Bill Unruh's KITP seminar on information loss and energy non-conservation stimulates a vigorous discussion of one of the key aspects of the black hole information problem.
The question is whether pure states can evolve into mixed states (decohere) without energy loss. The answer is of course yes, but many (perhaps most) black hole researchers are under the impression that a famous paper by Banks, Peskin and Susskind showed that information loss due to black hole evaporation must lead to observable (even catastrophic) energy non-conservation. (Theorists who accept the BPS argument all believe that the information is somehow encoded in the outgoing Hawking radiation, which may indeed be true, but it doesn't follow from BPS!) Unruh and Wald refuted this claim (to my satisfaction) years ago, but the subject is still controversial. The video at the link is entertaining even if you're not an expert on this topic. Bill's counterexamples are quite elementary.
Unfortunately, I missed this talk as I was giving a colloquium at UC Irvine the same day. At lunch the day before I urged Bill to "lay down the law" ;-)
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3 comments:
And then there is always this
http://inspirehep.net/record/653376?ln=en
During my engineering studies I only got enough math and physics to carry me through "daily engineering life" so this is way over my head. After the first few minutes I'm lost.
Still it's a fascinating video. It's obvious that the speaker has mastery of his subject. It's obvious that his public knows the subject too and that very little information has to be exchanged to get the message across. I cannot fathom the details hiding beneath all the concise abstractions but there must be a lot of content in the simple matrix formula that is being discussed. It's interesting to see deep experts at work and the information "compression" that is part of the job.
Interesting to think about the hidden worlds that the the blogosphere opens for us. Before the internet I could never have "direct" contact with deep physics experts. Probably I would never have known they exist. Will these short and direct linkages change our world?
Great video but wouldn't it be even more impressive if all the scientists dressed like this:
http://www.flickr.com/photos/photonquantique/6834076348/
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