Asymptotic Safety, Singularities, and Gravitational Collapse

TL;DR

This paper investigates how asymptotic safety in quantum gravity might resolve classical singularities during gravitational collapse, showing that a vanishing or rapidly decreasing gravitational coupling can prevent singularity formation.

Contribution

It demonstrates that quantum effects via a running gravitational coupling can potentially avoid singularities in dust collapse scenarios.

Findings

A future singularity can be avoided if the gravitational coupling becomes zero at a finite energy scale.

Rapid approach of the coupling to zero at high energies can push singularities to infinite proper time.

Perturbation theory suggests a singularity still occurs at finite proper time despite quantum effects.

Abstract

Asymptotic safety (an ultraviolet fixed point with finite-dimensional critical surface) offers the possibility that a predictive theory of quantum gravity can be obtained from the quantization of classical general relativity. However, it is unclear what becomes of the singularities of classical general relativity, which, it is hoped, might be resolved by quantum effects. We study dust collapse with a running gravitational coupling and find that a future singularity can be avoided if the coupling becomes exactly zero at some finite energy scale. The singularity can also be avoided (pushed off to infinite proper time) if the coupling approaches zero sufficiently rapidly at high energies. However, the evolution deduced from perturbation theory still implies a singularity at finite proper time.