  The contraction of a spin-1/2 representation of the de Sitter group SO(3,2)
yields a translation operator that consists of the usual momentum operator plus
a second order term, the "momentum spin" as described by F. Guersey. The
contribution of momentum spin to the kinematics of a multiparticle system in a
tangential space of anti de Sitter space is analyzed. It is shown that it can
be described by a perturbation term with the structure of the interaction term
of quantum electrodynamics. An evaluation of the corresponding coupling
constant reproduces Wyler's heuristic formula for the electromagnetic coupling
constant.
