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I post con tag "Stephen Hawking" archivio

Il trionfo della mente sulla materia

Res publica   14.03.18  

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."

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La tesi di Stephen Hawking

Geek   23.10.17  

La tesi di dottorato di Stephen Hawking sulle implicazioni dell'espansione dell'universo, discussa a Cambridge nel 1966, è gratuitamente scaricabile dal sito dell'università.

By making my PhD thesis Open Access, I hope to inspire people around the world to look up at the stars and not down at their feet; to wonder about our place in the universe and to try and make sense of the cosmos.
Anyone, anywhere in the world should have free, unhindered access to not just my research, but to the research of every great and enquiring mind across the spectrum of human understanding.

Each generation stands on the shoulders of those who have gone before them, just as I did as a young PhD student in Cambridge, inspired by the work of Isaac Newton, James Clerk Maxwell and Albert Einstein. It's wonderful to hear how many people have already shown an interest in downloading my thesis - hopefully they won't be disappointed now that they finally have access to it!

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Qualcosa sfugge ai buchi neri

Geek   27.01.14  

Stephen Hawking rivoluziona la sua stessa teoria sui buchi neri tentando di conciliarla con la seconda legge della termodinamica. Un orizzonte apparente sostituirebbe l'orizzonte degli eventi permettendo a energia e informazioni di sfuggire, in alcuni casi, al campo gravitazionale di un buco nero.

Most physicists foolhardy enough to write a paper claiming that "there are no black holes" -- at least not in the sense we usually imagine -- would probably be dismissed as cranks. But when the call to redefine these cosmic crunchers comes from Stephen Hawking, it's worth taking notice. In a paper posted online, the physicist, based at the University of Cambridge, UK, and one of the creators of modern black-hole theory, does away with the notion of an event horizon, the invisible boundary thought to shroud every black hole, beyond which nothing, not even light, can escape.

In its stead, Hawking's radical proposal is a much more benign "apparent horizon", which only temporarily holds matter and energy prisoner before eventually releasing them, albeit in a more garbled form.

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