Inequivalent clocks in quantum cosmology

          @misc{ scivideos_PIRSA:21060113,
            doi = {10.48660/21060113},
            url = {https://pirsa.org/21060113},
            author = {Gielen, Steffen},
            keywords = {Quantum Foundations},
            language = {en},
            title = {Inequivalent clocks in quantum cosmology},
            publisher = {Perimeter Institute for Theoretical Physics},
            year = {2021},
            month = {jun},
            note = {PIRSA:21060113 see, \url{https://scivideos.org/pirsa/21060113}}
          }
          

Abstract

Quantum cosmology faces the problem of time: the Universe has no background time, only interacting dynamical degrees of freedom within it. The relational view is to use one degree of freedom (which can be matter or geometry) as a clock for the others. In this talk we discuss a cosmological model of a flat FLRW universe filled with a massless scalar field and a perfect fluid. We study three quantum theories based on three different choices of (relational) clock and show that, if we require the dynamics to be unitary, all three make drastically different predictions regarding resolution of the classical (Big Bang) singularity or a possible quantum recollapse at large volume. The talk is based on [arXiv:2005.05357] and a second paper to appear on arXiv in May 2021. We plan to give two talks: one covering the foundations and general properties of the model, and one showing detailed results and physical interpretation. (We will merge these talks into one if the organisers decide to accept only one talk.)