CAMBRIDGE, England - 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 and cosmologist was diagnosed with Lou Gehrig's disease when he was a 21-year-old student at Cambridge University. Most people die within a few years of the diagnosis, called motor neurone disease in the United Kingdom. On Sunday, Hawking will turn 70.
"I don't know of anyone who's survived this long," said Ammar al-Chalabi, director of the Motor Neurone Disease Care and Research Centre at King's College London. He does not treat Hawking and described his longevity as "extraordinary."
Some experts said the type of care Hawking has, including about a dozen health workers 24 hours a day, may have extended his life.
"The disease can sometimes stabilize, and then the kind of care delivered may be a factor in survival," said Virginia Lee, a brain-disease expert at the University of Pennsylvania School of Medicine. "Remaining mentally alert is also extremely important, and he has clearly done that."
Hawking first gained attention with his 1988 book, A Brief History of Time, a simplified overview of the universe. It sold more than 10 million copies worldwide. His subsequent theories have revolutionized modern understanding of concepts like black holes and the big bang theory of how the universe began.
To mark his birthday Sunday, Cambridge University is holding a public symposium on "The State of the Universe," featuring talks from 27 leading scientists, including Hawking. For 30 years, he held a mathematics post at the university once held by Sir Isaac Newton. Hawking retired from that post in 2009 and is now research director at the university's Centre for Theoretical Cosmology.
Hawking achieved all that despite being nearly entirely paralyzed and in a wheelchair since 1970. He now communicates only by twitching his right cheek. Since battling pneumonia in 1985, Hawking has needed round-the-clock care and relies on a computer and voice synthesizer to speak.
A tiny infrared sensor sits on his glasses, hooked up to a computer. The sensor detects Hawking's cheek pulses, which select words displayed on a computer screen. The chosen words are then spoken by the voice synthesizer. It can take up to 10 minutes for Hawking to formulate a single sentence.
"The only trouble is [the voice synthesizer] gives me an American accent," the Briton wrote on his website.
It took Hawking four years to write his most recent book, The Grand Design, missing his publisher's original deadline.
Hawking declined requests for an interview, but personal assistant Judith Croasdell spoke to the AP, describing her boss as remarkably patient. "The way he communicates can seem frustratingly slow to most people, but he doesn't let that impede his thinking," she said.
After a brief hospital stay, Hawking told her that he spent the time thinking about black holes.
Hawking's fame has led to guest appearances on some of his favorite television shows including The Simpsons and Star Trek.