Running coupling of particles when they approach close to each other
The strong, electromagnetic and weak interaction are probably just different sides of a common interaction that manifests itself at very high temperatures. The intensity of the interactions is controlled by a so-called running coupling parameter that is individual for each of them. These parameters are called running because they change with decreasing distance between interacting particles, which is associated with an increase of the probability of virtual particle-antiparticle pairs to be created. At a very small distance, all the three parameters are almost equal to each other — the coupling parameter of the strong interaction decreases rapidly with decreasing distance, that of the weak interaction decreases slowly, and the electromagnetic coupling parameter increases. The coincidence of coupling parameters of all the three interactions is an amazing fact and may be the result of their unification, which is called the Great Unification.