Monday, December 28, 2009

Black Hole Created! Sorta.

Scientists have created a black hole in a Bose-Einstein condensate.

Well, an acoustic black hole. Not a real black hole.

But they may get some perfectly genuine Hawking radiation out of it, so it's still cool.

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. That sets up the possibility of all kinds of fun and games: in theory, physicists can reproduce with sound and BECs whatever wicked way gravity has with light.

Today, Oren Lahav and his mates at the Israel Institute of Technology, in Haifa, say that they've created the sonic equivalent of a black hole in a BEC. That's some achievement, given that physicists have wondered about this possibility for some 30 years, and various groups with the ability to create BECs have been racing to create acoustic black holes.


The general idea is to set up a supersonic flow of atoms within the BEC. Sound waves moving against this flow can never make any ground. So the region where the flow changes from subsonic to supersonic is an event horizon. Any sound waves (or phonons) created inside the event horizon can never escape because the flow there is supersonic. That's the black hole . . .

One reason why sonic black holes are so highly prized is that they ought to produce Hawking radiation. Quantum mechanics predicts that pairs of "virtual" phonons with equal and opposite momentum ought to be constantly springing in and out of existence in BECs.

If one of this pair were to cross the event horizon, it would be sucked into the black hole, never to escape. The other, however, would be free to go on its way. This stream of escapees would be the famous, but as yet unobserved, Hawking radiation.

As with a lot of articles in the arXiv, the comments section is at least as interesting as the text itself.

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2 Comments:

Blogger Ralf the Dog said...

What if this sound black hole grows uncontrollably and eats all the sound on the Earth? This could be sonic Armageddon!!!!!

9:55 AM  
Blogger Dave Bishop said...

Although I admit that physics was never my strong point, I'm beginning to think that at least some physicists may be making this stuff up!

5:03 AM  

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