Physical Society Colloquium

Nearly Perfect Fluidity: From cold atoms to hot quarks and gluons

Thomas Schaefer

Department of Physics
North Carolina State University

A dimensionless measure of fluidity is the ratio of shear viscosity to entropy density. In this talk I will argue that fluidity is a sensitive probe of the strength of correlations in a fluid. I will also discuss evidence that the two most perfect fluids ever observed are also the coldest and the hottest fluid ever created in the laboratory. The two fluids are cold atomic gases (~10^-6 K) that can be probed in optical traps, and the quark gluon plasma (~10¹² K) created in heavy ion collisions at RHIC and the LHC. Remarkably, both fluids come close to a bound on the shear viscosity that was first proposed based on calculations in string theory, involving the non-equilibrium evolution of back holes.