A magnetic monopole is a proposed fundamental particle in particle physics that would carry an isolated magnetic charge: in other words, a single magnetic pole. Unlike an ordinary magnet, which has both a north and a south pole, a monopole would present only a north pole or only a south pole. No confirmed example has been observed in nature to date.

Conceptual background

Classical magnetism, as seen in bar magnets and in electromagnets, arises from microscopic electric currents and aligned atomic magnetic moments and always produces dipoles — paired north and south poles. A magnetic monopole, if it exists, would be a source (or sink) of magnetic field in the same way an electric charge is a source or sink of electric field.

Theoretical motivations

Monopoles appear in several theoretical frameworks. Early work showed that including a single monopole could explain why electric charge is quantized. More elaborate particle theories, including certain grand unified theories and some formulations of string theory, predict monopole-like objects as part of their spectrum. In those contexts, monopoles can have very large masses and unusual properties compared with the particles of the Standard Model.

Experimental searches and current status

Searches for monopoles have taken many forms: direct laboratory experiments, analyses of accelerator collision data, searches for trapped monopoles in ancient materials, and studies of cosmic-ray and astrophysical signals. So far, none of these efforts has produced results that meet the standards required to claim a discovery. Consequently, the existence of magnetic monopoles remains an open question.

Why this matters

  • Discovery of a monopole would require changes to how we describe electromagnetic fields and could provide evidence for physics beyond the Standard Model.
  • Monopoles would offer an explanation for the observed quantization of electric charge if the theoretical connections are correct.
  • Even without direct detection, searches for monopoles help constrain theoretical models and guide the development of new experiments.

Because the idea connects deep theoretical arguments with concrete experimental searches, the magnetic monopole continues to be a subject of active interest across theoretical and experimental branches of particle physics.