Both AdS/CFT duality
and more general reasoning from quantum gravity point to a rich collection of
boundary observables that always evolve unitarily. The physical quantum gravity
states described by these observables must be solutions of the spatial
diffeomorphism and Wheeler-deWitt constraints, which implies that the state
space does not factorize into a tensor product of localized degrees of freedom.
The "firewall" argument that unitarity of black hole evaporation is
incompatible with a regular near horizon region is based on such a
factorization, hence is not applicable in quantum gravity. A version of black
hole complementarity resolves the apparent conflict. (I will also discuss
doubts and questions.)