GROWTH OR DECAY OF COSMOLOGICAL INHOMOGENEITIES AS A FUNCTION OF THEIR EQUATION OF STATE

We expand Einstein's equations in the synchronous gauge in terms of a purely space-dependent, ''seed,'' metric. The (nonlinear) solution acc urately describes a universe inhomogeneous at scales larger than the H ubble radius. We show that the inhomogeneities grow or decay, as time increases, depending on the equation of state for the matter (supposed to be a perfect fluid). We then consider the case when matter is a sc alar field with an arbitrary potential. Finally we discuss the general ity of the model and show that it is an attractor for a class of gener ic solutions of Einstein's equations.