To clarify, there is an important distinction between a case where helium gas is allowed to expand starting from room temperature, and where liquid helium is allowed to boil. The two cases are distinguished first by the fact that the latter involves a phase change (liquid to gas, soaking up enthalpy of vaporization) and second by the fact that they will occur at vastly different temperatures (the critical temperature of helium is about 5 kelvin, so you're never going to have liquid helium above that temperature &mdash; liquid helium will always be at a temperature below its inversion point if you're working under atmospheric pressure).  TenOfAllTrades(talk) 13:12, 18 May 2010 (UTC)

By down I meant a decrease in temperature, I'm not too sure where the "down" came from lol. But thanks a lot for the explanation! 173.179.59.66 (talk) 05:52, 18 May 2010 (UTC)
 * When liquids boil, they absorb energy to change in the gaseous state. When air is pressurized it gets hotter. I can feel on an air pump sometimes that it gets hotter. Some gases may not behave in that way, but I think liquid helium becomes cold when it is released due to the rapid boiling, cooling it to very low temperatures. --Chemicalinterest (talk) 11:58, 18 May 2010 (UTC)
 * That's a good answer. Going into detail about isentropic processes and entropy and Joule–Thomson effect is way, way overboard for the question actually asked. Vespine (talk) 03:45, 19 May 2010 (UTC)

I think the anwers above are unclear, the throttling explanation seems to be about the temperature of the exiting gas after expansion, the question was about the temperature of the can and that has more to do with boiling and maybe isentropic expansion. Gr8xoz (talk) 00:21, 20 May 2010 (UTC)

percent of atmosphere
What percent of the entire Earth's atmosphere including that which is absorbed and released by water, etc. is released by human lungs of an average adult male upon exhaling? 71.100.0.29 (talk) 04:27, 18 May 2010 (UTC)
 * From Atmosphere of Earth we have total mass of 5, from Lung volumes we have average male Tidal volume (Vt) of 500ml, from Density of air we have 1.2 kg/m3. A cubed meter is 1000l so 500ml of air is 1/2000th of 1.2kg = 6kg per breath. So it's just (6) / (5) x 100 to get your percentage, i'm no good with so many zeros, my guess is 1.2%, but I could be off by an order of magnitude or two. Someone better at maths can help me out. ;) Vespine (talk) 06:27, 18 May 2010 (UTC)
 * Your calculations look correct. --Chemicalinterest (talk) 12:00, 18 May 2010 (UTC)
 * Strange. I was no good with symbolic equations which contained space and used x's in place of *'s. I consulted with several of my friends as did you and they advised that I use the following symbology and syntax to get the following results. Many thanks human. May we also have exchange good like this in future time. (6 * (10^(-4))) / (5 * (10^18))) * 100 = 1.2 × 10-20 —Preceding unsigned comment added by 71.100.0.29 (talk) 18:54, 18 May 2010 (UTC)

Best extrasolar planet candidates for habitable moons based only on irradiance?
What discovered extrasolar planets are the best candidates for habitable moons based on the heat/irradiance they, the planets, receive from their parent star? 1366 W/m2 being the Earth's solar constant, therefore also the Moon's. Clarifying: since it doesn't seem obvious to everyone, I meant only possible habitable temperature, based on albedo/emissivity similar to the Earth, and irradiance comparable to what the Earth receives. 24.78.178.235 (talk) 06:44, 18 May 2010 (UTC)


 * Presumably, what you are getting at is the habitable zone, because this level of stellar radiation would yield a temperature near the triple point of water. We have a nice listing at Extraterrestrial liquid water.  At this time, extrasolar planets are on the bare edge of detection; I know of no research claims about detection of a moon around an extrasolar planet.  On the other hand, moons seem commonplace in our own solar system, so it seems plausible that any large extrasolar planet (and some dwarf planets, too) could be capable of having "habitable" moons in stable orbits.  Of course, a necessary precursor to the question is, "define habitable".  Nimur (talk) 09:08, 18 May 2010 (UTC)


 * With present detection methods, it's unlikely we're going to be able to detect moons around extrasolar planets unless they are truly gigantic and very close to the parent star - or perhaps are in an eclipsing orbit from our perspective and are large compared to the parent planet (like our moon or the Pluto/Charon pair). The odds of either of those things being true seem rather slim.  If we're going to try and guess, we'd have to think in terms of large planets in the habitable zone of their parent stars - and just kinda hope that they'd have large enough moons with inhabitable atmospheres - but we don't have much evidence of the probability of that happening because we only know about the planets in our own solar system...of which there is just one (or arguably two or three) in the habitable zone.  We have: List of extrasolar planets which contains all the data you need to estimate which are in the habitable zone - but it doesn't look like anyone did the actual calculations to enter that fact into the tables. SteveBaker (talk) 13:29, 18 May 2010 (UTC)


 * A note about the "habitable zone". This refers to a planet which is the proper distance from the star for liquid water.  In the case of a moon around a huge planet (the only ones we can currently detect), the moon is not only heated by the star, but also from radiation and tidal warming from the planet, so the moon could be further away from the star and still have liquid water. StuRat (talk) 21:38, 19 May 2010 (UTC)


 * Nice point, but a very different question from the one I asked, did you read it? 24.78.178.147 (talk) 09:30, 21 May 2010 (UTC)


