  Because the initial shape of the QGP in a heavy ion collision is anisotropic,
the momentum distribution becomes anisotropic after a short time. This leads to
plasma instabilities, which may help explain how the plasma isotropizes. We
explain the physics of instabilities and give the latest results of numerical
simulations into their evolution. Nonabelian interactions cut off the size to
which the soft unstable fields grow, and energy in the soft fields subsequently
cascades towards more ultraviolet scales. We present first results for the
power spectrum of this cascade.
