Negatively charged particles that spin around the positive centre of the atom in circles called energy levels. Their mass is so small it is nearly zero. Positively charged particles that are ...
It came when the one electron of the hydrogen atom transitioned from the 2P 1/2 energy level to the 2S 1/2 level ... and it's easiest via Feynman diagrams. "Two-loops" refers to the Feynman ...