We argue that an expanding quark-gluon plasma has an anomalous viscosity,
which arises from interactions with dynamically generated color fields. We
derive an expression for the anomalous viscosity in the turbulent plasma domain
and apply it to the hydrodynamic expansion phase, when the quark-gluon plasma
is near equilibrium. The anomalous viscosity dominates over the collisional
viscosity for weak coupling and not too late times. This effect may provide an
explanation for the apparent ``nearly perfect'' liquidity of the matter
produced in nuclear collisions at the Relativistic Heavy Ion Collider without
the assumption that it is a strongly coupled state.Comment: Final version accepted for publicatio
