Magnetic Monopoles

In addition to the “Cone of Silence” patent I discussed in an earlier post, the most recent issue of New Scientist has an interesting article about the search for a magnetic monopole, along with the Higgs boson one of the more elusive beasts in the particle physics menagerie.  You probably remember playing with and studying magnets in school science classes.  Each one had a North and a South pole; opposite poles attract each other, and similar poles repel each other:

If magnets seem rather bipolar, that’s because they are. Every magnet has two poles, a north and a south. Like poles repel, unlike poles attract. No magnet breaks the two-pole rule – not the humblest bar magnet, not the huge dynamo at the heart of our planet. Split a magnet in two, and each half sprouts the pole it lost. It seems that poles without their twins – magnetic “monopoles” – simply do not exist.

In the classical theory of electricity and magnetism, as embodied in Maxwell’s equations, a free positive or negative electric charge can exist.  But the existence of a free magnetic charge (equivalent to a magnetic monopole) is ruled out by Gauss’s law of magnetism:

This has always seemed a bit curious, given that electricity and magnetism are in most ways symmetrical, two sides of the same coin.  In fact, except for the exclusion of magnetic charge, Maxwell’s equations are symmetrical with respect to interchanging the electric and magnetic fields.

In a 1931 paper [PDF here] in the Proceedings of the Royal Society, Dirac showed that the existence of magnetic monopoles could explain the quantization of electric charge, but so far no one has managed to observe one.  The article reviews recent research that seems to have uncovered a special “sub-species” of magnetic monopoles in certain compounds.  (There is a note from Lawrence Berkeley Laboratory summarizing aspects of the search for magnetic monopoles here [PDF].)

This result is potentially quite interesting in itself; for example, as the article poinnts out, it might be possible to use this knowledge to create much denser computer memories.  But it is also an illustration of how far from our ordinary intuition quantum physics can take us.  This is what the physicist Richard Feynman was talking about when he wrote, in The Character of Physical Law, “I think I can safely say that nobody understands quantum mechanics.”   We can look at the theory, and extract predictions of what we should find from the mathematics; but our ordinary, everyday intuition about the physical world often just gets in the way.  To paraphrase some advice Feynman gave on another occasion, don’t make yourself crazy trying to figure out how it can be like that, because no one understands how it can be like that.