The Issue of Time in Generally Covariant Theories

          @misc{ pirsa_PIRSA:21060108,
            doi = {10.48660/21060108},
            url = {https://pirsa.org/21060108},
            author = {Gambini, Rodolfo},
            keywords = {Quantum Foundations},
            language = {en},
            title = {The Issue of Time in Generally Covariant Theories},
            publisher = {Perimeter Institute},
            year = {2021},
            month = {jun},
            note = {PIRSA:21060108 see, \url{https://pirsa.org}}
          }
          

Abstract

A possible solution of the problem of time in quantum gravitational systems is presented based on a relational description between the parameterized Dirac observables of the system under consideration and the clocks. The use of physical clocks required by a quantum gravitational description of time is shown to induce a loss of unitarity. The evolution is described by a Lindblad-type master equation unless it is possible to construct a perfect clock. I show that fundamental uncertainties in time measurements could arise due to quantum and gravitational effects, leading to the conclusion that there is always a loss of unitarity induced by the use of physical clocks. The extension of the analysis to physical reference frames in totally constrained systems is sketched.