The physicist and author of A Brief History of Time has died at his home in Cambridge. His children said: ‘We will miss him for ever’
Tributes poured in on Wednesday to Stephen Hawking, the brightest star in the firmament of science, whose insights shaped modern cosmology and inspired global audiences in the millions. He died at the age of 76 in the early hours of Wednesday morning.
A brief history of Stephen Hawking's Brief History of Time Read more
In a statement that confirmed his death at home in Cambridge, Hawking’s children said: “We are deeply saddened that our beloved father passed away today. He was a great scientist and an extraordinary man whose work and legacy will live on for many years. His courage and persistence with his brilliance and humour inspired people across the world.
“He once said: ‘It would not be much of a universe if it wasn’t home to the people you love.’ We will miss him for ever.”
For fellow scientists and loved ones, it was Hawking’s intuition and wicked sense of humour that marked him out as much as the fierce intellect that, coupled with his illness, came to symbolise the unbounded possibilities of the human mind.
“Stephen was far from being the archetypal unworldy or nerdish scientist. His personality remained amazingly unwarped by his frustrations,” said Lord Rees, the astronomer royal, who praised Hawking’s half century of work as an “inspiring crescendo of achievement.” He added: “Few, if any, of Einstein’s successors have done more to deepen our insights into gravity, space and time.”
The Canadian astronaut Chris Hadfield lamented on Twitter that “Genius is so fine and rare”, while Theresa May noted Hawking’s “courage, humour and determination to get the most from life was an inspiration.” The US rock band Foo Fighters was more succinct, calling Hawking a “fucking legend.”
I’m not afraid of death, but I’m in no hurry to die. I have so much I want to do first Stephen Hawking
Hawking was driven to Wagner, but not the bottle, when he was diagnosed with motor neurone disease in 1963 at the age of 21. Doctors expected him to live for only two more years. But Hawking had a form of the disease that progressed more slowly than usual. He survived for more than half a century.
Hawking once estimated he worked only 1,000 hours during his three undergraduate years at Oxford. In his finals, he came borderline between a first- and second-class degree. Convinced that he was seen as a difficult student, he told his viva examiners that if they gave him a first he would move to Cambridge to pursue his PhD. Award a second and he threatened to stay. They opted for a first.
Those who live in the shadow of death are often those who live most. For Hawking, the early diagnosis of his terminal disease, and witnessing the death from leukaemia of a boy he knew in hospital, ignited a fresh sense of purpose. “Although there was a cloud hanging over my future, I found, to my surprise, that I was enjoying life in the present more than before. I began to make progress with my research,” he once said. Embarking on his career in earnest, he declared: “My goal is simple. It is a complete understanding of the universe, why it is as it is and why it exists at all.”
He began to use crutches in the 1960s, but long fought the use of a wheelchair. When he finally relented, he became notorious for his wild driving along the streets of Cambridge, not to mention the intentional running over of students’ toes and the occasional spin on the dance floor at college parties.
The life of Stephen Hawking – in pictures Read more
Hawking’s first major breakthrough came in 1970, when he and Roger Penrose applied the mathematics of black holes to the universe and showed that a singularity, a region of infinite curvature in spacetime, lay in our distant past: the point from which came the big bang.
Penrose found he was able to talk with Hawking even as the latter’s speech failed. Hawking, he said, had an absolute determination not to let anything get in his way. “He thought he didn’t have long to live, and he really wanted to get as much as he could done at that time.”
There is no heaven or afterlife for broken-down computers; that is a fairy story for people afraid of the dark Stephen Hawking
In 1974 Hawking drew on quantum theory to declare that black holes should emit heat and eventually pop out of existence. For normal-sized black holes, the process is extremely slow, but miniature black holes would release heat at a spectacular rate, eventually exploding with the energy of a million one-megaton hydrogen bombs.
His proposal that black holes radiate heat stirred up one of the most passionate debates in modern cosmology. Hawking argued that if a black hole could evaporate, all the information that fell inside over its lifetime would be lost forever. It contradicted one of the most basic laws of quantum mechanics, and plenty of physicists disagreed. Hawking came round to believing the more common, if no less baffling, explanation that information is stored at a black hole’s event horizon, and encoded back into radiation as the black hole radiates.
