Gravity seminar - Ted Jacobson [ONLINE] Seminar

Abstract: In their seminal 1977 paper, Gibbons and Hawking (GH) audaciously applied concepts of quantum statistical mechanics to ensembles containing black holes, finding that a semiclassical saddle point approximation to the partition function recovers the laws of black hole thermodynamics. In the same paper they insouciantly applied the formalism to the case of boundary-less de Sitter space (dS), obtaining the expected temperature and entropy of the static patch. The remarkable apparent success of this approach to quantum gravity has since remained a problematic puzzle. I'll first describe the original work, some problems and puzzles concerning it, and proposed resolutions. Next I'll offer an interpretation of the meaning of the dS sphere path integral, and then extend that to a computation of the number of quantum states of a spatial ball at any fixed volume. The result is the exponential of the Bekenstein-Hawking entropy of its boundary, indicating the holographic nature of nonperturbative quantum gravity in generic finite volumes of space.