Wikipedia:Reference desk/Archives/Science/2013 April 16

= April 16 =

World population of brown rat
What is the global population of brown rat? --Yoglti (talk) 01:49, 16 April 2013 (UTC)
 * Brown rat doesn't seem to have totals, but you can infer some things from the article, i.e. the estimated ratio of rats to humans. ←Baseball Bugs What's up, Doc? carrots→ 02:14, 16 April 2013 (UTC)

How are subatomic particle conceptualized?
If they cannot be seen through the most advanced electron microscope, how are they discovered? How are their properties known? How atomic structure known when it cannot be seen? --Yoglti (talk) 02:37, 16 April 2013 (UTC)


 * See electron, proton, and neutron, for starters. Someguy1221 (talk) 02:52, 16 April 2013 (UTC)


 * If I hit you in the back of the head with a baseball bat, you know roughly what happened, even if you didn't see me do it. There are ways of extracting information from the world that do not involve your eyes.  To answer the question a bit more seriously, the best way to think about this is a combination of geometry and quantum mechanics.
 * 1) We know that atom consists of a dense, highly packed nucleus and a diffuse area occupied by electrons thanks to the contributions of Ernest Rutherford and his gold foil experiment. Rutherford had a theoretical basis in models developed by Hantaro Nagaoka.
 * 2) We know that electrons cannot be physically orbiting the nucleus like a planet orbits the sun, because according to classical mechanics, such particles should be shedding energy all the time (per the Larmor formula), and thus spiraling in towards the nucleus. We know that the atom is stable (that is, electrons don't spiral into the nucleus), so they can't work like that.
 * 3) We know that energy is quantized (that is, energy must exist in discrete amounts, not as a continuum of values) because of the ultraviolet catastrophe.
 * 4) Thus we know that electrons must exist as a particle "smeared out" in space, and whose energy can only have certain values. Those values are based on a set of integer values known as the quantum numbers, and if you feed those integers into the correct equations (known as wavefunctions, or the Schroedinger equations) you get geometric shapes which define the regions in space around the positive nuclei which are where the electrons are.  Now, conceptually, you can think of an electron as either a) a three-dimensional standing wave anchored at the nucleus and shaped like these orbitals or b) a probability distribution graphed on a three dimensional graph with the nucleus at the origin.  Either or both explanations fit with the basic theory of what an electron is and how it behaves.
 * 5) This mathematics is weird insofar as the kind of physics it describes does not in any way match how any object behaves that your senses are used to working with. That is, what happens at the atomic level simply does not work like anything your senses have experienced.  We have various models of atomic-level behavior that attempt to make analogous pictures so we can tie in behavior to experience, but these are all to varying degrees wrong (but then again all models are wrong, some are useful.) These various models, such as VSEPR theory, hybridization theory, atomic orbitals, molecular orbital theory are quite useful in describing how atoms interact with each other to produce the geometric shapes that experiments tell us that they have when they do so.
 * Hope that helps some. -- Jayron  32  04:47, 16 April 2013 (UTC)
 * If somebody hits you on the back of the head with a baseball bat and you ever know what happens, he had better not get a place on the team! Wnt (talk) 21:28, 16 April 2013 (UTC)
 * Sub-atomic particles can be detected with equipment such as cloud chambers, bubble chambers and other devices listed in Category:Particle detectors. Gandalf61 (talk) 07:52, 16 April 2013 (UTC)


 * At some level, you also have to ask, "what's so special about seeing?" Seeing just means your eyes are receiving photons (yet another subatomic particle) bouncing off of other things. It's just another means of detection, one that itself has its downsides (you can only see in a very tiny range of the electromagnetic spectrum, for example). Does one completely lose the ability to perceive the world when one's eyes are closed, or when one is blind? --Mr.98 (talk) 11:49, 16 April 2013 (UTC)


