John A. Wheeler, a visionary physicist and teacher who helped invent the theory of nuclear fission, gave black holes their name and argued about the nature of reality with Albert Einstein and Niels Bohr, died Sunday morning at his home in Hightstown, N.J. He was 96.
The cause was pneumonia, said his daughter Alison Wheeler Lahnston.
Dr. Wheeler was a young, impressionable professor in 1939 when Bohr, the Danish physicist and his mentor, arrived in the United States aboard a ship from Denmark and confided to him that German scientists had succeeded in splitting uranium atoms. Within a few weeks, he and Bohr had sketched out a theory of how nuclear fission worked. Bohr had intended to spend the time arguing with Einstein about quantum theory, but “he spent more time talking to me than to Einstein,” Dr. Wheeler later recalled.
As a professor at Princeton and then at the University of Texas in Austin, Dr. Wheeler set the agenda for generations of theoretical physicists, using metaphor as effectively as calculus to capture the imaginations of his students and colleagues and to pose questions that would send them, minds blazing, to the barricades to confront nature.
Max Tegmark, a cosmologist at the Massachusetts Institute of Technology, said of Dr. Wheeler, “For me, he was the last Titan, the only physics superhero still standing.”
Under his leadership, Princeton became the leading American center of research into Einsteinian gravity, known as the general theory of relativity — a field that had been moribund because of its remoteness from laboratory experiment.
“He rejuvenated general relativity; he made it an experimental subject and took it away from the mathematicians,” said Freeman Dyson, a theorist at the Institute for Advanced Study across town in Princeton.
Among Dr. Wheeler’s students was Richard Feynman of the California Institute of Technology, who parlayed a crazy-sounding suggestion by Dr. Wheeler into work that led to a Nobel Prize. Another was Hugh Everett, whose Ph.D. thesis under Dr. Wheeler on quantum mechanics envisioned parallel alternate universes endlessly branching and splitting apart — a notion that Dr. Wheeler called “Many Worlds” and which has become a favorite of many cosmologists as well as science fiction writers.
Recalling his student days, Dr. Feynman once said, “Some people think Wheeler’s gotten crazy in his later years, but he’s always been crazy.”
John Archibald Wheeler — he was Johnny Wheeler to friends and fellow scientists — was born on July 9, 1911, in Jacksonville, Fla. The oldest child in a family of librarians, he earned his Ph.D. in physics from Johns Hopkins University at 21. A year later, after becoming engaged to an old acquaintance, Janette Hegner, after only three dates, he sailed to Copenhagen to work with Bohr, the godfather of the quantum revolution, which had shaken modern science with paradoxical statements about the nature of reality.
“You can talk about people like Buddha, Jesus, Moses, Confucius, but the thing that convinced me that such people existed were the conversations with Bohr,” Dr. Wheeler said.
Their relationship was renewed when Bohr arrived in 1939 with the ominous news of nuclear fission. In the model he and Dr. Wheeler developed to explain it, the atomic nucleus, containing protons and neutrons, is like a drop of liquid. When a neutron emitted from another disintegrating nucleus hits it, this “liquid drop” starts vibrating and elongates into a peanut shape that eventually snaps in two.
Two years later, Dr. Wheeler was swept up in the Manhattan Project to build an atomic bomb. To his lasting regret, the bomb was not ready in time to change the course of the war in Europe and possibly save his brother Joe, who died in combat in Italy in 1944.
Dr. Wheeler continued to do government work after the war, interrupting his research to help develop the hydrogen bomb, promote the building of fallout shelters and support the Vietnam War and missile defense, even as his views ran counter to those of his more liberal colleagues.
Dr. Wheeler was once officially reprimanded by President Dwight D. Eisenhower for losing a classified document on a train, but he also received the Atomic Energy Commission’s Enrico Fermi Award from President Lyndon B. Johnson in 1968.
When Dr. Wheeler received permission in 1952 to teach a course on Einsteinian gravity, it was not considered an acceptable field to study. But in promoting general relativity, he helped transform the subject in the 1960s, at a time when Dennis Sciama, at Cambridge University in England, and Yakov Borisovich Zeldovich, at Moscow State University, founded groups that spawned a new generation of gravitational theorists and cosmologists.
One particular aspect of Einstein’s theory got Dr. Wheeler’s attention. In 1939, J. Robert Oppenheimer, who would later be a leader in the Manhattan Project, and a student, Hartland Snyder, suggested that Einstein’s equations had made an apocalyptic prediction. A dead star of sufficient mass could collapse into a heap so dense that light could not even escape from it. The star would collapse forever while spacetime wrapped around it like a dark cloak. At the center, space would be infinitely curved and matter infinitely dense, an apparent absurdity known as a singularity.
