James Cronin
Scientist who showed the laws of physics are not immutable
JAMES CRONIN, who has died aged 84, shared the 1980 Nobel Prize in Physics, with Val Fitch, for demonstrating that there was a flaw in the central belief held by scientists almost since the time of Galileo: that the laws of physics are immutable.
One finding of modern physics is that every elementary particle has a matching antiparticle with equal and opposite charge. Upon contact the two annihilate one another. Working at the US Brookhaven National Laboratory in the early 1960s, Cronin and Fitch found that matter and antimatter obeyed slightly different laws of physics.
Using a newly built Alternating Gradient Synchrotron accelerator, the two men investigated the behaviour of unstable subatomic particles known as kaons (or K mesons), which a Yale physicist, Robert Adair, had suggested had strange properties.
Kaons have a lifetime of only fractions of a second, but during that life they oscillate rapidly between kaons and their antimatter counterpart, antikaons. According to the laws of physics as they were then understood, the particles should have undergone the same number of transitions in each direction before they decayed.
To their surprise, however, Cronin and Fitch discovered that the transition from antikaon to kaon occurred about half a per cent less frequently. Nature, it seemed, had a slight preference for kaons.
When Cronin and Fitch published their results in 1964, there was widespread scepticism, but experiments in other laboratories confirmed their findings. That meant that nature, on relatively rare occasions, violates what scientists called CP symmetry, a principle that states that the laws of physics should be the same if a particle is interchanged with its antiparticle.
At the time, there was no scientific consensus about the origins of the universe. It was only a year later, when radio astronomers discovered incontrovertible evidence that the universe had begun in a Big Bang, that the issue of how matter and antimatter survived their mutual suicide pact became a burning issue.
In 1967 Andrei Sakharov, the Russian dissident and physicist, published a list of conditions that would allow matter to survive the Big Bang. The list included the kind of discrepancy that Cronin and Fitch had discovered, suggesting that, after the primeval explosion, antimatter could have decayed slightly more rapidly than matter, leaving behind the matter that constitutes the universe as we know it.
James Watson Cronin was born on September 29 1931 in Chicago, where his father was studying for a PhD in Classics at the university. The family later moved to Dallas, Texas, where his father became a professor of Classics at Southern Methodist University. James took a degree there in Physics and Mathematics in 1951.
He went on to the University of Chicago where he studied under Enrico Fermi and Murray GellMann, and wrote a thesis on experimental nuclear physics under Samuel Allison.
In 1955 he joined the Brookhaven laboratory as an assistant physicist and met Val Fitch, who took him to Princeton University in 1958. He remained there until 1971, when he was appointed the University Professor of Physics at the University of Chicago, remaining there until and after his official retirement in 1997.
In later life, he and a colleague initiated the Pierre Auger Project, a $50 million collaboration of more than 250 scientists in 17 nations to track down the sources of powerful cosmic rays that periodically bombard Earth.
He married, in 1954, Annette Martin, with whom he had two daughters, one of whom predeceased him, and a son. Annette died in 2005, and in 2006 he married Carol Champlin, who survives him with his children. James Cronin, born September 29 1931, died August 25 2016