Electrons rule our world, but not so long ago they were only an idea. This month marks the 120th anniversary of a profound and influential creation, the electron theory of Dutch physicist Hendrik Antoon Lorentz. His electron was not merely a hypothesized elementary particle; it was the linchpin of an ambitious theory of nature. Today physicists are accustomed to the notion that a complete description of nature can rise out of simple, beautiful equations, yet prior to Lorentz that was a mystic vision.
For most physicists the memorable peak of 19th-century physics is the theory of electrical and magnetic fields, capped by James Clerk Maxwell’s mathematical synthesis of 1864. Then a haze settles, until the 20th-century massifs of relativity and quantum theory poke through. That foggy folk history obscures the bridge between—itself a brilliant achievement, built through heroic labor.
Lorentz’s achievement was to purify the message of Maxwell’s equations—to separate the signal from the noise. The signal: four equations that govern how electrical and magnetic fields respond to electric charge and its motion, plus one equation that specifies the force those fields exert on charge. The noise: everything else!
Now one had definite equations for the behavior of tiny bodies with specified mass and charge. Could one use those equations to rebuild the description of matter on a new foundation, starting from idealized “atoms” of charge? This was the burden of Lorentz’s electron theory. Starting with his 1892 paper, Lorentz and his followers used the electron theory to explain one property of matter after another—conduction of electricity and of heat, dielectric behavior, reflection and refraction of light, and more. Thus, they laid the groundwork for the subjects we now call electronics and materials science.