The generation property of particles refers to the 3 different rest mass variants of each type of fermion, forming a mass hierarchy. For example:
- • The electron is a lepton with charge -1, rest mass \(9.109 \times 10^{-31}\) kg.
- • The muon is just like an electron, with mass ~207x heavier. It is unstable and decays into an electron.
- • The tau is just like a muon except it is 17x heavier, and is also unstable and ultimately ends up as an electron as well, through multiple different pathways.
Lepton generation is a weakly conserved property. It is conserved for example when a muon decays into an electron, because it also must release one muon neutrino and one electron antineutrino. However, neutrinos themselves do not conserve their generation properties, due to neutrino oscillation among the three different generations. This strange phenomenon may provide important insight into the nature of spin and its relationship to mass, all tied up in the weak interaction.