Wikipedia:Reference desk/Archives/Science/2016 August 14

= August 14 =

Request of book suggestions for neuroscience/neurology
Hello. I am interested in learning about the human brain and nervous system in general. I am especially interested in the low level details, specifically the molecular biology aspect of neuroscience and psychopharmacology. Could you please suggest relevant books?.

Relevant background: I am accustomed to reading scientific literature of life sciences (I wrote a big part of skin whitening; my addition includes pharmacology and molecular biology. Here is a relevant edit.). My knowledge about neuroscience is limited and comes mainly from reading scientific papers about psychoactive drugs and some books written for clinical practitioners. I am looking for something with more focus on theory and scientific background compared to pragmatic application than books of this type. I have read a part the following books:



Regards and thanks in advance. Mario Castelán Castro (talk) 00:28, 14 August 2016 (UTC).


 * To begin with, I assume but should make sure you're familiar with PubMed. From PubMed you can get papers, many of which are free.  For an interlibrary loan of the others there's Sci-Hub and Libgen.  Of course The Pirate Bay and such proper torrenting sites may be of some value to those more interested in university-style textbooks.  My feeling is that choosing a specific textbook is a little more iffy - I think people are more often moved by practical concerns than objective cost-is-no-object universal assessments, because few people really obtain and read all the different textbooks, though professors can get a lot of free stuff from publishers trying to make their students pay as much as possible.  Still, you can go and look for coursebooks on university sites like  and that should give you an idea; just pick a university and see what they like.


 * Thanks. I was aware of the existence of those resources. I was looking for specific book recommendations. I will take into account your suggestion of looking into university coursebooks. Mario Castelán Castro (talk) 16:29, 15 August 2016 (UTC).


 * If you want to gain a broad knowledge base (and don't mind spending some money), perhaps a good recommendation would be Principles of Neural Science, which is widely used for first-year courses for graduate students in neuroscience. Looie496 (talk) 15:52, 16 August 2016 (UTC)

The concept of species
At school, I was taught that two living creatures belonging to different species could not produce fertile offspring. Thanks to Wikipedia, I have learnt it's not true at all. Ligers are not sterile, and there are some case of fertility even between hybrids whose parents belong to different genera (e.g. beefalo) or even to different (sub)families. (e.g. wholphin). I think the concept of species should be dramatically revised. Is there any scientist who has proposed such a thing? Thanks in advance.--Carnby (talk) 09:12, 14 August 2016 (UTC)


 * The definition you cite is only one of over 20 (I think) which scientists have proposed or actually use in various contexts, and is the first one taught in schools because it is the simplest and easiest to grasp: however, it is an over-simplification if not actually a "lie-to-children" – that is, it's not actually true when examined in detail, but provides an initial foundation for the later learning of much more complex ideas which may be closer to the truth.
 * Read our article Species (and follow up some of the links from it) to find out about some other definitions. {The poster formerly known as 87.81.230.195} 2.123.26.60 (talk) 09:30, 14 August 2016 (UTC)


 * What will really cook your noodle is when you read on about ring species. :)
 * There are actually a fair number of species separated by hybrid zones. The key thing about maintaining multiple species is that interbreeding doesn't have to be impossible, just disfavored in evolutionary terms.  If you have two types of butterflies, each of which mimics a butterfly that has a bitter taste, then those two types are OK but mixing them leads to deaths, so they may stay separate.  (But their genes for color may also get shuffled together into a small pile called a supergene so that when they do interbreed, the odds of having one of the survivable color patterns is better than average)


 * An interesting consequence of the ability of so many species to hybridize is that if the environment suddenly changes and no species is well-suited to any niche, such as if you warm the planet, cut down the forests, build roads everywhere, plant crops and dumpsters at key locations etc., then they can get together and hybridize without penalty. This gives them much greater diversity, hybrid vigor, and the ability to produce hybrid species.  This is going on all over the world now and the resulting invasive species are better suited to fight back against humans.  I think we may find the creation of new species is more of a problem to us than the extinction of so many old ones. Wnt (talk) 12:28, 14 August 2016 (UTC)


