Wikipedia:Reference desk/Archives/Science/2015 July 19

= July 19 =

Does shaving your armpits make them smell less bad?
^Topic Malamockq (talk) 01:08, 19 July 2015 (UTC)


 * See AndyTheGrump (talk) 01:17, 19 July 2015 (UTC)

Lesbians
Does the "lesbian bed death" theory change depending on whether the couple are composed of both lipstick lesbians, both stone butch, or a lipstick lesbian and a stone butch? — Preceding unsigned comment added by 147.91.1.41 (talk) 01:54, 19 July 2015 (UTC)


 * Can someone who's good with WP:AfD explain which criterion would be best for deleting this 30+ year-old fringe nonsense based on the "work" of one rather un-noteworthy author? Thanks. μηδείς (talk) 10:08 pm, Today (UTC−4)
 * See WP:GNG and WP:NTEMP. According to the guidelines, if it was notable 30 years ago, it's still notable today. Tevildo (talk) 15:51, 19 July 2015 (UTC)
 * According to the article you've just linked, it is a fringe theory which has been fairly thoroughly debunked by mainstream sociologists who study these things seriously. So, the answer to your question is "the answer doesn't matter because the theory itself isn't sound".  -- Jayron 32 02:51, 19 July 2015 (UTC)
 * That's a really dismissive and unhelpful approach. The guy specifically asked whether the theory changed based on those factors - in other words, does the theory/its adherents postulate that those factors matter.  You might as well answer a question about Aristotle's theories on gravitation with "it doesn't matter because he was wrong." -Elmer Clark (talk) 05:14, 21 July 2015 (UTC)

If civilisation collapsed, could humanity have another industrial age?
Have we drilled and mined all the oil and coal within easy reach that if society collapsed and humanity went into a primitive state the industrial revolution could never happen again? 2.102.184.233 (talk) 06:58, 19 July 2015 (UTC)


 * At the top of the page, it says "We don't answer requests for opinions, predictions or debate." Ian.thomson (talk) 07:15, 19 July 2015 (UTC)


 * I'd mine rubbish tips for plastic to burn. Also a great resource for other raw materials. I'd guess that a charcoal fuelled industrial economy would be possible, but would not be easy. However, knowing the answers in advance helps a lot.Greglocock (talk) 07:39, 19 July 2015 (UTC)


 * Statement of the obvious, but we use fossil fuel because it's cheaper, not because it's the only energy source. There's no reason other than the economics of extraction that industries tend to run on fossil fuels—Brazilian industry runs on sugarcane and the nation hasn't fallen apart yet. There are plenty of potential natural sources of oil that wouldn't require processing to be usable in an non-industrial society—palm, rape, soy, even whale. – iridescent  08:52, 19 July 2015 (UTC)


 * But the question is if any of those energy sources would be available in the quantity needed to fuel an industrial age, keeping in mind that our current production methods for many of them rely on fossil fuels. I'm sure you can harvest some of those using traditional farming methods (plowing with draft animals, etc.), but the quantity would likely be way less. StuRat (talk) 18:35, 19 July 2015 (UTC)


 * Why would humanity need another industrial age? If "society collapsed" there would be certain problems which would have to be addressed. But there would likely be certain knowledge retained from prior to the "collapse". The presence of that knowledge would imply a different path forward than the path previously taken by humanity prior to the industrial age. A collapse of society is a possibility but a complete loss of information is unlikely. Bus stop (talk) 19:07, 19 July 2015 (UTC)


 * The question was whether it would be possible, not desirable. --174.88.133.35 (talk) 04:59, 20 July 2015 (UTC)


 * It would be possible but it would differ from the previous industrial age because information would be available that was not available the first time around. Bus stop (talk) 05:04, 20 July 2015 (UTC)


 * It's not just information that is needed. For example, they may have plans for a nuclear power plant, but they still can't build one without massive resources, like money, skilled manpower, tools, raw materials, roads, ports, etc. StuRat (talk) 13:18, 20 July 2015 (UTC)


