Black hole firewalls, smoke and mirrors Academic Article uri icon


  • The radiation emitted by a black hole (BH) during its evaporation has to have some degree of quantum coherence to accommodate a unitary time evolution. We parametrize the degree of coherence by the number of coherently emitted particles N coh and show that it is severely constrained by the equivalence principle. We discuss, in this context, the fate of a shell of matter that falls into a Schwarzschild BH. Two points of view are considered: that of a stationary external observer and that of the shell itself. From the perspective of the shell, the near-horizon region has an energy density proportional to N coh 2 in Schwarzschild units. So, if N coh is parametrically larger than the square root of the BH entropy S BH 1/2, a firewall or more generally a “wall of smoke” forms and the equivalence principle is violated while the BH is still semiclassical. To have a degree of coherence that is parametrically smaller than S B...

publication date

  • January 1, 2014