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Many people claim that we should observe lots of particle-like magnetic monopoles, e.g.:

"Joseph Polchinski, a string theorist, described the existence of monopoles as "one of the safest bets that one can make about physics not yet seen"" from https://en.wikipedia.org/wiki/Magnetic_monopole

or "The magnetic monopole problem, sometimes called the exotic-relics problem, says that if the early universe were very hot, a large number of very heavy, stable magnetic monopoles would have been produced." from https://en.wikipedia.org/wiki/Cosmic_inflation

But clearly we don't - I wanted to ask about looking the simplest answer: that there is duality between electricity and magnetism, allowing to freely switch them - how do they know to expect magnetic monopoles, not electric instead? We observe the latter as charged particles.

Another basic argument is that e.g. Dirac monopoles need these 1D topological structures/vortices, like required for QCD flux tubes/quark strings connecting quark and anti-quark: electric not magnetic charges. There is widely used string hadronization to simulate LHC collisions: assuming they decay into standard particles - electric not magnetic monopoles. If there also exist dual QCD flux tubes/quark strings decaying into magnetic monopoles, why don't they observe them e.g. in LHC collisions?

What are the reasons they expect magnetic monopoles, instead of just switching to dual formulation and call them electric (charged particles)?

Jarek Duda
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that there is duality between electricity and magnetism, allowing to freely switch them

In fact, the equations of electromagnetism are almost dual except for that the equations imply that although there are electric monopoles there are no such thing as magnetic monpoles. The equations can be modified by the introduction of a magnetic current and then this makes them fully dual and then these equations predict magnetic monopoles. These equations are listed on the Magnetic Monopole page on Wikipedia.

What are the reasons they expect magnetic monopoles, instead of just switching to dual formulation and call them electric (charged particles)?

One argument, first described by Dirac, is that the existence of magnetic monopoles in the quantum theory implies that electric charge is discrete (and dually we would expect magnetic charge to be discrete). This obviously holds experimentally. And is one theoretical argument for magnetic monopoles.

Mozibur Ullah
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