His lab was the universe

Everyone knew of Stephen Hawking's cosmic brilliance, but few could comprehend it. Not even top-notch astronomers.

Hawking, who died at his home in Cambridge, England, on Wednesday at age 76, became the public face of science genius. He appeared on "Star Trek: The Next Generation" and "The Big Bang Theory," voiced himself in "The Simpsons" cartoon series and wrote the bestseller "A Brief History of Time." He sold 9 million copies of that book, though many readers didn't finish it. It's been called "the least-read bestseller ever." Hollywood celebrated his life in the 2014 Oscar-winning biopic "The Theory of Everything."

In some ways, Hawking was the inheritor of Albert Einstein's mantle of the genius-as-celebrity.

"His contribution is to engage the public in a way that maybe hasn't happened since Einstein," said prominent astronomer Wendy Freedman, former director of the Carnegie Observatories. "He's become an icon for a mind that is beyond ordinary mortals. People don't exactly understand what he's saying, but they know he's brilliant. There's perhaps a human element of his struggle that makes people stop and pay attention."

With Einstein, most people are familiar with e=mc2, but they don't know what it means. With Hawking, his work was too complicated for most people, but they understood that what he was trying to figure out was basic, even primal.

"He was asking and trying to address the very biggest questions we were trying to ask: the birth of the universe, black holes, the direction of time," said University of Chicago cosmologist Michael Turner. "I think that caught people's attention."

And he did so in an impish way, showing humanity despite being in a wheelchair with ALS, the degenerative nerve disorder known in the U.S. as Lou Gehrig's disease. He flew in a zero-gravity plane. He made public bets with other scientists about the existence of black holes and radiation that emanates from them — losing both bets and buying a subscription to Penthouse for one scientist and a baseball encyclopedia for the other.

"The first thing that catches you is the debilitating disease and his wheelchair," Turner said. But then his mind and the "joy that he took in science" dominated. And while the public may not have understood what he said, they got his quest for big ideas, Turner said.

Andy Fabian, an astronomer at Hawking's University of Cambridge and president of the Royal Astronomical Society, said Hawking would start his layman's lectures on black holes with the joke: "I assume you all have read 'A Brief History of Time' and understood it." It always got a big laugh.

"You'd find the average astronomer such as myself doesn't even try to follow the more esoteric theories that (Hawking) pursued the last 20 years," Fabian said. "I've been to talks Hawking has given and cannot follow them myself."

Hawking, who was born 300 years to the day after Galileo died, was the Lucasian Professor of Mathematics at Cambridge University. It was the same post that Isaac Newton held. Both physicists and astrophysicists claimed him as their own. And much of Hawking's work was in the field of cosmology, a deep-thinking branch of astronomy that tries to explain the totality of the universe.

Hawking's title "is not relevant here; what matters is what his brain did," said Neil deGrasse Tyson, director of New York's Hayden Planetarium. "We claim him as an astrophysicist because his laboratory was the universe."

And Hawking's black hole work in the mid-1970s made a crucial connection in physics. Until Hawking discovered radiation coming from black holes — named "Hawking radiation" after him — the two giant theories in physics, Einstein's general relativity and quantum mechanics, often conflicted. Hawking was the first to show they connected, which Turner and others described as breakthrough at the time.