In this approximation, the energy levels are different because of a different effective mass, "m"*, in the energy equation (see electron energy levels for a derivation):::formula_3where:: is the charge magnitude of the electron (same as the positron),: is Planck's constant,: is the electric constant (otherwise known as the permittivity of free space),: is the reduced mass::::formula_4:where and are, respectively, the mass of the electron and the positron (which are "the same" by definition as antiparticles).