Wikipedia:Reference desk/Archives/Science/2013 November 27

= November 27 =

Correct approach to deriving the shell theorem?
I know the easy approach to proving the shell theorem is to take a point particle, integrate all the force elements over an infinitesimally thin shell, integrate over all shells, and then integrate all the point particles. I now asked myself, why not do it all at once? The problem is that it arises in a nested volume integral.

Here, let V1 and V2 represent the regions occupied by my two spherical objects (assuming they do not overlap). Let the center of the first object be at the origin, and let d be a displacement vector between a mass element in the first object and another mass element in the other object, taken to point towards the second object. Let dM be a mass element of the first object and dm a mass element of the second. Let u, v, and w represent the position of dm and x, y, and z the position of dM (u=v=w=x=y=z=0 at the center of V1, the u-axis coincides with the x-axis, the v-axis with the y-axis, and the w-axis with the z-axis). Let f(R) and g(r) be the densities of the two objects respectively (they are functions of the radius only, as required by the shell theorem), and finally, let the center of the second sphere be located at a displacement vector of X=. G is the universal gravitation constant.

Then: $$\mathbf{F} = -G \iiint\limits_{V_1} ( \iiint\limits_{V_2} \frac{dm*\mathbf {d}}{d^3}) dM = -G \iiint\limits_{V_1} f(\sqrt{x^2+y^2+z^2}) (\iiint\limits_{V_2} \frac{\mathbf{d}*g(\Vert \mathbf{d} - \mathbf{X} \Vert)}{d^3} dV_2) dV_1$$ $$=-G \iiint\limits_{V_1} (\iiint\limits_{V_2}\frac{f(\sqrt{x^2+y^2+z^2}) ((u-x)\mathbf\hat{i}+(v-y)\mathbf\hat{j}+(w-z)\mathbf\hat{k})g(\sqrt{(u-x-A)^2+(v-y-B)^2+(w-z-C)^2}) dV_2}{((u-x)^2+(v-y)^2+(w-z)^2)^\frac{3}{2}})dV_1$$

In the integration, X is fixed but arbitrary, so the six variables of integration are u, v, w, x, y, and z. As you can see, I don't have many ideas on how this reduces to (using my notation) $$\mathbf{F}=\frac{-GMm\mathbf{X}}{X^3}$$, because f and g are arbitrary continuous functions of one variable that determine the densities of the two objects as functions of their radii, and entire integrand is very convoluted. If I were to evaluate the whole thing using one set of substitutions, then the Jacobian determinant would have to be of order 6 (!). Therefore, I have to do something to simplify the mathematics. I know this is a convoluted approach, but really, this is what is really done when we apply the shell theorem - summing up the forces contributed by all the possible pairs of mass elements. If the above notation is not correct, how would this "all-at-once" approach be executed?--Jasper Deng (talk) 01:39, 27 November 2013 (UTC)


 * At another glance, $$-G \iiint\limits_{V_1} f(\sqrt{x^2+y^2+z^2}) dV_1$$ reduces to -GM, but the remaining integrand is still overly convoluted.--Jasper Deng (talk) 01:46, 27 November 2013 (UTC)
 * Oh, wait, you can't do that because the second integral is a function of x,y, and z.--Jasper Deng (talk) 01:49, 27 November 2013 (UTC)

I will note that this is equivalent to showing that the shell theorem is valid regardless of what f and g are (as long as they are continuous).--Jasper Deng (talk) 01:00, 29 November 2013 (UTC)


 * This is not a good approach to proving shell theorem. There are two statements to shell theorem and it is not necessary to do integrals to show either of them. 1) There is net force on a particle inside an infinitesimally thin mass shell. To show this we see that there is a 1-to-1 relationship between microscopic elements either side of the test particle whose forces cancel in the infinitesimal limit, thus there is no net force. 2) There force on a mass outside the shell acts as if concentrated at the centre. For this we take a similar approach and show that if we vary the radius of the shell by a small amount there there is a 1-to-1 relationship between mass elements such that the net change in force caused by the pair of them due to the variation in radius is zero, hence we are at liberty to collapse the shell to its centre without changing the force on the test particle. — Preceding unsigned comment added by 109.158.148.43 (talk) 22:43, 29 November 2013 (UTC)
 * This answer is unfortunately not acceptable for my purposes because it does not rigorously show why that is so. The shell theorem article uses Riemann sums, and I insist on a method using Riemann sums.--Jasper Deng (talk) 23:04, 29 November 2013 (UTC)
 * Show why what is so? I didn't show anything, I just outlined the arguments. They're perfectly good arguments which just show that the force integral (or Riemann sum as you insist) over a spherical mass is zero/(the same as a point mass at its centre) for a test particle inside/(outside) the sphere by construction, when constructed in the right way. See here: . Its much more elegant than actually bothering to evaluate these nested integrals. Besides, if you insist, at least give up trying to use Cartesian coordinates, there's nothing to be gained by denying the symmetry of the problem.  — Preceding unsigned comment added by 109.158.148.43 (talk) 00:02, 30 November 2013 (UTC)
 * What I was thinking of was to use two parallel spherical coordinate systems, one for x, y, and z, and another for u, v, and w, and then taking the Jacobian of that six-way transformation. But the problem that remains, which the document you linked does not take into account, is that there's no dependence on f and g.--Jasper Deng (talk) 00:28, 30 November 2013 (UTC)
 * You haven't used any spherical coordinates, you have used only Cartesian coordinates, besides spherical coordinates arent appropriate either, your problem has cylindrical symmetry. You appear to not understand the purpose of shell theorem tohugh, it is not just a mathematical curiosity which can be shown by doing some integrals, the point of it is to show that (in your terms) the form of f and g is irrelevant, and thus one can avoid having to ever do the integrals which you are trying to do in your 'proof'.
 * No, I've gone through the usual proof outlined in the article and know that it's the reason why Newton could publish his law of universal gravitation (he had previously had doubts about it not applying to anything but point particles). You're not really answering my question - I do tend to insist that the "true" method here, which is done by Riemann sums, works. It suffices, I shall say, to show that if I can transform coordinates here in a suitable manner, I can convert it to the integrals used in the article.--Jasper Deng (talk) 21:49, 30 November 2013 (UTC)
 * So far as I know, [representing a planet with a point mass using] the shell theorem is relying on two things: first, that the integral of the forces from a homogeneous spherical shell happens to work out to be (from outside) equal to a point mass at the center, second, that most things like planets are fairly close to equal density within each spherical shell, and third, that you're looking at the planet from outside, so you don't need to work out what proportion of the mass is below you to get the gravity. These assumptions break down under certain circumstances, like in lower lunar orbits on account of the mascons of the Moon, where it might make sense to do the entire 3D integral based on some model you've worked up of the mass distribution throughout the object.  But if you want to do it other than numerically you may end up leaking purple tapioca at the eardrums. :) Wnt (talk) 23:31, 1 December 2013 (UTC)


