Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: QuantumClue on 10/01/2011 19:58:16

Title: Are Black Holes possible?
Post by: QuantumClue on 10/01/2011 19:58:16

Perhaps the next best thing has now been created in a lab. Physicists have managed to create a sonic black hole which may have the elusive Hawking Radiation!!!

http://www.stardrive.org/index.php?option=com_content&view=article&id=3050:physicists-create-sonic-black-hole-in-the-lab&catid=43:science&Itemid=82

This is big news indeed.

Title: Are Black Holes possible?
Post by: Bill S on 10/01/2011 20:18:53

QC, you have brought us back to a question that seems to crop up quite frequently.  BHs are mathematically possible, but are mathematical possibilities necessarily physical possibilities?

Title: Are Black Holes possible?
Post by: QuantumClue on 10/01/2011 20:35:12

I wanted to approach the OP as a rhetorical question, because now by definition, we have created a black hole, which has got me positively excited! :)

Title: Are Black Holes possible?
Post by: JP on 11/01/2011 01:27:10

Yes, black holes probably exist.  The validity of the singularity in the model is a big question, but away from the singularity, GR still predicts a black hole exists.

This experiment is really cool, but bear in mind that it's not a gravitational black hole.  They constructed a setup to behave similarly for certain wavelengths of sound, but the physical principles are different.  It isn't a bending of space-time, and I wouldn't expect it to cause time dilation effects.  It also probably can't absorb too much sound energy without breaking down (at least the optical black holes I've seen proposed have that problem).  It would still be cool if they could simulate Hawking radiation within this setup, though.

Title: Are Black Holes possible?
Post by: QuantumClue on 11/01/2011 02:03:40

Oh completely. When I say a black hole, I should have said a Sonic Hole. Just a mistake.

But yes, still very tantalizing! Can't wait to see if they do actually observe the radiation. If they do, it may mean a nobel prize in the midst for Hawking.

Title: Are Black Holes possible?
Post by: Foolosophy on 11/01/2011 06:11:17

There is monumental difference between a sonic black hole that does not allow sound waves to escape and a theoretical black hole that doesnt allow anything at all to escape.

Byt this rationale I can call the inlet on my vaccum cleaner a "Black hole"

Title: Are Black Holes possible?
Post by: QuantumClue on 11/01/2011 15:24:28

The difference is a matter of escape velocity and density.

Title: Are Black Holes possible?
Post by: JP on 11/01/2011 16:35:22

Ok, I'm familiar with optical black holes, but I think this is the same idea.  Basically you can tailor a material in such a way that light rays behave like matter around a black hole.  If a light ray passes the event horizon, it is inevitably forced to go to the center of the optical black hole.  The mathematics actually works out so that the behavior of light rays is modeled by the same equations as the motion of objects around a black hole.

I don't see why this couldn't be done for sound, and it seems like that's what they're doing here.  In my opinion calling it a "black hole" is over-hyping it a bit, but if sound follows the same equations as mass does near a real black hole, it should allow some properties of black holes to be examined in the lab.

Title: Are Black Holes possible?
Post by: QuantumClue on 11/01/2011 17:27:25

Yes they seem quite similar. Except optical black holes do not emit radiation, whilst sonic black holes can.