paper

The reliability horizon for semi-classical quantum gravity: Metric fluctuations are often more important than back-reaction

arXiv:gr-qc/9702041 · doi:10.1016/S0370-2693(97)01226-4

Abstract

In this note I introduce the notion of the ``reliability horizon'' for semi-classical quantum gravity. This reliability horizon is an attempt to quantify the extent to which we should trust semi-classical quantum gravity, and to get a better handle on just where the Planck regime resides. I point out that the key obstruction to pushing semi-classical quantum gravity into the Planck regime is often the existence of large metric fluctuations, rather than a large back-reaction. There are many situations where the metric fluctuations become large long before the back-reaction is significant. Issues of this type are fundamental to any attempt at proving Hawking's chronology protection conjecture from first principles, since I shall prove that the onset of chronology violation is always hidden behind the reliability horizon.

6 pages; ReV_TeX 3.0; two-column format. Revisions: Central definitions and results essentially unchanged. Discussion of the relationship between this letter and the Kay-Radzikowski-Wald singularity theorems greatly extended and clarified. Discussion of reliability horizon near curvature singularities modified. Several references added. Minor typos fixed. Technical TeX modifications

References in corpus (4)

Cited by in corpus (13)