  It is widely believed that the assumption of homogeneity is a good zero{\it
th} order approximation for the expansion of our Universe. We analyze the
correction due to subhorizon inhomogeneous gravitational fields. While at early
times this contribution (which may act as a negative pressure component) is
perturbatively subdominant, we show that the perturbative series is likely to
diverge at redshift of order 1, due to the growth of perturbations. So, the
homogeneous Friedmann equation can not be trusted at late times. We suggest
that the puzzling observations of a present acceleration of the Universe, may
just be due to the unjustified use of the Friedmann equation and not to the
presence of a Dark Energy component. This would completely solve the
coincidence problem.
