Quantum self-gravitating collapsing matter in a quantum geometry

TL;DR

This paper explores how loop quantum gravity modifies the classical picture of collapsing matter and black hole formation, eliminating singularities and allowing quantum tunneling scenarios such as baby universes or white holes.

Contribution

It demonstrates the quantization of a collapsing null shell in spherically symmetric loop quantum gravity and shows the resolution of singularities and new quantum tunneling possibilities.

Findings

Singularity inside black holes is resolved by loop quantum gravity.

The shell can traverse the classical singularity.

Possible tunneling into baby universes or white holes.

Abstract

The problem of how space-time responds to gravitating quantum matter in full quantum gravity has been one of the main questions that any program of quantization of gravity should address. Here we analyze this issue by considering the quantization of a collapsing null shell coupled to spherically symmetric loop quantum gravity. We show that the constraint algebra of canonical gravity is Abelian both classically and when quantized using loop quantum gravity techniques. The Hamiltonian constraint is well defined and suitable Dirac observables characterizing the problem were identified at the quantum level. We can write the metric as a parameterized Dirac observable at the quantum level and study the physics of the collapsing shell and black hole formation. We show how the singularity inside the black hole is eliminated by loop quantum gravity and how the shell can traverse it. The construction is compatible with a scenario in which the shell tunnels into a baby universe inside the black hole or one in which it could emerge through a white hole.