  We investigate black hole formation by a spherically collapsing thin shell of
matter in AdS space. This process has been suggested to have a holographic
interpretation as thermalization of the CFT on the boundary of the AdS space.
The AdS/CFT duality relates the shell in the bulk to an off-equilibrium state
of the boundary theory which evolves towards a thermal equilibrium when the
shell collapses to a black hole. We use 2-point functions to obtain information
about the spectrum of excitations in the off-equilibrium state, and discuss how
it characterizes the approach towards thermal equilibrium. The full holographic
interpretation of the gravitational collapse would require a kinetic theory of
the CFT at strong coupling. We speculate that the kinetic equations should be
interpreted as a holographic dual of the equation of motion of the collapsing
shell.
