Wikipedia:Reference desk/Archives/Science/2014 June 10

= June 10 =

An unusual relationship.
What is the correct terminology used in astronomy, to describe a system of two non-stellar celestial bodies, which share an atmosphere in a state of equilibrium? Plasmic Physics (talk) 00:02, 10 June 2014 (UTC)


 * I was not aware such a thing was possible. I should expect that two such bodies would need to be in a rapid orbit about each other, and that the orbit would rapidly decay due to atmospheric friction.  So, it wouldn't be stable at all. StuRat (talk) 00:12, 10 June 2014 (UTC)


 * Empirical evidence suggests that there is such an example within our own solar system. I'm not going to reveal their identity yet, in case it causes a divergence from the query. That being said, I can divulge that the mean atmospheric pressure is less than half a Pascal. Plasmic Physics (talk) 00:19, 10 June 2014 (UTC)


 * A pascal (unit) is less than 100,000th the Earth's atmospheric pressure, so I wouldn't think that would qualify as an "atmosphere". (At some low pressure the entire solar system could be said to have an atmosphere, then the galaxy, as well.) StuRat (talk) 00:24, 10 June 2014 (UTC)


 * I suppose they (the research group) are using an equilibrium constraint, where mixing has reached a steady-state. For example, Jupiter's atmospheric composition is completely different from the Earth's, and so they do not have a shared atmosphere. Plasmic Physics (talk) 00:34, 10 June 2014 (UTC)


 * There is no obvious reason why two tidally locked bodies could not share an atmosphere, with a non-negligible pressure and with negligible decay in their orbits: there is no mechanisms by which they can shed angular momentum except by radiation (gravitational and EM), which we can ignore for these purposes. The only problem I can think of is whether one or both the bodies would disintegrate, as suggested in Roche limit. —Quondum 00:53, 10 June 2014 (UTC)


 * Does that limit apply to a pair of black holes ? If not, maybe that could work, as long as they are considered "non-stellar bodies". StuRat (talk) 01:08, 10 June 2014 (UTC)


 * Thanks for the link, it led me to a possible answer: Roche-system. The system that is being considered is dwarf planet system of Pluto and Charon. Plasmic Physics (talk) 01:07, 10 June 2014 (UTC)


 * Temperatures are so low there that I wouldn't expect much gas, and hence much atmosphere. StuRat (talk) 01:09, 10 June 2014 (UTC)


 * Low gravity, leads to low pressure, which leads to a low sublimation point, which leads to a higher vapour pressure. You're correct in saying that there isn't much atmosphere, but much is by definition, a relative term. Just as relative to Jupiter, Earth doesn't have much of an atmosphere. Plasmic Physics (talk) 01:17, 10 June 2014 (UTC)


 * To be specific, I've read the Rocheworld article. Plasmic Physics (talk) 01:35, 10 June 2014 (UTC)
 * Astronomical distances are widely underestimated. The distance between Earth and moon is 22x the Earth diameter. Our Atmosphere extends only up to 1,000 km (Exosphere) which is way less than the 384,000 km distance to the moon. I dont think its physically possible to even construct a fitting model with your parameters within Kepler's laws of planetary motion, not to speak of chances for survival, in astronomical dimensions of time, for such a constellation. --Kharon (talk) 03:42, 10 June 2014 (UTC)


 * Just to be certain, you're also talking about the Pluto-Charon system? I'm not sure how your answer relates. Plasmic Physics (talk) 03:50, 10 June 2014 (UTC)
 * Its quite similar with Pluto and Charon. The Distance between them is 9 times Plutos Diameter. Atmosphere is bound by Physics aswell btw. so its height is connected to the body's gravitation as is a "save" or "possible" Orbit of another Body. This is just another example of fictional novels that completely disqualify the term Science in science fiction, which to be fair is unfortunately something veeery common. --Kharon (talk) 04:26, 10 June 2014 (UTC)


