Conformal time in a black-hole universe with torsion

TL;DR

This paper explores how torsion in Einstein-Cartan gravity prevents black hole singularities, leading to a universe that bounces and expands, with conformal time used to analyze potential observational signatures.

Contribution

It derives the dynamics of a universe formed inside a black hole with torsion, highlighting the role of conformal time in testing early universe signatures.

Findings

Black hole collapse avoids singularity due to torsion-induced repulsion.

The interior universe undergoes a bounce before expanding.

Conformal time helps connect early universe models with CMB observations.

Abstract

In the Einstein-Cartan-Sciama-Kibble theory of gravity, the intrinsic spin of fermionic matter generates spacetime torsion and induces gravitational repulsion at extremely high densities. This repulsion prevents the collapsing spin-fluid matter in a black hole from forming a singularity. Instead, the interior of a black hole with a stiff equation of state becomes a new universe, which contracts until a (big) bounce and then expands. We derive the equations describing the dynamics of our Universe, formed in such a scenario, in terms of the conformal time which is a convenient variable for testing signatures of the contracting phase in the Cosmic Microwave Background radiation.