  Triple-gluon elastic scatterings are briefly reviewed since the scatterings
explain the early thermalization puzzle in Au-Au collisions at RHIC energies. A
numerical solution of the transport equation with the triple-gluon elastic
scatterings demonstrates gluon momentum isotropy achieved at a time of the
order of 0.65 fm/c. Triple-gluon scatterings lead to a short thermalization
time of gluon matter.
