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.
The image of Stephen Hawking – who has died aged 76 – in his motorised wheelchair, with head contorted slightly to one side and hands crossed over to work the controls, caught the public imagination, as a true symbol of the triumph of mind over matter. As with the Delphic oracle of ancient Greece, physical impairment seemed compensated by almost supernatural gifts, which allowed his mind to roam the universe freely, upon occasion enigmatically revealing some of its secrets hidden from ordinary mortal view.
Of course, such a romanticised image can represent but a partial truth. Those who knew Hawking would clearly appreciate the dominating presence of a real human being, with an enormous zest for life, great humour, and tremendous determination, yet with normal human weaknesses, as well as his more obvious strengths. It seems clear that he took great delight in his commonly perceived role as “the No 1 celebrity scientist”; huge audiences would attend his public lectures, perhaps not always just for scientific edification.
The scientific community might well form a more sober assessment. He was extremely highly regarded, in view of his many greatly impressive, sometimes revolutionary, contributions to the understanding of the physics and the geometry of the universe.
Hawking had been diagnosed shortly after his 21st birthday as suffering from an unspecified incurable disease, which was then identified as the fatal degenerative motor neurone disease amyotrophic lateral sclerosis, or ALS. Soon afterwards, rather than succumbing to depression, as others might have done, he began to set his sights on some of the most fundamental questions concerning the physical nature of the universe. In due course, he would achieve extraordinary successes against the severest physical disabilities. Defying established medical opinion, he managed to live another 55 years.
His background was academic, though not directly in mathematics or physics. His father, Frank, was an expert in tropical diseases and his mother, Isobel (nee Walker), was a free-thinking radical who had a great influence on him. He was born in Oxford and moved to St Albans, Hertfordshire, at eight. Educated at St Albans school, he won a scholarship to study physics at University College, Oxford. He was recognised as unusually capable by his tutors, but did not take his work altogether seriously. Although he obtained a first-class degree in 1962, it was not a particularly outstanding one.
He decided to continue his career in physics at Trinity Hall, Cambridge, proposing to study under the distinguished cosmologist Fred Hoyle. He was disappointed to find that Hoyle was unable to take him, the person available in that area being Dennis Sciama, unknown to Hawking at the time. In fact, this proved fortuitous, for Sciama was becoming an outstandingly stimulating figure in British cosmology, and would supervise several students who were to make impressive names for themselves in later years (including the future astronomer royal Lord Rees of Ludlow).
Sciama seemed to know everything that was going on in physics at the time, especially in cosmology, and he conveyed an infectious excitement to all who encountered him. He was also very effective in bringing together people who might have things of significance to communicate with one another.
When Hawking was in his second year of research at Cambridge, I (at Birkbeck College in London) had established a certain mathematical theorem of relevance. This showed, on the basis of a few plausible assumptions (by the use of global/topological techniques largely unfamiliar to physicists at the time) that a collapsing over-massive star would result in a singularity in space-time – a place where it would be expected that densities and space-time curvatures would become infinite – giving us the picture of what we now refer to as a “black hole”. Such a space-time singularity would lie deep within a “horizon”, through which no signal or material body can escape. (This picture had been put forward by J Robert Oppenheimer and Hartland Snyder in 1939, but only in the special circumstance where exact spherical symmetry was assumed. The purpose of this new theorem was to obviate such unrealistic symmetry assumptions.) At this central singularity, Einstein’s classical theory of general relativity would have reached its limits.
Meanwhile, Hawking had also been thinking about this kind of problem with George Ellis, who was working on a PhD at St John’s College, Cambridge. The two men had been working on a more limited type of “singularity theorem” that required an unreasonably restrictive assumption. Sciama made a point of bringing Hawking and me together, and it did not take Hawking long to find a way to use my theorem in an unexpected way, so that it could be applied (in a time-reversed form) in a cosmological setting, to show that the space-time singularity referred to as the “big bang” was also a feature not just of the standard highly symmetrical cosmological models, but also of any qualitatively similar but asymmetrical model.
