The Internal Structure of Black Holes

Abstract

Theoretical investigations of black-hole interiors aim to understand the geometry of spacetime inside generic black holes. Progress has been significant in the last decade. The singularities inside spherical, charged black holes are now well understood: a null singularity along the Cauchy horizon precedes a spacelike, central singularity. The singularity along the Cauchy horizon is weak, in the sense that tidal distortion of extended bodies is finite there. The nature of the Cauchy horizon singularity inside rotating black holes is also well understood; the divergence of curvature is dominated by the propagating modes of the gravitational field leading to an intuitive picture of the singularity as a singular shock wave propagating along the Cauchy horizon. I review the evidence in favour of this picture of the black hole interior, and comment briefly on directions for further research.