Wikipedia:Reference desk/Archives/Science/2015 May 2

= May 2 =

Reflex
The head of my toothbrush has a textured back side for tongue cleaning. As most people who have tried it will discover, rubbing on your tongue can trigger a somewhat unpleasant reflex. Subjectively, it feels like your diaphragm or some muscle near your stomach contracts rapidly. My first question is: what reflex is this? (I looked up gag reflex but the description doesn't seem to fit.) From the Web, I found the advice that making a tight fist while you clean your tongue would make the reflex less likely to trigger. I was a little skeptical but I tried it anyway. To my surprise it actually worked and worked surprisingly well! My second question is: how does making a tight fist interfere with the triggering of the reflex? --108.16.202.123 (talk) 00:01, 2 May 2015 (UTC)


 * You might find its to do with the sympathetic nervous system and the parasympathetic nervous system. Clenching a fist evokes the later. A toothbrush in the gob evokes the former. One can not have both systems in total equilibrium. OK. Before any smarty-pants says anything – he didn't t say he was 'Meditating' whist he brushed. --Aspro (talk) 00:36, 2 May 2015 (UTC)

question (humans fertilizing other animals)
can human sperm fertilize any animals other than humans? like how lions can fertilize tigers to creater "ligars" and donkeys and horses can make "mules" — Preceding unsigned comment added by 112.18.66.14 (talk) 11:18, 2 May 2015 (UTC)
 * Hybrid species can only form if the two parents are reasonably closely related. Humans' closest extant relatives, the common chimp and the bonobo (pygmy chimp), split from the human-chimp ancestor about 6million years ago, so we can't produce offspring with them. It is speculated that human ancestors could interbred with now extinct neanderthals. I've taken th liberty of adding a more descriptive title for your question LongHairedFop (talk) 11:26, 2 May 2015 (UTC)
 * (e/c):No. Our article at Parahuman is not the greatest, but gives some background. See also Humanzee. Matt Deres (talk) 11:28, 2 May 2015 (UTC)
 * As our humanzee article sort of says, I don't think we can completely rule it out. The fact that there are no recent examples anyone is aware of may suggest it isn't possible, but we don't really know if there have been many attempts. Even with overlapping ranges, there are good reasons why this is far less likely to occur than with many other hybrids with overlapping ranges which may have observed examples. Definitely the experiments have been too limited to conclusively rule it out. And there's a fair chance we aren't going to get many more. The chromosal differences suggest any hybrid probably won't be fertile, but as our article says they may not rule out a non-fertile hybrid offpsring. Nil Einne (talk) 13:28, 2 May 2015 (UTC)
 * As noted above by several people, the best we can say, based on current research, is "We're pretty sure we cannot, but would not be shocked if we could". There has been considerable research showing that there were likely Neanderthal-human hybrids, for example, and when there were times in our past history when there were several, closely related species of either Homo or Australopithecus species living in close proximity, such interspecies hybrids would have been likely.  But as noted, today, there is not currently a species which is closely related enough to humans to allow for successful hybridization.  -- Jayron 32 14:25, 2 May 2015 (UTC)
 * The thing is, I don't think we can say "we're pretty sure we cannot". At best we can say "we have no evidence that we can, and some evidence and reasons to think we can't, such that it would be surprising but not shocking if it could happen". Nil Einne (talk) 12:08, 3 May 2015 (UTC)
 * Unless people admit to seriously attempting the experiment, we have no actual data. Humanzee discusses this.  But there's no "physical law" that bars humans from impregnating chimpanzees, or even hamsters for that matter - there is only the empirical sense that the former is dubious, the latter out of keeping with other empirical data. Wnt (talk) 22:05, 2 May 2015 (UTC)

many worlds, infinity
Some theoretical physicists, disliking the Copenhagen interpretation of quantum mechanics, have put forward instead a many-worlds theory which posits the existence of perhaps an infinite number of universes besides our own. In this theory, what exactly does "infinite" mean?

In mathematics, functions can become arbitrarily small or large, "tending" toward infinity; Georg Cantor developed the idea of transfinite numbers. These are not finite, bur neither do they attain the status of the higher, ideal absolute infinite.

The many-worlds theory is based on mathematics which I certainly don't understand. What does it add up to? Can infinity be comprehended in physical terms? Is it something that just gets bigger and bigger? Or is it merely an abstraction? Is there any relationship to "reality"?

