Darkness has fallen on Cambridge, England, and on a damp and chilly evening King's Parade is filled with students and faculty. Then, down the crowded thoroughfare comes the University of Cambridge's most distinctive vehicle, bearing its most distinguished citizen. In the motorized wheelchair, boyish face dimly illuminated by a glowing computer screen attached to the left armrest, is Stephen William Hawking, 46, one of the world's greatest theoretical physicists. As he skillfully maneuvers through the crowd, motorists slow down, some honking their horns in greeting. People wave. "Hi, Stephen," they shout.
A huge smile lights up Hawking's bespectacled face, but he...