Stephen Hawking: The Theoretical Physicist Who Read the Mind of God

Few figures in the modern history of science have so completely fused the work of the theoretical physicist with the role of the cultural icon as Stephen William Hawking, the Cambridge cosmologist who, from a wheelchair to which he was confined by motor neuron disease for fifty-five years and through a synthesised voice that became, in his last decades, one of the most recognisable sounds in the English-speaking world, transformed the public understanding of black holes, of the origin of the universe, and of the place of human consciousness within a cosmos that seemed at once incomprehensibly large and rigorously rational. He was, by general agreement of his peers, one of the most important theoretical physicists of the second half of the twentieth century, the man who in 1974 had brought together the previously incompatible domains of general relativity, quantum mechanics, and thermodynamics in a single equation describing the temperature of a black hole and who had thereby opened the most fertile field of theoretical physics of the following half-century. He was also, by general agreement of the reading public, the most popular and most widely read scientific writer of his generation, the author of A Brief History of Time, the book that sold more than twenty-five million copies in forty languages and that more readers bought, started, and failed to finish than perhaps any other serious volume of the late twentieth century. He was a celebrity who appeared on The Simpsons, on Star Trek, on Pink Floyd albums, and at the opening ceremony of the Paralympic Games; he was a public intellectual whose pronouncements on artificial intelligence, on extraterrestrial life, on the future of humanity, and on the existence of God commanded the front pages of newspapers around the world; he was, in his last decade, an emblem of human endurance and intellectual triumph against physical adversity whose face and voice had become almost as universally recognisable as those of Albert Einstein in the previous century.

The juxtaposition of intellectual mastery and physical disability that defined his public image was not a sentimental construction of the press. It was the central, irreducible fact of his adult life. He had been a healthy and vigorous undergraduate at University College, Oxford, an oarsman, a coxswain in the college boat club, a young man of conventional academic gifts but without obvious distinction, when in the autumn of 1962 — at the very beginning of his graduate work in Cambridge, just past his twenty-first birthday — he began to fall over, to slur his words, to lose dexterity in his hands. The diagnosis the following spring of amyotrophic lateral sclerosis, the form of motor neuron disease most often called Lou Gehrig's disease in the United States, came with the bleak medical assessment that he had at most two or three years to live. He outlived that prognosis by fifty-three years. He completed his doctorate, married Jane Wilde, fathered three children, took the Lucasian Chair of Mathematics at Cambridge that Isaac Newton had once held, wrote the canonical theoretical papers on the singularity theorems of general relativity and on the quantum mechanics of black holes, watched his physical capacities decline year by year until in 1985 a tracheotomy following a near-fatal bout of pneumonia took away his voice and forced him onto the speech synthesiser that became his trademark, and continued to think, to compute, to publish, to teach, to lecture, and to travel until the spring of 2018, when he died at his home in Cambridge at the age of seventy-six.

The body of theoretical work that he produced over those years has been one of the most consequential in the modern history of physics. With Roger Penrose, in a series of papers between 1965 and 1970, he established the singularity theorems of general relativity, which proved that under very general conditions Einstein's gravitational equations predicted the existence of points of infinite curvature — singularities — at the centres of black holes and at the beginning of the universe. With James Bardeen and Brandon Carter, in 1973, he formulated the four laws of black hole mechanics, which exhibited the formal mathematical analogy between black holes and ordinary thermodynamic systems. In a paper of January 1974 that altered the trajectory of theoretical physics, he showed that the laws of quantum mechanics imply that black holes are not in fact perfectly black but radiate thermal radiation, the so-called Hawking radiation, at a temperature inversely proportional to their mass, with the consequence that black holes slowly evaporate over time and, paradoxically, appear to destroy the information about whatever had fallen into them. The black hole information paradox to which this discovery gave rise has remained, half a century later, one of the deepest unsolved problems in theoretical physics, and the field of research it generated — black hole thermodynamics, the holographic principle, the connection between quantum entanglement and the geometry of spacetime — constitutes the most active frontier of contemporary research on the unification of gravity and quantum mechanics. With James Hartle, in 1983, he proposed the no-boundary condition for the wave function of the universe, an attempt to apply the principles of quantum mechanics to cosmology and to remove from physical theory the initial singularity at the Big Bang. He continued to publish significant papers on these subjects until the year of his death.

These were the achievements that earned him election to the Royal Society at the age of thirty-two, the Albert Einstein Medal in 1979, the Lucasian Chair the same year, the Wolf Prize in 1988, the Copley Medal in 2006, and a long list of other honours from learned societies and universities around the world. They did not earn him the Nobel Prize in Physics, for the simple reason that Hawking radiation, the discovery that should have led to a Nobel by every customary measure, has not yet been experimentally confirmed; the temperature of even a stellar-mass black hole is so low — about a hundred-millionth of a degree above absolute zero — that the radiation is far below the threshold of current astronomical detection, and the Nobel Foundation has consistently refused to award the prize for theoretical work that lacks experimental confirmation. The omission was, by his late years, a standing complaint of his friends and admirers; he himself professed never to have minded it, observing that he had every other honour the discipline could offer and had no need of a Nobel to fix his place in the history of science.

But it was the public face of Hawking, more than the professional achievements, that made him the great popular icon of late twentieth-century science. The publication in April 1988 of A Brief History of Time, a short volume of popular cosmology that he had written in painful longhand over six years and that was issued by Bantam Books after his original publisher Cambridge University Press had questioned its commercial viability, transformed him overnight into a global celebrity. The book remained on the Sunday Times bestseller list for two hundred and thirty-seven consecutive weeks, sold more than twenty-five million copies in its various editions, was translated into forty languages, and gave its title to a 1991 Errol Morris documentary that brought Hawking's face and voice to a still wider audience. From that point onward he was no longer simply a Cambridge professor; he was the most famous scientist in the world, a man whose pronouncements on any topic commanded headlines and whose physical struggle against motor neuron disease made him a figure of inspiration to disabled people and to the general public alike. He appeared in cameos on The Simpsons (more than once), on Star Trek: The Next Generation (where he played poker with Newton and Einstein in the holodeck of the Enterprise), on The Big Bang Theory, in Pink Floyd's song Keep Talking and on their album The Division Bell, and at countless public events including the opening ceremony of the 2012 Paralympic Games in London. He gave the Reith Lectures on the BBC, met with American presidents, addressed the United Nations, took a parabolic flight to experience weightlessness at the age of sixty-five, planned (though never made) a journey on Richard Branson's Virgin Galactic, and provided in The Theory of Everything, the 2014 biographical film in which Eddie Redmayne won the Academy Award for Best Actor for portraying him, a portrait that introduced his life to a still wider audience.

The biography that follows traces in detail the long path from the wartime Oxford in which he was born in January 1942 to the Cambridge in which he died in March 2018: the childhood in St Albans and the eccentric, intellectually intense home environment of the Hawking family, the schooldays at St Albans School in which his abilities were recognised by some teachers and overlooked by others, the undergraduate years at Oxford in which he combined a brilliant casual mastery of physics with a determination not to be seen to work too hard, the move to Cambridge in 1962 and the immediate onset of the symptoms of motor neuron disease, the doctoral work under Dennis Sciama that brought him into contact with Roger Penrose and the theoretical revolution then beginning in general relativity, the great discoveries of the 1970s on the thermodynamics and quantum mechanics of black holes, the long and increasingly difficult marriage to Jane Wilde, the celebrity that followed A Brief History of Time, the second marriage to his nurse Elaine Mason, the divorce and reconciliation with Jane, the steady physical decline punctuated by extraordinary intellectual productivity, the cultural ubiquity of his later years, and the universal recognition that followed his death. It is a story in which the most abstract speculations of mathematical physics, the practical realities of severe physical disability, the dynamics of a complicated personal life, and the dynamics of late twentieth-century celebrity are interwoven into a single human life of remarkable will, remarkable luck, and remarkable consequence.

Birth and Family in Oxford

Stephen William Hawking was born on 8 January 1942 in the city of Oxford, in the war-darkened England of the second winter of the Second World War, on the three-hundredth anniversary, by the family's later count, of the death of Galileo Galilei. The coincidence of the anniversary with his birth was something his family always mentioned and that he himself made much of in interviews and in his memoir; he liked to observe that he had been born exactly three centuries to the day after the death of one of the founders of the modern physical sciences, and on the same date in the eighteenth century on which the planet Uranus had been discovered. The historical coincidence flattered a sense, present in him from his earliest years, that he was destined for a life within the great tradition of physical science, and it became one of the standing pieces of the public Hawking persona — the kind of detail that journalists invariably mentioned and that gave to a life of considerable physical adversity a faintly providential cast.

The wartime circumstances of his birth were, however, less providential than mundane. His parents, Frank Hawking and Isobel Walker Hawking, lived during the early years of the war in Highgate in north London, where Frank worked as a medical researcher at the National Institute for Medical Research at Hampstead. The Battle of Britain in the summer of 1940 and the prolonged bombing of London in the months that followed had made the capital a dangerous place to bring a child into the world, and the publishers of medical and scientific books in Oxford had reached an informal agreement with their German counterparts, who similarly arranged for their authors' wives to give birth in safer locations away from Berlin, that the city of Oxford with its preserved scholarly status would be respected by both belligerents and would not be bombed. Stephen's mother was sent, accordingly, to Oxford for the latter stages of her pregnancy, lodging with a relative in the suburb of Headington and giving birth in the John Radcliffe Hospital at the foot of Headington Hill on the cold January morning that became Stephen's birthday. He was the first of four children, followed in due course by his sisters Mary (born 1943) and Philippa (born 1946) and by an adopted brother Edward, who joined the family in 1955.

The Hawkings were not, in the conventional sense, members of the English educated upper-middle class to which their professional positions might have suggested they belonged. They were, rather, an eccentric and intellectually intense family of recent academic origin, comfortable in their distinctive household habits but only loosely integrated into the social conventions of their neighbours and colleagues. Frank Hawking (1905–1986) was the son of a Yorkshire farmer who had lost most of his money in the agricultural collapse of the late nineteenth century; he had risen by his own efforts through the Yorkshire grammar schools and a scholarship to University College, Oxford, where he read medicine and afterwards specialised in tropical diseases. He had spent the 1930s in East Africa, working as a research scientist on diseases such as bilharzia and African sleeping sickness, and had returned to England only at the outbreak of the war to take up his post at the Hampstead institute. He was a tall, gaunt, austere man of considerable scientific ability and considerable eccentricity, with a stutter that had marked him from boyhood, with an inability to make small talk, with a fierce devotion to his work and to his children, and with a settled conviction that the rest of the world was generally less intelligent and considerably more frivolous than the Hawkings.

Stephen's mother, Isobel Eileen Walker (1915–2013), was the daughter of a Glasgow general practitioner and had been one of the first generation of women to read for an Oxford degree in philosophy, politics, and economics, taking her BA from Saint Hugh's College in 1935. She was a woman of strong political convictions, a Liberal and later a Labour Party supporter who through her later years remained an active member of the Campaign for Nuclear Disarmament, a freethinker in religious matters in a country still nominally Christian, a reader of Russian novelists and German philosophers, a smoker, a wearer of slacks at a period when respectable Englishwomen wore dresses, and a person of considerable practical capability who had worked during the war as a medical secretary at the same Hampstead institute where she had met Frank. She and Frank had married in 1940 and had set up house together in a tall narrow brick terrace at 14 Hillside in Highgate, which they continued to inhabit through the early years of their marriage and the early years of their children.

