  We present a field theory description for the non-perturbative splitting and
joining of baby universes in Euclidean Jackiw-Teitelboim (JT) gravity. We show
how the gravitational path integral, defined as a sum over topologies, can be
reproduced from the perturbative expansion of a Kodaira-Spencer (KS) field
theory for the complex structure deformations of the spectral curve. We use
that the Schwinger-Dyson equations for the KS theory can be mapped to the
topological recursion relations. We refer to this dual description of JT
gravity as a `universe field theory'. By introducing non-compact D-branes in
the target space geometry, we can probe non-perturbative aspects of JT gravity.
The relevant operators are obtained through a modification of the JT path
integral with Neumann boundary conditions. The KS/JT identification suggests
that the ensemble average for JT gravity can be understood in terms of a more
standard open/closed duality in topological string theory.
