ALAN LIGHTMAN WAS NEVER PERFECTLY suited to a life of hard-core science. The raw materials were always there, to be sure. "As a boy, I was socially inept and I did a lot of experiments," he says, describing the time he fashioned an electrical transformer that created static on all the neighborhood TV sets. But he also had an undeniable literary bent. "From as far back as I can remember, I built rockets and wrote poetry," he says. "I've always felt torn between two worlds."

He hasn't felt shy about trying to reconcile them, as his published works (including two books of essays on what he calls "the human side of science") and current job titles at MIT (professor of science and writing and senior lecturer in physics)attest. But only this year has Lightman, 44, fused art and science in a way that has made people take notice. Einstein's Dreams, his first work of fiction, has charmed his literary peers ("intellectually provocative...and so very beautifully written," declared author Salman Rushdie) and spent three months on The New York Times best-seller list.

It's an unlikely coup for a book starring the father of relativity. The novel imagines Albert Einstein in the months before he published his revolutionary theory, lost in nightly reveries about the nature of time. How would humanity be affected, his dreams ask, if time ran in circles, had an end point or flowed more slowly at higher altitudes? "People are fascinated with time," says Lightman. "I think readers are relating to things in the book that are already in their subconscious."

Lightman also hopes they'll relate more to Einstein and his ilk. "I wanted to contrast the waking, stereotyped genius who is insensitive to people to the sleeping Einstein, who I speculate is very tuned in to people," he says. "I believe that in order to be really creative you have to feel for people. A lot of scientists have trouble with social relationships and go inward, but deep down there's this sensitivity and humanness."

The eldest of four sons born to a Memphis movie-theater owner and his dance-teacher wife, Lightman was a solitary youth whose schoolboy poetry sought existential truths—"who I was, what I was like before I was born, whether people live forever." He majored in physics at Princeton—figuring, "It would be easier to go from science back to writing than vice versa"—got his Ph.D. at Caltech and did postdoctoral work at Cornell. While there he met Jean Greenblatt, an urban-planning student and painter. "I responded to her artistic side, and I think she responded to mine," says Lightman, who married her in 1976. "She's told me that if I had been just a scientist, she wouldn't have been interested."

While teaching astronomy and physics at Harvard—which he did between 1976 and 1988—Lightman decided to try writing professionally. Inspired by science popularizers Steven Jay Gould and Lewis Thomas as well as by essayist E.B. White, Light-man began writing essays in the early '80s on such topics as the diversity of snowflakes and the physics principles underlying ballet. His aim was to humanize science for lay readers by showing its connections to art and literature. "We've all gotten so specialized," he says, "and that makes communication more difficult."

The essays, which were first published in such magazines as the Smithsonian and The New Yorker, led to popular science books, a college physics textbook for humanities students and, eventually, fiction—a leap Light-man found terrifying. He wrote Dreams in 1991, holed up in the Maine summer home that he and Jean, now 40 and a full-time painter, share with daughters Elyse, 12, and Kara, 6. "I promised myself that if I wasn't happy with what I'd done, I'd fold up my saddlebags and move on," he says. But he was happy—and so were his editors.

Lightman, who's already working on a new novel, has cultivated friends who share his interests. "I like humanities people who aren't defensive about science and physicists who'll call me up to have lunch and not just talk about physics." He still feels torn between two worlds, but not to worry. "I've learned," he says with a smile, "how to live with it."