The key parameter which allows one to calculate the effects of BBN is the number of photons per baryon. This parameter corresponds to the temperature and density of the early universe and allows one to determine the conditions under which nuclear fusion occurs. From this we can derive elemental abundances. Although the baryon per photon ratio is important in determining elemental abundances, the precise value makes little difference to the overall picture. Without major changes to the Big Bang theory itself, BBN will result in mass abundances of about 75% of H-1, about 25% helium-4, about 0.01% of deuterium, trace amounts (on the order of 10−10) of lithium and beryllium, and no other heavy elements. (Traces of boron have been found in some old stars, giving rise to the question whether some boron, not really predicted by the theory, might have been produced in the Big Bang. The question is not presently resolved.) That the observed abundances in the universe are generally consistent with these abundance numbers is considered strong evidence for the Big Bang theory.
agenda item NL
Jun 6 2014 to Nov 7 2014