Wikipedia:Reference desk/Archives/Science/2016 January 30

= January 30 =

Sewing machine oil
What is it made from and what properties does it have for suitability in sewing machines?--213.205.192.13 (talk) 00:48, 30 January 2016 (UTC)


 * One special consideration is that it shouldn't stain, in case it gets on the fabric. A highly volatile oil that will dissipate on it's own would also be better than one which would require detergent to remove, as some fabrics, like felt, might be too fragile for that.  Also, it shouldn't stink, so petroleum-based oils might not be the best choice.  All of this would mean it would need to be applied frequently, though. StuRat (talk) 00:59, 30 January 2016 (UTC)
 * See here. -- Jayron 32 04:00, 30 January 2016 (UTC)
 * See also Reference desk/Archives/Science/2015 March 18. DMacks (talk) 03:43, 31 January 2016 (UTC)

The odds against us being here
Some lifeform billions of years ago had eggs. Most of the eggs died. We are the decendant of the egg that survived, right?

So, is there any way to guess at the odds against that lifeform's DNA surviving to this day? Or the other way around, is there any way to take a ballpark guess at the odds against a person making it this far? Anna Frodesiak (talk) 01:27, 30 January 2016 (UTC)


 * Did you ask pretty much the same question sometime in the last year? If so, wherever it's archived might contain some answers. ←Baseball Bugs What's up, Doc? carrots→ 01:32, 30 January 2016 (UTC)


 * Hi Baseball Bugs. Did I? I don't remember asking. I do have a terrible memory. I am very sorry if I did. Anna Frodesiak (talk) 03:06, 30 January 2016 (UTC)
 * My memory is no better. :) I recall a question like it, but I don't recall the author. ←Baseball Bugs What's up, Doc? carrots→ 09:07, 30 January 2016 (UTC)


 * The earliest lifeforms didn't lay eggs. As for the odds of a fragment of DNA surviving lots of generations unchanged, that depends on the importance of that fragment.  If it was absolutely critical to survival, then only organisms with it would survive, and would therefore pass it down.  On the other hand, if the DNA fragment is of no value whatsoever, then it probably won't last long, with random mutations deleting or altering it (see genetic drift versus natural selection). StuRat (talk) 01:35, 30 January 2016 (UTC)


 * Hi StuRat. I don't really mean DNA, but more ancestry, as in parents' parents' parents' all the way back. Anna Frodesiak (talk) 03:56, 30 January 2016 (UTC)


 * DNA is the primary mechanism of inheritance of traits. However, let me try to address this "odds" question differently.  Let's say you roll a fair ten-sided die 12 times, to get the numbers 3,8,1,6,3,9,0,1,4,7,2,9.  The odds of you then rolling the same sequence again would be one in a trillion.  However, that doesn't mean you look at the numbers you already rolled and say "Wow, there was only a one in a trillion shot of rolling that sequence and yet I did, what amazing luck !", as you could have said that about whatever sequence you happened to roll.  The same is true of the random events that created you.  If the dice were rolled a bit differently, and somebody else was born instead of you, they could have also looked back and said it took an amazing number of "lucky rolls" to get them. StuRat (talk) 08:33, 30 January 2016 (UTC)


 * The odds of a fact being the case are exactly 1, and we cannot replay the movie. That being said, replaying the movie from the beginning is the theme of Stephen J. Gould's Wonderful Life.  He interestingly pointed out the fact that if the dog had not been caught, one single Labrador retriever would likely have driven the Kiwi extinct. μηδείς (talk) 04:09, 30 January 2016 (UTC)
 * Thank you, μηδείς. I will try to get that book. I am sorry I keep asking questions that are so hard to answer. I think the problem is that I don't quite know how to ask them properly. Best, Anna Frodesiak (talk) 04:22, 30 January 2016 (UTC)


 * What!?!? Never.  As the official bête noire of the RD, I can certify that you have never asked an offending question.  (I do still find it hard to believe you are not related to the Frodesiaks of Passyunk Avenue.  But that's a side issue.) μηδείς (talk) 04:57, 30 January 2016 (UTC)


