Institute for Advanced Study Informal Astrophysics Seminar

ABSTRACT: There are two sides to every story and to most well constructed equations. In Poisson's equation and its generalization by Einstein we normally have on the left sides of those equations the descriptors of gravity and on the right its sources, matter in Newton's theory and energy (the stress-energy tensor, T, really) in Einstein's. There have been several attempts to make modifications on the right --- to the theory of gravity --- while the description of the sources has not been subjected to as much discussion. This talk will describe a derivation of the stress-energy tensor from kinetic theory without introducing the Chapman-Enskog iterative procedure. The derivation will be outlined for the nonrelativistic case and the result in the relativistic case will be reported afterwards. The cosmological solutions (FRWL... and a second one) found with the relativistic version of T will be given along with an estimate of the entropy production in the second solution.