The household that the Hawkings established in Highgate, and later (from 1950) in the cathedral town of St Albans in Hertfordshire, was distinctly unconventional by the standards of their professional class. The family read at the table during meals, each member with a different book propped against the jam pot or the salt cellar, and Frank in particular had been known to read scientific journals throughout dinner and to make conversational responses without lifting his eyes from the page. The family owned a battered car of advanced age that had been converted by Frank himself from a London taxi cab, in which the Hawkings drove on family holidays to camping sites on the Norfolk coast and which became a standing local joke in St Albans. The family lived in a large but ill-maintained Victorian house at 14 Hillside Road from 1950 onward, the heating of which Frank refused to upgrade on principle, so that the children grew up in a series of rooms of varying degrees of cold and damp, with the cellars frequently flooded and the wallpaper peeling, and with bicycles, books, scientific apparatus, and the leavings of the family's various intellectual enthusiasms strewn through the corridors and the unused servants' rooms upstairs. Stephen would later say that he had not realised until well into adolescence that not all families lived in this way and that the conventional middle-class household of the period was, in fact, the norm rather than the exception.

The intellectual culture of the family was set principally by Frank, who treated his children from their earliest years as junior scientists in training. He read to them the standard children's books — Treasure Island, Just William, the Sherlock Holmes stories — but interspersed these with his own choice of more adult fare; he insisted that his children learn the principles of mathematics and the elements of biology from the age at which they could hold a book; he encouraged them to make their own scientific apparatus from materials around the house and to take long walks in the country to observe the natural world. The conversation at the family dinner table, when reading was not in progress, ranged through the political news of the day, the latest scientific developments, the books that any member of the family was then reading, and a steady stream of family jokes, allusions, and private references that bound the four children together as a small intellectual tribe distinguished from the wider world by its own special language. Stephen, the eldest, took naturally to this regime. He was, his mother would later say, a quiet and observant child who absorbed everything that was said around him and who from a very early age showed a particular interest in machines, in the workings of things, in how the visible motions of the physical world were produced by hidden underlying mechanisms.

The Hawking Family: an Eccentric Inheritance

The eccentricity of the Hawking household was not an accidental quirk; it was a self-conscious cultivation by Frank Hawking of a way of life that he considered properly intellectual, properly serious, and properly indifferent to the social conventions of the English middle class to which he belonged by his profession but to which he had always felt himself, as the upwardly mobile son of an impoverished Yorkshire farmer, only marginally connected. The cultivation took several characteristic forms. The first was a stringent intellectual seriousness — an assumption that the proper occupation of a Hawking child was to read, to learn, to think, and to argue, and that the social activities of the children of their neighbours, with their parties and their dances and their conventional sporting enthusiasms, were unworthy of the family's time and energy. The second was a deliberate frugality — Frank refused to spend money on clothes, on cars, on heating, on the visible appurtenances of professional respectability, and the family lived in straitened circumstances even when the household income from Frank's research posts and Isobel's part-time secretarial work would have allowed considerably more comfort. The third was a defensive isolation — the family did not entertain neighbours, did not join the local clubs and societies of the cathedral town in which they lived, and considered themselves a distinct minority whose values diverged from those of the surrounding community. The fourth was a quiet but settled intellectual snobbery — the assumption that the Hawkings were more intelligent, better informed, and more serious than the people around them, and that the proper response of the children to social interactions was a polite reserve that masked an inner assessment of the other person's intellectual quality.

The atmosphere of the Hawking household was therefore, by the standards of conventional English middle-class life in the 1940s and 1950s, both stimulating and slightly oppressive. It was stimulating because it took the intellectual development of the children seriously, encouraged them to think for themselves, gave them the run of an extensive library, supplied them with adult conversation from their earliest years, and treated their childhood pursuits as serious matters worthy of adult attention. It was oppressive because it set them apart from their peers, made it difficult for them to form ordinary friendships outside the family, and instilled in them, in varying degrees, a sense of being not quite like other people. Stephen would later describe his childhood as broadly happy but distinctly odd; his sister Mary, who became a doctor, would say with some bitterness that the family had paid the price for the parents' ambitions in social isolation and emotional reserve; his sister Philippa, who became a writer, would describe the household in tones of affectionate exasperation.

The Hawking children all turned out, in their different ways, distinctly intellectual. Mary became a medical practitioner of considerable accomplishment, working principally as a general practitioner in the National Health Service. Philippa became a journalist and author who wrote, among other things, biographical books on her brother. Edward, the adopted brother, who came into the family as a baby in 1955, was the least obviously academic of the four and would die young of an accidental fall in 1989, an event that distressed Stephen deeply. The four children together formed, in the closed atmosphere of the Hawking household, a small intellectual tribe with their own private jokes, their own shorthand references, and their own settled assumption that the world outside the family was generally less interesting than the world within. This sibling closeness would persist throughout Stephen's life and would be one of the constant emotional supports of his adult years, even after the family was scattered and the parents had died.

The intellectual style that Stephen absorbed from this household — sceptical, undeferential, mathematically rigorous, contemptuous of received wisdom, prone to seek the underlying mechanism behind the visible appearance — was the style he would carry with him into his scientific work. He would always be a theorist who attacked received positions with relish, who took pleasure in finding paradoxes in the conventional understanding of a subject, who delighted in the moment at which a careful argument forced a familiar position to give way to an unfamiliar one. His provocative public statements in later life — that black holes were not really black, that the universe had no beginning in time, that there was no need for a God to set the universe going, that philosophy was dead, that humans should colonise space within a century to avoid extinction — were of a piece with this inherited family style. They were the expressions, in the language of late twentieth-century physical theory and public commentary, of the Hawking habit of mind: intellectually serious, undeferential, willing to follow an argument to a conclusion that startled the audience, and indifferent to the conventional pieties of the surrounding culture.

Childhood in St Albans

The family moved from Highgate to St Albans in 1950, when Stephen was eight years old, in consequence of Frank's appointment to a senior research position at the National Institute of Medical Research at Mill Hill, north of London. St Albans was a cathedral town of some forty thousand inhabitants in southern Hertfordshire, twenty miles north of London on the old Roman road of Watling Street, distinguished by its great Norman cathedral (built on the site of the martyrdom of Saint Alban, the first British Christian martyr), by the surviving Roman ruins of Verulamium on its western edge, and by the wooded chalk hills of the Chiltern country immediately to the north. The Hawkings bought a large but dilapidated three-story Victorian house at 14 Hillside Road, a few minutes' walk from the centre of the town, and settled into the property that would remain the family home for the next half-century.

The St Albans of the 1950s was an unhurried country town with a clear sense of its own historical importance, a strong civic culture, several private schools of long standing, and a population that, although it included the usual range of professional and commercial families, retained a small-town character considerably less metropolitan than that of London twenty miles to the south. The Hawking children grew up in this environment and in due course attended its various schools, with Stephen enrolling first at a local primary school and then, at the age of eleven, gaining a place at St Albans School, the leading boys' grammar school of the town and the school in which he would receive his secondary education.

The childhood years in St Albans were, by Stephen's later account, contented and intellectually active. He spent a great deal of time with his sisters and (after 1955) his adopted brother, exploring the woods and fields around the town, playing elaborate invented games of their own devising, building scratch model trains and electronic gadgets, and reading widely from the family library. His particular passions, in these years, were trains (he had an extensive Hornby OO-gauge model railway in the attic, which he and his father expanded over many years) and games of his own invention, including a complex board game called Risk that he and a school friend devised in adolescence and that involved the management of imaginary fleets, armies, and economies according to elaborate rules. He was, in this period, an ordinary if somewhat reserved English schoolboy with a particular bent for mechanical things and for the kind of intellectual play that arises naturally in a household where the parents take ideas seriously.

He was, by his own account, not a precociously talented boy in any of the conventional schoolboy categories. He learned to read late by the standards of his class — he was nearly eight before he could read fluently — and he was never one of the leading pupils in primary school. His handwriting was poor and remained poor throughout his life; his work was often untidy; his teachers occasionally remarked on the gap between his evident intelligence and the indifferent quality of his school output. He was small for his age and not particularly athletic, though he liked walking and running and would later, at Oxford, take up rowing. The intellectual gifts that would mark his adult career were not yet, in childhood, especially conspicuous. He was, in his own later phrasing, "the type of boy who is bottom but one in the class, but who knows the answer when the teacher gets stuck on a problem."

School Days at St Albans School

Stephen entered St Albans School in 1953 at the age of eleven, having gained admission to the form generally reserved for boys of academic promise. The school, founded in 948 and one of the oldest schools in England, was a leading boys' grammar school with a strong sixth form, a substantial sports programme, and a settled academic culture in which boys of intelligence were expected to perform creditably without being celebrated as prodigies. The atmosphere of the school was that of a typical English grammar school of the 1950s — academic, mildly competitive, athletically inclined, run by masters in academic gowns who addressed the boys by their surnames and who took for granted that the principal function of the school was to prepare its pupils for the universities. Stephen settled into this environment with the same combination of intellectual quickness and casual application that would mark his later school and undergraduate years. He was a competent but not outstanding pupil through the lower forms, distinguished from his classmates by an evident analytical intelligence but not by any conspicuous diligence or ambition.

The friends he made at the school would be among the most important of his life. The most consequential were a small group of boys with whom he formed, around the age of fifteen, an informal scientific and intellectual circle. They built electronic devices together (Stephen, with characteristic ambition, embarked at fifteen on the construction of a primitive electronic computer from used telephone-exchange relays, a project on which his friends collaborated and which they called LUCE — the Logical Uniselector Computing Engine), they argued about mathematics, physics, philosophy, and religion, they read widely beyond the school curriculum, and they formed the kind of close adolescent friendships that often shape a person's later intellectual identity. Among them were John McClenahan, Basil King, and Michael Church; King and Church would remain his close friends through their adult lives, and McClenahan would become a doctor and visit him in later years. The group together exemplified a type — the bright English schoolboy of the immediate postwar era, ambitious and unconventional, more comfortable with abstract ideas than with conventional social codes, headed almost without exception for Oxford or Cambridge and for professional careers in science, medicine, or the higher reaches of the civil service.

Stephen's academic performance at St Albans was creditable but uneven. He was always near the top of his year in mathematics and physics, generally good in chemistry and reasonably so in Latin and modern languages, weaker in English literature and in art. His tendency, observable already in adolescence, was to grasp the principles of a subject quickly and to lose interest once the principles were mastered; the careful, plodding, application that produced top examination results bored him, and he had to be roused to serious effort by an upcoming examination. His teachers were aware of the gap between his abilities and his application. A school report from his last year noted with mild irritation that "his behaviour in class is generally satisfactory, but he has an annoying tendency to assume that he knows the answer before he has worked through the problem." The same teacher would later, when Stephen had become famous, observe that the annoying tendency had turned out to be one of his most useful intellectual habits.

The decisive school influence on his eventual choice of subject was his mathematics master, Dikran Tahta, a young teacher of Armenian descent who had taken his own mathematics degree at Cambridge and who brought to the senior mathematics classroom a sense of the subject as a creative enterprise rather than as a mechanical drill. Tahta encouraged the brighter pupils to think about mathematics as a kind of intellectual game, to attack problems by their own methods, to consider mathematics as a discipline with a long history and a distinctive aesthetic, and to read widely in popular and semi-technical literature about the subject. Stephen, in his later memoir Brief Answers to the Big Questions, would identify Tahta as the single teacher who had most decisively shaped his intellectual development, and would write that without Tahta he might not have become a physicist at all. When Hawking won his Lucasian Chair in 1979 he wrote to Tahta to thank him, and the two corresponded for many years afterwards.

The Choice of University and Subject

The question of where and what to read at university occupied the family for some time during Stephen's sixteenth and seventeenth years. Frank Hawking was insistent that Stephen should follow him to University College, Oxford, where Frank himself had read medicine and where he retained close ties to several of the dons; he was equally insistent that the subject should be a scientific one, though he had no particular preference between physics, mathematics, and chemistry. Frank's reasoning, which he laid out in his characteristic detailed way over many family dinner conversations, was that Stephen had the intellectual capacity to do science at the highest level, that science offered a securer career than the humanities, and that University College had the right traditions and the right tutors to bring out the best in him.

