Transcript: In the big bang model it’s possible to calculate the abundance of light elements created by fusion reactions in the early phases of the expansion. This is called cosmic nucleosynthesis. The calculations depend on only one fundamental parameter of the universe which is the density of protons and neutrons. Although dark matter dominates normal matter, dark matter interacts so weakly that it’s not relevant for the calculations of nucleosynthesis in the early universe. These calculations lead to a prediction of the mass fraction abundance of certain light elements. They predict that helium 4 should be about one quarter relative to hydrogen, that deuterium or heavy hydrogen should be at an abundance of ten to the minus four relative to hydrogen, that helium 3 should have an abundance of about ten to the minus five relative to hydrogen, and lithium 7 an abundance of one part in a billion or ten to the minus nine relative to hydrogen. It’s a stunning success of the big bang model that the observed abundances of these four light element species agree within the errors of the predictions of the big bang model.