 * Not being able to "replay the movie" is, of course, a variant of the anthropic principle in the sense that the universe which produced the current state it is in is the only possible universe which could exist to produce the current state it is in. Historically, this was also part of the conjectures of Gottfried Leibniz and "Pangloss" in Candide, see Best of all possible worlds; the notion that we must live in the only way history could have turned out, and it couldn't have possibly been better or different. -- Jayron 32 05:03, 30 January 2016 (UTC)
 * I don't quite agree with your interpretation, Jayron32, but I do agree that anyone interested in the topic should be familiar with the items to which you have linked. The bottom line is that any such "replaying" would be imaginary.  Physically, there is no way to do it, Doctor Who and The City on the Edge of Forever unwithstanding. μηδείς (talk) 06:09, 30 January 2016 (UTC)
 * If one wants to take it to a physics, rather than a metaphysics, issue, concepts such as the arrow of time, causality, entropy, the Second law of thermodynamics, and Minkowski space all require the fundamental concept of "we can't ever change the past so the present is the only possible present we could ever have." Of course, there are some interpretations of quantum mechanics which break principles of causality, and all principles of modern physics fly in the face of the clockwork universe such that all behavior at the fundamental particle level is stochastic and thus entirely unpredictable.  So, if you want the physics answer, depending on your perspective, the odds are either "exactly 1 in 1" (that is purely deterministic) or "exactly 1 in infinity" (or never repeatable and thus purely unique).  Interestingly, the answer is likely only one or the other (always or never) rather than any odds in between those two.  Or in simpler terms, to paraphrase Murray Gell-Mann (among others, probably) "That which is not forbidden is mandatory".  -- Jayron 32 06:39, 30 January 2016 (UTC)
 * Thank you so much, μηδείς. I do not mean to be a nuissance here. I promise to get better at phrasing the question. Perhaps this is better:


 * And I'm not asking just for fun. I really want to know. At dinner last night, people were saying it is important to have kids to keep the genetic line going. Someone said that a person's mom and her mom etc. beat the odds time and time again, especially when that mom was a squirrel way back when (bigger litters). Our parents are always the ones who made it. Anna Frodesiak (talk) 06:29, 30 January 2016 (UTC)
 * Or, the kid could say "I had a 100% chance of survival, because I didn't get hit by the car that killed my sibling" (or disease, or whatever). Stats are merely personal perspective under the illusion of mathematical indeterminacy.  See Lies, damned lies, and statistics.  -- Jayron 32 06:41, 30 January 2016 (UTC)


 * It would be 50% chance only if it was a prerequisite that one brother would die before reproducing. Just because one died out of 2 doesn't make it 50% chance. This is more of a maths question than a science question. Think of a pack of cards and draw one. You have a 100% chance of picking a card, 25% chance it is a diamond and a 2% chance it's an ace of diamonds. So from point of view of the end result it's 2% but all cards where 2%, so it not that surprising a card was drawn. So each individual being alive now has an almost vanishing probability of being here (think how many sperm does man produce in his lifetime). If you add all the probabilities up they are 1, so your answer depends on your view point. So at the start of life, you being you is extremely unlikely, but it's extremely likely something will be there (planet wide extinction excepted). As for the other way around this maybe workout able. How likely was it that Y-chromosomal Adam would be Y-chromosomal Adam, and not one of the other humans alive at the time, I don't know but maybe answerable. Dja1979 (talk) 06:56, 30 January 2016 (UTC)
 * You have a 50% chance of picking one of either of two cards before you pick them. You have a 100% chance of having already picked the card you already picked because it is in your hand right now and the other isn't. Stats are only useful in deciding the likelihood of future events.  Events which have happened cannot be undone, and thus have already occurred to a known certainty.  Schrodinger's cat is genuinely alive or genuinely dead even if you don't look, regardless of whatever the chance was that the particle would have decayed before it did.  -- Jayron 32 07:06, 30 January 2016 (UTC)


 * Or as Richard Feynman put it: "You know, the most amazing thing happened to me tonight. I was coming here, on the way to the lecture, and I came in through the parking lot. And you won't believe what happened. I saw a car with the license plate ARW 357. Can you imagine? Of all the millions of license plates in the state, what was the chance that I would see that particular one tonight? Amazing!" --71.119.131.184 (talk) 08:32, 30 January 2016 (UTC)


