We propose a novel scheme to classify the different options for resolution of the black hole loss of information problem that is independent of the details of the underlying theory of quantum gravity. We distinguish first between radical options, which require a quantum theory of gravity which has large deviations from semiclassical physics on macroscopic scales, such as nonlocality or endowing horizons with special properties not seen in the semiclassical approximation, and conservative options, which do not need such help. Among the conservative options, we conclude that restoring unitary evolution relies on elimination of singularities. We argue that this should hold also in the anti-de Sitter/conformal field theories correspondence.

• Received 21 December 2009

DOI:https://doi.org/10.1103/PhysRevD.81.064009