Stephen Hawking was a theoretical physicist and cosmologist best known for advancing theoretical models on black holes and cosmic inflation, which he discusses in his popular writing on time and space.
Hawking's university education began in , when, at age 17, he attended University College, Oxford, to study physics. Seeking a PhD at University of Cambridge, Hawking was disappointed to learn that the esteemed astronomer Fred Hoyle — who is now famous for coining the term ' Big Bang ' theory by mocking it on radio — wouldn't be taking any more students. His supervisor was a relatively unknown researcher by the name of Dennis Sciama.
What Sciama lacked in fame he more than made up for in mentorship, encouraging a young Hawking to follow his interests. Where Hoyle was dismissive of the Big Bang, Hawking became its champion.
Following Roger Penrose's work on the infinitely dense point of spacetime at the centres of black holes, Hawking used the mathematics of general relativity to argue the origins of the Universe itself could be found in similar physics. In , Hawking and Penrose published their now famous theory on cosmological singularities, which describes the starting energy of the Universe all contained in an infinitely small volume.
Half an hour into the lecture a huge crash breaks the spell. He is crumpled at an odd angle, shaking violently. Is he dying? Murmur, murmur, murmur. Hawking led a full and complete life, despite his illness, and his scientific work inspired generations of students to study problems of gravity and quantum mechanics. This article will touch upon a few of his primary scientific accomplishments — in particular, his work on classical gravity and singularities, his famous results on black-hole thermodynamics and Hawking radiation, and his efforts to quantize gravity.
As a young man, Hawking worked on general relativity, investigating the problem of how black holes form. His mastery of geometrical methods allowed him to prove a set of remarkable theorems about the circumstances under which swirling clouds of matter undergo gravitational collapse, giving rise to gravitational singularities.
A Taken together, the Penrose—Hawking singularity theorems provide strong evidence for the necessary formation of black holes in our universe. It is a prediction that has been confirmed both by observational evidence of galactic X-ray sources such as Cygnus X-1, and by the recent and spectacular findings from the Laser Interferometer Gravitational-Wave Observatory LIGO , which has detected the gravitational waves emitted by colliding black holes.
Consequently, Hawking and colleagues noted that the area of the horizon was analogous to entropy in the second law of thermodynamics: according to which entropy does not decrease, and tends to increase. But now there is a problem. But what is the temperature of a black hole? After all, it is black and, at least classically, no radiation can escape from it.
In Hawking solved the problem of black-hole temperature in spectacular fashion. General relativity is about the reconciliation of different perceptions of the universe. Special relativity reconciles the perceptions of observers moving at different velocities, but all perceiving the speed of light to be the same.
General relativity reconciles the perceptions of different observers who choose to assign different coordinate systems to events in a curved space—time. Once quantum mechanics is thrown into the mix, a remarkable feature arises: inertial observers and accelerated observers have an entirely different perception of the vacuum state — the state with no particles.
In quantum field theory, the vacuum is not empty — it bubbles with virtual particle—antiparticle pairs. An inertial observer sees those virtual pairs come into existence and then go away again before they can be detected. Consequently, gravitational fields can create particles. The black hole radiates.
His calculations were confirmed by a variety of alternative approaches, which showed that Hawking radiation was a ubiquitous feature of space—times with horizons, including de Sitter space, and space—time as viewed by an accelerated observer. The result also spurred interest in the theory of quantum entanglement.
The entropy of the Hawking radiation can then be identified with the entanglement entropy of the black hole, where the number of bits of entanglement is proportional to the area of the event horizon.
Hawking radiation is regarded by physicists as the one truly reliable result that we actually possess about quantum mechanics and gravity. However, it seems safe to say that Hawking radiation is the one result on quantum mechanics and gravity that is accepted by the entire community of physicists working on the subject. A Brief History of Time also wasn't as easy to understand as some had hoped.
So in , Hawking followed up his book with The Universe in a Nutshell , which offered a more illustrated guide to cosmology's big theories. In , Hawking authored the even more accessible A Briefer History of Time , which further simplified the original work's core concepts and touched upon the newest developments in the field like string theory.
Together these three books, along with Hawking's own research and papers, articulated the physicist's personal search for science's Holy Grail: a single unifying theory that can combine cosmology the study of the big with quantum mechanics the study of the small to explain how the universe began.
This kind of ambitious thinking allowed Hawking, who claimed he could think in 11 dimensions, to lay out some big possibilities for humankind.
