Magnetic Monopoles
One explanation: there exists magnetic charge, just like electric charge. An entity which carried this magnetic charge would be called a magnetic monopole (having + or - magnetic charge).
How can you isolate this magnetic charge?
Try cutting a bar magnet in half:
- In fact no attempt yet has been successful in finding magnetic monopoles in nature.
- Many searches have been made, due primarily to fact that existence of monopole could give an explanation (within framework of QM) for the quantization of electric charge (argument of Dirac)