985. What is the physical nature of magnetism? Is it a wave or particle phenomenon or an undefined energy like gravity? — GA, Paisley, Scotland
Magnetism is one sector of the electromagnetic interactions of matter. From a classical perspective, magnetism consists of an energy-containing field that surrounds magnetic poles and that exerts forces on other magnetic poles. At a higher classical level, magnetism and magnetic fields are part of the full electromagnetic interaction, meaning that they are inextricably mixed with electricity and electric fields. Finally, from a full quantum mechanical perspective, magnetism is associated with energy-containing quantum fields, the fields of quantum electrodynamics, that govern the electric and magnetic interactions of matter. These quantum electrodynamic interactions are mediated by virtual photons, cousins of the real photons that include light and radio waves. From this quantum viewpoint, magnets interact with one another by exchanging virtual photons and, like all quantum objects, these photons are emitted and absorbed like particles but travel as waves. Thus magnetism is both a wave and particle phenomenon. It isn't undefined at all; in fact, quantum electrodynamics is probably the most well-established and precise theory in modern physics.