Astronomy

What's the point with Hawking Radiation?

What's the point with Hawking Radiation?


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I saw that Black Holes can evaporate because of Hawking radiation. Because pair of particle, antiparticle can spawn at any point of the space, the antiparticle could be absorbed by the black hole and the particle go outside of it, like if the black hole where "lightning".

But, if one element of the pair can be absorbed by the black hole, isn't there an equal probability of that the particle will be absorbed, too?

I could imaginate that the probability of fluctuation of going into 0 with an equal probability of +1 or -1 mass over time is nonnull, also that's why black hole could evaporate, or something like it?


I cannot show this or prove it but the main idea, in simplest terms, is that a matter-antimatter pair, near the event horizon, will form. A member of this pair will decay back into the event horizon and be absorbed by the black hole. The other particle will decay out into the free space.


Hawking radiation

Hawking radiation is supposed to emanate from black holes because black holes have a temperature. A black hole has to be about 3 times the solar mass. A black hole with a few times the mass of the sun would have a temperature of only one ten millionth of a degree above absolute zero. This is much lower than the 2.7 K ambient temperature of the microwave background radiation.
We know that the second law of thermodynamics requires that heat only flow from a hotter to a colder body. Thus it would seem Hawking radiation would not be practically possible in the present universe - it is only a theoretical principle.
As for mini black holes in the early universe, even though mini black holes would be hotter, the early universe would also have been hotter. So mini black holes would radiate and explode only if they were hotter than the ambient temperature.

What do you guys have to say about this temperature differential issue?


"Black holes can only get bigger" - huh?

Note that this conclusion does not mean Hawking radiation definitely does not happen, or should no longer be considered as a possible prediction. It means we don't really know either way. As the same paper says in its abstract:

"[A] definitive theoretical treatment will require an understanding of quantum gravity in at least some regimes. Until then, no compelling theoretical case for or against radiation by black holes is likely to be made."

At the bottom of p. 3, the paper says that this possibility is unlikely:

"These results strongly suggest that the conventional wisdom as regards the formation of black hole is correct and that the semiclassical radiation does not prevent the formation of the event horizon."

I have not claimed that in semiclassical GR semiclassical radiation prevents the formation of the event horizon. A paper which makes such a claim is

Gerlach, U.H. (1976). The mechanism of blackbody radiation from an incipient black hole, Phys Rev D 14(6) 1479-1508.

I'm neutral about this question. My point is simply that QG is unknown, that we can have QG effects if the surface time dilation reaches factors like ##10^ <100>t_/t_##, and if we assume that unknown QG effects stop the collapse once such a factor is reached, then we can used the Paranjape paper to see that there will be no Hawking radiation. (If we think that this needs more justification than simply "stable stars don't radiate".) For this sufficiently simple argument I have no reference in the literature.


Hawking Points in the Cosmic Microwave Background

SAN DIEGO , Aug. 16, 2018 /PRNewswire/ -- Images of the night sky appear to show 'Hawking Points' – direct evidence of the existence of Hawking radiation from a previous aeon.

Sir Roger Penrose has proposed our Universe is one of a series of universes – 'eons' – where the big bang of each has its origin in the remote future of the previous one. Now a paper released to the arXiv with Daniel An of SUNY Maritime College , New York and Krzysztof Meissner of the University of Warsaw finds that images of the CMB background radiation show evidence of black hole evaporation from a previous Universe in accordance with his theory.

One of Stephen Hawking's most famous predictions was that black holes are not black but rather a very dark grey. Black holes are extremely cold objects but they are not at absolute zero and by the laws of thermodynamics should 'glow' – radiating heat in the form of low temperature photons and neutrinos.

At the centre of our galaxy is a super massive black hole. In around four billion years our galaxy will collide with Andromeda, our nearest galactic neighbour, and its much larger supermassive black holes will merge with ours. This event will give off a vast energy pulse as the two black holes spin around each other and merge. Over the ensuing millennia other galaxies in our cluster will collide with us leaving one enormous black hole surrounded by an extinct dust cloud. But this is not the end…

Our universe is expanding and as it cools over the next googol (10 100 ) years the black holes will start to glow in the night sky. Although this 'glow' is extremely faint – a temperature much less than one ten millionth of a degree above absolute zero – it will last for perhaps a googol years, and when viewed from the next aeon these glowing black holes – Hawking Points – will be amongst the largest continuous energy sources in the CMB night sky. The reason we do not see these points without computer analysis is they are very faint and the early universe has scattered them over a large area. What once was a point is now a disk around five times the diameter of our moon.

Careful analysis of the night sky has found around 30 of these points in the cosmic microwave background map. Five of these points coincide with previously discovered concentric circles in the CMB sky. Interestingly one of the points coincides with the observation window of the BICEP 2 observatory opening up the ability to examine coincidences with the magnetic field patterns which CCC would also predict at Hawking Points.

The full arXiv Paper can be found at https://arxiv.org/abs/1808.01740.

About the Penrose Institute
The Penrose Institute is a research organisation whose mission is to understand the human mind, the cosmos and the laws of physics that govern them.
Web: www.penroseinstitute.com
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About Sir Roger Penrose
Sir Roger Penrose is Emeritus Professor at the Mathematical Institute of the University of Oxford , winner of the Copley Medal and the Wolf Prize in Physics, which he shared with Stephen Hawking .

