  Hydrodynamical modeling of heavy ion collisions at RHIC suggests that the
quark-gluon plasma (QGP) "thermalizes" in a remarkably short time scale, about
0.6 fm/c. We argue that this should be viewed as indicating fast
isotropization, but not necessarily complete thermalization, of the
non-equilibrium QGP. Non-Abelian plasma instabilities can drive local
isotropization of an anisotropic QGP on a time scale which is faster than
ordinary perturbative scattering processes. As a result, we argue that
theoretical expectations based on weak coupling analysis are not necessarily in
conflict with hydrodynamic modeling of the early part of RHIC collisions,
provided one recognizes the key role of non-Abelian plasma instabilities.
