De Sitter Quantum Gravity and the Emergence of Local Algebras

Abstract

Quantum gravity is expected to be fundamentally non-local, yet our understanding of the early universe—especially during inflation—relies heavily on local quantum field theory in curved spacetime, often modeled by de Sitter space. This raises a key question: how does local physics emerge from a quantum gravity theory where true observables must be gauge-invariant and thus non-local? In this talk, the speaker will explore how relational observables in perturbative quantum gravity around de Sitter space can approximate local field operators under the right conditions. We will see that such approximations break down near certain “minimal” spatial slices after a short time, but remain valid over much larger regions—particularly deep in the future or past, or within a static patch—offering insight into how local physics might arise in a cosmological context.


About the Speaker

Mr. YU Xuyang is a PhD student in the Department of Physics at the University of California, Santa Barbara, where he works under the supervision of Prof. Donald MAROLF. His research focuses on quantum gravity in cosmological spacetimes, particularly the emergence of locality in de Sitter space and the construction of gauge-invariant observables, with or without an observer. Prior to his graduate studies, Mr. Yu earned his BA in Physics and Mathematics from the University of California, Berkeley, in 2022. As an undergraduate, he was actively involved in research on quantum gravity and random quantum circuits.


About the Center for Fundamental Physics

For more information, please refer to https://cfp.hkust.edu.hk/.


For Attendees' Attention

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