Stephen himself, somewhat to his father's frustration, had developed a strong preference for mathematics, the subject in which he had been most successful at school and which he found the most aesthetically satisfying. Frank objected to this preference on practical grounds — he doubted, on the experience of his own profession, that there were enough good jobs for mathematicians, and he believed that physics would offer more career flexibility. The compromise, eventually reached, was that Stephen would read for the Natural Sciences honours school at Oxford, with physics as his principal subject and with such mathematics as the syllabus required; he would also, in due course, sit the entrance scholarship examination for University College in the standard way.

He sat the scholarship examination in March 1959, at the age of seventeen, and won an Open Scholarship in Natural Sciences, the most senior award the college offered. The scholarship paid for his tuition and most of his living costs and was a substantial mark of academic distinction. He matriculated at University College, Oxford, in October 1959, three months after his eighteenth birthday — a young undergraduate even by the standards of the period, surrounded by men two or three years his senior who had completed their National Service before going up to the university. His age, his physical immaturity, and his lack of social confidence made the first year of Oxford one of the most difficult periods of his early life, but it was also the period in which his intellectual self-confidence began visibly to grow.

Undergraduate Years at Oxford

University College in 1959 was one of the older Oxford colleges, founded in 1249, occupying a row of buildings on the High Street between the Examination Schools and Magdalen College. It had a strong tradition in the natural sciences but, in the late 1950s, a settled social culture of well-bred Englishmen of conventional academic preparation, most of them educated at public schools, most of them having done National Service before coming up, most of them comfortable in the social codes of the older universities. Stephen, who was none of these things — grammar-school educated, exempt from National Service because he had been too young, socially uncertain, more interested in ideas than in social position — found the first year at the college difficult. He kept to himself, did the minimum work required to satisfy his tutors, and felt himself an outsider in a society that took for granted forms of confidence he had not yet acquired.

The physics teaching at Oxford in 1959 was, by his own later assessment, indifferent in the lecture rooms and excellent in the tutorial system. The lectures, given by the senior physicists of the university to large classes in the Clarendon Laboratory and the Examination Schools, he often skipped on the principle that he could learn the same material more efficiently from textbooks. The tutorials, by contrast, given in pairs or trios by college tutors in their rooms on a weekly basis, he found stimulating and useful; his principal tutor in physics was Robert Berman, a young experimental physicist of Magdalen College who taught Stephen for his entire three undergraduate years and who would later say that Stephen was the cleverest pupil he had taught in twenty years at Oxford. Berman set him problems each week, listened to his solutions, found the errors and the elegant simplifications, and gradually trained him in the patient analytical habits that distinguish the working physicist from the merely intelligent undergraduate.

The Hawking who emerged in his second and third undergraduate years was a more confident young man than the one who had arrived in 1959. He had, by then, fallen in with the boat club at University College and had taken up rowing — first as an oarsman and then as a coxswain, a small man directing the rhythm of the larger oarsmen in the eight, a role that suited his slight build and his analytic temperament. He joined the standard social rituals of college life, drank beer in college bars, attended the smaller parties of his contemporaries, and acquired a circle of friends with whom he would remain in contact for many years. He developed a reputation, in his college, as a clever and casual young man who could solve any physics problem set him in a fraction of the time it took his contemporaries but who refused, on principle, to be seen to work hard. The pose was, by his own later admission, partly affectation and partly an expression of a genuine intellectual confidence that did not need the visible labour to confirm itself.

His tutors estimated that during his three years at Oxford he did, on average, an hour or two of academic work per day — a small fraction of the labour put in by his more conscientious contemporaries, and almost the minimum compatible with completing the course. The casualness, however, masked a real intellectual mastery. When the time came for the Final Examination in Natural Sciences (Physics) in the summer of 1962, he sat the examinations confident that he would do well but uncertain whether his casual study habits had been adequate to secure the First Class degree he wanted in order to be admitted to graduate study. The result was, as is famous in the legend that surrounds him, borderline. His paper was a First on some questions and a Second on others; the examiners, uncertain how to classify him, called him in for an oral examination, at which he was asked what he intended to do in life. He replied that if he were given a First he would go to Cambridge to do graduate work in cosmology, but if he were given a Second he would stay at Oxford. The examiners, presented with a candidate of evident brilliance who would punish them by remaining in Oxford if they marked him down, gave him a First.

The Move to Cambridge

The choice of Cambridge, rather than continuing at Oxford, for graduate work was deliberate. The senior cosmologist at Oxford in 1962 was Dennis Sciama's contemporary William McCrea at the Royal Holloway College of the University of London, and the principal Oxford theoretician of general relativity was Sir Hermann Bondi, who was based at King's College London rather than at Oxford itself. The most distinguished British cosmologist of the older generation, Fred Hoyle, was at Cambridge, and the most active younger theorist of general relativity in the country was Dennis Sciama, who held a research fellowship at Trinity College, Cambridge, and was building up what would become one of the great research groups of late twentieth-century theoretical physics. Stephen had hoped, when he applied for graduate work, to be admitted to work with Hoyle, but Hoyle was full, and he was offered instead a position with Sciama at the new Department of Applied Mathematics and Theoretical Physics, the DAMTP, which had been established a few years earlier on the Free School Lane site in central Cambridge.

He moved to Cambridge in October 1962, taking up rooms at Trinity Hall College, where he had been admitted as a postgraduate student. The DAMTP, at this period, was a small department of about twenty research staff and as many graduate students, housed in an undistinguished building on Silver Street that had been converted from the old printing house of the Cambridge University Press. The atmosphere was informal and intellectually charged. The department's senior figures included the Lucasian Professor Paul Dirac (one of the founders of quantum mechanics, then in his early sixties), the applied mathematician George Batchelor (the head of department), the cosmologist Hermann Bondi (visiting from London), and the theorists Roger Penrose (then a Reader at Birkbeck College London but increasingly attached to Cambridge), Dennis Sciama, and Brandon Carter (a graduate student a few years senior to Stephen). The student culture of the department was that of a small, tightly knit research community in which graduate students worked closely with senior figures and in which the customary distance between students and professors that prevailed in older Oxford colleges had largely dissolved.

Stephen, however, did not feel at home in this environment in his first months. He had, during his last year at Oxford and his summer between Oxford and Cambridge, become aware of certain bodily oddities that puzzled him. He had fallen down a flight of stairs at Oxford during his last term, recovered without obvious injury, but had no memory of the fall afterwards. He had taken several falls while skating with friends in the long Christmas vacation of 1961–62. His handwriting, never very legible, had become noticeably worse. He had begun to notice difficulty with simple tasks such as tying his shoelaces. These were minor things, individually insignificant, but in the autumn of 1962, after he arrived at Cambridge, the symptoms intensified. He fell several times in his first weeks at Trinity Hall. He had increasing difficulty in walking up the stairs to his rooms. His speech began to slur slightly when he was tired. His parents noticed the changes when he returned home to St Albans for Christmas in December 1962 and insisted, against his protests, that he see a specialist.

Diagnosis with Motor Neuron Disease

The medical investigations that followed in January and February 1963 were exhaustive and inconclusive in their first phase. Stephen was admitted for two weeks to the hospital in St Bartholomew's in London, where he underwent a battery of neurological tests, blood tests, X-rays, and a then-novel procedure called a myelogram in which a contrast dye was injected into his spinal column and the resulting images studied for evidence of nerve damage. He was kept in the hospital, in a ward of considerably older men with various advanced neurological conditions, for two weeks during which he had little to do but read and observe the suffering of his ward-mates — an experience he would later describe as one of the most distressing of his life and one that, somewhat paradoxically, helped him reconcile himself to his own diagnosis when it came. The young man across from him, dying slowly of leukaemia, gave him a sense of his own comparative good fortune that he never afterwards lost.

The diagnosis was delivered to him by his consultant in February 1963, shortly before his twenty-first birthday. He was told that he had amyotrophic lateral sclerosis, a form of motor neuron disease — a progressive neurodegenerative condition in which the motor neurons of the central nervous system, the cells that control voluntary muscle movement, degenerate and die over a period of years, leading inexorably to paralysis of the voluntary muscles, eventual difficulty in swallowing and breathing, and, in most cases, death within two to five years of diagnosis. The condition was untreatable, irreversible, and would progress at a rate that could not be reliably predicted but that would, on average, leave him bedridden within a few years and dead within three to five. His cognitive faculties would be unaffected; his mind would remain entirely intact while his body decayed around it.

The diagnosis was a devastating shock. He fell into a period of deep depression that lasted several months, during which he lost interest in his graduate work, drank heavily by his own subsequent account, and spent much of his time alone in his rooms at Trinity Hall. He had recurring dreams of being executed, which he later interpreted as a sense of the brevity of the time he might have left. He thought of giving up his graduate work, on the reasoning that there was no point in beginning a doctoral thesis that he would not live to complete. He thought, too, in passing, of suicide, though without acting on the thought.

Two events of the spring and summer of 1963 turned him gradually around. The first was his meeting, at a New Year's party in St Albans just before his diagnosis, of a young woman named Jane Wilde, an eighteen-year-old undergraduate at Westfield College, London, reading modern languages. They had been introduced through a mutual friend and had been corresponding intermittently through the early winter; after the diagnosis they continued to correspond and gradually fell into a deepening attachment that became, by the summer, an explicit love affair. Stephen would later say that meeting Jane was the thing that gave him a reason to go on with his life; the prospect of a marriage, a family, and some years of shared happiness, however short, gave him a horizon to work toward, and the depression that had followed the diagnosis began slowly to lift. The second event was the slow realisation, through the spring and summer of 1963, that his condition was not progressing as rapidly as the doctors had predicted. He continued to fall occasionally, his speech remained slightly affected, but he did not become rapidly worse. By the time he returned to Cambridge for the new academic year in October 1963, he had begun cautiously to hope that he might in fact live considerably longer than the two or three years he had been given.

He was right. His form of motor neuron disease, it would later become clear, was an unusually slow-progressing one — what doctors would eventually describe as a juvenile-onset variant with a relatively benign course. The reasons for the slow progression were and remain unclear; some specialists have speculated that the disease may have stabilised in some neurons even as it progressed in others, others that he had an unusual genetic variant, others that the steady cognitive activity of his theoretical work may have offered some neuroprotective effect. Whatever the cause, the practical effect was that he would, against every prediction, live for fifty-five years after his diagnosis — more than ten times the average for the disease. His physical capacities would, however, decline steadily over those decades, until he was completely paralysed and dependent on machinery for breathing, for speaking, and for almost every aspect of his daily life. The trajectory of his physical decline, set against the trajectory of his intellectual achievement, would be the great drama of his adult life.

Engagement and Marriage to Jane Wilde

Stephen and Jane Wilde became engaged in October 1964 and were married on 14 July 1965 in a small ceremony at Trinity Hall Chapel in Cambridge. Jane was, at the time of the engagement, a nineteen-year-old undergraduate at Westfield College, London, reading modern languages with a specialisation in medieval Spanish and Portuguese poetry; she came from a family rather more conventionally middle class than the Hawkings — her father was a civil servant in the Treasury and her mother a housewife in St Albans — and she was a devout member of the Church of England, a faith that would become an increasingly important point of difference between her and her husband in the decades to come. She was a serious, intelligent, kind, and somewhat unworldly young woman who had no clear sense, when she became engaged to Stephen, of what marriage to a man with a progressive and ultimately fatal neurological condition would involve. She would write many years later, with considerable retrospective candour, that if she had fully understood the implications she might not have gone through with the marriage; but she had loved Stephen, had wanted to support him, and had reasoned that even a few years of married happiness would be worth the suffering at the end.

The marriage gave Stephen, for the first time since his diagnosis, a stable emotional foundation and a clear set of practical motivations. He had to earn enough to support a family; he had to complete a doctoral thesis and to find a research position; he had to do, in short, what any ambitious young man of his profession did, and the disease meant that he had to do it quickly and under pressure. The combination of urgency and stability proved an extraordinary stimulus. The Stephen Hawking who returned to his graduate work in October 1963 was a different scholar from the one who had arrived a year earlier. He was no longer drifting; he was working with the focused intensity of a man who knew he had limited time, and the casual brilliance that had marked his Oxford undergraduate years was now harnessed to a sustained programme of theoretical research.

