2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/35172A recently introduced discrete formalism allows to solve the problem of time in quantum gravity in a relational manner. Quantum mechanics formulated with a relational time is not exactly unitary and implies a fundamental mechanism for decoherence of quantum states. The mechanism is strong enough to render the black hole information puzzle unobservable.6 pages, to appear in the proceedings of DICE 2004 (Piombino, Italy)General Relativity and Quantum Cosmologytext