Brane-world Cosmology

Brane-world models, where observers are restricted to a brane in a higher dimensional spacetime, offer a novel perspective on cosmology. I discuss some approaches to cosmology in extra dimensions and some interesting aspects of gravity and cosmology in brane-world models. COSMOLOGY AFTER EINSTEIN A century after Einstein first proposed his theory of relativity, it has become a cornerstone of the physical sciences. Four dimensional spacetime provides the setting for describing physical processes and in particular provides the dynamical framework for cosmological models of our expanding Universe. It was the general theory of relativity, proposed by Einstein in 1915, that for the first time provided equations with which to describe the dynamics of spacetime. Einstein’s equation GAB +ΛgAB = 8πGNTAB , (1) relates the intrinsic curvature, GAB, of the metric, gAB, to the local energy-momentum, TAB, while allowing for the possibility of a non-zero cosmological constant, Λ. Consistency with Newtonian gravity in the weak-field, slow-motion limit is ensured by the appearance of Newton’s constant, GN , in the constant of proportionality. In much of modern cosmology Einstein’s tensor equation (1) conveniently reduces to the Friedmann constraint equation