ELECTRICITY and magnetism are two sides of the same coin. There is supposed to be a deep symmetry between them. So why, when we see lone electrical charges such as electrons or protons, do we never see a lone magnetic pole ā a monopole?
They are almost certainly out there: monopoles plays a pivotal role in the widely accepted āgrand unified theoriesā, for example. GUTs suggest that the four forces of nature arose from one superforce that existed until moments after the big bang.
The trouble is, our universe is thought to contain no more than one of these āGUT monopolesā for every 1029 protons and neutrons in atomic nuclei: if there were any more than that, our most sensitive searches would have found one.
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And itās not like we can make them for ourselves. GUT monopoles are thought to be so massive that we donāt have powerful enough particle accelerators to create any. Not that this seems to bother physicists too much. Joe Polchinski, a theorist at the Kavli Institute for theoretical physics in Santa Barbara, California, has said that the existence of monopoles āseems like one of the safest bets that one can make about physics not yet seenā.
In the 1930s, Paul Dirac gave us an even better reason to believe in monopoles, when he showed that their existence would in turn explain the existence of electrons. āDirac monopoles could be of any mass,ā says Kimball Milton at the University of Oklahoma in Norman. So these monopoles could well turn up in our particle accelerators or in the decay products of cosmic ray collisions in the upper atmosphere.
Several searches have been carried out, but with no success. Does that mean we should give up? āWe still might find relic monopoles in cosmic rays, so there is always hope,ā says Milton.
He shares Polchinskiās confidence in monopoles. The fact that their existence is consistent with all known physics means they are almost certainly out there, he reckons. Milton believes in the principle espoused by the famous physicist Murray Gell-Mann: anything that is not forbidden is compulsory. āMagnetic monopoles are consistent with quantum mechanics; therefore they should exist,ā says Milton.
Read more: 13 more things that donāt make sense
