Electric charges are everywhere, but there is still no evidence of magnetic monopoles. That remains true even after a new report of the most sensitive search to date for monopole production at accelerator energies. 1 The report, by the CDF-detector collaboration at the Fermilab Tevatron collider, concludes that more than 1012 proton–antiproton collisions over several months in the world’s highest-energy collider produced not even one pair of magnetic monopoles.
In 1894 Pierre Curie pointed out that the absence of monopoles is all that mars the symmetry of the Maxwell equations with regard to electric and magnetic fields (see the box below). Serious modern interest in the possible existence of magnetic monopoles began with a famous 1931 paper by Paul Dirac. 2 He showed that a consistent quantum mechanical treatment of a system comprising an electron of electric charge –e and a monopole of magnetic charge g required that...