--Halcatalyst (talk) 18:28, 2 May 2015 (UTC)


 * You ask if infinity can be comprehended in physical terms. That's an easy enough question to answer.  No, it cannot.  As to whether the number of alternate worlds is aleph-null, aleph-one, or what, I am guessing that that would depend on how often one assumed that forking occurred.  There are other interpretations of quantum mechanics that don't have the hand-wave quality of the Copenhagen interpretation or the hand-wave quality of the many-worlds interpretation, but they may be other types of hand-waves.  Robert McClenon (talk) 18:36, 2 May 2015 (UTC)


 * If I understand correctly, there is no physical quantity or dimension which is truly infinite instead of just very big. Infinity is only as an abstract mathematical concept. As a visual representation, a perfect circle is equivalent to an infinite-sided polygon. However, perfect circles only exist only in the imagination, because any real image is still represented by some quanta, atoms, photons, etc, which have finite dimensions and quantities. Although, I suppose a circle of infinite radius will cancel out this graininess, but then is will also have zero curvature, not to mention, not fit inside the universe. Plasmic Physics (talk) 11:57, 3 May 2015 (UTC)


 * The one area where humans seem to have no problems imagining infinities is in time. We find it hard to imagine that time will ever 'stop' or 'end' in the future - or in the past for that matter - time for us is 'obviously' infinite, it's an easy concept to grasp.  To the contrary, the idea that time 'started' at the big bang (or might 'end' in a 'big crunch') is something people simply cannot grasp...nearly everyone immediately demands to know what there was 'before' the big bang and seem unable to grasp the concept that time (at least in the past) was not infinite - and therefore that there was no 'before' in that case.  So the best way to analogize an infinite universe is to conflate time and distance and imagine travelling through an infinite space at a respectable speed - and never reaching the 'end'...that seems quite comprehensible to me because I've now gently mapped distance into time, where the infinities seem not to mess with my brain too much!


 * So a single infinite universe becomes an approachable concept.


 * But an infinite NUMBER of parallel universes is a much harder sell. And in truth, I don't think there has to be an infinite number unless our present universe is infinite in extent.  If you imagine a teeny-tiny universe containing just you and a six-sided dice, which you roll once a second to produce random 'quantum events' - then your universe forks into six possible futures each time you roll the dice.  Ten seconds after your personal 'big bang' when you started to roll the dice, there are 6x6x6x6x6x6x6x6x6x6 parallel universes - one of which had you rolling ten sixes in a row, on of which got all ones...and one amongst many, many other boring ones that has 6,2,3,1,5,2,3,5,6,2.  It doesn't take long for the number of dice-universes to get huge...after just one day of this, there are 6(60x60x24) parallel universes - which is an insanely large number.


 * In the real universe...even just the part of it that we can observe...there are 1080 particles undergoing quantum events at some ungodly speed - so the number of parallel universes created since the big bang is a number so large that finding a way to express it requires (literally) a whole branch of mathematics...but it's not infinite...unless our universe is also infinite. SteveBaker (talk) 16:54, 3 May 2015 (UTC)
 * Hmm, I know this is off-topic, but ... you really think infinite space is harder to grasp than infinite time? ISTR that some ancient philosopher concluded that space had to be infinite, because otherwise when you got to the end, what happens when you thrust your spear past that?  There's a possible answer to that, now, in that the Universe may (but also may not) have a compact topology like that of the 3-sphere, so that you could always thrust your spear farther but nevertheless space would be finite, but I think that's harder for the average person to follow than the idea of infinite space is, no?  --Trovatore (talk) 01:08, 5 May 2015 (UTC)
 * (Pinging because this is pretty high up on the page and he may not see it otherwise.) --Trovatore (talk) 05:10, 5 May 2015 (UTC)


