I consider some of the issues we face in trying to understand dark energy. I discuss how the averaging problem confuses our potential understanding of dark energy by considering the backreaction from density perturbations to second-order in the concordance model: this effect leads to at least a 10% change in the observed value of the deceleration parameter, and could be significantly higher. Large Hubble-scale inhomogeneity has not been investigated in much detail, and could conceivably be the cause of apparent cosmic acceleration. I discuss void models which defy the Copernican principle in our Hubble patch, and describe how we can potentially rule out these models.

University of Cape Town