How generic are null spacetime singularities?

Abstract

The spacetime singularities inside realistic black holes are sometimes thought to be spacelike and strong, since there is a generic class of solutions (BKL) to Einsteins equations with these properties. We show that null, weak singularities are also generic, in the following sense: there is a class of vacuum solutions containing null, weak singularities, depending on 8 arbitrary (up to some inequalities) analytic initial functions of 3 spatial coordinates. Since 8 arbitrary functions are needed (in the gauge used here) to span the generic solution, this class can be regarded as generic.