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What's the point with Hawking Radiation? - Astronomy


Has Stephen Hawking been wrong for the last 30 years?

Stephen Hawking is the most famous scientist on the planet. His popular science book 'A Brief History of Time' was a publishing sensation, staying at the top of the bestseller lists longer than any other book in recent history. But behind the public face lies an argument that has been raging for almost 30 years.

Hawking shot to fame in the world of physics when he provided a mathematical proof for the Big Bang theory. This theory showed that the entire universe exploded from a singularity, an infinitely small point with infinite density and infinite gravity. Hawking was able to come to his proof using mathematical techniques that had been developed by Roger Penrose. These techniques were however developed to deal not with the beginning of the Universe but with black holes.

Science had long predicted that if a sufficiently large star collapsed at the end of its life, all the matter left in the star would be crushed into an infinitely small point with infinite gravity and infinite density &ndash a singularity. Hawking realised that the Universe was, in effect, a black hole in reverse. Instead of matter being crushed into a singularity, the Universe began when a singularity expanded to form everything we see around us today, from stars to planets to people. Hawking realised that to come to a complete understanding of the Universe he would have to unravel the mysteries of the black hole.

Taming the black hole

Hawking and his fellow physicists embarked on an extraordinary intellectual expedition &ndash to tame the black hole. The period from the early 70s to the early 80s became known as the golden age of black hole research. Slowly physicists were coming to understand this most destructive force of nature.

But Hawking realised that there was something missing from the emerging picture. All work on black holes to that point used the physics of the large-scale Universe, the physics of gravity first developed by Newton and then refined by Einstein's theories of general and special relativity.

Hawking realised that to come to a full understanding of black holes, physicists would also have to use the physics of the small-scale Universe the physics that had been developed to explain the movements of atoms and sub-atomic particles, known as quantum mechanics. The problem was that no one had ever combined these two areas of physics before. But that didn't deter Hawking. He set about developing a new way to force the physics of quantum mechanics to co-exist with Einstein's relativity within the intense gravity of a black hole.

Hawking radiation

After months of work Hawking came up with a remarkable result. His equations were showing him that something was coming out of the black hole. This was supposed to be impossible. The one thing that everyone thought they knew about black holes was that things went in but nothing, not even light itself, could escape.

But the more Hawking checked, the more he was convinced he was right. He could see radiation coming out of the black hole. Hawking then realised that this radiation (later called Hawking Radiation) would cause the black hole to evaporate and eventually disappear.

Although Hawking's theories about black hole evaporation were revolutionary, they soon came to be widely accepted. But Hawking knew that this work had far more fundamental consequences. In 1976 he published a paper called 'The Breakdown of Predictability in Gravitational Collapse'. In it he argued that it wasn't just the black hole that disappeared. All the information about everything that had ever been inside the black hole disappeared too.

Are there limits to what science can know?

In everyday life we're used to losing information but according to physics this isn't supposed to happen. Physics has it that information is never really lost, it just gets harder to find. Physicists cling on to this idea because it's their link with either the past or the future. If information is lost then science can never know the past or predict the future. There are limits to what science can know.

For many years no one took much notice of Hawking's ideas until a fateful meeting in San Francisco. Hawking presented his ideas to some of the world's leading physicists. In the audience were Gerad t'Hooft and Leonard Susskind, two leading particle physicists. They were shocked. Both realised that Hawking's 'breakdown of predictability' applied not only to black holes but to all processes in physics. According to Susskind, if Hawking's ideas were correct then it would infect all physics, there would no longer be any direct link between cause and effect. Physics would become impotent.

Since that meeting the 'information paradox' has become one of the most fundamental and most difficult problems in physics. Arguments effectively boiled down into two camps. On the one side were Susskind and those who believed that Hawking was wrong: information could not be lost. On the other were Hawking and those who believed that physics would have to be rewritten to take into account the uncertainty about information that Hawking had uncovered.

For 20 years arguments raged. Neither side was willing to admit defeat. Until a paper emerged by a brilliant young Argentinean mathematician known as Juan Maldacena. It claimed to be a rigorous mathematical explanation of what happened to information in black holes. It showed that information was not lost. Hawking, it seemed, was on the losing side. But he was not convinced.

Hawking set to work with a young research student, Christophe Galfard, to try to pick apart the Maldacena paper. They thought they could use the same mathematical techniques employed by Maldacena to prove that information was in fact lost. But after two years they still could not prove their thesis.

Solving the paradox

Then disaster struck. Hawking was taken ill with pneumonia and rushed to hospital. Doctors feared for his life. He was kept in hospital for over three months. But whilst others fussed over his health, Hawking was thinking. Finally, on what many feared might be his death bed, he thought he'd come across what had eluded him for the past 30 years &ndash a solution to the information paradox.

Once again Hawking defied the doctors' dire predictions and was soon back at work, working on a new proof for the information paradox. Then in July 2004, at one of the most prestigious conferences in physics, Hawking made a dramatic announcement. He claimed to have solved the information paradox. But to the surprise of many in the audience he was not at the conference to defend his long held belief that information was lost in black holes, instead he claimed that he could now prove the opposite.

Hawking presented the outline of a proof that he hoped would at last solve the problem that he had posed almost 30 years earlier. But despite the bold claims, some physicists remain unconvinced. Over a year has passed since the conference and he has still not presented a fully worked mathematical proof to back up his ideas.

