Speaker: Marco Bruni
Location: Imperial College, London
There is fundamental gap in the way we do Cosmology: we use a homogeneous isotropic background, relativistic perturbation theory to model small early universe fluctuations and their initial evolution, then we expand N-body simulation boxes assuming this background, mostly a LCDM cosmology, modelling structure formation with Newtonian gravity. While this may be perfectly satisfactory, at a time when a deluge of new data will be soon available and alternatives to LCDM are explored, including modified theories of gravity, it becomes worth investigating relativistic effects, such as light propagation in a inhomogeneous universe and possible effects in structure formation, within the standard LCDM General Relativistic cosmology. In this talk I will briefly outline various lines of investigations on these issues, focusing in particular on a class of exact solutions of Einstein Equations describing non-linear inhomogeneities in a flat LCDM background that may be applied to study relativistic effects in a simplified setting. I will then briefly describe a new post-Newtonian cosmological formalism that should allow to investigate these issues realistically, including small-scale non-linear Newtonian cosmology and horizon scale first-order relativistic perturbation theory in a unified framework.