The binding energy between the proton and neutron is deuterium is only due to the dispersal of charge and hence very weak . Then two such deuterium atoms come closer. Under Favorable conditions all the four nucleons of the two -deuterium atoms may get close packed. A lot of excess energy gets trapped in the interstitial space between the nucleons. Protons with a high energy packed inside moves toward this interstitial space with excess energy.
Neutrons prevent the squashing of the interstitial space.
Thus Helium the second most abundant element in the universe is born. Also the strong nuclear force having a consequence of the energy trapped in the interstitial space manifest them for the first time. Evolution of other elements, especially radioactive elements and their decay modes present an interesting study, which will be taken up after a while. Now a few words to justify the title As a chemist preoccupied with optical activity I was surveying the literature to know more about matter Radiation interaction. Various grand unification theories came across made me more curious about the origin of universe.