2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/193345Given the insight steming from string theory, the origin of the black-hole (BH) information puzzle is traced back to the assumption that it is physically meaningful to trace out the density matrix over negative-frequency Hawking particles. Instead, treating them as virtual particles necessarily absorbed by the BH in a manner consistent with the laws of BH thermodynamics, and tracing out the density matrix only over physical BH states, the complete evaporation becomes compatible with unitarity.8 pages, revised, title changed, to appear in Eur. Phys. J. CHigh Energy Physics - TheoryGeneral Relativity and Quantum Cosmologytext