Local and non-local measures of acceleration in relativistic cosmology
Tuesday 19 June 2012
to 14:15 at
Tim Clifton (Queen Mary, University of London)
Current cosmological observations, when interpreted within the framework of a homogeneous and isotropic Friedmann-Lemaitre-Robertson-Walker (FLRW) model, strongly suggest that the Universe is entering a period of accelerating expansion. This is usually taken to mean that the expansion of space itself is accelerating. In a general spacetime, however, this is not necessarily true. In this talk I will attempt to clarify this point by considering a handful of local and non-local measures of acceleration in
three different inhomogeneous cosmological models. Each of these measures reduce to the same quantity in the limit of exact spatial homogeneity and isotropy, but in spacetimes that are only statistically homogeneous and isotropic we fi nd that the acceleration inferred from observations made over large scales does not necessarily bear any resemblance to the average of the local acceleration of space itself. This demonstrates that observations made in an inhomogeneous universe can imply acceleration without the existence of dark energy.