If you liked the eerie whimsy of Italo Calvino's Invisible Cities, Steven Millhauser's Little Kingdoms, or Jorge Luis Borges's Labyrinths, you will love Alan Lightman's ethereal yet down-to-earth book Einstein's Dreams. Lightman teaches physics and writing at the Massachusetts Institute of Technology, helping bridge the light-year-size gap between science and the humanities, the enemy camps C.P. Snow famously called The Two Cultures. Einstein's Dreams became a bestseller by delighting both scientists and humanists. It is technically a novel. Lightman uses simple, lyrical, and literal details to locate Einstein precisely in a place and time--Berne, Switzerland, spring 1905, when he was a patent clerk privately working on his bizarre, unheard-of theory of relativity. The town he perceives is vividly described, but the waking Einstein is a bit player in this drama. The book takes flight when Einstein takes to his bed and we share his dreams, 30 little fables about places where time behaves quite differently. In one world, time is circular; in another a man is occasionally plucked from the present and deposited in the past: "He is agonized. For if he makes the slightest alteration in anything, he may destroy the future ... he is forced to witness events without being part of them ... an inert gas, a ghost ... an exile of time." The dreams in which time flows backward are far more sophisticated than the time-tripping scenes in Kurt Vonnegut's Slaughterhouse-Five, though science-fiction fans may yearn for a sustained yarn, which Lightman declines to provide. His purpose is simply to study the different kinds of time in Einstein's mind, each with its own lucid consequences. In their tone and quiet logic, Lightman's fables come off like Bach variations played on an exquisite harpsichord. People live for one day or eternity, and they respond intelligibly to each unique set of circumstances. Raindrops hang in the air in a place of frozen time; in another place everyone knows one year in advance exactly when the world will end, and acts accordingly. "Consider a world in which cause and effect are erratic," writes Lightman. "Scientists turn reckless and mutter like gamblers who cannot stop betting.... In this world, artists are joyous." In another dream, time slows with altitude, causing rich folks to build stilt homes on mountaintops, seeking eternal youth and scorning the swiftly aging poor folk below. Forgetting eventually how they got there and why they subsist on "all but the most gossamer food," the higher-ups at length "become thin like the air, bony, old before their time." There is no plot in this small volume--it's more like a poetry collection than a novel. Like Stephen Hawking's A Brief History of Time, it's a mind-stretching meditation by a scientist who's been to the far edge of physics and is back with wilder tales than Marco Polo's. And unlike many admirers of Hawking, readers of Einstein's Dreams have a high probability of actually finishing it.