The direction of time in quantum mechanics

Abstract

The quantum decoherence effect, which is known to destroy quantum interferences at a macroscopic level, is also the most efficient cause of irreversibility. Most of this paper is devoted to a non-technical description of the present theoretical state of the art concerning this effect. It implies a privileged direction of time, which coincides with the one usually associated with thermodynamics. A few considerations concerning consistent quantum histories are also added, because they introduce a third direction of time, the logical one, which coincides with the first two and can be shown moreover to be universal, i.e. the same for two arbitrary regions in the universe.