Chapter 5

In this chapter, Stephen Hawking discusses the history of our understanding of matter, from the ancient Greek belief in four elements to the discovery of atoms and the realization that they are made up of smaller building-block particles called quarks. He also covers the four fundamental forces that govern matter, and the efforts to unify these forces into a single theory. Hawking also discusses three symmetries called C, P, and T that are believed to be important in understanding the universe, including why it has very little antimatter.