 * (ec)I added a photo of Pluto and Charon above. They don't really look like my idea of a Rocheworld.  Pluto is more than 2000 km across, so Charon would be at really high altitude.  Of course the scale height would be vastly lower greater due to the low gravity, but still... I would need some convincing there's a pascal of air filling all that vastness of space.
 * If there were, though... I wonder what a billion year red giant phase of the Sun would do with that atmosphere. I imagine it would become considerably thicker... Wnt (talk) 04:27, 10 June 2014 (UTC)
 * I'm guessing you mean the scale height is greater. —Tamfang (talk) 05:08, 10 June 2014 (UTC)
 * Sorry, thanks. Wnt (talk) 16:52, 10 June 2014 (UTC)


 * Some back-of-the-envelope calculations give Pluto's scale height as being about 15 kilometers; Charon would be about a thousand scale heights away. For comparison, Earth's moon is 50,000 scale heights away, and "outer space" is considered to start at about 13 scale heights.  --Carnildo (talk) 00:45, 11 June 2014 (UTC)


 * Here is the source link so that you can form an informed opinion: . Plasmic Physics (talk) 04:36, 10 June 2014 (UTC)
 * Ah, 6 × 1019 N2/m2 of surface isn't very much pressure at all, is it? Wnt (talk) 05:00, 10 June 2014 (UTC)


 * Nope, but that doesn't stop it from being interesting. Plasmic Physics (talk) 05:07, 10 June 2014 (UTC)
 * Its starting to become trolling if you try to connect some possible scenario where Charon may end up catching some Particles of the former Atmosphere of Pluto, it couldnt keep to be proof for a Rocheworld. Your source is not about "sharing one Atmosphere" but just some silly spindoctor-rhetorics on scientific facts to fit some wanted evidence that infact is clearly neither evident nor will it ever be. If i do a dump in the Wood and you step on that space 5 years later that does not mean we share body fluids altho you might be able to find some molecules on your shoe that where in me once (might have to mark them radioactive at start to actually proof). --Kharon (talk) 05:46, 10 June 2014 (UTC)


 * Look, before you accuse me of trolling, as far as I'm concerned, my original question has been answered, which was concerning the semantic implication of a hypothesis. Whether or not the system is in fact a Roche-system, is irrelevant to my query. That concern is an point of interest, however, not raised by me. Plasmic Physics (talk) 06:09, 10 June 2014 (UTC)


 * Hey, we're all trolling, exploring off-the-wall ideas on purpose. Science trolling is fun. :) Wnt (talk) 16:52, 10 June 2014 (UTC)

Air planet
Suppose you have an icy planet roughly the size of Earth made of pure water, ammonia, maybe methane. It migrates inward toward a sun and becomes an ocean planet. The star gets a bit hotter and even the water becomes gaseous, and if there is a strong stellar wind, or it is a long-lived red dwarf star, eventually almost all of the hydrogen from the planet's atmosphere goes away. I'm thinking that this ought to leave you with a planet pretty much made out of air - oxygen, nitrogen, carbon dioxide - maybe with a few lifeforms or other complex molecules floating in the nearly zero-gee environment. Have such planets been postulated, or even searched for? Wnt (talk) 05:15, 10 June 2014 (UTC)


 * It will not be a universal near zero-g environment though, that only occurs when the molecules are travelling at or greater than escape velocity. In any every other case, they should fall-in toward the core of the planet, developing a density gradient as a result of Brownian motion. Plasmic Physics (talk) 05:33, 10 June 2014 (UTC)


 * Well, what I mean is that if you have a planet with roughly the mass of the Earth, made almost entirely of air, any rare solid matter could swirl around in winds near the planet's core where there is quite low gravity. (High pressure, though!) Wnt (talk) 05:37, 10 June 2014 (UTC)


 * Still, why do you suppose that the gravity will be low in the core, despite the high mass density? Plasmic Physics (talk) 05:42, 10 June 2014 (UTC)


 * Well, the shell theorem. In general, gravity is lower inside a planet; for instance, it is lower inside the Earth (though first it goes up because the iron inside the Earth is denser than the rock above).  At the center, of course, nothing knows which way to fall. Wnt (talk) 05:53, 10 June 2014 (UTC)


 * I imagine such a planet to be of a size intermediate of Neptune and Earth, to have a carbon core with a multiple layered ocean. Where each layer consists of a different supercritical component. With an atmosphere of nitrogen and oxygen, with layered clouds of nitrogen oxides, carbon oxides, carbon nitrides, and perhaps some carbon-nitrogen oxides. At one Earth mass, it is not dense enough for metallic phases to form. Plasmic Physics (talk) 06:00, 10 June 2014 (UTC)


