How many types of elementary particles are there?
We have a thing called the standard model, which is based on about 60 particles, but there may be many more. These are just the ones that have a low energy, so we can detect them. The 1960s and 1970s could be considered a heyday of particle physics, when many subatomic particles—and not just elementary ones, it turns out—were being discovered. Could you talk a little bit about the events leading up to your discovery of the quark? That was very dramatic for me. I had been working for years on the properties of particles that participated in the strong interaction. This is the interaction responsible for holding the nucleus of the atom together. The family of strongly interacting particles includes the neutrons and protons; those are the most familiar ones. But now tens, dozens, hundreds of other particles were being discovered in experiments in which protons collided with each other in particle accelerators. There were lots and lots of energy states in which we saw relatives—cousins—of
