Linking Topological Quantum Field Theory and Nonperturbative Quantum Gravity

TL;DR

This paper establishes a nonperturbative quantum gravity framework with boundary conditions leading to a boundary Hilbert space composed of SU(2) Chern-Simons theories, confirming holographic bounds and categorical dimension structures.

Contribution

It constructs a boundary Hilbert space for quantum gravity using Chern-Simons theories, linking boundary measurements to interior states and confirming holographic principles.

Findings

Boundary Hilbert space is a direct sum of SU(2) Chern-Simons state spaces.

Chern-Simons level relates to cosmological constant and gravitational constant.

Holographic bounds are confirmed in the large area, small cosmological constant limit.

Abstract

Quantum gravity is studied nonperturbatively in the case in which space has a boundary with finite area. A natural set of boundary conditions is studied in the Euclidean signature theory, in which the pullback of the curvature to the boundary is self-dual (with a cosmological constant). A Hilbert space which describes all the information accessible by measuring the metric and connection induced in the boundary is constructed and is found to be the direct sum of the state spaces of all $SU(2)$ Chern-Simon theories defined by all choices of punctures and representations on the spatial boundary $\cal S$. The integer level $k$ of Chern-Simons theory is found to be given by $k= 6\pi /G^2 \Lambda + \alpha$, where $\Lambda$ is the cosmological constant and $\alpha$ is a $CP$ breaking phase. Using these results, expectation values of observables which are functions of fields on the boundary may be evaluated in closed form. The Beckenstein bound and 't Hooft-Susskind holographic hypothesis are confirmed, (in the limit of large area and small cosmological constant) in the sense that once the two metric of the boundary has been measured, the subspace of the physical state space that describes the further information that the observer on the boundary may obtain about the interior has finite dimension equal to the exponent of the area of the boundary, in Planck units, times a fixed constant. Finally,the construction of the state space for quantum gravity in a region from that of all Chern-Simon theories defined on its boundary confirms the categorical-theoretic ``ladder of dimensions picture" of Crane.