But Hawking is a stubborn man. If Hawking is going to change his mind on a view he held for almost 30 years then it will be with his own proof, in his own time. In spite of failing health and increasing problems communicating with his colleagues, he is still working on the proof. If he succeeds in completing a proof that convinces his colleagues, he will not only have solved one of the most difficult problems in physics but he will have managed to have produced ground breaking work at the very end of his career. A feat that even his hero Einstein could not accomplish.


Contents

Family

Hawking was born on 8 January 1942 [24] [25] [26] in Oxford to Frank (1905–1986) [27] [28] and Isobel Eileen Hawking ( née Walker 1915–2013). [29] [30] [31] [32] Hawking's mother was born into a family of doctors in Glasgow, Scotland. [33] [34] His wealthy paternal great-grandfather, from Yorkshire, over-extended himself buying farm land and then went bankrupt in the great agricultural depression during the early 20th century. [34] His paternal great-grandmother saved the family from financial ruin by opening a school in their home. [34] Despite their families' financial constraints, both parents attended the University of Oxford, where Frank read medicine and Isobel read Philosophy, Politics and Economics. [30] Isobel worked as a secretary for a medical research institute, and Frank was a medical researcher. [30] [35] Hawking had two younger sisters, Philippa and Mary, and an adopted brother, Edward Frank David (1955–2003). [36] [37]

In 1950, when Hawking's father became head of the division of parasitology at the National Institute for Medical Research, the family moved to St Albans, Hertfordshire. [38] [39] In St Albans, the family was considered highly intelligent and somewhat eccentric [38] [40] meals were often spent with each person silently reading a book. [38] They lived a frugal existence in a large, cluttered, and poorly maintained house and travelled in a converted London taxicab. [41] [42] During one of Hawking's father's frequent absences working in Africa, [43] the rest of the family spent four months in Mallorca visiting his mother's friend Beryl and her husband, the poet Robert Graves. [44]

Primary and secondary school years

Hawking began his schooling at the Byron House School in Highgate, London. He later blamed its "progressive methods" for his failure to learn to read while at the school. [45] [38] In St Albans, the eight-year-old Hawking attended St Albans High School for Girls for a few months. At that time, younger boys could attend one of the houses. [44] [46]

Hawking attended two independent (i.e. fee-paying) schools, first Radlett School [46] and from September 1952, St Albans School, [26] [47] after passing the eleven-plus a year early. [48] The family placed a high value on education. [38] Hawking's father wanted his son to attend the well-regarded Westminster School, but the 13-year-old Hawking was ill on the day of the scholarship examination. His family could not afford the school fees without the financial aid of a scholarship, so Hawking remained at St Albans. [49] [50] A positive consequence was that Hawking remained close to a group of friends with whom he enjoyed board games, the manufacture of fireworks, model aeroplanes and boats, [51] and long discussions about Christianity and extrasensory perception. [52] From 1958 on, with the help of the mathematics teacher Dikran Tahta, they built a computer from clock parts, an old telephone switchboard and other recycled components. [53] [54]

Although known at school as "Einstein", Hawking was not initially successful academically. [55] With time, he began to show considerable aptitude for scientific subjects and, inspired by Tahta, decided to read mathematics at university. [56] [57] [58] Hawking's father advised him to study medicine, concerned that there were few jobs for mathematics graduates. [59] He also wanted his son to attend University College, Oxford, his own alma mater. As it was not possible to read mathematics there at the time, Hawking decided to study physics and chemistry. Despite his headmaster's advice to wait until the next year, Hawking was awarded a scholarship after taking the examinations in March 1959. [60] [61]

Undergraduate years

Hawking began his university education at University College, Oxford, [26] in October 1959 at the age of 17. [62] For the first eighteen months, he was bored and lonely – he found the academic work "ridiculously easy". [63] [64] His physics-tutor, Robert Berman, later said, "It was only necessary for him to know that something could be done, and he could do it without looking to see how other people did it." [4] A change occurred during his second and third years when, according to Berman, Hawking made more of an effort "to be one of the boys". He developed into a popular, lively and witty college-member, interested in classical music and science-fiction. [62] Part of the transformation resulted from his decision to join the college boat-club, the University College Boat Club, where he coxed a rowing-crew. [65] [66] The rowing-coach at the time noted that Hawking cultivated a daredevil image, steering his crew on risky courses that led to damaged boats. [65] [67] Hawking estimated that he studied about 1,000 hours during his three years at Oxford. These unimpressive study habits made sitting his finals a challenge, and he decided to answer only theoretical physics questions rather than those requiring factual knowledge. A first-class honours degree was a condition of acceptance for his planned graduate study in cosmology at the University of Cambridge. [68] [69] Anxious, he slept poorly the night before the examinations, and the final result was on the borderline between first- and second-class honours, making a viva (oral examination) with the Oxford examiners necessary. [69] [70]

Hawking was concerned that he was viewed as a lazy and difficult student. So, when asked at the viva to describe his plans, he said, "If you award me a First, I will go to Cambridge. If I receive a Second, I shall stay in Oxford, so I expect you will give me a First." [69] [71] He was held in higher regard than he believed as Berman commented, the examiners "were intelligent enough to realise they were talking to someone far cleverer than most of themselves". [69] After receiving a first-class BA (Hons.) degree in physics and completing a trip to Iran with a friend, he began his graduate work at Trinity Hall, Cambridge, in October 1962. [26] [72] [73]

