“Physics is a subject that requires sitting down, putting pen to paper, and working out equations. Somehow he was able to do it all in his head.”

That was Pran Nath, Matthews Distinguished University Professor of Physics at Northeastern, and he was reflecting on the genius of Stephen Hawking, the renowned Cambridge University physicist who died on Wednesday at the age of 76.

Nath twice invited Hawking to Northeastern to speak at his International Symposium on Particles, Strings, and Cosmology. He came in 1990 and 1991—the symposium’s first two years of existence—and gave talks on wormholes, black holes, and baby universes. When Nath took the symposium to the United Kingdom in 2011, Hawking served on the local organizing committee.

“People came from all over the country to hear him talk at Northeastern,” Nath recalls, adding that one Boston TV station ranked Hawking’s 1990 lecture among the city’s biggest events of the year. “They were camped outside Blackman Auditorium so they could get in.”

‘The most amazing thing about him’

At 21, Hawking was diagnosed with Lou Gehrig’s disease and was told he had fewer than three years to live. He ended up living for 55 more years and producing some of the most important cosmological research on gravity and the properties of black holes. His 1998 book A Brief History of Time: From the Big Bang to Black Holes sold 10 million copies worldwide, while his life was the subject of the 2014 film The Theory of Everything.

Nath recalls Hawking’s seemingly boundless energy. After his 1990 lecture at Northeastern, it was late and program organizers were tired, but Hawking insisted on visiting the Museum of Fine Arts. “It was incredible how much energy he had in spite of his disability. That was the most amazing thing about him.”

For Nath, Hawking was an independent thinker who “didn’t follow any conventional rules.” At a celebratory dinner at the Colonnade Hotel in Boston following the 1990 symposium, a Harvard physicist asked him a “yes” or “no” question about the interplay between particle physics and cosmology. “There was silence for a minute or two,” Nath recalls, while Hawking used his computer-based communication system to formulate a rather lengthy response. “From there I understood that he wasn’t the type of person to buy some conventional description of something whether it had to do with physics or anything else. He would give you his own view.”

At one point, Nath’s assistant asked Hawking about the charm quark, a type of elementary particle. His response? “That’s not my area of expertise.” Says Nath: “He never pretended to know more than he did.”

According to him, Hawking ranks among the greatest physicists of all time. He’s right up there with Albert Einstein, who developed the theory of relativity, and Richard Feynman, an important contributor to quantum theory. “If you take into account Hawking’s contribution to humanity and his unwillingness to be cowed by his disability, he would be close to the very top.”