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First Acoustic Black Hole Created

Posted by Soulskill on from the for-music-that-really-sucks dept.

KentuckyFC writes "One of the many curious properties of Bose Einstein Condensates (BECs) is that the flow of sound through them is governed by the same equations that describe how light is bent by a gravitational field. Now, a group of Israeli physicists have exploited this idea to create an acoustic black hole in a BEC. The team created a supersonic flow of atoms within the BEC, a flow that prevents any phonon caught in it from making headway. The region where the flow changes from subsonic to supersonic is an event horizon, because any phonon unlucky enough to stray into the supersonic region can never escape. The real prize is not the acoustic black hole itself but what it makes possible: the first observation of Hawking radiation. Quantum mechanics predicts that pairs of phonons with opposite momentum ought to be constantly springing in and out of existence in a BEC. Were one of the pair to stray across the event horizon into the supersonic region, it could never escape. However, the other would be free to go on its way. This stream of phononic radiation away from an acoustic black hole would be the first observation of Hawking radiation. The team hasn't gotten that far yet, but it can't be long now before either they or their numerous competitors make this leap."

14 of 165 comments (clear)

  1. And the news is where? by Opportunist · · Score: 5, Funny

    I got a shot Bose amp here, and any sound you put in turns into silence. Voila, accustic black hole.

    I'd sell this baby for cheap, too!

    --
    We used to have a Bill of Rights. Now, with the rights gone, all we have left is the bill.
    1. Re:And the news is where? by goombah99 · · Score: 4, Funny

      I'm giving my Bosewave radio new respect and standing a couple steps away from it just in case.

      --
      Some drink at the fountain of knowledge. Others just gargle.
  2. at last, the dream is realized! by Tumbleweed · · Score: 4, Funny

    "In one ear and out the other."

  3. Sort of Hawking Radiation by Colonel+Korn · · Score: 4, Informative

    That's somewhere in between a metaphor for Hawking Radiation and the real thing. It's not true HR, but it would be a nice demonstration if they were to get it to work, especially if they could show some sort of analog to black hole "evaporation," which is the main implication of HR. I suppose that should naturally happen as the separation of the pairs sucks energy from the BEC and slows the fluid inside, shrinking the event-horizon-analogue.

    Also, let's get properly flowing BEC layers in our noise canceling headphones!

    --
    "I zero-index my hamsters" - Willtor (147206)
    1. Re:Sort of Hawking Radiation by DriedClexler · · Score: 4, Interesting

      That's somewhere in between a metaphor for Hawking Radiation and the real thing.

      Not a physicist, but here's how I think the metaphor between the experiment and the real thing is supposed to work:

      Speed of light: maximum speed information can travel through a vacuum ("the void")
      Speed of sound: maximum speed information can travel through a medium composed of atoms ("substance")

      (When aircraft go supersonic, the air they run into is incapable of "preparing" to be hit, in a manner of speaking...)

      We can't create stuff that goes faster than the speed of light, but we can create stuff that goes faster than the speed of sound. And just as you can't go fast enough to come back through an event horizon, information can't propagate fast enough in the experiment to go back across the subsonic/supersonic boundary. This shows us what it looks like to be in a situation like that of a black hole.

      By the way, there's a similar, cheaper experiment you can do: pop a hole in a pressurized container. The gas cannot escape it (at the outlet) faster than the local speed of sound, which is obtained whenever the ratio of pressure inside to pressure outside exceeds a critical value. One gas dynamics professor said I can think of it like this: "even though a higher pressure ratio creates a greater pressure potential difference, the gas inside the tank cannot 'learn' of the greater difference because that would require information to go *into* the tank, *against* the gas that is escaping at the speed of sound"

      Kind of like in the setup described in the article...

      --
      Information theory is life. The rest is just the KL divergence.
    2. Re:Sort of Hawking Radiation by blincoln · · Score: 4, Informative

      We can't create stuff that goes faster than the speed of light, but we can create stuff that goes faster than the speed of sound.

      We can't create stuff that goes faster than the speed of light in a vacuum. We create things that travel faster than the speed of light in other media all the time. The blue Cherenkov Radiation glow in fission reactors is caused by particles exceeding the speed of light in water, and creating a light shockwave analogous to the sound shockwave that e.g. supersonic aircraft produce.

      /nitpick

      --
      "...always new atoms but always doing the same dance, remembering what the dance was yesterday." -Richard Feynman
  4. 86 says by Anonymous Coward · · Score: 4, Funny

    Let's use the cone of silence, chief!

  5. Phonon ey? by Snowblindeye · · Score: 4, Insightful

    I knew light was quantized, but I had seriously never heard of Phonons, or that sound can be quantized as well.

    Well, apparently it can: Phonon

  6. Not the first Acoustic Black Hole by GameGod0 · · Score: 4, Interesting

    Black holes in a Bathtub by E. Berti (2005):
    www.iop.org/EJ/article/1742-6596/8/1/013/jpconf5_8_013.pdf

    The argument basically goes that when you unplug your bathtub, there's a certain point at which waves generated past the "event horizon" near the hole never escape the hole. It's an interesting read, but I was under the impression that this is basically the same thing, albeit not an effect that arises from quantum field theory.

  7. DONT DO IT SCIENTISTS! by nausea_malvarma · · Score: 4, Funny

    You'll create a BLACK HOLE that ENGULFS THE EARTH! Just like the LHC!

    1. Re:DONT DO IT SCIENTISTS! by Ukab+the+Great · · Score: 5, Funny

      Or even worse, the Earth will continue to exist and be entirely populated by mimes.

  8. Is it me or does this story scream Spinal Tap? by revjtanton · · Score: 5, Funny

    "Nigel Tufnel: The numbers all go to eleven. Look, right across the board, eleven, eleven, eleven and...
    Marty DiBergi: Oh, I see. And most amps go up to ten?
    Nigel Tufnel: Exactly.
    Marty DiBergi: Does that mean it's louder? Is it any louder?
    Nigel Tufnel: Well, it's one louder, isn't it? It's not ten. You see, most blokes, you know, will be playing at ten. You're on ten here, all the way up, all the way up, all the way up, you're on ten on your guitar. Where can you go from there? Where?
    Marty DiBergi: I don't know.
    Nigel Tufnel: Nowhere. Exactly. What we do is, if we need that extra push over the cliff, you know what we do?
    Marty DiBergi: Put it up to eleven.
    Nigel Tufnel: Eleven. Exactly. One louder.
    Marty DiBergi: Why don't you just make ten louder and make ten be the top number and make that a little louder?
    Nigel Tufnel: [pause] These go to eleven."
    "Nigel Tufnel: It's like, how much more black could this be? and the answer is none. None more black. "

  9. Great by segfault7375 · · Score: 4, Funny

    Sweet, now I just have to trick my wife into standing in it.. ah peace

  10. Re:I guess this proves... by Abreu · · Score: 5, Funny

    Actually, I have another reference to make...

    So, does this mean that the octirion bells in Unseen University clock tower emit Hawking Radiation?

    --
    No sig for the moment.