Marika Taylor, a former student of Hawking’s and now professor of theoretical physics at Southampton University, remembers how Hawking announced his U-turn on the information paradox to his students. He was discussing their work with them in the pub when Taylor noticed he was turning his speech synthesiser up to the max. “I’m coming out!” he bellowed. The whole pub turned around and looked at the group before Hawking turned the volume down and clarified the statement: “I’m coming out and admitting that maybe information loss doesn’t occur.” He had, Taylor said, “a wicked sense of humour.”
Hawking’s run of radical discoveries led to his election in 1974 to the Royal Society at the young age of 32. Five years later, he became the Lucasian professor of mathematics at Cambridge, arguably Britain’s most distinguished chair, and a post formerly held by Isaac Newton, Charles Babbage and Paul Dirac, one of the founding fathers of quantum mechanics.
Hawking’s seminal contributions continued through the 1980s. The theory of cosmic inflation holds that the fledgling universe went through a period of terrific expansion. In 1982, Hawking was among the first to show how quantum fluctuations – tiny variations in the distribution of matter – might give rise through inflation to the spread of galaxies in the universe. In these tiny ripples lay the seeds of stars, planets and life as we know it. “It is one of the most beautiful ideas in the history of science,” said Max Tegmark, a physics professor at MIT.
But it was A Brief History of Time that rocketed Hawking to stardom. Published for the first time in 1988, the title made the Guinness Book of Records after it stayed on the Sunday Times bestsellers list for an unprecedented 237 weeks. It sold 10m copies and was translated into 40 different languages. Some credit must go to Hawking’s editor at Bantam, Peter Guzzardi, who took the original title: “From the Big Bang to Black Holes: A Short History of Time”, turned it around, and changed the “Short” to “Brief”. Nevertheless, wags called it the greatest unread book in history.
Hawking married his college sweetheart, Jane Wilde, in 1965, two years after his diagnosis. She first set eyes on him in 1962, lolloping down the street in St Albans, his face down, covered by an unruly mass of brown hair. A friend warned her she was marrying into “a mad, mad family”. With all the innocence of her 21 years, she trusted that Stephen would cherish her, she wrote in her 2013 book, Travelling to Infinity: My Life With Stephen.
In 1985, during a trip to Cern, Hawking was taken to hospital with an infection. He was so ill that doctors asked Jane if they should withdraw life support. She refused, and Hawking was flown back to Addenbrooke’s Hospital in Cambridge for a lifesaving tracheotomy. The operation saved his life but destroyed his voice. The couple had three children, but the marriage broke down in 1991. Hawking’s progressive condition, his demands on Jane, and his refusal to discuss his illness, were destructive forces the relationship could not endure, she said. Jane wrote of him being “a child possessed of a massive and fractious ego,” and how husband and wife became “master” and “slave”.
My goal is simple. It is a complete understanding of the universe, why it is as it is and why it exists at all Stephen Hawking
Four years later, Hawking married Elaine Mason, one of the nurses employed to give him round-the-clock care. The marriage lasted 11 years, during which Cambridgeshire police investigated a series of alleged assaults on Hawking. The physicist denied that Elaine was involved, and refused to cooperate with police, who dropped the investigation.
Hawking was not, perhaps, the greatest physicist of his time, but in cosmology he was a towering figure. There is no perfect proxy for scientific worth, but Hawking won the Albert Einstein award, the Wolf prize, the Copley medal, and the Fundamental Physics prize. The Nobel prize, however, eluded him.
He was fond of scientific wagers, despite a knack for losing them. In 1975, he bet the US physicist Kip Thorne a subscription to Penthouse that the cosmic x-ray source Cygnus X-1 was not a black hole. He lost in 1990. In 1997, Hawking and Thorne bet John Preskill an encyclopaedia that information must be lost in black holes. Hawking conceded in 2004. In 2012, Hawking lost $100 to Gordon Kane for betting that the Higgs boson would not be discovered.