Some of the assumptions in my original theorem seem less natural in the cosmological setting than they do for collapse to a black hole. In order to generalise the mathematical result so as to remove such assumptions, Hawking embarked on a study of new mathematical techniques that appeared relevant to the problem.
A powerful body of mathematical work known as Morse theory had been part of the machinery of mathematicians active in the global (topological) study of Riemannian spaces. However, the spaces that are used in Einstein’s theory are really pseudo-Riemannian and the relevant Morse theory differs in subtle but important ways. Hawking developed the necessary theory for himself (aided, in certain respects, by Charles Misner, Robert Geroch and Brandon Carter) and was able to use it to produce new theorems of a more powerful nature, in which the assumptions of my theorem could be considerably weakened, showing that a big-bang-type singularity was a necessary implication of Einstein’s general relativity in broad circumstances.
A few years later (in a paper published by the Royal Society in 1970, by which time Hawking had become a fellow “for distinction in science” of Gonville and Caius College, Cambridge), he and I joined forces to publish an even more powerful theorem which subsumed almost all the work in this area that had gone before.
In 1967, Werner Israel published a remarkable paper that had the implication that non-rotating black holes, when they had finally settled down to become stationary, would necessarily become completely spherically symmetrical. Subsequent results by Carter, David Robinson and others generalised this to include rotating black holes, the implication being that the final space-time geometry must necessarily accord with an explicit family of solutions of Einstein’s equations found by Roy Kerr in 1963. A key ingredient to the full argument was that if there is any rotation present, then there must be complete axial symmetry. This ingredient was basically supplied by Hawking in 1972.
The very remarkable conclusion of all this is that the black holes that we expect to find in nature have to conform to this Kerr geometry. As the great theoretical astrophysicist Subramanyan Chandrasekhar subsequently commented, black holes are the most perfect macroscopic objects in the universe, being constructed just out of space and time; moreover, they are the simplest as well, since they can be exactly described by an explicitly known geometry (that of Kerr).
The life of Stephen Hawking – in pictures Read more
Following his work in this area, Hawking established a number of important results about black holes, such as an argument for its event horizon (its bounding surface) having to have the topology of a sphere. In collaboration with Carter and James Bardeen, in work published in 1973, he established some remarkable analogies between the behaviour of black holes and the basic laws of thermodynamics, where the horizon’s surface area and its surface gravity were shown to be analogous, respectively, to the thermodynamic quantities of entropy and temperature. It would be fair to say that in his highly active period leading up to this work, Hawking’s research in classical general relativity was the best anywhere in the world at that time.
Hawking, Bardeen and Carter took their “thermodynamic” behaviour of black holes to be little more than just an analogy, with no literal physical content. A year or so earlier, Jacob Bekenstein had shown that the demands of physical consistency imply – in the context of quantum mechanics – that a black hole must indeed have an actual physical entropy (“entropy” being a physicist’s measure of “disorder”) that is proportional to its horizon’s surface area, but he was unable to establish the proportionality factor precisely. Yet it had seemed, on the other hand, that the physical temperature of a black hole must be exactly zero, inconsistently with this analogy, since no form of energy could escape from it, which is why Hawking and his colleagues were not prepared to take their analogy completely seriously.
Hawking had then turned his attention to quantum effects in relation to black holes, and he embarked on a calculation to determine whether tiny rotating black holes that might perhaps be created in the big bang would radiate away their rotational energy. He was startled to find that irrespective of any rotation they would radiate away their energy – which, by Einstein’s E=mc2, means their mass. Accordingly, any black hole actually has a non-zero temperature, agreeing precisely with the Bardeen-Carter-Hawking analogy. Moreover, Hawking was able to supply the precise value “one quarter” for the entropy proportionality constant that Bekenstein had been unable to determine.