Doctoral Work Under Dennis Sciama

Dennis William Sciama (1926–1999) was, in 1962, a young Reader in physics at Cambridge in his late thirties, a slim, intense, energetic theorist with a particular interest in general relativity and cosmology. He had taken his PhD under Paul Dirac at Cambridge in the early 1950s, had written a doctoral thesis on Mach's principle (the suggestion that the inertia of local bodies is somehow determined by the distribution of matter throughout the universe), had spent several years as a research fellow at Trinity College, Cambridge, and had built up by the early 1960s a small but increasingly distinguished research group at the DAMTP. He was, by every account of his many students, a remarkable supervisor — intensely interested in his students' work, available to discuss problems at any hour, ferociously well-read in the current literature, generous with ideas and equally generous in handing his ideas to his students for development. His pupils, taken together, would later constitute a roster of the most distinguished British cosmologists and theoretical physicists of the late twentieth century: Stephen Hawking, Martin Rees (later Astronomer Royal and Master of Trinity), George Ellis (Hawking's eventual collaborator on The Large Scale Structure of Space-Time), Brandon Carter, John Barrow, and many others.

The intellectual atmosphere of the Sciama group in the mid-1960s was that of a small and tightly knit research community working on the foundational problems of general relativity and cosmology. The principal questions of the field were then in flux. The discovery in 1965 of the cosmic microwave background radiation by Arno Penzias and Robert Wilson at Bell Laboratories had given strong empirical support to the Big Bang model of cosmic origin, displacing the rival steady-state theory that Hoyle, Bondi, and Thomas Gold had developed in the late 1940s and that Sciama had himself defended through most of the 1950s; the abrupt change in the theoretical landscape this discovery required was being absorbed in the Cambridge group through 1965 and 1966. Roger Penrose, then a young theorist at Birkbeck College London, had in early 1965 published a paper proving that the gravitational collapse of a star massive enough to overcome all internal pressures must lead inevitably to a singularity — a region of infinite density and curvature — at its centre. The implications of this result for the broader theory of gravitational collapse, for the structure of black holes (a term not yet in common use), and for the question of the singularity at the beginning of the universe were not at all clear. The Cambridge group around Sciama was the natural place for these implications to be worked out.

Stephen, in his second year of graduate work, settled on a thesis topic that would address exactly these questions. He proposed to study, by means of the global geometric techniques that Penrose had developed, the question of whether the universe as a whole must contain a singularity at its origin — an initial Big Bang singularity at which the laws of classical physics break down. The question was the cosmological mirror image of Penrose's question about the collapse of stars; it asked, in effect, whether the universe must have had a definite beginning in time. Working through 1964 and 1965, using and extending Penrose's methods, Hawking proved a series of theorems showing that under very general conditions — conditions met by the actual observed universe — the equations of general relativity require the existence of an initial singularity at a finite time in the past. The result, published in his doctoral thesis Properties of Expanding Universes in October 1965 and in a series of journal papers between 1965 and 1970, established him at the age of twenty-three as a theorist of the first rank in his field.

Singularity Theorems and the Penrose Collaboration

The collaboration with Roger Penrose, which began in earnest in 1965 and continued for the next five years, produced the most important sustained body of mathematical work of Hawking's career — the so-called Penrose-Hawking singularity theorems, a series of papers that established under increasingly general conditions that the equations of general relativity, taken as exact, predict the existence of singularities both at the centres of black holes and at the beginning of the universe. The theorems are a triumph of geometric analysis. They do not depend on any assumption of symmetry, and they do not depend on the details of the matter content of the universe; they show, by purely geometric arguments about the global structure of spacetime, that under conditions of positive energy density and a few other reasonable physical assumptions, geodesics — the trajectories of freely falling particles — must in certain circumstances terminate at points of infinite curvature.

The implications of the singularity theorems were and remain profound. On the one hand, they confirmed that the singularities that Schwarzschild had found in 1916 at the centre of his exact solution of Einstein's equations were not artefacts of the symmetry of his particular solution but were generic features of gravitational collapse in general relativity; on the other, they showed that the Big Bang model of cosmic origin, which had previously appeared to depend on assumptions of homogeneity and isotropy, was in fact much more robust than had been thought. They left general relativity, in effect, predicting its own breakdown: under the conditions of black hole formation and of the very early universe, the theory implied that its own equations would fail to describe physical reality. The natural conclusion, drawn by Hawking and Penrose and most other workers in the field, was that general relativity must in those regimes be replaced by a more fundamental theory — a quantum theory of gravity, integrating the principles of general relativity with those of quantum mechanics. The search for that theory of quantum gravity, which Hawking would pursue for the rest of his career and which remains unfinished today, was set in motion by the singularity theorems.

The collaboration with Penrose was, in the end, the most important intellectual partnership of Hawking's working life. Penrose, eight years older, more mathematically sophisticated, more philosophically inclined, and with a wider intellectual range than Hawking, brought to the collaboration the geometric methods that made the theorems possible and the patient, careful style of mathematical argument that characterised his work. Hawking brought a quicker intuition for physical implications, a greater willingness to take provocative theoretical positions, and a remarkable capacity for combining geometric and algebraic techniques. The two would in due course follow somewhat different paths — Penrose toward the philosophical foundations of physics and toward his idiosyncratic theory of consciousness, Hawking toward the quantum mechanics of black holes and the cosmological wave function — but their early collaboration formed the basis of an enduring intellectual friendship that would continue until Hawking's death.

Research Fellowship at Gonville and Caius

Hawking submitted his doctoral thesis in October 1965 and was awarded the PhD in March 1966. The thesis, Properties of Expanding Universes, was already the basis of three published papers, including the most famous of them, "Singularities in the Universe," which appeared in the Physical Review Letters in October 1965. On the strength of these papers he was awarded, in March 1965, a research fellowship at Gonville and Caius College, Cambridge — one of the older Cambridge colleges, with a strong scientific tradition (its alumni included William Harvey and Francis Crick), and a college to which he would remain affiliated for the rest of his life. The fellowship gave him a small salary, rooms in college, dining rights at the high table, and three years (subsequently extended) of complete freedom to pursue his research without teaching obligations. It was a remarkable institutional appointment for a young man of twenty-three with a fatal neurological condition; the college had been advised by Sciama and others that Hawking was a young theorist of exceptional promise whose probable short life made it important to give him every opportunity to do his work.

The Hawkings settled into married life in Cambridge in the latter half of 1965, taking a series of progressively larger flats in the centre of the city as their family grew. Their first child, a son named Robert, was born in 1967; a daughter Lucy followed in 1970, and a third child, Timothy, in 1979. Jane took on, in addition to her own academic studies — she would, despite the demands of marriage and motherhood, complete a PhD in medieval Spanish poetry at Westfield in 1981 — the principal burden of running the household, caring for her increasingly disabled husband, and managing the practical details of his daily life. The marriage in these years was happy by all accounts. Stephen could still, in the late 1960s, walk with two sticks and could climb stairs slowly; he could feed himself, dress himself, and write by hand, though with difficulty; he travelled for conferences, played with his small children, attended college dinners, and lived in most respects the life of a young Cambridge don, albeit one whose physical capacities were gradually narrowing year by year.

Black Hole Mechanics and the Four Laws

The work that occupied Hawking through the late 1960s and the early 1970s, and that culminated in the great discovery of 1974, concerned not the singularities at the centres of black holes (which the Penrose theorems had already established) but the much subtler question of the behaviour of the horizon — the surface surrounding the black hole inside which not even light can escape and which therefore defines the boundary between the visible universe and the unreachable interior. The geometry of the horizon, and the way it changes when matter or energy falls into the black hole, became Hawking's principal preoccupation in this period, and the results he derived in a series of papers between 1970 and 1973 laid the mathematical foundation for everything that came afterwards.

The first key result, derived in 1970 and published in the following year, was what became known as the area theorem: the proof that, in classical general relativity, the total surface area of the event horizon of a black hole can never decrease in any physical process. If two black holes merge, the area of the horizon of the resulting black hole must be at least as large as the sum of the areas of the original two; if matter or radiation falls into a black hole, the area of its horizon must increase by an amount at least equal to the equivalent area associated with the infalling matter. The area theorem was a striking and beautiful result of pure geometry, derived using the same global techniques that had given Hawking and Penrose the singularity theorems, and it gave the area of the horizon the character of an irreducibly monotonic quantity — something that always grows, never shrinks, irrespective of the details of the physical process.

The analogy to the second law of thermodynamics, which states that the entropy of a closed system never decreases, was immediately noticed by alert observers. Most prominently, the young Israeli-American physicist Jacob Bekenstein, then a graduate student of John Wheeler at Princeton, proposed in his 1972 doctoral thesis that the analogy was not merely formal but substantive: that black holes really do have an entropy proportional to the area of their horizons, and that this entropy must be combined with the entropy of the matter outside the black hole in any complete formulation of the second law of thermodynamics. The proposal was, on its face, radical and strange. Entropy in thermodynamics is associated with temperature; if a black hole has entropy, it must also have a temperature; but a black hole that has a temperature must radiate energy at that temperature; but a black hole, by the classical definition of the term, cannot radiate anything at all, since nothing can escape from inside its event horizon.

Hawking initially rejected Bekenstein's proposal as a misuse of the formal analogy. In a paper of 1973, written with Bardeen and Brandon Carter, he formulated what came to be known as the four laws of black hole mechanics — a set of theorems that exhibited a precise mathematical analogy between the variables describing the equilibrium of a black hole (surface gravity, area, mass, angular momentum, electric charge) and the variables of ordinary thermodynamics (temperature, entropy, energy, work). The four laws of black hole mechanics looked exactly like the four laws of thermodynamics: a zeroth law stating that the surface gravity is constant over the horizon of a stationary black hole; a first law expressing the energy balance for processes involving black holes; a second law (the area theorem) stating that the horizon area never decreases; a third law stating that the surface gravity cannot be reduced to zero by any finite sequence of operations. But Hawking, Bardeen, and Carter explicitly noted in their paper that the analogy was formal only; the physical interpretation of the black hole quantities as thermodynamic ones, as Bekenstein had proposed, faced the insurmountable obstacle that a black hole could not, in classical general relativity, have a temperature at which it might radiate. The four laws were, in Hawking's view in 1973, a striking mathematical curiosity, not a physical reality.

The Discovery of Hawking Radiation

The discovery that black holes do, after all, radiate — the discovery that bears Hawking's name and that constitutes the most important single contribution he made to theoretical physics — came in the latter half of 1973 and was published in the most cited single paper of his career, "Particle Creation by Black Holes," which appeared in the journal Communications in Mathematical Physics in August 1975, with a preliminary announcement in Nature in March 1974. The discovery was unexpected. Hawking had begun, in mid-1973, to investigate what happens to the laws of quantum field theory near the horizon of a black hole — not with any expectation of overturning the classical result that black holes do not radiate, but in order to make the apparent analogy between black hole mechanics and thermodynamics still more obviously formal by showing that quantum effects did not change the classical picture. The calculation was a careful one: Hawking considered a scalar field in the curved spacetime around a black hole that had formed by the gravitational collapse of a star, computed the quantum vacuum state of the field at very early times (before the collapse) and at very late times (long after the collapse), and asked whether the two vacuum states agreed.

