Perfect Quantum Cosmological Bounce

TL;DR

This paper presents an exact quantum cosmological model demonstrating a smooth, unitary bounce through the classical singularity, incorporating conformal matter, anisotropies, and perturbations.

Contribution

It introduces an exact path integral solution for quantum cosmology with conformal matter, extending to anisotropic and inhomogeneous universes, providing a consistent quantum bounce framework.

Findings

Universe passes smoothly through the singularity

Exact quantum gravity path integral achieved

Semiclassical paths circumvent the singularity

Abstract

We study quantum cosmology with conformal matter comprising a perfect radiation fluid and a number of conformally coupled scalar fields. Focusing initially on the collective coordinates (minisuperspace) associated with homogeneous, isotropic backgrounds, we are able to perform the quantum gravity path integral exactly. The evolution describes a "perfect bounce", in which the Universe passes smoothly through the singularity. We extend the analysis to spatially flat, anisotropic universes, treated exactly, and to generic inhomogeneous, anisotropic perturbations treated at linear and nonlinear order. This picture provides a natural, unitary description of quantum mechanical evolution across a cosmological bounce. We provide evidence for a semiclassical description in which all fields pass "around" the cosmological singularity along complex classical paths.