Quantum Stress Tensor Fluctuations and their Physical Effects

TL;DR

This paper reviews quantum stress tensor fluctuations, their effects on gravitational fields, and implications for early universe inflation, highlighting correlations, non-gravitational effects, and observational signatures.

Contribution

It provides a comprehensive overview of recent work on stress tensor fluctuations, emphasizing their physical effects and role in cosmological inflation.

Findings

Stress tensor fluctuations cause observable gravitational effects.

Fluctuations influence cosmological density perturbations.

Bounds on inflation duration are derived from fluctuation effects.

Abstract

We summarize several aspects of recent work on quantum stress tensor fluctuations and their role in driving fluctuations of the gravitational field. The role of correlations and anticorrelations is emphasized. We begin with a review of the properties of the stress tensor correlation function. We next consider some illuminating examples of non-gravitational effects of stress tensors fluctuations, specifically fluctuations of the Casimir force and radiation pressure fluctuations. We next discuss passive fluctuations of spacetime geometry and some of their operational signatures. These include luminosity fluctuations, line broadening, and angular blurring of a source viewed through a fluctuating gravitational field. Finally, we discuss the possible role of quantum stress tensor fluctuations in the early universe, especially in inflation. The fluctuations of the expansion of a congruence of comoving geodesics grows during the inflationary era, due to non-cancellation of anticorrelations that would have occurred in flat spacetime. This results in subsequent non-Gaussian density perturbations and allows one to infer an upper bound on the duration of inflation. This bound is consistent with adequate inflation to solve the horizon and flatness problems.