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

Matt Visser
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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.

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Matt Visser. 1997-06-18. The reliability horizon for semi-classical quantum gravity: Metric fluctuations are often more important than back-reaction. https://doi.org/10.1016/s0370-2693(97)01226-4

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