Coherent states quantization and affine symmetry in quantum models of gravitational singularities

TL;DR

This paper uses affine covariant quantization to address singularities and the problem of time in quantum cosmology, demonstrating singularity resolution and unitary evolution in simplified models.

Contribution

It introduces a novel application of affine quantization to cosmological models, showing singularity removal and providing insights into quantum gravitational dynamics.

Findings

Classical singularities are replaced by bounces in quantum models.

Affine quantization yields a unitary evolution in cosmological scenarios.

Quantum dynamics with internal degrees of freedom offer new perspectives on the problem of time.

Abstract

We employ the framework of affine covariant quantization and associated semiclassical portrait to address two main issues in the domain of quantum gravitational systems: (i) the fate of singularities and (ii) the lack of external time. Our discussion is based on finite-dimensional, symmetry-reduced cosmological models. We show that the affine quantization of the cosmological dynamics removes the classical singularity and univocally establishes a unitary evolution. The semiclassical portrait based on the affine coherent states exhibits a big bounce replacing the big-bang singularity. As a particularly interesting application, we derive and study a unitary quantum dynamics of the spatially homogenous, closed model, the Mixmaster universe. At the classical level it undergoes an infinite number of oscillations before collapsing into a big-crunch singularity. At the quantum level the singularity is shown to be replaced by adiabatic and nonadiabatic bounces. As another application, we consider the problem of time. We derive semiclassical portraits of quantum dynamics of the Friedman universe with respect to various internal degrees of freedom. Next we compare them and discuss the nature of quantum evolution of the gravitational field.