 * One thing to consider is the smaller scale of events. I've heard that about 1 out of every 4 pregnancies results in a miscarriage. I don't if that's true, but let's suppose it is. That means at the momenr you were conceived, you had about a 75% chance of not being miscarried. Any sort of mishap would have its own probabilities, but let's say you go your nine months and are successfully born. So far so good. Now consider other statistical probabilities. There's a 100 percent probability that you're going to die eventually, but there will be stats on what you're more or less likely to die from and at what age. ←Baseball Bugs What's up, Doc? carrots→ 09:24, 30 January 2016 (UTC)
 * It will depend on whether a miscarriage is defined as applying to all fertilised eggs or only those that have implanted in the womb, but this quote from a current BBC news article is relevant:
 * "Out of every 100 fertilised eggs, fewer than 50 reach the early blastocyst stage, 25 implant into the womb and only 13 develop beyond three months.
 * Thus a fertilised egg has only a 17% chance (not 75%) of resulting in a live birth, but of the non-surviving 83% only 52% (13 in 25) of those implanted or 13% overall would be classically termed a miscarriage. {The poster formerly known as 87.81.230.195} 185.74.232.130 (talk) 16:27, 1 February 2016 (UTC)


 * Hmmmm...


 * All of the arguments about the probability of me being here being 1.0 are rather facetious. If I win the lottery - that doesn't change how improbable that event was at the time when the random number was generated.  So we can ask:  "at the time the first egg was produced what was the probability of that egg producing a being that would fall within the parameters of a recognizable human being on or before the year 2016?" - that's a perfectly valid question that statistics should be able to answer if the data were available about the various probabilities along the way.


 * So, that dealt with - can we say anything meaningful at all about the odds?


 * My feeling is that we don't have remotely enough information. The path taken by evolution is simultaneously driven by pure chance (due to quantum randomness and chaos theory randomness) - and also shaped by the nature of the environment.  That's why we have such different organisms occupying the exact same ecological niche in different parts of the world.  Since the overall inputs to the problem (the chemical and geological makeup of our planet - inputs from the sun, the moon, comets and meteors) could be considered largely constant - the random nature of the weather and genetic mutation and sexual reproduction is likely to be the main source of subsequent randomness.  But the amount of that randomness is really hard to estimate.


 * The odds have to come out to be a truly astronomically low chance though. The probability of a being exactly like us being here is insanely small.   When the crew of the USS Enterprise arrive at a planet with beings just exactly like us, and behaving just like 1920's Chicago - and it's put down to "Parallel Evolution"...um...No.  Just no!  It comes about because the show had a low budget and the sets and costumes were available for cheap!


 * But the odds of there being some kind of intelligent being are likely to be much higher - it's interesting to wonder whether life inevitably turns up intelligence eventually - or whether it's also astronomically unlikely. In that case, we can point to the fact that creatures like the octopus are pretty smart - and they developed that intelligence entirely independently of mammals - so it seems that being intelligent is something that does emerge fairly easily from the randomness.  But whether it was inevitable that we'd have (for example) ten fingers seems much, much less likely.


 * So whether that first egg would ultimately result in exactly a human being seems insanely unlikely. But whether it would produce some kind of intelligent race of creatures seems very much higher...perhaps even close to a certainty if life continues to thrive for long enough and the environment is sufficiently complex to cause intelligence to be a useful adaptation.


 * SteveBaker (talk) 16:28, 30 January 2016 (UTC)


 * More formally stated, the conditional probability that an event occurs, given that we have already observed the event, is a mathematically distinct concept from the probability of the event before it was observed. Nearly all scientists would agree that the conditional probability that an event occurs, given that we have already observed the event is almost certainly exactly one.  This is almost a convoluted definition of causality.
 * Only a few very esoteric postmodern philosophers would disagree with the statement that an event we have observed actually did occur. For an example of such mind-bending logic, consider reading the writings of Jorge Borges, whose fiction put forward the catastrophically wonderful idea that factual object-reality only exists consequent to the creation of an encyclopedia defining those facts, and the brains that think they are reading that encyclopedia who all agree to hron object reality back into existence, at the expense of causality, not to mention the hroning of meaningful language.  Maybe extra-terrestrials, too?  Nobody is certain.  But Borges' work is not really science - it is fictions, I hope.  Nimur (talk) 16:56, 30 January 2016 (UTC)


