Nuclear physics is the study of the interaction of particles in a nucleus: protons and neutrons. Its goal is to understand the behavior of the nucleus. In early days of nuclear physics, this involved study of radioactivity and the nature of the atom itself; by the end of the twentieth century, it was primarily concerned with the strong nuclear force, which binds the nucleus together despite the protons' electric charge repulsion pushing the nucleons apart.

Despite the sophistication of their field of study, nuclear physicists basically do variations on one experiment: the collision. All nuclear physics experiments consist of either a beam of particles hitting a stationary target or of two beams hitting each other. It is often compared to smashing a Swiss watch and trying to deduce its mechanism from watching what parts fly out. This method has had surprising success and his historically used...