2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/50575If particle creation is described by a Bogoliubov transformation, then, in the Heisenberg picture, the raising and lowering operators are time dependent. On the other hand, this time dependence is not consistent with field equations and the conservation of the stress-energy tensor. Possible physical interpretations and resolutions of this inconsistency are discussed.7 pagesHigh Energy Physics - TheoryGeneral Relativity and Quantum Cosmologytext