The behavior of the muon is well understood, but its role as one of the elementary particles is unknown.
The muon is unstable, eventually undergoing a radioactive decay into an electron.
That is, if the muon did not exist, what effect would this have on the structure of matter?
Although the muon does not experience nuclear forces, it can interact weakly with nuclei.
An elementary particle in the lepton family having a mass 209 times that of the electron, a negative electric charge, and a mean lifetime of 2.2 × 10-6 seconds. The muon was originally called the mu-meson and was once thought to be a meson. See Table at subatomic particle.