henry (11/09/82)
A recent item in Science (15 Oct 1982, page 274) indicates that there is now a strong suspicion that magnetic monopoles, if they exist, would catalyze the (as-yet hypothetical) decay of the proton. It has been pointed out that the various Grand Unified Theories (the current hot theories in particle physics) all predict that the magnetic monopole would have a very odd structure. In its core, circa 10**-30 cm across (essentially a dimensionless point even on the subnuclear scale), one finds conditions not seen elsewhere in the universe since the Big Bang: the electromagnetic, nuclear, and weak forces are one and the same, and various particles are similarly indistinguishable (for example, the quark, electron, and neutrino are identical). As one moves outward from the core, the various stages of "symmetry breaking" last seen instants after the Big Bang appear, until on the outside the only remnant of the funniness inside is the magnetic field. Now, the core of the monopole is so small that this would seem to be of no practical significance. However, quarks in particular turn out to be able to interact with this core with a probability independent of the size of the core. Exactly what happens to such a quark depends on the details of the particular G.U.T. However, any theory which allows for the decay of the proton also predicts that interaction with a monopole core can transform a quark into an antiquark. Thus, when a monopole wanders into a proton (or neutron), one of the proton's quarks dives into it, comes back out as an antiquark -- and the proton explodes. After assorted intermediate particles go their way, the proton has been converted to energy (plus a scattering of neutrinos). The monopole is unchanged. The bad news is that astronomical evidence strongly suggests that proton decay is impossible, monopoles are extremely infrequent, or the as-yet-unsettled cross-section for the quark/monopole-core reaction is very small. If one assumes that proton decay is possible, that the Cabrera event last spring was really a monopole, and that the cross-section is something reasonable, one expects to see X-ray emission from neutron stars with trapped monopoles, and we don't. Given no X-rays, any sort of plausible cross-section, and proton decay (which is not yet certain, but the early experiments have already given some very suggestive results), the Cabrera event is ridiculously unlikely. The puzzle is unsolved as yet. The good news is that the various proton-decay experiments now being set up will make excellent tests of this theory, because the passage of a monopole through one of their detector chambers would be a truly spectacular event. The REALLY good news is, if the theories prove correct and the negative astronomical evidence can be reconciled somehow, then monopoles are catalysts for the direct conversion of matter to energy. And quite apart from its other uses, that's just what the doctor ordered for powering starships.
heliotis (11/09/82)
I had been taught that magneteic monopoles do not exist, by definition of magnetism. (Something about what happens to electric fields when relativity is taken into account). Can anyone confirm or contradict this? Jim Heliotis
gwyn@BRL@sri-unix (11/12/82)
From: Doug Gwyn <gwyn@BRL> Re: magnetic monopole existence The conventional Maxwell differential equations for the electromagnetic field do not include magnetic sources (monopoles). These equations can be brought into patently invariant form under special-relativistic (Lorentz) transformations. However, magnetic sources can be added (analogously to electric charge density) and still maintain Lorentz-invariance. The asymmetry in the equations is what normally makes people desire to restore symmetry by postulating magnetic charges . Since in fact there is abundant evidence for electric charge and none for magnetic charge, the real question changes to "why aren't there any magnetic charges in reality?". They are NOT ruled out on special-relativistic grounds. (By the way, one should beware of "by definition" arguments!) One possible explanation for the absence of magnetic charges can be found in "classical" unified field theory a la Einstein-Schrodinger. In the best of these theories, an equation can be derived from general-invariance arguments that is usually interpreted as the exact vanishing of magnetic charge density. This IS a relativistic result, but in a much deeper sense than usual. Indeed, I would venture to say that no more than a few dozen people understand what Einstein was trying to do with his unified field theory effort; certainly the usual textbook statements about this show lack of understanding. Other possible explanations may be found in specifically quantum theories, although I am not an expert in that area. (Also, from the searches for magnetic monopoles, I would guess that these theories do NOT explain their absence.)