Inhomogeneity implies Accelerated Expansion

The Einstein equations for an inhomogeneous irrotational dust universe are analysed. A set of mild assumptions, all of which are shared by the standard FLRW type scenarios, results in a model that depends only on the distribution of scalar spatial curvature. If the shape of this distribution is made to fit the structure of the present universe, with most of the matter in galaxy clusters and very little in the voids that will eventually dominate the volume, then there is a period of accelerated expansion after cluster formation, even in the absence of a cosmological constant.