 * We don't have enough data to work from to make even a ballpark guess, Anna. It seems likely that some primordial DNA is contained in what we call Junk DNA, the sequences of DNA which aren't expressed (that we're aware, anyway) as proteins in the human body and aren't responsible for how our bodies work and look.  But we don't have a way of identifying any particular unexpressed DNA sequence with that first organism you posit.  And for all we know, there are things in our "working" DNA that can be traced back to the first organism.  We just don't have a clue what. loupgarous (talk) 01:29, 31 January 2016 (UTC)

Very interesting indeed. I'm trying to get my head around the idea that "...Stats are only useful in deciding the likelihood of future events...". I've read everything above and think I get it. Thank you all. Sorry for the can-of worms question. Anna Frodesiak (talk) 01:39, 31 January 2016 (UTC)
 * I wouldn't sweat the "stats are only good for future events" thing - a trivial re-wording of your question would have fixed that - and our respondents should have realised that was your intention because anyone who understands that the probability of an event that's already happened is 1.0 would never have asked exactly what you did. So, it was reasonable to assume that you meant to ask what the future probability would have been at the time that first egg was laid.  But sadly, there just isn't any way to estimate that probability - and the precise details of what is meant by "egg" and "human" would have drastic repercussions for whatever answer we could possibly give - and that would result in much more confusion! SteveBaker (talk) 16:32, 31 January 2016 (UTC)


 * I'd like to comment on something more fundamental, . The question "What was the probability I would be me" can be looked at in two ways.  Probability deals with potentialities in undetermined circumstances.  Hence, if you asked, "Given a population of people with these genomes, what is the probability that an individual with a certain genome might randomly be born by the mating of two parents from that population?" it can be answered.  It is a mere question of possible assortments.


 * But, if you get to the point of an actual existing being asking, "What is the chance that I am me?" or, even better, "Why was I born a middle-class child of Jews and Catholics in NY, instead of being the future British monarch?" then you are reduced to the banal, "What is the chance that any given person is the future King of England" (At this point, about 6/15 billion.) Or the tautological, "Why (what is the chance that) was I born me?"


 * The question, "Why am I me,?" is the equivalent to, "Why am I my body?" That question, "Why am I my body?" depends on the implicit assumption of Cartesian Dualism, the notion that we are "Ghosts in a Shell" and that our souls could have been born in different bodies. I don't know your belief system, but if you are not a believer in the supernatural, "Why is my soul in my body?" is an incoherent question that is raised only because our Western culture is thoroughly dualist in all its major assumptions.  (Even materialists tacitly accept this in the notion that the self is an illusion, because they accept that there is a dichotomy between the physical and the spiritual.)


 * I was actually asked by someone, "How come I was born a white American, not a little girl in China?" I told her that she actually was a little girl in China, but that her soul had gotten switched.  She said, "That makes no sense!" to which I responded, "No, it doesn't, does it?"


 * μηδείς (talk) 20:16, 1 February 2016 (UTC)


 * I agree - these questions of 'self' get messy. I often debate with my wife on this one.  She finds the concept of death without any continuation of 'self' extremely hard to cope with.  So I'll ask whether reincarnation as a new born baby at the moment of your death is an acceptable alternative...and, yes, for most people it is hugely more acceptable.  Even when I point out that you'd have absolutely zero memory of your previous self - still, most people find reincarnation vastly preferable to absolute non-existence.  This is an odd thing because there really is no difference between the two possibilities.
 * So our OP needs to consider just how much difference would be acceptable. Would 'you' still be 'you' if you'd inherited the gene for lactose intolerance?  Most people would say "yes".  But what if you were of the opposite gender - still "yes"?  What if you were born as a chimpanzee?  Well, now, probably no...but there is more raw genetic difference between a human female and a human male than between a human and a chimpanzee of the same gender.  People's concept of the range of possible 'self' are strange - and that makes the statistics of the question even more impossible to cope with.  But even with a precise definition of what change you'd except and still "be you" - we still don't have remotely enough information for even a wild-assed-guess. SteveBaker (talk) 14:49, 2 February 2016 (UTC)


