The Magnetic Monopole  Ninety Years Later

In 1931 Dirac showed that the coexistence of magnetic monopoles and quantum mechanics requires that electric charge is quantized; all subsequent attempts to explain charge quantization also involve monopoles. After reviewing the history of magnetic monopoles,including it’s possible relevance to dark matter, I will turn to the three problems of electric-magnetic scattering: Weinberg’s discovery that the scattering amplitudes are not  Lorentz invariant, the requirement that scattering states cannot be written as products of one-particle states,and the possible violation of baryon number and gaugecharges in Grand Unified Theories