Probing Backreaction Effects with Supernova Data
Seikel, Marina (University of Cape Town)

As the Einstein equations are non-linear, spatial averaging and temporal evolution do not commute. Therefore, the evolution of the averaged universe is affected by local inhomogeneities. It is, however, highly controversial how large these cosmological backreaction effects are. Using Buchert's averaging formalism and perturbation theory up to second order, one can calculate the effects of backreaction on the measurements of the Hubble rate in the nearby universe. The size of the effect depends on the size and shape of the volume that is averaged over. The theory is then compared to actual measurements of the Hubble rate using the supernova data of the Constitution set up to a redshift of 0.1.