Sayyed Rassouli - 'Volume as a Clock: Observers and Topology Change in Quantum Gravity'

Thursday 15 Oct 2026, 14:00 → 16:00 Asia/Seoul

Different notions of time arise from different choices of observer. In cosmological settings, a particularly natural choice is spacetime volume, which is conjugate to the cosmological constant. This gives rise to unimodular time, deparametrizing the Wheeler–DeWitt equation into a Schrödinger-like evolution equation. I will first explain how this construction appears in arbitrary dimensions, with particular emphasis on the four-dimensional case.

I will then use a two-dimensional toy model to quantise global Lorentzian de Sitter space, where quantum mechanically there is a region in which topology change can occur. More generally, I will explain how adding these types of observers and clocks classically encodes topology change and orientation change, and how this structure can be associated with a Morse function. I will also show the holography of such observers in the context of near horizon black holes.