 * As a general rule you can't really "see" most sub-micron particles either (everything from large colloids, to proteins and polymers, and most small molecules fall into this category). For reference 1 micron = 1000 nm = 10000 angstroms, where your typical atom is on the order of an angstrom, thus by definition a sub-atomic particle is at least 10,000 times smaller than the smallest thing we can resolve optically.  There are however plenty of non-controversial methods for detecting things we can't see. (+)H3N-Protein\Chemist-CO2(-) 12:58, 16 April 2013 (UTC)
 * A necessary clarification is that I'm referring specifically to optically resolvable phenomena here. I wouldn't count scattering and diffraction as "seeing", but they are examples of "non-controversial methods for detecting things we can't see".  (+)H3N-Protein\Chemist-CO2(-) 13:03, 16 April 2013 (UTC)

Inter-species sexual attraction
I noticed the discussion Reference_desk/Science, a thought came into my mind. We known some species are sexually attracted to another species, this makes hybrid animals possible. For example, a zebra may be sexually attracted to a member of another species. This makes Zebroid possible. A male donkey may be sexually attracted to a female horse. If inter-species attraction exists in nature, why humans are not sexually attracted to a gorilla or a chimpanzee? --Yoglti (talk) 08:18, 16 April 2013 (UTC)


 * They're not? --TammyMoet (talk) 10:22, 16 April 2013 (UTC)


 * Bestiality is what it's called. However normal people find non-humans distinctly unenticing.  If you think you might like it with a gorilla, which would most likely think you are as ugly as you think he/she is, there's probably something in the DSM (http://en.wikipedia.org/wiki/DSM-5) to cater for you - if not, there should be.  Wickwack 120.145.25.214 (talk) 10:28, 16 April 2013 (UTC)


 * As for the possibility of hybrid, see humanzee. --Mr.98 (talk) 11:56, 16 April 2013 (UTC)


 * I also don't think that mules or zebroids are common in nature; they primarily come about in captivity. Consider the teals. In captivity, a green-winged teal and a blue-winged teal can successfully breed, especially if they have no conspecific mates available. But in the wild they do not tend to not interbreed, presumably because sexual selection usually works to keep reproduction occurring only between very similar mates. So, to answer your question, I think you are inferring the general from the specific. Just because something can occur does not mean it is common. And I'm sure you could find at least one human person that reports sexual attraction to chimps. SemanticMantis (talk) 15:27, 16 April 2013 (UTC)
 * Do the chicks come out as teal-winged teals? --Trovatore (talk) 18:22, 16 April 2013 (UTC)
 * Ha, no, still green, at least this for this one . But a clutch of hybrid siblings will show a lot of variety, so some might have more teal coloring. SemanticMantis (talk) 19:34, 16 April 2013 (UTC)
 * Who is that person? --Yoglti (talk) 15:51, 16 April 2013 (UTC)
 * Resembles a cow. ←Baseball Bugs What's up, Doc? carrots→ 21:31, 16 April 2013 (UTC)

Changing species through genetic engineering
Is it possible to change the species of an organism through genetic engineering? --Yoglti (talk) 08:19, 16 April 2013 (UTC)


 * You may be interested in the definition of species, "a group of organisms capable of interbreeding and producing fertile offspring". Naturally, two species are different if their members are unable to breed and produce fertile offspring with one another. Genetically engineering an organism to be incapable of interbreeding with its original species, but still capable of breeding with other genetically modified organisms, is given a theoretical treatment in this paper, specifically the section on "extreme underdominance". Such a thing could be considered a new species, by definition. Genetically modifying an organism to be capable of breeding with an existing and distinct species (such as creating a dog that can breed with a cat) is a much more difficult proposition. Such a feat would basically require overcoming reproductive isolation. For very closely related species, this may be doable, but for distantly related species, the reproductive barrier is likely near impassible. Someguy1221 (talk) 08:55, 16 April 2013 (UTC)
 * I would say yes. I can't provide a reference, but only personal experience. Humans regularly turn into Trolls. --Onorem♠Dil 16:02, 16 April 2013 (UTC)


 * Quick question: Is HeLa still a member of the Homo sapiens species? 64.56.89.2 (talk) 17:46, 16 April 2013 (UTC)


