  In this paper, we study the evolution of a dense system of gluons, such as
those produced in the early stages of ultra-relativistic heavy ion collisions.
We describe the approach to thermal equilibrium using the small angle
approximation for gluon scattering in a Boltzmann equation that includes the
effects of Bose statistics. In the present study we ignore the effect of the
longitudinal expansion, i.e., we restrict ourselves to spatially uniform
systems, with spherically symmetric momentum distributions. Furthermore we take
into account only elastic scattering, i.e., we neglect inelastic, number
changing, processes. We solve the transport equation for various initial
conditions that correspond to small or large initial gluon phase-space
densities. For a small initial phase-space density, the system evolves towards
thermal equilibrium, as expected. For a large enough initial phase-space
density the equilibrium state contains a Bose condensate. We present numerical
evidence that such over-populated systems reach the onset of Bose-Einstein
condensation in a finite time. The approach to condensation is characterized by
a scaling behavior that we briefly analyze.
