A toy model for a baby universe inside a black hole

TL;DR

This paper introduces a simplified model of an expanding universe within a black hole, connecting classical collapse with quantum effects to suggest a potential resolution of singularities.

Contribution

It proposes a novel toy model that combines classical and semi-classical physics to describe a baby universe inside a black hole.

Findings

The model demonstrates a phase transition from collapse to expansion at high density.

Quantum corrections can halt collapse and induce a bounce.

The approach offers a possible reconciliation between classical black hole solutions and quantum singularity resolution.

Abstract

We present a dynamical toy model for an expanding universe inside a black hole. The model is built by matching a spherically symmetric collapsing matter cloud to an expanding Friedmann-Robertson-Walker universe through a phase transition that occurs in the quantum-gravity dominated region, here modeled with semi-classical corrections at high density. The matching is performed on a space-like hyper-surface identified by the co-moving time at which quantum-gravity induced effects halt collapse. The purpose of the model is to suggest a possible reconciliation between the observation that black holes are well described by the classical solutions and the fact that the theoretical resolution of space-time singularities leads to a bounce for the collapsing matter.