3d gravity and Teichmuller TQFT

I will describe a proposal that relates AdS_3 quantum gravity to a topological quantum field theory known as ``Teichmuller TQFT.’’ This proposal clarifies the relationship between pure AdS_3 quantum gravity and two copies of SL(2,R) Chern-Simons theory and resolves some well-known issues with this lore. I will argue that moreover this proposal provides a practical framework for the computation of 3d gravity partition functions, and will describe how it elucidates various aspects of the recent ensemble interpretation of semiclassical 3d gravity. (Based on work in progress with Lorenz Eberhardt and Mengyang Zhang.)