Stephen Hawking, the prodigious British theoretical cosmologist who became an international celebrity, died at his home in Cambridge, U.K., early today, at the age of 76. Hawking, who spent his entire career at the University of Cambridge, suffered from amyotrophic lateral sclerosis, a degenerative nerve disease with which he was diagnosed in his 20s. The disease confined Hawking to a wheelchair for most of his adult life and eventually rendered him capable of speaking only through a computer-controlled voice synthesizer. Nevertheless, Hawking made seminal contributions to astrophysics, particularly in the study of black holes, veritable holes in the fabric of the universe.
“Stephen was far from being the archetype unworldly or nerdish scientist—his personality remained amazingly unwarped by his frustrations and handicaps,” Martin Rees, a cosmologist at the University of Cambridge, and the United Kingdom’s astronomer royal, said in a statement. “He had robust common sense, and was ready to express forceful political opinions.”
Scientifically, Hawking’s name will forever be tied to black holes, the ultraintense gravitational fields left behind when massive stars collapse under their own gravity into infinitesimal points. Within a certain distance of the point, which defines the black hole’s event horizon, gravity grows so strong that nothing, not even light, can escape. That fact suggested that the bizarre objects would be completely black.
However, in 1974 Hawking argued that black holes would radiate energy after all. Physicists had come to understand that, thanks to quantum uncertainty, the vacuum of empty space constantly roils with particle-antiparticle pairs flitting in and out of existence too quickly to be directly detected. Hawking realized that if such a pair popped into existence on the event horizon of a black hole, one particle might fall in past the event horizon while the other escaped to distant space. Thus, quantum mechanics would allow the black hole to slowly radiate energy back into space, and even, eventually, to evaporate. The presumed flux of particles from a black hole is known as Hawking radiation.
Starting from that point, Hawking argued that black holes must have a temperature. He and Jacob Bekenstein, an Israeli-American theoretical physicist who died in 2015, then concluded that the objects possess an entropy proportional to their surface areas. The advance laid the groundwork for the entire formalism of black hole thermodynamics. It has led to, among other things, the conjecture that our entire universe is in some respects like a hologram. Hawking radiation has never been observed, however, as it is expected to be far too weak to be spotted with any conceivable technology. Perhaps for that reason, Hawking was never honored with science’s most prestigious award, the Nobel Prize. He racked up numerous other awards however, including the Royal Society’s Copley Medal in 2006 and the Presidential Medal of Freedom in 2009.
Hawking was also known for making scientific wagers. Perhaps most famously he bet John Preskill, a theorist at the California Institute of Technology in Pasadena, that information that falls into a black hole would be lost from the universe forever, an idea that is inimical to quantum mechanics, which assumes information is never truly destroyed. Hawking saw no way for the information in, say, a computer chucked into a black hole to emerge unscrambled in the randomness Hawking radiation. Preskill and others argued that some as-yet-unknown principle would preserve the information. Hawking conceded the bet in 2004, presenting Preskill with an encyclopedia of baseball facts and statistics—a permanent record of arcane information. The issue remains controversial, however.
Hawking also became a celebrity, especially after the publication in 1988 of his first of seven popular books, A Brief History of Time. Inspiring people both through his deep insights into the most mysterious corners of the cosmos and his ability to succeed in spite of a disease that had been expected to take his life at an early age, Hawking became an inspiration to people the world over, appearing in several TV shows. Twice married and divorced, Hawking was father to three children—two sons and a daughter—by his first wife, Jane Hawking.
At his 75th birthday party in Cambridge last year, Hawking urged people to “look up at the stars and not down at your feet” and to explore the wonders of the world around them. “Be curious,” he said, according to a University of Cambridge statement, “and however difficult life may seem, there is always something you can do, and succeed at. It matters that you don’t just give up.”