 * He probably meant we would aim for electricity and not an inefficient steam engine and then use that for a few decades and later recapitulate the entire 19th century. If we did that and there were literally no civilization it would take thousands of years for someone to think of the stirrup. Sagittarian Milky Way (talk) 17:13, 20 July 2015 (UTC)


 * The more interesting/immediate question is whether the planet will survive. In a "collapse of civilization", does it ever become truly infeasible for small local entities and barbarian regimes like ISIS to extract shale oil and such to power their local and longer-range wars?  I don't know.  If we could manage to roast the Earth in a runaway greenhouse effect we wouldn't have to worry about the next cycle. Wnt (talk) 12:19, 20 July 2015 (UTC)

Engineering in business
Is engineering in the workplace less mathematical than engineering in college and academia? 176.27.11.220 (talk) 11:35, 19 July 2015 (UTC)
 * Yes. In the workplace, an engineer's skill with math is used more to comprehend the math that others have used in explanatory documents than in actually applying math to solve problems. The other major change when transitioning from academia to the workplace is the increased use of written language. In academia, engineering students don't get a lot of practice at written language but in the workplace engineers are using written language on a daily basis to explain and persuade. Many graduate engineers initially display inadequate skills with written language. Dolphin  ( t ) 13:16, 19 July 2015 (UTC)


 * In the workplace engineers tend to 'specialize' and not need the wide verity of mathematical skill they learnt in university. However, across the whole of industry I would say that it is on par with academia. The two can't be separated, as industry also performs its own R&D. Its from this feedback process  that collages get feedback as to exactly what courses  to offer the next generation of  future slaves graduates and where to direct resources into their own university’s blue skies research. On balance, collage just bring 'the knowns'  to a wider audience. So to answer you question. Yes, math is as widely used in the work place as  in hallowed institutions.--Aspro (talk) 15:01, 19 July 2015 (UTC)


 * Many engineers - even those who specialize in areas other than computer design - spend a lot of time performing computer programming. To quote Edsger Dijkstra, one of the founders of modern computer theory, programming is one of the most difficult branches of applied mathematics.
 * Now that we have cheap and omnipresent calculating machines, it is unlikely that an employed engineer will need to perform arithmetic very often. However, engineers conduct mathematics every day.  After you study more engineering mathematics at the university tiers, the distinction (and the relationship) between arithmetic and mathematics will become more clear.  Nimur (talk) 17:22, 19 July 2015 (UTC)


 * Disagree on one little point. Programming is one of the most exciting branches of applied mathematics. After all. One doesn’t climb Mount Everest just because it difficult (only masochists do that). It is the human drive, to willingly suffer those hardships to reach the highest peak. That is the reward. To stand upon top -with the rest of the world below you.--Aspro (talk) 23:18, 19 July 2015 (UTC)


 * The answer is, it depends. I have had to learn quite a lot of additional maths in both of my specialisations (NVH and vehicle dynamics), but equally there is a quite a lot of my university maths I don't use at all. However the average oompa loompa (http://www.urbandictionary.com/define.php?term=Oompa+Loompas+of+Science) seems quite happy not to bother with anything beyond excel used/misused at a fairly basic level. Iimagine there are many engineers who use statistics at a fairly advanced level compared with what they learned in university. Greglocock (talk) 01:53, 20 July 2015 (UTC)


 * Yes, I can agree with the above. When one specializes one uses one skill to go beyond what one was taught. Nimur comment puzzles me a little though. Does he mean arithmetic  long hand. i.e., with pencil and paper?  I went  on to learn (not very well) log tables (and on entering industry), slide rules (which, over forty years on, still work without having their batteries replaced even once) and then big desk top calculating machines with nixie tube displays. What ever means ones uses to perform arithmetic, one is still performing  arithmetic.--Aspro (talk) 21:21, 21 July 2015 (UTC)

Hybrid cars: Nickel-Metal Hydride or lithium-ion battery?
How does it come that the nickel-metal hydride battery was chosen for the Prius (until 2015 at least)? As I understand, when you brake, the car stores the energy into the battery. However, are nickel-metal hydride batteries appropriate for this kind of fast loading? And besides price, does nickel-metal hydride have any advantage in comparison to a lithium-ion battery? And what was the reason of the newly introduction of a lithium-ion battery for the Prius 2015?--Yppieyei (talk) 15:55, 19 July 2015 (UTC)


