"Monopole detection is an open problem in experimental physics. Within theoretical physics, some modern approaches assume their existence. Joseph Polchinski, a prominent string-theorist, described the existence of monopoles as "one of the safest bets that one can make about physics not yet seen."
Look at the table in that article, one shows Maxwell's equations today, and one with the introduction of magnetic monopoles. Obviously, there must be monopoles because that makes the equations symmetric. So they must be there, but they just are not detected. Does anyone know of any experiments that they are going to do soon to try to detect these?