 * I did read it, several times. But, even with the clarification, I still don't quite know what you're asking. StuRat (talk) 15:09, 21 May 2010 (UTC)

Candidate Chart
These are all from Luminosity article.
 * $$L = 4\pi R^2\sigma T^4 \,$$
 * $$L = 4\pi f\ d^2\ $$

If Radius/Temperature unknown, then:
 * Lstar = 0.0813 &middot; diststar2 &middot; 10(&minus;0.4 &middot; mstar) &middot; $$L_{\odot}$$

Therefore:
 * $$ f=  (R^2\sigma T^4 ) / d^2\  $$

I don't mean to show anyone up, I was looking for anyone else who could do this, and this should have been easy for anyone who presumed to answer here. 24.78.178.147 (talk)
 * Best ref desk candidate for being a jerk based only on attitude in answering own question? 63.17.50.130 (talk) 01:02, 23 May 2010 (UTC)
 * Attitude? - These are formulas. Check that attitude of the people who answer, they all want to change the question so they can lecture on their opinions, it's pathetic. Why if they couldn't answer they question did the assume their opinion mattered? Change it to the "opinion desk" and I'll admit I'm wrong on that. 24.78.178.147 (talk) 02:15, 23 May 2010 (UTC)
 * By the way "retard," it sounds like you were saying I as a "jerk" to myself.24.78.178.147 (talk) 02:18, 23 May 2010 (UTC)


 * OP gave some examples, but technically the question was not answered. 24.78.166.69 (talk) 06:25, 29 September 2010 (UTC)

annealing aluminium from H-18 to H-O
We are blanking aluminium circles. We use alloy 1050 and 3003. During blanking we use H18 coils (hardness is H-18). After blanking we want to anneal these circles from H-18 to H-O temper. We have box type (batch type) Oven. We know we need to keep this in 343° to 413° C temperature to anneal these from H-18 to H-O but how much time is required to be kept in this temperature in a box type oven ? Can anybody help us out in this ? —Preceding unsigned comment added by Ashvora (talk • contribs) 07:31, 18 May 2010 (UTC)


 * Not sure, but might I suggest trial and error ? That is, anneal it a bit, take it out, cool it, and test it, then anneal it some more, until you figure out the right length of time. StuRat (talk) 21:33, 19 May 2010 (UTC)

Type of intermodal container
These containers seem common in trains in japan (not the tanks - the boxes). http://commons.wikimedia.org/wiki/File:JRF_19D-33700.JPG or http://commons.wikimedia.org/wiki/File:JNR_Container.jpg I don't think they are '10ft ISO's', but maybe they are? - does anyone know what standard they are? Can they be stacked..? Thanks. Sf5xeplus (talk) 12:00, 18 May 2010 (UTC) I think its something to do with this http://ja.wikipedia.org/wiki/JR%E8%B2%A8%E7%89%A9%E3%81%AE%E3%82%B3%E3%83%B3%E3%83%86%E3%83%8A%E5%BD%A2%E5%BC%8F - are these stackable? any compatability with ISO containers. Also does anyone know why 12ft length seems so popular when elsewhere 20ft+ is normal.? Can anyone give a link to background on this topic? thanks. (in particular: why was ISO standard not used) Sf5xeplus (talk) 13:47, 18 May 2010 (UTC)

length of menstruation
Why does menstruation take 2-7 days, rather than a short time (e.g. an hour or so)? After reading the articles on menstruation and the menstrual cycle, it states the normal length of the menstruation is 2-7 days, which I knew. But what I am curious is about is WHY it takes this long. I'm not sure if this is easy to answer, but it seems that it is a process that could happen quite quickly, rather than taking a few days, but it doesn't. Ballchef (talk) 12:33, 18 May 2010 (UTC)


 * Given the discomfort level many women feel during (and prior) to their menstruation, I'm not sure compressing that into a shorter timespan would be such a great thing - pain might multiply while the time divides, you know? In evolutionary terms, it might simply be better for women to be moderately uncomfortable for a longer period of time than extremely uncomfortable for a shorter, but still sizable, period of time. Matt Deres (talk) 14:09, 18 May 2010 (UTC)

It's serious business, and serious business generally isn't over in the blink of an eye. Vranak (talk) 14:34, 18 May 2010 (UTC)
 * That's not a reason. Vimescarrot (talk) 17:06, 18 May 2010 (UTC)
 * Well if sexuality was a light and breezy affair, then people wouldn't have any reason to menstruate, let's put it that way. Vranak (talk) 21:16, 18 May 2010 (UTC)
 * That makes absolutely no sense. --Tango (talk) 21:35, 18 May 2010 (UTC)
 * Exactly. Vranak (talk) 21:52, 18 May 2010 (UTC)


