Il trionfo della mente sulla materia

Stephen Hawking ricordato dal New York Times.

He went on to become his generation's leader in exploring gravity and the properties of black holes, the bottomless gravitational pits so deep and dense that not even light can escape them.

That work led to a turning point in modern physics, playing itself out in the closing months of 1973 on the walls of his brain when Dr. Hawking set out to apply quantum theory, the weird laws that govern subatomic reality, to black holes. In a long and daunting calculation, Dr. Hawking discovered to his befuddlement that black holes — those mythological avatars of cosmic doom — were not really black at all. In fact, he found, they would eventually fizzle, leaking radiation and particles, and finally explode and disappear over the eons.

Nobody, including Dr. Hawking, believed it at first — that particles could be coming out of a black hole. "I wasn't looking for them at all," he recalled in an interview in 1978. "I merely tripped over them. I was rather annoyed."

That calculation, in a thesis published in 1974 in the journal Nature under the title "Black Hole Explosions?," is hailed by scientists as the first great landmark in the struggle to find a single theory of nature — to connect gravity and quantum mechanics, those warring descriptions of the large and the small, to explain a universe that seems stranger than anybody had thought.

The discovery of Hawking radiation, as it is known, turned black holes upside down. It transformed them from destroyers to creators — or at least to recyclers — and wrenched the dream of a final theory in a strange, new direction.

"You can ask what will happen to someone who jumps into a black hole," Dr. Hawking said in an interview in 1978. "I certainly don't think he will survive it."

"On the other hand," he added, "if we send someone off to jump into a black hole, neither he nor his constituent atoms will come back, but his mass energy will come back. Maybe that applies to the whole universe."

Dennis W. Sciama, a cosmologist and Dr. Hawking's thesis adviser at Cambridge, called Hawking's thesis in Nature "the most beautiful paper in the history of physics."