How quantum is the big bang?

TL;DR

This paper derives effective equations for quantum cosmology models, revealing that quantum correlations significantly influence the big bang bounce, and the impact depends on the quantum state's properties.

Contribution

It provides a comprehensive derivation of effective equations including quantum correlations, highlighting their crucial role in the big bang singularity.

Findings

Quantum fluctuations have minimal effect on the bounce.

Quantum correlations can potentially eliminate the bounce.

The regularization of the big bang depends on the quantum state's properties.

Abstract

When quantum gravity is used to discuss the big bang singularity, the most important, though rarely addressed, question is what role genuine quantum degrees of freedom play. Here, complete effective equations are derived for isotropic models with an interacting scalar to all orders in the expansions involved. The resulting coupling terms show that quantum fluctuations do not affect the bounce much. Quantum correlations, however, do have an important role and could even eliminate the bounce. How quantum gravity regularizes the big bang depends crucially on properties of the quantum state.