Observations and inhomogeneity in cosmology
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
We interpret distance measurements from nearby galaxies, type Ia supernovae, and gamma-ray bursts in the light of a cosmological model that incorporates a spatial averaging technique to account for the inhomogeneous distribution of structure in the late-epoch Universe and the consequent importance of the location of the observer. In the timescape cosmology it is suggested that dark energy is a misidentification of gravitational energy gradients---and consequently of the relative calibration of clocks and rulers---in a complex inhomogeneous structure. This model is consistent with the current supernova and gamma-ray burst data within the limits imposed by our understanding of the systematic uncertainties, to the extent that a Bayesian model comparison with the standard model yields a preference for the timescape model that is “not worth more than a bare mention”. In the spirit of the timescape model, of attempting to understand the astrophysics with as few cosmological assumptions as possible, we perform a model-independent analysis of galaxy distances in the local Universe. We find that the rest frame of the Local Group provides a more uniform Hubble expansion field than the rest frame of the CMB. We find that the dipole in the Hubble expansion field coincides with the dipole in the CMB temperature with a correlation coefficient of -0.92, and that this pattern is induced within 60 h⁻¹ Mpc, provided the variation in the distance-redshift relation due to the formation of structure is taken into account.