This, in its turn, results in forms for the spatially integrated net values of electric charge [q.sub.0], magnetic moment [M.sub.0], mass [m.sub.0] obtained from the mass-energy relation
by Einstein, and spin [s.sub.0].
The energy of photons and their electromagnetic radiation field also have to be regarded as an equivalent mass due to Einstein's mass-energy relation
. This raises the additional question whether full symmetry also requires the photon to have a positive or negative gravitational mass, as given by
Einstein's mass-energy relation
suggested the total energy of a particle ([epsilon]) is connected to its mass (m), [epsilon] = [mc.sup.2].