Calmet & Hsu: Quantum hair and black hole information

In summary, the new paper by Hawking et al. claims to solve the information paradox by revealing that black holes have "hair", i.e. properties in addition to mass, charge, and spin. However, there are many concerns about this approach, including that it is just using a framework of plain old QFT, and that it is wrong because the values of the multipoles (or some quantum functions involving them) are effectively quantized and there is simply not enough states for these coefficients to distinguish a large number of states.
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atyy
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https://www.bbc.com/news/science-environment-60708711
Scientists claim hairy black holes explain Hawking paradox

https://arxiv.org/abs/2112.05171
Quantum Hair and Black Hole Information
Xavier Calmet, Stephen D.H. Hsu
It has been shown that the quantum state of the graviton field outside a black hole horizon carries information about the internal state of the hole. We explain how this allows unitary evaporation: the final radiation state is a complex superposition which depends linearly on the initial black hole state. Under time reversal, the radiation state evolves back to the original black hole quantum state. Formulations of the information paradox on a fixed semiclassical geometry describe only a small subset of the evaporation Hilbert space, and do not exclude overall unitarity.
 
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I didn't find your post until I made a post on the same subject:

In an interview with the BBC:
"Prof Calmet's "yes hair theorem", published in the journal Physical Review Letters is revolutionary. It claims to resolve the Hawking paradox which has deeply troubled physicists ever since Prof Hawking came up with it in the 1970s."

I have not found the "Physical Review Letters" article, but it is apparently based on this short arxiv posting:
( Black Holes in Quantum Gravity )
( https://arxiv.org/pdf/2202.02584.pdf )

See also (same author):
https://arxiv.org/pdf/2112.05171.pdf

The PRL article is Quantum Hair from Gravity.

It seems to be quite a bit more extensive that either arxiv article (2202.02584 or 2112.05171).
 
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The arxiv version of "Quantum Hair from Gravity" is here.

I have not had time to read it yet, but I have doubts and concerns.

The concern is that this sounds rather a lot like Hawking's last paper, "Soft Hair on Black Holes", by Hawking, Perry, and Strominger - which also claimed to solve the information paradox by revealing that black holes have "hair", i.e. properties in addition to mass, charge, and spin. Why don't they mention it?

In the 2016 paper by Hawking et al, the new properties have to do with behavior of a black hole's space-time under certain transformations at infinity. These "BMS" charges correspond to the presence of ultra-low-energy gravitons in the space-time, if I understand correctly. It's a topic that Strominger has researched a lot.

One of the authors of "Quantum Hair and Gravity", Steve Hsu, blogs that the missing information is in the quantum state of the graviton field, specifically wavefunction components that deviate from the semiclassical approximation used in the original derivation of Hawking radiation.

(Incidentally, there was another occasion (2005) when Hawking declared that the information paradox could be resolved - something to do with space-time topology changes always disappearing in the long run?)

The 2016 paper by Hawking et al was critically discussed at Jacques Distler's blog (Lubos Motl provided a summary of the discussion). The most comprehensible theme, is that Hawking et al are working in the framework of quantum field theory, but study of quantum black holes has already revealed that they have a kind of gravitational nonlocality beyond quantum field theory, so the framework is inherently too simple to yield the resolution they claim.

This is my doubt about the new paper - they are also just using a framework of plain old QFT, so some version of this "nonlocality critique" should apply again.

It would be nice if @Haelfix appeared and had something illuminating to say. :-)
 
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  • #4
mitchell porter said:
This is my doubt about the new paper - they are also just using a framework of plain old QFT, so some version of this "nonlocality critique" should apply again.
This may not be specifically what you are addressing, but my thought is that transfer of information from an object that descends into an event horizon into the BH environment has to start well before it reaches the EH.

Also, I have never been a fan of locality. I don't think I could build a universe where locality is strictly enforced.
 
  • #5
Some heavy criticism of this whole approach here:

So these authors effectively claim that some large entropy may be controllably stored in the coefficients of some multipole expansions of gravitational fields – which effectively remember most of the information about the mass distribution, and therefore the identity of the source of gravity. But it is simply wrong because the values of the multipoles (or some quantum functions involving them) are effectively quantized and there is simply not enough states for these coefficients to distinguish a large number of states (so that you could explain the macroscopic entropy of things like black holes). At the end, we know that some degrees of freedom do allow this high entropy to be justified, derived, or calculated, but these authors' claim that they can derive the "hair" in a controllable way by these naive methods is simply wrong.
 
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