  It is shown that the excellent scaling of the elliptic flow found for all
centralities, species and energies from RHIC to the LHC for $p_{T}$ less than
the saturation momentum is a consequence of the energy lost by a parton
interacting with the color field produced in a nucleus-nucleus collision. In
particular, the deduced shape of the scaling curve describes correctly all the
data. We discuss the possible extensions to higher $p_{T}$, proton-nucleus and
proton-proton collisions as well as higher harmonics.