 * One method is by making paracentric inversions or balanced translocations. If you have enough of these in your new lineage, it should be difficult if not impossible for it to interbreed with the original.  After that, you just have to make it look cool. :) Wnt (talk) 18:01, 16 April 2013 (UTC)
 * HeLa specifically addresses the HeLa species question. Vespine (talk) 23:21, 16 April 2013 (UTC)
 * Yeah, but unfortunately it gets it wrong by overemphasizing a silly suggestion by a single researcher. Chimeric human cell lines are not distinct species, and no nomenclature organization has accepted the notion that "Helacyton gartleri" is a species. - Nunh-huh 01:19, 18 April 2013 (UTC)

Orbit
According to Prime meridian, "Satellites changed the reference from the surface of the Earth to its center of mass around which all satellites orbit regardless of surface irregularities." Is that right? Would a satellite really orbit around the centre of mass of an irregular object? I understand that for perfectly spherically symmetrical objects the mass can be considered concentrated at the centre, but I thought there was no similar simplification for irregular bodies. 86.176.213.231 (talk) 11:46, 16 April 2013 (UTC)


 * See Center of mass, and Barycentric coordinates (astronomy). An orbiting body will be perturbed throughout its orbit by an irregular mass, but once you get far enough away, those irregularities in the gravitational field start to smooth out and the force is pretty much constant in the direction of the center of mass. 38.111.64.107 (talk) 11:54, 16 April 2013 (UTC)


 * In the context of that section, which is talking about centimetre-scale precision, I doubt that "pretty much" is good enough... 86.176.213.231 (talk) 11:58, 16 April 2013 (UTC)


 * Correct, which is why anything meant to stay in orbit for a long time has station-keeping abilities. However, the center of mass will certainly be the largest contributor to the orbit - the irregular distribution will perturb it from that orbit, but it makes a lot more sense to try to maintain an orbit around the center of mass than the center of the Earth. — Preceding unsigned comment added by 38.111.64.107 (talk) 12:07, 16 April 2013 (UTC)


 * Oh right, when it says "around which all satellites orbit" do you think it means that satellites are maintained in such an orbit using regular corrections, rather than that they will naturally maintain (exactly) such an orbit? If so, I think I will change the article to try to make that clearer. 86.176.213.231 (talk) 14:05, 16 April 2013 (UTC)


 * To first order, the satellite's orbit will naturally form an ellipse, one focus of which is at the centre of mass. Instability of the orbit is caused by second order effects which are due to the fact that the satellite is not actually a point mass. Gandalf61 (talk) 15:35, 16 April 2013 (UTC)


 * You meant that the Earth is not a point mass, not the satellite, right? --140.180.241.109 (talk) 16:25, 16 April 2013 (UTC)


 * Both. Tidal forces will apply to the satellite - consider that the far side of the satellite and the near side are forced to orbit at the same rate, even though a point in orbit at the far side should take slightly longer to complete an orbit than one on the near side. Interaction from other bodies such as the moon and sun also causes disturbances. 38.111.64.107 (talk) 17:49, 16 April 2013 (UTC)

Identification query: blue mushroom in the PNW
Here's a photo making the rounds on the interwebs, originally from a Seattle-area blogger. One tag might indicate it grows in the Pacific Northwest. I'd like to know its name, and also whether those blue-green colors are natural or were camera-enhanced. -- Deborahjay (talk) 14:17, 16 April 2013 (UTC)


 * It's a Trametes versicolor - and our article shows examples with all sorts of colors. SteveBaker (talk) 14:44, 16 April 2013 (UTC)

mathmetics
how we can say that 1 by infinity is equal to 0? — Preceding unsigned comment added by ARIF MIKAT (talk • contribs) 14:51, 16 April 2013 (UTC)


 * The limit of 1/x for x to infinity is zero. This means that for any small number epsilon, you can always find a number y such that for all x larger than y you are closer to zero than epsilon. You can easily that y can be chosen 1/epsilon. So, no matter how small you make epsilon, for large enough x, you will be closer to zero than that epsilon. Count Iblis (talk) 15:11, 16 April 2013 (UTC)


 * Or...you have one cake, using a very sharp knife you divide it equally amongst an infinite number of people, it's pretty clear that they each get no cake whatever. The tricky question is: "Where did the cake go?" SteveBaker (talk) 16:01, 16 April 2013 (UTC)
 * I wouldn't say that was in any way "clear"... 86.129.16.178 (talk) 17:00, 16 April 2013 (UTC)