 * I don't personally think it's harder to grasp - but many people do. A 4-dimensional hypersphere allows there to be a finite universe and yet have no awkward "boundaries"...so that's an easy sell...but it may simply not be true.  The thing that hurts my head about an infinite (and somewhat homogeneous) universe is covered in a piece I wrote over on medium.com (my current addiction!), which brings all of the difficult intellectual problems of many-worlds into a single world.  So for me, the problem is not of imagining the infinite volume - it's in fully comprehending the consequences of that. SteveBaker (talk) 17:08, 5 May 2015 (UTC)
 * OK, thanks, I guess that is a plausible explanation of what could lead some people to draw back from the notion of infinite space. For me, I just don't see those "problems" as all that problematic.  Sure, in some remote galaxy, there's some lucky dog who looks a lot like you or me.  And?  What has he to do with us?
 * Could be partly just a matter of getting used to it. I can't really tell anymore.  The paradox of the Hilbert Hotel has not struck me as paradoxical in a great many years; I can't really recall whether it ever did. --Trovatore (talk) 17:28, 5 May 2015 (UTC)
 * The number of worlds should be something like eS where S is the entropy in natural units. This paper estimates the entropy of the visible universe at about 10104, so if that were the whole universe (which it's not), the number of worlds would be around e10 104, a large but finite number which is, incidentally, comparable to a googolplex. The whole universe, if finite, is probably much larger; e.g. this (extremely speculative) paper suggests a lower bound of $$10^{10^{10^{122}}}$$ Mpc on the diameter of the whole universe, which would put the total worlds at over $$e^{10^{10^{10^{122}}}}$$, which is still a lot less than infinity. -- BenRG (talk) 23:04, 4 May 2015 (UTC)


 * I have trouble with absolute infinity, and I think most physicists would also reject the idea. Maybe some seriously support it; if there are any, I would like to hear their arguments. Invoking absolute infinity seems to me to be the ultimate form of hand waving. Larger or small without bound, that's fine; but absolute infinity is just a concept.


 * Could it be that absolute infinity is implied or necessitated by any of the varieties of string theory or some other rigorous mathematics? If so, do the theorists say the math points to reality, or is it just an intellectual game? Is what they are doing mathematical or physical or philosophical? I would say it's clearly philosophical if they claim it's BOTH mathematical and physical.


 * I know that mathematics describes the world in an amazing way, but that doesn't mean any mathematics describes "reality." --Halcatalyst (talk) 15:40, 5 May 2015 (UTC)
 * Do you think space terminates? Do you think it wraps around?  If it neither terminates nor wraps around, then it must be actually infinite.  (BTW, I think you mean actual infinity rather than absolute infinity.)  --Trovatore (talk) 15:48, 5 May 2015 (UTC)
 * Some people (not me!) like to imagine a finite amount of volume with 'stuff'...like stars, dust clouds, galaxies...in it - embedded in an infinite volume of space. That's kinda comforting in that it keeps the 'stuff' to a manageable quantity - and it feels like our normal experience of things that kinda taper off into nothingness.   With that comfortable feeling in mind, they can quietly ignore the infinities of space because it's boring and empty.  However, that model is hard to support from a physics perspective...and for people who've thought hard enough about it, it leaves the problems of an actual infinity of space to worry about. SteveBaker (talk) 17:08, 5 May 2015 (UTC)

Hummingbird moths seem to love an area of my yard that the article doesn't say is a proper habitat for them, why?
I just planted some ornamental grass near where a black drain pipe I attached to one of the gutters' drain spouts lets out a few hours ago, and the area is now swarming with these guys. They seem to love the swampy clay soil and hiding in the grass. Last I checked there were about 10 of them buzzing around, small and newly hatched mostly. However, the article doesn't list that as one of their favored habitats. What are they doing there, what are they eating and where are they living that they seem to like so much? There aren't even any flowers nearby. — Preceding unsigned comment added by 70.106.145.150 (talk) 18:31, 2 May 2015 (UTC)
 * The obvious conclusion is that they never read the Wikipedia article. ←Baseball Bugs What's up, Doc? carrots→ 21:33, 2 May 2015 (UTC)
 * This writeup has a lot of detail. ←Baseball Bugs What's up, Doc? carrots→ 21:38, 2 May 2015 (UTC)
 * Thanks, I think that answered it. According to the article you posted, a likely explanation might be that the cocoons and larvae were already on the grass before I planted it, and I just never noticed until they started turning into hummingbird moths. Grass does make flowers, so maybe these moths' parents pollinated the grass then laid eggs on it. There weren't any of their preferred flowers around where the grass used to be, so I guess they could've been eating what was pretty much the only thing around to eat. --70.106.145.150 (talk) 00:46, 3 May 2015 (UTC)
 * The cocoons/pupae and (fully grown) larvae of this sort of moth (Sphingidae) are typically around the size of your thumb or larger: I think you'd have likely noticed them while you were planting. You might not have noticed eggs, but (a) eggs are only laid on one or a few specific food plants (varying from moth species to species - this species seems to have more catholic tastes than most of its relatives), and (b) the developmental cycle from eggs to moth takes several weeks to several months (some hawk moths even "hibernate" through the winter as pupae buried in the soil). I think it most likely that the moths have always been present (at certain times of the year) in your general neighborhood, and that by planting the grass you have created a Microclimate they find congenial. They may even be finding the "swampy clay soil" ideal to drink from. (You describe them as "mostly small and newly hatched", but moths do not grow significantly after they have emerged and expanded their wings, and it takes a trained eye to estimate even roughly how old they are.) {The poster formerly known as 87.81.230.195} 2.218.13.204 (talk) 20:18, 4 May 2015 (UTC)