 * Well, I was picturing a planet roughly the size of Earth, since gas giants are common enough. Also, while I'm postulating "enough" solar wind, there comes a point where I can't plausibly postulate blowing away all the hydrogen from a heavy planet.  Since we think that planets like Mars lost oceans and atmosphere to solar wind, that much at least seems plausible to me with a long-lived star and no magnetic field and high solar wind.  More to the point, I was asking about air giants, not metal giants.  Even so... thanks for cueing me to that metallic oxygen occurs at only 1320 atmospheres of pressure, which is only 7 scale heights down from sea level pressure at Earth gravity, roughly 60 km.  But I don't know if there's a metallic nitrogen or how the "alloy" of these gasses would act.  Also, I don't know how small a mass you could make an air world without it all evaporating, maybe you could avoid the gravity and depth needed to make a metallic phase? Wnt (talk) 06:16, 10 June 2014 (UTC)


 * Larry Niven's novel The Integral Trees postulates a gas torus, in orbit around a neutron star, that is inhanbited by various native lifeforms and has been colonised by humans. Gandalf61 (talk) 11:55, 10 June 2014 (UTC)


 * I don't think an air planet can exist, because gravity is determined not just by the total mass, but by the density of that mass. Since gases are not at all dense, that means the gravity will be too low to hold it all together.  If you argue that the pressure would be high enough to make the gas dense, then it would form a liquid. StuRat (talk) 12:31, 10 June 2014 (UTC)


 * The above sentence is so wrong in so many places, I don't even know where to begin correcting it. -- Jayron  32  15:08, 10 June 2014 (UTC)




 * As I have no idea what you object to, it's hard to refute, but lets start with a typical phase diagram which shows that gases do tend to become liquids or solids as pressure increases. StuRat (talk) 15:14, 10 June 2014 (UTC)


 * The behavior of supercritical fluid is still something I don't have a good intuitive sense for. It is "somewhere between liquid and gas", but when I was looking up during my previous question at Reference_desk/Archives/Science/2013_July_5 I had the impression that it doesn't have very much viscosity; I'm thinking that to the eye it can "pass" for a gas.  With a critical pressure of just 50 atm, oxygen is definitely going to reach that phase.   (according to  ordinary air has a critical pressure of 550 psi, which is even less)  I think that deep divers (>640 feet) at ambient pressures exist and should therefore be breathing oxygen supercritical fluid --- however, they breathe fancy mixtures like Hydrox (breathing gas), and I'll admit I'm ignorant of whether these mixtures avoid (perhaps are designed to avoid) reaching their critical pressure.  So for this question of whether they exist I'm inclined to arbitrarily define that an "air planet" counts as existing if it has a supercritical fluid in much of its center, but not if it has a metallic phase there.


 * The density argument is a good one - clearly an air planet would have density not much more than an eighth that of Earth. Earth has density 5.5, liquid nitrogen 0.807, and I wouldn't expect much different from a supercritical fluid under high pressure.  However, 8x volume is only 2x radius, leaving a planet with 1/4 Earth "surface gravity" but nonetheless a 2x slower decrease of gravity at higher altitudes than a genuinely smaller Mars-like world would have, which makes the well deeper and harder to escape.  I suppose I could work atmospheric escape calculations to work how all this plays out; but the premise of an air world depends on having preferential loss of hydrogen atmosphere rather than oxygen, nitrogen, carbon dioxide, and being made entirely of air it has its entire mass to play with, so I'm thinking this ought to be in roughly the right size range. Wnt (talk) 16:47, 10 June 2014 (UTC)


 * Where do you get that the density of air is only 1/8th that of, say, water ? The density of air at STP is 0.0012 kg/L, while for water it is 1 kg/L.  That's 833 times less dense.  And the Earth is even more dense at 5.515 kg/l.  And, that's assuming 1 g.  As you lower the acceleration due to gravity, the gas becomes even less dense, hence lowering the gravity more, etc.  StuRat (talk) 17:14, 10 June 2014 (UTC)


