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Subject: Re: How will scientists recognize a magnetic monopole if they ever find one?

Date: Sun May 17 03:32:15 1998
Posted by Ricky J. Sethi
Position: PhD

Hi Ronaldo,

Magnetic monopoles, as you probably already know, are basically theorized particles that no one has found yet. Symmetry in Maxwell's equations seems to suggest the existence of magnetic monopoles, the magnetic equivalent of electric "monopoles", but no observed phenomenon actually requires their existence. If it did exist, though, among other things it would explain electric charge quantization (i.e., the fact that electric charge only comes in units of e). Many theories, most notably gauge theories, predict or require the existence of magnetic monoples. Specifically, quantum mechanics predicts their existence but does not require it.

Monopoles are theorized to have a minimum magnetic "charge" of G=e/2(alpha), also known as the Dirac charge (named after P.A.M. Dirac who first showed the quantization of magnetic charges), where (alpha) = 1/137 (see Sakurai's Modern Quantum Mechanics pp. 140-143 for a derivation of this result). This is quite amazing because it predicts that magnetic charge is quantized! However, as Prof. Sakurai reiterated in his book so well, quantum mechanics doesn't require the existence of magnetic monopoles. "However, it unambiguously predicts that a magnetic charge, if it is ever found in nature, must be quantized in units of [G]."

These predicted monopoles would also be very heavy. The predictions of some gauge theories place the smallest at weights of about 1000 protons. This suggests diameters for such monopoles on the order of 1000 times smaller than protons. So why don't we see all these monopoles out there? It has been suggested that magnetic monopoles must have been produced in great amounts in the start of the universe but inflation seems to have whittled them down to the level of one per particle horizon. Another problem is that the energies required to create such massive particles are so large... our current particle accelerators can't even come close. Thus the detection of magnetic monopoles itself is a sizeable task. The two most widely used methods are induction (which measures the monopole's magnetic charge) and ionization (which depends on a magnetic charge producing greater ionization than electrical charges with the same velocity). I hope this helped. There is plenty more information out there on the net. You might want to run a search on Yahoo being sure to include keywords such as "magnetic monopole", superstring theory, etc.

Good hunting!

Rick.


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