monopole.wiki

A magnetic monopole is a hypothetical elementary particle that is an isolated magnet with only one magnetic pole -- a north pole without a south pole, or vice versa. In contrast, every known magnet has both a north and south pole (a magnetic dipole).

The concept was first proposed by Paul Dirac in 1931, who showed that the existence of even a single magnetic monopole would explain the quantization of electric charge observed in nature.

Dirac's argument begins with the observation that if magnetic monopoles exist, then electric charge must be quantized. This is known as the Dirac quantization condition.

In 1974, Gerard 't Hooft and Alexander Polyakov independently showed that certain grand unified theories (GUTs) necessarily produce magnetic monopoles as topological defects during symmetry-breaking phase transitions in the early universe.

These GUT monopoles would be extremely massive -- approximately 10^16 GeV, far beyond the reach of current particle accelerators. Their predicted abundance in the early universe was one of the motivations for Alan Guth's theory of cosmic inflation.

The most famous candidate detection was the Valentine's Day event of February 14, 1982, when Blas Cabrera's SQUID magnetometer at Stanford University recorded a single event consistent with one Dirac magnetic charge.

Major experimental programs include MACRO at Gran Sasso (1989-2000), the MoEDAL detector at CERN (2010-present), and various IceCube analyses searching for relativistic magnetic monopoles in Antarctic ice.

In 2009, researchers observed emergent magnetic monopoles in spin ice materials -- frustrated magnets where the crystal structure forces magnetic moments into configurations that behave exactly as Dirac predicted.

These quasiparticle monopoles can be created, moved, and measured in laboratory conditions, providing direct experimental access to monopole dynamics even in the absence of fundamental monopoles.