Brain Makeover: #9. Particle Physics

All matter is made from quarks and leptons

The primary parts of the nucleus of the atom are the positively charged proton and the electrically neutral neutron. During the twentieth century it was discovered that there are literally hundreds of other particles—all unstable—that take part in various interaction at the atomic level. These can be divided into two major classes: there are hadrons that exist inside the nucleus and participate in the strong interaction, and leptons that do not. Protons and neutrons are both hadrons, while the electron is an example of a lepton. One way of thinking about atoms, then, is to say that their nuclei are made of hadrons, while leptons (electrons) in orbit complete the structure.

More recently, it was realized that all of the hundreds of hadrons can be understood as different combination of particles more fundamental still—particles called quarks. In this scheme, then, the quarks make up the hadrons that constitute the nucleus, while the leptons in orbit complete the atoms that make up all matter.