Swimming with a Crowd: Collective Behavior of Active Suspensions

Bacterial suspensions and extracts of cytoskeletal filaments and motor proteins are examples of assemblies of interacting self-driven units that form active complex fluids. These systems exhibit fascinating collective behavior, including nonequilibrium phase transitions, novel long-range correlations, and pattern formation on mesoscopic scales. In this talk I will review our work on using nonequilibrium statistical physics to derive a continuum description of active suspensions from specific models of single particle dynamics. Specifically I will highlight the role of physical interactions, such as excluded volume and medium-mediated hydrodynamic couplings, in controlling the large-scale behavior.