Graduate years

Hawking's first year as a doctoral student was difficult. He was initially disappointed to find that he had been assigned Dennis William Sciama, one of the founders of modern cosmology, as a supervisor rather than the noted astronomer Fred Hoyle, [74] [75] and he found his training in mathematics inadequate for work in general relativity and cosmology. [76] After being diagnosed with motor neurone disease, Hawking fell into a depression – though his doctors advised that he continue with his studies, he felt there was little point. [77] His disease progressed slower than doctors had predicted. Although Hawking had difficulty walking unsupported, and his speech was almost unintelligible, an initial diagnosis that he had only two years to live proved unfounded. With Sciama's encouragement, he returned to his work. [78] [79] Hawking started developing a reputation for brilliance and brashness when he publicly challenged the work of Fred Hoyle and his student Jayant Narlikar at a lecture in June 1964. [80] [81]

When Hawking began his graduate studies, there was much debate in the physics community about the prevailing theories of the creation of the universe: the Big Bang and Steady State theories. [82] Inspired by Roger Penrose's theorem of a spacetime singularity in the centre of black holes, Hawking applied the same thinking to the entire universe and, during 1965, he wrote his thesis on this topic. [83] [84] Hawking's thesis [85] was approved in 1966. [85] There were other positive developments: Hawking received a research fellowship at Gonville and Caius College at Cambridge [86] he obtained his PhD degree in applied mathematics and theoretical physics, specialising in general relativity and cosmology, in March 1966 [87] and his essay "Singularities and the Geometry of Space–Time" shared top honours with one by Penrose to win that year's prestigious Adams Prize. [88] [87]

1966–1975

In his work, and in collaboration with Penrose, Hawking extended the singularity theorem concepts first explored in his doctoral thesis. This included not only the existence of singularities but also the theory that the universe might have started as a singularity. Their joint essay was the runner-up in the 1968 Gravity Research Foundation competition. [89] [90] In 1970, they published a proof that if the universe obeys the general theory of relativity and fits any of the models of physical cosmology developed by Alexander Friedmann, then it must have begun as a singularity. [91] [92] [93] In 1969, Hawking accepted a specially created Fellowship for Distinction in Science to remain at Caius. [94]

In 1970, Hawking postulated what became known as the second law of black hole dynamics, that the event horizon of a black hole can never get smaller. [95] With James M. Bardeen and Brandon Carter, he proposed the four laws of black hole mechanics, drawing an analogy with thermodynamics. [96] To Hawking's irritation, Jacob Bekenstein, a graduate student of John Wheeler, went further—and ultimately correctly—to apply thermodynamic concepts literally. [97] [98]

In the early 1970s, Hawking's work with Carter, Werner Israel, and David C. Robinson strongly supported Wheeler's no-hair theorem, one that states that no matter what the original material from which a black hole is created, it can be completely described by the properties of mass, electrical charge and rotation. [99] [100] His essay titled "Black Holes" won the Gravity Research Foundation Award in January 1971. [101] Hawking's first book, The Large Scale Structure of Space-Time, written with George Ellis, was published in 1973. [102]

Beginning in 1973, Hawking moved into the study of quantum gravity and quantum mechanics. [103] [102] His work in this area was spurred by a visit to Moscow and discussions with Yakov Borisovich Zel'dovich and Alexei Starobinsky, whose work showed that according to the uncertainty principle, rotating black holes emit particles. [104] To Hawking's annoyance, his much-checked calculations produced findings that contradicted his second law, which claimed black holes could never get smaller, [105] and supported Bekenstein's reasoning about their entropy. [104] [106]

His results, which Hawking presented from 1974, showed that black holes emit radiation, known today as Hawking radiation, which may continue until they exhaust their energy and evaporate. [107] [108] [109] Initially, Hawking radiation was controversial. By the late 1970s and following the publication of further research, the discovery was widely accepted as a significant breakthrough in theoretical physics. [110] [111] [112] Hawking was elected a Fellow of the Royal Society (FRS) in 1974, a few weeks after the announcement of Hawking radiation. At the time, he was one of the youngest scientists to become a Fellow. [113] [114]

Hawking was appointed to the Sherman Fairchild Distinguished Visiting Professorship at the California Institute of Technology (Caltech) in 1974. He worked with a friend on the faculty, Kip Thorne, [115] [8] and engaged him in a scientific wager about whether the X-ray source Cygnus X-1 was a black hole. The wager was an "insurance policy" against the proposition that black holes did not exist. [116] Hawking acknowledged that he had lost the bet in 1990, a bet that was the first of several he was to make with Thorne and others. [117] Hawking had maintained ties to Caltech, spending a month there almost every year since this first visit. [118]

1975–1990

Hawking returned to Cambridge in 1975 to a more academically senior post, as reader in gravitational physics. The mid-to-late 1970s were a period of growing public interest in black holes and the physicists who were studying them. Hawking was regularly interviewed for print and television. [119] [120] He also received increasing academic recognition of his work. [121] In 1975, he was awarded both the Eddington Medal and the Pius XI Gold Medal, and in 1976 the Dannie Heineman Prize, the Maxwell Medal and Prize and the Hughes Medal. [122] [123] He was appointed a professor with a chair in gravitational physics in 1977. [124] The following year he received the Albert Einstein Medal and an honorary doctorate from the University of Oxford. [125] [121]

