Speaker
Pierre Mourier
(Centre de Recherche Astrophysique de Lyon, École Normale Supérieure de Lyon)
Description
Properties and dynamics of an inhomogeneous Universe can be described through regional spatial averaging of scalar observables. In relativistic cosmology, the resulting averaged quantities will depend on the choice of space-like hypersurfaces defining the spatial slices of averaging. I will present a general averaging framework that applies to any choice for such a foliation, and the resulting effective evolution equations for a region of an arbitrary source fluid. It combines a 3+1 "slicing" formalism used to define the averaging hypersurfaces with the general 1+3 "threading" that defines the fluid flow. I will stress the interest of an averaging procedure that focusses as much as possible on intrinsic properties of the fluid content. This helps avoiding artificial dependencies in the choice of foliation. I will also present an example of foliation choices that are themselves built from the fluid flow and that provide compact and transparent averaged evolution equations.