 * These kinds of questions are taken seriously by philosophers of Bayesian probability. For example, the doomsday argument argues that the chances of being born roughly in the middle of all humans ever born is most probable, and so one can extrapolate from the number of humans ever born the number of humans ever to be born.  (I do not count myself a believer in this particular argument, however.)  The anthropic principle is also relevant.   S ławomir  Biały  23:51, 1 February 2016 (UTC)
 * An even scarier version of that kind of argument is in "The Great Filter". The short version of which is that our inability to discover intelligent alien life out there in the universe means that either life is exceedingly unlikely to arise spontaneously, so we're the only ones - or that civilisations self-destruct very soon after they form - so the alien civilizations are all dead.  If we can't find a huge abundance of intelligent aliens out there - then either the formation of life is exceedingly rare - or we're going to befall some horrible disaster in the very near future.  Better hope we don't find evidence of primitive life on Mars...because that would mean that life does arise easily - and therefore we're all going to die very soon!  (Statistically speaking) SteveBaker (talk) 14:59, 2 February 2016 (UTC)
 * Bayesian analysis seems to me to partake of voodoo, sometimes. The most successful applications of it I'm aware of was when the US Navy's maverick oceanographer  John P. Craven had fellow specialists look at all the data surrounding the loss of a submerged object in deep water, and make bets (bottles of liquor were most often at stake) on where the object was.  Craven's odd application of Bayesian analysis worked well enough to find a hydrogen bomb lost in deep water after the Palomares incident in 1966, then the  USS Scorpion despite conventional analysis of the available evidence pointing away from the spot he and his specialists predicted - which is where the doomed ship was eventually found. loupgarous (talk) 01:58, 2 February 2016 (UTC)
 * Wisdom of the crowd is a good description of that phenomenon. SteveBaker (talk) 14:59, 2 February 2016 (UTC)
 * In the case of the search for USS Scorpion, the "crowd" - the Navy's senior decision-makers and salvage experts (convinced they'd found three scraps of debris from USS Scorpion far to the west of where Craven's Bayesian analysis predicted) was wrong.  USNS Mizar, the oceanographic ship detailed to find USS Scorpion, was only permitted to look where Craven's calculations pointed AFTER the Scorpion wasn't found where the crowd's conventional wisdom pointed.  And that's when the Scorpion was found.  loupgarous (talk) 05:22, 3 February 2016 (UTC)

Is electricity made up of electromagnetic or mechanical waves?
I know the difference between electromagnetic and mechanical waves (see, ); so since sound is a mechanical wave, and AC power can be heard, that would seem to indicate that electricity is a mechanical wave as well. But I thought that it was electromagnetic. Which is it? Eman 235 / talk 01:58, 30 January 2016 (UTC)


 * It's not a mechanical wave, and the sound isn't directly from the waves. Read your link to see the explanation (for an analogy, light could also create sound, if it warms something up that then expands or contracts) .  Also note the dual wave/particle model of electricity (as well as light, etc.).  The electron is the particle representation of a quanta of electricity. StuRat (talk) 02:04, 30 January 2016 (UTC)


 * Oh, I see. Electricity, under some circumstances, can cause a mechanical wave, but it isn't one itself. I'm assuming that AC is electromagnetic waves; but what is DC? Eman 235 / talk  02:34, 30 January 2016 (UTC)
 * See Direct current--213.205.192.13 (talk) 03:52, 30 January 2016 (UTC)
 * AC is not electromagnetic waves, AC can cause electromagnetic waves in the radio frequency. Read Larmor formula for some background for the mathematics.  "When any charged particle (such as an electron, a proton, or an ion) accelerates, it radiates away energy in the form of electromagnetic waves."  Alternating current consists of electrons vibrating back and forth in place; to change direction the constantly accelerate and decelerate, thus generating a regular radio frequency wave; this is the source of what is called mains hum, which is what happens when this radio frequency wave is picked up by audio equipment.  DC doesn't cause waves, but it does generate an electromagnetic field, see Ampère's circuital law, or Faraday's law of induction which is just the inverse of that.  -- Jayron 32 03:55, 30 January 2016 (UTC)
 * Hmmm Jayron, I would have said that dc in a stationary conductor can only create a magnetic field (not an electromagnetic field. But maybe you are now going to provre me wrong! :)--213.205.192.13 (talk) 04:06, 30 January 2016 (UTC)
 * All electric fields are magnetic fields, and visa-versa. You can, of course, describe such a field using only the magnetic force, or using only the electric force, but in reality, the two forces coexist at right angles to each other.  Electromagnetic_field discusses the historical separation of the two "fields" into distinct force fields, and the work of James Clerk Maxwell in marrying the two into a single concept, see also Maxwell's equations which describe the interrelationship between electric fields and magnetic fields into a single "electromagnetic field".  The modern field of quantum electrodynamics preserves this marrying of the two forces, and applies principles of quantum theory to it.  -- Jayron 32 04:55, 30 January 2016 (UTC)