In 1979, Hawking was elected Lucasian Professor of Mathematics at the University of Cambridge. [121] [126] His inaugural lecture in this role was titled: "Is the End in Sight for Theoretical Physics?" and proposed N=8 Supergravity as the leading theory to solve many of the outstanding problems physicists were studying. [127] His promotion coincided with a health-crisis which led to his accepting, albeit reluctantly, some nursing services at home. [128] At the same time, he was also making a transition in his approach to physics, becoming more intuitive and speculative rather than insisting on mathematical proofs. "I would rather be right than rigorous", he told Kip Thorne. [129] In 1981, he proposed that information in a black hole is irretrievably lost when a black hole evaporates. This information paradox violates the fundamental tenet of quantum mechanics, and led to years of debate, including "the Black Hole War" with Leonard Susskind and Gerard 't Hooft. [130] [131]

Cosmological inflation – a theory proposing that following the Big Bang, the universe initially expanded incredibly rapidly before settling down to a slower expansion – was proposed by Alan Guth and also developed by Andrei Linde. [132] Following a conference in Moscow in October 1981, Hawking and Gary Gibbons [8] organised a three-week Nuffield Workshop in the summer of 1982 on "The Very Early Universe" at Cambridge University, a workshop that focused mainly on inflation theory. [133] [134] [135] Hawking also began a new line of quantum-theory research into the origin of the universe. In 1981 at a Vatican conference, he presented work suggesting that there might be no boundary – or beginning or ending – to the universe. [136] [137]

Hawking subsequently developed the research in collaboration with Jim Hartle, [8] and in 1983 they published a model, known as the Hartle–Hawking state. It proposed that prior to the Planck epoch, the universe had no boundary in space-time before the Big Bang, time did not exist and the concept of the beginning of the universe is meaningless. [138] The initial singularity of the classical Big Bang models was replaced with a region akin to the North Pole. One cannot travel north of the North Pole, but there is no boundary there – it is simply the point where all north-running lines meet and end. [139] [140] Initially, the no-boundary proposal predicted a closed universe, which had implications about the existence of God. As Hawking explained, "If the universe has no boundaries but is self-contained. then God would not have had any freedom to choose how the universe began." [141]

Hawking did not rule out the existence of a Creator, asking in A Brief History of Time "Is the unified theory so compelling that it brings about its own existence?", [142] also stating "If we discover a complete theory, it would be the ultimate triumph of human reason – for then we should know the mind of God" [143] in his early work, Hawking spoke of God in a metaphorical sense. In the same book he suggested that the existence of God was not necessary to explain the origin of the universe. Later discussions with Neil Turok led to the realisation that the existence of God was also compatible with an open universe. [144]

Further work by Hawking in the area of arrows of time led to the 1985 publication of a paper theorising that if the no-boundary proposition were correct, then when the universe stopped expanding and eventually collapsed, time would run backwards. [145] A paper by Don Page and independent calculations by Raymond Laflamme led Hawking to withdraw this concept. [146] Honours continued to be awarded: in 1981 he was awarded the American Franklin Medal, [147] and in the 1982 New Year Honours appointed a Commander of the Order of the British Empire (CBE). [148] [149] [150] These awards did not significantly change Hawking's financial status, and motivated by the need to finance his children's education and home-expenses, he decided in 1982 to write a popular book about the universe that would be accessible to the general public. [151] [152] Instead of publishing with an academic press, he signed a contract with Bantam Books, a mass-market publisher, and received a large advance for his book. [153] [154] A first draft of the book, called A Brief History of Time, was completed in 1984. [155]

One of the first messages Hawking produced with his speech-generating device was a request for his assistant to help him finish writing A Brief History of Time. [156] Peter Guzzardi, his editor at Bantam, pushed him to explain his ideas clearly in non-technical language, a process that required many revisions from an increasingly irritated Hawking. [157] The book was published in April 1988 in the US and in June in the UK, and it proved to be an extraordinary success, rising quickly to the top of best-seller lists in both countries and remaining there for months. [158] [159] [160] The book was translated into many languages, [161] and ultimately sold an estimated 9 million copies. [160]

Media attention was intense, [161] and a Newsweek magazine-cover and a television special both described him as "Master of the Universe". [162] Success led to significant financial rewards, but also the challenges of celebrity status. [163] Hawking travelled extensively to promote his work, and enjoyed partying and dancing into the small hours. [161] A difficulty refusing the invitations and visitors left him limited time for work and his students. [164] Some colleagues were resentful of the attention Hawking received, feeling it was due to his disability. [165] [166]

He received further academic recognition, including five more honorary degrees, [162] the Gold Medal of the Royal Astronomical Society (1985), [167] the Paul Dirac Medal (1987) [162] and, jointly with Penrose, the prestigious Wolf Prize (1988). [168] In the 1989 Birthday Honours, he was appointed a Companion of Honour (CH). [164] [169] He reportedly declined a knighthood in the late 1990s in objection to the UK's science funding policy. [170] [171]

1990–2000

Hawking pursued his work in physics: in 1993 he co-edited a book on Euclidean quantum gravity with Gary Gibbons and published a collected edition of his own articles on black holes and the Big Bang. [172] In 1994, at Cambridge's Newton Institute, Hawking and Penrose delivered a series of six lectures that were published in 1996 as "The Nature of Space and Time". [173] In 1997, he conceded a 1991 public scientific wager made with Kip Thorne and John Preskill of Caltech. Hawking had bet that Penrose's proposal of a "cosmic censorship conjecture" – that there could be no "naked singularities" unclothed within a horizon – was correct. [174]