 * Per Menstruation, the length of time has to do with the rate of cell growth for the uterine lining. This sort of low-level biological parameter is not easily changed - cells simply can not divide and multiply significantly faster.  Our article links to some evolutionary biology research on the advantages and disadvantages of the process, e.g. The evolution of endometrial cycles and menstruation. Mostly, this evolutionary process was driven by the balance between the utility of internal fertilization versus the energy and nutrient cost to sustain this very complex process.  Keep in mind that evolution is not a steady progression towards "optimal" - it is simply survival of the fittest random mutation during every intermediate step - so the development of modern menstruating mammals is the result of prior forms.  See also, estrous, for a related process in other mammals.  Nimur (talk) 00:58, 19 May 2010 (UTC)
 * Brilliant answer thanks! But still it wont stop my girlfriend from complaining. Ballchef (talk) 03:33, 19 May 2010 (UTC)
 * See Menstrual extraction for a quick painless method —Preceding unsigned comment added by 79.76.203.64 (talk) 18:56, 19 May 2010 (UTC)
 * And possibly illegal, depending on the Jurisdiction... Buddy431 (talk) 03:42, 20 May 2010 (UTC)

physics
when a hole is made from north pole of the earth to the south pole of the earth and a ball is put into it what is the time period of the oscillation of the ball —Preceding unsigned comment added by Mai ca lal jai kison (talk • contribs) 14:24, 18 May 2010 (UTC)
 * Question has come up before:
 * http://en.wikipedia.org/wiki/Wikipedia:Reference_desk/Archives/Science/2009_September_17#Gravity_at_the_center_of_a_body
 * http://en.wikipedia.org/wiki/Wikipedia:Reference_desk/Archives/Science/2009_September_11#Path_through_Earth
 * Answer in second link - some simplfiying assumptions are made to get an answer.77.86.10.27 (talk) 14:34, 18 May 2010 (UTC)
 * There's some more explane here http://answers.yahoo.com/question/index?qid=20080519084940AAMjRd0 77.86.10.27 (talk) 14:40, 18 May 2010 (UTC)
 * There's a step by step guide to one derivation in "A: The basic setup" http://amath.colorado.edu/courses/2460/2007fall/Labs/lab2/ 77.86.10.27 (talk) 14:40, 18 May 2010 (UTC)
 * Reliable looking answer here http://physics.ucsd.edu/students/courses/summer2008/managed/physics2a/documents/chap15.pdf Question 70 page 15 "The magnitude of the gravitational acceleration inside Earth is given..." 77.86.10.27 (talk) 14:43, 18 May 2010 (UTC)
 * But how would it be possible to keep such a hole from being completely flooded? :-) 67.170.215.166 (talk) 01:07, 19 May 2010 (UTC)
 * People here are not saying it is possible, just assuming no water or air, or lava in the hole. :-) Graeme Bartlett (talk) 12:43, 19 May 2010 (UTC)

Alkali acids
Is an alkali like NaOH an acid? --Chemicalinterest (talk) 15:37, 18 May 2010 (UTC)
 * OH- as an acid : see this quote :"The oxide ion, O2−, is the conjugate base of the hydroxide ion, OH−"
 * Na+ is also a weak lewis acid
 * In water it's always a base, the opposite of an acid.77.86.10.27 (talk) 15:42, 18 May 2010 (UTC)
 * So that means that OH- is the conjugate acid of O2-? --Chemicalinterest (talk) 15:58, 18 May 2010 (UTC)
 * Yes.77.86.10.27 (talk) 15:59, 18 May 2010 (UTC)
 * I plan to improve the articles dealing with chemicals that have a pH above 7. Do you think it would be good to add it, or it would just confuse people saying that a base is also an acid? --Chemicalinterest (talk) 16:03, 18 May 2010 (UTC)
 * Probably not a good idea to add - since any molecule with a hydrogen is potentially an acid - eg methane, hydrogen gas, etc. too many
 * It's sort of mentioned already in Superbase.
 * As far as I can tell the definition at Alkali is 100% correct already.
 * I think Alkali salts would be better moved to Basic salt : that's the only change I can see needs doing - not sure what other people will think.77.86.10.27 (talk) 16:19, 18 May 2010 (UTC)

Square wheels
Can anyone provide a proof/derivation for why the square wheel riding on catenaries thing works, as shown in the article? 173.179.59.66 (talk) 15:39, 18 May 2010 (UTC)
 * It looks like the wheel corner gets "stuck" in the down curve, but just rolls right out. Round wheels probably wouldn't work on there unless they are much bigger. --Chemicalinterest (talk) 16:05, 18 May 2010 (UTC)
 * And a round wheel would provide a bouncy ride (i.e., would never "work" in the same way): as it rises and falls over each bump, the axle does too. When the size of the square is perfectly matched to the dimensions of the catenary, the axle remains at a fixed height. Proof is just a bunch of calculus: probably start by assuming length of one side of the square is the same as the length of one arch of the catenary (they remain touching as the roll past each other). That means at any x position, you know the height of the catenary and also (by some trig) the offset of the center of the square from that x. And then (by some more trig) the distance from the center straight down to the height of contact. Our catenary article says square or any larger polygon can be used, and has a cite to more reading about this unusual geometric phenomenon. DMacks (talk) 18:43, 18 May 2010 (UTC)
 * One possibly non-obvious assumption that (I think) will need to be made is constant ratio of angular velocity to linear velocity. no idea what can happen if this isn't assumed (disclaimer: I've assumed what I've said is correct rather than actually knowing). not right on second thoughts.77.86.10.27 (talk) 19:50, 18 May 2010 (UTC)
 * I started trying to prove the catenary equation from the height of the axle, but then I found a much neater and more elegant proof here (along the lines suggested by DMacks above). The method can be extended to any regular polygon by truncating the catenary at a point corresponding to the exterior angle.   D b f i r s   20:36, 19 May 2010 (UTC)