To his astonishment, they did not agree. The state that looked like a vacuum at early times — that is, contained no particles — looked, at late times, like a state filled with thermal radiation, emitted from the black hole at a temperature inversely proportional to its mass. A black hole of one solar mass, the calculation showed, would radiate at a temperature of about sixty nanokelvin, far below the temperature of the cosmic microwave background and therefore quite undetectable in practice. A black hole of one micrometre radius (with a mass comparable to that of a large mountain) would, by contrast, radiate at a temperature of millions of kelvin, brighter than a small star, and would in fact rapidly evaporate, ending in a final burst of high-energy gamma radiation that might in principle be detectable from anywhere in the observable universe. The radiation, moreover, had the precise spectrum of thermal black-body radiation, governed by exactly the relationship between temperature, entropy, and area that Bekenstein had proposed two years earlier. The formal analogy between black hole mechanics and thermodynamics was, after all, a substantive physical identity. Black holes have real temperatures and real entropies; the entropy is exactly a quarter of the horizon area in natural units; and the second law of thermodynamics — when reformulated as the generalised second law, requiring the sum of black hole entropy and ordinary entropy outside black holes to never decrease — is restored to its place as a universal principle of physics.

The implications were stunning. Hawking radiation, in the first place, meant that black holes were not the absolute prisons that classical general relativity had described. They radiated, slowly lost mass, and eventually — over time scales fantastically long for stellar-mass black holes but very short for the small primordial black holes that might have formed in the early universe — would evaporate completely, disappearing in a final flash of high-energy radiation. The radiation, in the second place, established a deep and previously unsuspected connection between three of the most fundamental theories of modern physics — general relativity (which describes gravity and spacetime), quantum mechanics (which describes the behaviour of matter and radiation at the smallest scales), and thermodynamics (which describes the statistical behaviour of large collections of particles). The fact that all three theories could be combined into a single consistent description of the behaviour of a black hole suggested, for the first time, that the long-sought unification of gravity with quantum mechanics might be achievable, and it set in motion a research programme — black hole thermodynamics, the holographic principle, string theory's approach to quantum gravity — that has dominated theoretical physics for the past fifty years.

The 1974 paper was at first received with scepticism. Hawking gave the first public announcement of the result at a conference at the Rutherford Laboratory in Oxford in February 1974, in front of an audience that included most of the leading British relativists. The chairman of the session, the Cambridge cosmologist John Taylor, immediately stood up and declared that the result must be wrong. Penrose was more receptive, and over the following months, as other theorists checked the calculation and found that it was correct, the result became gradually accepted. By the end of 1974, Hawking radiation had become one of the most celebrated theoretical results in modern physics; in March 1974, Hawking was elected a Fellow of the Royal Society at the age of thirty-two, one of the youngest physicists to be so honoured. By 1976 the result had been independently confirmed by several different theoretical methods. In the half-century since its publication, the original 1975 paper has been cited more than eleven thousand times in the technical literature, and the field of black hole thermodynamics it created has remained one of the most active areas of theoretical research.

The Black Hole Information Paradox

A consequence of Hawking radiation that Hawking himself recognised within a few years of his discovery has, in the decades since, become perhaps the most discussed unresolved problem in theoretical physics. The radiation emitted by a black hole has, according to Hawking's calculation, an exactly thermal spectrum — that is, it carries no information beyond the temperature of the radiation, which depends only on the mass of the black hole. If a book, an encyclopaedia, or a person were to fall into a black hole, the information they contained would, in the classical picture, simply disappear behind the event horizon. If the black hole then evaporated completely by Hawking radiation, the information would, it seemed, be lost forever; the final state of the universe, after the black hole had gone, would contain less information than the initial state. The conclusion conflicted directly with one of the deepest principles of quantum mechanics — the principle of unitarity, which requires that the evolution of any quantum system preserves information about its initial conditions in a definite mathematical sense. If Hawking radiation destroyed information, quantum mechanics itself would have to be modified.

Hawking, in a 1976 paper titled "Breakdown of Predictability in Gravitational Collapse," took the radical position that quantum mechanics would indeed have to be modified to accommodate the loss of information into black holes. He proposed that the standard quantum-mechanical description, in which states evolve from initial conditions to final conditions in a way that preserves information, would have to be replaced, in the presence of black holes, by a more general formalism that allowed information to be genuinely lost. The proposal was bold and provocative, and it was rejected by most of his colleagues, who were unwilling to abandon the principle of unitarity. The black hole information paradox, as the issue came to be called, was set up: either quantum mechanics is wrong, or general relativity is wrong, or the description of Hawking radiation as a purely thermal process is incomplete.

The paradox provoked decades of intense theoretical work. In 1997 Hawking made a famous bet with the American theorist John Preskill that information was indeed lost in black hole evaporation; Preskill bet that it was preserved. In 2004 Hawking publicly conceded the bet, having become convinced by developments in string theory — particularly Juan Maldacena's 1997 discovery of the AdS/CFT correspondence, which showed that gravitational physics in a certain class of spacetimes is mathematically equivalent to a unitary quantum field theory on the boundary — that information must be preserved after all. He delivered a baseball encyclopaedia to Preskill in fulfilment of the wager, observing that information could in principle be recovered from the encyclopaedia "but with great difficulty." The concession did not settle the paradox; it remained unclear, and remains unclear to this day, exactly how the information that falls into a black hole is encoded in the radiation that emerges, and the puzzle has driven much of the most innovative theoretical work in physics of the early twenty-first century, including the holographic principle, the firewall paradox of 2012, and the more recent work of Penington, Almheiri, and others on the so-called Page curve. The black hole information paradox is the great unfinished question that Hawking left to his successors, and the field has not yet caught up with him.

The Lucasian Chair

By the late 1970s, Hawking had been recognised throughout the international physics community as the leading theoretical cosmologist of his generation. The Royal Society fellowship in 1974 had been followed by a procession of further honours: the Eddington Medal of the Royal Astronomical Society in 1975, the Albert Einstein Award (the most prestigious American honour in theoretical physics) in 1979, the Pius XI Gold Medal from the Vatican Pontifical Academy of Sciences (a slightly ironic award given his eventual public atheism) in 1975. His scientific publications continued at a rapid pace; The Large Scale Structure of Space-Time, the monograph he had co-authored with George Ellis on the geometric foundations of general relativity, had appeared in 1973 and had become the standard reference of the field, and a steady stream of further technical papers had followed. He had grown a substantial doctoral following at Cambridge, with students including Don Page, Gary Gibbons, Bernard Whiting, and many others who would go on to distinguished careers in their own right.

In 1979, the year of his thirty-seventh birthday, he was elected to the Lucasian Chair of Mathematics at Cambridge, the most prestigious chair in mathematical physics in the English-speaking world. The chair, founded in 1663 by a bequest from Henry Lucas, had been held by some of the most distinguished mathematicians and physicists in history — Isaac Newton (1669–1702), George Stokes (1849–1903), Charles Babbage (1828–1839), Paul Dirac (1932–1969), and Hawking's own predecessor, James Lighthill (1969–1979). He held the chair for thirty years, until his statutory retirement at the age of sixty-seven in 2009, and presided during that time over the rapid expansion of Cambridge cosmology and theoretical physics into one of the leading centres of research in the world. The Lucasian Chair gave him not only a permanent position, but a global platform; from 1979 onward, his pronouncements on any topic in physics were attended to with the seriousness that the chair commanded.

His inaugural lecture as Lucasian Professor, "Is the End in Sight for Theoretical Physics?", delivered in April 1980, expressed a characteristic Hawking provocation: the suggestion that the unification of all the forces of nature in a single fundamental theory might be achieved within twenty years, and that the discipline of theoretical physics, having achieved its central goal, might effectively be complete by the end of the twentieth century. The prediction was, in the event, wide of the mark; forty-five years later, no fully satisfactory theory of quantum gravity has been formulated, the various unification programmes (string theory, loop quantum gravity, asymptotic safety) have not succeeded in producing a single accepted framework, and the experimental confirmation of any such theory remains as distant as it was when Hawking spoke. But the lecture set the tone of his Lucasian tenure: ambitious, public, attentive to the largest theoretical questions of the discipline, and willing to make predictions that might be embarrassed by subsequent events.

The No-Boundary Proposal and Collaboration with Hartle

Hawking's principal scientific preoccupation through the 1980s was the application of the principles of quantum mechanics to cosmology — the attempt to formulate a quantum theory of the universe as a whole, and in particular to give a quantum description of the initial conditions at the Big Bang. The singularity theorems had shown that classical general relativity broke down at the beginning of the universe; the analogue of Hawking radiation, applied to the universe rather than to a black hole, suggested that quantum effects must become important at the earliest moments; the question was how to construct a coherent quantum picture of cosmic origins.

The most influential proposal he made on this topic was the no-boundary condition, which he formulated in collaboration with the American theorist James Hartle of the University of California at Santa Barbara in a paper of 1983 titled "Wave Function of the Universe." The proposal was that the wave function of the universe — the quantum-mechanical object that describes the state of the universe as a whole — should be defined by a particular Euclidean path integral, in which the sum is taken over all compact four-dimensional geometries with no boundary in the past. The mathematical content of the proposal was that imaginary time at the beginning of the universe is treated on the same footing as space, so that there is no special instant that one would call the beginning of time. The universe, on this picture, has no boundary at the beginning; the question "what was before the Big Bang?" is, on this proposal, ill-formed, because the Big Bang is not a moment in time but a region in which time itself emerges from a more fundamental geometric description.

The no-boundary proposal was a striking and characteristically Hawking attempt to remove from cosmological theory the metaphysical embarrassment of an initial singularity. Hawking himself was fond of summarising the proposal in the phrase that "the boundary condition of the universe is that it has no boundary," and the picture he gave in A Brief History of Time, in which the four-dimensional geometry of the early universe is compared to the smooth rounded southern pole of a sphere, became one of the most widely quoted images of late twentieth-century popular cosmology. Whether the no-boundary proposal is in fact the correct description of cosmic origins remains, half a century after its formulation, an open question; the proposal is one of several competing approaches to quantum cosmology, and the rapidly developing field of cosmological inflation has somewhat shifted the focus of theoretical attention. But the no-boundary proposal stands as one of the most original and influential ideas in quantum cosmology, and the body of work it generated — by Hawking, Hartle, Don Page, Stephen Hawking's many doctoral students, and a host of subsequent workers — has been a continuing presence in the theoretical literature.

The Tracheotomy and the Voice

Through the 1970s and the early 1980s the physical progression of Stephen Hawking's motor neuron disease continued at a slow but inexorable pace. He had lost the use of his legs by the early 1970s and had been confined to a wheelchair from then on; his arms and hands had progressively weakened through the decade; by the early 1980s he could no longer feed himself, dress himself, or hold a pen. His speech, always slightly affected since the diagnosis, had grown progressively more slurred as the muscles of his throat and tongue weakened, until by the early 1980s only those who knew him well could understand him; he was generally accompanied to lectures and conferences by a research student or by Jane, who would translate his slurred speech into intelligible English for the audience.

In August 1985, while he was attending a conference at CERN in Geneva, Hawking contracted a severe pneumonia. He was admitted to a hospital in Geneva in a critical condition, was placed on a ventilator, and the doctors gave him only a small chance of survival. Jane was flown to Geneva from Cambridge to be with him. The doctors offered her the option of disconnecting the ventilator and allowing him to die, on the grounds that even if he survived the pneumonia he would never be able to breathe or speak without artificial support and his quality of life would be greatly diminished. She refused. He was flown back to Cambridge, where the surgeons at Addenbrooke's Hospital performed a tracheotomy — an incision in the front of the neck through which a breathing tube could be permanently inserted — that saved his life but cost him his voice forever. He emerged from the hospital after several weeks unable to make any sound, communicating only by raising his eyebrows in response to others holding up letters of the alphabet to him.