 * Let me repeat: the point of shell theorem is you are never required to do volume integrals. If you look again at the article, you will see there are no volume integrals.
 * You clearly are not getting the whole reason I asked this question and are being of no help. The shell theorem can only be extended to solid spheres because of further integration that is dimensionally equivalent to volume integration.--Jasper Deng (talk) 05:30, 3 December 2013 (UTC)
 * True, I misspoke. I was thinking of a common use of the shell theorem (as I've added in brackets above) but the shell theorem itself is, well, about the shell. Wnt (talk) 14:39, 4 December 2013 (UTC)
 * (To be clear, that comment wasn't directed to you, but at the IP's comment immediately below your comment).--Jasper Deng (talk) 20:38, 4 December 2013 (UTC)

Historical humans and race
Did the historical early humans were of different races like today or were one race? If they were one race then what did they look like, and if they had different race, how many and how did each look like? Also, which races of today have Neanderthal genes?74.14.28.186 (talk) 04:00, 27 November 2013 (UTC)


 * I don't know. I suppose it depends if you believe in God !.--122.111.241.205 (talk) 04:12, 27 November 2013 (UTC)


 * See Homo sapien and Neanderthal. --DHeyward (talk) 04:15, 27 November 2013 (UTC)


 * I don't know what it has to do with god, and to DHeyward, which races today will have a Neanderthal admixture? In history of Homo Sapien, did it start with one race or many race?74.14.28.186 (talk) 04:24, 27 November 2013 (UTC)


 * The OP's IP address geolocates to Toronto, so one possibility is that he is thinking of the traditional US/Canadian view of race, with blacks, whites, hispanics, etc. The current most popular, out of Africa, view is that humans didn't start out that way. They would have been a fairly homogeneous group, with the current differences evolving as people settled in different parts of the world. HiLo48 (talk) 04:31, 27 November 2013 (UTC)


 * I agree !.--Die Antwoorde (talk) 04:27, 27 November 2013 (UTC)
 * I kinda meant race in genetic sense and skeletal sense, you can tell from bones and genes and the appearance the race of individual, and if they were homogenous, what did they look like? And how did the different races adapt, how they developed different appearance and genome, and were there mental adaptations like brain function, behaviour, intellgence and that kind of thing? How did it help the different races?74.14.28.186 (talk) 04:47, 27 November 2013 (UTC)
 * The above is yet another twist on the same racist theme by the Toron-troll. I've turned him in and he should be blocked soon. ←Baseball Bugs What's up, Doc? carrots→ 05:12, 27 November 2013 (UTC)
 * Should have added the IP that refactored my original response and his kind edit summary here. --DHeyward (talk) 10:11, 27 November 2013 (UTC)

To explain how is this racist, please?74.14.28.186 (talk) 05:23, 27 November 2013 (UTC)


 * I think that the original question is valid and not racist.--Dr. Madhattan (talk) 06:22, 27 November 2013 (UTC)
 * ...even if based on ignorance of what race really is. HiLo48 (talk) 07:39, 27 November 2013 (UTC)


 * Touche. Die Antwoorde (talk) 07:45, 27 November 2013 (UTC)


 * Our Neanderthal article says "An estimated 1 to 4 percent of the DNA in Europeans and Asians (French, Chinese and Papua probands) is non-modern, and shared with ancient Neanderthal DNA rather than with Sub-Saharan Africans (Yoruba and San probands)". On the other hand, Neanderthal genome project says "99.7% of the base pairs of the modern human and Neanderthal genomes are identical". So colour me confused. Can someone explain how to reconcile these two statements ? Gandalf61 (talk) 12:11, 27 November 2013 (UTC)


 * Not an expert, but I find the "99.7% base pairs" to be somewhat misleading. As I understand it, we share somewhere around 70% with fruit flies and over 99% with chimpanzee's.  I suspect the difference is when comparing uniquely human DNA between various groups do we find 1-4% of it being shared with ancient neanderthal DNA.  As I understand it, the human genome went through a "narrowing" experience where most variations died off and then recovered with all modern DNA traceable to the narrowed surviving strain.  How and when ancient neanderthal DNA would have re-entered or whether the narrowing was not universal is what I believe is the focus of research.  --DHeyward (talk) 14:24, 27 November 2013 (UTC)


 * (ec)The problem is that 99.7% of base pairs being identical between two species doesn't tell you much. We share 98.8% of our DNA with Chimpanzees, and 50% of our DNA is shared with bananas - men and women have only 97% of our DNA in common...so a male human shares much more DNA with male chimpanzees than with female humans (which, my wife tells me, explains a lot!).  But base-pair comparisons are not the same thing as numbers of genes shared.  Take (for example) the gene that allows adults to digest lactose: "LCT".   It only differs by a single base-pair from the defective version of that gene that causes lactose intolerance.  But look at the numbers here:


 * The LCT gene contains about 50,000 base-pairs - only one of which has to be wrong for it to be counted as "the gene for lactose intolerance" rather than "the gene that allows us to digest lactose".
 * We have about 20,000 genes.
 * Human DNA contains about 3,000,000,000 base-pairs.


