Area and time

          @misc{ pirsa_PIRSA:25060009,
            doi = {10.48660/25060009},
            url = {https://pirsa.org/25060009},
            author = {Kirklin, Joshua},
            keywords = {Quantum Gravity, Quantum Information},
            language = {en},
            title = {Area and time},
            publisher = {Perimeter Institute},
            year = {2025},
            month = {jun},
            note = {PIRSA:25060009 see, \url{https://pirsa.org}}
          }
          

Abstract

A diffeomorphism-invariant definition of physical subsystems is crucial for understanding local quantum information in gravity. Recent toy models have made progress by adding observers with clocks and imposing boost invariance, thereby enabling a rigorous von Neumann algebraic definition of generalized entropy. But they depend on auxiliary degrees of freedom and leave infinitely many diffeomorphisms unaddressed. It is natural to ask what happens when one tries to surmount these limitations. I’ll show that including null translations lets us prove a version of the generalized second law beyond the semiclassical regime, with potential direct implications for black hole information. Then I’ll outline how the area degrees of freedom on a null surface define a quantum null time coordinate, and show how to use it to construct dressed operators invariant under all null diffeomorphisms (work in progress with Laurent Freidel.)