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If there is a “holy grail” to be found in modern astrophysics, it probably has something to do with finding out what’s going on inside of black holes. Since no light escapes from their event horizons, studying their insides directly is impossible. As if that wasn’t bad enough, our best theories tend to break down inside the event horizon, limiting our ability to study them even theoretically with present models.
Despite all that, there are ways to get at the behavior of black holes. A recent line of work is approaching the problem in a different way—by analogy. Rather than trying to observe real black holes or trying to simulate them mathematically, researchers are constructing analogs of black holes. These constructions can be observed in a lab, right here on Earth.
Of course, scientists have no way of creating an actual gravitational singularity on a table-top, so they had to rely on the next best thing. The essence of a black hole is that it has an event horizon—a point of no return from which no light can escape. By analogy, in a fluid, there can be a point of no return for sound waves. If, for example, the fluid is moving faster than the speed of sound, no sound can outrun the fluid to escape in the opposite direction. That’s the basic idea behind a new experiment published in the journal Nature Physics (abstract) —an experiment that apparently makes a Hawking radiation laser out of a sonic black hole.
[Additional Coverage]: http://www.universetoday.com/115307/hawking-radiation-replicated-in-a-laboratory/
(Score: 2) by aristarchus on Thursday October 30 2014, @07:20AM
Maybe I have not been keeping up with physics: What the hell is a phonon? A sound "particle"? Prey tell! And a roton must be a rotating sound particle. Yes, this does keep the analogy intact. But what the?
(Score: 0) by Anonymous Coward on Thursday October 30 2014, @01:03PM
Exactly. A phonon is a quasiparticle describing the basic excitation of a mechanical wave (that is, a sound wave).
(Score: 0) by Anonymous Coward on Thursday October 30 2014, @04:02PM
Sorry, I should have been a bit clearer. As the AC above says, you're exactly right -- a phonon is a "quasiparticle", basically a quantum of sound, in roughly the same way a photon is a quantum of radiation. So far as I know (and I'm very far from being an expert in superfluid Helium) the roton was originally thought to be linked with vortices but may or may not actually be so. In any event, it's either a different form of quasiparticle that arises specifically in superfluid He, or it's a different aspect of the phonons in superfluid He. (And the distinction between those is a bit arbitrary anyway.)
-- boristhespider