 * It's easy to get confused between two types of wave here. Electricity is a wave because electrons have this duality between being particles and being waves.  So even DC electricity is a wave.   Then, we may choose to vary the amount of electricity we pass down a wire - or even reverse it's flow over time - that's AC.  So the waves we make when we use AC power (which oscillate at 50 or 60 times per second depending on where you live) are really just variations in the flow rate of the electricity.  If you look on a smaller timescale - like if you looked at the electricity for just a millisecond - then AC and DC wouldn't look all that different.


 * Perhaps an analogy might help. We see waves on the ocean going by maybe once every few seconds - but we also see tides - which cause the ocean to go up and down over the course of about half a day.  So imagine the electromagnetic wave to be like the ocean waves and the AC current variation being like the tide.


 * Another closer analogy would be AM radio - where there is the frequency of the radio broadcast (maybe around 1MHz - a million vibrations per second) - and then the frequency of the sound imposed on top of that at a few thousand vibrations per second...in that case, the electromagnetic wave is yet a third wave.


 * And as others have said - you can't directly hear the electricity - but they may cause some physical effect that converts them into mechanical vibrations that you can hear. You won't hear the electromagnetic wave itself - but rather the AC variation in that wave which (at 50 to 60 vibrations per second) is a soft hum at the lower end of our hearing range when converted to sound waves in the air.
 * SteveBaker (talk) 16:04, 30 January 2016 (UTC)
 * The Larmor formula has no application to DC in a stationary conductor because no electrons are being accelerated and, as 213.205.192.13 correctly says, only a stationary Magnetic field is produced. Electromagnetic radiation is launched wherever there is simultaneous production of an oscillating E and H field oriented so as to give a finite value to S = E X H where S is the Poynting vector. AC power frequency is usually 50 or 60 Hz and its distribution unintentionally causes some electromagnetic radiation, mostly at harmonic frequencies since the length of wiring to create an efficient Dipole antenna at such low fundamental frequency would be as long as 1250 to 1500 km. Mains hum treats the sound associated with mains AC and should have made clear to the OP that one does not "hear the electricity", one may only hear mechanical sound waves produced via an intermediate process such as coupling into an audio system (stray capacitance, poor grounding and/or poor supply regulation contribute) or Magnetostriction in a transformer core. Electromagnetic waves travel in a vacuum whereas mechanical waves do not. The Electron has mass and charge but is not itself a wave. A "wave nature" is ascribed to the electron by De Broglie and Schrödinger meaning that a wave equation predicts the probability of finding its actual position, but I cannot support the claim that "DC electricity is a wave". Wave function treats this subject in quantum mechanics but the OP is clearly asking about classical mechanical waves i.e. Sound. AllBestFaith (talk) 16:47, 30 January 2016 (UTC)


