Superluminal propagation of light in gravitational field and non-causal signals: some comments

TL;DR

This paper analyzes claims that quantum corrections to photon propagation in gravitational fields could allow superluminal and non-causal signals, concluding that such signals do not exist under realistic conditions.

Contribution

It refutes previous claims by showing that superluminal propagation does not lead to non-causal signals when realistic photon velocities are considered.

Findings

No non-causal signals are found in the model.

Superluminal propagation does not imply causality violation.

Previous assumptions about signal velocity independence are invalid.

Abstract

We examine the recent statement by A. Dolgov and I. Novikov that superluminal propagation of light, which is induced by the quantum corrections to the photon propagation in gravitational field, permits non-causal signal propagation. For this purpose we examine the possibility of the existence of non-causal signals in the model case, when characteristic cone of the signal is outside the usual light cone in Minkowski space-time, as it take place in the case of the photon propagation in gravitation field with quantum corrections taking into account. In such model the signal propagates along invariant intervals. It is shown that there are no non-causal signals in the considered model. The recent statement of A. Dolgov and I. Novikov was obtained by using additional supposition that velocity of the signal with respect to the emitter is independent from its motion. Such supposition does not valid in the case of the photon propagation in gravitational field.