For Eugenie and David on the occasion of their marriage, July 2003
The equations depict the fusion of hydrogen nuclei to form helium, a sequence known as the proton-proton cycle. The sequence begins with two protons joining together to form deuterium, a positron and a neutrino. The deuterium nucleus fuses with another proton to form a helium-3 nucleus, releasing gamma radiation in the process. Finally, two helium-3 nuclei fuse to form helium-4 and two protons.
In the equation p is a proton, d is a deuterium nucleus, e+ is a positron, h is a neutrino, the photon of gamma radiation is γ, 3He is a helium-3 nucleus and 4He is a helium-4 nucleus.
The proton-proton cycle lies at the heart of star formation and is the primary source of energy radiated from the Sun. The Earth is bathed in this light–without it, the vast majority of life here could not exist.