 * So if we imagine two people who are identical twins - except that one of them is lactose intolerant - their DNA is identical to within one part in three billion, but their genes are only identical to within one part in twenty thousand. As percentages, those two numbers are radically different - yet both descriptions are talking about a single base-pair difference.  Now, the question is whether the Neanderthal article is talking about percentages of base-pairs or percentages of genes.  The article also qualifies that percentage as being of "non-modern" DNA - so it's (presumably) excluding genetic changes since the time of extinction of Neanderthals - where the Neanderthal genome project is talking about the amount of difference between modern humans and Neanderthal...but doesn't really make sense because it's saying that we're more like neanderthals now than we were back in "non-modern" times?!?


 * There are plenty of other sources of confusion possible here. You'll also find articles saying that (for example) first cousins share 12.5% of their DNA...which as a strict count of base-pairs is clearly nonsense because that would our cousins more different from us (by far) than we are from bananas!  What is probably meant is that 12.5% of the natural genetic variation that makes us unique from other humans is the same between first cousins...which would mean that (of course) we're much more similar to each other than we are to chimpanzees, neanderthals or bananas.


 * I agree that both articles should qualify those percentages much more carefully...it's a mess.
 * SteveBaker (talk) 14:51, 27 November 2013 (UTC)

http://www.nature.com/news/mystery-humans-spiced-up-ancients-sex-lives-1.14196 - truth is, we still know fairly little and our ideas continue to change rapidly. Wnt (talk) 23:34, 1 December 2013 (UTC)

How to produce magnesium carbonate?
I want to produce 100g of magnesium carbonate by using magnesium sulfate and sodium bicarbonate. How much magnesium sulfate and sodium bicarbonate do I need? And how much water do I need to mix it up? Thank u :-) — Preceding unsigned comment added by 110.159.119.154 (talk) 06:54, 27 November 2013 (UTC)
 * This appears to be a stoichiometry question. Are you doing this for homework?--Jasper Deng (talk) 07:10, 27 November 2013 (UTC)
 * How you do it is to work out how many moles of magnesium carbonate you want to make. Work out your chemical formula.  Work out how many moles of each ingredient you want, then multiply by the formula weight of each raw material to work out the mass required.  You will have to know the amount of water in the magnesium sulfate hydrate that you have. Graeme Bartlett (talk) 00:53, 28 November 2013 (UTC)

Adding nitrogen gas to chemical bottle to protect from moisture in the air
I have DEPC in a bottle which is still unopened. The manufacturer's instructions state that moisture from the air will cause it to decompose and so a layer of nitrogen (or argon) gas should be layered over the DEPC before closing the bottle. I have access to liquid nitrogen. Can this be used to protect the chemical from the atmosphere? The mist surrounding nitrogen is presumably water vapour from the air, right? I don't want that getting to the DEPC! --78.148.107.181 (talk) 09:23, 27 November 2013 (UTC)


 * What is DEPC? See Guiness in the composition section.  N2 is used in bottling.  Also, nitrogen, especially in the large commercial liquid nitrogen tanks, are very dangerous as an asphyxiation hazard.  Don't do it indoors if you don't have oxygen sensors.  Unlike CO2, your body does not react to higher levels of nitrogen (or Argon or Helium) and people pass out and then die before they even know the oxygen level is low.  There is no feeling of shortness of breath or anxiety like with CO2.  Many have died working with nitrogen in confined spaces..  --DHeyward (talk) 10:07, 27 November 2013 (UTC)


 * Diethyl pyrocarbonate? Depending on what you are using it for, the minimal amount of decomposition resulting from moisture in the air trapped in the bottle as you close it might be acceptable.  Liquid nitrogen would not be an ideal source of dry nitrogen because of the impracticality of handling a small amount of it without exposing it to air causing condensation of moisture, as you suggest.  Laboratories commonly have inert gas lines, such as dry nitrogen.  If you access to something like that, that would be ideal - blow a light stream of nitrogen into the top of the bottle as you are closing it.  Otherwise, just minimize the amount of time you have the bottle opened to air. -- Ed (Edgar181) 10:21, 27 November 2013 (UTC)
 * I agree, a lab will either have an inert gas line for such purpose, or high-purity, dry nitrogen from a cylinder with a pressure regulator. If it's not the first time DEPC is being used, so if you're asking us because you don't want to bother the people who will know the correct procedure at your lab, reconsider. If it is the first time DEPC will be used, then consider buying a flushing system before proceeding, or take Edgar181's advice and minimize the amount of time the bottle is open. Don't improvise, in my experience, when improvised procedures go wrong, the results are often much worse than the problem one was trying to fix. Ssscienccce  (talk) 11:52, 27 November 2013 (UTC)


 * I know we have carbon dioxide lines but I think they might be solely for connecting to cell culture incubators. I already consulted people in our lab and they were unaware that the manufacturer advises this protection from atmospheric moisture. 129.215.47.59 (talk) 12:53, 27 November 2013 (UTC)
 * There will be very few biology labs with a nitrogen line, as the OP says, CO2 lines are common, but N2 certainly not (I've never seen them anyway). Anyway, might be better to make up a stock solution in a suitable solvent (EtOH?), rather than opening the stock bottle repeatedly. Must admit having never made up stocks myself, don't use it much. People are far too paranoid in RNA work! Fgf10 (talk) 16:57, 27 November 2013 (UTC)
 * If you're looking for dry nitrogen in a biological department/institute try a serious biochemistry lab, a structural biology lab or a protein production core facility - these are the people that seem to have cylinders of it in our institute. You can take some back to your lab in a balloon attached to some sort of valve with a rubber band - attach it to a needle to fill the bottle with nitrogen before closing. As far as being too paranoid around RNA, that does rather depend on what you are doing - if you are just doing some basic qPCR on large samples (and make sure you reverse transcribe with random hexamers like you're supposed to) then yes, excess paranoia is not justified, but if you are trying to, for example, do long-read cDNA sequencing from tiny amounts of non-optimal starting material a healthy paranoia is just what you need. I have to say that most biology labs have probably been using DEPC for years without the precaution of storage under inert gas, but then most biology labs probably wouldn't notice if their DEPC was totally ineffective. Equisetum (talk &#124; contributions) 21:26, 27 November 2013 (UTC)


