Speaker
Description
The present epoch Universe is inhomogeneous on < 100/h Mpc scales, opening up the possibility of backreaction - that average cosmic expansion is significantly different from that of the standard FLRW geometry at late epochs. Realizing this possibility means confronting unsolved open questions in general relativity, in particular the nonlocal nature of gravitational energy in coarse-graining matter and geometry. The timescape scenario is a phenomenologically viable model without dark energy which addresses these issues. In this talk I will focus on observational signatures of inhomogeneity and backreaction, including the Clarkson-Bassett-Lu (CBL) test that with Euclid satellite data should distinguish backreaction models from the concordance FLRW model in the next decade. While conceding a bet I made with Padmanabhan 10 years ago on the basis of current data, I offer a new bet on the CBL test for the coming age of "precision cosmology".