The Unbearable Beingness of Light, Dressing and Undressing Photons in Black Hole Spacetimes

TL;DR

This paper explores how gravitational tidal forces near black holes affect photons, revealing phenomena like superluminal propagation and field amplification, and discusses their implications for causality and unitarity in gravitational theories.

Contribution

It introduces a novel analysis of photon behavior in black hole spacetimes using null congruences and Penrose limits, highlighting unique gravitational effects on light.

Findings

Superluminal low-frequency photon propagation near black holes

Amplification of the renormalized photon field in strong gravity

Resolution of apparent causality and unitarity violations

Abstract

Gravitational tidal forces acting on the virtual e+ e- cloud surrounding a photon endow spacetime with a non-trivial refractive index. This has remarkable properties unique to gravitational theories including superluminal low-frequency propagation, in apparent violation of causality, and amplification of the renormalized photon field, in apparent violation of unitarity. Using the geometry of null congruences and the Penrose limit, we illustrate these phenomena and their resolution by tracing the history of a photon as it falls into the near-singularity region of a black hole.