Vacuum and semiclassical gravity: a difficulty and its bewildering significance

TL;DR

This paper reviews longstanding issues in semiclassical models of vacuum decay, highlighting technical and conceptual challenges, and discusses their significance for understanding quantum gravity.

Contribution

It identifies and analyzes fundamental difficulties in semiclassical vacuum models, emphasizing their implications for quantum gravity research.

Findings

General results relevant for Euclidean and Lorentzian dynamics

Identification of technical and conceptual issues in models

Discussion of significance for quantum gravity

Abstract

We review a long-standing difficulty in some semiclassical models of vacuum and vacuum decay. Surprisingly enough these models, careless of their transparent formulation, are affected by, both, technical and conceptual issues. After proving some general results that are relevant for, both, the Euclidean and Lorentzian sectors of their dynamics, we briefly highlight their importance in connection with the issues discussed before, arguing that their solution might be interesting in our quest for quantum gravity.