Quantum Gravity in 2 + 1 Dimensions: The Case of a Closed Universe.
Published Web Locationhttps://doi.org/10.12942/lrr-2005-1
In three spacetime dimensions, general relativity drastically simplifies, becoming a "topological" theory with no propagating local degrees of freedom. Nevertheless, many of the difficult conceptual problems of quantizing gravity are still present. In this review, I summarize the rather large body of work that has gone towards quantizing (2 + 1)-dimensional vacuum gravity in the setting of a spatially closed universe.