 * As you pointed out, the vast majority of the air planet will be "supercritical fluid", which though having many gas-like properties, has density nearly equal to that of the liquid. (A NOAA source I cited above mentions that specifically for supercritical air) Wnt (talk) 17:30, 10 June 2014 (UTC)


 * OK, but where did that 1/8th the density of Earth estimate come from for supercitical fluid air ? StuRat (talk) 20:17, 10 June 2014 (UTC)
 * Well, it was "something like 0.807" / 5.5, rounded to 8 so that I could be clear with the factors of 2. This hasn't risen to the level of a genuine calculation yet, so I thought that was close enough. Wnt (talk) 02:43, 11 June 2014 (UTC)

laws of physics on earth
Are there any examples on Earth where the established laws of physics go "out the window", as it were? Rare moments where different or no laws of physics apply to a given situation? Like how near black holes in space the laws of physics get screwy K4t84g (talk) 08:40, 10 June 2014 (UTC)


 * I'm just going to go out on a limb, and say... no. Plasmic Physics (talk) 08:43, 10 June 2014 (UTC)


 * Of course not. They wouldn't be established as laws of physics if they didn't describe the world we actually inhabit with a degree of accuracy far beyond the needs of everyday life. AlexTiefling (talk) 09:16, 10 June 2014 (UTC)


 * Probably the closest thing to what you're looking for is covered in List of unsolved problems in physics. Nil Einne (talk) 10:28, 10 June 2014 (UTC)


 * From my reading of multiverse, the answer could be "yes". --178.190.48.47 (talk) 10:36, 10 June 2014 (UTC) Oops, not logged in.  --Cookatoo.ergo.ZooM (talk) 10:37, 10 June 2014 (UTC)


 * Would you care to explain? The OP asked for Earth-bound examples, and multiverse is explicitly about purely hypothetical cosmologies. AlexTiefling (talk) 10:38, 10 June 2014 (UTC)


 * There are cases where Newtonian physics goes out the window, and you must invoke the theory of relativity, quantum dynamics, etc., to explain something.  A Bose-Einstein condensate is one such example.  StuRat (talk) 12:37, 10 June 2014 (UTC)


 * Have you ever had a situation where you thought something happened one way, but later learned your original assumptions were wrong, and had to change what you think? Like, say, for example, you had ten dollars you left on your dresser.  And then, one day, it wasn't there.  Since you share a room with your brother, you totally thought he stole it.  So, you go through your whole day accusing your brother of stealing your money, and accusing him, and thinking ill thoughts of him.  And then, like three days later, you realize that it just fell off the back of the dresser and got stuck there.  And then you stop thinking your brother is an asshole, and actually feel kinda bad about thinking what you thought in the first place?  Yeah, that's exactly how science works, including the laws of physics.  -- Jayron  32  15:06, 10 June 2014 (UTC)
 * Yeah isn't it totally kinda like awesome to post about science stuff using Valleyspeak about someone thinking someone is an ***hole eeewh! Like EEEWH! 84.209.89.214 (talk) 13:01, 11 June 2014 (UTC)


 * In other words, the laws of physics, as the scientific community knows them, can never be wrong, because when they find a situation where they are wrong, they change the "laws" so they are right. Richard-of-Earth (talk) 18:08, 10 June 2014 (UTC)


 * Sort of. Sometimes - such as just after the Michelson-Morley experiment was verified - the extant laws are known to be wrong, but there's no replacement law that's any better. Right now we're in the opposite position - there are several advanced formulations of the laws, such as string theory and loop quantum gravity that are equally good at describing the world we've got; what we need is better experiments (probably higher-energy ones, in bigger particle accelerators) or better cosmological data (probably older, more distant, more detailed astronomical readings) to distinguish between them. There are things (like the gravitational problems described as dark matter) that our verified theories don't properly address, but they're restricted to only a handful of situations; we haven't got a sufficient range of different kinds of observation to take those concepts further. The standard model is made of bits everyone agrees on. AlexTiefling (talk) 20:01, 10 June 2014 (UTC)
 * The Michelson-Morley experiment may have produced a negative result, but that is hardly the same thing as "verification". The bottom line is that in some contexts the concept of "an aether" is rather useless, while in others it actually makes quite a bit of sense (when considering the principle of inertia, for example). See Aether theories.Sebastian Garth (talk) 02:58, 11 June 2014 (UTC)


