How physicists will remember Stephen Hawking

 Researchers are still pondering puzzles posed by the cosmologist

COSMOLOGICAL STAR During a career that spanned more than half a century, Stephen Hawking deduced new properties of mysterious chasms in spacetime.

THE WORLD IN HDR/SHUTTERSTOCK

Stephen Hawking, a black hole whisperer who deciphered the mysteries of the universe's most enigmatic objects, left a legacy of cosmic puzzles and inspired a generation of scientists who grew up reading his books.

Hawking's most famous discovery — that black holes aren't wholly black, but emit feeble radiation — was still causing dispute when he died on March 14 at the age of 76.

Hawking "truly, really cared about the truth and attempting to uncover it," according to Harvard University physicist Andrew Strominger, who worked with him. Hawking "dedicated his entire life to gaining a better grasp of the physical cosmos around us."

Hawking spent the rest of his life at the University of Cambridge, where he received his Ph.D. in 1965 and continued to study cosmology. Hawking lost use of his body as a result of a degenerative disease called amyotrophic lateral sclerosis, or ALS, and finally needed a wheelchair and a voice synthesizer to communicate. His passion to learn more about nature remained unquenchable.

Hawking discovered in 1974 that black holes radiate a faint glow of particles, which was one of the most significant discoveries of his career. This phenomenon derives from quantum mechanics, which claims that space is filled with a sea of transitory particles and antiparticles. These "virtual" particles generally annihilate in an instant, but if one of them is lost within a black hole's event horizon, or barrier, its companion can escape, resulting in Hawking radiation.

As a result, black holes can slowly dissipate and vanish. This led to an unsolved paradox: if you throw an encyclopedia into a black hole, the information will be lost eventually. However, quantum physics states that information can never be destroyed.

There have been numerous remedies recommended for this issue, but none has proven to be successful. Hawking and colleagues proposed a solution in 2016: black holes may have "soft hair," low-energy particles that would keep track of what fell within. The research is still being worked on by Hawking's partners, including Strominger. The conundrum, which exists at the intersection of two seemingly irreconcilable theories — quantum mechanics, which describes the extremely small, and general theory of relativity, which explains gravity — could eventually lead to the discovery of a unified theory of quantum gravity.

Hawking also made numerous additional contributions, including research into spacetime curvature during the Big Bang and the likelihood of small black holes forming in the early universe. According to Harvard theoretical astrophysicist Avi Loeb, despite their revolutionary nature, Hawking's theories remained purely speculative. For example, no direct detection of Hawking radiation has ever been made. "Unfortunately, that is why he did not receive the Nobel Prize," Loeb explains.

Despite this, Hawking gained a level of celebrity among scientists that is unheard of. He was a master at making complex science understandable to the general audience. Hawking inspired innumerable future scientists and science aficionados with his writings, most notably the best-selling A Brief History of Time, first published in 1988. (Including the author of this article). Katie Mack of North Carolina State University in Raleigh, a theoretical cosmologist, first read the novel when she was about ten years old. "It was fascinating to me at the time," she recalls. "When I learned that Stephen Hawking was referred to as a cosmologist, I declared that I wanted to be one as well." According to Mack, Hawking inspired dozens of her coworkers in a similar way.

Even in his final months, Hawking continued to work on studies. An article on which he was a coauthor, and which was updated in the weeks leading up to his death, looked at the physics of multiverses, or the potential that there are many more worlds than our own.

Hawking's funeral was held on March 31. His ashes will be placed later this year in Westminster Abbey in London, with the ashes of other famous British scientists such as Isaac Newton and Charles Darwin.