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Comments: 165 +- Science: First Acoustic Black Hole Created on Wednesday June 10 2009, @11:30AM
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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."
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And the news is where? (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!
Re:And the news is where? (Score:5, Funny)
I'm giving my Bosewave radio new respect and standing a couple steps away from it just in case.
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I think "Bose" is just the American way to write "Böse", which is German for "evil". Fits pretty well, doesn't it? *puts on double-layered tinfoil overall*
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Hmm... I can only judge it by my shot Bose amp, and no, it doesn't make a sound when you switch it off. Actually, it seems to be permanently on, because even when I flip the switch you still don't hear anything.
OMG, I hope I didn't break the sound universe.
I guess this proves... (Score:4, Funny)
that in space, no one can hear you scre...
Re:I guess this proves... (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?
Parent
at last, the dream is realized! (Score:5, Funny)
"In one ear and out the other."
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"In one ear and out the other."
Except that, in this case, it went in one ear and got stuck.
Consumer applications (Score:2)
Sort of Hawking Radiation (Score:5, 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!
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Ok, so the Bose Noise Canceling headphones create these so called "Acoustic Blackholes" in the ears of the headphones to eliminate noise. But wont the radiation cause brain cancer or something??
This will never sell!
Re:Sort of Hawking Radiation (Score:5, 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...
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Re:Sort of Hawking Radiation (Score:5, 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.
Parent
Re:Sort of Hawking Radiation (Score:4, Interesting)
Arguably, light travels faster in a Casimir cavity than in a vacuum. Really, there's no reason to suppose that "emtpy space" represents the medium through which light flows the fastest, merely that it's somewhere close.
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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"
I really don't like that explanation... it makes it seem like the pressure differential is "known" to the gas inside the cylinder via some sort of acoustically-transmitted information. My initial reaction was "HUH" and my secondary reaction was "ok, I don't buy that."
After a little work on Google, I discovered that the effect really exists, but I think this link describes it better (emphasis mine): [engsoft.co.kr]
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That's somewhere in between a metaphor for Hawking Radiation and the real thing.
This isn't really a metaphor exactly. If the equations governing two systems are the same, then we expect the behavior to be the same, and we can describe them in the same terms. Phonons themselves are a good example of this: a phonon is hardly the sort of thing that you would intuitively think of as a particle, but because the equations governing phonons are the same as those governing quantum mechanical particles, physicists describe phonons as particles. Subatomic particles themselves bear very little resemblance to the 'billiard ball' particles that most people imagine. I think that it would be better to say that Hawking radiation is just an effect predicted for systems obeying certain equations, and in that sense, both the acoustic and traditional black holes exhibit completely real Hawking Radiation.
It is true that getting 'acoustic Hawking radiation' wouldn't constitute absolute proof that Black Holes do the same thing - our model may be wrong. What it will do do is provide proof that, assuming our model is correct, Hawking radiation is real, and there isn't some unanticipated effect which invalidates the theory.
I take your point, and you may easily have more expertise than I do (non-specialist grad quantum mechanics classes and a couple undergrad astro classes along with some casual enthusiasm for the subject). My understanding of Hawking radiation is that the split virtual pair explanation isn't physically accurate, but that tunneling of particles through the event horizon is the more physically valid explanation.
1) I'm not aware of an analogous effect that will work for phonons. Tunneling itself is on the wron
From the tone of the description (Score:2)
From the enthusiastic tone of the description, this sounds like Nobel Prize material.
Yet, I cannot judge it well enough.
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The real prize is not the acoustic black hole itself but what it might makes possible: the first observation of something analogous to Hawking radiation. The Theory of Quantum mechanics predicts that pairs of phonons with opposite momentum ought to be constantly springing in and out of existence in a BEC. Theoretically, 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
86 says (Score:4, Funny)
Let's use the cone of silence, chief!
Phonon ey? (Score:5, 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 [wikipedia.org]
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Everything is quantized if you're looking at it at a small enough scale.
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"Phonos" are basically "crystal oscillations". Enter the concept of "reciprocal space": it's basically the Fourier transform of the real 3D space, and is very commonly used in solid state physics.
Now as you probably know, a clean frequency (i.e. a sinus wave) in the time domain results to a single peak in the Fourier-Transform (i.e. in the frequency domain). And similar for phonons: a clean crystal oscillation (i.e. a single-frequency sound wave propagating through a medium) in 3D space results in the equiv
Not Hawking Radiation (Score:3, Informative)
There is an analogy there in the macro physics but that doesn't mean the small scale stuff like QM will be mirrored.
You can model gravity in the orbital mechanics sense with a marble and vertical cone that tapers at 1/square(height). That doesn't mean it will do anything relativistic or quantum mechanical.
Re:Not Hawking Radiation (Score:4, Interesting)
Parent
maybe we can use this to... (Score:3, Interesting)
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Yes, when will humanity invent this mysterious technology that allows us to avoid reality TV and cable news? This device, known to SciFi writers as the "off switch" may forever be the stuff of fiction.
I buy it (Score:3, Funny)
Not the first Acoustic Black Hole (Score:5, Interesting)
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.
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Little known science fact: the LHC *is* a bathtub, and the Compact Muon Solenoid is merely a frontage for a giant yellow rubber duck [woostercollective.com].
This will all be explored in Dan Brown's upcoming novel.
DONT DO IT SCIENTISTS! (Score:5, Funny)
Re:DONT DO IT SCIENTISTS! (Score:5, Funny)
Or even worse, the Earth will continue to exist and be entirely populated by mimes.
Parent
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Time to arm the motherless penguins with loaves of pumpernickel.
Acoustic Black Hole (Score:3, Funny)
What does it sound like? (Score:2)
Dudley? (Score:2)
Weaponize it and use it against car stereos. (Score:3, Interesting)
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I'm bassuming there's an unintended 'B' in that sentence..
I had an acoustic black hole before... (Score:2)
Is it me or does this story scream Spinal Tap? (Score:5, Funny)
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. "
Great (Score:5, Funny)
Phonon != Photon! (Score:3, Insightful)
How do you infer from the effects of phonons, that the same happens to photons? If they had the same effects, this would mean that luminiferous aether would exist. Which as far as we know, is not true, and replaced by the theory of relativity. Or would it be the effect of a quantized space-time? And would those quantums then be some kind of particles?
Or is the analogy just wrong, except for some subsets? ^^
Not so fast... (Score:4, Funny)
what would happen... (Score:3, Interesting)
we all know photon pairs are connected. an observation on changes the state of the other. (quantum entanglement) but what happens if one of a pair of photons enters a black hole and the other remains outside?
does quantum entanglement still exist fo these photons? does the photon still exist inside the black hole or does it disintegrate or change state? if so: what would happen to the other photon outside?
i call whatever will happen the Fuzzums effect ;)
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It's like Monster Cables for speakers.
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The reality is, most people don't have super-discriminating ears, and are therefore not really capable of telling much difference between any speakers.
You don't need super-discriminating ears to know that Bose systems sound like shit. It's perfectly obvious. Bose doesn't even do well against inexpensive systems, let alone ones in the Bose price-range.