Gary Steigman, an astronomer whose pioneering studies of the Big Bang helped show that most of the matter in the universe was not made of atoms — a finding that led to the modern conception of a universe awash in dark matter being pushed into an infinite night by dark energy — died April 9 in Columbus, Ohio. He was 76.
Ohio State University, where he was an emeritus professor of physics and astronomy, said the cause was injuries he had suffered in a fall.
Dr. Steigman, a big-city street kid turned astrophysicist, was a tall, curly-haired, gregarious straight talker who was not one to shy away from intellectual combat.
“He’s the only person I know who would use the word ‘bogus’ in a referee report,” said Robert Scherrer, of Vanderbilt University, referring to the peer reviews that papers go through before being published.
Dr. Steigman was one of the ringleaders of cosmology in an era in which astronomy and particle physics were merging. It was a time when scientists were asking giant questions about the cosmos — like why matter and galaxies exist — and seeking answers in the relationships between quantum particles, formed when the universe was a split-second old and ablaze with energies beyond the dreams of earthly particle accelerators.
The universe, Dr. Steigman and his colleagues liked to say, was the poor man’s particle accelerator.
The 1980s saw an explosion of ambitious new ideas about the universe, and Dr. Steigman’s work put him at the center of it, though with something of a calming effect.
As Michael Turner, of the University of Chicago, put it, “During the halcyon days of a new theory a week, when young scientists were having too much fun, Gary often provided the adult supervision and wise guiding hand.”
Gary Steigman was born in New York City in 1941, to Charles and Pearl Steigman, and grew up in the Bronx, a fan of the New York Giants baseball team across the Harlem River. He passed up taking the entrance exam for the selective Bronx High School of Science because he wanted to be “normal,” he once said.
Nevertheless, science and the universe beckoned. He graduated with a bachelor’s degree in physics from the City University of New York in 1961 and then obtained a doctorate from New York University in 1968. It was there, in his thesis, working under Malvin A. Ruderman, that Dr. Steigman made his first contribution to cosmology.
After research stints at Cambridge University and the California Institute of Technology, Dr. Steigman taught at Yale and at the Bartol Research Foundation, part of the University of Delaware, before joining the faculty at Ohio State.
He spent many summers at the Aspen Center for Physics in Colorado, where scientists talk through problems over picnic tables under the trees and on hikes in the Rockies. Dr. Steigman was a longtime trustee of the center and a member of its advisory board.
“This is a way you can enjoy a high lifestyle without a high salary,” Mr. Steigman told an interviewer one day over canapés at the home of a center benefactor.
He was recruited to Ohio State in 1986 to found a cosmology center, which would include both astronomers and physicists.
‘When young scientists were having too much fun, Gary often provided the adult supervision and wise guiding hand.’
Around the same time, he began a relationship with a Brazilian astronomer, Sueli Viegas, from the Institute of Astronomy, Geophysics and Atmospheric Sciences at the University of São Paulo, whom he had met at a conference in Rio de Janeiro. They married in 2004, after Viegas had retired from São Paulo.
Besides Viegas, Dr. Steigman leaves a stepdaughter, Cibele Aldrovandi; a stepson, Leonardo Aldrovandi; and two nieces. A previous marriage had ended in divorce.
Mr. Steigman became an expert in the study of the nuclear reactions that took place in the first three minutes of creation. In those moments, the universe converted primordial hydrogen, the simplest element, into heavier elements like helium and lithium, which made up the first stars. (The rest of the elements needed to make planets and people would be manufactured in stars.)
It was in Aspen one day that he and a former office mate, David N. Schramm, of the University of Chicago, discovered that they had both made the same breakthrough: According to the Big Bang equations, the amount of primordial helium produced was crucially dependent on how many kinds of ghostly, nearly massless elementary particles there were in the universe.
At the time, particle physicists had suspected that there were three kinds, or generations, of neutrinos, each representing a different family of the elementary particles that make up nature. But as their particle accelerators had gone to higher and higher energies, they had discovered more and more generations.
Mr. Steigman and Schramm combined forces with James Gunn, now at Princeton, to write a paper declaring that based on helium abundances, there could be no more than seven families of elementary particles.
“The trend was for more numbers of neutrinos as accelerators went to higher energies,” Schramm recalled in an interview before his death in 1997. “We said the trend wasn’t going to continue. There was no statement from particle physics on the number of generations. It could be a thousand. For the first time cosmology was giving something back to physics.”