AdS-CFT correspondence and the information paradox

The information paradox in the quantum evolution of black holes is studied within the framework of the anti--de Sitter--conformal field theory (AdS-CFT) correspondence. The unitarity of the CFT strongly suggests that all information about an initial state that forms a black hole is returned in the Hawking radiation. The CFT dynamics implies an information retention time of the order of the black-hole lifetime. This fact determines many qualitative properties of the nonlocal effects that must show up in a semiclassical effective theory in the bulk. We argue that no violations of causality are apparent to local observers, but the semiclassical theory in the bulk duplicates degrees of freedom inside and outside the event horizon. Nonlocal quantum effects are required to eliminate this redundancy. This leads to a breakdown of the usual classical-quantum correspondence principle in Lorentzian black-hole spacetimes.