A magnetic monopole is a hypothetical particle that carries a single magnetic pole. Paul Dirac suggested in the 1930s that there should exist in nature a fundamental unit of magnetism, just as there exists a fundamental unit of electricity, the electron. This hypothetical particle is called the magnetic monopole because, unlike any known particle or magnet, it has only one magnetic pole. It is currently believed that if such an object does exist it must be very massive in order to explain why it has not been observed in high-energy experiments to date.