Prof. Istvan Szapudi on "A Concordance Cosmology without Dark Energy"

Thursday Apr 27, 2017, 3:30 PM → 4:30 PM Pacific/Honolulu

112 (Watanabe Hall)

According to the separate universe conjecture, spherically symmetric sub-regions in an isotropic universe behave like mini-universes with their own cosmological parameters. This is an excellent approximation in both Newtonian and general relativistic theories. We estimate local expansion rates for a large number of such regions, and use the volume-averaged increment of the scale parameter at each time step in an otherwise standard cosmological N-body simulation. The particle mass, corresponding to a coarse graining scale, is an adjustable parameter. This mean field approximation neglects tidal forces and boundary effects, but it is the first step towards a non-perturbative statistical estimation of the effect of non-linear evolution on the expansion rate, often associated with backreaction. Using our algorithm, a volume- averaged simulation with the Ω_m = 1 Einstein–de Sitter setting in each region closely tracks the expansion and structure growth history of a ΛCDM cosmology, and we confirm the numerical results with analytic calculations as well. The approximately shared expansion history guarantees consistency with the concordance model and, due to small but characteristic differences, our model can be distinguished from the standard ΛCDM model by future precision observations. Furthermore, our model naturally resolves the emerging tension between the local Hubble constant and the Planck best-fitting cosmology.