  We uncover a surprising correspondence between a non-perturbative formulation
of three-dimensional Lorentzian quantum gravity and a hermitian two-matrix
model with ABAB-interaction. The gravitational transfer matrix can be expressed
as the logarithm of a two-matrix integral, and we deduce from the known
structure of the latter that the model has two phases. In the phase of weak
gravity, well-defined two-dimensional universes propagate in proper time,
whereas in the strong-coupling phase the spatial hypersurfaces disintegrate
into many components connected by wormholes.
