A magnet has a north and a south pole. If you cut that magnet in two, you get two magnets, each with its own north and south poles. No matter how far you subdivide a magnetic material, this is what happens. Both north end and south end. Theory and indirect measurements support the existence of matter with just one pole: a monopole. Scientists have searched in all kinds of materials -- in particle colliders, in moon dust, in cosmic radiation -- to no avail.