Stephen Hawking Turning 70

British scientist Stephen Hawking has decoded some of the most puzzling mysteries of the universe, but he has left one mystery unsolved: How he has managed to survive so long with such a crippling disease. The physicist was diagnosed with Lou Gehrig's disease when he was a 21-year-old at Cambridge. Most people die within a few years: Hawking will turn 70 on Sunday.

"I don't know of anyone who's survived this long," says the director of the Motor Neurone Disease Care and Research Centre in London. The author of A Brief History of Time has achieved his greatness despite being nearly entirely paralyzed and in a wheelchair since 1970. He now communicates only by twitching his right cheek. Since catching pneumonia in 1985, Hawking has needed around-the-clock care and relies on a computer and voice synthesizer to speak. "The only trouble is (the voice synthesizer) gives me an American accent," he wrote on his website. (Hawking also is looking for an assistant.)