8 ms·
Scientists find upper limit for the speed of sound
- soneca 6y agoVery well-written progressive explanation of the experiment that I, a total layman, could understand the basics. And it made me curious to know more about those mentioned constants that relate to different physical phenomena. Edit: one doubt I have though, can it still be called an ”experiment” if it is “just” a calculation in a computer and not actually a measurement in the physical world?
- contravariant 6y ago>Edit: one doubt I have though, can it still be called an ”experiment” if it is “just” a calculation in a computer and not actually a measurement in the physical world? The article doesn't use the word 'experiment' anywhere.
- soneca 6y agoYes, but I did. I was wondering if it would be correct to use it in this case.
- totony 6y agoExperiments are used in the scientific method to invalidate hypothesss. I'd say that yes, a simulation is an experiment, since it can do that.
- whatshisface 6y agoPure logic can also invalidate hypotheses sometimes, but pure logic isn't experimental.
- Retric 6y agoPure thought experiments are useful because they make predictions which can then be validated. It’s part of the basic foundations of science, otherwise you’re just curve fitting across all exponential data.
- whatshisface 6y agoSure but thought experiments are not actual experiments. In fact thought experiments are... exactly the same as simulations.
- Retric 6y agoTo be more clear a pure thought experiment doesn’t invalidate a theory on it’s own. It’s the conflict between the results and either past or future observations/experiments that invalidates the theory. Plenty of theories that gave what seemed like insane results happened to work out.
- zaroth 6y agoAbsolutely agree. Fun fact; > Gedankenexperiment, (German: “thought experiment”) term used by German-born physicist Albert Einstein to describe his unique approach of using conceptual rather than actual experiments in creating the theory of relativity. It would be ridiculous to say that experiments can only be done physically. Thought experiments are responsible for developing one of the most famous theories known to man.
- smogcutter 6y agoA simulation is only as good as the model it’s based on. So sure, it’s an experiment, but one that’s only valid within the context of the model. Validating the model itself would take a “real” experiment.
- totony 6y agoMost experiments are only valid within the context of a model. Calculating X-ray diffraction patterns only matter because of how we model orbitals and light diffraction for example.
- smogcutter 6y agoWhat I’m fumbling to get at is that a physical experiment can tell you that your model is flawed in ways that simulation alone can’t. If you don’t already understand the double slit experiment, you’re unlikely to simulate light in a way that reproduces its results.
- totony 6y agoYes, each have their advantages, e.g. here the speed of sound couldnt have been calculated in these circumstances. The simulation could've also revealed flaws and disproved the theory w/r to itself.
- remram 6y agoThey can perform experiments to validate the more generic result: the relation between the speed of sound and the mass of the atoms. The specific result about solid hydrogen will still be an extrapolation though.
- colechristensen 6y agoI don’t think strict definitions that allow putting things into well defined “experiment” and “not experiment” bins really matter. Being understood matters, and in science context is all important, but being understood just doesnt depend on strict definitions of common words like that, and when it does those words are explicitly defined instead of left for assumptions. It is the kind of questions about scientific literacy you see quite a bit, loading terms with really consequential definitions and then asking at the edge cases... the answer usually lies in a combination of correcting usage that feels a little odd while also trying to break down the assumption of the question itself, in other words rejecting the premise. It’s like the many arguments about the usage of the word “theory” especially when with the pejorative “just a theory”, the reality is scientists would never be confused by an odd usage of the word and themselves don’t place much importance on it. “mu”
- foota 6y agoWhile not mind blowing, this result is somewhat surprising to me.
- brmgb 6y agoThe result in itself as presented in the article derives from a somewhat easy to follow train of thoughts: - sound is a longitudinal wave propagating through a medium; - its speed of propagation depends on some properties of said medium; - thus a physical uperbound on these properties imply an uperbound on the speed of sound. The fact that an upper limit exists is in itself obvious (we already knew one: the speed of light in a vacuum). Properly deriving it is the interesting part.
