One of the most basic properties of magnetism is that a magnet always has two
poles, north and south, which cannot be separated into isolated poles, i.e.,
magnetic monopoles. However, there are strong theoretical arguments why
magnetic monopoles should exist. In spite of extensive searches they have not
been found, but they have nevertheless played a central role in our
understanding of physics at the most fundamental level.Comment: 22 pages, 7 figures. To be published in Contemporary Physic
