What happened to the black hole firewall theory? Back in 2012, some physicists apparently came up with strong evidence that one of three things must be wrong for black holes to work the way we thought they did:

  1. Unitarity
  2. the Equivalence Principle or
  3. the Event Horizon.

It seems that for a week the media had a flurry of reports that physicists including Stephen Hawking were dumping the event horizon for things like an "apparent horizon" and then... silence. I haven't heard anything about the firewall theory since.

Are physicists still trying to work out a solution? Did someone realize that the theory was flawed in some way? It seemed like a big deal at the time so I find it odd that it seems that no one is talking about it right now, although that might just be my over-reliance on general media for physics news.

  • $\begingroup$ Can you explain better your last sentence? $\endgroup$ – Rexcirus Mar 31 '16 at 13:21
  • $\begingroup$ @Rexcirus just meant that I tend to get most of my news about physics from general media because I'm not from very involved in the field. It might be that there were some developments and it the general media didn't think it was interesting enough to talk about. Does that make more sense? $\endgroup$ – Nullius in Verba Mar 31 '16 at 16:43
  • $\begingroup$ There's no dumping the event horizon for the apparent horizon. They are two distinct things that were known about in the '70s. The main problem is that if you are looking at a black hole that completely evaporates, depending on the details of the evaporation you don't even necessarily have an event horizon. $\endgroup$ – Jerry Schirmer Apr 15 '16 at 21:03
  • $\begingroup$ Ironically, the apparent horizon is defined in a way that is closer to the popular science notion of what an event horizon is than the event horizion itself -- the apparent horizon is the closed surface from which light marginally cannot escape. $\endgroup$ – Jerry Schirmer Apr 15 '16 at 21:04
  • $\begingroup$ (for completeness, the event horizon is "the boundary of the past of the singularity") $\endgroup$ – Jerry Schirmer Apr 15 '16 at 21:07

The field of quantum black holes is a hot topic of research right now, and the firewall proposal is still being debated.

I have the feeling that no one really takes the proposal seriously. By saying this I don't mean that it was a bad paper, on the contrary it's a nice thought experiment that forced us to think even more about the black hole information paradox. The point is that the authors found an inconsistency between the three main assumptions they have made, that is (1) local quantum field theory description is valid, (2) unitarity and (3) smoothness at the horizon. Actually there are more assumptions, and one can question if they are appropriate. Anyway, they assumed that the most conservative viewpoint was to give up the smoothness and to introduce a firewall at the horizon.

The argument is subtle and some authors claimed to have debunked the proposal, but it's fair to say that a conclusive argument against the proposal is still missing.


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