Quantum Cosmology with many fluids and the choice of cosmological time
  In this work we propose the quantization of a cosmological model describing
the primordial universe filled with five barotropic fluids, namely: radiation,
dust, vacuum, cosmic strings and domain walls. We intend to identify which
fluid is best suited to provide phenomenologically the temporal variable in
accordance with the observable universe. Through the Galerkin spectral method
and the finite difference method in the Crank-Nicolson scheme (vacuum case),
the quantum cosmological solutions are obtained and compared. We, also, compare
the quantum cosmological solutions with the corresponding classical ones. The
vacuum case is especially interesting because it provides a tunneling
transition mechanism from the quantum to the classical phase and the
possibility of calculating quantum tunneling probabilities.
