the big bang

If the general relativity was correct, the universe would begin with a infinity temperature and density in the singularity of the great initial explosion. As the universe was expanding, the temperature of radiation was diminishing. During the first three minutes, as the universe was cooling up to billion degrees, the protons and neutrons would have started combining, forming cores of helium, hydrogen and other elements. Hundreds of thousands of years later, when the temperature had fallen to a few thousands of degrees, the electrons would have been stopped sufficiently to be able to be captured by the light nucleuses and to form atoms.