How to think about... Particles

2019-03-15 10:16:01

Dorling Kindersley/Getty By Catherine Brahic and Richard Webb WHEN picturing particles, David Kaiser freely confesses to physically incorrect thoughts. “With great respect to my forebears, I personally still do start off picturing marbles,” says Kaiser, a physicist at the Massachusetts Institute of Technology. “Little round objects spinning around and around.” The picture has intuitive appeal. Surely the fundamental particles that make up matter are tiny, indivisible objects with concrete properties such as position and mass? Since the dawn of quantum mechanics, the theory that governs their workings, we have known that particles do spin – or at least possess a property superficially similar to the rotation of spherical bodies that we call spin. Peer any closer, though, and you rapidly start losing your marbles. The rot started in experiments that shot supposedly fundamental particles at other particles and saw them shatter – rather unlike what you would expect for indivisible units of matter. In fairly quick succession in the 20th century, atoms turned out to be nuclei orbited by electrons, nuclei turned out to be protons and neutrons, and protons and neutrons got subdivided into even smaller particles, known as quarks and gluons. But those smaller particles are just smaller marbles, right? Perhaps, except that other quantum experiments show that these particles can sometimes pass through walls,