 * We need to carefully review a few terms:
 * electrons, the small points that carry electric charge
 * electric current, any movement of electrons (or any other charged item)
 * the electric field, a physical effect that exerts force on any charged particle
 * the magnetic field, a physical effect that exerts force on any moving charged particle
 * electromagnetic waves, a special behavior that electric- and magnetic- fields may exhibit to propagate energy as a wave
 * Electricity is a little bit difficult to describe, because it involves all of these concepts at the same time. Every time an electron moves, it affects an electromagnetic field.  Every time an electromagnetic field exists, it affects electron motion.  We have lots of names for these effects, including the Lorentz force equation, and the very important Maxwell's equations.  To understand these concepts, you must know that electrons affect electromagnetic fields, and electromagnetic fields affect electrons.
 * This circular logic is formally described using the mathematics of a differential equation. It so happens that the equation relating electric fields, magnetic fields, and moving point-charges can be represented as a wave equation.  In other words, we can have a stable wave that describes a movement of electrons, and a change in electric- and magnetic- fields.  However, not every case involves a propagating wave.  For example, a steady DC current moving down a long, straight wire, can be adequately described (and we can solve all the field equations) without bringing up a propagating wave.  So, electric current always involves an electric- and magnetic- field, but only yields an electromagnetic wave in some conditions.
 * When you use electricity in every day life, the energy can be carried by both the electromagnetic wave and by the movement of electrons. The exact details depend on how you're using that energy: for example, in a low-voltage DC lightbulb, the majority of energy that heats your filament is conveyed by the movement of electrons.  Electrons lose kinetic energy by bouncing around in a resistive element, heating the wire until it is hot enough to glow.  We can write a simple equation - Ohm's law - to describe the energy transfer, and we don't need to consider any wave behavior at all, for this case.
 * In the antenna of a handheld radio transmitter, electrons move back and forth, swaying across a very short distance. Energy is carried along the wire, and out into the air, by an electric field and a magnetic field.  For a well-designed radio, we can nearly ignore the kinetic energy carried by the electrons in that antenna - the resistive losses are nearly zero.
 * In the microprocessor inside a computer, each transistor turns "on" and "off" to signify a digital, logical bit. To turn one single transistor "on", a voltage is applied at the "gate" of a field-effect transistor.  This voltage applies an electric field over the device's "channel"; and electrons can flow across the channel.  Energy is carried by the electrons, which we call the "switching current"; and energy is also carried by the changes in the electric field, which we call the "digital signal."  If we switch the bits between zero and one, some energy is also lost in the form of an electromagnetic wave, which we call "electromagnetic interference," because that energy lost as a wave is unwanted.
 * If we zoom in and solve the equations rigorously, we find that there is always some component of energy in the electron-movement and some component of energy in the electromagnetic field. In the simple cases, we can use straightforward approximations and simpler equations so our work isn't so hard.  Half of the work when you study electrical engineering is learning when you may safely use simplified approximations, and when you must solve the full-form, difficult equations.
 * Nimur (talk) 17:32, 30 January 2016 (UTC)


 * I'm not satisfied by the answers so far. I'm thinking that if you have ten amps of current in a wire, that's 10 coulomb per second, or 6.242×1019 electrons per second.  Electron mass is 9.10938215(45)×10-28 g, so that's 5.686 x10-8 g, or 56.86 nanograms of electrons per second pass through a given point in the wire.  Now that doesn't seem like very much, though I'll admit, I'm not sure how to convert the fact of it being batted back and forth each 1/60 second into a number I can compare to something.  But to give an example, a 20-microliter drop of water will make a sound when it hits a surface, and that weighs 20 milligrams.  If you atomize water to the point where it is mere nanoliters, it will be more like a mist striking a surface and I don't think you'd hear it.  So though electrons are definitely physically moving, they do so with extraordinary lightness and ease compared to the things we know, and they are extraordinarily potent in carrying charge. Wnt (talk) 23:45, 30 January 2016 (UTC)
 * Most of the time, "mains hum" is referring to radio noise that can couple into an amplifier or a speaker. Speakers are mechanical devices that are designed to transduce electrical signals into acoustic signals.  In that case, the unwanted electromagnetic signal is added on top of the desired electromagnetic signal, and that is why you hear it.  This is common because a weak signal is usually amplified before it is played on a speaker.
 * In the exceptional case of very high currents, passive elements (like the wires themselves) can transduce electrical current directly into acoustic noise. The transduction of electric current into acoustic noise is mainly because such very large currents can create oscillating thermal changes, and because electrostatic forces cause the material to attract and repel other objects (including other parts of the same wire).  These effects can result in mechanical movement of the bulk material.  Essentially, in those cases, the wires are acting as a very poor-quality speaker.  You are not hearing acoustic noise due to electrons impacting anything.  Most of the time, you don't actually hear anything at all, until the energy is intentionally converted to acoustic vibrations.
 * Nimur (talk) 00:07, 31 January 2016 (UTC)

