2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/228933I critically examine the notion of ``irreversibility,'' and discuss in what sense it applies to the spontaneous creation of particles in external fields. The investigation reveals that particle creation in very strong fields can only be described by a non-Markovian transport theory.4 pages REVTeXHigh Energy Physics - TheoryGeneral Relativity and Quantum CosmologyNuclear Theorytext