Spin fluctuations and black hole singularities: the onset of quantum gravity is spacelike

TL;DR

This paper investigates how quantum fluctuations in black hole spin lead to a spacelike onset of quantum gravity, affecting the nature of singularities and potentially offering observational insights.

Contribution

It introduces a microcanonical ensemble for spin fluctuations in black holes and demonstrates that quantum gravity onset is spacelike, impacting singularity understanding.

Findings

Quantum fluctuations make the onset of quantum gravity spacelike.

Average over black hole geometries alters singularity nature.

Potential observational tests for quantum gravity effects.

Abstract

Due to quantum fluctuations, a black hole of mass $M$ represents an average over an ensemble of black hole geometries with angular momentum. This observation is apparently at odds with the fact that the curvature singularity inside a rotating black hole is timelike, while the one inside a non-rotating black hole is spacelike. Is the average of timelike singularities really spacelike? We use the Bekenstein-Hawking entropy formula to introduce a microcanonical ensemble for spin fluctuations and show that the onset of quantum gravity is always spacelike. We discuss the impact of this result on singularity resolution in quantum gravity and hint at the possibility of an observational test.