 * NiMH are far less likely to undergo the infamous venting with flames that lithium batteries are famous for. See Plug-in electric vehicle fire incidents, Lithium-ion battery and Nickel–metal hydride battery. Nil Einne (talk) 16:28, 19 July 2015 (UTC)


 * NiMH batteries also have less of a tendency to degrade when recharged in hot temperatures, as anyone who lives in a hot climate and buys a phone or laptop with a non-replaceable lithium battery generally finds out within a couple of years. – iridescent  16:32, 19 July 2015 (UTC)


 * Also note that, while that would qualify as fast charging if it all went into a single cell, that it's spread out over all the batteries in the entire car, so that it's not much charging at all into each. I suppose they could also use a flywheel or capacitor to store the energy temporarily, to slow the charging even more (or reuse it directly from those sources). StuRat (talk) 18:30, 19 July 2015 (UTC)


 * The LiOn, used in mobile phones, tablets and notebooks are known to be usedful for three years. To keep it useful for longer time the Prius operats its battery between 40 to 90 percent charge, only. Do you known an owner of a Prius who needed to renew the battery? -- Hans Haase (有问题吗) 20:08, 19 July 2015 (UTC)


 * There are lots of Prius' owners renewing the battery. You can find loads of used Prius batteries on eBay, and even buy a single module of it. The Li-ion battery is new, as said by the OP, so there are not many of this around yet. --Scicurious (talk) 03:14, 20 July 2015 (UTC)


 * Checkout BMW i3 and Tesla Model S.--Phil Holmes (talk) 12:54, 20 July 2015 (UTC)

Singularities
If singularities are in fact impossible in our universe, then each black hole must excrete its matter somewhere. Does this excretion have to be in this universe or can the matter be ported to another universe?--81.147.170.83 (talk) 16:34, 19 July 2015 (UTC)
 * You have stated a premise as if it is a fact: if a then b ...
 * You have not shown a; why do you believe singularities are impossible?
 * You have not established the validity of the logical implication: why do you believe that this implies black holes must excrete matter somewhere?
 * It is not efficient to start chasing down a logical consequence when neither the truth of the statement, or its premise, has yet been established.
 * So, let's start over... where are you reading about black holes? How have you reached the point where these questions even come up?  Have you started by reading our article, black hole, and then following up with the reference material in that article?
 * To study black holes meaningfully, you need to learn a lot of prerequisite mathematics and physics. This way, we can quickly refer to preestablished concepts, like the conservation of mass flux or the mass-energy equivalence or the complicated geometry of spacetime that follows from a treatment of gravity in general relativity.  If you haven't mastered these concepts first, it will be hard to efficiently communicate about black holes with any scientific merit.  For example, we will want to determine whether mass, or mass flux, is a conserved quantity - and whether this statement is true in the exotic circumstances near a black hole.  That's a complicated scenario!  As a prerequisite, are you already familiar and able to work with these quantitative concepts in non-exotic scenarios?
 * Nimur (talk) 16:44, 19 July 2015 (UTC)


 * As far as black holes excreting matter, this seems to happen in our own universe, from each black hole, but over a very long time frame (except for micro black holes). See Hawking radiation. StuRat (talk) 16:51, 19 July 2015 (UTC)
 * While Hawking radiation is a real phenomenon, it is not directly a consequence of the original premise ("singularities are impossible", a premise which is neither confirmed nor refuted by the existence of Hawking radiation). This is important: scientific hypotheses must be precise and testable, and our conclusions must be commensurate to the evidence.  Nimur (talk) 16:57, 19 July 2015 (UTC)


 * Most if not all physicists would agree with "singularities are impossible". But I don't know how you got from that to "each black hole must excrete its matter somewhere". -- BenRG (talk) 19:09, 19 July 2015 (UTC)