This radiation coming from black holes that Hawking predicted is now, very appropriately, referred to as Hawking radiation. For any black hole that is expected to arise in normal astrophysical processes, however, the Hawking radiation would be exceedingly tiny, and certainly unobservable directly by any techniques known today. But he argued that very tiny black holes could have been produced in the big bang itself, and the Hawking radiation from such holes would build up into a final explosion that might be observed. There appears to be no evidence for such explosions, showing that the big bang was not so accommodating as Hawking wished, and this was a great disappointment to him.
These achievements were certainly important on the theoretical side. They established the theory of black-hole thermodynamics: by combining the procedures of quantum (field) theory with those of general relativity, Hawking established that it is necessary also to bring in a third subject, thermodynamics. They are generally regarded as Hawking’s greatest contributions. That they have deep implications for future theories of fundamental physics is undeniable, but the detailed nature of these implications is still a matter of much heated debate.
Hawking himself was able to conclude from all this (though not with universal acceptance by particle physicists) that those fundamental constituents of ordinary matter – the protons – must ultimately disintegrate, although with a decay rate that is beyond present-day techniques for observing it. He also provided reasons for suspecting that the very rules of quantum mechanics might need modification, a viewpoint that he seemed originally to favour. But later (unfortunately, in my own opinion) he came to a different view, and at the Dublin international conference on gravity in July 2004, he publicly announced a change of mind (thereby conceding a bet with the Caltech physicist John Preskill) concerning his originally predicted “information loss” inside black holes.
Following his black-hole work, Hawking turned his attentions to the problem of quantum gravity, developing ingenious ideas for resolving some of the basic issues. Quantum gravity, which involves correctly imposing the quantum procedures of particle physics on to the very structure of space-time, is generally regarded as the most fundamental unsolved foundational issue in physics. One of its stated aims is to find a physical theory that is powerful enough to deal with the space-time singularities of classical general relativity in black holes and the big bang.
Hawking’s work, up to this point, although it had involved the procedures of quantum mechanics in the curved space-time setting of Einstein’s general theory of relativity, did not provide a quantum gravity theory. That would require the “quantisation” procedures to be applied to Einstein’s curved space-time itself, not just to physical fields within curved space-time.
With James Hartle, Hawking developed a quantum procedure for handling the big-bang singularity. This is referred to as the “no-boundary” idea, whereby the singularity is replaced by a smooth “cap”, this being likened to what happens at the north pole of the Earth, where the concept of longitude loses meaning (becomes singular) while the north pole itself has a perfectly good geometry.
To make sense of this idea, Hawking needed to invoke his notion of “imaginary time” (or “Euclideanisation”), which has the effect of converting the “pseudo-Riemannian” geometry of Einstein’s space-time into a more standard Riemannian one. Despite the ingenuity of many of these ideas, grave difficulties remain (one of these being how similar procedures could be applied to the singularities inside black holes, which is fundamentally problematic).
There are many other approaches to quantum gravity being pursued worldwide, and Hawking’s procedures, though greatly respected and still investigated, are not the most popularly followed, although all others have their share of fundamental difficulties also.
To the end of his life, Hawking continued with his research into the quantum-gravity problem, and the related issues of cosmology. But concurrently with his strictly research interests, he became increasingly involved with the popularisation of science, and of his own ideas in particular. This began with the writing of his astoundingly successful book A Brief History of Time (1988), which was translated into some 40 languages and sold over 25m copies worldwide.
Undoubtedly, the brilliant title was a contributing factor to the book’s phenomenal success. Also, the subject matter is something that grips the public imagination. And there is a directness and clarity of style, which Hawking must have developed as a matter of necessity when trying to cope with the limitations imposed by his physical disabilities. Before needing to rely on his computerised speech, he could talk only with great difficulty and expenditure of effort, so he had to do what he could with short sentences that were directly to the point. In addition, it is hard to deny that his physical condition must itself have caught the public’s imagination.
Although the dissemination of science among a broader public was certainly one of Hawking’s aims in writing his book, he also had the serious purpose of making money. His financial needs were considerable, as his entourage of family, nurses, healthcare helpers and increasingly expensive equipment demanded. Some, but not all, of this was covered by grants.
