Gravitational energy as dark energy: Cosmic structure and apparent acceleration

Abstract

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. Here I discuss the timescape scenario, in which cosmic acceleration is understood as an apparent effect, due to gravitational energy gradients that grow when spatial curvature gradients become significant with the nonlinear growth of cosmic structure. I discuss conceptual issues related to the averaging problem, and their impact on the calibration of local geometry to the solutions of the volume-average evolution equations corrected by backreaction, and the question of nonbaryonic dark matter in the timescape framework. I further discuss recent work on defining observational tests for average geometric quantities which can distinguish the timescape model from a cosmological constant or other models of dark energy.

24 pages, 14 figures, to appear in the Proceedings of the Conference on Two Cosmological Models, Universidad Iberoamericana, Mexico City, 17-19 November, 2010

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Cited by in corpus (5)

• Cosmic acceleration from modified gravity with Palatini formalism
• Conformally Friedmann-Lemaitre-Robertson-Walker cosmologies
• Cosmic structure, averaging and dark energy
• The effect of cosmic inhomogeneities on the average cosmological dynamics
• Perspectives for studying the dark energy at z>2 with galaxy surveys