Planetary rings
Why some planets have rings and others do not have? —Preceding unsigned comment added by 113.199.143.2 (talk) 17:43, 18 May 2010 (UTC)
 * We don't know. Planetary rings are a big mystery. --Tango (talk) 18:28, 18 May 2010 (UTC)
 * But our Planetary ring article does have some information about the origins of them. DMacks (talk) 18:32, 18 May 2010 (UTC)
 * Note that planetary rings tend to be associated with gas giant planets such as Saturn; this suggests (but does not in itself prove) that there's a certain minimum size of planet below which it cannot acquire a ring. FWiW 67.170.215.166 (talk) 01:11, 19 May 2010 (UTC)
 * In fact, all of the gas giants in our solar system have rings: Rings of Jupiter, Rings of Saturn, Rings of Uranus, Rings of Neptune. Buddy431 (talk) 03:40, 20 May 2010 (UTC)

Dark Chocolate icing
I have a chocolate icing made of 49% dark chocolate and 51% melted margarine. After leaving it in the fridge for too long it turned to moose(?). Heating the sauce in a microwave caused the margarine and chocolate to separate so now there is melted chocolate sludge in a pool of melted margarine. How do i get the two to become one sauce again? Btw, 5 minutes of mixing did nothing. Simply south (talk) 18:30, 18 May 2010 (UTC)
 * A high speed electric whisk should emulsify it again hopefully. (maybe like this http://www.cookingtime.co.uk/index.php?act=viewProd&productId=1095 ? )77.86.10.27 (talk) 18:32, 18 May 2010 (UTC)
 * Adding some (or a lot) of cream might help as well.77.86.10.27 (talk) 18:35, 18 May 2010 (UTC)
 * I would like to still use it as icing but will try the whisk. Thanks. Simply south (talk) 18:38, 18 May 2010 (UTC)
 * According to http://chocomap.com/chocolate-making-tempering.php it's "chocolate seize" and cannot be reversed - I think cream may help solve this though..77.86.10.27 (talk) 18:40, 18 May 2010 (UTC)
 * If it has seized (and not just separated out) there are a thousand and one things you can try.. http://www.google.co.uk/search?q=chocolate+seize&hl=en&start=10&sa=N 77.86.10.27 (talk) 18:44, 18 May 2010 (UTC)
 * Thank you. Simply south (talk) 18:47, 18 May 2010 (UTC)
 * Turned to moose!!! Goddarn, take the dang thing outside and shoot it!!!! If it turned to mousse then follow the suggested advice. Caesar&#39;s Daddy (talk) 20:24, 18 May 2010 (UTC)
 * Swedish Chef tried it.DMacks (talk) 21:39, 18 May 2010 (UTC)
 * "First moose, then squirrel!" Edison (talk) 21:51, 18 May 2010 (UTC)

Aether vs. Quintessence
How did the powers that be determine that "aether" was not an acceptable term for "quintessence", when their definitions are from the same classic Greek idea? —Preceding unsigned comment added by 165.212.189.187 (talk) 18:44, 18 May 2010 (UTC)
 * They're not the same -
 * aether http://en.wiktionary.org/wiki/aether means air
 * qunntessence http://en.wiktionary.org/wiki/quintessence means fifth essence
 * Classical elements only have 4 elements - thus air cannot be a fifth essence ??? 77.86.10.27 (talk) 18:55, 18 May 2010 (UTC)

The aether wikipedia article refers to it as a proposed "fifth element" why? —Preceding unsigned comment added by 165.212.189.187 (talk) 19:00, 18 May 2010 (UTC) I'm not talking about semantics I'm talking about the ideas and theories behind the words. —Preceding unsigned comment added by 165.212.189.187 (talk) 19:04, 18 May 2010 (UTC)
 * Sorry my mistake (Ἀήρ was normal air) here Aether (mythology)
 * Quintessence is another term for aether ???77.86.10.27 (talk) 19:25, 18 May 2010 (UTC)
 * What exactly is it you are talking about? do you mean that Quintessence (physics) is different from definitions of aether ?77.86.10.27 (talk) 19:28, 18 May 2010 (UTC)


 * Giving them the same name would be confusing because they are used for completely different scientific theories. --Tango (talk) 19:32, 18 May 2010 (UTC)
 * In the Roman and medieval natural philosophy deriving from Aristotle, aether and quintessence were indeed synonymous—see Aether (classical element). Who is it who "determine[d] that 'aether' was not an acceptable term for 'quintessence'"? Deor (talk) 21:53, 18 May 2010 (UTC)


 * As for why Aristotle posited such a fifth element, C. S. Lewis explains it well (The Discarded Image, pp. 3–4):


 * Aristotle, being interested both in biology and in astronomy, found himself faced with an obvious contrast. The characteristic of the world we men inhabit is incessant change by birth, growth, procreation, death, and decay. And within that world such experimental methods as had been achieved in his time could discover onlty an imperfect uniformity.... But the world studied by astronomy seemed quite different.... So far as he could find out, the celestial bodies were permanent; they neither came into existence nor passed away. And the more you studied them, the more perfectly regular their movements seemed to be.... It seemed reasonable to suppose that regions which differed in every observable respect were also made of different stuff. Nature was made of the four elements, earth, water, fire, and air. Air, then (and with air Nature, and with Nature inconstancy) must end before Sky began. Above the air, in true Sky, was a different substance, which he called aether.