 * DEPC is hydrolysed to EtOH and CO2, so if an EtOH solution is acceptable then the OP has nothing to worry about. A quick calculation shows that if a 1 liter bottle is used for small doses of 2 ml, and each time 20 ml air at 20°C and 50% humidity enters the bottle, then by the time there's 100 ml DEPC left it will have absorbed 20mg water, and therefore contain about 100 mg ethanol. Assuming DEPC + H2O -> 2EtOH + 2CO2 is the only reaction that occurs, but that's something I'm not sure about. If it's stable at room temperature then why does it have to be stored at 2 to 8 degrees C, and why do I find references to a publication titled "Spontaneous hazardous chemical explosion of unopened bottles of diethyl pyrocarbonate"... Ssscienccce  (talk) 22:34, 27 November 2013 (UTC)


 * It is not hard to rig a nitrogen bottle to a line with a needle on the end. You put a rubber septum on the stock bottle insert your positive pressure nitrogen line and insert your needle or canula to draw off your sample. No difficult contruction required. Standard practice when your chemicals burst into flame in open air. 75.41.109.190 (talk) 20:16, 27 November 2013 (UTC)

Penguins near the South Pole
How close, at best, can penguins (no matter the species) come to the South pole? --80.122.110.238 (talk) 12:33, 27 November 2013 (UTC)


 * According to Penguin, they spend about half their time in the water, so it's unlikely they would venture very far from the ocean. Given that, whatever the closest penguin habitat is to the geographic south pole, would be about as close as they would get to it. ←Baseball Bugs What's up, Doc? carrots→ 12:55, 27 November 2013 (UTC)


 * I suggest you watch the documentary March of the Penguins. The Emperor penguins walk far inland on Antarctica to breed, apparently to get away from any predators.  A secondary benefit might be the elimination of the unfit from the breeding pool, as they can't make the journey.  And they also seem to fast the whole time, living off their fat stores.  It's an amazing feat. StuRat (talk) 21:20, 27 November 2013 (UTC)


 * If you look at the breeding areas of the Emperor penguin they probably come to as near as something like 1000km of the pole. They'd probably be quite happy wandering around the pole in the middle of Winter, it's just there isn't any food around there and they're safe enough where they do breed. Dmcq (talk) 13:03, 27 November 2013 (UTC)


 * Looking at that range again i looks like they go within 500km of the pole. Dmcq (talk) 13:09, 27 November 2013 (UTC)


 * Are you looking at the map? The text says 77°. If the Emperor penguin gets closest (and I suspect it does) then this says they reach 78° south which is about 720 nmi from the South Pole. Thincat (talk) 13:24, 27 November 2013 (UTC)


 * This set me thinking about the famous Worst Journey in the World to get an Emperor penguin egg at Cape Crozier for which our article now says "Cape Crozier is within a restricted area and permission is required to visit it". The Heroic Age of Antarctic Exploration has drawn to a close! Thincat (talk) 13:33, 27 November 2013 (UTC)


 * Presumably the penguins are exempt from that restriction? ←Baseball Bugs What's up, Doc? carrots→ 13:40, 27 November 2013 (UTC)


 * The map at Emperor penguin shows it living further than 85° south (I think). But is this really true? Antarctic Plateau specifically says penguins don't live there "... because there is nothing there for them to eat". Thincat (talk) 13:52, 27 November 2013 (UTC)


 * The southernmost point of the Amundsen Coast is just over 300 mi (500km) from the pole; that's not the plateau (which rises dramatically just south of there). But it is the depths of the Ross Ice Shelf, so I too don't see what penguins (who live off fish) would eat there either. -- Finlay McWalterჷTalk 14:02, 27 November 2013 (UTC)


 * Yes, I was wrong to mention the plateau. This suggests they (and Adelie penguins) live on the northern edge of the Ross Ice Shelf but no further south. 78° near enough. Thincat (talk) 14:35, 27 November 2013 (UTC)

If I get the map straight, there is a little bit of breeding (green) area within 80°, close to 81°, which would mean a distance of roughly 1000-1100 km. --KnightMove (talk) 19:11, 27 November 2013 (UTC)

Old style mechanical railway signal boxes
Why did the signalmen always use a cloth when operating the levers?  Spinning Spark  14:14, 27 November 2013 (UTC)


 * "The steel lever handles were cleaned every week with emery cloth and it was more than my life’s worth to pull a lever by grasping it with my hands as this would corrode the metal. It was necessary to hold the lever with a duster provided so as not to tarnish the brightwork."  AndyTheGrump (talk) 14:19, 27 November 2013 (UTC)


 * As an engineer that has pulled lots of leavers I can't believe that for a moment. It take a lot of force to change a point and the lever is 'round'. Meaning all the force is exerted on only a very small part of your hand and doing that all day long will soon make your hands painful. The signal man's duster or cloth spreads that force out. See here at 3mins and 36 seconds [] That is why manual cars have big knobs at the end of a gear shift stick and commercial vehicles have even bigger ones.--Aspro (talk) 00:13, 28 November 2013 (UTC)


 * Did the signalmen always use a cloth when operating the levers? HiLo48 (talk) 23:57, 27 November 2013 (UTC)


 * It was at least extremely common. I have seen it done that way in numerous old films and documentaries.  Just search You Tube for "signal box" and you will find lots of videos of signalmen doing it.  Oddly, the first You Tube result doesn't use a cloth, but he is only a relief signalman and the location, Brewery Sidings, might be significant!  Spinning  Spark  01:39, 28 November 2013 (UTC)

Suicide
Do any other animals (or living things) commit suicide? Or is this phenomenon only seen in humans? Thanks. Joseph A. Spadaro (talk) 20:11, 27 November 2013 (UTC)


 * Bees invariably die after stinging - which they do in protection of their hives. So yes, there is at least one kind of animal that does that kind of thing. SteveBaker (talk) 20:28, 27 November 2013 (UTC)


 * Thanks, Steve. Well, your answer made me re-think my original question.  The bee situation is not really a suicide, correct?  That is, they don't choose to end their life; they choose to sting (which then has the "side-effect" of ending their life).  For example, say that I saw that a child was about to get hit by a car; I jump in front of the car to save the child's life; the child is saved, but I die.  I would not really call that a "suicide", even though I made a choice that had the effect of losing my life.  That is (sort of) how I see the bee stinging situation; it is a death, but not really a suicide.  So ... I guess what I meant in my original question was more along the lines of this:  do any other animals/living beings commit suicide in the same way that humans do (i.e., they are typically sad and/or depressed; they feel that life is not worth living, for whatever reason; and, as such, they make an affirmative decision to end their life)?  Thanks.   Joseph A. Spadaro (talk) 20:49, 27 November 2013 (UTC)