 * Teaching the kids that cross-species can't produce fertile offspring could be a subtle way of teaching Creationism and denying Evolution. ←Baseball Bugs What's up, Doc? carrots→ 15:36, 14 August 2016 (UTC)


 * That's nearly as bad as teaching them that "good" and "evil" do not coincide with "agree with the current national sentiment" and "disagree with the current national sentiment". --Stephan Schulz (talk) 15:55, 14 August 2016 (UTC)


 * Bingo. :) ←Baseball Bugs What's up, Doc? carrots→ 16:01, 14 August 2016 (UTC)


 * Could it be also to avoid possible racial problems, given human beings of all ethnic groups crossing themselves are able to produce fertile offspring? Breaking the basic concept of species could make someone think all human beings do not belong to the same species...--Carnby (talk) 09:27, 15 August 2016 (UTC)
 * On the other hand, unless my biology is way off, Donald Trump and I won't be able to produce offspring (and I'm very much not eager to try). I hope that means we are not the same species! --Stephan Schulz (talk) 12:08, 15 August 2016 (UTC)
 * Ha ha. The overly simplistic definition doesn't say that all organisms of the same species can interbreed; humans are hardly unusual in having male and female for reproduction.  Robert McClenon (talk) 17:56, 15 August 2016 (UTC)
 * The concept of a species is even more difficult to define in organisms that reproduce asexually. There the offspring are genetically identical to the parent, except for random genetic mutations.  So, what level of mutations need to accumulate before we call it a new species ?  Should we just pick an arbitrary amount of DNA in common for two organisms to be considered the same species ? StuRat (talk) 17:45, 14 August 2016 (UTC)
 * I agree that the concept of species is difficult when applied to organisms that reproduce asexually. A blatant example of what I think is a false species is E. coli, in which there are many so-called varieties (or sub-species) that have very different implications for humans, many being essentially commensal or even mutualistic, but a few of them being pathogenic and so either very amensal or parasitic.  Robert McClenon (talk) 17:56, 15 August 2016 (UTC)


 * I don't see a link yet to species problem, which is what this is really about. All Wnt's good links are related, but this is the top-level concept. SemanticMantis (talk) 14:58, 15 August 2016 (UTC)


 * The two simple answers to User:Carnby are that, most importantly, "species" is a concept, biological species concept, and concepts are tools used by humans to understand reality; they do not impose rules on reality (although they may closely reflect reality).
 * And secondly, that what is important is gene flow between populations. Two species may hybridize along a band where they meet. (I know this happens with a European and a Eurasian pair of crow species in Eastern Europe, yet they remain distinct.) The offspring may also be fertile.  But the offspring may be relatively maladapted, not as large, say, as the Eastern species, hence poor hunters of the local food, and not as fecund as the Western species, hence quickly being out-bred.  (This is a made up example.)
 * If the hybrids are at a significant disadvantage to the "purebreds", gene flow will be minimal enough to prevent the species from merging, although they can interbreed. μηδείς (talk) 17:46, 15 August 2016 (UTC)


 * If we're getting at that level of thinking on the issue of "concepts", other relevant concepts would be Heuristic, Scientific modelling, scientific theory, etc. As Medeis so excellently put it; the thing we call a "species" is not a function of reality, it is a function of human being's need to understand reality.  We invent categories, concepts, models, theories, heuristics, etc.  as a means of organizing and categorizing reality to make it easier to understand.  As George E. P. Box so eloquently put it "All models are wrong, but some models are useful".  Insofar as the concept of a "species" better helps us understand the various relationships between living things, it's a useful concept for us to have.  But no such concept is ever rigorously correct all the time, and we get all sorts of "edge cases" (like ring species noted above) where our definitions break down. It doesn't make the concept worthless, the concept of a species is still very useful at all levels of understanding, and we need to use it, but we also need to understand its limitations.  As another aphorism goes the exception proves the rule, and one must understand not only the rules, but the exceptions and why they are exceptions, and also understand that the exceptions don't invalidate the general rule.  -- Jayron 32 17:55, 15 August 2016 (UTC)