To invite Hawking to a conference always involved the organisers in serious calculations. The travel and accommodation expenses would be enormous, not least because of the sheer number of people who would need to accompany him. But a popular lecture by him would always be a sell-out, and special arrangements would be needed to find a lecture hall that was big enough. An additional factor would be the ensuring that all entrances, stairways, lifts, and so on would be adequate for disabled people in general, and for his wheelchair in particular.
He clearly enjoyed his fame, taking many opportunities to travel and to have unusual experiences (such as going down a mine shaft, visiting the south pole and undergoing the zero-gravity of free fall), and to meet other distinguished people.
The presentational polish of his public lectures increased with the years. Originally, the visual material would be line drawings on transparencies, presented by a student. But in later years impressive computer-generated visuals were used. He controlled the verbal material, sentence by sentence, as it would be delivered by his computer-generated American-accented voice. High-quality pictures and computer-generated graphics also featured in his later popular books The Illustrated Brief History of Time (1996) and The Universe in a Nutshell (2001). With his daughter Lucy he wrote the expository children’s science book George’s Secret Key to the Universe (2007), and he served as an editor, co-author and commentator for many other works of popular science.
He received many high accolades and honours. In particular, he was elected a fellow of the Royal Society at the remarkably early age of 32 and received its highest honour, the Copley medal, in 2006. In 1979, he became the 17th holder of the Lucasian chair of natural philosophy in Cambridge, some 310 years after Sir Isaac Newton became its second holder. He became a Companion of Honour in 1989. He made a guest appearance on the television programme Star Trek: The Next Generation, appeared in cartoon form on The Simpsons and was portrayed in the movie The Theory of Everything (2014).
It is clear that he owed a great deal to his first wife, Jane Wilde, whom he married in 1965, and with whom he had three children, Robert, Lucy and Timothy. Jane was exceptionally supportive of him in many ways. One of the most important of these may well have been in allowing him to do things for himself to an unusual extent.
He was an extraordinarily determined person. He would insist that he should do things for himself. This, in turn, perhaps kept his muscles active in a way that delayed their atrophy, thereby slowing the progress of the disease. Nevertheless, his condition continued to deteriorate, until he had almost no movement left, and his speech could barely be made out at all except by a very few who knew him well.
He contracted pneumonia while in Switzerland in 1985, and a tracheotomy was necessary to save his life. Strangely, after this brush with death, the progress of his degenerative disease seemed to slow to a virtual halt. His tracheotomy prevented any form of speech, however, so that acquiring a computerised speech synthesiser came as a necessity at that time.
In the aftermath of his encounter with pneumonia, the Hawkings’ home was almost taken over by nurses and medical attendants, and he and Jane drifted apart. They were divorced in 1995. In the same year, Hawking married Elaine Mason, who had been one of his nurses. Her support took a different form from Jane’s. In his far weaker physical state, the love, care and attention that she provided sustained him in all his activities. Yet this relationship also came to an end, and he and Elaine were divorced in 2007.
A brief history of Stephen Hawking's Brief History of Time Read more
Despite his terrible physical circumstance, he almost always remained positive about life. He enjoyed his work, the company of other scientists, the arts, the fruits of his fame, his travels. He took great pleasure in children, sometimes entertaining them by swivelling around in his motorised wheelchair. Social issues concerned him. He promoted scientific understanding. He could be generous and was very often witty. On occasion he could display something of the arrogance that is not uncommon among physicists working at the cutting edge, and he had an autocratic streak. Yet he could also show a true humility that is the mark of greatness.
Hawking had many students, some of whom later made significant names for themselves. Yet being a student of his was not easy. He had been known to run his wheelchair over the foot of a student who caused him irritation. His pronouncements carried great authority, but his physical difficulties often caused them to be enigmatic in their brevity. An able colleague might be able to disentangle the intent behind them, but it would be a different matter for an inexperienced student.
To such a student, a meeting with Hawking could be a daunting experience. Hawking might ask the student to pursue some obscure route, the reason for which could seem deeply mysterious. Clarification was not available, and the student would be presented with what seemed indeed to be like the revelation of an oracle – something whose truth was not to be questioned, but which if correctly interpreted and developed would surely lead onwards to a profound truth. Perhaps we are all left with this impression now.
