2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/93342It is demonstrated that, making minimal changes in ordinary quantum mechanics, a reasonable irreversible quantum mechanics can be obtained. This theory has a more general spectral decompositions, with eigenvectors corresponding to unstable states that vanish when $t \to \infty .$ These ''Gamov vectors'' have zero norm, in such a way that the norm and the energy of the physical states remain constant. The evolution operator has no inverse, showing that we are really dealing with a time-asymmetric theory. Using Friedrichs model reasonable physical results are obtained, e. g. : the remaining of an unstable decaying state reappears, in the continuous spectrum of the model, with its primitive energy.30 pages, latex, no figures, email of first author castagni@iafe.uba.arQuantum Physicstext