Classical and quantum cosmology with York time

TL;DR

This paper addresses the problem of time in quantum gravity by using York time to deparameterize the ADM action, solving the Hamiltonian constraint exactly in a minisuperspace model, and exploring classical and quantum dynamics with potential for perturbation theory.

Contribution

It introduces a novel approach to quantum gravity using York time, providing exact solutions and a new interpretation of the Hamiltonian as volume, with implications for quantum perturbations.

Findings

Exact Hamiltonian solution in minisuperspace model

Classical dynamics recovered via Hamiltonian interpretation as volume

Quantum trajectories match classical de~Broglie-Bohm trajectories

Abstract

We consider a solution to the problem of time in quantum gravity by deparameterisation of the ADM action in terms of York time, a parameter proportional to the extrinsic curvature of a spatial hypersurface. We study a minisuperspace model together with a homogeneous scalar field, for which we can solve the Hamiltonian constraint exactly and arrive at an explicit expression for the physical (non-vanishing) Hamiltonian. The scale factor and associated momentum cease to be dynamical variables, leaving the scalar field as the only physical degree of freedom. We investigate the resulting classical theory, showing how the dynamics of the scale factor can be recovered via an appropriate interpretation of the Hamiltonian as a volume. We then quantise the system in the Schr\"odinger picture. In the quantum theory we recover the dynamics of the scale factor by interpreting the spectrum and expectation value of the Hamiltonian as being associated with volume rather than energy. If trajectories in the sense of de~Broglie-Bohm are introduced in the quantum theory, these are found to match those of the classical theory. We suggest that these trajectories may provide the basis for a perturbation theory in which both background and perturbations are quantised.