He was convinced that time travel is possible, and that humans may indeed colonize other planets in the future. In September , Hawking spoke against the idea that God could have created the universe in his book The Grand Design. Hawking previously argued that belief in a creator could be compatible with modern scientific theories.
In this work, however, he concluded that the Big Bang was the inevitable consequence of the laws of physics and nothing more. The Grand Design was Hawking's first major publication in almost a decade. Within his new work, Hawking set out to challenge Isaac Newton 's belief that the universe had to have been designed by God, simply because it could not have been born from chaos.
In a very simple sense, the nerves that controlled his muscles were shutting down. At the time, doctors gave him two and a half years to live. Hawking first began to notice problems with his physical health while he was at Oxford — on occasion he would trip and fall, or slur his speech — but he didn't look into the problem until , during his first year at Cambridge.
For the most part, Hawking had kept these symptoms to himself. But when his father took notice of the condition, he took Hawking to see a doctor. For the next two weeks, the year-old college student made his home at a medical clinic, where he underwent a series of tests. Eventually, however, doctors did diagnose Hawking with the early stages of ALS. It was devastating news for him and his family, but a few events prevented him from becoming completely despondent.
The first of these came while Hawking was still in the hospital. There, he shared a room with a boy suffering from leukemia. Relative to what his roommate was going through, Hawking later reflected, his situation seemed more tolerable. Not long after he was released from the hospital, Hawking had a dream that he was going to be executed.
He said this dream made him realize that there were still things to do with his life. In a sense, Hawking's disease helped turn him into the noted scientist he became. Before the diagnosis, Hawking hadn't always focused on his studies.
With the sudden realization that he might not even live long enough to earn his Ph. As physical control over his body diminished he'd be forced to use a wheelchair by , the effects of his disease started to slow down.
Over time, however, Hawking's ever-expanding career was accompanied by an ever-worsening physical state. By the mids, the Hawking family had taken in one of Hawking's graduate students to help manage his care and work. He could still feed himself and get out of bed, but virtually everything else required assistance. In addition, his speech had become increasingly slurred, so that only those who knew him well could understand him. In he lost his voice for good following a tracheotomy. The resulting situation required hour nursing care for the acclaimed physicist.
It also put in peril Hawking's ability to do his work. The predicament caught the attention of a California computer programmer, who had developed a speaking program that could be directed by head or eye movement. The invention allowed Hawking to select words on a computer screen that were then passed through a speech synthesizer.
At the time of its introduction, Hawking, who still had use of his fingers, selected his words with a handheld clicker. Eventually, with virtually all control of his body gone, Hawking directed the program through a cheek muscle attached to a sensor.
Through the program, and the help of assistants, Hawking continued to write at a prolific rate. His work included numerous scientific papers, of course, but also information for the non-scientific community. Hawking's health remained a constant concern—a worry that was heightened in when he failed to appear at a conference in Arizona because of a chest infection.
In April, Hawking, who had already announced he was retiring after 30 years from the post of Lucasian Professor of Mathematics at Cambridge, was rushed to the hospital for being what university officials described as "gravely ill," though he later made a full recovery. Photo: Frederick M. In , Hawking's research turned him into a celebrity within the scientific world when he showed that black holes aren't the information vacuums that scientists had thought they were.
In simple terms, Hawking demonstrated that matter, in the form of radiation, can escape the gravitational force of a collapsed star. Another young cosmologist, Roger Penrose, had earlier discovered groundbreaking findings about the fate of stars and the creation of black holes, which tapped into Hawking's own fascination with how the universe began. Hawking was named a fellow of the Royal Society at the age of 32, and later earned the prestigious Albert Einstein Award, among other honors.
He also earned teaching stints at Caltech in Pasadena, California, where he served as visiting professor, and at Gonville and Caius College in Cambridge. In August , Hawking appeared at a conference in Sweden to discuss new theories about black holes and the vexing "information paradox.
In a March interview on Neil deGrasse Tyson 's Star Talk , Hawking addressed the topic of "what was around before the Big Bang" by stating there was nothing around. He said by applying a Euclidean approach to quantum gravity, which replaces real time with imaginary time, the history of the universe becomes like a four-dimensional curved surface, with no boundary. He suggested picturing this reality by thinking of imaginary time and real time as beginning at the Earth's South Pole, a point of space-time where the normal laws of physics hold; as there is nothing "south" of the South Pole, there was also nothing before the Big Bang.
In , at the age of 65, Hawking made an important step toward space travel. While visiting the Kennedy Space Center in Florida, he was given the opportunity to experience an environment without gravity.
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