Thread identification
I've often run across a 15/32" dia, 32 tpi thread on electrical devices, such as these Eaton toggle switches, which are labeled 15/32-32 NS-2A in the engineering diagram. What standard does this thread belong to, and do we have a relevant article?

Our Unified Thread Standard article makes no mention of a 15/32" dia thread, and the largest 32 tpi thread is on the 3/8" Extra Fine (UNEF), with the 7/16" UNEF being 28 tpi. I'm guessing that NS may refer to an American National Standard, but the American National Standards Institute defines the Unified Thread Standard mentioned above.  Is the 15/32-32 a holdover from an older national standard? -- ToE 18:36, 2 May 2015 (UTC)
 * The "NS" designation is Unified National Special (which is a redirect to Unified Thread Standard). It's mentioned in the last paragraph of the "Designation" section, although I agree it could be more prominent. Tevildo (talk) 19:04, 2 May 2015 (UTC)
 * Thanks Tevildo. I don't know if there is a better place to read about the NS specification than this Iranian copy of ASME B1.1-2003, but I cant find any information there for any 15/32" dia thread.  Pg. 127, Table C-2 gives three 7/16" UNS threads (at 18, 24, and 27 TPI) and five 1/2" USN threads at (12, 14, 18, 24, and 27 TPI). -- ToE 00:49, 3 May 2015 (UTC)
 * Yes - UNS is a designation for any thread that has the same threadform as the standard types, but doesn't appear in the standard UNC, UNF or UNEF tables. It's generally used when the manufacturer wants a thread that's finer than UNEF, or with an unusual diameter - one (fairly) common thread is 0.390-27 UNS.  Almost by definition, there can't be a table of "standard" UNS threads.  Tevildo (talk) 09:41, 3 May 2015 (UTC)
 * That makes sense. I had expected it to have a special name, given how common it seems to be, but I suppose NS is special in its own way. -- ToE 13:10, 5 May 2015 (UTC)

Why does infrared need a line of sight but radio doesn't?
Old wireless game controllers used infrared and TV remotes still use infrared sensors and both need a line of sight and a visible sensor in order to work (the shiny black thing usually mounted on the front of tvs and such). However radio like bluetooth or wifi do not need a line of sight and do not have a visible sensor. Why is this? Is it because radio wavelengths are longer than infrared wavelengths? Malamockq (talk) 20:17, 2 May 2015 (UTC)


 * Basically, yes. Note that even BT and wifi perform better with line of sight, since their wavelengths aren't all that long (about 5 inches / 12 cm). Short Brigade Harvester Boris (talk) 20:35, 2 May 2015 (UTC)


 * Radio waves generally travel in straight lines, but can pass through some solid objects, like walls.--Phil Holmes (talk) 10:52, 3 May 2015 (UTC)


 * It is to do with the tropospheric bending  of electromagnetic waves. It depends on their wave length. The sorter the wave length the more line of sight (ie visible and infra-red). Very long wave lengths ( VLFcan circle the Earth.--Aspro (talk) 16:20, 3 May 2015 (UTC)
 * I don't think the question is really getting to the scale of tropospheric bending or circling the Earth. We're talking about wifi vs. television remotes, not short-wave radio vs. television remotes. --OuroborosCobra (talk) 16:23, 3 May 2015 (UTC)