Hawking is survived by his children.
• Stephen William Hawking, physicist, born 8 January 1942; died 14 March 2018, aged 76.
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.
Advertisement Continue reading the main story
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.
Photo
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.
Advertisement Continue reading the main story
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.
Advertisement Continue reading the main story
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.
Advertisement Continue reading the main story
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.
Advertisement Continue reading the main story
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.”
Video
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.
Advertisement Continue reading the main story
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.
Photo
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.
Sebelum tutup usia, Stephen Hawking pernah memperingatkan agar umat manusia harus mulai meninggalkan Bumi dalam kurun 30 tahun. Hal itu untuk menghindari kemusnahan akibat kelebihan penduduk dan perubahan iklim
Peringatan astrofisikawan disampaikan dalam festival sains Starmus di Trondheim, Norwegia. Dalam kesempatan itu, ia mengatakan bahwa membangun koloni di Mars dan Bulan serta menciptakan dunia baru di sana merupakan hal yang sangat penting.
Menurutnya, hanya menjadi masalah waktu sebelum Bumi kita hancur akibat serangan asteroid, lonjakan suhu, dan kelebihan populasi.
"Saya yakin bahwa manusia harus meninggalkan Bumi. Bumi menjadi terlalu kecil bagi kita, sumber daya fisik kita terkuras pada tingkat yang mengkhawatirkan," ujar pria kelahiran 8 Januari 1942 itu.
"Kita telah memberi Bumi hadiah bencana, seperti perubahan iklim, kenaikan suhu, berkurangnya lapisan es kutub, penggundulan hutan, dan berkurangnya spesies hewan."
"Ketika kita telah mencapai krisis yang sama di dalam sejarah, biasanya ada tempat lain untuk dijajah, Columbus melakukannya pada tahun 1492 ketika ia menemukan dunia baru. Tapi sekarang tidak ada dunia baru. Tidak ada utopia di sekitar Bumi. Kita kehabisan ruang dan satu-satunya tempat untuk dikunjungi adalah dunia lain," ujar Stephen Hawking.
Ilmuwan asal Inggris itu juga mengatakan bahwa Bumi pada akhirnya akan terkena serangan asteroid yang menimbulkan kerusakan skala besar.
"Ini bukan fiksi ilmiah,ini dijamin oleh hukum fisika dan probabilitas," kata Hawking. "Manusia yang tetap berada di Bumi berisiko akan musnah."
Hawking mengatakan, Bulan dan Mars adalah tempat terbaik untuk memulai koloni pertama. Ia menyebut bahwa pangkalan di Bulan dapat didirikan dalam 30 tahun dan di Mars selama 50 tahun.
Namun, Hawking juga menyarankan untuk meninggalkan Tata Surya dan berkelana ke sistem bintang terdekat, yakni Alpha Centauri. Di sana para ilmuwan meyakini ada planet layak huni yang dikenal sebagai Proxima B.
Stephen Hawking mengatakan bahwa pesawat bertenaga nuklir yang digerakkan oleh cahaya atau sejumlah bentuk energi baru, memungkinkan manusia melakukan perjalanan selama bertahun-tahun cahaya.
Menurutnya, sebuah langkah kecil pertama telah dilakukan oleh miliarder Rusia, Yuri Milner melalui proyek Breakthrough Start Shot. Proyek tersebut mengirimkan sebuah pesawat kecil "nanocraft" untuk melakukan perjalanan selama empat tahun cahaya ke Alpha Centauri, sistem bintang terdekat ke Bumi.
"Jika kita berhasil, kita akan mengirimkan probe ke Alpha Centauri," ujar Hawking.
"Sudah jelas kita memasuki era ruang baru. Kita berdiri di ambang era baru. Kolonisasi manusia dan planet lainnya bukan lagi fiksi ilmiah, hal itu bisa jadi fakta sains."
