A Brief History of Time: From the Big Bang to Black Holes by Stephen W. Hawking, introduction by Carl Sagan Bantam, 198 pp., $18.95

“My goal is simple. It is complete understanding of the universe, why it is as it is and why it exists at all.”

—Stephen Hawking, 1981

Stephen Hawking opens his new book with a marvelous old anecdote. A famous astronomer, after a lecture, was told by an elderly lady, who was perhaps under the influence of Hinduism, that his cosmology was all wrong. The world, she said, rests on the back of a giant tortoise. When the astronomer asked what the tortoise stands on, she replied: “You’re very clever, young man, very clever. But it’s turtles all the way down.”

Most people, Hawking writes, would find this cosmology ridiculous, but if we take the turtles as symbols of more and more fundamental laws, the tower is not so absurd. There are two ways to view it. Either a single turtle is at the bottom, standing on nothing, or it’s turtles all the way down. Both views are held by leading physicists. David Bohm and Freeman Dyson, to mention two, favor the infinite regress—wheels within wheels, boxes inside boxes, but never a final box.1 Hawking is on the other side. He believes that physics is finally closing in on the ultimate turtle. But before discussing his stimulating book, which climaxes with this amazing prediction, I shall say something about the book’s even more extraordinary author.

Hawking, age forty-four, is the Lucasian Professor of Mathematics at Cambridge University, a chair held by Isaac Newton and Paul Dirac. Few living physicists could occupy this chair more deservedly, even though, as many by now know, Hawking has for two decades been confined to a wheelchair. He is already a legend, not just because of his brilliant contributions to theoretical physics, but also for his courage, optimism, and humor in the face of a crippling illness. Lou Gehrig’s disease may be gnawing away at his body, but it has left his mind intact. Hawking actually sees himself as fortunate. He has chosen a profession in which he can work entirely inside his head, and his disability has freed him from numerous academic chores.

A tracheostomy made necessary by a pneumonia attack in 1985 has silenced his voice. He speaks by way of a computer and speech synthesizer attached to his wheelchair. Because the synthesizer was made in California, he apologizes to strangers for his American accent. He has a devoted wife and three children. He has visited the United States some thirty times, Moscow seven times, and flown around the world. At a Chicago discotheque he once wheeled onto the floor and spun his chair in time to the music.

A Brief History of Time is Hawking’s first popularly written book. Warned that every equation would cut sales in half, he has left out all formulas except Einstein’s famous E = mc2, which he hopes will not frighten half his readers. Hawking’s prose is as informal and clear as his topics are profound. Work that he accomplished during what he calls his…