It tells us whether the arguments Hawking made are validThe dynamics of an acoustic hole are the same as a gravitational one -- so the sound waves act around an acoustic hole exactly as light waves do around a (uncharged, non-rotating) gravitational black hole. If Hawking's arguments, which are still basically the only result we've got marrying gravity and quantum mechanics together, are valid then we'll see Hawking radiation from an acoustic black hole. Since it's pretty impossible to make a black hole in the lab (and, yeah, that includes the LHC, the theories that would produce black holes there are pretty speculative stuff), this is more or less our only concrete and cheap way of testing the interaction of gravity with quantum effects.
The thing I'd add is that an acoustic black hole is like a normal black hole except it only works on sound waves. The easiest way of imagining one is to get a tube and wrap it on itself and send water through at just below the speed of sound. In the direction of the flow, as viewed from the lab, the sound waves are moving at almost, but not quite, twice the speed of sound. Opposing the flow, they're almost stationary. If you now squeeze the tube then the flow goes supersonic at that point. In the supersonic patch sound waves can't travel against the flow -- they're swept along regardless, like sperm trying to swim up the Niagara Falls. At the point where the flow goes supersonic you've got an acoustic event horizon, while at the point it goes subsonic again you'd have another horizon (that one would correspond to a white hole).
Interesting stuff. Not actually that *useful* but if I wanted to be any use to humanity I wouldn't have done theoretical physics and then sat about on B3ta drawing magenta cocks onto Snoopy cartoons.
(The thing I'd add is that an acoustic black hole is like a normal black hole except it only works on sound waves. The easiest way of imagining one is to get a tube and wrap it on itself and send water through at just below the speed of sound. In the direction of the flow, as viewed from the lab, the sound waves are moving at almost, but not quite, twice the speed of sound. Opposing the flow, they're almost stationary. If you now squeeze the tube then the flow goes supersonic at that point. In the supersonic patch sound waves can't travel against the flow -- they're swept along regardless, like sperm trying to swim up the Niagara Falls. At the point where the flow goes supersonic you've got an acoustic event horizon, while at the point it goes subsonic again you'd have another horizon (that one would correspond to a white hole).
Interesting stuff. Not actually that *useful* but if I wanted to be any use to humanity I wouldn't have done theoretical physics and then sat about on B3ta drawing magenta cocks onto Snoopy cartoons.
boris the spider,
Tue 8 Dec 2009, 21:23,
archived)
curious.I'm not convinced they're an exact analogy but they might shed some light on things, so to speak.
(
Moon Girl Technologies horrendous beanbag,
Tue 8 Dec 2009, 21:34,
archived)
The analogy isn't at all exactI got the words the wrong way round, but it's the kinematics that are analogous. The dynamics are totally fucked. Meaning that the geodesics are the same (so Hawking's arguments are safe; they didn't rely on the Einstein equations) but the Einstein equations coupling them to matter are totally different. In relativity that's just the Einstein equations in their horrible non-linear glory. In acoustic holes it's pure non-relativistic wave equations -- you don't need to look at quantum fluids to get acoustic holes, you can build them in any perfect fluid. So the dynamics are governed by Newtonian mechanics.
Still, it is an interesting curiosity. There's a small but entertaining group of physicists trying to use these arguments to get a totally different picture on quantum gravity and the standard model by getting it from emergent systems in condensed matter. If you're actually interested, Volovik put up "The Universe in a Helium Droplet" on his website for free download a few years back; he basically found pretty mucha ll the symmetries of the standard model and of relativity emerging from perturbations in superfluid Helium II. The dynamics were totally wrong again, but the symmetries were all there. If someone can find a system where the symmetries *and* the dynamics emerge, then the conventional picture of finding unification by pushing to ever-higher energies and adding symmetry after symmetry will be overturned.
Which would be nice.
(Still, it is an interesting curiosity. There's a small but entertaining group of physicists trying to use these arguments to get a totally different picture on quantum gravity and the standard model by getting it from emergent systems in condensed matter. If you're actually interested, Volovik put up "The Universe in a Helium Droplet" on his website for free download a few years back; he basically found pretty mucha ll the symmetries of the standard model and of relativity emerging from perturbations in superfluid Helium II. The dynamics were totally wrong again, but the symmetries were all there. If someone can find a system where the symmetries *and* the dynamics emerge, then the conventional picture of finding unification by pushing to ever-higher energies and adding symmetry after symmetry will be overturned.
Which would be nice.
boris the spider,
Tue 8 Dec 2009, 21:47,
archived)
You know what,that is simultaneously both surprising and not surprising, somehow.
( Moon Girl Technologies horrendous beanbag,
Tue 8 Dec 2009, 21:53,
archived)
Bloody physicistsAn uncharged non-rotating black hole?
What good is that in the real world, I ask you?
(What good is that in the real world, I ask you?
littlefish I like cheese,
Tue 8 Dec 2009, 22:16,
archived)
ABSOLUTELY NONEREAL black holes are like REAL men. Errr, spinning around and round and with a healthy electric field, and emitting a constant stream of radiation. In men that's called "farting". Also, they've got another universe hidden inside them. Through the ring.
I'm going to shut up now. I think that would be a good idea.
(I'm going to shut up now. I think that would be a good idea.
boris the spider,
Tue 8 Dec 2009, 22:31,
archived)