Black Hole Interiors

The interiors of Kerr or Reissner-Nordström black holes have "inner" horizons which enclose their singularity and delineate the domain of predictability of all equations of wave equation type -- including the Einstein equations themselves. However, these inner horizons are often classically dynamically unstable and get turned into some sort of singularity by perturbations. Thus, the true nature of the black hole interior (though not exterior) is drastically different from that suggested by the exact solutions. Recent work has shown that, actually, semi-classical quantum effects dominate classical ones very near the inner horizons. Quantum effects not only to lead to instabilities of the inner horizon even in cases where strong cosmic censorship fails classically, but they also drastically change the geometric nature of the singularity at the inner horizon.