 * —Deor (talk) 23:28, 18 May 2010 (UTC)

Tango, what are the two different theories, just the basics, thanks.98.221.254.154 (talk) 00:54, 19 May 2010 (UTC)
 * See luminiferous aether and quintessence (physics). Both of them are supposed to pervade all of space (and time), but aside from that they have nothing in common. -- BenRG (talk) 07:07, 19 May 2010 (UTC)


 * At an attempt at clarification - "aether" is a defunct theory for most scientists - so reusing a synonym won't be a problem for the majority of people.
 * If you want to know who repurposed the word I think the article Ostriker, Jeremiah P., and Paul Steinhardt, "The Quintessential Universe", Scientific American, vol. 284, no. 1 (January 2001) may be the place to start.
 * http://iopscience.iop.org/0264-9381/17/13/101/fulltext this article dates from 2000 - was that the original aim? to find out who coined the term 'quintessence' relating to dark matter?77.86.10.27 (talk) 11:42, 19 May 2010 (UTC)

This was in the aether theories article: The general attitude to this amongst physicists[who?] today is that although it is purely a matter of semantics, Einstein's comments stretch the word "aether" too far: it is argued that an "aether" with no mechanical properties doesn't correspond to the historical idea of aether, and so it is potentially misleading to apply this name to the spacetime field of general relativity.[citation needed]. Note the [who?] and [citation needed]. If it is so well known that the two theories are not the same why not update these? —Preceding unsigned comment added by 165.212.189.187 (talk) 13:26, 19 May 2010 (UTC)
 * Is this the sort of thing you wanted - , if the problem was different please be WP:BOLD or discuss on the relevant talk pages. I'm not sure what you want but I don't see anywhere in the articles problems. 77.86.10.27 (talk) 20:25, 19 May 2010 (UTC)

Whatever, even after reading both articles several times i still cant see a definitive difference between the two. Its like saying that originally a cucumber was considered a vegetable but now that it really is a fruit it should be renamed. —Preceding unsigned comment added by 98.221.254.154 (talk) 01:17, 20 May 2010 (UTC)
 * (Please link to the pages you are talking about)
 * The terms "Aether" and "Quintessence" are practically synonymous in their original meaning. But, they are not synonymous in later usages of the word.
 * If you want more info. please be more specific than 'i don't get it' because nobody can help you with that problem.!77.86.108.78 (talk) 11:00, 20 May 2010 (UTC)

So youre saying that meanings change over time. That is what I don't get. If their original meanings are practically identical then WHAT happened to change the meanings???165.212.189.187 (talk) 14:39, 20 May 2010 (UTC)
 * Yes, meanings of words change over time. This happens a lot.
 * In the meanings of the words in Aether (classical element) and Quintessence are synonymous only when "aether" refers to a fifth form of matter: because quintessence means "fifth essence", in later uses of the word "aether" such as Luminiferous aether where it does not refer to a fifth state of matter the two words are not neccesarily synonymous. Similarly Quintessence does not directly have the same meaning as Aether (mythology).


 * The earliest meanings are
 * Aether - name one of the gods - see Aether (mythology) and a reference to "upper air" (at least as early as Hesiod 8th century BC)
 * Aether - as an element - comes later = probably by Aristotle - 5th century BC - approx 300 years later.
 * Quintessence - means "fifth element/essence"
 * They're not the same meaning except when refering to Aether (classical element) when they happen to have the same overall meaning.
 * If you need more explanation please ask on the humanities or language desk as they would be better placed to explain the etymology, origins and meanings of these words.
 * To put it brutally to you - when you say "when their definitions are from the same classic Greek idea? " you were originally completely wrong : if you drop that assumption and read the articles everything should become clear. 77.86.115.45 (talk) 15:11, 20 May 2010 (UTC)

Native American Cradle Board and Infant Behavior Differences
Someone told me that when infants were placed in these cradle boards before they were able to walk that these infants were much less fussier and happier than of those infants who did not grow up these? Is this true? Please let me know if I did not make myself clear. Reticuli88 (talk) 18:51, 18 May 2010 (UTC)


 * It seems clear enough. But I don't know off hand of any scientific reason for this.--Chemicalinterest (talk) 21:04, 18 May 2010 (UTC)


 * See swaddling. StuRat (talk) 21:26, 19 May 2010 (UTC)

Right angles
Do right angles occur naturally? Jacob Lundberg (talk) 20:07, 18 May 2010 (UTC)
 * It depends on how perfect you want the right angle to be. Halite, for example, forms an isometric crystal, but as you'll see from the pictures, some of the angles are not quite exact. Matt Deres (talk) 20:18, 18 May 2010 (UTC)
 * Galena, too; and staurolite crystals can be twinned at right angles, as in the infobox image. Deor (talk) 21:44, 18 May 2010 (UTC)
 * Some fossils such as trilobites and strophomenid brachiopods (e.g. File:Leptaena sp + Rhynchonella sp.2 - Silurico medio.JPG) come pretty close to having right angles, such that they can be used to measure angular strain in deformed rocks by structural geologists. Mikenorton (talk) 20:47, 18 May 2010 (UTC)
 * A vine hanging to the ground, or a tree like the one to the right (if viewed from far enough away)? Comet Tuttle (talk) 22:08, 18 May 2010 (UTC)
 * If you break a silcon wafer (as used to make integrated circuits) that is 1-0-0 orientation, many of the pieces will form perfect right angles. --Phil Holmes (talk) 07:39, 19 May 2010 (UTC)
 * There are three right angles in space.77.86.10.27 (talk) 11:43, 19 May 2010 (UTC)
 * Yes they do, they are just rare. For example is two rocks are smashed against each other by waves, and a piece breaks off one, there are huge number of angles the corner where the piece broke off could take. It might by wild chance be 90 degrees, but it's unlikely. It's extremely unlikely to be 72.143554 degrees as well. There are just so many that any one happening is wild chance.--92.251.177.211 (talk) 20:42, 22 May 2010 (UTC)

