Chapter 5 Elementary Particles and the Forces of Nature Summary and Analysis

People before the 20th century maintained relatively simple views of the universe. Today physicists have continually discovered the higher and higher complexities, where the elements number far more than four, and atoms are made of many kinds of particles.

Einstein observes Brownian motion—the movement of dust particles suspended in water—and proposes that the movement of atoms causes the Brownian motion. He publishes the idea in a 1905 paper. In 1911, Ernest Rutherford demonstrates that an atom is made up of electrons orbiting a nucleus made up of protons, and in 1932, James Chadwick discoveres the neutron. The model of the atom consisting of electrons, protons and neutrons persists until the 1960s, when Murray Gell-Mann determines that atomic particles are make up of sub-atomic particles he calls...