I first encountered Stephen Hawking in Ida Noyes Hall, an imposing neo-Gothic building on the south edge of the University of Chicago’s sprawling campus. It was the winter of 1996, and I was attending the Texas Symposium on Relativistic Astrophysics (which, in spite of the name, is not always held in Texas). I was still pretty new to the world of science journalism. But I was already a longtime science nerd with a keen interest in physics and the universe. And of course, I knew who Stephen Hawking was. (Everyone did, his runaway bestseller “A Brief History of Time” being almost a decade old by this time.) But I had never seen him with my own eyes until that evening, at a reception in one of the hall’s banquet rooms.

Space and time were Hawking’s playthings.

The only analogy that comes to mind is what it might have been like to catch sight of Elvis. Sure, you’ve seen hundreds of photos — but there he is in the flesh. The first thing that struck me was how small that flesh actually was. Diagnosed at the age of 21 with ALS, a motor neuron disease, Hawking required round-the-clock care. In Chicago — and at each conference I would see him at in later years — at least one attendant (often more) was always by his side. But then, it’s not his body that reached out to grasp the farthest reaches of the cosmos — it was his mind that did.

And what a mind it was. The origin of the universe, the physics of black holes, the ultimate nature of space and time — these were his passions. He tackled the big questions head-on. “My goal is simple,” he wrote early in his career. “It is complete understanding of the universe, why it is as it is and why it exists at all.”

One can speculate — idly, I think — about whether he was “the new Einstein,” or the greatest living physicist, or merely one of the top 10, or wherever one imagines he fits into the pantheon of great thinkers. I often asked physicists, privately, what they thought about this. As long as they were sure we were off the record, they’d take their evaluation down slightly. Not far, just a notch. Hawking was brilliant, obviously, but the comparisons to Einstein, I was told, were a bit of a stretch. (For the opposite perspective — that Hawking was underrated — see Amanda Gefter’s insightful essay in The Atlantic.) One physicist told me that Hawking’s work was of “Nobel caliber.” That’s already high praise. Of course, he never received the Nobel; the prize committee likes ideas that have been successfully tested, and his work was highly theoretical, almost impossible to put to the test.

Space and time were Hawking’s playthings. His best-known work involved black holes. In the mid-1970s, Hawking argued that black holes must radiate energy; eventually, they may evaporate into nothingness.

Does that matter? To physicists, it very much does. They worry quite a lot about “information,” and they’re pretty sure that information can neither be created nor destroyed. But what if that information somehow found its way into a black hole? Although we could no longer access it, as long as the black hole persisted, we could imagine that the information was “safe.” But if the black hole itself disappears in a puff of Hawking radiation, the information seems to be gone for good. Something doesn’t seem right. Physicists have been arguing about the “information loss paradox” since Hawking first wrote about it, and it continues to stir fierce debate.

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That was Hawking the physicist, but the Hawking who connected with a worldwide audience — the one who appeared on “The Simpsons,” “Star Trek: The Next Generation,” “The Big Bang Theory,” and beyond — was Hawking the promoter of science. And make no mistake, he enjoyed these forays into pop culture. When delivering public lectures, he would always include a clip from one of his TV appearances; often, it was the iconic scene from “Next Gen” in which he plays poker with Newton, Einstein, and Data. And it always drew thunderous applause. Even when Hawking wasn’t on TV, you never knew when his name would come up. In the “Simpsons” episode where Homer accidentally disappears into the “third dimension,” he laments, “I wish I’d read that book by that wheelchair guy.” There was never any doubt who he meant.

He whispered not only to the black holes, but to us. We were lucky to be within earshot.

And we knew the book, too. Not everyone read it, but millions bought it. Published in the spring of 1988, “A Brief History” surprised everyone, including its author, with its success. It has since been translated into 35 languages and has sold more than 10 million copies worldwide. Hawking liked to joke that he had sold more books on physics than Madonna had on sex. The book included the just one equation — E=mc2 — but plenty of references to God (metaphorical as they were).

Young science buffs, in particular, were hooked. Natalie Wolchover, now a senior writer at Quanta Magazine, remembers reading the book as a wide-eyed 13-year-old. “A Brief History” was “this incredible book [that] introduced me to physics, and made me decide to devote my life to it,” she tweeted this morning. Emily Conover, who now covers physics for Science News, was similarly mesmerized by the book as a teenager. “Thinking about ‘A Brief History of Time’ takes me back to cozy winter evenings spent by the fireplace in my parents’ house, pondering mysteries of the universe,” she tweeted. She thanked Hawking for introducing her to “the beauty of physics.”

After “A Brief History” came the deluge: Suddenly, physicists everywhere were writing would-be popular books, with varying levels of success. Some, like Brian Greene and Roger Penrose, cranked the science up a notch, adding rigorous technical details where Hawking had provided only broad brushstrokes; others, like Neil deGrasse Tyson and Janna Levin, strove to make the science as digestible as possible for a lay audience. Many more steered a middle ground, hoping beyond hope to duplicate Hawking’s success. (Somehow, scientists, as a group, developed a reputation for being poor communicators. I don’t know how this notion took root. Many, though perhaps not most, are brilliant writers, through few have managed to duplicate Hawking’s mixture of easygoing style, engaging ideas, and humor.)

My own attempt to interview Hawking did not go well. As we happened to share an elevator on one occasion, I asked him to what extent string theory was likely to prove a steppingstone toward a ‘theory of everything.’ Bad move. As soon as the words had left my lips, I regretted not asking a question that more readily lent itself to a yes-or-no reply. He said “yes.”

The death of Stephen Hawking leaves a hole in the world of physics. There are and will be other great minds. But Hawking, who was born 300 years to the day after the death of Galileo, and who happened to leave this world on Einstein’s 139th birthday, was, and will remain, special. Conover says she cried as she wrote of Hawking as the “black hole whisperer” earlier today. He whispered not only to the black holes, but to us. We were lucky to be within earshot.

Dan Falk (@danfalk) is a science journalist based in Toronto and a former Knight Science Journalism fellow. His books include “The Science of Shakespeare” and “In Search of Time.”