In 1971 he returns to Chicago as professor of physics, the fact that the new Fermilab Accelerator was being built near Chicago made this move an attractive one. He is now professor emeritus there.

Cronin moves to Princeton University in the fall of 1958.  He is much involved in the development of the spark chamber as a practical research tool.

Cronin returns to Princeton in 1965.

James Cronin shares the 1980 Nobel Prize in Physics with Val Fitch for their discovery of the CP symmetry violation. Physicists used to assume that certain symmetries characterize nature: Physical laws should be the same if right and left are exchanged and if matter is replaced by antimatter. But Cronin and Fitch have discovered that the matter-antimatter symmetry can be violated in certain subatomic reactions, and also that symmetry under time-reversal is not always valid.

In 1955 Cronin moves to the Brookhaven Cosmotron, a newly completed particle accelerator.  While at Brookhaven, he meets Val Fitch, who invites him to Princeton.

He joins with Val Fitch to study certain subatomic reactions. Using a proton accelerator at Brookhaven National Laboratory, they examine the radioactive decay of kaons, which consist of one half ordinary matter and the other half antimatter. They find that a reaction run in reverse does not merely retrace the path of the original reaction. This phenomenon is known as CP violation.

He gains an undergraduate degree in physics and mathematics in 1951 from Southern Methodist University, where his father teaches Greek and Latin. 

In September 1951, he progresses to the University of Chicago for his PhD, studying under the likes of Enrico Fermi, Maria Goeppert-Mayer and Murray Gell-Mann, who stirred his interest in the new field of particle physics. He receives his PhD in 1955.

He grows up in Dallas,Texas. His primary and secondary education is provided by the Highland Park Public School System. In high school his natural interest in science is encouraged by an excellent physics teacher.

Following the discovery in the summer of 1964, he spends a year in France, working at the Centre d’Études Nucleaires at Saclay. In addition to the research, he enjoys learning French and assimilating the culture of another country. One of the greatest joys in his life is giving a lecture in French at the College de France.

At the University of Chicago he meets his future wife, Annette Martin, in the summer of 1953. They marry in September 1954. 

James Watson Cronin is born in Chicago.