On inhomogeneous models of the early universe

Although many authors have studied the behaviour of homogeneous models near the cosmological singularity, more general inhomogeneous models, up to now, have not been considered. Some characteristic properties of these models which may be qualitatively different from the homogeneous case are studied. Reviews are given about the anti-Newtonian and post-anti-Newtonian approximation in the general case, including not only velocity-dominated approximation, but also rotational modes. A simple one-dimensional anisotropic collapse is shown which may appear in the course of evolution. The wave propagation is treated near the singularity, which can appear only in inhomogeneous models, and it is shown that, before the Kasner or oscillatory stage, there is a stage in which the propagation is dominant. A canonical formalism for wave propagation is expressed