Information paradox, dismissed?

[ShayanJ]

One of the important problems in modern physics is BH information paradox, which is the problem with non-unitarity of Hawking radiation. But now there is this paper which says that this process is actually unitary and so BH information paradox is, not solved, but dismissed. I'm posting this thread to discuss this paper because it seems to me that this is an important paper.

 

[Demystifier]

I think that the paper does not resolve the BH information paradox and should not have been published in Phys. Rev. Lett. Let me explain.

The evolution described in the paper is manifestly unitary because it is based on the Schrödinger equation (15). However, this is not so much different from the standard Hawking analysis. The standard Hawking analysis is based on the Bogoliubov transformation (not Schrödinger equation), which is also known to be manifestly unitary. The outside Hawking radiation is correlated with inside Hawking quanta, so information is conserved.

But if the Bogoliubov transformation is manifestly unitary, then where is the problem with unitarity? The problem appears when one takes into account the backreaction on the metric. Due to radiation, the black hole must shrink. But then, when the black hole becomes very small, how can all those inside Hawking quanta fit into such a small black hole? That's (one version of) the BH information paradox.

On the other hand, the paper above does not even consider the backreaction and hence does not really address the true BH information paradox. All what this paper shows is that, if we ignore questions of that form, then the evolution appears to be manifestly unitary. But that's something what we already knew with the standard Bogoliubov transformation.

In other words, the paper solves only a straw man version of the BH information problem (not the true BH information problem), which was already solved a long time ago (albeit, in a slightly different technical form).

 

[Demystifier]

Let me also use this thread to advertise one of my own papers on BH information paradox. In
http://lanl.arxiv.org/abs/1502.04324 [JCAP 04 (2015) 002]
I argue that there may be nothing fundamentally wrong or inconsistent if unitarity is really violated by Hawking radiation.

 

[TrickyDicky]

I argue that there may be nothing fundamentally wrong or inconsistent if unitarity is really violated by Hawking radiation.

Not a popular line of thought, in view of the great lengths that are gone to in order to keep violations of unitarity from the standard quantum formalism(either relativistic or not) even if it takes ignoring crucial features of the theory like dynamics basis-dependence or regularization.