 * Aha, to left is the exact example I was thinking of, the Carrion crow and the Hooded crow which interbreed along a belt through west/central Europe, and were once considered one species, but which maintain their distinctness, with minimal gene flow. See Mayr pp 220-1, with map on second page.  μηδείς (talk) 22:17, 15 August 2016 (UTC)


 * The origin of "species" may be helpful here. ←Baseball Bugs What's up, Doc? carrots→ 00:12, 16 August 2016 (UTC)

Why the sun angle at sunrise and sunset?
A little while before sunset in the northern US, in summer, the shadow cast by a lamppost lies due east, because, naturally, the sun sets "in the west." But later, before the sun disappears entirely, the shadow shifts a bit to the south, indicating the sun is slightly north of due west. Similarly in the morning, the sun rises slightly north of east. The north side of a building receives some direct sun at sunrise and sunset. Is this just due to the Earth's tilt on its axis? Edison (talk) 14:02, 14 August 2016 (UTC)


 * Yes, it is caused by the sun's tilt on its axis. The northward setting and rising of the sun is greatest close to the summer solstice. As we approach the winter solstice the effect will reverse -- the sun will set or rise south of west or east. Search "solar azimuth" to get the details and online calculators. Shock Brigade Harvester Boris (talk) 14:08, 14 August 2016 (UTC)


 * The Sun's axis is irrelevant to this question. The relevant fact is that the Earth's axis is oriented in a way that's about 23.5&deg; away from being perpendicular to the ecliptic (the plane of the Earth's orbital motion around the Sun).  This angle is often spoken of as a "tilt", but that word suggests that the ecliptic is horizontal; a better word is "obliquity".  See axial tilt. --69.159.9.219 (talk) 23:10, 14 August 2016 (UTC)


 * And of course, just outside the Arctic Circle, around the summer solstice, the sun rises only a smidgen east of due north and sets the same distance west of due north. 86.141.140.162 (talk) 14:42, 14 August 2016 (UTC)


 * Wouldn't that be the Antarctic Circle ? StuRat (talk) 14:45, 14 August 2016 (UTC)


 * Neither, actually (hint: think about the meaning of "summer"). Shock Brigade Harvester Boris (talk) 14:56, 14 August 2016 (UTC)


 * Hmm. Unless I'm mistaken, it's true just outside both of the Arctic or Antarctic circles during the solstice that happens during the northern summer. Just outside the Arctic circle it takes the long way around, through true south, while just outside the Antarctic circle, it sneak up near true north, hops just over it, and goes down again. Of course I'm very bad with things like left/right, east/west and good/bad...they all seem somewhat arbitrary. --Stephan Schulz (talk) 15:05, 14 August 2016 (UTC)


 * The part that says "smidgen east of due north" would be wrong for the Arctic circle. There the Sun never appears to the N. StuRat (talk) 17:41, 14 August 2016 (UTC)


 * Not true. On or within the Arctic Circle, the Sun appears due north at midnight on the summer solstice (and on nearby dates depending on how far you are within the Arctic Circle). Loraof (talk) 19:03, 14 August 2016 (UTC)


 * I'd like to see a source for that claim, please. StuRat (talk) 12:56, 15 August 2016 (UTC)


 * See midnight sun and realise that the Earth turns around once every 24 hours with respect to the sun. Under midnight sun conditions, the sun is permanently above the horizon for 24 hours per day, and consequently appears at all directions of the compass (except exactly at the North pole, where compass directions break down in general). --Stephan Schulz (talk) 13:08, 15 August 2016 (UTC)


 * But they said "On or within the Arctic Circle, the Sun appears due north at midnight on the summer solstice". It's the due north part that seems wrong.  I can imagine a glow below the horizon to the N, but is the Sun actually directly visible from the Arctic Circle, at sea level, to the N ?  Maybe it depends on just how flat the surface is there.  StuRat (talk) 14:26, 16 August 2016 (UTC)


