© Photograph by William E. Sauro, The New York Times via Reuters Professor Freeman J. Dyson of ​the Institute for Advanced Stu​dy in Princeton is shown at Ja​dwyn Hall where he had an offi​ce and taught, November 15, 19​72.

A great figure in 20th-century physics, Freeman J. Dyson—the theorist who unified the world of the atom and the electron, a critic of nuclear weapons tests, a designer of space civilizations, and a steadfast climate change contrarian—died on February 28, 2020, in Princeton, New Jersey. He was 96 years old.

At his death, Dyson still maintained an office at the Institute for Advanced Study (IAS) in Princeton, New Jersey, where he took up residence in 1953 as a professor of physics. The IAS confirmed Dyson's passing to National Geographic.

"No life is more entangled with the Institute and impossible to capture—architect of modern particle physics, free-range mathematician, advocate of space travel, astrobiology and disarmament, futurist, eternal graduate student, rebel to many preconceived ideas including his own, thoughtful essayist, all the time a wise observer of the human scene," Robbert Dijkgraaf, director of the IAS, said in a statement. "His secret was simply saying yes to everything in life, till the very end."

When Dyson began his appointment at the IAS, Albert Einstein still roamed the grounds. Though he would later be called an "heir" to his renowned colleague, Dyson never came up with a general theory of anything. Modest, shy, and self-effacing, he was always content to work with others on their ideas.

"I'm not a person for big questions," he told Quanta Magazine shortly after his 90th birthday. "I look for puzzles. I look for interesting problems that I can solve. I don't care whether they're important or not, and so I'm definitely not obsessed with solving some big mystery. That's not my style."

"He did not propose radical new ideas, but instead helped clean up the details of the theories first proposed in the quantum revolution of the 1920s," said Declan Fahy, an associate professor of communications at Dublin City University in Dublin, Ireland, who studies scientists as public intellectuals. "In the 1940s and 1950s, he and others proved experimentally that the theories were correct, and this resulted ultimately in the theory of quantum electrodynamics, which describes how atoms behave. It's hugely significant in science, but does not capture public imagination in the same way as string theory."

Dyson became famous for translating the ideas of Richard Feynman and two other physicists into more accessible mathematical calculations in a seminal 1949 paper, "The Radiation Theories of Tomonaga, Schwinger, and Feynman." But before that, he and Feynman spent four memorable days driving from upstate New York to Albuquerque that included not only deep, inspirational conversations but also taking shelter from an Oklahoma flood in a brothel.

Despite Dyson's key role in synthesizing their ideas, he was overlooked in 1965 when Feynman, Harvard physicist Julian Schwinger, and Japanese scientist Sin-Itiro Tomonaga won the Nobel Prize for their work on the physics of elementary particles.

Though he was passed over for the Nobel—his 2000 Templeton Prize cited that work as his "most useful contribution to science"—Dyson's improvement of the early understanding of how atoms behave was a major advance from earlier ideas regarding both relativity and quantum mechanics, said Virginia Trimble, a physicist at the University of California at Irvine.

"You could say that, without this understanding, you wouldn't have modern computers or telephones or digital cameras," she said.

You also wouldn’t have certain radiation therapies used for cancer to this day. In the late 1950s, building on an idea by Edward Teller, Dyson led a team that designed and patented the TRIGA (which stands for Training, Research, Isotopes, General Atomic), a small, low-power nuclear reactor that is still used in research hospitals to produce medical isotopes to treat various forms of cancer.

Dyson's nuclear energy work also extended to the Air Force's secret Project Orion, which sought to build a spaceship propelled by exploding atomic bombs that would take humans to the farthest reaches of the solar system. The fantastical venture was canceled after NASA opted for more conventional rockets and the nuclear test ban treaty put an end to aboveground atomic experiments.

Dyson's interest in nuclear weapons also brought controversy. As a member during the Vietnam War of JASON, a defense industry advisory panel, he spearheaded research on the feasibility of using small, tactical nuclear weapons against the enemy. His ease in separating the technical from the moral aspects of the project made him a target of the anti-war movement.

Still, the scientist had other, less divisive ideas that became the stuff of science fiction. His hypothetical Dyson Sphere, a megastructure that would encompass a star to capture its energy, was portrayed in novels and in an episode of TV's Star Trek: The Next Generation. The hypothetical Dyson tree would grow on comets to support future space colonists.

Proud not to be a Ph.D.

Freeman John Dyson was born on December 15, 1923, in Crowthorne, England. His father was the prominent British composer Sir George Dyson, and his mother, Mildred Atkey, was a social worker. He was a math prodigy who by the age of 5 had calculated how many atoms were in the sun.

Dyson attended Winchester College, where his father was a music instructor, before working as a civilian targeting analyst for the Royal Air Force during World War II.

Not long after earning a degree in mathematics from Cambridge University in 1945, Dyson moved to the United States. He enrolled at New York's Cornell University and, despite lacking a Ph.D., was a professor there from 1951 to 1953. Although he would eventually receive some two dozen honorary degrees, Dyson never completed his doctorate. Instead, he became an outspoken opponent of the "Ph.D. system," which he called "an abomination" that discouraged many budding scientists, especially women.

After Dyson's mentor at Cornell, physicist Hans Bethe, wrote a letter to Robert Oppenheimer at the Institute for Advanced Study, Dyson was invited to become a fellow. It was there that he wrote his epochal paper on quantum electrodynamics, which launched his career and led to a permanent place at the institute.

The versatile scientist worked on a wide range of areas in theoretical physics. While Wolfgang Pauli won the Nobel Prize for his exclusion principle stating that no two electrons in an atom can have identical quantum numbers, it was Dyson and mathematician Andrew Lenard who later proved it definitively.

Dyson wrote more than a dozen books that made complex scientific and moral concepts comprehensible to nonspecialists. Among his best-selling books are Origins of Life and Weapons and Hope, which won the National Book Critics Circle Award for general nonfiction in 1984.

The scientist, who became a U.S. citizen in 1957, married twice and had six children. His two children with mathematician Verena Huber Dyson are technology venture capitalist Esther Dyson and science historian George Dyson. In 1958, he married Imme Jung, his wife for more than 60 years when he died. She and their daughters Dorothy, Mia, Rebecca, and Emily, as well as 16 grandchildren, also survive him.

So, too, does his controversial stance on climate change.

Dyson's criticism of climate science grew out of his own involvement with the JASON group and developed amid the nuclear winter debate with Carl Sagan and others. In his own simple climate model, Dyson underplayed the effects of greenhouse gases. Atmospheric physicists savaged his model for going against a broad consensus. That stung Dyson, who insisted that "global warming is grossly exaggerated as a problem." His skepticism continued to bring scathing criticism during his final years, as evinced in a New York Times Magazine article headlined "The Civil Heretic."

"An important theme in his popular science books was the value of the scientific contrarian," Fahy said. "At the end of his life, it was this issue that increasingly came to define him in public, rather than his vital contributions to physics."

Dan Vergano and Michael Greshko contributed to this article.