 * If you insist on that interpretation of your question, then we cannot possibly answer it. We don't really know for 100% sure what other people are really thinking - let alone animals.  Can we be sure that people who commit suicide really understand what death truly means?  If we can't be sure with people - then we stand no chance.  Every conceivable instance we might come up with can always be countered with "Did they really know they'd die - did they truly understand what death actually is?"...so we have no answer for you. SteveBaker (talk) 21:02, 27 November 2013 (UTC)


 * Thanks, again. Two points.  (Point 1) Certainly, we do indeed know how/what human beings are really thinking.  No?  I think there is a lot of data about human suicide.  Perhaps, we can't know "100%" of what the dead person was thinking (of course).  But, there are suicide survivors, etc., that provide quite a bit of data about the human phenomenon of suicide.  It's not as if we are "stabbing in the dark", as far as human suicide is concerned.  (Point 2)  I thought I remember reading/seeing somewhere about how elephants (or was it apes?) expressed grief, sadness, etc., at the death of one of their own; and they even had some sort of funeral ritual.  Which led me to the thought that animals, on some level, can experience sadness and grief (and perhaps depression?).  Who knows (of course)?  But, I wondered if science ever studied this phenomenon among animals.  Thanks.   Joseph A. Spadaro (talk) 21:08, 27 November 2013 (UTC)


 * I think we can at least infer what animals understand. For example, elephants will go out of their way to visit the bones of their dead relatives.  This implies that they associate those bones with their memories of those relatives, and have some concept of death. StuRat (talk) 21:07, 27 November 2013 (UTC)


 * I think an essential component of suicide is understanding what death is and that your actions will result in your death. I doubt if a bee qualifies here.  There are also animals that, when stressed, will stop eating until they die, but I doubt if that's intentional suicide.  Whales sometimes beach themselves repeatedly, and this might be suicide, or maybe their navigation system is just messed up somehow.  It's not clear.  See whale beaching. StuRat (talk) 20:56, 27 November 2013 (UTC)


 * I have an abandoned cat whose kittens recently died pulling one of those hunger strikes right now. So far, no note or list of demands. But, from a human perspective, she seems depressed as hell. She certainly knows death exists, if not how to make it. I'd wager a bee knows what's going to happen, as it's likely seen it before. But hive animals basically have infinite clone lives, and the queen is who matters, so suicide isn't the major decision it is for others, if individual bees even can decide. InedibleHulk (talk) 04:51, 28 November 2013 (UTC)


 * I definitely think some animals can be depressed. The most intelligent birds seem to be particularly susceptible, and I believe there is even a drug marketed to owners with depressed dogs.  However, many animals probably can't envision their own death, even if they are aware of the deaths of others. StuRat (talk) 11:31, 1 December 2013 (UTC)


 * In general, humans can talk and animals can't. That makes it all the more difficult to know what's in an animal's head. That doesn't mean human suicides are readily explainable all the time. But at least there's a chance. Some years ago I recall seeing some show about suicides on the Golden Gate Bridge. They had a couple of survivors, who both said that the moment they let go, they wished they hadn't. I expect a lot of suicides don't necessarily want to die, they just want the pain to go away. ←Baseball Bugs What's up, Doc? carrots→ 22:40, 27 November 2013 (UTC)


 * How come this is a very long thread but no one has given the answer that Wikipedia has an article on animal suicide?  Spinning Spark  09:08, 28 November 2013 (UTC)


 * Wow, thanks. I did not know that article existed.  I will take a look at it.   Joseph A. Spadaro (talk) 16:21, 28 November 2013 (UTC)


 * I have no doubt that we can come up with plenty of examples of animals who killed themselves - my example at the start of this thread (bees, stinging in defense of their hive) is one such situation. However, our OP has now stipulated that we must consider the motives and whether the animal fully comprehends the idea of death.  I can't imagine any way to reliably do that.  In the case of the dog who seemingly committed suicide by drowning itself - we don't know whether it thought that by staying underwater for long enough, it might become less depressed - or perhaps it would be able to sleep better or something.  Maybe it was just curious about what might happen if it resisted the temptation to breathe.  We truly cannot ever really know that.  Hence we cannot answer this (modified) version of the question...it's totally impossible. SteveBaker (talk) 15:01, 28 November 2013 (UTC)


 * Actually, the animal suicide article (referred to above) suggests otherwise. Joseph A. Spadaro (talk) 16:24, 28 November 2013 (UTC)


 * It's true that we cannot know for certain what an animal is feeling emotionally. We also do not know for certain what other humans are feeling, but the scientific principle of accepting the explanation that requires the fewest assumptions until forced otherwise by observation would lead us to assume that other humans feel emotions as we do ourselves whenever they exhibit behaviours or physiological responses that we would associate with a given emotion.  I believe others feel grief because I recognise the emotion I have felt myself.  Extending that principle to animals is merely sticking to scientific reasoning.  For instance, it is known that elephants appear to mourn dead relatives.  At one time, a typical scientist response to such suggestions would be "no, no, animals don't have emotions, they just act on instinct".  In more recent years it has become accepted that elephants do indeed feel grief..  Spinning  Spark  15:29, 28 November 2013 (UTC)
 * And seem to wrap their heads around vengeance and angst. InedibleHulk (talk) 01:01, 29 November 2013 (UTC)

Thanks, all, for the above input. It was very helpful. Much appreciated. Joseph A. Spadaro (talk) 14:42, 29 November 2013 (UTC)


 * The animal suicide article is basically synthesis heapt upon nonsense, and should be deleted if not better sourced. μηδείς (talk) 03:18, 2 December 2013 (UTC)

Is it a fact that ghosts are/aren't real?
In a discussion, a user argued that it is fact that there is no such thing as ghosts. Regarding the validity of this statement, is it a proven fact that ghosts do not exist? I understand that here are skeptics, but is there any hard evidence that they do not exist? Admiral Caius (talk) 20:27, 27 November 2013 (UTC)
 * It's hard to prove a negative.