He lectured at the White House during the Clinton administration – his oblique references to the Monica Lewinsky episode were evidently lost on those who screened his speech – and returned in 2009 to receive the presidential medal of freedom from Barack Obama. His life was played out in biographies and documentaries, most recently The Theory of Everything, in which Eddie Redmayne played him. He appeared on The Simpsons and played poker with Einstein and Newton on Star Trek: The Next Generation. He delivered gorgeous put-downs on The Big Bang Theory. “What do Sheldon Cooper and a black hole have in common?” Hawking asked the fictional Caltech physicist whose IQ comfortably outstrips his social skills. After a pause, the answer came: “They both suck.”
Hawking has argued that for humanity to survive it must spread out into space, and has warned against the worst applications of artificial intelligence, including autonomous weapons.
Stephen Hawking – obituary by Roger Penrose Read more
Hawking was happy to court controversy and was accused of being sexist and misogynist. He turned up at Stringfellows lap dancing club in 2003, and years later declared women “a complete mystery”. In 2013, he boycotted a major conference in Israel on the advice of Palestinian academics.
Some of his most outspoken comments offended the religious. In his 2010 book, Grand Design, he declared that God was not needed to set the universe going, and in an interview with the Guardian a year later, dismissed the comforts of religious belief.
“I regard the brain as a computer which will stop working when its components fail,” he said. “There is no heaven or afterlife for broken-down computers; that is a fairy story for people afraid of the dark.”
He spoke also of death, an eventuality that sat on a more distant horizon than doctors thought. “I’m not afraid of death, but I’m in no hurry to die,” he said. “I have so much I want to do first.”
What astounded those around him was how much he did achieve. He leaves his three children, from his first marriage to Jane Wilde, and three grandchildren.
(CNN) Stephen Hawking , the brilliant British theoretical physicist who overcame a debilitating disease to publish wildly popular books probing the mysteries of the universe, has died, according to a family spokesman. He was 76.
Considered by many to be the world's greatest living scientist, Hawking was also a cosmologist, astronomer, mathematician and author of numerous books including the landmark "A Brief History of Time," which has sold more than 10 million copies.
With fellow physicist Roger Penrose, Hawking merged Einstein's theory of relativity with quantum theory to suggest that space and time would begin with the Big Bang and end in black holes. Hawking also discovered that black holes were not completely black but emit radiation and would likely eventually evaporate and disappear.
"A star just went out in the cosmos," Lawrence Krauss, a theoretical physicist and cosmologist, wrote on Twitter. "We have lost an amazing human being."
Hawking suffered from ALS (amyotrophic lateral sclerosis) , a neurodegenerative disease also known as Lou Gehrig's Disease, which is usually fatal within a few years. He was diagnosed in 1963, when he was 21, and doctors initially gave him only a few years to live.
The disease left Hawking wheelchair-bound and paralyzed. He was able to move only a few fingers on one hand and was completely dependent on others or on technology for virtually everything -- bathing, dressing, eating, even speech.
Hawking used a speech synthesizer that allowed him to speak in a computerized voice with an American accent.
"I try to lead as normal a life as possible, and not think about my condition, or regret the things it prevents me from doing, which are not that many," he wrote on his website.
"I have been lucky that my condition has progressed more slowly than is often the case. But it shows that one need not lose hope."
Cosmologist Stephen Hawking on October 10, 1979, in Princeton, New Jersey.
Hawking was married twice. He and his first wife, Jane Wilde, wed when he was still a graduate student and remained together for 30 years before divorcing in 1995. Hawking was later married for 11 years to Elaine Mason, one of his former nurses.
Hawking was born in Oxford, England, on what an auspicious date: January 8, 1942 -- the 300th anniversary of the death of astronomer and physicist Galileo Galilei.
In an exclusive interview with CNN in October 2008, Hawking said that if humans can survive the next 200 years and learn to live in space, then our future will be bright.
"I believe that the long-term future of the human race must be in space," Hawking told CNN's Becky Anderson.
"It will be difficult enough to avoid disaster on planet Earth in the next 100 years, let alone next thousand, or million. The human race shouldn't have all its eggs in one basket, or on one planet. Let's hope we can avoid dropping the basket until we have spread the load."
