Editing Magnetism (section)

=== Magnetic monopoles ===
{{main|Magnetic monopole}}
Since a bar magnet gets its ferromagnetism from electrons distributed evenly throughout the bar, when a bar magnet is cut in half, each of the resulting pieces is a smaller bar magnet. Even though a magnet is said to have a north pole and a south pole, these two poles cannot be separated from each other. A monopole—if such a thing exists—would be a new and fundamentally different kind of magnetic object. It would act as an isolated north pole, not attached to a south pole, or vice versa. Monopoles would carry "magnetic charge" analogous to electric charge. Despite systematic searches since 1931, {{As of|2010|lc=on}}, they have never been observed, and could very well not exist.<ref>Milton mentions some inconclusive events (p. 60) and still concludes that "no evidence at all of magnetic monopoles has survived" (p.3). {{cite journal|last=Milton|first=Kimball A.|title=Theoretical and experimental status of magnetic monopoles|journal=Reports on Progress in Physics|volume=69|issue=6|date=June 2006|pages=1637–1711|doi=10.1088/0034-4885/69/6/R02|arxiv=hep-ex/0602040|bibcode = 2006RPPh...69.1637M|s2cid=119061150}}.</ref>

Nevertheless, some [[theoretical physics]] models predict the existence of these [[magnetic monopoles]]. [[Paul Dirac]] observed in 1931 that, because electricity and magnetism show a certain [[symmetry]], just as [[Quantum electrodynamics|quantum theory]] predicts that individual [[positive charge|positive]] or [[negative charge|negative]] electric charges can be observed without the opposing charge, isolated South or North magnetic poles should be observable. Using quantum theory Dirac showed that if magnetic monopoles exist, then one could explain the quantization of electric charge—that is, why the observed [[elementary particles]] carry charges that are multiples of the charge of the electron.

Certain [[grand unified theories]] predict the existence of monopoles which, unlike elementary particles, are [[solitons]] (localized energy packets). The initial results of using these models to estimate the number of monopoles created in the [[Big Bang]] contradicted cosmological observations—the monopoles would have been so plentiful and massive that they would have long since halted the expansion of the universe. However, the idea of [[Cosmic inflation|inflation]] (for which this problem served as a partial motivation) was successful in solving this problem, creating models in which monopoles existed but were rare enough to be consistent with current observations.<ref>{{cite book|first=Alan|last=Guth|author-link=Alan Guth|title=The Inflationary Universe: The Quest for a New Theory of Cosmic Origins|isbn=978-0-201-32840-0|publisher=Perseus|year=1997|oclc=38941224|url-access=registration|url=https://archive.org/details/inflationaryuniv0000guth}}.</ref>