Dr. Wheeler at first resisted this conclusion, leading to a confrontation with Dr. Oppenheimer at a conference in Belgium in 1958, in which Dr. Wheeler said that the collapse theory “does not give an acceptable answer” to the fate of matter in such a star. “He was trying to fight against the idea that the laws of physics could lead to a singularity,” Dr. Charles Misner, a professor at the University of Maryland and a former student, said. In short, how could physics lead to a violation itself — to no physics?
Dr. Wheeler and others were finally brought around when David Finkelstein, now an emeritus professor at Georgia Tech, developed mathematical techniques that could treat both the inside and the outside of the collapsing star.
At a conference in New York in 1967, Dr. Wheeler, seizing on a suggestion shouted from the audience, hit on the name “black hole” to dramatize this dire possibility for a star and for physics.
The black hole “teaches us that space can be crumpled like a piece of paper into an infinitesimal dot, that time can be extinguished like a blown-out flame, and that the laws of physics that we regard as ‘sacred,’ as immutable, are anything but,” he wrote in his 1999 autobiography, “Geons, Black Holes & Quantum Foam: A Life in Physics.” (Its co-author is Kenneth Ford, a former student and a retired director of the American Institute of Physics.)
In 1973, Dr. Wheeler and two former students, Dr. Misner and Kip Thorne, of the California Institute of Technology, published “Gravitation,” a 1,279-page book whose witty style and accessibility — it is chockablock with sidebars and personality sketches of physicists — belies its heft and weighty subject. It has never been out of print.
In the summers, Dr. Wheeler would retire with his extended family to a compound on High Island, Me., to indulge his taste for fireworks by shooting beer cans out of an old cannon.
He and Janette were married in 1935. She died in October 2007 at 99. Dr. Wheeler is survived by their three children, Ms. Lahnston and Letitia Wheeler Ufford, both of Princeton; James English Wheeler of Ardmore, Pa.; 8 grandchildren, 16 great-grandchildren, 6 step-grandchildren and 11 step-great-grandchildren.
In 1976, faced with mandatory retirement at Princeton, Dr. Wheeler moved to the University of Texas.
At the same time, he returned to the questions that had animated Einstein and Bohr, about the nature of reality as revealed by the strange laws of quantum mechanics. The cornerstone of that revolution was the uncertainty principle, propounded by Werner Heisenberg in 1927, which seemed to put fundamental limits on what could be known about nature, declaring, for example, that it was impossible, even in theory, to know both the velocity and the position of a subatomic particle. Knowing one destroyed the ability to measure the other. As a result, until observed, subatomic particles and events existed in a sort of cloud of possibility that Dr. Wheeler sometimes referred to as “a smoky dragon.”
This kind of thinking frustrated Einstein, who once asked Dr. Wheeler if the Moon was still there when nobody looked at it.
But Dr. Wheeler wondered if this quantum uncertainty somehow applied to the universe and its whole history, whether it was the key to understanding why anything exists at all.
“We are no longer satisfied with insights only into particles, or fields of force, or geometry, or even space and time,” Dr. Wheeler wrote in 1981. “Today we demand of physics some understanding of existence itself.”
At a 90th birthday celebration in 2003, Dr. Dyson said that Dr. Wheeler was part prosaic calculator, a “master craftsman,” who decoded nuclear fission, and part poet. “The poetic Wheeler is a prophet,” he said, “standing like Moses on the top of Mount Pisgah, looking out over the promised land that his people will one day inherit.” Wojciech Zurek, a quantum theorist at Los Alamos National Laboratory, said that Dr. Wheeler’s most durable influence might be the students he had “brought up.” He wrote in an e-mail message, “I know I was transformed as a scientist by him — not just by listening to him in the classroom, or by his physics idea: I think even more important was his confidence in me.”
Dr. Wheeler described his own view of his role to an interviewer 25 years ago.
“If there’s one thing in physics I feel more responsible for than any other, it’s this perception of how everything fits together,” he said. “I like to think of myself as having a sense of judgment. I’m willing to go anywhere, talk to anybody, ask any question that will make headway.
“I confess to being an optimist about things, especially about someday being able to understand how things are put together. So many young people are forced to specialize in one line or another that a young person can’t afford to try and cover this waterfront — only an old fogy who can afford to make a fool of himself.
“If I don’t, who will?”