 * We can say that there is absolutely zero scientific evidence for their existence - and that if they did exist, it would violate all manner of scientific principles that we believe to be well-established.


 * People keep attributing all sorts of qualities to ghosts that would make them undetectable (they are invisible, maybe they only show up to people who believe in them, maybe they are insubstantial, maybe...maybe, maybe)- this is probably an unfalsifiable hypothesis. The question you have to ask is that if there is no solid evidence of the existence of something - why would you believe in it instead of all of the other infinite number of things for which there is also no evidence.  Why would you believe in ghosts, but not (for example) believe my claim that there are families of purple piano-playing Aardvarks living in caves on the dark side of the moon?  If you (more reasonably) say that all unprovable things are equally likely - then there are a literal infinity of things that you'd have to believe in.  At that point, you realize that this is impossible - and the only logical way to proceed is to believe in none of them...until/unless some evidence appears to confirm them.  This is the essence of ideas such as Russel's teapot and Occams razor which, while not hard-and-fast rules, are never the less rational ways to proceed with you life. SteveBaker (talk) 20:39, 27 November 2013 (UTC)
 * Another interesting thought is that, if ghosts hang out where they died, you would expect a far greater density of ghosts in places like Rome, which have been heavily populated for centuries. So, I'd expect constant ghost sightings there. StuRat (talk) 20:51, 27 November 2013 (UTC)
 * Who says there aren't frequent sightings in Rome? ←Baseball Bugs What's up, Doc? carrots→ 22:24, 27 November 2013 (UTC)
 * If they were, say, 1000 times more common there than in newly populated areas, I'd think this trend would have been noticed. StuRat (talk) 08:07, 3 December 2013 (UTC)
 * A logical, scientific (mathematical, formal) proof needs a given system of Well-defined elements and rules for drawing conclusions. In law and juridiction an evidence is subject to being qualified by Court or judge in its worthiness and relevance. "In the area of oral and written communication such as conversation, dialog, rhetoric, etc., a proof is a persuasive perlocutionary speech act, which demonstrates the truth of a proposition." [cit.: Proof_(truth)].


 * I'm afraid, none of these apply for `appearances´ or other mental phenomena ;o])   You can also not give any `hard evidence´, that you like apples and dislike peers, just like proving an equation. .. Yet phenomena related to human brain are being studied, examined and explored and obvious or well funded statements be made about dreams, déja vu´s, hallucinations and many more. The words "proof, hard evidence, fact" do'nt make sense in terms of individual, subjective perception of non-physical things. --217.84.99.238 (talk) 13:51, 28 November 2013 (UTC) Senseful, reasonable proving in this way is - heaven thanks! - `ghostproof´. ;o]) --217.84.99.238 (talk) 14:06, 28 November 2013 (UTC)


 * A bridge for consent: the notion of "belief" applies very well. "In the areas of epistemology and theology, the notion of justification plays approximately the role of proof [..]" [cit.: Proof_(truth)] (justification of a personal or common belief). So, what is one´s `personal reality´ needn´t be another´s. Ghost can thus be part of culture, even though they don't exist. O.-o --217.84.99.238 (talk) 14:27, 28 November 2013 (UTC)
 * I don't think anyone disputes that the belief in ghosts exists. In the words of Philip K. Dick, "Reality is that which, when you stop believing in it, doesn't go away."  TenOfAllTrades(talk) 14:34, 28 November 2013 (UTC)
 * Ghosts that can observe our World without affecting it cannot exist. They would cause decoherence which can be detected. Experiments are being done to see if besides environmental decoherence there exists a fundamental decoherence. The results of these experiments also set a limit on the rate of information transfer between our World and the Ghost World. Count Iblis (talk) 21:46, 29 November 2013 (UTC)


 * If you take the time back and forth, parallel universes are created, if you returns the time on the dead person, and revival it by changing its course, you will apply a transparent effect in parallel for his body in this world. And some reference in science term are the many worlds theory. Thanks water nosfim


 * TV Tropes has some half serious questions and answers about ghosts here--Pacostein (talk) 18:21, 30 November 2013 (UTC)


 * I'm late to the party and the posters above have done an excellent job sounding erudite. As XKCD covered, though, yeah, for all practical purposes, we can be pretty damned sure that there are no ghosts that receive/emit light/sound or move objects within the developed world. Even Africa already has a phone in every third person's hand, but presumably it'll take a decade or so until most of them are camera-equipt. — Llywelyn II   16:05, 4 December 2013 (UTC)

Eating indigestible foods: what's the point?
As the title suggests, I want to find out what benefit the human body receives from eating foods generally seen as indigestible.

My reason for asking is that I'm quite curious as to why we consume foods such as Sweetcorn and Broad (Lima) beans, where we essentially see most of what goes in, "come out" pretty much intact.

Do we actually derive any nutritional benefit from foods we basically don't break down during the digestive process?

Thanks in advance for any help.

CharlieTheCabbie (talk) 22:02, 27 November 2013 (UTC)


 * See Dietary fiber. When I were a lad, this was the universal panacea for all known medical conditions, although medical opinion seems to have changed. Tevildo (talk) 22:21, 27 November 2013 (UTC)


 * Also note that what appears to come out undigested isn't necessarily so. Corn, for example, has an indigestible shell, and a digestible interior.  Since each corn kernel is open at the end, where it was ripped from the cob, the digestive juices get inside and remove the nutrients.  The reverse could also be true, where a food is broken down into a paste, but not digested, even though no sign of it is visible "at the other end". StuRat (talk) 00:32, 28 November 2013 (UTC)


 * Sort of seems like a waste to just throw away the bottle. InedibleHulk (talk) 04:59, 28 November 2013 (UTC)


 * Sweetcorn kernels only '"come out" pretty much intact' if you have swallowed them whole without chewing. Alansplodge (talk) 08:43, 28 November 2013 (UTC)