At Cambridge, he held the position of Lucasian Professor of Mathematics -- the prestigious post previously held by Sir Isaac Newton, widely considered one of the greatest scientists in modern history -- for 30 years until 2009.
Yet Hawking once said if he had the chance to meet either Newton or Marilyn Monroe, he would opt for the movie star.
After stepping down, Hawking continued to work at the university as director of research at the Institute for Theoretical Cosmology. The following year, he co-authored "The Grand Design" with Leonard Mlodinow.
After the book was published in 2010, Hawking told CNN that science can explain the universe without the need for a creator.
"Gravity and quantum theory caused universes to be created spontaneously out of nothing," Hawking said in 2010. "God may exist, but science can explain the universe without the need for a creator."
"Science is increasingly answering questions that used to be the province of religion," he added.
JUST WATCHED Hawking on the creation of the universe (2010) Replay More Videos ... MUST WATCH Hawking on the creation of the universe (2010) 02:12
Hawking became a hero to math and science geeks and a pop-culture figure, guest-starring as himself on "Star Trek: The Next Generation" and "The Simpsons." His life was dramatized in the 2014 movie, "The Theory of Everything."
He had at least 12 honorary degrees and was awarded the CBE in 1982. A CBE, or Commander in the Most Excellent Order of the British Empire, is considered a major honor for a British citizen and is one rank below knighthood.
Despite being a British citizen he was awarded the Presidential Medal of Freedom, the US's highest civilian honor, in 2009 by President Barack Obama.
In September 2016, Hawking joined 375 "concerned" scientists in penning an open letter criticizing then-presidential candidate Donald Trump, citing the threat of climate change and blasting his push for the US to leave the Paris accord.
"His passing has left an intellectual vacuum in his wake," tweeted Neil deGrasse Tyson. "But it's not empty. Think of it as a kind of vacuum energy permeating the fabric of spacetime that defies measure."
His passing has left an intellectual vacuum in his wake. But it's not empty. Think of it as a kind of vacuum energy permeating the fabric of spacetime that defies measure. Stephen Hawking, RIP 1942-2018. pic.twitter.com/nAanMySqkt — Neil deGrasse Tyson (@neiltyson) March 14, 2018
Hawking leaves behind three children and three grandchildren. "We are deeply saddened that our beloved father passed away today," Hawking's children, Lucy, Robert and Tim, said in a statement. "He was a great scientist and an extraordinary man whose work and legacy will live on for many years. His courage and persistence with his brilliance and humor inspired people across the world."
"He once said, 'It would not be much of a universe if it wasn't home to the people you love.' We will miss him forever."
Using the Hubble Space Telescope and other sophisticated tools of observation and analysis, however, astronomers have identified hundreds of objects that are too massive and dark to be anything but black holes, including a supermassive one at the center of the Milky Way. According to current theory, the universe should contain billions more.
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As part of his Ph.D. thesis in 1966, Dr. Hawking showed that when you ran the film of the expanding universe backward, you would find that such a singularity had to have existed sometime in cosmic history; space and time, that is, must have had a beginning. He, Dr. Penrose and a rotating cast of colleagues went on to publish a series of theorems about the behavior of black holes and the dire fate of anything caught in them.
A Calculation in His Head
Dr. Hawking’s signature breakthrough resulted from a feud with the Israeli theoretical physicist Jacob Bekenstein, then a Princeton graduate student, about whether black holes could be said to have entropy, a thermodynamic measure of disorder. Dr. Bekenstein said they could, pointing out a close analogy between the laws that Dr. Hawking and his colleagues had derived for black holes and the laws of thermodynamics.
Dr. Hawking said no. To have entropy, a black hole would have to have a temperature. But warm objects, from a forehead to a star, radiate a mixture of electromagnetic radiation, depending on their exact temperatures. Nothing could escape a black hole, and so its temperature had to be zero. “I was very down on Bekenstein,” Dr. Hawking recalled.
