Fluctuations of Energy Density and Validity of Semiclassical Gravity

TL;DR

This paper investigates the fluctuations of energy density in quantum fields and argues that their magnitude does not invalidate semiclassical gravity, emphasizing the quantum nature of matter fields over the theory's limitations.

Contribution

It clarifies that large energy density fluctuations are due to quantum effects, not a failure of semiclassical gravity, challenging prior claims.

Findings

Variance to mean-squared ratio is of order unity but does not imply failure of semiclassical gravity.

Energy density fluctuations are inherently quantum and do not undermine the validity of semiclassical gravity.

The results support the consistency of semiclassical gravity despite large quantum fluctuations.

Abstract

From calculations of the variance of fluctuations and of the mean of the energy density of a massless scalar field in the Minkowski vacuum as a function of an intrinsic scale defined by the world function between two nearby points (as used in point separation regularization) we show that, contrary to prior claims, the ratio of variance to mean-squared being of the order unity does not imply a failure of semiclassical gravity. It is more a consequence of the quantum nature of the state of matter field than any inadequacy of the theory of spacetime with quantum matter as source.