"THERE ARE NO MAGNETIC MONOPOLES". The garish pink capitals in which the lecturer chalked those words up on the blackboard remain etched in my mind, an indelible memory from my first year as an undergraduate physicist. That was 1997. How the world has changed.
Or not. The cosmic monopole remains as elusive as ever. This freely moving particle, predicted by many grand theories of the universe, is thought to carry a single quantum of magnetic "charge", rather as an electron carries a single unit of electric charge. As far as we can tell, though, nature only supplies magnetic charges, or poles, in pairs - the inseparable north and south poles of the bar magnets beloved of school science demonstrations, for example. Why, we are not quite sure.
But it turns out we can make our own monopoles (New Scientist, 9 May 2009, p 29)
. If imbued with a quantum-mechanical property known as spin, individual atoms act as tiny bar magnets with north and south poles. Get the atoms' polar axes to align, and the material itself becomes magnetic.