It turns out that when a particle decays it changes into a less massive particle and a force-carrier particle (a gluon or W/Z). These force carriers may then decay into other particles. So, a particle can't just change into another particle type; there is an intermediate force-carrier particle which mediates particle decays.

In many cases, these temporary force-carrier particles seem to violate the conservation of energy because they exist at extremely high energies. However, these particles exist so briefly that no rules are broken (such particles are called virtual particles ).