Informal Pizza Seminar

Accelerated expansion from structure formation

Syksy Rasanen

I discuss the backreaction of inhomogeneities on the expansion of the universe. The average behaviour of an inhomogeneous spacetime is not given by the Friedmann-Robertsen-Walker equations. The new terms in the exact equations hold the possibility of explaining the observed acceleration without a cosmological constant or new physics. In particular, the coincidence problem may be solved by a connection with structure formation. I discuss an exact toy model where gravitational collapse induces accelerating expansion.