Scientific Seminars

The Backreaction Conjecture to explain Dark Energy

Thomas Buchert
CRAL, Observatoire de Lyon

2012-06-12    16.00    Merate - POE

The standard model of cosmology rests on a homogeneous-isotropic solution of Einstein's laws of gravitation. The so-called "concordance model" fixes the parameters of this model in conformity with available observational data. Accepting this model leads to a number of unresolved issues related to the conjecture of existence of Dark Matter and Dark Energy. To resolve these, one either seeks to generalize the laws of gravitation, or one assumes the existence of new fundamental fields providing challenges for particle physics. In this talk we focus on a third possibility that is conservative by not generalizing the laws of Einstein and by not including any new fundamental field. We present and motivate by first principles a set of effective (i.e. spatially averaged) Einstein equations that govern the regional and global dynamics of inhomogeneous cosmological models. In this framework we discuss the recently advanced conjecture that backreaction effects - due to fluctuations in matter and geometry - may provide a `classical' explanation of the Dark Energy problem. Interestingly, such an explanation also touches on the Dark Matter problem through the same effect, but investigated on smaller scales. We also discuss implications for observational cosmology and present first strategies to observationally confirm the advanced conjecture.