Exact Results in Quantum Theory

The strong cosmic censorship hypothesis requires that the stress tensor diverges at a Cauchy horizon, in order to prevent the breakdown of determinism associated to the non-unique extension beyond it. However, it has recently been established that at the Cauchy horizon of near extremal Reissner-Nordström-deSitter (RNdS) black holes the divergence of classical field perturbations becomes weak enough to allow for a non-unique extension (as a weak solution) beyond the Cauchy horizon, indicating a violation of strong cosmic censorship. In contrast, for quantum fields on RNdS we find that the degree of divergence of the expectation value of the renormalized stress tensor near the Cauchy horizon is state-independent, universal, and strong enough to save strong cosmic censorship and to drastically change the nature of the singularity inside the black hole. Based on joint work with Stefan Hollands, Christiane Klein, Bob Wald.