January_2016_East_Asia_cold_wave in Thailand.
Your article for the January 2016 East Asia cold wave reads: "Temperatures in Bangkok, Thailand fell to 16 °C (61 °F), and 14 people in Thailand died from the cold.". How the hell can 16 °C (61 °F) even kill people? it is not even cold. --Bidfevnörsk (talk) 14:50, 30 January 2016 (UTC)


 * The deaths weren't in Bangkok, The supporting cite is the second one, http://www.bangkokpost.com/news/general/840592/cold-wave-causes-14-deaths, which says the deaths were inChainat province, and Udon Thani, and Chai Nat, and Samut Prakan, and Nakhon Ratchasima, Sakon, and most of the victims had underlying health problems. The temperatures in these areas may have been lower than in Bangkok. IIRC, many homes in Thailand don't have heating, as it very rarely gets cold. LongHairedFop (talk) 15:20, 30 January 2016 (UTC)


 * I think it's all about the huge change from normal. It's almost always around 30°C, so 16 - and less - is a huge shock-to-the-system. And as stated, almost nobody has heating. — Preceding unsigned comment added by 81.108.18.234 (talk) 16:17, 30 January 2016 (UTC)


 * Note beyond the fact most of those affected probably experienced lower temperatures, already had health problems and the absence of heating, there's also likely to be an absence of clothing or even blankets (if they have any) suitable for lower temperatures. Remember that while sure, many people may be fine wearing just a thin t-shirt or shirt and if they're lucky think long pants (or similar), not everyone will be. And beyond the shock to the system of such an abnormally low temperature, there's also the lack of experience and understanding (including from friends, relatives and neighbours to keep an eye on the vunerable). It may be a bit easier than with a heatwave, still you get similar things where temperatures in the low 30s°C can be a significant concern in some places. Nil Einne (talk) 16:42, 30 January 2016 (UTC)


 * Bangkok is a city at sea level. Both of these facts raise the average temperature compared with the surrounding countryside.   The average January temperature is five degrees lower in Phetchabun Province (still on the plain) and even colder in the northern mountains where there is sometimes a light frost.    D b f i r s   18:09, 30 January 2016 (UTC)


 * Did it rain ? If you are soaking wet, those temps could contribute to making you sick.  And they may have leaky houses and a lack of waterproof clothes, if the high temps normally make getting wet not an issue.  Wind would also be a contributing factor. StuRat (talk) 18:24, 30 January 2016 (UTC)

Volcano
What kind of volcano is mount Konocti and mount Shasta? And Dormant? Extinct? 208.91.28.66 18:44, 30 January 2016 (UTC) — Preceding unsigned comment added by 208.91.28.66 (talk)


 * I linkified your Q. Please read those articles for answers. StuRat (talk) 19:14, 30 January 2016 (UTC)
 * (ec)Mount Shasta is considered by the USGS as a "very high threat volcano", so dormant not extinct. Mount Konocti has a "high threat potential" according to the USGS , so dormant and not extinct either. Mikenorton (talk) 19:15, 30 January 2016 (UTC)


 * The Volcano article should answer your general questions. The two you mention would be stratovolanoes, and the difference between dormant and extinct is somewhat a matter of opinion. ←Baseball Bugs What's up, Doc? carrots→ 19:17, 30 January 2016 (UTC)


 * Although some volcanoes are definitely extinct! Alansplodge (talk) 15:36, 31 January 2016 (UTC)


 * Having an old castle on top doesn't necessarily mean it's extinct, as some volcanoes can lay dormant for thousands of years (700K for Yellowstone !). StuRat (talk) 03:45, 1 February 2016 (UTC)
 * I think that more than 300 million years is probably long enough to be sure. Mikenorton (talk) 09:47, 1 February 2016 (UTC)
 * You beat me to it! See Castle Rock, Edinburgh for the details. Alansplodge (talk) 11:08, 1 February 2016 (UTC)