The Abundance of Helium and Hydrogen
More evidence of the Big Bang Theory is the abundance (large number) of the "light elements" Hydrogen and Helium found in the universe. The high percentage of helium in particular is consistent with the Big Bang Theory. All other models and theories gave smaller percentages of Helium. It is believed that no process since the Big bang could alter the ratio of Hydrogen and Helium so what happened at the Big bang should explain the current abundance and ration of hydrogen and helium. When the universe was extremely hot, protons and neutrons were produced in equal numbers. The neutrons decayed at a fast rate. In an expanding universe however the neutrons combined to form deuterium and helium. This stopped the neutron decay.
The hydrogen helium abundance helps scientists to model the expansion rate of the universe. If it had expanded faster then there would have been more stable neutrons and therefore more helium. If it were slower, the universe would have been hotter for longer and the neutrons would have been unstable therefore less helium abundance.
The diagram below explains the theory:
The hydrogen helium abundance helps scientists to model the expansion rate of the universe. If it had expanded faster then there would have been more stable neutrons and therefore more helium. If it were slower, the universe would have been hotter for longer and the neutrons would have been unstable therefore less helium abundance.
The diagram below explains the theory: