  A Big Bang universe consisting, before recombination, of H, D, 3He, 4He, 6Li,
and 7Li ions, electrons, photons, and massless neutrinos, at closure density,
with a galaxy-size perturbation spectrum but no large-scale structure, will
evolve into the universe as we now observe it. Evolution during the first
billion years is controlled by radiation. Globular clusters are formed by
radiatively-driven implosions, galaxies are formed by radiatively triggered
gravitational collapse of systems of globular clusters, and voids are formed by
radiatively-driven expansion. After this period the strong radiation sources
are exhausted and the universe has expanded to the point where further
evolution is determined by gravity and universal expansion.
