PIRSA:08120034

Backreaction from Averaging in Cosmology

APA

Paranjape, A. (2008). Backreaction from Averaging in Cosmology. Perimeter Institute for Theoretical Physics. https://pirsa.org/08120034

MLA

Paranjape, Aseem. Backreaction from Averaging in Cosmology. Perimeter Institute for Theoretical Physics, Dec. 11, 2008, https://pirsa.org/08120034

BibTex

          @misc{ scivideos_PIRSA:08120034,
            doi = {10.48660/08120034},
            url = {https://pirsa.org/08120034},
            author = {Paranjape, Aseem},
            keywords = {Cosmology},
            language = {en},
            title = {Backreaction from Averaging in Cosmology},
            publisher = {Perimeter Institute for Theoretical Physics},
            year = {2008},
            month = {dec},
            note = {PIRSA:08120034 see, \url{https://scivideos.org/pirsa/08120034}}
          }
          

Aseem Paranjape Tata Institute of Fundamental Research (TIFR)

Talk numberPIRSA:08120034
Source RepositoryPIRSA
Talk Type Conference
Subject

Abstract

There is an ongoing debate in the literature concerning the effects of averaging out inhomogeneities (``backreaction\'\') in cosmology. In particular, it has been suggested that the backreaction can play a significant role at late times, and that the standard perturbed FLRW framework is no longer a good approximation during structure formation, when the density contrast becomes nonlinear. After a brief introduction to the problem, I will show using Zalaletdinov\'s covariantaveraging scheme that as long as the metric of the universe can be described by the perturbed FLRW form, the corrections due to averaging remain negligibly small. Further, using a fully relativistic and reasonably generic model of pressureless spherical collapse, I will show that as long as matter velocities remain small (which is true in this model even at late times), the perturbed FLRW form of the metric can be explicitly recovered. Together with the observation that real peculiar velocities are in fact nonrelativistic, these results imply that the backreaction remains small even during nonlinear structure formation.