1. Diffusion Approximation for a Photon Gas Interacting with a Plasma via the Compton Effect
2. P. J. E. Peebles,Physical Cosmology(Princeton U.P., Princeton, NJ, 1971), p. 200.
3. Entropy Generation and the Survival of Protogalaxies in an Expanding Universe
4. S. R. de Groot, W. A. van Leeuwen, and Ch. G. van Weert,Relatiuistic Kinetic Theory, Principles and Applications(North-Holland, Amsterdam, 1980).
5. J. Ehlers, inGeneral Relativity and Cosmology (Proceedings of the International School of Physics “Enrico Majorana,” Course 47), edited by R. K. Sachs (Academic, New York, 1971), particularly pp. 47–51.