Particle Physics: 1950–2023

By the 1950’s, electrons, protons and neutrons were thought to be the fundamental building blocks of matter. Measurements of cosmic rays in cloud chambers or photographic emulsion plates, during the 1930s and 1940s, however, suggested the existence of other particles as well. In 1936, the American physicists Carl Anderson (1905–1991) and Seth Neddermeyer (1907–1988) found a weakly interacting particle that they named the muon, in their cloud chamber. In the chamber, particles were identified by vapor trails that were left behind their passage in the apparatus. In an other kind of cosmic-ray detector, photographic emulsions plates were often positioned at high-altitude mountain locations for long periods of time. Following the development of the plates, microscopic viewing of the emulsion often revealed tracks of charged particles.