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Einstein guarantees safe passage through a black hole horizon

Professors Abramowicz, Kluzniak, and Lasota of the Copernicus Astronomical Center in Warsaw demonstrated in a Physical Review Letters paper (March 7 issue) that the extensively discussed firewalls in astrophysical black holes are in fact excluded by Einstein's gravity.

Firewalls burning up all observers falling into a black hole were thought to be the "most conservative" resolution of the information paradox in black holes. The information paradox arises from the contradiction between quantum mechanics, which guarantees that no information is lost (for pure states), and general relativity, which predicts the existence of black holes where information is lost forever.

For 20 years it was thought that the paradox had been solved with the suggestion that the information comes out in the form of subtle correlations in Hawking radiation (Susskind et al. 1993), but a recent paper (Almheiri et al. 2013) pointed out that this would lead to difficulties, and suggested instead the presence of firewalls. Hawking radiation emitted in the early phases of black hole evolution would have to be quantum-mechanically entangled with the radiation emitted later on, while at the same time being entangled with the radiation falling into the black hole. As it turns out, an observer falling into the black hole would then have too much information.

The way out of this difficulty proposed by Almeiri et al. is to require the disentanglement of radiation coming out of the black hole and radiation falling into the black hole, which in turn creates near the horizon of an otherwise non-quantum (massive) black hole a Planck density wall of fire where the infalling observer perishes. However,  Abramowicz, Kluzniak, and Lasota point out that the proposed firewalls can exist only for minuscule black holes of mass less than the Planck mass (twenty millionths of a gram). Thus, the information paradox remains and requires a different solution.


Picture: Sketch of a black hole firewall.