Relational Time as a Stochastic Variable in ADM Gravity

TL;DR

This paper proposes a stochastic scalar field clock within ADM gravity to address the problem of time, leading to a diffusive quantum time evolution that preserves diffeomorphism invariance and background independence.

Contribution

It introduces a novel stochastic approach to time in canonical quantum gravity, integrating out quantum fluctuations to derive a Schrödinger-like evolution.

Findings

Derives an effective noise term from quantum fluctuations.

Recasts time as a diffusive process emerging from quantum indeterminacy.

Maintains diffeomorphism invariance and background independence.

Abstract

The problem of time in canonical quantum gravity remains one of the most significant challenges, primarily due to the "frozen" formalism emerging from the Wheeler-DeWitt equation. Within the ADM formalism, we introduce a novel approach in which a scalar field is treated as a stochastic clock. By imposing a divergence-free condition on the scalar momentum, we integrate out quantum gravitational fluctuations and derive an effective noise term via the Hubbard-Stratonovich transformation. This noise drives dynamic adjustments in spacetime foliations, enabling a Schrodinger-like evolution that preserves diffeomorphism invariance and, upon noise averaging, maintains unitary evolution. Interestingly, by introducing stochastic variations in the foliations, the quantum indeterminacy of the clock recasts time as a diffusive process emerging from quantum fluctuations, where correlations between matter and geometry replace an absolute time parameter. This provides a potential pathway for understanding quantum time evolution while maintaining background independence in canonical quantum gravity.