2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/204440We 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.11 pages, LaTeX, 4 figure; talk given at the workshop "From Quantum to Emergent Gravity: Theory and Phenomenology", June, 11-15 2007, Trieste, Italy (http://www.sissa.it/app/QGconference); submitted to the "Proceedings of Science" (http://pos.sissa.it)General Relativity and Quantum CosmologyHigh Energy Physics - Theorytext