 * I understand what they are saying: "Matter can not forever go in one direction (into the black hole) without ever going the other way". I'm not sure that I agree with that argument, though, as it could forever go into the black hole at an ever decreasing rate, or perhaps just stop going anywhere at some point.  StuRat (talk) 20:58, 19 July 2015 (UTC)


 * Black holes grow larger and more massive as they accrete matter. They're no different in that regard from any other gravitationally bound object. The matter doesn't have to go anywhere; it's just there. -- BenRG (talk) 00:31, 20 July 2015 (UTC)


 * I could see someone coming to this conclusion based on the peculiarities of space in a black hole. Specifically, that standing still over a period of time is impossbile - the future is down, and all that. One might conclude that if matter can't sit still, but it is blocked from moving down, it must go somewhere else. Someguy1221 (talk) 05:17, 20 July 2015 (UTC)


 * The matter actually is excreted, via Hawking radiation. The OP is grasping toward the ongoing theoretical question of whether information (as well as mass) gets destroyed in a black hole, or if it comes out in some way in the Hawking radiation.  I think current belief is that things fall into a black hole, they get thoroughly disassembled, but they do come back out after a very long time. Wnt (talk) 12:16, 20 July 2015 (UTC)
 * Ok let me put this more simply without any assumptions. Where does all the matter that falls into a black hole go?--81.147.170.83 (talk) 14:50, 20 July 2015 (UTC)
 * In plain English, the matter goes near the black hole. This plain English description would also apply to matter that falls onto a planet: if a meteorite falls onto Earth, the meteorite (and all the fragments and gases and matter) all ends up going "near" Earth.  The plain English description - "near" - is not precise enough to capture the details that make black holes different from ordinary stuff.
 * To measure where something goes, you must define position (and distance) using some coordinate scheme. To understand black holes, you must recognize that in general relativity, gravitation manifests as a distortion of the coordinates.  As mass accumulates, the warping of space and time increases: the measurement of position becomes more complicated.  When and where you make the measurement becomes much more important.  Your answer is dramatically different if you are within a certain distance from the "center" of the accumulating matter - the Schwartzchild radius.
 * Conceptually, there is no "hole": there's just a big massive object. But, unlike other big massive objects you are familiar with, this object is so massive that the effect of its gravity changes the definition of position in a way we cannot ignore.  The best way to describe this change accurately is to start writing out equations.  Are you looking for a resource that will walk you through those equations?
 * If you would like to look at how we could formalize the defintion of "position," you can read our more technical articles on black holes. For example, take a look at the radial distance element in our article, Eddington–Finkelstein coordinates.  This tells us about the path that an object would travel for one simplification of a black hole.  Do you know how to use a differential path element to work with position, distance, and trajectory?  Does this math make sense to you?  You will probably need to spend some time reviewing algebraic geometry and calculus; and that's just to understand the result.  To understand the derivation - in other words, why this is the answer - you will need to study some fairly difficult physics, too.
 * Nimur (talk) 15:57, 20 July 2015 (UTC)
 * For more reading: our article on Gullstrand–Painlevé coordinates includes a worked example-problem for an object falling into a black hole. Again, the reader is expected to have a very strong background in mathematical physics.  The equation solutions are not very difficult; but their derivations, and the conceptual implications, are quite complicated.  Nimur (talk) 20:36, 20 July 2015 (UTC)
 * I may not actually understand all any of the above, but I remember reading that Hawking radiation could be thought of as a quantum tunneling effect for particles at the singularity. Searching Google delivers various hits for this idea (mainly Arxiv papers of, to me, unknown canonicity), including our own article.  So we say that particles that fall into a black hole fall "into" the singularity, but in truth a particle isn't at any one particular place; there is variation in where it really is by measurement.  Very, very rarely this variation in measurement is so far that it is outside the black hole entirely.  Now one of many things I don't know is if anyone has a way to measure Hawking radiation and see if it matches theory for all the particles sitting at the center of the hole, rather than (say) sitting in a shell just under the event horizon or whatever, in which case I assume there'd be more Hawking radiation.  There's some kind of comparison to Unruh radiation but I think that kind of begs the question if there were some structure inside the hole we don't know about. Wnt (talk) 21:35, 20 July 2015 (UTC)