 * "The point" of eating food is not always nutritional, many foods taste good and provide a pleasant experience in their consumption. Corn certainly is good to eat, not so sure about broad beans. What is the point of meringues or sticky-toffee pudding or fried/toasted bread - I mean, all that hassle with dubious nutritional value? Richard Avery (talk) 14:19, 28 November 2013 (UTC)


 * Seems like someone needs to learn about properly chewing. Dauto (talk) 14:36, 28 November 2013 (UTC)


 * I do chew properly, but in a previous job I had a lot of contact with the "out" end of food, and it made me curious. Not everyone chews well, and it's quite possible to see faecal matter with seemingly undigested food in it.  It just lead me to question how it benefitted us.  Thanks anyhow.  CharlieTheCabbie (talk) 14:43, 28 November 2013 (UTC)


 * What lovely job was this ? StuRat (talk) 17:47, 28 November 2013 (UTC)


 * I used to work as a porter/assistant in a nursing home for the Elderly, and one of my jobs was to assist with cleaning out commodes, spraying off and washing bedsheets where residents had...well, I'll leave you to guess the rest. :) CharlieTheCabbie (talk) 21:19, 28 November 2013 (UTC)


 * Hopefully in your current job, presumably as a cab driver, most of the passengers don't leave any feces behind as a tip. StuRat (talk) 03:54, 29 November 2013 (UTC)

Killing animals with carbon dioxide
If I'm not mistaken, the UK Home Office approves the use of carbon dioxide for killing (some?) animals in certain circumstances. Is this considered humane? My understanding is that carbon dioxide build up is what causes the unpleasant aspects of suffocation, whereas nitrogen gas would be much more peaceful. Is it to ensure safety of the operators? --78.148.107.250 (talk) 23:46, 27 November 2013 (UTC)


 * Wikipedia has an article titled hypercapnia on the subject. If that doesn't answer your question, links and references in that article, or at least searching other media with that term, may help. - Jayron  32  00:06, 28 November 2013 (UTC)


 * I agree that it's not very humane. However, it does have the advantage that, if a little leaks out, it won't harm humans, whereas other poisonous gases certainly could, so require much stricter handling. StuRat (talk) 00:27, 28 November 2013 (UTC)


 * (EC, glad to see certain refdeskers responding who obviously have no idea what they're talking about.....) Yes, exposure to CO2 is a Schedule 1 approved method under the Animals (Scientific Procedures) Act. Although I personally normally prefer cervical dislocation unless working with large groups of animals, exposure to CO2 is a very effective method for sacrifice. In my experience with mice and rats, they are not particularly stressed, the key is the legally mandated slowly rising concentration. Animals will be somewhat agitated at first when put in the CO2 chamber, but will quickly become lethargic and drift off pretty peacefully. All this of course only happens when the concentration is correct. There are still unfortunately impatient people who use an excessive concentration, in which case animals will be far more agitated and stressed almost immediately. EDIT: above mentioned 'other poisonous gasses' are most certainly not allowed, as I mentioned, the main alternatives are cervical dislocation and injection of an overdose of drugs such as pentobarbital. EDIT2: also, the other consideration for using CO2 over cervical dislocation is whether neck/brainstem tissues need to be harvested intact for histology etc, as these get severely damaged in cervical dislocation. Fgf10 (talk) 00:38, 28 November 2013 (UTC)


 * See Animal euthanasia. It talks about concentrations and using anesthetics and a bit on nitrogen.  It would seem minimal agitation would mean both a minimum and maximum flow rate.  Also Inert gas asphyxiation has details. --DHeyward (talk) 00:50, 28 November 2013 (UTC)


 * Here in the USA, we mainly use captive bolt stunners (what, no article?) to slaughter animals. The advantage is, it kills the animal instantly -- like a bullet through the head. 24.23.196.85 (talk) 01:51, 28 November 2013 (UTC)
 * Redirect added. --Tardis (talk) 02:05, 28 November 2013 (UTC)
 * I'm pretty sure that's for cows and horses. Broilers, small rodents and pigs all use the anesthetic properties of CO2 at the correct flow and concentrations to limit hypercapnia responses.  For pigs, they are bled out while unconscious.  Broilers are sometimes stunned in an electrified bath.  Only male broilers are kept.  Females are destroyed. --DHeyward (talk) 03:21, 28 November 2013 (UTC)
 * One other point, I don't know of any animals commercially used for slaughter for human consumption are killed through any other mechanism than being bled out (except for wild game killed by hunters or farmers that use their meat for their own consumption). Stunning either by captive bolt, electric shock or CO2 merely render them unconscious.  The damage may be fatal but the animal does not die between stunning and slaughter.  Animals that are euthanized prior to bleeding out are generally not fit for human consumption. For example, a cow that stumbles out of a chute and breaks a leg 10 feet from the stunning floor will be euthanized by a vet and at that point (dead) is unfit for human consumptions.  The methods may eventually prove fatal but the goal is that the animal is alive and unable to feel pain when it is slaughtered.  Stunning is different than using method for euthanizing pests or injured animals but the goal of minimizing suffering is the same.  --DHeyward (talk) 07:45, 28 November 2013 (UTC)


 * This is a common question on Reference Desk, and often provokes misinformed answers. It is humane when done correctly.  The fact is, CO2 in low concentrations stimulates breathing with no ill effects (that's why it is used in in the mix with gas fire suppression in computer rooms and aircraft flight decks), at somewhat higher but low percentage concentrations causes distress that builds up over time, but at high concentrations causes pain-free and distress-free unconsciousness, followed by death.  The trouble with the hypercapnia article wrt this question is that it is written from the viewpoint of surviving abnormal CO2 concentrations, and stops at the 7% limit described in the article.  When CO2 is used to kill animals in abbatoirs, a higher concentration is used.  If the animals are removed to fresh air before death, they may recover consciousness with severe brain damage and be very distressed, but since the idea is to kill them while they are unconscious, this is not a problem.  Except that the main disadvantage of CO2, apart from the time required (a bolt fired into the brain is a lot quicker, as is electrocution) is that poorly run or poorly supervised abatoirs may not wait long enough for death to occur. 1.122.117.242 (talk) 01:02, 28 November 2013 (UTC)

