  The role of topology change in a fundamental theory of quantum gravity is
still a matter of debate. However, when regarding string theory as
two-dimensional quantum gravity, topological fluctuations are essential. Here
we present a third quantization of two-dimensional surfaces based on the method
of causal dynamical triangulation (CDT). Formally, our construction is similar
to the c = 0 non-critical string field theory developed by Ishibashi, Kawai and
others, but physically it is quite distinct. Unlike in non-critical string
theory the topology change of spatial slices is well controlled and regulated
by Newton's constant.