Fear of the dark
What does the latest research have to say about fear of the dark? Has evolutionary psychology tackled this topic? Barbara Ehrenreich popularized the fear of predators explanation in Blood Rites (1997), but surely Steven Pinker and others have opined on the matter? Any pointers would be helpful. Viriditas (talk) 21:05, 18 May 2010 (UTC)
 * In an earlier discussion on ghosts in the archive, it says that people generally use the sense of sight to detect most objects. In the dark, they don't have that sense fully, so they are restricted. The sense of hearing becomes much better, so a floorboard creacking could sound like someone sneaking up. It unsettles you. --Chemicalinterest (talk) 21:07, 18 May 2010 (UTC)
 * Yes, that's true. But many children are afraid of the dark, such that they imagine monsters and see fearful shapes in everyday objects, such as trees.  Ehrenreich's explanation, that as primates, we were once prey for predators at night, explains a great deal.  I'm wondering if anyone has followed up on this line of thought (early humans as prey) since 1997. Viriditas (talk) 21:11, 18 May 2010 (UTC)
 * I can't seem to find any more recent research than what you point out. Ehrenreich's hypothesis doesn't make a great deal of sense to me, what would be the point of being scared of the dark before we had a way of making light ourselves (i.e. fire)? What's more, being scared of the dark, and presumably making a fuss to your parents, would be disadvantageous as any predators out there would be directed right to you. CI's suggestion seems reasonable, being in the dark makes you more sensitive to other senses and can make you more paranoid. Perhaps children haven't learnt what all the possible sounds that they hear in the dark could represent, and being on the safe side, are therefore scared of them. 86.7.19.159 (talk) 21:45, 18 May 2010 (UTC)
 * Why would the predators be directed at you if you make a fuss or increase your alertness? I think they'd have an easier time if you stand still, fearless, while taking no precautions against the mysterious shape sneaking up on you.  --99.237.234.104 (talk) 04:02, 19 May 2010 (UTC)
 * I don't think it requires any special explanation. We are primarily visual animals: that's how we find food, notice dangers, etc. Being in the dark takes away our primary means of sensing the world outside out bodies - heck, even within our bodies. When you stub your toe, you don't try using proprioception and inner pain sensors to determine how badly it's hurt, you twist your leg into an ungodly position and risk falling flat on your ass to see it. Like the posters above, I'm not too impressed with Ehrenreich's idea; like David Jones' An Instinct for Dragons it seeks to provide a theory when the bald facts might be explanation enough. Matt Deres (talk) 22:48, 18 May 2010 (UTC)
 * As I remember from my childhood, fear of the dark is mainly fear of what might be hidden in the dark. Ehrenreich's explanation seems so, well, obvious, that I'm surprised there is any controversy about it.  It's not clear how it could be tested by an experiment though. Looie496 (talk) 00:50, 19 May 2010 (UTC)
 * Sorry for hitching a ride on someone else's question, but what possible explanations might there be for a person (such as myself) actually being more comfortable in the dark than in daylight? As a child I was scared of many things (dogs, bulldozers, power-line towers, etc., etc.), but I was never really scared of the dark -- I was actually more comfortable in the dark than in daylight.  Thanks in advance 67.170.215.166 (talk) 01:18, 19 May 2010 (UTC)
 * I find darkness calm and relaxing too, maybe you associate it with peace and rest. Not every single little aspect of human nature necessarily has to have a categorized condition. I'm not an expert so I could be wrong about this one. But I mean, NOT being afraid of spiders isn't a "condition" right? So why would NOT being afraid of the dark be one? Maybe the condition you are looking for is "slightly uncomfortable during the day time", maybe you have daytime anxiety disorder. ;) Vespine (talk) 05:36, 19 May 2010 (UTC)

Reduction of alkali metals
Why can some alkali metals be reduced by weaker reducing agents? An example would be cesium caesium reduced by magnesium. Does it have something to do with gaseous equilibrium? --Chemicalinterest (talk) 21:50, 18 May 2010 (UTC)
 * If entropy can be increased so that the Gibbs free energy is positive then things that seem to go against the energy barrier can happen. So yes if cesium can be produced as a low density gas in the reaction it will depart from the scene and not react back the other way. Graeme Bartlett (talk) 08:45, 19 May 2010 (UTC)
 * PS I hope you are not trying this at home. Graeme Bartlett (talk) 08:46, 19 May 2010 (UTC)
 * No I only have tiny amounts of lithium that burn brightly but I saw in cesium production that cesium dichromate is reacted with zirconium metal to yield cesium gas. I thought the dichromate would be a much stronger oxidizing agent than the Cs+ ion. But the cesium ion oxidizes the dichromate to form cesium gas. --Chemicalinterest (talk) 11:58, 19 May 2010 (UTC)
 * That sounds an unlikely mechanism, more likely the zirconium reduces the dichromate and the cesium ions. If you make that cesium compound hot enough it will make cesium vapour all by itself. When you get brown dwarfs or giant planets you will find alkali metal vapour lines in the spectrum. Graeme Bartlett (talk) 12:32, 19 May 2010 (UTC)
 * It doesn't mean the alkali metals are in the planet, it could mean that compounds of them exist. (Both Na and NaCl release a specific spectrum.) --Chemicalinterest (talk) 21:39, 19 May 2010 (UTC)

