Dark Energy Without Dark Energy
David L Wiltshire
(University of Canterbury, NZ)
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Below scales of about 100/h Mpc our universe displays a complex inhomogeneous structure dominated by voids, with clusters of galaxies in sheets and filaments. The coincidence that cosmic expansion appears to start accelerating at the epoch when such structures form has prompted a number of researchers to question whether dark energy is a signature of a failure of the standard cosmology to properly account, on average, for the distribution of matter we observe. Several ideas have been put forward, with much debate and controversy. I will discuss the debate and the key issues which involve both the change to average cosmic evolution from backreaction, and the solution to the "fitting problem", How do our own observations relate to average quantities when the variance of local geometry becomes significant? I suggest that properly understanding these issues yields a viable cosmology, in which dark energy is recognized as a mis-identification of gravitational energy gradients associated with inhomogeneous structures, purely in general relativity with matter obeying the strong energy condition. A number of quantifiable and testable predictions will be presented, and present and future observational prospects discussed.