 * I'll try to make it clearer for you. Your statement is incorrect - you mean to say that the limit of 1/x, as x approaches infinity, is zero.  If you don't understand limits, i'll dissect each part for you.  A limit is the value of an equation as the x variable approaches a specified number.  If I say that x is approaching infinity, then I'm really asking, "What is the value of this equation as x gets larger and larger?" How large is it getting? Really large.
 * So let's say we plug in 10 for x. 1/10 is .1.  Now let's say we increase X so that X is now 100. 1/100 is .01.  Let's say that we increased x even more, so that x is 100,000.  Well, 1/100,000 is .00001.
 * It can be seen that as we make x larger and larger (as x approaches infinity), the value for the equation is getting smaller and smaller - it's approaching zero. It doesn't become zero, but rather approaches zero.  So the limit for 1/x as x approaches infinity is zero. -- Jethro   B  19:08, 16 April 2013 (UTC)
 * P.S. Limits are crucial for calculus and the definition of the derivative. Calculus itself is important for many fields of life, and can actually be a lot of fun if you understand the few basic concepts that it has (except some integrals, those can be killers). -- Jethro   B  19:10, 16 April 2013 (UTC)


 * I think the fact that they are killers IS what makes them fun. (never shy away from a puzzle). Dauto (talk) 20:01, 16 April 2013 (UTC)
 * Don't get me wrong - I love puzzles! One of the things I love about calculus is that you sometiesm need to piece together several concepts to answer just one question.  If you're familiar with the AP Calculus AB course, for example, there are really only about 10 or so concepts in the calculus course, and the rest is just applying these concepts.  For the Calculus BC Course, it's mainly applying these concepts some more, with about 2 new concepts.
 * However, there are year-long courses just on solving integrals, since there are so many types of integrals that have different ways to solve them. When you first learn just a few types, and you get an integral that you need to rearrange somehow or change the integrand somehow and then solve, it's a fun challenge.  But when you need to recall which way out of so many different ways is necessary for solving that integral, it can get tedious! Or use Wolfram Alpha, shh!!!
 * That's a bit of a tangent though (see what I did there?) -- Jethro  B  01:26, 17 April 2013 (UTC)


 * One could say that 1 by infinity is an infinitesimal - some amount of cake that is less than any positive real amount of cake, but more than zero (which is where the cake goes). But this really should have been filed under WP:Reference desk/Mathematics ! Wnt (talk) 21:25, 16 April 2013 (UTC)


 * Prove that an infinitesimal is a nonzero number. Plasmic Physics (talk) 08:45, 17 April 2013 (UTC)
 * This just makes me think of people attempting to reject the idea that 0.999999999999999999999... is equal to 1. Nyttend (talk) 11:54, 17 April 2013 (UTC)


 * In case you're implying it: I'm not rejecting that idea. Plasmic Physics (talk) 12:03, 17 April 2013 (UTC)
 * Oh, no, I'm sorry; I meant that the limit-related explanations given to the original question sound like some of the proofs for 0.9999999, since both are proving that number A is equal to number B although none of the numerals in A are in B. Neither one sounds right, and I still have to fight my inclination to think of 0.9999999999 as being less than 1.00000000000.  Nyttend (talk) 12:51, 17 April 2013 (UTC)
 * See here and here. Count Iblis (talk) 13:17, 17 April 2013 (UTC)
 * To be clear, I'm leaving this one up to the article. If you can resolve the point either way, by all means, cite your sources and add to it.  Infinities are one aspect of mathematical philosophy that tend to arouse particular suspicion.  There are so many things you can do with them that make perfect sense until they ... just ... don't. Wnt (talk) 15:04, 17 April 2013 (UTC)