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To settle the question, Dr. Hawking decided to investigate the properties of atom-size black holes. This, however, required adding quantum mechanics, the paradoxical rules of the atomic and subatomic world, to gravity, a feat that had never been accomplished. Friends turned the pages of quantum theory textbooks as Dr. Hawking sat motionless staring at them for months. They wondered if he was finally in over his head.
When he eventually succeeded in doing the calculation in his head, it indicated to his surprise that particles and radiation were spewing out of black holes. Dr. Hawking became convinced that his calculation was correct when he realized that the outgoing radiation would have a thermal spectrum characteristic of the heat radiated by any warm body, from a star to a fevered forehead. Dr. Bekenstein had been right.
Dr. Hawking even figured out a way to explain how particles might escape a black hole. According to quantum principles, the space near a black hole would be teeming with “virtual” particles that would flash into existence in matched particle-and-antiparticle pairs — like electrons and their evil twin opposites, positrons — out of energy borrowed from the hole’s intense gravitational field.
They would then meet and annihilate each other in a flash of energy, repaying the debt for their brief existence. But if one of the pair fell into the black hole, the other one would be free to wander away and become real. It would appear to be coming from the black hole and taking energy away from it.
But those, he cautioned, were just words. The truth was in the math.
“The most important thing about Hawking radiation is that it shows that the black hole is not cut off from the rest of the universe,” Dr. Hawking said.
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It also meant that black holes had a temperature and had entropy. In thermodynamics, entropy is a measure of wasted heat. But it is also a measure of the amount of information — the number of bits — needed to describe what is in a black hole. Curiously, the number of bits is proportional to the black hole’s surface area, not its volume, meaning that the amount of information you could stuff into a black hole is limited by its area, not, as one might naïvely think, its volume.
That result has become a litmus test for string theory and other pretenders to a theory of quantum gravity. It has also led to speculations that we live in a holographic universe, in which three-dimensional space is some kind of illusion.
Andrew Strominger, a Harvard string theorist, said of the holographic theory, “If it’s really true, it’s a deep and beautiful property of our universe — but not an obvious one.”
To ‘Know the Mind of God’
The discovery of black hole radiation also led to a 30-year controversy over the fate of things that had fallen into a black hole.
Dr. Hawking initially said that detailed information about whatever had fallen in would be lost forever because the particles coming out would be completely random, erasing whatever patterns had been present when they first fell in. Paraphrasing Einstein’s complaint about the randomness inherent in quantum mechanics, Dr. Hawking said, “God not only plays dice with the universe, but sometimes throws them where they can’t be seen.”
Many particle physicists protested that this violated a tenet of quantum physics, which says that knowledge is always preserved and can be retrieved. Leonard Susskind, a Stanford physicist who carried on the argument for decades, said, “Stephen correctly understood that if this was true, it would lead to the downfall of much of 20th-century physics.”
On another occasion, he characterized Dr. Hawking to his face as “one of the most obstinate people in the world; no, he is the most infuriating person in the universe.” Dr. Hawking grinned.
Dr. Hawking admitted defeat in 2004. Whatever information goes into a black hole will come back out when it explodes. One consequence, he noted sadly, was that one could not use black holes to escape to another universe. “I’m sorry to disappoint science fiction fans,” he said.
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Despite his concession, however, the information paradox, as it is known, has become one of the hottest and deepest topics in theoretical physics. Physicists say they still do not know how information gets in or out of black holes.
Raphael Bousso of the University of California, Berkeley, and a former student of Dr. Hawking’s, said the present debate had raised “by another few notches” his estimation of the “stupendous magnitude” of Dr. Hawking’s original discovery.
In 1974, Dr. Hawking was elected a Fellow of the Royal Society, the world’s oldest scientific organization; in 1979, he was appointed to the Lucasian chair of mathematics at Cambridge, a post once held by Isaac Newton. “They say it’s Newton’s chair, but obviously it’s been changed,” he liked to quip.
Dr. Hawking also made yearly visits to the California Institute of Technology in Pasadena, which became like a second home. In 2008, he joined the Perimeter Institute for Theoretical Physics in Waterloo, Ontario, as a visiting researcher.
Having conquered black holes, Dr. Hawking set his sights on the origin of the universe and on eliminating that pesky singularity at the beginning of time from models of cosmology. If the laws of physics could break down there, they could break down everywhere.