 * If you were Thule, Greenland born and raised (Represent! Uqauhiq Atauhiq Naammayuittuq!) you'd see the Sun due north so often you wouldn't bat an eye at it. In parts of the Arctic the Sun gets almost as high while due north as it ever gets in December in Detroit. Sagittarian Milky Way (talk) 14:59, 16 August 2016 (UTC)


 * The ecliptic is the name for the apparent path of the sun, projected onto the celestial sphere. In reference to your horizon, the ecliptic moves; but in reference to the sun, tautologicially, the ecliptic is stationary.  Those articles include equations that define the path's coordinates, and you can see how the path depends on the time of year and your position on Earth.  It might help to visualize the coordinates if you use an astronomy software package like Celestia or Stellarium.  Nimur (talk) 15:20, 14 August 2016 (UTC)


 * The celestial equator is due east and west (parallax is not naked eye at this distance) but you are in the northern hemisphere so above head has to be the northern celestial hemisphere. This is accomplished by having the zenith being your latitude and the equator slanting to the south. The Sun cannot change latitude much in only 1/365th of an Earth orbit so it'll rise, travel, and set near the equator on an equinox. The north celestial pole (NCP) is the same amount of degrees above due north as your latitude. On the June solstice the Sun's daily path has to be on the north side of the celestial equator and parallel to it because the Sun changes latitude very, very little during the day of the solstice and lines of latitude are by definition the direction of rotation. Thus it has to appear north of east because the equator is already as far north as something can rise without being in the northern half of the sky (both kinds of north). Sagittarian Milky Way (talk) 17:53, 14 August 2016 (UTC)


 * Alright, here's my stab it it. The Earth rotates on an axis between its north and south poles, and due to conservation of angular momentum that changes only very slowly, regardless of its orbit and other astronomical events.  Therefore, there is a celestial equator which, apart from precession of the equinoxes, is a fixed circle in space surrounding the Earth.
 * Now the Earth's orbit around the Sun is in a different plane, but that also has angular momentum, and it also stays constant on a human time scale. Therefore, looking out from Earth to Sun, we see the sun on the ecliptic, where the constellations of the Zodiac are located.  That is another circle that intersects the celestial equator.  They intersect in Pisces (constellation) (see the image at right there) and Virgo (constellation) (ditto), i.e. at the equinoxes, or at least, the spots where the Sun is to be found in the sky on the equinoxes, which I guess is why they call it precession of the equinoxes when the celestial equator moves ever so slowly.
 * So given these things, what do we know about summer? The sun is up high on the ecliptic, far from the celestial equator (well, as far as it can be, since the axial tilt between them is just 23.4 degrees, i.e. the width of the Arctic circle).  So it's making a circle around the sky as it moves, but it's not making the largest possible circle, but one that stays always north of the celestial equator by a constant amount.  Note: that means that, unlike at the equinox, in summer the Sun does not go to rest at a spot beneath the surface of the Earth directly opposite from where it is when we saw it (roughly - there's a whole story in that...) 12 hours previously.  To visualize this a little better, picture the Earth had a 90 degree axial tilt, and on the Solstice it sat right in front of Polaris, shining from the same spot day and night.  (Well, day anyway, the rest is a matter of definition...)  It's a little like that in Fairbanks, Alaska in the summer anyway, because north of the Arctic circle there are times when the entire smaller circle the Sun travels in during the course of a day is entirely contained within the above-ground sky.  Note that in this instance, the sun is relatively near the horizon in every direction, so the Sun does in fact appear due North right around midnight (unless you're at the North Pole, where the definition is problematic) . In less extreme positions, the Sun does not pass so far north, but in summer it will always be somewhere north of the celestial equator, and hence, when it reaches the horizon, it will be north of due west. Wnt (talk) 15:28, 15 August 2016 (UTC)


 * Thanks all. I just wanted to confirm the effect was due to more than being on a rotating globe. The tilt of the earth's axis does it. Edison (talk) 13:56, 16 August 2016 (UTC)

