Isotropic singularities in cosmological models

Motivated by the ideas of quiescent cosmology and the Weyl tensor hypothesis concerning the 'big bang', the authors give a geometric (and hence coordinate-independent) definition of the concept of 'isotropic singularity' in a spacetime. The definition generalises previous work on 'quasi-isotropic' and 'Friedmann-like' singularities, and some simple consequences of the definition are discussed. In particular it is shown that an isotropic singularity is a scalar polynomial curvature singularity at which the Weyl tensor is dominated by the Ricci tensor. Finally the authors impose the Einstein field equations with irrotational perfect fluid source. This enables a detailed description of the geometric structure of an isotropic singularity to be given. (author)