In a meeting at the Vatican in 1982, he suggested that in the final theory there should be no place or time when the laws broke down, even at the beginning. He called the notion the “no boundary” proposal.
With James Hartle of the Institute for Theoretical Physics in Santa Barbara, Calif., Dr. Hawking envisioned the history of the universe as a sphere like the Earth. Cosmic time corresponds to latitude, starting with zero at the North Pole and progressing southward.
Although time started there, the North Pole was nothing special; the same laws applied there as everywhere else. Asking what happened before the Big Bang, Dr. Hawking said, was like asking what was a mile north of the North Pole — it was not any place, or any time.
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By then, string theory, which claimed finally to explain both gravity and the other forces and particles of nature as tiny microscopically vibrating strings, like notes on a violin, was the leading candidate for a “theory of everything.”
In “A Brief History of Time,” Dr. Hawking concluded that “if we do discover a complete theory” of the universe, “it should in time be understandable in broad principle by everyone, not just a few scientists.”
He added, “Then we shall all, philosophers, scientists and just ordinary people, be able to take part in the discussion of why it is that we and the universe exist.”
“If we find the answer to that,” he continued, “it would be the ultimate triumph of human reason — for then we would know the mind of God.”
Until 1974, Dr. Hawking was still able to feed himself and to get in and out of bed. At Jane’s insistence, he would drag himself, hand over hand, up the stairs to the bedroom in his Cambridge home every night, in an effort to preserve his remaining muscle tone. After 1980, care was supplemented by nurses.
Dr. Hawking retained some control over his speech up to 1985. But on a trip to Switzerland, he came down with pneumonia. The doctors asked Jane if she wanted his life support turned off, but she said no. To save his life, doctors inserted a breathing tube. He survived, but his voice was permanently silenced.
Speaking With the Eyes
It appeared for a time that he would be able to communicate only by pointing at individual letters on an alphabet board. But when a computer expert, Walter Woltosz, heard about Dr. Hawking’s condition, he offered him a program he had written called Equalizer. By clicking a switch with his still-functioning fingers, Dr. Hawking was able to browse through menus that contained all the letters and more than 2,500 words.
Word by word — and when necessary, letter by letter — he could build up sentences on the computer screen and send them to a speech synthesizer that vocalized for him. The entire apparatus was fitted to his motorized wheelchair.
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Even when too weak to move a finger, he communicated through the computer by way of an infrared beam, which he activated by twitching his right cheek or blinking his eye. The system was expanded to allow him to open and close the doors in his office and to use the telephone and internet without aid.
Although he averaged fewer than 15 words per minute, Dr. Hawking found he could speak through the computer better than he had before losing his voice. His only complaint, he confided, was that the speech synthesizer, manufactured in California, gave him a new vocal inflection.
“Please pardon my American accent,” he used to say.
His decision to write “A Brief History of Time” was prompted, he said, by a desire to share his excitement about “the discoveries that have been made about the universe” with “the public that paid for the research.” He wanted to make the ideas so accessible that the book would be sold in airports.
He also hoped to earn enough money to pay for his children’s education. He did. The book’s extraordinary success made him wealthy, a hero to disabled people everywhere and even more famous.
The news media followed his movements and activities over the years, from visiting the White House to meeting the Dallas Cowboys cheerleaders, and reported his opinions on everything from national health care (socialized medicine in England had kept him alive) to communicating with extraterrestrials (maybe not a good idea, he said), as if he were a rolling Delphic Oracle.
Asked by New Scientist magazine what he thought about most, Dr. Hawking answered: “Women. They are a complete mystery.”
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In 1990, Dr. Hawking and his wife separated after 25 years of marriage; Jane Hawking wrote about their years together in two books, “Music to Move the Stars: A Life With Stephen Hawking” and “Traveling to Infinity: My Life With Stephen.” The latter became the basis of the movie “The Theory of Everything.”
In 1995, he married Elaine Mason, a nurse who had cared for him since his bout of pneumonia. She had been married to David Mason, the engineer who had attached Dr. Hawking’s speech synthesizer to his wheelchair.