After discovering his concession might have been premature, a new and more refined wager was made. This one specified that such singularities would occur without extra conditions. [175] The same year, Thorne, Hawking and Preskill made another bet, this time concerning the black hole information paradox. [176] [177] Thorne and Hawking argued that since general relativity made it impossible for black holes to radiate and lose information, the mass-energy and information carried by Hawking radiation must be "new", and not from inside the black hole event horizon. Since this contradicted the quantum mechanics of microcausality, quantum mechanics theory would need to be rewritten. Preskill argued the opposite, that since quantum mechanics suggests that the information emitted by a black hole relates to information that fell in at an earlier time, the concept of black holes given by general relativity must be modified in some way. [178]

Hawking also maintained his public profile, including bringing science to a wider audience. A film version of A Brief History of Time, directed by Errol Morris and produced by Steven Spielberg, premiered in 1992. Hawking had wanted the film to be scientific rather than biographical, but he was persuaded otherwise. The film, while a critical success, was not widely released. [179] A popular-level collection of essays, interviews, and talks titled Black Holes and Baby Universes and Other Essays was published in 1993, [180] and a six-part television series Stephen Hawking's Universe and a companion book appeared in 1997. As Hawking insisted, this time the focus was entirely on science. [181] [182]

2000–2018

Hawking continued his writings for a popular audience, publishing The Universe in a Nutshell in 2001, [183] and A Briefer History of Time, which he wrote in 2005 with Leonard Mlodinow to update his earlier works with the aim of making them accessible to a wider audience, and God Created the Integers, which appeared in 2006. [184] Along with Thomas Hertog at CERN and Jim Hartle, from 2006 on Hawking developed a theory of top-down cosmology, which says that the universe had not one unique initial state but many different ones, and therefore that it is inappropriate to formulate a theory that predicts the universe's current configuration from one particular initial state. [185] Top-down cosmology posits that the present "selects" the past from a superposition of many possible histories. In doing so, the theory suggests a possible resolution of the fine-tuning question. [186] [187]

Hawking continued to travel widely, including trips to Chile, Easter Island, South Africa, Spain (to receive the Fonseca Prize in 2008), [188] [189] Canada, [190] and numerous trips to the United States. [191] For practical reasons related to his disability, Hawking increasingly travelled by private jet, and by 2011 that had become his only mode of international travel. [192]

By 2003, consensus among physicists was growing that Hawking was wrong about the loss of information in a black hole. [193] In a 2004 lecture in Dublin, he conceded his 1997 bet with Preskill, but described his own, somewhat controversial solution to the information paradox problem, involving the possibility that black holes have more than one topology. [194] [178] In the 2005 paper he published on the subject, he argued that the information paradox was explained by examining all the alternative histories of universes, with the information loss in those with black holes being cancelled out by those without such loss. [177] [195] In January 2014, he called the alleged loss of information in black holes his "biggest blunder". [196]

As part of another longstanding scientific dispute, Hawking had emphatically argued, and bet, that the Higgs boson would never be found. [197] The particle was proposed to exist as part of the Higgs field theory by Peter Higgs in 1964. Hawking and Higgs engaged in a heated and public debate over the matter in 2002 and again in 2008, with Higgs criticising Hawking's work and complaining that Hawking's "celebrity status gives him instant credibility that others do not have." [198] The particle was discovered in July 2012 at CERN following construction of the Large Hadron Collider. Hawking quickly conceded that he had lost his bet [199] [200] and said that Higgs should win the Nobel Prize for Physics, [201] which he did in 2013. [202]

In 2007, Hawking and his daughter Lucy published George's Secret Key to the Universe, a children's book designed to explain theoretical physics in an accessible fashion and featuring characters similar to those in the Hawking family. [203] The book was followed by sequels in 2009, 2011, 2014 and 2016. [204]

In 2002, following a UK-wide vote, the BBC included Hawking in their list of the 100 Greatest Britons. [205] He was awarded the Copley Medal from the Royal Society (2006), [206] the Presidential Medal of Freedom, which is America's highest civilian honour (2009), [207] and the Russian Special Fundamental Physics Prize (2013). [208]

Several buildings have been named after him, including the Stephen W. Hawking Science Museum in San Salvador, El Salvador, [209] the Stephen Hawking Building in Cambridge, [210] and the Stephen Hawking Centre at the Perimeter Institute in Canada. [211] Appropriately, given Hawking's association with time, he unveiled the mechanical "Chronophage" (or time-eating) Corpus Clock at Corpus Christi College, Cambridge in September 2008. [212] [213]

During his career, Hawking supervised 39 successful PhD students. [3] One doctoral student did not successfully complete the PhD. [3] [ better source needed ] As required by Cambridge University policy, Hawking retired as Lucasian Professor of Mathematics in 2009. [126] [214] Despite suggestions that he might leave the United Kingdom as a protest against public funding cuts to basic scientific research, [215] Hawking worked as director of research at the Cambridge University Department of Applied Mathematics and Theoretical Physics. [216]