What happens to light directed towards the outside of a black hole?
Light cannot escape a black hole (per definition), but what do scientists postulate that happens to a light source directed towards the exterior of a black hole? Does the center of the black hole decelerate the photons? --Llaanngg (talk) 17:21, 14 August 2016 (UTC)


 * You mean like if there was a flashlight within the black hole? ←Baseball Bugs What's up, Doc? carrots→ 17:26, 14 August 2016 (UTC)
 * Yes BB. You need a flashlight in your blackhole, then it would show up all the bullshit you are about to emanate.--86.187.168.56 (talk) 00:07, 19 August 2016 (UTC)
 * no hair theorem re: flashlights in black holes. Sagittarian Milky Way (talk) 17:55, 14 August 2016 (UTC)


 * It seems like the only way to find out would be to go to one (just doing that would be fairly daunting) and then be willing to dive into it, and be willing to die if it comes to that. ←Baseball Bugs What's up, Doc? carrots→ 18:00, 14 August 2016 (UTC)


 * This theorem only implies that we can't observe it, not that nothing is happening. We could still speculate about further parameters.
 * Photo sphere seems to be the article about what happens to photons in a black hole.Hofhof (talk) 18:11, 14 August 2016 (UTC)
 * You can theorize all day long, but there's no substitute for going there and finding out what's happening (or trying to). ←Baseball Bugs What's up, Doc? carrots→ 19:54, 14 August 2016 (UTC)
 * Note that it's a Photon sphere (two words, one more 'n') around a black hole, not Photosphere, which exists around a star.
 * Note also that a photon sphere is outside the event horizon. The phenomenon is so odd that there is no stable orbit for light in the innermost region - it must either go out or fall in.  But it makes sense, really - the event horizon is where light headed straight out just barely can't get away at all, and light headed at a 90 degree angle isn't headed straight out, so it has to be further away than the event horizon to stay at a fixed distance from the hole. Wnt (talk) 20:18, 16 August 2016 (UTC)
 * Well, at some level it makes sense, but it's at variance with an intuition you might have developed from Newtonian celestial mechanics. Ordinarily, escape velocity does not depend on direction, just on whether you have enough kinetic energy to get out of the potential well.  With the obvious exception of directions that put you in an orbit that intersects the planet. --Trovatore (talk) 21:17, 16 August 2016 (UTC)
 * I suppose the difference might be that light can't decelerate. If you're taking off from Earth in a rocket, there are a range of escape trajectories that just barely beat gravity and go off to infinity at a slow speed, and orbits where the velocity drops to the point where something comes back in.  But for light, any beam that is moving even slightly away from the hole will never be coming back, period; if it is just slightly misaligned with the photon sphere I suppose it can make many near-orbits, but regardless what happens to its "kinetic energy" (in terms of the frequency of the photon) the further away it gets the faster it will be leaving. Wnt (talk) 14:44, 17 August 2016 (UTC)


 * Would time slow as it approached the center, such that it would take an infinite amount of time to reach it ? StuRat (talk) 18:42, 14 August 2016 (UTC)


 * From the point of view of a hypothetical observer falling into a black hole, all paths inside the event horizon reach the gravitational singularity in finite (local) time. Dragons flight (talk) 08:52, 15 August 2016 (UTC)