The recovery of his voice came through technology. A Californian computer scientist named Walt Woltosz, of Words Plus, Inc., had developed for his own mother-in-law (who also had motor neuron disease) a computer programme called Equalizer that allowed a disabled user to select words from a screen and have them spoken by a speech synthesiser. Woltosz heard of Hawking's condition through mutual contacts and donated a copy of the programme. Within a few weeks, the system was installed on a small computer attached to Hawking's wheelchair, and Hawking, by clicking a hand-held switch at the rate of about fifteen words a minute, could once again produce intelligible speech. The synthesised voice that the system produced — an American male voice produced by a Speech Plus CallText 5010 speech synthesiser — was not particularly natural-sounding by the standards of human speech, with a clipped, slightly mechanical quality and an American accent that was, by his own joke, "the only American accent that an Englishman has ever wanted to have." It would, over the next thirty-three years, become one of the most recognisable sounds in the world.

The speech synthesiser was modified and upgraded several times over the following decades, but Hawking refused all proposals to replace it with a more natural-sounding modern system. The voice, he said, had become part of his identity; people knew him by it; replacing it would be like losing his voice all over again. By the time of his death in 2018, the voice was running on emulated hardware, the original Speech Plus chips being long out of production, and the work of preserving the voice for him fell to a small team of engineers at Intel who maintained the system as a kind of digital heirloom. The voice survived him, and continues to be heard in archive recordings and in the films and television programmes in which he appeared.

A Brief History of Time

The book that made Stephen Hawking the most famous scientist in the world was not, at the time of its conception, intended to be a great popular work. Hawking had begun in the late 1970s to think about writing a popular book on cosmology — partly because he wanted to communicate to a wider public the extraordinary developments then taking place in his field, partly because he needed the money. The expenses of his disability were considerable; he required round-the-clock nursing care, special equipment, transport adapted for his wheelchair, and the salaries of the personal assistants and research assistants on whom he depended; his Cambridge professorial salary, while comfortable for an ordinary academic, was inadequate to cover these costs, and he had begun in the early 1980s to look for ways to supplement his income.

He worked on the book through the early 1980s, between papers on quantum cosmology and the no-boundary proposal, dictating early drafts to Jane and to research assistants, and producing first drafts of chapters between 1982 and 1984. The book that emerged was, in retrospect, an unusual one for the popular science genre. It was a serious attempt to present the most fundamental theoretical questions in cosmology — the nature of time, the structure of black holes, the origin of the universe, the search for a unified theory — in language that an intelligent general reader could follow without mathematical training. It was famously short, at about 200 pages in its first edition, but it was densely packed with ideas, and it required from its readers a degree of intellectual effort considerably greater than the average popular science book.

The publication history of the book was eventful. Hawking's original publisher, Cambridge University Press, demanded a complete rewrite when they received the first draft, complaining that the prose was too technical for the general reader. He took the manuscript instead to Bantam Books, the American trade publisher, after their editor Peter Guzzardi promised to give him serious editorial attention. Guzzardi worked with him through several drafts over more than three years, pushing him to make the book progressively more accessible, suggesting analogies, demanding that the more abstruse passages be simplified or removed. The famous remark that, on Guzzardi's advice, the book contained "only one equation" — Einstein's mass-energy equivalence E=mc² — was actually the result of a publishing-industry rule of thumb according to which every equation in a popular science book halves its potential audience.

A Brief History of Time was published in April 1988 by Bantam Books in the United States and by Bantam Press in the United Kingdom. It was an immediate and unprecedented commercial success. It went straight to the top of the New York Times bestseller list and remained on the various international bestseller lists for years afterwards. By 2001 it had sold more than ten million copies; by 2018, at the time of Hawking's death, more than twenty-five million copies in more than forty languages. The book had become a phenomenon, a cultural artefact transcending the popular science genre, a fixture of bookshop displays and bestseller lists for decades.

The book made its author rich. Hawking's royalties from A Brief History of Time and its successors gave him an income, by the late 1980s, considerably greater than his professorial salary, and allowed him to live on a scale that would otherwise have been impossible for an academic with his disability. The wealth supported the round-the-clock nursing care he required, the team of assistants who managed his communications and travels, and the various medical and technical interventions that prolonged his life through his last three decades. The book also made him a public figure on a scale that no British scientist had achieved since the days of Bertrand Russell, and the celebrity created by the book would dominate the rest of his life.

Public Celebrity and the Cultural Icon

The Hawking who emerged from the success of A Brief History of Time was a different public figure from the working theoretician who had written it. He was now a celebrity, recognised in the streets of any city in the world, sought after for interviews, public lectures, television appearances, and the endorsement of various causes. He embraced the role with characteristic relish. He made cameo appearances on television programmes — most famously on The Simpsons, on which he appeared in multiple episodes between 1999 and 2010, voicing a slightly exaggerated version of himself that became part of the show's running humour; on Star Trek: The Next Generation, in a 1993 episode in which he played a holodeck poker game with simulations of Newton and Einstein (the only person in history to play himself on the show); on The Big Bang Theory, the long-running American sitcom about theoretical physicists, on which he made several appearances from 2012 onward.

His face appeared in advertising campaigns — for British Telecom in the 1990s, for the National Health Service in support of stem cell research, for various charities supporting disability rights and motor neuron disease research. His voice was sampled by Pink Floyd in their 1994 song "Keep Talking" from The Division Bell, and again in 2014 in the song "Talkin' Hawkin'" from The Endless River. He appeared at major public events — the opening ceremony of the 2012 Paralympic Games in London, where he played a role symbolising the triumph of the human spirit over physical adversity; the funeral of Margaret Thatcher in 2013; numerous Royal Society events and Cambridge celebrations; the dedications of scientific institutes, observatories, and university buildings around the world. He was depicted in two major biographical films — Stephen Hawking, the 2004 BBC television film in which Benedict Cumberbatch portrayed him as a young man, and The Theory of Everything, the 2014 feature film in which Eddie Redmayne won the Academy Award for Best Actor for portraying him from his Oxford undergraduate days through the breakup of his first marriage.

The celebrity was not without its costs. Hawking's scientific colleagues, while generally proud of him, sometimes complained that his public statements oversimplified the complexities of theoretical physics; some of them grumbled that the public attention he received was disproportionate to his scientific contributions when compared with other contemporary theorists of comparable distinction (such as Roger Penrose, Edward Witten, or Frank Wilczek). He himself enjoyed the attention, exploited it for the causes he supported, but was aware of the danger that the public Hawking persona might come to overshadow the working physicist. He continued, throughout his celebrity years, to publish technical papers in the leading journals and to attend specialist conferences in his field, even as he simultaneously gave popular lectures to audiences of thousands.

Separation from Jane

The strains on Stephen and Jane Hawking's marriage, which had grown gradually through the 1970s as his disability worsened and the practical demands on Jane intensified, became acute in the years following the tracheotomy of 1985. Jane had been carrying, for over twenty years, a burden that few women would have accepted: the full responsibility for the practical running of a household with three children and a severely disabled husband whose care became more demanding with every passing year. She had completed her own PhD in 1981 amid these demands, an achievement that her husband and her academic colleagues did not always sufficiently appreciate. Her religious faith, which had grown stronger over the years as Stephen's increasingly public atheism had grown louder, was a source of comfort to her but a source of strain in the marriage.

After the tracheotomy, the round-the-clock professional nursing that Stephen now required was provided by a team of nurses, one of whom — Elaine Mason, a divorced mother of two who had been employed at the Hawking household from 1986 — gradually became a close personal companion to Stephen. The relationship that developed between Stephen and Elaine through the late 1980s caused increasing strain in the marriage. Jane, meanwhile, had developed a close friendship with Jonathan Hellyer Jones, the music director of the choir at St Mary the Less in Cambridge in which Jane sang; Jonathan had lost his own first wife to leukaemia in 1977 and had become a regular helper around the Hawking household and a friend to the children. The friendship between Jane and Jonathan, conducted entirely platonically with Stephen's awareness, would in time develop into a genuine love affair after the eventual separation.

Stephen and Jane separated in 1990 and divorced in 1995. The separation was, by all accounts on both sides, painful and acrimonious; Jane has written about it in two volumes of memoirs (Music to Move the Stars in 1999 and a substantially revised version, Travelling to Infinity, in 2007) with a candour that those who admire her husband have sometimes found uncomfortable. Stephen, for his part, did not write publicly about the breakdown of the marriage but allowed the implication to stand that the strains of his disability had simply been too great for the marriage to bear. The three children, by then largely adult — Robert was twenty-three, Lucy was twenty, Timothy was eleven at the time of the separation — were caught in the middle and would in different ways carry the strain of the parental conflict into their adult lives.

Marriage to Elaine Mason

Stephen Hawking married Elaine Mason in September 1995. Elaine, born in 1950, was eight years younger than Stephen, the divorced mother of two sons; she had a strong, vivid personality, was outspoken, occasionally tempestuous, and was, from the moment of the marriage, a controversial figure in the small Cambridge community. The marriage lasted eleven years, until 2006, and was throughout that period the subject of considerable gossip both in the press and in the family. Allegations of physical mistreatment of Stephen by Elaine surfaced in the British tabloid press in 2003 and 2004, leading to a police investigation; Stephen at the time refused to confirm or deny the allegations, the police closed the investigation without charges, and the matter was never publicly resolved.

What is clear, in retrospect, is that the marriage was a complicated and not always happy one. Stephen's children from his first marriage were largely estranged from Elaine; his sister Mary and his mother (who lived until 2013, dying at the age of ninety-eight) disliked her intensely; and many of his Cambridge friends and colleagues found her difficult. After the divorce from Elaine in 2006, Stephen reconciled gradually with Jane and with the children; in his last years he was on good terms with Jane (now married to Jonathan Hellyer Jones), spent frequent time with his children and grandchildren, and was attended in his daily care by a team of professional nurses managed by his eldest daughter Lucy, who had largely abandoned her own writing career to become her father's principal caretaker.

Continuing Scientific Work

Through the 1990s, the 2000s, and into the 2010s, despite the continuous decline in his physical capacities and the various interruptions caused by health crises, Hawking continued to publish papers in the leading journals of theoretical physics. The pace of his publication slowed compared with his most productive years in the 1970s, but he remained an active researcher to a degree unusual for theorists in their fifties and sixties, and his name continued to appear on important papers until the very end of his life. The principal areas of his continuing work were quantum cosmology (the development of the no-boundary proposal and its applications), the black hole information paradox (which he never abandoned and on which he revised his position several times), and the relationship between general relativity and the various approaches to quantum gravity that were being developed by the wider community.

In 2014 he wrote, in a paper titled "Information Preservation and Weather Forecasting for Black Holes," that "there are no black holes" — a deliberately provocative formulation of the more modest claim that, when quantum effects are properly taken into account, the event horizon of a black hole should be replaced by what he called an "apparent horizon," which can in time recede and release the information that had been trapped behind it. The paper was widely reported in the press as a dramatic reversal of his earlier views, though the technical content was considerably less dramatic than the headlines suggested. In 2016 he published, with the Cambridge theorist Malcolm Perry and the Harvard theorist Andrew Strominger, a substantial paper titled "Soft Hair on Black Holes," which proposed a mechanism by which the information that falls into a black hole could be encoded in soft, low-energy degrees of freedom near the horizon — a proposal that has been actively developed in the subsequent literature and that represents Hawking's last major contribution to the black hole information paradox.

His final scientific paper, "A Smooth Exit from Eternal Inflation?", written with the Belgian theorist Thomas Hertog and submitted to the journal less than a fortnight before his death, was published posthumously in May 2018. The paper proposed a refinement of the no-boundary proposal in which the universe emerges from a higher-dimensional geometry by a process of holographic projection, providing a possibly empirically testable prediction of the relative frequency of universes with different physical properties. It was, in form and substance, a remarkable demonstration that he was working at the frontier of his subject until literally the last days of his life.

Space Flight and the Zero-G Experience

A characteristic enthusiasm of Hawking's later years was for human space travel, which he believed essential for the long-term survival of humanity. He argued in lectures and in published interviews from the late 1990s onward that the various risks to which the human species was exposed on Earth — nuclear war, climate change, asteroid impact, pandemic disease, artificial intelligence run amok — made the establishment of self-sustaining human colonies on other worlds an urgent priority. He estimated, in various pronouncements, that humanity had between one hundred and one thousand years to colonise space before some catastrophic risk on Earth ended civilisation. The argument was a thoughtful application of probabilistic reasoning rather than a panicked prophecy, and it became one of the most widely reported public positions of his late years.