On 28 June 2009, as a tongue-in-cheek test of his 1992 conjecture that travel into the past is effectively impossible, Hawking held a party open to all, complete with hors d'oeuvres and iced champagne, but publicised the party only after it was over so that only time-travellers would know to attend as expected, nobody showed up to the party. [217]

On 20 July 2015, Hawking helped launch Breakthrough Initiatives, an effort to search for extraterrestrial life. [218] Hawking created Stephen Hawking: Expedition New Earth, a documentary on space colonisation, as a 2017 episode of Tomorrow's World. [219] [220]

In August 2015, Hawking said that not all information is lost when something enters a black hole and there might be a possibility to retrieve information from a black hole according to his theory. [221] In July 2017, Hawking was awarded an Honorary Doctorate from Imperial College London. [222]

Hawking's final paper – A smooth exit from eternal inflation? – was posthumously published in the Journal of High Energy Physics on 27 April 2018. [223] [224]

Marriages

Hawking met his future wife, Jane Wilde, at a party in 1962. The following year, Hawking was diagnosed with motor neurone disease. In October 1964, the couple became engaged to marry, aware of the potential challenges that lay ahead due to Hawking's shortened life expectancy and physical limitations. [125] [225] Hawking later said that the engagement gave him "something to live for". [226] The two were married on 14 July 1965 in their shared hometown of St Albans. [86]

The couple resided in Cambridge, within Hawking's walking distance to the Department of Applied Mathematics and Theoretical Physics (DAMTP). During their first years of marriage, Jane lived in London during the week as she completed her degree at Westfield College. They travelled to the United States several times for conferences and physics-related visits. Jane began a PhD programme through Westfield College in medieval Spanish poetry (completed in 1981). The couple had three children: Robert, born May 1967, [227] [228] Lucy, born November 1970, [229] and Timothy, born April 1979. [121]

Hawking rarely discussed his illness and physical challenges, even – in a precedent set during their courtship – with Jane. [230] His disabilities meant that the responsibilities of home and family rested firmly on his wife's increasingly overwhelmed shoulders, leaving him more time to think about physics. [231] Upon his appointment in 1974 to a year-long position at the California Institute of Technology in Pasadena, California, Jane proposed that a graduate or post-doctoral student live with them and help with his care. Hawking accepted, and Bernard Carr travelled with them as the first of many students who fulfilled this role. [232] [233] The family spent a generally happy and stimulating year in Pasadena. [234]

Hawking returned to Cambridge in 1975 to a new home and a new job, as reader. Don Page, with whom Hawking had begun a close friendship at Caltech, arrived to work as the live-in graduate student assistant. With Page's help and that of a secretary, Jane's responsibilities were reduced so she could return to her doctoral thesis and her new interest in singing. [235]

Around December 1977, Jane met organist Jonathan Hellyer Jones when singing in a church choir. Hellyer Jones became close to the Hawking family, and by the mid-1980s, he and Jane had developed romantic feelings for each other. [124] [236] [237] According to Jane, her husband was accepting of the situation, stating "he would not object so long as I continued to love him". [124] [238] [239] Jane and Hellyer Jones were determined not to break up the family, and their relationship remained platonic for a long period. [240]

By the 1980s, Hawking's marriage had been strained for many years. Jane felt overwhelmed by the intrusion into their family life of the required nurses and assistants. [241] The impact of his celebrity was challenging for colleagues and family members, while the prospect of living up to a worldwide fairytale image was daunting for the couple. [242] [186] Hawking's views of religion also contrasted with her strong Christian faith and resulted in tension. [186] [243] [244] After a tracheotomy in 1985, Hawking required a full-time nurse and nursing care was split across 3 shifts daily. In the late 1980s, Hawking grew close to one of his nurses, Elaine Mason, to the dismay of some colleagues, caregivers, and family members, who were disturbed by her strength of personality and protectiveness. [245] In February 1990, Hawking told Jane that he was leaving her for Mason, [246] and departed the family home. [148] After his divorce from Jane in 1995, Hawking married Mason in September, [148] [247] declaring, "It's wonderful – I have married the woman I love." [248]

In 1999, Jane Hawking published a memoir, Music to Move the Stars, describing her marriage to Hawking and its breakdown. Its revelations caused a sensation in the media but, as was his usual practice regarding his personal life, Hawking made no public comment except to say that he did not read biographies about himself. [249] After his second marriage, Hawking's family felt excluded and marginalised from his life. [244] For a period of about five years in the early 2000s, his family and staff became increasingly worried that he was being physically abused. [250] Police investigations took place, but were closed as Hawking refused to make a complaint. [251]

In 2006, Hawking and Mason quietly divorced, [252] [253] and Hawking resumed closer relationships with Jane, his children, and his grandchildren. [186] [253] Reflecting on this happier period, a revised version of Jane's book, re-titled Travelling to Infinity: My Life with Stephen, appeared in 2007, [251] and was made into a film, The Theory of Everything, in 2014. [254]

Disability

Hawking had a rare early-onset, slow-progressing form of motor neurone disease (MND also known as amyotrophic lateral sclerosis (ALS) or Lou Gehrig's disease), a fatal neurodegenerative disease that affects the motor neurones in the brain and spinal cord, which gradually paralysed him over decades. [21]

