2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/35998The ``reliability horizon'' for semi-classical quantum gravity quantifies the extent to which we should trust semi-classical quantum gravity, and gives a handle on just where the ``Planck regime'' resides. 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.Three pages, uses mprocl.sty To appear in the proceedings of the Eighth Marcel Grossmann Conference on General Relativity. (Jerusalem, Israel, June 1997) [Minor typo fixed in references.]General Relativity and Quantum CosmologyHigh Energy Physics - Theorytext