Different notions of time arise from different choices of observer. In cosmological settings, a particularly natural choice is the 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 dimension, with particular emphasis on the four-dimensional case.

As an explicit Holographic realisation, I will then focus on near-extremal black holes, whose low-energy throat dynamics is universally described by Jackiw–Teitelboim gravity. In this setting, promoting the vacuum cosmological constant to a dynamical top-form degree of freedom provides a bulk clock in the Henneaux–Teitelboim sense. Holographically, this modifies the usual Schwarzian boundary dynamics by coupling it to an additional U(1) phase mode, reproducing the universal low-energy structure familiar from complex SYK. Finally, I will show that the resulting boundary theory can be rewritten as a (0+1) dimensional observer action, making explicit the relation between the bulk volume clock and its holographic boundary counterpart. 

Biography

Mr. Farbod Rassouli is a 4th-year PhD student at the University of Nottingham. He is currently working on twofold: Quantum gravity, Topology change and Strong Phase Transition in QFT’s. 

He completed his Undergrad at Royal Holloway University of London (2017-2022) and Master in Science in Quantum Fields and Fundamental Forcer at Imperial College London (2022-2023). His research interest includes, quantum gravity in holographic setups, lower dimensional theories and observers in GR.

Inviter: Jie-Qiang Wu