Kinetic equations for ultrarelativistic particles in a Robertson-Walker   Universe and isotropization of relict radiation by gravitational interactions
  Kinetic equations for ultrarelativistic particles with due account of gravitational interactions with massive particles in the Robertson-Walker universe are obtained. On the basis of an exact solution of the kinetic equations thus obtained, a conclusion is made as to the high degree of the uniformity of the relict radiation on scales with are less than $10'$. 
Yu.G. Ignat'ev and A.A. Popov
gr-qc astro-ph.CO