Fluctuations of energy density and validity of semiclassical gravity

From calculations of the variance, or the fluctuations, and the mean 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 its mean squared being of the order unity does nor imply a failure of semiclassical gravity. It is more a consequence of the quantum nature of the stale of the matter field than any inadequacy of the theory of spacetime with quantum matter as source.