  Experimental results on azimuthal correlations in high energy nuclear
collisions (nucleus-nucleus, proton-nucleus and proton-proton) seem to be well
described by viscous hydrodynamics. It is often argued that this agreement
implies either local thermal equilibrium or at least local isotropy. In this
note, I present arguments why this is not the case. Neither local
near-equilibrium nor near-isotropy are required in order for hydrodynamics to
offer a successful and accurate description of experimental results. However, I
predict the breakdown of hydrodynamics at momenta of order seven times the
temperature, corresponding to a smallest possible QCD liquid drop size of 0.15
fm.
