5.07.16 14:15

Models of inhomogeneity and backreaction in cosmology: A status report

David L. Wiltshire (Canterbury University, NZ)

On scales < 100/h Mpc the Universe displays a complex cosmic web of inhomogeneity. The possibility of backreaction - that the growth of structures on small scales can change average cosmic expansion relative to a homogeneous isotropic FLRW cosmology - is a subject of much debate. A model-independent test of local expansion in our < 100/h Mpc neighbourhood using the COMPOSITE survey of 4534 cluster distances provides very strong Bayesian evidence against the assumption that the FLRW geometry plus local Lorentz boosts correctly describe cosmic expansion on all scales. I will further demonstrate using ray traced simulations of exact solutions of Einstein's equations constrained by both the CMB and local expansion, that a 0.5% differential expansion on 70/h Mpc scales can account for features that the FLRW model does not. There are potential implications for large angle CMB anomalies. Finally, I will discuss the status of observational tests of the timescape cosmology, a viable model with backreaction (and no dark energy) in  which there are also significant changes relative to FLRW evolution on large scales.


(please note the unusual time!)

Kategorie: Kolloquium