Unitarity, nonlocality, and black hole information

Hawking’s argument for black hole information loss is reassessed. A precise characterization of missing information in outgoing Hawking radiation is the entropy, computed from elements of the density matrix. The statement that these elements can be derived in a controlled semiclassical approximation is examined via a calculation of matrix elements of the stress tensor, and argued to be flawed because of large fluctuations in these quantities. Consequently, we lack a sharp derivation of information loss. The calculation moreover exhibits features of black hole complementarity. Fluctuations that have important interactions with infalling matter are those whose blueshifts produce cross-sections comparable to the size of the black hole, for example through strong gravitational dynamics. Together with previous arguments that local quantum field theory breaks down in such circumstances, as parametrized by the “locality bound,” this suggests a general argument for unitarity based on failure of locality. ⋆ Email address: [email protected]