  We obtain solutions to the coupled Schr\"odinger-Poisson equations. The
solutions describe the evolution of cold dark matter density perturbations in
an otherwise homogeneous expanding Friedmann universe. We discuss the
relationships between descriptions of cold dark matter in terms of a
pressureless fluid, in terms of a wavefunction, of a classical scalar field,
and a quantum scalar field. We identify the regimes where the various
descriptions coincide and where they differ.
