Classical Gravitational Back-Reaction

TL;DR

This paper investigates how a dense ensemble of classical gravitons, generated during inflation, can exert gravitational back-reaction to slow and potentially halt the universe's expansion, supporting a classical interpretation of quantum effects.

Contribution

It demonstrates that classical gravitons produced during inflation can self-gravitate sufficiently to influence the universe's expansion, providing a new perspective on quantum back-reaction effects.

Findings

Classical gravitons can slow the expansion rate.

Self-gravitation from gravitons can hold the universe together.

Quantum graviton creation leads to classical gravitational effects.

Abstract

The quantum gravitational back-reaction on inflation is based on the self-gravitation of infrared gravitons which are ripped out of the vacuum during inflation. The only quantum part of this process is the creation of gravitons; after they have emerged from the vacuum their behaviour is essentially classical. To test the thesis that a sufficiently dense ensemble of classical gravitons can hold the universe together in pure gravity with a positive cosmological constant, we compute the initial value and first time derivative of an invariant measure of the expansion rate for arbitrary classical initial value data. Our result is that the self-gravitation from the kinetic energy of an initial ensemble of gravitons can indeed slow expansion enough to hold the universe together.