Isotropization of the Quark Gluon Plasma

We report here recent analytical and numerical work on the theoretical treatment of the early stages of heavy ion collisions, that amounts to solving the classical Yang-Mills equations with fluctuating initial conditions. Our numerical simulations suggest a fast isotropization of the pressure tensor of the system. This trend appears already for small values of the coupling constant $\alpha_s$ . In addition, the system exhibits an anomalously small shear viscosity.