Hawking changes his mind about Black Holes

[Jormungandr]

[Lepton*]

Yes, the x-rays are emitted as thermal radiation from the accretion disk that forms outside of the event horizon of the black hole.

[lostdummy]

I must admit that I do not understand completely what is exactly 'problem' that Quantum mechanics has with previous black holes theory.

I mean, it seems to be related to 'information not comming back from black hole', but I didnt understand why it would be problem to QM. In that linked document I found only

[Lepton*]

I like to think of it in terms of entropy.

Entropy (S) is given by the number of possible states of a system (S = k ln(w), where w is the number of states and k is Boltzmann's constant). The popular way to think of entropy is that it is analogous to disorder. This isn't a great analogy, so it is vital to know the exact meaning of entropy, but it works for many cases (including this one).

We know from thermodynamics, and more precisely, from the extension of quantum mechanics to the bulk thermodynamical properties of a system -- it's called quantum information or something silly like that -- that entropy always increases. Hawking showed that a black hole should have an amount of entropy that is proportional to the area of the hole's event horizon. He also showed that black holes emit Hawking radiation, which is supposed to be a type of blackbody radiation (that is, it depends only on the temperature of the emitting body).

There is a contradiction here. Blackbody radiation doesn't carry away any entropy from the black hole because it is so simple. On the other hand, as the Hawking radiation is emitted, the black hole's mass shrinks according to E=mc^2, and the hole will shrink. In other words, the area of the event horizon will decrease without the entropy changing. This is a clear violation of quantum thermodynamics.

The problem is usually phrased in terms of "information" because that is what the researchers do. I hope that you've found this useful, and I also hope that I am correct in all I say (I think that I am).

[Lepton*]

I'll admit that I'm a bit of a Hawking fanboy. He was my childhood hero (I've always been a geek). Here is a marvelous proposal by Hawking and Hertog that (a) makes the string theory "landscape" a bit more tenable, and (b) seems to solve the fine-tuning problem. I wish I'd been able to find funding to attend the Strings 2006 conference in Beijing this week: I'd love to hear Hawking talk about this, and to hear what the rest of the community thinks about it.

[Dan]

[CzarJ]

If we haven't searched everywhere, we will, and if we'll find anything, we would have heard about it by now.

[Dan]

Your explanation leaves me unsatisfied. :-p

[Lepton*]

From special relativity, a particle moving backwards in time will have a negative energy. If we allow the possibility of negative energy states, then we could create free energy just by bumping these tachyons down to high negative energies. (in fact, they will decay down by themselves) So tachyons = infinite energy. For most physicists, that's enough. I find it comforting that, up to now, collider experiments can be explained with the current model of physics without needing to invoke any extra particles. Another way to look at it is to say that (unless we are missing something pretty obvious) energy is conserved up to the scales at which colliders can go (~1 TeV).

I've got to run to class, and then the D-Wave demo. I'll check back later and see if I can polish this up a bit.

[Dan]

I think I get it...but maybe it takes a lot of energy to "bum down" these things to a high negative enrgy. Maybe its necessary in this case to expend a lot of energy to give it negative energy so we don't end up with infinite energy?

I don't make sense. Let us know about the D-Wave demo though!