  We consider quantum general relativity in three dimensions with a positive
cosmological constant. The Hartle-Hawking wave function is computed as a
function of metric data at asymptotic future infinity. The analytic
continuation from Euclidean Anti-de Sitter space provides a natural integration
contour in the space of metrics, allowing us -- with certain assumptions -- to
compute the wave function exactly, including both perturbative and
non-perturbative effects. The resulting wave function is a non-normalizable
function of the conformal structure of future infinity which is infinitely
peaked at geometries where I^+ becomes infinitely inhomogeneous. We interpret
this as a non-perturbative instability of de Sitter space in three dimensional
Einstein gravity.
