"If Time Had No Beginning" Fay Dowker, Imperial College London - 3/10/21

Could the universe have had no beginning? I don’t mean, in raising this question, to deny or throw doubt on Big Bang cosmology and the existence in the past of a hot, dense state of Planckian curvature and temperature. But, in that case, how is the question to be interpreted given that-if we accept the standard cosmology- the Lorentzian manifold structure of spacetime breaks down at the Big Bang? Certainly, the continuum concept of time in our cosmological epoch “begins” at the Big Bang. Can we even ask what happened “before” that? The causal set approach to the problem of quantum gravity provides an arena in which to address the question of origins, in which it makes sense to ask what happened before the Big Bang and in which a clear distinction can be made between models of the universe which are “past infinite” and “past finite”. I will describe work with Stav Zalel and Bruno Bento in which we construct a framework for dynamics for causal sets which can result in past infinite universes.