A single pole of magnetism, divorced from its twin.
fig. 1 — radial field lines emanating from a single magnetic charge
For decades, experimentalists have swept superconducting loops through cosmic ray showers, analyzed geological samples from the ocean floor, and calibrated detectors at particle colliders — all seeking the singular signature of isolated magnetic charge.
fig. 2 — SQUID magnetometer readout, Feb. 14, 1982 (Cabrera event)
On Valentine's Day, 1982, Blas Cabrera's detector registered a single event consistent with a magnetic monopole passing through a superconducting loop. The flux changed by exactly one Dirac quantum. It has never been replicated.
fig. 3 — the Cabrera event: a single quantum jump in magnetic flux
Dirac showed in 1931 that if even one magnetic monopole exists anywhere in the universe, it would explain why electric charge is quantized. The existence of monopoles would complete the symmetry of Maxwell's equations.
fig. 4 — radial B-field from magnetic charge g (Dirac monopole)
The MoEDAL experiment at CERN's Large Hadron Collider continues the hunt. Cosmic ray observatories scan the sky. Condensed matter physicists create monopole analogues in spin ice. The particle remains theoretical — beautiful, necessary, absent.
The notebook remains open. The quest is unfinished.
status: searching