Quantum Gravitational Optics

TL;DR

This paper reviews recent advances in quantum gravitational optics, exploring how quantum effects in curved spacetime lead to phenomena like gravitational rainbows, birefringence, and potential superluminal propagation, challenging classical causality notions.

Contribution

It provides a comprehensive review of quantum light propagation in curved spacetime, highlighting new phenomena and discussing implications for causality and superluminal signals.

Findings

Quantum effects cause gravitational rainbows and birefringence.

Superluminal light propagation is theoretically possible.

Implications for causality and signal transmission are discussed.

Abstract

In quantum theory, the curved spacetime of Einstein's general theory of relativity acts as a dispersive optical medium for the propagation of light. Gravitational rainbows and birefringence replace the classical picture of light rays mapping out the null geodesics of curved spacetime. Even more remarkably, {\it superluminal} propagation becomes a real possibility, raising the question of whether it is possible to send signals into the past. In this article, we review recent developments in the quantum theory of light propagation in general relativity and discuss whether superluminal light is compatible with causality.