James W. Cronin, a physicist who shared a Nobel Prize for repudiating a fundamental principle of physics and explaining why the universe survived the Big Bang with anything in it, died on Thursday in St. Paul. He was 84.
His death was confirmed by the University of Chicago, where he was a professor emeritus. No cause was given.
In 1964, Dr. Cronin and Val Fitch of Princeton University were conducting experiments at Brookhaven National Laboratory on Long Island involving matter and antimatter: particles that have the same mass but hold opposite (though equal) charges, either positive or negative, compelling them to destroy each other on contact.
The researchers found that for all their similarities, the particles obeyed slightly different laws of physics: that there was, as Dr. Cronin put it, “a fundamental asymmetry between matter and antimatter.”
This contradicted a bedrock scientific principle known as charge-parity invariance, which had assumed that the same laws of physics would apply if the charges of particles were reversed from positive to negative or vice versa.
The finding, known as the Fitch-Cronin effect, bolstered the Big Bang theory, mainly by explaining why the matter and antimatter produced by the explosion did not annihilate each other, leaving nothing but light instead of a residue that evolved into stars, planets and people.
“We now believe this tiny difference led to us,” Michael S. Turner, an astrophysicist at the University of Chicago, said last year after Dr. Fitch died at 91.
Dr. Cronin and Dr. Fitch were awarded the Nobel Prize in Physics in 1980 for demonstrating charge-parity violation, which is brought about by decaying subatomic particles called kaons. But Dr. Cronin acknowledged that they had not completely solved a riddle of the universe.
“We know that improvements in detector technology and quality of accelerators will permit even more sensitive experiments in the coming decades,” he said at the time. “We are hopeful, then, that at some epoch, perhaps distant, this cryptic message from nature will be deciphered.”
Since then, scientists working at the SLAC National Accelerator Laboratory in California and at the Large Hadron Collider near Geneva have made further strides in decoding the different laws that govern matter and antimatter.
Dr. Cronin “inspired us all to reach further into the unknown with deep intuition, solid scientific backing and poetic vision,” Angela V. Olinto, a professor of astronomy and astrophysics, said in a statement released by the University of Chicago.
James Watson Cronin was born in Chicago on Sept. 29, 1931. His father, also named James, met Dr. Cronin’s mother, the former Dorothy Watson, in a Greek class at Northwestern University. The elder James Cronin became a professor of Latin and Greek at Southern Methodist University in Dallas.
Dr. Cronin’s infatuation with physics began in high school. He graduated in 1951 from Southern Methodist, where he majored in physics and mathematics. He received a doctoral degree from the University of Chicago, where he studied under Enrico Fermi, Edward Teller and Murray Gell-Mann. His thesis was on experimental nuclear physics.
Dr. Cronin’s first wife, the former Annette Martin, died in 2005. He is survived by their children, Emily Grothe and Daniel Cronin; his second wife, the former Carol Champlin McDonald; and six grandchildren.
After collaborating with Dr. Cronin at Brookhaven, Dr. Fitch, the son of a Nebraska rancher, recruited him to Princeton. Dr. Cronin was lured back to the University of Chicago in 1971, attracted in part by one of the world’s most powerful particle accelerators, which was being built at what is now known as the Fermi National Accelerator Laboratory, operated by the university in partnership with a consortium of other educational institutions. He was offered a post teaching physics, astronomy and astrophysics.
Dr. Cronin was later a leader of the Pierre Auger Observatory, a global consortium of scientists studying the cosmic rays that bombard Earth. He also edited a book, “Fermi Remembered,” inspired by a symposium in 2001 to commemorate the centennial of Mr. Fermi’s birth. (The two shared the same birth date, Sept. 29.)
“What’s significant about Fermi is if you look through his career, he never just did the same thing,” Dr. Cronin once said. “He kept moving on to new scientific challenges.”
Dr. Cronin became a professor emeritus in 1997.
Working with Dr. Fitch and using instruments they had devised, Dr. Cronin conducted his groundbreaking experiments when he was in his early 30s, less than a decade after he had received his doctorate. Why did it take the Nobel Committee 16 years to recognize their achievement?
“I don’t think that people recognized that this had something to do with one of the most fundamental aspects of nature, with the origin of the universe,” Dr. Cronin said in the 2006 book “Candid Science VI: More Conversations With Famous Scientists,” by Istvan Hargittai and Magdolna Hargittai. “I think that it took a while to realize this.”
He added: “For me, this was actually a good thing. I was much too young at that time to deal with such a thing as the Nobel Prize.”