 * It's down to that wavelength thing...some materials (like glass, for example) are transparent to visible light, but almost opaque to infra-red. Or think of colored glass where some colors of light can pass through while others cannot.  Extrapolate that out to other wavelengths - radio waves, for example - and some materials are opaque to them while others are transparent.  Radio waves are blocked by some materials and not by others - just like light is.
 * That tropospheric bending is more analogous to the way a lens works in the optical realm - a lens has a different refractive index than air - so the light bends as it passes into and out of it. Our atmosphere has a different refractive index than vacuum, so at the air gets gradually thinner at altitude, it bends the light (conveniently) back towards the earth's surface - which allows some frequencies of radio wave to curve over the horizon.  Some optical fibres work the same way with layers of glass of different refractive indices that bends the light around curves in the fibre.
 * So it's not a 'hard' difference between light and radio - they are all electromagnetic waves - it's just a matter of scale and materials. WiFi *is* attenuated by walls...a fact that is painfully obvious in my house, where I have places where I get zero reception and other places that are further away from the transmitter that work perfectly...it's all down to the number of walls and other obstacles in the way.
 * SteveBaker (talk) 16:35, 3 May 2015 (UTC)
 * Glass isn't quite transparent. More noticeable when there's a lot of light. Shine a flashlight in a window at the right angle, your eyes won't work any better than a blinded remote control will. But yeah, that's just nitpicking. InedibleHulk (talk) 13:02, 4 May 2015 (UTC)

How Long Can Sperm Survive in a Man's Body After Castration?
How long sperm can survive in a man's body after castration (Yes, castration, as in the removal of both of one's testicles)? Is there a maximum lifespan for sperm who reside in a man's body after castration (similarly to how 125-130 years is believed to be be the maximum lifespan for human beings without any anti-aging technology)? Serious question, for the record.

Also, I will make sure to ask a medical professional this question as well. Thus, this question is certainly not a substitute for medical advice. Futurist110 (talk) 22:42, 2 May 2015 (UTC)
 * In a perfect environment, sperm live about 5 days. See .  Outside the body, they live about 20 minutes: .  -- Jayron 32 03:13, 3 May 2015 (UTC)
 * Then why exactly does a vasectomy take months to become effective (assuming that re-canalization does not occur by that point in time)? Futurist110 (talk) 06:36, 3 May 2015 (UTC)
 * I suspect claims of eight weeks (as claimed here and here) are overkill, but, as the saying goes, I'm not the doctor (and neither is Jayron). WebMD also claims "several months". FWIW, that's nothing like the advice I got after getting snipped; the only waiting period I was given was that I needed the wound to heal and to take the (two) tests for sperm count with a few weeks. All part of the reason to talk with your doctor (but make sure you call it a vasectomy; requesting castration will initiate a very different conversation). Matt Deres (talk) 20:09, 3 May 2015 (UTC)
 * Thanks for this info. Also, for the record, I would like to point out that I do not want a vasectomy due to the fact that vasectomies can fail and I am completely unwilling to risk dealing with failure and with the possible consequences of failure (and for the record, abstaining from vaginal sex with any fertile and potentially fertile woman for the rest of my life is likewise completely unacceptable to me). Rather, I want to get castrated and I will do whatever is necessary in order to get this done (and as a gender-fluid/cross-dreaming person, castration has other benefits for me as well; however, the contraceptive benefit of castration is too nice to be ignored). The reason that I was asking about vasectomy here is because, as far as I know, the issue of surviving sperm applies to both vasectomy and to castration. Futurist110 (talk) 20:20, 3 May 2015 (UTC)
 * Well, that's all definitely a conversation that should be had between you and your doctor(s). I assume you're aware that abstaining from sex (vaginal or otherwise) may well be a consequence of castration whether you like it or not; the lack of testosterone typically causes a sharp reduction in sex drive. Some - but by no means all - eunuchs are also physically unable to maintain erections as well, probably for the same reason. Matt Deres (talk) 21:11, 3 May 2015 (UTC)
 * Yes, I agree about the conversation with a doctor part. As for the lack of a sex drive (due to a lack of testosterone), can't hormone replacement therapy deal with this? (And Yes, I know that hormone replacement therapy has its own issues as well; however, if transgender people can deal with this, then I can likewise deal with this. Also, for the record, I myself would probably prefer to take female hormones after castration if I will still somehow be able to maintain erections (with my penis, which I intend to keep indefinitely) indefinitely afterwards; however, I want to keep all of my options in regards to this. In addition, though, I would like to point out that a lack of a sex drive will probably be a good thing for me at certain times, but obviously not all of the time.) Futurist110 (talk) 22:22, 3 May 2015 (UTC)
 * As well as asking your questions to a suitable doctor, you should expect, if you propose to be castrated, to also be referred to various specialists, including a psychologist or psychiatrist who will evaluate your mental state. This is (at least in the UK) standard practice for operations of this kind. You should not attempt to perform the operation yourself, as, incorrectly performed, there are potentially dangerous side-effects. RomanSpa (talk) 09:43, 4 May 2015 (UTC)