- foota 6y agoThe jump from one to two is where I'm lost, mostly due to ignorance. Sound propagating is just molecules smacking into each other, but it's not evident to me why the speed this can happen at would be limited other than by the speed of the molecules. I guess one molecule won't immediately accelerate when it's "hit" by another and this causes the slow down?
- deostroll 6y ago> At those pressures, hydrogen becomes a fascinating metallic solid conducting electricity just like copper and is predicted to be a room temperature superconductor I didn't get the room temperature superconductor part.
- coolspot 6y agoIf you compress hydrogen to that pressure and keep it compressed in let’s say a really strong shell, then it will have superconductivity even at room temperature.
- rishav_sharan 6y agoQuick question, can you really have room temperature at that pressure? I thought extreme pressures would always result in extreme temperatures.
- wtallis 6y ago> I thought extreme pressures would always result in extreme temperatures. At least classically, it's the process of compressing that yields the extreme temperatures, not the state of having been compressed. If you maintain the pressure, the hot compressed material will transfer thermal energy to its surroundings until it has cooled back down to room temperature, and it does not require further work to be done on the compressed material to keep it compressed.
- gruturo 6y agoIf you keep it compressed, it will eventually cool down, but stay compressed.
- rbanffy 6y agoIf it's a solid in that state, will it remain a solid if you remove the container?
- layoutIfNeeded 6y ago
- ry454 6y agoIsn't it the same as the speed of light? If sound is an abstract wave-like signal, then it can be transmitted equally well with radio waves or molecules in the air. The paper should probably mention that it's the upper limit of sound in a atomic based medium.
- CobrastanJorji 6y agoLight waves are electromagnetic. Light can travel without a medium because the photons are themselves moving forward. They have a frequency, but the frequency is caused by movement side to side, on a different axis than their heading. Sound waves are physical. They are by definition in an atomic-based medium. Matter at the source of the sound is pushed, compressing it, which pushes the matter in front of it (uncompressing the original matter). If there's no matter to push, sound isn't a thing (thus nobody in space being able to hear you scream). It's not so much information being transmitted as matter being shoved. The frequency is amount of time between shoves, and that wave is in the direction of the motion (because the forward shoving is the frequency and the motion). Sound waves are not an abstract transmission of information. It's certainly true that you can encode a sound as an information and send that information electromagnetically, but that transmission is not itself sound. Similarly, you could measure the speed of traffic in LA, email those times to New York, and then drive some cars in New York in a way that produces the same traffic speed, but you did not transmit the traffic at the speed of light, and this exercise would not be meaningful to a discussion on the maximum velocity of a car.
- shawxe 6y agoI think OP is talking about the fact that it is possible to represent and transmit sound via an electromagnetic medium and that therefore this limit is not a limit on sound information (which is nothing but generic information that can be transmitted at the speed of light) but rather a limit on sound as it occurs physically (in the way that you've described).
- smogcutter 6y agoThe key word there is “represent”. Radio isn’t sound. If I make a recording and mail it to you, the delivery time isn’t “the speed of sound through the mail”. You can get into a whole thing about trees falling in forests and how a pressure wave only becomes sound when it’s interpreted as information, but that’s totally irrelevant to an experiment about pressure waves through a medium.
- srl 6y agoHere's the arxiv link, for those who want to read the original article paywall-free: https://arxiv.org/abs/2004.04818 https://arxiv.org/abs/2004.04818. To be clear, this isn't an unconditional speed limit. It appears to be something like "the maximum speed of sound in matter which consists of atoms" (maybe I've missed a few conditions). In particular, this speed limit is known to be violated inside of neutron stars (where the speed of sound is near 1/sqrt(3) times the speed of light, and may even exceed that). The paper also mentions a proposed lower bound on viscosity. This is the KSS bound (https://arxiv.org/abs/hep-th/0405231 https://arxiv.org/abs/hep-th/0405231), and various theories violating it have been constructed. The violations, of course, don't get mentioned nearly as much as the proposed (and all-but-debunked) bound.
