Bardeen has investigated the formation of perturbations during the early history of the universe. The growth rates depend on the choice of spacelike hypersurfaces on which the background metric is taken to be independent of position. Since in one coordinate system all density perturbations have zero amplitude at / = 0, while in another no density perturbations are zero at / = 0, the conclusion is that it is meaningless to talk about the growth rate or size of density perturbations in a

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... universe until a light signal has had time to cross the perturbation.