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In 2004, British newspapers reported that the Cambridge police were investigating allegations that Elaine had abused Dr. Hawking, but no charges were filed, and Dr. Hawking denied the accusations. They later divorced.
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His survivors include his children, Robert, Lucy and Tim, and three grandchildren.
‘There Is No Heaven’
Among his many honors, Dr. Hawking was named a commander of the British Empire in 1982. In the summer of 2012, he had a star role in the opening of the Paralympics Games in London. The only thing lacking was the Nobel Prize, and his explanation for this was characteristically pithy: “The Nobel is given only for theoretical work that has been confirmed by observation. It is very, very difficult to observe the things I have worked on.”
Dr. Hawking was a strong advocate of space exploration, saying it was essential to the long-term survival of the human race. “Life on Earth is at the ever-increasing risk of being wiped out by a disaster, such as sudden global nuclear war, a genetically engineered virus or other dangers we have not yet thought of,” he told an audience in Hong Kong in 2007.
Media playback is unsupported on your device Media caption Looking back on the life of Stephen Hawking
World renowned physicist Stephen Hawking has died at the age of 76.
He died peacefully at his home in Cambridge in the early hours of Wednesday, his family said.
The British scientist was famed for his work with black holes and relativity, and wrote several popular science books including A Brief History of Time.
At the age of 22 Prof Hawking was given only a few years to live after being diagnosed with a rare form of motor neurone disease.
The illness left him in a wheelchair and largely unable to speak except through a voice synthesiser.
In a statement his children, Lucy, Robert and Tim, said: "We are deeply saddened that our beloved father passed away today.
"He was a great scientist and an extraordinary man whose work and legacy will live on for many years."
They praised his "courage and persistence" and said his "brilliance and humour" inspired people across the world.
"He once said, 'It would not be much of a universe if it wasn't home to the people you love.' We will miss him forever."
A book of condolence has been opened at Gonville and Caius College in Cambridge, where Prof Hawking was a fellow.
Media playback is unsupported on your device Media caption Professor Brian Cox on the legacy and wonder of Hawking's work
Prof Hawking was the first to set out a theory of cosmology as a union of relativity and quantum mechanics.
He also discovered that black holes leak energy and fade to nothing - a phenomenon that would later become known as Hawking radiation.
Through his work with mathematician Sir Roger Penrose he demonstrated that Einstein's general theory of relativity implies space and time would have a beginning in the Big Bang and an end in black holes.
The scientist gained popularity outside the academic world and appeared in several TV shows including The Simpsons, Red Dwarf and The Big Bang Theory.
He was portrayed in both TV and film - recently by Oscar winner Eddie Redmayne in The Theory of Everything, which charted his rise to fame and relationship with his first wife, Jane.
The actor paid tribute to him, saying: "We have lost a truly beautiful mind, an astonishing scientist and the funniest man I have ever had the pleasure to meet."
Benedict Cumberbatch, who played Prof Hawking in a BBC drama, said he was "a true inspiration for me and for millions around the world".
Image copyright BBC/PA Image caption Stephen Hawking was portrayed on TV and film by Benedict Cumberbatch and Eddie Redmayne
His most famous book - A Brief History of Time - has now shot to the top of the Amazon Best Sellers list.
The Motor Neurone Disease Association, of which Prof Hawking had been a patron since 2008, reported that its website had crashed because of an influx of donations to the charity.
Factfile: Stephen Hawking
Born 8 January 1942 in Oxford, England
Earned place at Oxford University to read natural science in 1959, before studying for his PhD at Cambridge
By 1963, was diagnosed with motor neurone disease and given two years to live
Outlined his theory that black holes emit "Hawking radiation" in 1974
In 1979, he became the Lucasian Professor of Mathematics at Cambridge - a post once held by Sir Isaac Newton
Published his book A Brief History of Time in 1988, which has sold more than 10 million copies
In the late 1990s, he was reportedly offered a knighthood, but 10 years later revealed he had turned it down over issues with the government's funding for science
Tributes have poured in for Prof Hawking since the announcement of his death.
