Quantum cosmology as a cure for the three ailments of classical cosmology

Abstract

The standard big bang models of classical cosmology are known to possess three defects. The oldest known defect is the spacetime singularity whose existence seems inevitable within the classical framework. The second defect is the existence of a particle horizon which severly limits communications across the distant parts of the universe whose observed homogeneity therefore becomes inexplicable. Recently a third defect has been highlighted, viz., the required fine tuning of the early universe close to the flat spatial model in order to account for the present range of its mean density. We show here that the injection of quantum ideas holds out hope of a cure for all the three ailments described above. Using a simple path integral formalism for quantum cosmology we present arguments which suggest that (i) it is extremely unlikely that the universe evolved to the present state from quantum states of singularity and particle horizon; (ii) of all the possible Robertson-Walker models that could evolve out of quantum fluctuations of the empty Minkowski universe the flat model is overwhelmingly probable.