2022-06-20 Seminar Report

Dr. Daisuke Yoshida first motivated the expectation that the true quantum gravity, whatever its form turns out to be, should be free from singularities in the universe. The "singularity theorem" by Penrose states that a spacetime singularity arises under a set of certain assumptions. Flipping the argument around, if one admits that singularities are absent in our universe, at least one of the assumptions in the theorem needs to be abandoned. Dr. Yoshida discussed general properties that a non-singular universe must satisfy in order to avoid the singularity theorem. In particular, he found and explained that the universe must be, in some sense, smaller than the corresponding closed de Sitter spacetime. His talk stimulated the audience, and they continued discussions for long after his seminar.

Reported by Ryo Namba

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