Chapter 2 chronicles the explosion in the number of strongly interacting particles, and efforts to understand them. It ends with an introduction to the discovery of quarks (originally called “aces”), and the resistance to accepting them for what they are: real particles that live in a deeper layer of reality.

The concepts of quantum number, resonance, and scattering cross section are explained, and the theories meant to explain the existence of strongly interacting particles are elucidated, including Fermi and Yang’s composite pion, Sakata’s composite hadrons, Chew and Frautschi’s “bootstrap,” and Heisenberg’s nonlinear spinor theory. The discovery of quarks suggested by the anomalous suppression of phi decay is detailed, and the importance of anomalies in physics is highlighted. Two remarkable meson and baryon mass relations are given. Both positive and negative reactions to the idea of quarks as constituents of hadrons are presented. Chapters 1 and 2 describe the recurring chaos and confusion that existed during the time between the discoveries of radioactivity and quarks. Once discovered, the path to the acceptance of quarks as real particles was equally confusing.