All this may explain why the same man could write “we live on a shrinking and vulnerable planet which our lack of foresight is rapidly turning into a slum” and yet gently chide the sort of Americans who march against coal in Washington. Dyson has great affection for coal and for one big reason: It is so inexpensive that most of the world can afford it. “There’s a lot of truth to the statement Greens are people who never had to worry about their grocery bills,” he says. (“Many of these people are my friends,” he will also tell you.) To Dyson, “the move of the populations of China and India from poverty to middle-class prosperity should be the great historic achievement of the century. Without coal it cannot happen.” That said, Dyson sees coal as the interim kindling of progress. In “roughly 50 years,” he predicts, solar energy will become cheap and abundant, and “there are many good reasons for preferring it to coal.”

THE WORDS COLLEAGUES COMMONLY use to describe Dyson include “unassuming” and “modest,” and he seems the very embodiment of Newton’s belief that a man should strive for simplicity and avoid confusion in life. Dyson has been in residence at the institute since 1953, a time when Albert Einstein shared his habit of walking to work there, which Dyson still does seven days a week, to write on a computer and solve any problems that come across his desk with paper and pencil. (In his prime, legend held that he never used the eraser.) He and Imme have spent 51 happy years together in the same house, a white clapboard just over the garden fence from the stucco affair once inhabited by their former neighbors, the Oppenheimers. On some Sundays the Dysons pile into a car still decorated with an Obama bumper sticker and drive to running races, at which Dyson can be found at the finish line loudly cheering for the 72-year-old Imme, a master’s marathon champion. On many other weekends, they visit some of their 16 grandchildren. During the holiday season the Dysons routinely attend five parties a week, cocktail-soiree sprints at which guests tend to find him open-minded and shy: when friends’ wives give him a hug, he blushes. One of Dyson’s daughters, the Internet vizier Esther Dyson, says her father raised her without a television so she would read more, and has always been “just as interested in talking to” the latest graduate student to make the pilgrimage to Princeton “as he is the famous person at the next table.” Oliver Sacks says that Dyson has “a genius for friendship.”

But the truth is that Dyson is an elusive particle. To Edward Witten it is clear that Dyson has little use for string theory, the cutting-edge “theory of everything” that links quantum mechanics and relativity in an effort to describe no less than the nature of all things. Even so, Witten admits that there is a fever-dream quality to his conversations with Dyson: “I don’t always know what he disagrees with entirely. His attitudes are complicated. There are many layers.” Other people can be similarly intrigued and baffled. When I began spending time with Dyson and asked who his close friends are, the only name he mentioned was John McPhee’s, which surprised McPhee since he said he doesn’t often speak with Dyson even though McPhee teaches nearby at Princeton University. All six of Dyson’s children describe him as a loving, intensely devoted father and yet also suggest that this is a parent with, in the words of his son, George, core parts of him that have always seemed “remote.” William Press said he finds Dyson to be both a “deep” and “magnificently laudable person” and also mysterious and inscrutable, a man with contrarian opinions that Press suspects may be motivated by “a darker side he’s determined the world isn’t going to see.” When I asked Sacks what he thought about all this, he said that “a favorite word of Freeman’s about doing science and being creative is the word ‘subversive.’ He feels it’s rather important not only to be not orthodox, but to be subversive, and he’s done that all his life.”

Dyson says it’s only principle that leads him to question global warming: “According to the global-warming people, I say what I say because I’m paid by the oil industry. Of course I’m not, but that’s part of their rhetoric. If you doubt it, you’re a bad person, a tool of the oil or coal industry.” Global warming, he added, “has become a party line.”

What may trouble Dyson most about climate change are the experts. Experts are, he thinks, too often crippled by the conventional wisdom they create, leading to the belief that “they know it all.” The men he most admires tend to be what he calls “amateurs,” inventive spirits of uncredentialed brilliance like Bernhard Schmidt, an eccentric one-armed alcoholic telescope-lens designer; Milton Humason, a janitor at Mount Wilson Observatory in California whose native scientific aptitude was such that he was promoted to staff astronomer; and especially Darwin, who, Dyson says, “was really an amateur and beat the professionals at their own game.” It’s a point of pride with Dyson that in 1951 he became a member of the physics faculty at Cornell and then, two years later, moved on to the Institute for Advanced Study, where he became an influential man, a pragmatist providing solutions to the military and Congress, and also the 2000 winner of the $1 million Templeton Prize for broadening the understanding of science and religion, an award previously given to Mother Teresa and Aleksandr Solzhenitsyn — all without ever earning a Ph.D. Dyson may, in fact, be the ultimate outsider-insider, “the world’s most civil heretic,” as the classical composer Paul Moravec, the artistic consultant at the institute, says of him.

Climate-change specialists often speak of global warming as a matter of moral conscience. Dyson says he thinks they sound presumptuous. As he warned that day four years ago at Boston University, the history of science is filled with those “who make confident predictions about the future and end up believing their predictions,” and he cites examples of things people anticipated to the point of terrified certainty that never actually occurred, ranging from hellfire, to Hitler’s atomic bomb, to the Y2K millennium bug. “It’s always possible Hansen could turn out to be right,” he says of the climate scientist. “If what he says were obviously wrong, he wouldn’t have achieved what he has. But Hansen has turned his science into ideology. He’s a very persuasive fellow and has the air of knowing everything. He has all the credentials. I have none. I don’t have a Ph.D. He’s published hundreds of papers on climate. I haven’t. By the public standard he’s qualified to talk and I’m not. But I do because I think I’m right. I think I have a broad view of the subject, which Hansen does not. I think it’s true my career doesn’t depend on it, whereas his does. I never claim to be an expert on climate. I think it’s more a matter of judgement than knowledge.”

Image The Apprentice Scientist An Esay at Natarril History, age 6; the last page of a three-page treatise on Astronimy, age 5; and a sketch of a passenger-bearing spaceship from the unfinished science-fiction story Sir Phillip Robertss Erolunar Collision, age 9. Credit... Drawings by Freeman Dyson. Photographs from George Dyson.

Reached by telephone, Hansen sounds annoyed as he says, “There are bigger fish to fry than Freeman Dyson,” who “doesn’t know what he’s talking about.” In an e-mail message, he adds that his own concern about global warming is not based only on models, and that while he respects the “open-mindedness” of Dyson, “if he is going to wander into something with major consequences for humanity and other life on the planet, then he should first do his homework — which he obviously has not done on global warming.”