Faster than light' photons and charged black holes

TL;DR

This paper explores how photons in curved spacetime can exceed the speed of light due to quantum effects, challenging classical principles and analyzing birefringence near charged black holes.

Contribution

It demonstrates that quantum vacuum polarization causes superluminal photon velocities and violations of local Lorentz invariance in curved spacetime, with detailed analysis near charged black holes.

Findings

Photons can have velocities exceeding c in curved spacetime due to quantum effects.

Vacuum polarization leads to birefringence for electromagnetic and gravitational waves.

The Principle of Equivalence does not hold for interacting quantum fields in curved spacetime.

Abstract

Photons propagating in curved spacetime may, depending on their direction and polarisation, have velocities exceeding the ``speed of light'' c. This phenomenon arises through vacuum polarisation in QED and is a tidal gravitational effect depending on the local curvature. It implies that the Principle of Equivalence does not hold for interacting quantum field theories in curved spacetime and reflects a quantum violation of local Lorentz invariance. These results are illustrated for the propagation of photons in the Reissner-Nordstr\"om spacetime characterising a charged black hole. A general analysis of electromagnetic as well as gravitational birefringence is presented.