Prof Lord Martin Rees, the Astronomer Royal, who was at university with Prof Hawking when he was diagnosed, said his friend had "amazing willpower and determination".
Prime Minister Theresa May called him a "brilliant and extraordinary mind" and "one of the great scientists of his generation".
Labour leader Jeremy Corbyn praised the scientist for his "determination to explain the mysteries of the cosmos" and his "burning passion to protect our National Health Service."
Skip Twitter post by @NASA Remembering Stephen Hawking, a renowned physicist and ambassador of science. His theories unlocked a universe of possibilities that we & the world are exploring. May you keep flying like superman in microgravity, as you said to astronauts on @Space_Station in 2014 pic.twitter.com/FeR4fd2zZ5 — NASA (@NASA) March 14, 2018 Report
Sir Tim Berners-Lee, inventor of the web, said: "We have lost a colossal mind and a wonderful spirit. Rest in peace, Stephen Hawking," he said.
The vice chancellor of the University of Cambridge - where Prof Hawking had studied and worked - Professor Stephen Toope, said he was a "unique individual" who would be remembered with "warmth and affection".
Prof James Hartle, who worked with him to create the Hartle-Hawking wavefunction to explain the Big Bang, said Prof Hawking had a "unique" ability to "see through all the clutter in physics" and get to the point.
He told BBC Radio Four's Today programme: "My memory of him would be… first our work together as scientists and, second, as a human being whose whole story is a triumph over adversity [and] who inspired a lot of people, including me."
Skip Twitter post by @neiltyson His passing has left an intellectual vacuum in his wake. But it's not empty. Think of it as a kind of vacuum energy permeating the fabric of spacetime that defies measure. Stephen Hawking, RIP 1942-2018. pic.twitter.com/nAanMySqkt — Neil deGrasse Tyson (@neiltyson) March 14, 2018 Report
The comedian and presenter of the BBC's Stargazing Live Dara O'Briain said the scientist had an "immeasurable life" and "one of the few people I would call a hero of mine".
Theoretical physicist, professor Jim Al-Khalili, from Surrey University said Prof Hawking had a tremendous sense of humour.
He told BBC Radio Surrey: "He was a fun loving guy. Inside that shell, inside that body that was paralysed, was someone who was full of vigour, full of passion for life."
Hawking's discoveries
With the Oxford mathematician Roger Penrose, he showed that if there was a Big Bang, it must have started from an infinitely small point - a singularity
Black holes radiate energy known as Hawking radiation, while gradually losing mass. This is due to quantum effects near the edge of the black hole, a region called the event horizon
He predicted the existence of mini-black holes at the time of the Big Bang. These black holes would have shed mass until they vanished, potentially ending their lives in an explosion that would release vast amounts of energy
In the 1970s, Hawking considered whether the particles and light that enter a black hole were ultimately destroyed if the black hole evaporated. Hawking initially thought that this "information" was lost from the Universe. But the US physicist Leonard Susskind disagreed. These ideas became known as the information paradox. In 2004, Hawking conceded that the information must be conserved
British astronaut Tim Peake said Prof Hawking "inspired generations to look beyond our own blue planet and expand our understanding of the universe".
Gian Giudice, head of theoretical physics at the European nuclear research laboratory CERN, said Prof Hawking had a "great impact" on the centre's research, adding: "A giant of our field has left us, but his immortal contributions will remain forever."
Apple's co-founder Steve Wozniak said: "Stephen Hawking's integrity and scientific dedication placed him above pure brilliance,"
Image copyright AFP/Getty Images Image caption Stephen Hawking arrives on the red carpet with former wife Jane Hawking (L) and daughter Lucy Hawking (R).
In his 2013 memoir he described how he felt when first diagnosed with motor neurone disease.
"I felt it was very unfair - why should this happen to me," he wrote.
"At the time, I thought my life was over and that I would never realise the potential I felt I had. But now, 50 years later, I can be quietly satisfied with my life."
Speaking to the BBC in 2002, his mother, Isobelle, described him as a "very normal young man".
She said: "He liked parties. He liked pretty girls - only pretty ones. He liked adventure and he did, to some extent, like work."
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