An Old Puzzle Solved: Why the Mass of the Electron Is 0.511 MeV/c2

One of the main objectives in contemporary physics is the calculation of nuclear masses from first principles. In lattice QCD such first principle is the running mass of quarks, derived from the empirical mass value of the pion as reference. So far, it has not resulted into a theoretical verification of the rest mass of the electron. This mass is still considered as an independent phenomenological elementary quantity. In this article it is shown how the Structural Model of particle physics allows to do better, by proving that the rest mass of the electron can be derived by theory from the mass of the pion as reference.