Space and averaging in relativistic cosmology
Ecole Normale Superieure, Lyon, France
Time & Place
Wed, 20 Feb 2019 12:00:00 NZDT in Room 111, Jack Erskine Building
All are welcome
The present-day Universe is inhomogeneous, with a large-scale structure in matter distribution forming the so-called cosmic web surrounded by void regions. Nonlinear regional deviations from the homogeneous and isotropic cosmological models are thus expected, with potentially non-negligible consequences on the global or large-scale expansion dynamics. These "backreaction" effects of structure formation on the large-scale expansion can be described in a locally inhomogeneous general-relativistic model through a spatial averaging scheme. Such a scheme requires defining slices of three-dimensional space out of the model spacetime, i.e. a "3+1" split or foliation of spacetime.
I will first introduce the spatial averaging and backreaction notions by recalling the results in the framework of a pressureless and vorticity-free matter content described in the spatial frames where the cosmological fluid is at rest. I will then suggest the extension of such a model to general fluid sources that may model structure formation on most scales. I will discuss the influence in this cosmological context of the freedom in the choice of "space" in general relativity by presenting the averaged dynamics of a given set of matter particles in any foliation, and by examining the effects of changing the foliation considered.