Stephen Hawking at "Interstellar Live" in London on March 30, 2015.
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September 25, 2015 5:03 PM EDT

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.

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