 * In addition to the obvious mathematical flaw of "1 over infinity" as if infinity were a number... there is also the fact that there cannot possibly be an infinite number of people or of any organism... and that there is not an infinite quantity of molecules in any cake, no matter how large it might be. Even the standard phrase in limit theorems, "as x approaches infinity", is misleading. You can't "approach" infinity. It should be "as x gets larger and larger" or some equivalent phrase. ←Baseball Bugs What's up, Doc? carrots→ 15:08, 17 April 2013 (UTC)
 * Since maths, like geometric figures, are essentially abstractions, I don't think it matters whether or not there are infinite numbers of atoms or other objects. Perfect points, lines and circles can also be said to not exist in reality at all, yet these are very useful abstractions. Although infinitesimals are not comparable quantities (these are non- Archimedean), a sum of zeros is merely zero, but any sum of infinitesimal intervals can equal an interval: in the same sense that an infinite tree with one root can be subdivided into partitioned nodes of smaller fractional quantities an infinite number of times: {1,(a+b=1),(c+d+e+f=1),...}. With .999..., we have a very shallow tree with but one level of subdivision, although it has an infinite number of nodes: {1,(.9 + .09 + .009 + ... =1)}. It is a mistake, IMO, to claim that dividing any nonzero quantity an infinite number of times, as with the tree structure, that one will only obtain zeros though, which perhaps can be better understood with the Cantor set. With the construction of this set, there are two different entities; an infinite set of discrete points (each of these points has exactly zero width, of course, recall that any sum of zeros is zero) and a sum of excluded nonzero intervals which sum to the entire length of the original interval.  -Modocc (talk) 22:09, 17 April 2013 (UTC)


 * 1/infinity is typically undefined, but repeating the above answers: it can represent an infinitesimal and, moreover, it is only the limit of 1/x, as x approaches infinity, that is equal to zero. --Modocc (talk) 22:09, 17 April 2013 (UTC)

I think we did this one not long ago on the math refdesk. Here's one possible answer: Suppose you treat a cake as a subset of Euclidean 3-space (it isn't, of course, but if you want to make this into a math question you're going to have to make some accommodations.)  Then what happens if you partition the cake into infinitely many identical pieces (say "identical" means one piece differs from the other only by a rigid motion)?

Well, if you cut it into countably infinitely many pieces, then the answer is, none of the pieces can be Lebesgue measurable. So the "pieces" are of such an unwieldy form that you cannot say how much cake is in a given piece. You can cut it into measurable pieces if you have an uncountably infinite number of cake-eaters, and in that case they might be measurable (depends on some other things), but the measure of each piece is zero. So each person gets some cake, but so little that it has precisely zero volume.

Hope this helps. --Trovatore (talk) 22:26, 17 April 2013 (UTC)


 * This does not make a whole lot of sense to me (I've a computer science background thus my use of a tree data structure). If you add volumes which are precisely zero volume, then certainly these sum to zero volumes which sum to a zero volume (of cake). Or not?-Modocc (talk) 22:56, 17 April 2013 (UTC)
 * Well, this mathematical cake is composed of points, right? Specifically, cardinality of the continuum-many points.  $$2^{\aleph_0}$$ points.  What's the volume of a point?  It's zero.  But put them all together, and you ahve the whole cake. --Trovatore (talk) 00:46, 18 April 2013 (UTC)
 * Aye, but not because this makes any more sense to me though. ;( With the Cantor set, an abstract mathematical cake could be made from it. But it is the excluded intervals that sum to the original interval's length (or, in 3d, the cake's volume) and not the sum of its points (again, these have zero widths and therefore sum to zero). The mathematical cake of points does not represent the intervals, volumes or quantities which must be summed, thus the mistaken summation of what ought be zero quantities instead leads to the unintended doubling of the original interval/volume, as with the Banach–Tarski paradox. -Modocc (talk) 03:36, 18 April 2013 (UTC)
 * Well, vaguely like that, I suppose. But Banach–Tarski is a lot more troubling intuitively because there are only finitely many pieces.  Even countably many pieces means you run into trouble if you expect to expect them to be Lebesgue measurable, because Lebesgue measure is countably additive.  But with uncountably many pieces, all bets are off (though you might get some uncountable additivity depending on certain set-theoretic questions, but I've already taken you pretty far afield so I won't go there unless you ask). --Trovatore (talk) 03:57, 18 April 2013 (UTC)
 * Let's suppose you have a cake, or whatever object, that's of finite size but is somehow "solid". Or, to conceptualize it more practically, image a finite volume of empty space, and say you're going to allocate the space to a number of persons as if it were a cake. If it's 1 person, he/she gets the whole thing. If it's 2 persons, they each get half (1/2). If it's 3, they each get 1/3. And so on. The larger "n" gets, the smaller each portion "1/n" gets. "n" can never "equal" infinity, but it can "approach" (so to speak) infinity, i.e. it can get larger and larger. ←Baseball Bugs What's up, Doc? carrots→ 23:37, 17 April 2013 (UTC)


