  A way to reconcile general relativity and quantum field theory without
quantising the geometry is to demand the metric evolve stochastically. In this
article, we explore the consequences of such a proposal at early cosmological
times. We find the stochastic evolution results in the spatial metric diffusing
away from its deterministic value, generating phantom cold dark matter (CDM).
It is produced primarily at the end of the inflationary phase of the Universe's
evolution, with a statistical distribution that depends on the specifics of the
early-times cosmological model. We find the energy density of this phantom cold
dark matter is positive on average, a necessary condition to reproduce the
cosmological phenomenology of CDM, although further work is required to
calculate its mean density and spatial distribution. If the density is
cosmologically significant, phantom dark matter acts on the geometry in a way
that is indistinguishable from conventional CDM. As such, it has the potential
to reproduce phenomenology such as structure formation, lensing, and galactic
rotation curves. We conclude by discussing the possibility of testing hybrid
theories of gravity by combining measurements of the Cosmic Microwave
Background with tabletop experiments.