 * It will help you to understand the way light behaves if you have a good intuition about geodesics as they pertain to general relativity.
 * In many texts on the topic of gravity in general relativity, we talk about the circular or elliptical orbit of a planet as a sort of "straight line" in the curved space time. In other words, an inertial object follows a curved path around a massive central body.  If the orbiting body has more energy or a different momentum vector, that affects the curve of the specific trajectory it follows.
 * General relativity provides us a mathematical framework to describe the geometry of every possible trajectory that an object could follow.
 * By extension, we can say that inside a black hole, we can prove that there exist no possible curved paths that escape the black hole. This is, in essence, one way to define a black hole.  It is not easy to construct this kind of geometry for such a system, while also satisfying the mathematical equations that we call "general relativity."  Historically, we give credit to Steven Hawking and his co-workers for successfully writing the equations that govern space-time in a way that also yields a region of infinite curvature (from which there are no possible trajectories of escape).  For the real history buffs: singularities were hypothesized and demonstrated mathematically almost immediately after Einstein's equations were made known - for example, the Schwarzschild solution dates to c. 1916 - but these strange solutions weren't considered correct until many years later.  In fact, singularities were used as ammunition in the case against General Relativity as a viable theory).
 * So, what happens to a photon when it is "inside the black hole"? It is inside a region from which every possible path that photon can follow will not allow it to exit.  The details of how this is possible are best described using complicated mathematical geometry, and it is not very easy to visualize.  There are a few details and conundrums that seem paradoxical - for example, the region might appear to be of zero size - or it might appear to have a well defined spherical shape.  As far as I'm concerned, once you've reached even this level of description, it's meaningless to go any farther without putting down some math.
 * For me, the easiest way to learn relativity was to study electrodynamics: the math is just darned simpler. A great (and infamous) book to help is Jackson's Classical Electrodynamics.  The reason I suggest this approach is because once you define electromagnetic equations classically, you have developed so much practice writing equations in weird coordinate systems that throwing in another wacky coordinate transform (one whose definition simply takes account the spatial distribution of mass and energy) is actually pretty easy.  This is the approach that follows the historical evolution of general relativity.  In many universities, nowadays, the pedagogical mechanism is to teach general relativity as if the Einstein field equations come out of thin air.  That might be an easier way to learn them, but in my opinion, it has two flaws: first, it asks you (the student) to accept a complex form on faith rather than by derivation (which I feel is profoundly unscientific); and secondly, it makes it difficult to intuit the way that electromagnetic waves behave - identically (!) in both classical- and relativistic- contexts - and I feel that this insight is absolutely central to understanding relativity.  (You know how they keep calling c an invariant?  This actually means something.)
 * Here is a wonderful list of books - So... You want to teach yourself about general relativity...? from the University of Chicago. It's a list of books - and it is a loooooong list of books.  Do not underestimate the importance of this concept: it may take you four to six years of intensive study in mathematical physics before you are even ready to start studying the mathematics of general relativity.  This is a fact: very smart people (physics undergraduates!) who can dedicate all of their time to these studies still require four to six years of mathematical preparation before they take an introduction to general relativity.  If you believe that you can take a short-cut or somehow bypass this preparation, you are probably wrong.
 * Nimur (talk) 18:48, 14 August 2016 (UTC)


 * I don't know which path takes more time, or even if both take the same amount that you mention (4-6 years). However, according to there are two math paths:


 * 1. "differential geometry, which is calculus on arbitrarily curved surfaces, essentially.", "it is the older, more 'traditional' way of doing differential geometry and GR, and was the mathematical language that Einstein originally used when developing the theory."


 * And another:


 * 2. "The more modern approach uses all the tools and concepts of modern differential geometry - tangent spaces, the calculus of forms, Lie derivatives, and so on. "Hofhof (talk) 22:32, 14 August 2016 (UTC)


 * There's a lot of mischief in some of the black hole theories out there - fuzzball (physics) that I think doesn't really have anything but strings inside, or firewall (physics) to try to impose an Alexandrian solution on the knotty problem of information destruction in a black hole. In such models you can be destroyed the moment you pass the event horizon, but in the traditional model you can scarcely even notice as you pass.  The light goes outward as you see it, but your light cone is so rotated that even that trajectory now faces inward as seen from distant space.  So it's going away from you the luckless adventurer like it's light, but that isn't good enough to get it out.  (Does this mean that you're going faster than light?  Well, from the point of view of an outside observer, the singularity of the hole is in your future and you're veering into a spacelike path, and might even move a little into the "past", relative to a flat universe.  But only in a hypothetical view; they can't see any of this and the flat universe it takes this path relative to doesn't really exist!) Wnt (talk) 02:36, 15 August 2016 (UTC)