On averaged cosmologies.

We review some aspects of the backreaction problem. In a first part, using an averaging scheme generalized to arbitrary frames, we quantify the effect in the Poisson gauge of perturbation theory up to second order. The main result is the definition of a scale of homogeneity above which the backreaction effect becomes scale invariant. In a second part we present results about the structure of the effective lightcone in averaged cosmologies and show that a non-trivial structure due to the backreaction may allow to test the relevance of the backreaction effect as a solution to the dark energy conundrum with future data. [ABSTRACT FROM AUTHOR]