Abstract
Starting from a small perturbation in the initial data for a Robertson-Walker universe, it is shown that, in a small region of space-time, it is possible for large fluctuations to develop in both the metric and physical variables describing the Universe. The initial data are specified on a characteristic hypersurface in a region of perfect fluid filled space-time and the method of analysis of the field equations is based on the techniques introduced by Bondi, van der Burg and Metzner (1962).