So what is the actual mechanism behind the discomfort when you are unable to breathe? CO2, blood pH, something else? Thanks. Someguy1221 (talk) 01:15, 28 November 2013 (UTC)
 * See Hypercapnia --DHeyward (talk) 03:23, 28 November 2013 (UTC)


 * I've seen the article. It neither mentions the pain in the lungs nor describes the mechanism connecting CO2 concentration to any symptoms. Someguy1221 (talk) 07:45, 28 November 2013 (UTC)
 * Signs and symptoms list "panic" for certain levels. But you are correct the exact mechanism is not listed but the reference cited for it does.  Catecholamines increase with increasing hypercapnic acidosis.  This can trigger the panic fight-or-flight response in humans.  Inhaled CO2  has the same effect as metabolically produced CO2  which is like physical exertion or holding breath underwater. Respiration normally is driven by the need of the body to remove metabolic CO2  The body can adapt to gradual changes in CO2 up to 3-4% and still maintain the same blood pH.  Sudden changes though, can upset the buffer balance and pH too quickly.  The hormonal response is not just pH related as other types of acidosis such as lactic acidosis does not trigger the same hormonal response.  Respiration also naturally decreases during sleep which causes dissolved blood CO2 to rise but the buffer process normally maintains the pH.  The concentration of C02 in the blood while asleep is similar to raising the atmospheric level to 2%  while awake (from the natural level of 0.03%).  I don't know if this is the narcotic effect.  --DHeyward (talk) 09:38, 28 November 2013 (UTC)
 * I think the OP is right, it has more to do with the safety of the people performing it: With nitrogen you get no warning signals, with CO2 you do. If "humane" was the main criterium, one wouldn't choose the one gas that alerts the body of asphyxia. Ssscienccce  (talk) 11:19, 28 November 2013 (UTC)
 * See here for some NIH guidelines.
 * As hinted there, there are some studies on the usage of various agents, trying to ascertain what methods are effective while least likely to cause distress, in the case of gases as some others have mentioned, this includes stuff such as flow rates, whether to prefill the chamber etc (or  from 1994). Remember also that if the animals are intended to be studied after death, you also need to avoid anything which will affect what will be studied . You also have to consider the risks of non perfect application, particularly with methods like cervical dislocation which require a fair degree of skill.
 * As with many things, without decent research you need to be careful about assuming what applies to humans will apply to other animals, particularly ones more distantly related or physically and physiologically different. For example, nitrogen doesn't actually appear to be effective for rodents, or at least rats . Argon is better, but still appears worse than carbon dioxide . There is a trend towards anaesthetics gases to replace carbon dioxide but as this source hints at but there's still some uncertainty over the effect of anaesthics.
 * Note, as mentioned in one of the earlier sources, sometimes methods may be combined or this may even be the recommendation, for example anaesthetic agents or carbon dioxide exposure followed by cervical dislocation.
 * BTW my response in 2012 Reference desk/Archives/Science/2012 February 13 may be of interest here, note that although the original question concerned baby mice where carbon dioxide is not recommended by most guidelines, my response largely concerned adult rodents, where it still often is considered acceptable.
 * P.S. Rereading my 2012 response, I was reminded about one thing which the sources I provided here also demonstrated. There does seem to be an assumption in some sources that if the method takes to long, it's not humane. Whereas arguably it's more important to try and ascertain discomfort and pain.
 * Of course if there is some discomfort, then the length of time will come in to play and you will ultimately get in to complicated questions over whether it's better to use a method which causes a relatively slow death with some minor discomfort or pain versus a method which causes a relatively quick death but greater level of discomfort or pain.
 * Tying this back in to what I said earlier, you may also have to consider whether to use a method with no discomfort 999 times when it goes right and major discomfort/pain the 1 time it goes wrong. (Of course trying to determine such statistics and determine the level of pain when things go wrong is going to be even more difficult than the generalised case, particularly for something like cervical dislocation.)
 * Nil Einne (talk) 12:49, 28 November 2013 (UTC)
 * They seem to use effective as a synonym for fast-acting, or efficient. Since in all three cases no oxygen is present, one could argue that with CO2 and argon the animal may be experiencing more stress causing it to expend its oxygen reserve more quickly.  Ssscienccce  (talk) 13:55, 28 November 2013 (UTC)
 * Indeed, it's ridiculous that the [abstract] (I don't have access to the full text) states that the nitrogen caused unconsciousness and death and then states that nitrogen was ineffective. They also say that the couldn't assess the distress of the rodents but I think it's telling that nitrogen didn't increase MAP or HR. 129.215.47.59 (talk) 14:26, 28 November 2013 (UTC)
 * I'm very surprised those studies used pre-filled chambers. That's always been a big no-no in any place I've ever worked. It causes far more distress to the animals. Fgf10 (talk) 15:51, 28 November 2013 (UTC)


 * The main advantage of CO2 over nitrogen is that it's heavy. So you can pipe some into a chamber with some mice at the bottom, let air escape from a tube at the top, and be pretty sure there are no unstirred voids of room air remaining inside it.
 * Some time ago from curiosity I tried breathing the CO2, which at first on its own as a gas (as in the chamber or in a soda bottle) just produces a "tired from exercise" feeling with the usual visual fireworks. Of course, I don't know how it goes all the way down the tunnel!  Breathing CO2 fog from a dry ice bucket through the nose produces an altogether different, unpleasant "soda up the nose" sensation, but it is, well, no better or worse than any time I've had soda go up my nose.
 * The main issue with mouse euthanasia, in my opinion, is that it is impossible to underestimate the resilience of fetal mice or newborn pups to asphyxiation, under conditions where adults die right away. You can assume they're dead after half an hour "not breathing" and find out you're wrong.  Personally, I favor the idea that after you're "sure" they're dead you crush them utterly (which isn't hard) to be positive about it, but I'm in no position to advise you. Wnt (talk) 22:07, 1 December 2013 (UTC)

Human genetics and prehistoric movement in East Asia
Could some of you guys with a background in genetics stop by Yangtze River and look over a study someone posted? It seems like the Chinese scientists involved are trying to prove an awful lot from a few corpses and (especially given the page gets 1k–2k views a day) I'm curious how justified they are in some of the abstract's assertions. — Llywelyn II   16:11, 4 December 2013 (UTC)