- linspace 6y agoThe article is open access under Creative Commons: https://advances.sciencemag.org/content/6/41/eabc8662 https://advances.sciencemag.org/content/6/41/eabc8662
- srl 6y agoHah! I didn't even bother to check, I'm so used to just going for the arxiv version when not on campus. (Usually has better formatting too.) Thanks for pointing that out.
- SubiculumCode 6y agoSooo disappointed that it wasn't the speed of light.
- guender 6y agoFundamentally, the square of the speed of sound is dP/drho at constant entropy (P - pressure, rho - density). There’s no limit to the speed of sound other than the speed of light. Obviously, density and pressure are medium variables and typically P = P(rho, ...).
- rbanffy 6y agoIt's fascinating that the upper bound of the speed of sound is analogous to the speed of light in a vacuum, but it's highest when propagating through the thing that's the complete opposite of a vacuum. Now I wonder what the speed of sound in, say, neutron-degenerate matter, would be.
- willis936 6y agoI’m not sure, but I bet it is highly dependent on your frame of reference. :)
- Maursault 6y ago> the thing that's the complete opposite of vacuum Solid matter is very nearly entirely empty space, and the vacuum state is not truly empty but instead contains fleeting electromagnetic waves and particles that pop into and out of existence.
- physicsgraph 6y agoThis paper is well written. I was able to extract the mathematics into the project I created to document the relations and steps of derivations [0]. [0] https://derivationmap.net/review_derivation/608598/?referrer=hnews_20201011 https://derivationmap.net/review_derivation/608598/?referrer...
- xaedes 6y agoWow, this derivationmap site looks very interesting. I desperatly want something like this for graph rewriting on abstract syntax trees. A fullscreen option for the d3 graph would be nice, this way it could leverage large monitors. Some interface for creating derivations directly from graph view would be amazing, but this is probably hard to get right.
- egberts1 6y agoIf you already have a yacc/bison in your project’s CLI or compiler parser, you could use `bison —graph=` then feed that graph file into DOT/gv layout for outputting to PNG or SVG.
- jwilk 6y agoNote that there are two approaches to calculating v in this artcile, and this derivation covers only the more hand-wavy one. For example, they drop the √f factor, because "[f]or most strongly bonded solids, f varies in the range of 1 to 4".
- MayeulC 6y ago> For example, [sound waves] move through solids much faster than they would through liquids or gases, which is why you're able to hear an approaching train much faster if you listen to the sound propagating in the rail track rather than through the air. I am sceptical, I don't think this makes a big difference until the train approaches the speed of sound. What makes a difference, however, is that the energy is constrained into moving one-dimensionally, along the rail, so that it travels much further.
- ink_13 6y agoThe speed of sound in steel is in the neighbourhood of 6000 m/s, whereas in air it's a mere 343 m/s.
- arghwhat 6y agoSound travels through steel ~17 times faster than through air at 1 atmosphere. At 500 meters, the "kachunck" of a train wheel going over a bump will take ~1.4 seconds to reach you by air, but only ~0.08 seconds to reach you through the rail. A pretty big difference.
- MayeulC 6y agoThe assumption behind my comment is: Most of the time, you only care about whether the train is coming. A 1-second advantage isn't really interesting. Of course, maybe that's the interesting part in that kind of situation? I doubt it, though. At 5km, sound will take 15 seconds to cover the distance. That's negligible compared to the time the train will take, assuming a good old train going at ~40 km/h (7'30"). Using the quoted 6 km/s, that gives ~ 0.8 s inside the rail. I admit I was initially expecting a smaller difference. But I still think that the 14 seconds advantage is negligible over just knowing that the train is arriving from a far away distance: to hear the train at all, wind needs to blow in the right direction, and the train needs not be too far away (~d^2 energy propagation, so ~log(d) in dB vs virtually no attenuation in a simplified model). I wish I had time to look up and compute the attenuation in both cases....
- 6y ago