  We analyze the results of an experimental setup that consist of two
statistically independent laser beams that cross, interfere and end at
detectors. At the beam intersection we place a thin wire at the center of a
dark interference fringe and analyze the complementarity inequality. We find
that the complementarity inequality is fulfilled provided we include a
scattering interaction. We find that this interaction is implicit in the
formalism of quantum theory; however, this interaction is active only when the
conservation laws are satisfied.
