Physics of BEC

Summary form only given, as follows. The physical basis of the theory being used to describe Bose-Einstein condensed (BEC) gases will be described. The simplest and indeed most successful approach uses mean field theories of the phenomena. In the case of the lowest temperatures reached, this theory reduces to the study of the Gross-Pitaevskii nonlinear Schrodinger equation. I will describe the extensions of mean field theory to finite temperatures and show how dynamics and damping can be included. I will address the links to superfluidity and time-evolving order parameters in general.