 * If 1/0 = infinity (or negative infinity) then 0 * infinity = ? Well, this is why it's crazy philosophy.  At least Trovatore gave us a link to read.  And what he said makes some sense - if you pick a particular slice, even from an infinite number of slices, you're counting it, and if it is spread over an uncountably large number of recipients then there will be none of the infinitesimal left. Wnt (talk) 23:33, 17 April 2013 (UTC)


 * I heartily agree each slice is and should be counted. :-) I do not quite understand as to what is being counted though with zero volumes. To count "infinitesimal" zeros seems to be not very rigorous at all. Either we are adding together zeros or not (perhaps there is some alternate way of interpreting zero volume). In any case, counting the infinite number of infinitesimal nodes that result from an infinite partitioning, (as with (.9 + ,09 +...)), but where the numbers get infinitely small as one progresses into the tree... well at least I can comprehend a summation of such infinitesimals (because each node must become infinitely small by definition); this kind addition makes sense to me no matter what the data is representing, whether it be volumes, mass or an arbitrarily large number of nonzero likes. -Modocc (talk) 23:56, 17 April 2013 (UTC)


 * Isn't f(x) = x/inf a non-injective function? Take this for example: f(x) = sin (x) → x = {arcsin (f(x)) + 2kπ|for k E Z}. Plasmic Physics (talk) 04:34, 18 April 2013 (UTC)


 * Notice: that function is only injective, if the k term is introduced. Plasmic Physics (talk) 04:52, 18 April 2013 (UTC)


 * Here is a link to the previous recent discussion on a similar question (I think its the one Trovatore is referring to above). -Modocc (talk) 00:41, 18 April 2013 (UTC)

Main Battle Tank
How can the crews of Leclerc tanks extract the ammo which is not in the autoloader (from inside the tank or outside the tank like T-72) I asked this question before but I think the one who answered me did not notice that I was asking about Leclerc also not only T-72 so he answered : from outside   Tank Designer (talk) 20:13, 16 April 2013 (UTC)


 * Here's a forum discussion (at the very bottom) that explains(?) the procedure from inside. On the top of the next page, it goes into a bit more detail, but the linked photos are blocked. Clarityfiend (talk) 00:59, 17 April 2013 (UTC)


 * Here's a more-convincing-sounding and easier-to-understand explanation from someone claiming to be a French tank commander. Search for 09:37 (reloading from outside), and 09:39 and 09:44 (theoretically from inside). Clarityfiend (talk) 01:17, 17 April 2013 (UTC)

Thank you very much Tank Designer (talk) 08:00, 17 April 2013 (UTC)

Planck microwave background data
I notice that the Planck microwave background data shown in isn't in our article yet (neither Planck (spacecraft) nor Cosmic microwave background radiation). There is an image at but it is unsatisfying for a few reasons:  the left edge is cropped off, and weirdly, when I click on "view image" (and presumably when I save it) I go from a reasonable-looking graphic to one that is slightly smaller with obvious jpeg damage. Above all, however... this time I want more than just one single Mollweide projection - I want the data itself, with the full spherical accuracy available, viewable from every possible perspective. That way if, say, I am hallucinating, say, a giant pentagram centered somewhere around 45N 5E, I can (in concept, at least, and ideally by some practical means) rotate to look straight up at it. So ... what options are available for actually seeing this data? Wnt (talk) 22:05, 16 April 2013 (UTC)


 * I haven't actually done it, but you should be able to download the data from here and then use a HEALPix viewer like SkyViewer. -- BenRG 00:31, 17 April 2013 (UTC)
 * The player works, and I found the map .. but the download is 1.7 GB! I may not actually look at it right this minute, but thanks! Wnt (talk) 15:02, 17 April 2013 (UTC)