Inhomogeneity effects in cosmology

This paper looks at how inhomogeneous spacetime models may be significant for cosmology. First it addresses how the averaging process may affect large-scale dynamics, with backreaction effects leading to effective contributions to the averaged energy-momentum tensor. Second, it considers how local inhomogeneities may affect cosmological observations in cosmology, possibly significantly affecting the concordance model parameters. Third, it presents the possibility that the universe is spatially inhomogeneous on Hubble scales, with a violation of the Copernican principle leading to an apparent acceleration of the universe. This could perhaps even remove the need for the postulate of dark energy.