1207.5192 (Raphael Bousso)

Observer Complementarity Upholds the Equivalence Principle    [PDF]

Raphael Bousso

Recently, it was argued that an observer falling towards a sufficiently old black hole encounters a firewall at the horizon. This would amount to a gross violation of the equivalence principle in low-curvature regions. However, in this argument, the infalling observer's description is informed by a distant observer's ultimate recovery of a pure state in the Hawking radiation. This assumes a global viewpoint and manifestly conflicts with observer complementarity. The infalling observer will find the early Hawking radiation to be consistent with unitary evolution. But he cannot verify the eventual complete purification of the outside state by the Hawking radiation that remains to be produced by the black hole he enters; this is operationally possible only for the outside observer. Thus, the absence of a firewall is self-consistent in the infalling causal diamond, and the equivalence principle need not be sacrificed to preserve unitarity.

View original: http://arxiv.org/abs/1207.5192