algae or other plants
Is there an algae or other plant that will grow in the arctic or elsewhere in sufficient quantities to absorb all of the excess carbon dioxide now produced by fossil fuels? 71.100.0.29 (talk) 22:43, 18 May 2010 (UTC)
 * Lichens grow in the Arctic some places. But they will not make any measurable difference to the carbon dioxide concentration. BTW, fossil fuels only put out a miniscule section of carbon dioxide compared to natural sources. If there is more carbon dioxide, plants will grow better, consuming more of it. (This may not be NPOV). --Chemicalinterest (talk) 22:46, 18 May 2010 (UTC)
 * That's not NPOV, it's false (unfortunately!) see soyface and have a read of Co2. Admittedly on a global scale it is very uncertain, along with changes in cloud cover, the response of forests to co2 is the biggest unknown in climate change models. 86.7.19.159 (talk) 08:05, 19 May 2010 (UTC)
 * Have you read Geoengineering and the various links? The most common proposal when it comes to using plants is ocean nourishment. Other proposals generally involve growing plants in a more normal fashion and then encapturing the carbon dioxide in some manner so it isn't released for a long time like Biochar and Bio-energy with carbon capture and storage. Nil Einne (talk) 23:08, 18 May 2010 (UTC)
 * But doesn't CO2 storage intail with it the long term danger of accidental or unintended release that would result in the deaths of trillions of animals, if not render animal life extinct? 71.100.0.29 (talk) 00:53, 19 May 2010 (UTC)
 * The straightforward method of "storage" is to grow plants such as trees, and then bury them underground. Calculations show that a depth of 10 feet would take them out of circulation for hundreds of years. I think its pretty clear that any unintended release from this reservoir would be extremely gradual. In any case, to get a fix on the numbers, compensating for the CO2 we add each year would require removing several billion tons of carbon from the system, and there is no way that can be done with lichen. Looie496 (talk) 00:57, 19 May 2010 (UTC)
 * Well I do know of a case in Florida in which a lot of tress were found underwater that had been there for a long time. When the trees were removed they were found not only to be free of decay but strong enough to use for building material. Not only that the trees had taken on aesthetic qualities which allowed them to be used to build furniture that was highly valued and returned to the excavators hundreds of fold of their initial investment. On those ground the idea might not only be good for sequestering carbon dioxide but making your descendants thousands of fold rich, owing also to inflation. 71.100.0.29 (talk) 01:18, 19 May 2010 (UTC)
 * Looie, I know this has been suggested (biochar) but what's the point in this until we stop digging up coal?! Why waste energy storing trees when they could just be burnt instead and the coal could be left in the ground? 86.7.19.159 (talk) 08:05, 19 May 2010 (UTC)
 * You can't make furniture out of coal. 71.100.0.29 (talk) 16:19, 19 May 2010 (UTC)
 * Exactly. It's really worse than that.  Just look at the amount of coal it takes to feed a single power plant.  It's something like one or two mile-long trains full of coal per day!  Now, for carbon sequestration to work, you'd need AT LEAST one or two mile-long trains full of tree timber to be buried someplace PER DAY.  It's actually an awful lot more than that because trees contain water and the carbon is reacted with oxygen and other stuff that means that to sequester the carbon from one ton of coal requires more like three tons of old-growth trees or five tons of pine or other fast-growth trees.  So just imagine your little power station - covering a few hundred acres - then think about the size of forest and the scale of activity you'd need to fill up maybe 10 mile-long trains with cut lumber every single DAY, 365 days out of the year!! (And to do that sustainably!)  In previous Ref Desk questions, I've done the math on this - and to cover the current coal consumption (ignoring gas and oil) of the USA alone, you'd need to plant an area more than twice the size of the USA with trees and harvest and bury them all every 15 years!  Furthermore - you'd have to do all of that harvesting, hauling and sequestering without using any more energy in the process...or you'll need even more area and even more harvesting, hauling and sequestering!!  Plus, you can't just dump trees in a handy lake someplace - it'll fill up amazingly fast - and besides, trees have this annoying tendancy to float!  This is so far from being a practical proposition that it's completely laughable. SteveBaker (talk) 15:03, 19 May 2010 (UTC)
 * I believe it would be feasible to remove carbon biologically at a cost of $100 per ton or less. The problem is that currently coal itself only costs a bit more than $100 per ton (it was up to $150 before the economic crisis hit, but was as low as $30 back in 2000).  That means that to finance the removal of all the carbon you'd have to impose a tax of close to 100% on coal, which is obviously a problem.  For any other energy source it would be far less of a burden though.  Even for crude oil you'd only have to charge about a 20% surtax, by my calculations.  I doubt that the political will is there, but I feel this is something the world could handle if it decided to. Looie496 (talk) 20:41, 19 May 2010 (UTC)
 * That's just bullshit! It can't possibly work!  It's not enough to "remove" this carbon "biologically" - it's still got to go someplace.  You burn the two mile-long coal trains worth of coal - you somehow capture the many cubic kilometers of CO2 that this produces (every day!) and "biologically" you do what with it?  The material has to go somewhere - conservation of mass and conservation of energy guarantees that!  If your magic biology turns the CO2 back into carbon then it's going to need considerably more energy to do that than you got out of the coal in the first place (conservation of energy).  If you're planning on using photosynthesis as the source of that energy than you have to use sunlight to do that - and you STILL have 10 mile-long trains full of whatever residue your biological process leaves behind...but hey - if that stuff is so rich in carbon - why not burn it?  Well, if you can produce/capture more energy/carbon with your biological process - then why bother burning the coal in the first place?  Simply build a closed-loop system where you burn a gazillion tons of bio-residue, turn it into CO2 - which your mysterious process then (photosynthetically) turns back into bio-residue that you can then burn.  No coal, no coal-trains, no mining disasters, etc.   What you've just invented is a solar power plant.  The idea of taxing coal and all that nonsense would magically go away - and since your process can capture the CO2 from burning $100 worth of coal (or bio-residue) for just $100 - the process you describe should be just as cheap as burning coal.  So either what you are talking about is complete bullshit - or you've just solved the world's energy crisis and we can shut down all of the coal-fired power plants.  I suspect, it's not the latter!  SteveBaker (talk) 15:04, 20 May 2010 (UTC)
 * The way to get rid of the biocarbon is to bury it. The problem with using plant carbon directly as a power source is that it doesn't burn very well and isn't easy to transport-- it would probably have to be converted to charcoal, which is an expensive process.  As I said, I believe it would be feasible to grow trees or other high carbon plants, harvest them, and bury them, for a cost on the order of $100 per ton of carbon.  I'm not at all sure it would be possible to make a ton of charcoal for $100.  Making biofuels (i.e. synthetic oil or alcohol) is at least an order of magnitude more expensive.Looie496 (talk) 17:33, 21 May 2010 (UTC)
 * Put simply, no, because if there was a plant or algae that could grow there it already would be. Take a look at antarctic flora - very few plants can grow there. Reasons for this are multiple: enzyme reactions become very slow, photoinhibition increases, photosynthesis decreases and water is less available at cold temperatures. To fix plants need to open their stomata but if there is no water available (or if it's ice) then this won't happen. If (when) the arctic ice cap melts in the summer, more  will be fixed but the change in albedo from ice to water will far outweigh any benefit of increased photosynthesis. A more promising idea is to use cacti growing in deserts (which use the water efficient CAM photosynthesis) to fix carbon and sequester this elsewhere. But as I said above, doing this while still using fossil fuels is pretty pointless. 86.7.19.159 (talk) 08:05, 19 May 2010 (UTC)


