How generic are null spacetime singularities?

TL;DR

This paper demonstrates that null, weak singularities are as generic as spacelike, strong ones inside black holes, based on a class of vacuum solutions depending on multiple arbitrary functions.

Contribution

It introduces a class of vacuum solutions with null, weak singularities depending on eight arbitrary functions, showing their genericity in black hole interiors.

Findings

Null, weak singularities are generic in vacuum solutions.

The class depends on eight arbitrary functions, indicating broad applicability.

Null singularities are as common as spacelike, strong singularities in black holes.

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.