 * Perhaps the OP is thinking of something like Superfluidity? Like StuRat said, this isn't a violation of the laws of physics, but it is an example of something that seems to defy them if you're thinking in Newtonian terms. OldTimeNESter (talk) 19:36, 10 June 2014 (UTC)


 * Yes, and for several reasons. (1) The laws of physics have no limit. (If you don't believe me then just hop on over to the news-stand for the latest copy of your favorite science rag - chances are, some new effect will be described somewhere therein!) (2) Due to our own inherent limitations as human beings, some phenomena will simply defy scientific explanation (example: consciousness). (3) Insofar as science is really just a bunch of methods of approximation, we will never be able to predict anything with complete accuracy, and thus there will always be something observed that just doesn't fit "the model". Sebastian Garth (talk) 02:40, 11 June 2014 (UTC)


 * The OP may also be thinking of so-called gravity hills. Although these are nothing but optical illusions, many of them have become tourist traps&mdash;under names like "Magnetic Hill", "Vortex", and "Mystery Spot"&mdash;and are often promoted on the pretense that, as the OP put it, the established laws of physics go out the window there. --69.158.92.137 (talk) 03:47, 11 June 2014 (UTC)


 * There used to be an actual magnetic hill in the Ural Mountains, but that one didn't break any laws of physics either. 24.5.122.13 (talk) 04:36, 11 June 2014 (UTC)

Dog hearing
Which sounds of speech do dogs hear best, and which (if any) are they unable to hear? 24.5.122.13 (talk) 20:42, 10 June 2014 (UTC)


 * This is partly answered at Dog. Dog hearing is much better than human, and there is probably no sound a human can make that is inaudible to a dog.  According to  the maximum sensitivity of dog hearing occurs between 200 and 15,000 Hz.  Humans cannot hear at all much above the upper figure but dog hearing goes much higher.  The average frequency of a male speaking voice is below 200 Hz so dogs can probably hear female voices better than males when in normal conversation.  Dog hearing does not go down quite as low as human, the lower limit for dogs is given as 40 Hz in our article compared to 13 Hz for humans.  Thus the thing they will have most difficulty with is very low-pitched sounds like the lowest notes of a church organ.  But even then, such sounds are harmonic rich and the harmonics are easily heard by both dogs and humans even if the root note is hard to hear.  Besides, very low base notes can be felt as vibrations through the ground.  Spinning  Spark  23:05, 10 June 2014 (UTC)


 * So, dogs can hear all sounds of speech, but they hear high sounds better than low? 24.5.122.13 (talk) 00:13, 11 June 2014 (UTC)


 * There is a range of frequencies over which they hear best. Outside this band, both for higher and lower frequencies, hearing sensitivity decreases.  Spinning  Spark  01:04, 11 June 2014 (UTC)


 * So for a male voice, which sounds of speech would fall into the range, and which would fall outside? I'm trying to think of a good name for a SAR dog, and this might help.  I mean, for example, in the English-speaking world, "Rover" is a popular name for dogs, and in Russia, the two most common dog names are "Bobik" (for small dogs) or "Barbosa" (for big dogs) -- does this have anything to do with the dog's optimal hearing range? 24.5.122.13 (talk) 04:28, 11 June 2014 (UTC)
 * I have heard that dogs respond better to 'hard' consonants such as P,K,G,T, compared to 'soft' consonants like L,S,M. Also, dogs seem to respond more to pitch than shape/color of the sound. So, whatever name you pick, try to always say it in the same pitch, and perhaps pick a name that starts with a 'hard' consonant. (Sorry, no refs at present, but you might find similar info by googling). SemanticMantis (talk) 14:49, 11 June 2014 (UTC)
 * Thanks! 24.5.122.13 (talk) 01:19, 12 June 2014 (UTC)

