Quantization in black hole backgrounds

TL;DR

This paper examines the limitations of semiclassical quantum field theory in black hole backgrounds, highlighting potential breakdowns of the weak-coupling expansion and implications for quantum gravity's non-perturbative, possibly non-local, nature.

Contribution

It analyzes the validity of the weak-coupling expansion in quantum gravity near black holes and discusses the potential necessity of non-perturbative, non-local effects.

Findings

Weak-coupling expansion may break down due to strong gravitational fluctuations.

Coupling between fluctuations becomes significant around time M^3.

Current calculations of black hole information loss are unreliable.

Abstract

Quantum field theory in a semiclassical background can be derived as an approximation to quantum gravity from a weak-coupling expansion in the inverse Planck mass. Such an expansion is studied for evolution on "nice-slices" in the spacetime describing a black hole of mass M. Arguments for a breakdown of this expansion are presented, due to significant gravitational coupling between fluctuations, which is consistent with the statement that existing calculations of information loss in black holes are not reliable. For a given fluctuation, the coupling to subsequent fluctuations becomes of order unity by a time of order M^3. Lack of a systematic derivation of the weakly-coupled/semiclassical approximation would indicate a role for the non-perturbative dynamics of gravity, and possibly for the proposal that such dynamics has an essentially non-local quality.