Radio-frequency identification
The IT media keep telling us about the promised advantages of clothing with computers woven in to them but why doesn't clothing have cheap RFID chips already? !!! The poor (and understaffed) Northumbria Police are having ask members of the public for information to solve the  mystery of a Beach Towel stolen in broad daylight. Had the owners been able to buy a Beach Towel with such a RFID chip woven in, these scums (beach bums), would by now have been apprehended by now -as soon as their motel scanner registered that they where carrying a Beach Towel that had been taken without the owner's consent. Isn't that more useful that a pair of computerized Bermuda shorts that can instantly give you the value of $\pi$ to 106 decimal places?--Aspro (talk) 19:46, 19 July 2015 (UTC)


 * Your external link doesn't work for me. This one does.  Rojomoke (talk) 19:55, 19 July 2015 (UTC)


 * Thanks. Both links work for me, so perhaps my link only works in the UK. I can't  see how the newsindex in the URL makes and regional difference. Can any geek  shine light on this? --Aspro (talk) 20:29, 19 July 2015 (UTC)
 * Huh, now yours works. Must have been a temporary glitch.  BTW, I'm in the UK. Rojomoke (talk) 21:55, 19 July 2015 (UTC)


 * Uhm. Wondering, that as it was Sunday night, the website may have been under going a little weekend maintenance? That can make normal access problematical. --Aspro (talk) 23:30, 19 July 2015 (UTC)


 * So you want to install RFID readers in every room, all linked to a central database, at a cost of millions, to catch beach towel thieves ? Also consider the loss of privacy ("Looks like Mrs. X's panties ended up in My Mr. Y's bedroom again !").  Please tell me you asked this question as a joke.  StuRat (talk) 20:54, 19 July 2015 (UTC)


 * Well... So OK...  You are  honest enough to admit that My Y's bedroom frequently gets  littered with Mrs. X's panties, but RFID could be of use to Mr X (who bought her knickers  in the first place)  and wants to get his property back (these days - designer panties don't come cheap – ask any woman). Is this not,  the position the beach towel owner found themselves in? Fortunately, here in the UK, we have a police force that leaps into action in order to maintain zero tolerance.  If ever these guys get caught they are facing at least three life sentences. --Aspro (talk) 22:37, 19 July 2015 (UTC)


 * This is I suspect not a serious question, but I will say that there are much simpler ways to mark clothes - you can order embroidered or printed name tags for a few pence each from various online shops, or just write the name on using a wash-fast marker pen - and they're about as difficult to remove from a piece of clothing as an RFID tag would be (since you can just snip it out or whack it with a magnet to mess up the chip). Some clothes and bags do already have chips sewn into their labels (I had a coat that caused me massive problems when a stock-checking tag sewn into the pocket lining somehow reactivated and began triggering alarms in every shop) but these are for stock-tracking, shop security and luggage tracking, rather than protecting later owners from theft. Smurrayinchester 09:06, 20 July 2015 (UTC)


 * Yeah, but it's harder to have a drone fly over and keep constant surveillance over what every laundry tag says. See  for an idea.  Why do you think the spy-industrial complex wants to put a "short-range" radio connection in everything you use, if they couldn't read it at short range? Wnt (talk) 12:13, 20 July 2015 (UTC)


 * Hotel towels with RFID chips starting hitting the media about 2011. It's worth a quick google if you want to find out more. shoy (reactions) 18:30, 20 July 2015 (UTC)


 * In NZ it hasn't been uncommon for jackets and coats sold in some shops to have RFID tags, probably for over 10 years. It's not so fun when as Smurraryinchester mentioned, store security systems get triggered by them, even stores which have never and are never likely to sell these items because they are a house brand of another store. Of course even worse than a coat/jacket is a reusable shopping bag which again may be housebranded but active security systems in stores not owned by the same company, but perhaps not the store you purchased it from. As Summaryinchester mentioned, these RFID tags are intended for the store use and I'm totally sure they actually have a unique per item identification. Nil Einne (talk) 20:10, 20 July 2015 (UTC)