  We study heavy ion collisions at strong 't Hooft coupling using AdS/CFT
correspondence. According to the AdS/CFT dictionary heavy ion collisions
correspond to gravitational shock wave collisions in AdS_5. We construct the
metric in the forward light cone after the collision perturbatively through
expansion of Einstein equations in graviton exchanges. We obtain an analytic
expression for the metric including all-order graviton exchanges with one shock
wave, while keeping the exchanges with another shock wave at the lowest order.
We read off the corresponding energy-momentum tensor of the produced medium.
Unfortunately this energy-momentum tensor does not correspond to ideal
hydrodynamics, indicating that higher order graviton exchanges are needed to
construct the full solution of the problem. We also show that shock waves must
completely stop almost immediately after the collision in AdS_5, which, on the
field theory side, corresponds to complete nuclear stopping due to strong
coupling effects, likely leading to Landau hydrodynamics. Finally, we perform
trapped surface analysis of the shock wave collisions demonstrating that a bulk
black hole, corresponding to ideal hydrodynamics on the boundary, has to be
created in such collisions, thus constructing a proof of thermalization in
heavy ion collisions at strong coupling.
