Canonical quantization of (2+1)-dimensional gravity

We consider the quantum dynamics of both open and closed two-dimensional universes with ‘‘wormholes’’ and particles. The wave function is given as a sum of freely propagating amplitudes, emitted from a network of mapping class images of the initial state. Interference between these amplitudes gives nontrivial scattering effects, formally analogous to the optical diffraction by a multidimensional grating; ‘‘bright lines’’ correspond to the most probable geometries.