Quantum mechanics and the arrow of time

          @misc{ pirsa_PIRSA:10040110,
            doi = {10.48660/10040110},
            url = {https://pirsa.org/10040110},
            author = {Maccone, Lorenzo},
            keywords = {Quantum Information},
            language = {en},
            title = {Quantum mechanics and the arrow of time},
            publisher = {Perimeter Institute},
            year = {2010},
            month = {apr},
            note = {PIRSA:10040110 see, \url{https://pirsa.org}}
          }
          

Abstract

The arrow of time dilemma: the laws of physics are invariant for time inversion, whereas the familiar phenomena we see everyday are not (i.e. entropy increases). I show that, within a quantum mechanical framework, all phenomena which leave a trail of information behind (and hence can be studied by physics) are those where entropy necessarily increases or remains constant. All phenomena where the entropy decreases must not leave any information of their having happened. This situation is completely indistinguishable from their not having happened at all. In the light of this observation, the second law of thermodynamics is reduced to a mere tautology: physics cannot study those processes where entropy has decreased, even if they were commonplace. I will discuss the possible limitations that stem from recent typicality results in employing this as a complete self-consistent solution to the arrow of time dilemma.