On Wednesday, Stephen Hawking’s family announced the legendary physicist had died at age 76. It’s an enormous loss for space enthusiasts of all ages, but physicists tell *Inverse* there’s an additional layer of sadness for them.

*Inverse* asked physicists across the world to explain Hawking’s greatest scientific achievement, and it’s clear the *Brief History of Time* author challenged the community to think differently about the universe while touching millions of lives along the way.

## Leo Stein, Postdoctoral Researcher at Caltech

“His greatest accomplishment was his discovery that black holes radiate. This has led to now more than four decades of head-scratching — more than four decades later, we still don’t understand how to cope with this fact,” Stein tells *Inverse*. “But it highlights one of the crucial thought experiments for constructing a consistent theory of quantum gravity — how do you keep black holes from destroying information as they evaporate and disappear? Hawking’s calculation led to thousands of publications trying to make sense of the puzzle.”

“Socially: His popular writing excited generations of science enthusiasts. I bet if you did a survey of scientists my age, a good chunk of them would’ve read *A Brief History of Time* or one of his other popular books when they were kids.”

## Chanda Prescod-Weinstein, Astrophysicist

“Hawking’s belief that spending time sharing science with the public was a good is the reason I am a physicist,” tells *Inverse.* “My entire career he has been an example, especially when I became physically disabled and was for some time bedridden and realizing I would likely be in chronic pain for life.”

## Seán Bartz, Visiting Assistant Professor at Macalester College

“Hawking’s greatest scientific contributions were in advancing our understanding of black holes,” tells *Inverse*. “He was instrumental in taking black holes from a nebulous idea to objects that could be studied with precision. Black hole thermodynamics is something that I use in my research as a means of studying nuclear physics. Hawking radiation tells us about the fate of black holes and possibly our entire universe.”

## Robert McNees, Physicist

“It is difficult to single out one result, or even a group of closely related results, and call it ‘Stephen Hawking’s greatest scientific achievement.’ There were so many profound accomplishments across general relativity, quantum field theory, and cosmology that picking just one feels like an act of neglect. But if I had to choose one area, it would be his work transitioning from the classical laws of black hole mechanics to the quantum mechanical picture of black holes as fully thermodynamical objects. In 1973, Hawking, Bardeen, and Carter developed an elegant set of four laws governing the “mechanics” of all black holes — basic rules that explained how quantities like the mass, area of the event horizon, or surface gravity of a black hole change throughout very general physical processes. The rules bore a striking resemblance to the familiar laws of thermodynamics.

But if you’d asked me for his greatest achievement, and hadn’t specified ‘scientific,’ I think 13-year-old me would probably push adult me out of the way and say, ‘He makes me want to understand the universe.’”

## Sabine Hossenfelder, Physicist

“I think his greatest achievement was to inspire huge numbers of people to think about space, time, and the origin of the universe — knowledge that before him was stuck in obscure corners of academia,” tells *Inverse.*

## James Beacham, Particle Physicist at CERN

“He worked on many vital things in his career, but Stephen Hawking’s most significant and alarming scientific achievement is definitely the calculation that black holes can radiate and thus shrink and die,” he tells *Inverse.* “It’s a wonderful example of how, by simply and elegantly following through with the set of equations governing theories of nature — in this case quantum mechanics and general relativity — one arrives at a totally bizarre but mathematically sound conclusion. In the case of Hawking-Bekenstein radiation this concept is taken to its extreme, because the math part is pretty mundane and almost trivial, and the conclusion is bonkers. Just by doing a certain type of coordinate transformation near a black hole — that is, just by choosing a different set of coordinates to describe the physics going on, of which there are always many choices in physics, but they should all, at the end of the day, describe the same physics — you end up with the conclusion that particles are being emitted from the event horizon of the black hole! But nothing is supposed to be able to escape from a black hole!

This is a very odd but inescapable, inevitable conclusion of the math, and we love that in physics.”

Ad astra, Dr. Hawking. Thank you for everything.

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