perceptual motion

 * For sure this is a fake. We know this because (a) 100% of perpetual motion machine claims have been fakes - it's exceedingly unlikely that this one is not  (b) about 90% of YouTube "science" videos are faked - and 100% of the "amazing" ones and (c) free energy nuts are obsessed with magnets because they don't understand them and feel that there must, obviously, be some way to extract the "obvious" energy from them.  However, they don't understand the difference between "force" and "energy".  Getting forces for free is easy - getting energy for free is impossible.
 * The only remaining question is how they faked it...and there are a bazillion ways that could have happened. There is ample space within the frame and the drum to hide motors, batteries, electromagnets, air-jets, etc.  There is also ample scope for camera trickery and computer graphics.
 * The machine they are playing with is a simple variation of the SMOT - with the magnets wrapped around a drum and the vertically moving bar behaving like the ball in the regular SMOT. SMOTs don't work for very well-understood reasons....but they do *seem* to be coming very close to working - and that means that a lot of poorly-educated are "inventors" working insanely hard to eliminate friction or slightly tweak the setup in the hope of just getting it that tiny bit further to the point where it would run perpetually.   Sadly, the smallest amount of understanding of the laws of thermodynamics would prevent this enormous waste of human effort...but that's not likely to happen.
 * In the early parts of the video, (which may well *not* be faked), he's inadvertently supplying energy to the drum by pulling the metal bar away from and towards the drum. The energy required to do that will be more than it takes to accelerate the drum...so that could easily be real.   However, in the final demonstration, where the bar is being lifted away by the cam that's driven by the drum, the cam would rob the spinning drum of kinetic energy faster than the falling piece of metal would increase it and the machine would stop within a few revolutions.
 * Incidentally, a more efficient (but still non-functioning) machine would have the drum be the shape of the cam and the metal arm be stationary. This would eliminate the sliding friction and reduce the machine to a single moving part. But it still wouldn't work.
 * Bottom line is that we know for 100% sure that this is a fake. It's exhausting to have to understand HOW it was faked - there are just too many of these bullshit videos and the idiots who present them seem to have boundless energy for fooling gullible people.
 * If this were real, the "inventor" wouldn't be showing it to you on YouTube, he'd be selling it to the power generation companies for billions and billions of dollars.
 * SteveBaker (talk) 17:03, 12 June 2014 (UTC)
 * "If he could really write encyclopedia-level articles, the "editor" wouldn't be doing it for free on Wikipedia, he'd be working for Encyclopedia Britannica for hundreds and hundreds of dollars." Just sayin' 190.204.168.25 (talk) 17:23, 12 June 2014 (UTC)
 * You get what you pay for. ←Baseball Bugs What's up, Doc? carrots→ 19:13, 12 June 2014 (UTC)
 * Well considering less than 19% of your contributions are to the mainspace, I don't think you are really in a position to be critiquing other editors on their encyclopedia writing skills. If it wasn't clear, my point was that people do contribute their time and energy for free. Wikipedia is an example of that. So why wouldn't someone with the same "free & open source" ethos give away their invention on youtube?
 * It's remotely possible - but we'd still be talking Nobel Prize in Physics for sure, accolades throughout the future of humanity, BILLIONS of dollars in licensing fees from power companies, car manufacturers, etc.  Writing for Wikipedia isn't remotely like that - for one thing, you can't just get a job writing encyclopedia articles - Brittannica are going down the toilet, the job never involved writing so much as editing what experts in the field wrote - and it just didn't ever pay much.  Writing non-fiction books is similarly pointless...I've been invited to write tech books MANY times, and each time, I'd be earning less than minimum-wage to do it.  A better comparison might be donating software to the OpenSource community - but then it's generally people who needed that software for their own purposes who decide to donate it so that other people will help to maintain it.   The people who donate time to the Linux kernel are perhaps being more generous with their time - they could probably earn $50/hour doing it as a job.   But finding a true, for real, working perpetual motion machine would make you more well known than Albert Einstein - a true saviour of the world - impossibly rich, respected by absolutely everyone.
 * If this thing worked - we'd be seeing it all over the news...it would be the biggest story in the history of mankind...by far!
 * However, it doesn't work because it can't possibly work - so it's not big news - and since it's one of a bazillion other faked YouTube 'science' videos - we can simply place it firmly on the "UTTER BULLSHIT" pile and move on with our lives.
 * SteveBaker (talk) 14:39, 13 June 2014 (UTC)