When he was 21, Stephen Hawking learned he had motor neurone disease.
Doctors told him he had a few years to live.
He’s now 72 and one of the foremost physicists alive — a professor at the University of Cambridge, an investigator of black holes, and the author of the bestselling book, A Brief History of Time.
Here are a dozen quotes showing Hawking’s approach to science and to life.
On Disability
“My advice to other disabled people would be, concentrate on things your disability doesn’t prevent you doing well, and don’t regret the things it interferes with. Don’t be disabled in spirit, as well as physically.”
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On Priorities
“My goal is simple. It is a complete understanding of the universe, why it is as it is and why it exists at all.”
— Stephen Hawking’s Universe, 1985
On Free Will
“I have noticed that even people who claim everything is predetermined and that we can do nothing to change it, look before they cross the road.”
— Black Holes and Baby Universes and Other Essays, 1994
On Humor
“Life would be tragic if it weren’t funny.”
— The New York Times Magazine, 2004
On His IQ
“I have no idea. People who boast about their I.Q. are losers.”
— The New York Times Magazine, 2004
On What He Think About All Day
“Women. They are a complete mystery.”
His Advice to His Three Children
“One, remember to look up at the stars and not down at your feet. Two, never give up work. Work gives you meaning and purpose, and life is empty without it. Three, if you are lucky enough to find love, remember it is there and don’t throw it away.”
On Why He Writes for a Popular Audience
“I put a lot of effort into writing A Briefer History at a time when I was critically ill with pneumonia because I think that it’s important for scientists to explain their work, particularly in cosmology. This now answers many questions once asked of religion.”
On the Value of String Theory
“When we understand string theory, we will know how the universe began. It won’t have much effect on how we live, but it is important to understand where we come from and what we can expect to find as we explore.”
On His Health
“When I was first diagnosed with ALS, I was given two years to live. Now 45 years later, I am doing pretty well.”
On God
“God may exist, but science can explain the universe without a need for a creator.”
On Hitting Roadblocks
“It is no good getting furious if you get stuck. What I do is keep thinking about the problem but work on something else. Sometimes it is years before I see the way forward. In the case of information loss and black holes, it was 29 years.”
This article originally appeared on Business Insider
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