In April 2007, at the age of sixty-five, he experienced weightlessness in a parabolic flight aboard the modified Boeing 727 operated by the Zero Gravity Corporation. The flight, which took off from Cape Canaveral and made eight parabolic arcs over the Atlantic, allowed him to float in weightlessness for a total of about four minutes — the first time in over forty years that he had been free of the support of his wheelchair. He was attended by four physicians and two nurses during the flight, and emerged from it visibly elated. He had hoped to follow the parabolic flight with an actual journey to space aboard one of Richard Branson's Virgin Galactic suborbital craft, with which he had reserved a seat; the persistent delays in the Virgin Galactic programme, however, meant that the suborbital flight did not take place during his lifetime, and the actual experience of space remained, at his death, one of the unfulfilled ambitions of his life.

Religion and Philosophy

Stephen Hawking's public position on questions of religion and metaphysics was, by the standards of the working physicists of his generation, unusually direct. The famous closing sentence of A Brief History of Time — that a complete unified theory of physics would allow us to "know the mind of God" — had given the book a flavour of theistic openness that had probably contributed to its commercial success and that some religious readers had taken as an expression of cautious agreement with traditional theism. By the time of his next major popular book, The Grand Design (co-written with Leonard Mlodinow and published in 2010), Hawking had made his position considerably more explicit. The opening chapter of The Grand Design declared that "philosophy is dead" (a statement that caused considerable irritation in philosophy departments around the world), and the book concluded with the proposition that the laws of modern physics — in particular the law of gravity and the principles of quantum mechanics — allow the universe to come into existence spontaneously, with no need for a divine creator. "It is not necessary to invoke God to light the blue touch paper and set the universe going," he wrote.

The position was a consistent one with his philosophical convictions, which had hardened over the decades from the agnostic deism of his early years to a firm naturalistic atheism in his later ones. He came to regard religion as, at best, a comforting illusion and at worst an obstacle to the rational understanding of the world; he was particularly impatient with the various forms of creationism and intelligent design that were enjoying a revival in the United States in the 1990s and 2000s, and he was scathing about claims that the apparent fine-tuning of physical constants for the emergence of life required a divine explanation. The famous statement attributed to him in his final book, Brief Answers to the Big Questions (published posthumously in 2018), summarises the position with characteristic directness: "There is no God. No one created the universe and no one directs our fate." The position is, in his book, defended with arguments drawn from his own theoretical work — the no-boundary proposal, in particular, removes the apparent need for an initial cause of the universe, since on that proposal there is no first moment of time at which causation could begin.

Politics and Causes

Hawking's political views, expressed publicly throughout his life, were broadly those of the British liberal-left of the educated metropolitan classes. He was a lifelong supporter of the National Health Service, which had been founded the year after his birth and on which he depended for the entirety of his medical care; he wrote and spoke frequently in defence of the NHS against what he saw as the Conservative government's attempts to privatise it. He was a supporter of nuclear disarmament, following his mother's lifelong commitment to the cause. He was a strong supporter of the European project and an outspoken opponent of the United Kingdom's withdrawal from the European Union, signing public letters and giving interviews against Brexit in 2016 and 2017. He supported the cause of disabled people's rights and gave frequent interviews and lectures on the question of how society should treat its most physically vulnerable members.

He was a supporter of the boycott of Israel by international academics over the Israeli occupation of the Palestinian territories, declining in 2013 to attend a major scientific conference in Jerusalem hosted by the Israeli President Shimon Peres in protest at Israeli policy — a decision that caused considerable controversy and that brought him into conflict with several of his Jewish scientific colleagues. He was vocally critical of the American invasion of Iraq in 2003, which he described as a "war crime," and supported the cause of various humanitarian interventions in other parts of the world. He was, on most political questions, an articulate spokesman of a kind of British rationalist liberalism that had been a recognisable strand in the country's public life since the days of Bertrand Russell.

Retirement from the Lucasian Chair

Hawking reached the statutory retirement age of sixty-seven in January 2009 and was required by Cambridge tradition to vacate the Lucasian Chair. His successor in the chair was the theoretical physicist Michael Green, a leading figure in string theory and a colleague of Hawking's of long standing. The transition was managed without difficulty. Hawking was appointed to a research professorship at Cambridge — a position created for him at the Centre for Theoretical Cosmology of which he was the founding director and which he continued to lead in his retirement — and he kept his offices in the DAMTP and his research staff in unchanged form. The retirement from the chair was, in practical terms, a change in title rather than a change in activity; he continued to direct doctoral students, to participate in research seminars, to attend international conferences, and to publish papers at much the same rate as before.

The Centre for Theoretical Cosmology, established in 2007 with substantial private funding, brought together the Cambridge groups working on quantum gravity, cosmology, and related topics, and provided an institutional vehicle for Hawking's continuing research activities in his retirement years. The centre attracted some of the leading theorists of his field — Malcolm Perry, Gary Gibbons, Paul Townsend, Nick Manton, Mihalis Dafermos, and the younger generation of Cambridge cosmologists — and remained, until his death and beyond, one of the leading research groups in the field internationally.

Later Popular Work

In addition to A Brief History of Time, Hawking wrote a number of further popular books that extended and updated the picture for general readers. The Universe in a Nutshell (2001) was a kind of sequel to A Brief History of Time, with a heavier emphasis on visual illustration and a more advanced treatment of the developments of the 1990s, particularly the new ideas in string theory and braneworld cosmology. A Briefer History of Time (2005), co-written with Leonard Mlodinow, was a simplified rewriting of the original book intended for readers who had found the 1988 version difficult. The Grand Design (2010), also with Mlodinow, dealt with the multiverse hypothesis and the question of cosmic fine-tuning. My Brief History (2013) was a slim autobiographical memoir, the only sustained personal narrative he ever published. Brief Answers to the Big Questions (2018, posthumous) collected his answers to ten of the questions most often posed to him in his public lectures, covering the existence of God, the future of humanity, the dangers of artificial intelligence, the prospects for space travel, and other topics of his late preoccupation.

In collaboration with his daughter Lucy, he also wrote a series of children's books beginning with George's Secret Key to the Universe (2007), aimed at introducing young readers to the fundamental ideas of modern cosmology in the context of a friendly adventure story. The series, which Lucy continued to develop after his death, has remained popular with younger readers and has introduced his ideas to an audience that the more demanding adult books could not reach.

Honours, Awards, and the Nobel That Never Came

The list of honours, awards, and academic distinctions that Hawking accumulated over his fifty-year career is one of the most extensive of any modern scientist. He was elected a Fellow of the Royal Society at the age of thirty-two in 1974, one of the youngest physicists ever so honoured. He was awarded the Eddington Medal of the Royal Astronomical Society in 1975, the Maxwell Medal of the Institute of Physics in 1976, the Heineman Prize for Mathematical Physics of the American Institute of Physics in 1976, the Albert Einstein Medal of the Albert Einstein Society in Switzerland in 1979, the Royal Astronomical Society Gold Medal in 1985, the Wolf Prize in Physics in 1988, the Britannica Award in 1989, the Copley Medal of the Royal Society in 2006 (the oldest and most prestigious of the Royal Society's awards), the Presidential Medal of Freedom from President Barack Obama in 2009, the Russian Special Fundamental Physics Prize in 2012, and dozens of other prizes and medals from learned societies, governments, and private foundations around the world. He received more than fifteen honorary degrees from universities including Oxford, Princeton, Yale, Harvard, Cambridge itself, the University of Chicago, the Sorbonne, and many others. He was created a Companion of Honour by the Queen in 1989 (the rank in the British honours system reserved for those whose national contribution has been considered transcendent), having previously been appointed Commander of the Order of the British Empire in 1982.

The one major honour he did not receive was the Nobel Prize in Physics. The reason, as has been widely discussed and as he himself frequently acknowledged with characteristic dry humour, was simple: the Nobel committee requires experimental confirmation of theoretical discoveries before it makes an award in physics, and Hawking radiation — the discovery for which he would, by every other measure, have deserved a Nobel — has not been experimentally confirmed. The temperature of even a stellar-mass black hole is so far below the temperature of the cosmic microwave background that the radiation is overwhelmed by the background and is, by current astronomical techniques, undetectable. There have been various proposals over the years for indirect experimental confirmations of the effect — using analogue black holes constructed from sound waves in fluids, from optical fibres, or from Bose-Einstein condensates — and at least one of these analogue experiments (by Jeff Steinhauer at the Technion in Israel) reported a positive result in 2014, but the analogue experiments are not generally considered to count, by the Nobel committee's standards, as confirmations of the original theoretical prediction. The Nobel that did not come was a standing complaint of his friends and a frequent subject of his own jokes; he observed in interviews that he had every other honour in the discipline and did not particularly need a Nobel to fix his place in the history of his subject.

Final Years and the Farewell Decade

The decade between Hawking's retirement from the Lucasian Chair in 2009 and his death in 2018 was a remarkable one by any measure. His physical capacities had narrowed by 2009 to a startlingly small repertoire: he could move only the muscles of one cheek, which controlled a cursor on his computer screen by means of an infrared sensor mounted to his glasses, and the muscles of his throat in the very limited way that allowed him to swallow. He could not move his hands or his arms, could not turn his head, could not breathe without assistance, and was fed through a tube. His daily care required a team of nurses on three eight-hour shifts and a smaller team of personal assistants who managed his communications, his computer, and his appointments. The cost of this care was approximately a million pounds a year by the late 2000s, paid for from his book royalties, his lecture fees, and various private foundations that had been established to support him.

Yet within these severe limitations he continued to function as a working physicist of remarkable productivity. He gave the BBC Reith Lectures in January 2016 (a series of two lectures titled "Do Black Holes Have No Hair?" that updated his views on the black hole information paradox); he published, with Andrew Strominger and Malcolm Perry, the influential 2016 paper on soft hair at black hole horizons; he continued to direct doctoral students and to participate actively in conferences; he travelled, with great logistical effort, to scientific meetings around the world. He gave lectures in Beijing, Mumbai, San Francisco, Cape Town, Buenos Aires, and Reykjavik. He served as an honorary consultant to the Breakthrough Listen project for the detection of extraterrestrial intelligence, founded by the Russian-Israeli billionaire Yuri Milner in 2015. He participated in the Breakthrough Starshot initiative, an ambitious proposal to launch nanoscale spacecraft to the Alpha Centauri star system at twenty per cent of the speed of light. He spoke publicly about the existential risks facing humanity from artificial intelligence, climate change, and overpopulation, and he repeatedly urged humans to colonise other planets as a hedge against terrestrial disaster.

He was the subject, in this last decade, of an increasingly affectionate public attention that bordered on national reverence. The 2014 release of The Theory of Everything, in which Eddie Redmayne portrayed him with such sympathetic precision, introduced his life story to a new generation of viewers. His public appearances in his last years had the character of a national institution making one of its periodic gestures: the audience knew that what they were seeing was finite, that the man before them had defied every medical prediction by half a century, that they were watching the last working chapters of one of the great lives of their era. The press treated him with a deference and affection unusual in the relations between scientists and journalists. He, for his part, continued to make provocative public statements and to enjoy the attention.

Death and Funeral

Stephen Hawking died at his home at 5 West Road, Cambridge, in the early hours of 14 March 2018, in the company of his three children, at the age of seventy-six. The date of his death was, by the kind of cosmic coincidence that the family always noted, both Pi Day (the date 3.14 in American calendar notation, mathematically significant as the first three digits of the constant ?) and the anniversary of the birth of Albert Einstein in 1879. The cause of death was attributed to the long-term complications of his motor neuron disease; he had grown progressively weaker through the early months of 2018, had been unable to attend several scheduled engagements in the preceding weeks, and had, in his last days, lost the ability to operate even the single muscle that controlled his speech synthesiser. His daughter Lucy, who had been managing his care in his last years, was with him at the moment of his death, as were his sons Robert and Timothy and his first wife Jane.

