No Cover Image

Book chapter 504 views

Causality and Superluminal Light / Graham Shore

Time and Matter, Pages: 45 - 66

Swansea University Author: Graham, Shore

Abstract

The causal properties of curved spacetime, which underpin our sense of time in gravitational theories, are defined by the null cones of the spacetime metric. In classical general relativity, it is assumed that these coincide with the light cones determined by the physical propagation of light rays....

Full description

Published in: Time and Matter
Published: Singapore World Scientific 2006
Online Access: http://arxiv.org/abs/gr-qc/0302116
URI: https://cronfa.swan.ac.uk/Record/cronfa17507
Tags: Add Tag
No Tags, Be the first to tag this record!
Abstract: The causal properties of curved spacetime, which underpin our sense of time in gravitational theories, are defined by the null cones of the spacetime metric. In classical general relativity, it is assumed that these coincide with the light cones determined by the physical propagation of light rays. However, the quantum vacuum acts as a dispersive medium for the propagation of light, since vacuum polarisation in QED induces interactions which effectively violate the strong equivalence principle (SEP). For low frequencies the phenomenon of gravitational birefringence occurs and indeed, for some metrics and polarisations, photons may acquire {\it superluminal} phase velocities. In this article, we review some of the remarkable features of SEP violating superluminal propagation in curved spacetime and discuss recent progress on the issue of dispersion, explaining why it is the high-frequency limit of the phase velocity that determines the characteristics of the effective wave equation and thus the physical causal structure.
College: College of Science
Start Page: 45
End Page: 66