2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/34453The definition of entropy obtained for stationary black holes is extended in this paper to the case of non-stationary black holes. Entropy is defined as a macroscopical thermodynamical quantity which satisfies the first principle of thermodynamics. In the non-stationary case a volume term appears since the solution does not admit a Killing vector.General Relativity and Quantum Cosmologytext