Imagine a world where time is circular, where everything repeats itself exactly, endlessly. In this world "every handshake, every kiss, every birth, every word" has happened a million times before and will be repeated a million more times in the future. Or imagine a world where time runs backwards, or is discontinuous, or takes the form of a nightingale. These are some of the concepts of time that Alan Lightman, who teaches physics and writing at M.I.T., describes in his new novel, Einstein's Dreams.

In this tiny tome Lightman takes an entirely new approach to Einstein's theory of relativity, which scientists and writers have been trying to explain ever since Einstein proposed the theory in 1905. According to the theory, gravity causes time to slow down. The theory forever disproves and rejects the old-fashioned notion of absolute time. Lightman imagines what dreams Einstein might have had while concocting his theory, dreams that don't even seem too fantastical after one accepts the fact that time is not absolute.

Lightman's Einstein, a 26-year-old patent clerk in Bern, Switzerland, is tormented with dreams about time. Every night he envisions a new world where time affects the inhabitants of Bern differently. Each vision is organized like a fable, ending with an important message for the reader on how to live life best.

In one vision, people must learn how to adapt to a world without memory. The people who are happiest have abandoned the past and have "decided that it matters not if yesterday they were rich or poor, educated or ignorant, proud or humble, in love or empty-hearted--no more than it matters how a soft wind gets into their hair." In another world, where houses are on wheels and zoom around the city, it is discovered that time moves more slowly for people in motion. In this world, however, the happiest people are those who have stopped competing to live in the fastest house, but instead "rise in the morning, take baths, eat plaited bread and ham, work at their desks, listen to music, talk to their children, lead lives of satisfaction."

Lightman relates these fantasies of time with beautiful simplicity and intensity, as well as ironic humor. Although some of images used seem cliched, the visions of lovers stopped in time and grandparents growing young again still touch the reader and force one to reconsider accepted conceptions of time. Surprisingly enough, Lightman bases many of the dreams on real physics. In a vision derived from the theory that gravity stops time in a black hole, Einstein dreams that in the center of time, time freezes. Even the vision in which time branches into three dimensions has scientific backing.

After reading Einstein's Dreams, one feels disconcerted and confused. Living in a world filled with uncertainties, time provides regularity and predictability. In Lightman's worlds, however, this is not true. Although these dreams only exist in the wonderful imagination of Lightman, one has to wonder if some of these visions hold true for this world as well.