The death was announced to the world the morning of 14 March in a statement from his family, and was the leading news story in every major newspaper in the world for the following several days. Tributes were received from heads of government, from the Pope, from leading scientists, from celebrities, and from the disabled and physically afflicted who had taken him as an emblem of human endurance. The Queen, in a personal statement, described him as a man "whose work and example have inspired millions." President Donald Trump described him as a "brilliant scientist and an amazing man." Roger Penrose, his old collaborator, wrote a long obituary in The Guardian that emphasised the scientific significance of his work and the personal qualities — wit, determination, intellectual independence, and a kind of stoic cheerfulness in the face of catastrophe — that had marked him throughout his life.

The private funeral was held at Great Saint Mary's, the university church in Cambridge, on 31 March 2018. The service was Anglican in form (a choice made by his children in deference to the family's connection with the Church, and despite his own atheism, which the family considered to be a private matter that should not determine the form of the funeral); the music included Pie Jesu from the Fauré Requiem, sung by his daughter-in-law Marion Eddington, and a piece composed for the occasion by Cheryl Frances-Hoad. The mourners included Jane Wilde Hawking, all three children and their families, his sister Mary, and a small group of his closest scientific colleagues. The remains were cremated and the ashes were preserved for the public interment that took place several weeks later.

On 15 June 2018 Hawking's ashes were interred in the nave of Westminster Abbey, in a plot between the graves of Sir Isaac Newton (who had been buried there in 1727) and Charles Darwin (who had been buried there in 1882). The choice of resting place was a deliberate and resonant one: it placed him among the two greatest figures of the British scientific tradition, in the spot where two of the greatest scientific minds of the past three centuries lay buried. The memorial service that accompanied the interment was attended by approximately a thousand people, including many of the leading figures of British public life and several thousand members of the public who had assembled outside the abbey. The eulogies were delivered by the Astronomer Royal Martin Rees, who had been Hawking's contemporary as a graduate student under Sciama; by his daughter Lucy; and by the British actor Benedict Cumberbatch, who had played him in the 2004 BBC biographical film. The European Space Agency, in a gesture of remarkable cosmic poetry, transmitted a recording of a specially-composed musical setting of his synthesised voice toward the supermassive black hole at the centre of the galaxy 1A 0620-00, the nearest known black hole to Earth, on the day of the interment; the radio signals are expected to reach the black hole some three thousand years from now.

Scientific Legacy

The scientific legacy that Hawking left to his successors is in the first instance the body of his published technical work — some two hundred and fifty papers in the leading journals of physics, the textbook The Large Scale Structure of Space-Time written with George Ellis, the various edited proceedings and lecture collections, and the influence on doctoral students and collaborators that distributed his ideas across the international research community. The most consequential of these contributions are easily identified. The singularity theorems with Penrose established the inevitability of singularities in general relativity and showed that classical gravitational physics implies its own breakdown. The four laws of black hole mechanics revealed the formal analogy between general relativity and thermodynamics. The discovery of Hawking radiation made the analogy substantive and opened the field of black hole thermodynamics. The no-boundary proposal with Hartle gave the first serious quantum-mechanical model of the origin of the universe. The black hole information paradox provoked half a century of intense theoretical activity that has not yet ended.

In the second instance, the legacy includes a research community — the long line of his doctoral students, postdoctoral collaborators, and intellectual disciples — that has continued his work and extended it in directions he did not himself foresee. Bernard Carr, Don Page, Gary Gibbons, Bernard Whiting, Malcolm Perry, Marika Taylor, Thomas Hertog, and many others were trained by Hawking at Cambridge and have gone on to distinguished careers in their own right; their students in turn constitute the third and fourth generation of the Hawking school. The Centre for Theoretical Cosmology at Cambridge, which he founded in 2007, continues as one of the leading research institutions in his field and as a permanent institutional memorial to his life.

In the third instance, the legacy is to the wider field of theoretical physics, which since the 1970s has been preoccupied with the questions Hawking raised and has only partly solved. The black hole information paradox remains, half a century after Hawking's 1976 paper, one of the great unsolved problems of theoretical physics; the various proposed solutions — the AdS/CFT correspondence, the firewall paradox, the soft hair proposal, the Page curve calculations, the recent work on replica wormholes by Penington, Almheiri, Engelhardt, and others — all draw their inspiration from Hawking's original framing of the problem. The connection between quantum entanglement and the geometry of spacetime that has emerged from this work, and the holographic principle (proposed by Gerard 't Hooft and Leonard Susskind partly in response to Hawking's puzzle), have become central organising ideas in modern theoretical physics. The quantum cosmology that grew from the no-boundary proposal remains an active research field. The investigation of the singularities of general relativity, and of the conditions under which they can be expected to occur in physical models, is a continuing area of research. Hawking's work, in short, is not a closed chapter of physics; it is one of the most active chapters of contemporary physics, and the questions he posed are still driving the discipline forward.

Cultural Legacy and the Hawking Icon

The cultural legacy is, if anything, broader still. Hawking transformed the public perception of theoretical physics in his lifetime, made cosmology a familiar subject of dinner-table conversation, and demonstrated that a working theoretician could be a celebrity of the first rank without abandoning the standards of his discipline. The model he provided — of a scientist who participated fully in the public conversation about his subject, who wrote popular books that did not condescend to their readers, who appeared in television programmes and films and at major public events, who spoke out on the political and ethical issues of his time — has been imitated by many subsequent scientists, with varying degrees of success. The "celebrity scientist" of the early twenty-first century, a recognisable cultural type that includes Neil deGrasse Tyson, Brian Cox, Michio Kaku, and many others, traces its lineage in large part to the public Hawking of the 1990s and 2000s.

The image of Hawking — the small man in the wheelchair, the metallic voice, the slightly cocked head and the wide intelligent eyes — became one of the most recognisable images of the late twentieth century, on a par with the iconic images of Albert Einstein and Mahatma Gandhi from the earlier period. The image carried an extraordinary symbolic weight: it represented at once the triumph of the human mind over the body, the dignity of the disabled, the power of disciplined thought to transcend physical limitation, the rationalist conviction that the universe can be understood by patient analysis, and the persistence of will in the face of mortal adversity. The widespread use of the Hawking image in advertisements, in public service announcements, in school textbooks, and in popular culture more broadly attests to the symbolic power that his life and figure acquired. He had become, in his last decade, less a man than an icon — a figure whose meaning was independent of the particular contents of his theoretical work and whose significance extended into domains far beyond physics.

The cultural legacy is also a legacy of inspiration to people with disabilities and to the wider public concerned with the rights and the support of disabled people. Hawking, who had himself relied throughout his adult life on the National Health Service, on his family, on his nurses, and on the various technological aids that enabled him to function, became from the 1980s onward one of the most prominent public advocates for the rights and the welfare of disabled people. He spoke and wrote frequently about the prejudices and the practical obstacles that disabled people face, about the importance of adequate medical care and social support, about the value of education and meaningful work for the disabled, and about the dangers of medical decisions made on the assumption that a disabled life is not worth living. His example — that one of the most disabled people in modern public life had also been one of its most consequential — was a standing rebuke to the assumptions that the disabled cannot or should not lead full lives.

Conclusion: the Meaning of Stephen Hawking

The life of Stephen Hawking, viewed from the perspective of the years since his death, is among the most singular human stories of the past century. The combination of profound theoretical achievement, severe and progressive physical disability, sustained personal will, and global public celebrity has no exact precedent in the history of modern science. He was not the most original theoretical physicist of his generation — Roger Penrose, Edward Witten, Stephen Weinberg, Frank Wilczek, and several others have stronger claims to that title on purely scientific grounds; he was not the deepest popular communicator of science — Carl Sagan, Richard Feynman, and several others have arguably greater claims to that distinction. He was, however, the singular figure who combined achievement and communication and personal example in a way that no other scientist of his era did, and the result of that combination was a cultural presence of unique and lasting significance.

The scientific contributions, considered on their own, would have placed him among the leading theoretical cosmologists of the late twentieth century. The singularity theorems with Penrose, the four laws of black hole mechanics, the discovery of Hawking radiation, the no-boundary proposal — these are achievements of the first rank in mathematical physics, and they have shaped the direction of the discipline for half a century. Together they amount to perhaps the most consequential body of theoretical work in gravitational physics since the original development of general relativity by Einstein. Whether or not they would, on their own, have made him a household name, they make him a permanent figure in the history of theoretical physics.

The combination of these contributions with the public role of A Brief History of Time and its successors, with the cultural ubiquity of the Hawking image in his later years, and with the extraordinary personal narrative of survival and achievement against motor neuron disease, made him in addition one of the great public figures of his time. He helped to shape the public understanding of cosmology in a generation when the questions of the origin and structure of the universe became matters of widespread popular curiosity. He provided a model — for disabled people, for working scientists, for any reader of his books — of how a human life can be lived with intellectual seriousness and personal dignity in the face of severe physical and emotional adversity. He was, in his last years, the most universally recognised scientist in the world, and his face and voice had passed from the technical literature of theoretical physics into the broader vocabulary of late twentieth-century culture.

The grave in Westminster Abbey, between Newton and Darwin, on which is inscribed the now-famous equation S = (kc³ A) / (4?G) — the Hawking-Bekenstein formula for the entropy of a black hole — is the appropriate resting place for a man who placed himself, by his work, in the central line of British scientific thought from Newton through Maxwell and Dirac to the present. He had said, in many of his public interviews, that he had no patience with the question of personal meaning or the question of what happens after death; he believed that the brain was a complicated machine that ceased to function at death, that consciousness did not survive the physical organism, and that the appropriate human response to mortality was to make the most of the time available. The pattern of his own life — fifty-five years lived against every medical prediction, packed with achievement and engagement of a kind that even healthy contemporaries rarely matched — was the most eloquent argument his views could have had.

The cosmic perspective he had spent his life developing, the long view back to the Big Bang and forward into the unfathomable depths of the future, had a certain consolatory power in the face of his own approaching death. He liked to say that humans were unusually fortunate creatures, the products of fourteen billion years of cosmic evolution, capable of comprehending the laws of nature and of contemplating the cosmos that had made them. To have lived seventy-six years as one of the most distinguished representatives of that comprehending species, and to have left behind a body of work that had advanced the understanding of nature in fundamental and permanent ways, was, by his own measure, an outcome that any human being might be grateful for. The fact that he had done it from a wheelchair, against fifty-five years of progressive paralysis, communicating in his last decades through a single twitch of a muscle in his cheek, was the additional and almost incidental detail that made his life a story for the ages.

The Hawking who died in his Cambridge bedroom in March 2018 was the same Stephen Hawking who, fifty-five years earlier in February 1963, had been told in a London hospital that he had perhaps two years to live. He had used the intervening half-century to do work that had altered the trajectory of modern theoretical physics, to write books that had introduced cosmology to millions of readers, to raise a family, to participate in the public conversation of his time, to support the causes he believed in, and to demonstrate by the example of his own life that the limits of physical possibility are not always the limits of human achievement. The chapter of human history that begins with his diagnosis and ends with his interment in Westminster Abbey is one of the most remarkable in the modern record. Whatever the eventual fate of his theoretical work — whether the black hole information paradox is solved in the next decade or the next century, whether the no-boundary proposal is confirmed or refuted, whether Hawking radiation is ever experimentally detected — the life he lived has already taken its permanent place in the larger story of human achievement, and the example of his persistence will continue, long after the technical details of his physics have been absorbed into the standard textbooks, to remind those who learn of him that intelligence, will, and the patient pursuit of understanding can, in the right combination, produce outcomes that even the most informed prediction would not have imagined possible.