Cosmology with quantum matter and a classical gravitational field

I consider a hybrid cosmological model with a classical gravitational field and a quantized massive scalar field in spherically symmetric gravity. The interaction between classical and quantum fields is described using the formalism of ensembles on configuration space, an approach that provides an alternative to semiclassical gravity. After giving an outline of the formulation as it applies to spherically symmetric gravity, I discuss a particular solution that is analogous to the Einstein universe of classical relativity.