 * Strange that you should ask that question, as this has already happened in the past, see azolla event causing a global cooling catastrophe. Graeme Bartlett (talk) 08:43, 19 May 2010 (UTC)


 * It's worth pointing out that the original "sequestration" was the biogenic creation of fossil fuel in the first place: algae and peat absorbed atmospheric carbon by normal methods - photosynthesis and plant respiration (but over the course of hundreds, thousands, or millions of years). Then, those plants died and were buried (all the while, containing the carbon that they are made out of).  Over geologic timescales, this kerogen turned into petroleum and other fossil fuel by geochemical, thermal, and even biological alteration.  Now we are re-extracting this former plant-matter.  The problem is that we have become so good at extracting it, that we can pull carbon out of the ground at a rate significantly faster than ordinary/natural plant life-cycles and geology can put it back into the ground.  (At least, this is our concern, evidenced by the growing carbon concentration in our atmosphere). This is why there is research into carbon sequestration - we are looking for other ways to help improve the rate of carbon "re-absorption" - whether those methods are biological, mechanical, or otherwise.  When we contemplate the scales, though, it just boils down to this: something must put the billions of tons of carbon that we extract back in the ground.  Nimur (talk) 13:50, 19 May 2010 (UTC)
 * Interesting, DYK that only 70 years of photosynthesis were ever stored as fossil fuels? (Can't find the figures at the moment, but it does show that we could in theory remove from the atmosphere relatively quickly once we stop producing it.) 131.111.30.21 (talk) 15:43, 19 May 2010 (UTC)

The key point here is that it's not enough for the plants to grow (thereby absorbing CO2). Something has to happen to the plants when they get old and die. If they simply sit there and decay - or are eaten by animals or are burned in a forest fire or something - then the carbon that they locked away will simply be released back into the atmosphere again and we're back to square one. If (somehow) the plant gets buried and instead of decaying and producing more CO2 and methane and other nasty greenhouse gasses - they get (ultimately) sequestered and after a gazillion years turn into coal and oil. This locks away the carbon and so long as no stupid humans come and dig it up again and burn it - it can be quite effective. But simply growing some moss and doing nothing else would only have a short-term benefit - roughly of the order of the lifespan of the first generation of plants...after that, the rate that these plants are absorbing CO2 would be balanced by the rate at which the extra plant decay adds to the CO2/Methane levels. SteveBaker (talk) 15:03, 19 May 2010 (UTC)