Hawking had experienced increasing clumsiness during his final year at Oxford, including a fall on some stairs and difficulties when rowing. [255] [256] The problems worsened, and his speech became slightly slurred. His family noticed the changes when he returned home for Christmas, and medical investigations were begun. [257] [258] The MND diagnosis came when Hawking was 21, in 1963. At the time, doctors gave him a life expectancy of two years. [259] [260]

In the late 1960s, Hawking's physical abilities declined: he began to use crutches and could no longer give lectures regularly. [261] As he slowly lost the ability to write, he developed compensatory visual methods, including seeing equations in terms of geometry. [262] [263] The physicist Werner Israel later compared the achievements to Mozart composing an entire symphony in his head. [264] [265] Hawking was fiercely independent and unwilling to accept help or make concessions for his disabilities. He preferred to be regarded as "a scientist first, popular science writer second, and, in all the ways that matter, a normal human being with the same desires, drives, dreams, and ambitions as the next person." [266] His wife, Jane Hawking, later noted: "Some people would call it determination, some obstinacy. I've called it both at one time or another." [267] He required much persuasion to accept the use of a wheelchair at the end of the 1960s, [268] but ultimately became notorious for the wildness of his wheelchair driving. [269] Hawking was a popular and witty colleague, but his illness, as well as his reputation for brashness, distanced him from some. [267]

When Hawking first began using a wheelchair in the late 1970s he was using standard motorised models. The earliest surviving example of these chairs was made by BEC Mobility and sold by Christie's in November 2018 for £296,750. [270] Hawking continued to use this type of chair until the early 1990s, at which time his ability to use his hands to drive a wheelchair deteriorated. Hawking used a variety of different chairs from that time, including a DragonMobility Dragon elevating powerchair from 2007, as shown in the April 2008 photo of Hawking attending NASA's 50th anniversary [271] a Permobil C350 from 2014 and then a Permobil F3 from 2016. [272]

Hawking's speech deteriorated, and by the late 1970s he could be understood by only his family and closest friends. To communicate with others, someone who knew him well would interpret his speech into intelligible speech. [273] Spurred by a dispute with the university over who would pay for the ramp needed for him to enter his workplace, Hawking and his wife campaigned for improved access and support for those with disabilities in Cambridge, [274] [275] including adapted student housing at the university. [276] In general, Hawking had ambivalent feelings about his role as a disability rights champion: while wanting to help others, he also sought to detach himself from his illness and its challenges. [277] His lack of engagement in this area led to some criticism. [278]

During a visit to CERN on the border of France and Switzerland in mid-1985, Hawking contracted pneumonia, which in his condition was life-threatening he was so ill that Jane was asked if life support should be terminated. She refused, but the consequence was a tracheotomy, which required round-the-clock nursing care and the removal of what remained of his speech. [279] [280] The National Health Service was ready to pay for a nursing home, but Jane was determined that he would live at home. The cost of the care was funded by an American foundation. [281] [282] Nurses were hired for the three shifts required to provide the round-the-clock support he required. One of those employed was Elaine Mason, who was to become Hawking's second wife. [283]

For his communication, Hawking initially raised his eyebrows to choose letters on a spelling card, [284] but in 1986 he received a computer program called the "Equalizer" from Walter Woltosz, CEO of Words Plus, who had developed an earlier version of the software to help his mother-in-law, who also suffered from ALS and had lost her ability to speak and write. [285] In a method he used for the rest of his life, Hawking could now simply press a switch to select phrases, words or letters from a bank of about 2,500–3,000 that were scanned. [286] [287] The program was originally run on a desktop computer. Elaine Mason's husband, David, a computer engineer, adapted a small computer and attached it to his wheelchair. [288]

Released from the need to use somebody to interpret his speech, Hawking commented that "I can communicate better now than before I lost my voice." [289] The voice he used had an American accent and is no longer produced. [290] [291] Despite the later availability of other voices, Hawking retained this original voice, saying that he preferred it and identified with it. [292] Originally, Hawking activated a switch using his hand and could produce up to 15 words a minute. [156] Lectures were prepared in advance and were sent to the speech synthesizer in short sections to be delivered. [290]

Hawking gradually lost the use of his hand, and in 2005 he began to control his communication device with movements of his cheek muscles, [293] [294] [295] with a rate of about one word per minute. [294] With this decline there was a risk of his developing locked-in syndrome, so Hawking collaborated with Intel researchers on systems that could translate his brain patterns or facial expressions into switch activations. After several prototypes that did not perform as planned, they settled on an adaptive word predictor made by the London-based startup SwiftKey, which used a system similar to his original technology. Hawking had an easier time adapting to the new system, which was further developed after inputting large amounts of Hawking's papers and other written materials and uses predictive software similar to other smartphone keyboards. [186] [285] [295] [296]

By 2009, he could no longer drive his wheelchair independently, but the same people who created his new typing mechanics were working on a method to drive his chair using movements made by his chin. This proved difficult, since Hawking could not move his neck, and trials showed that while he could indeed drive the chair, the movement was sporadic and jumpy. [285] [297] Near the end of his life, Hawking experienced increased breathing difficulties, often resulting in his requiring the usage of a ventilator, and being regularly hospitalised. [186]

Disability outreach

Starting in the 1990s, Hawking accepted the mantle of role model for disabled people, lecturing and participating in fundraising activities. [298] At the turn of the century, he and eleven other humanitarians signed the Charter for the Third Millennium on Disability, which called on governments to prevent disability and protect the rights of the disabled. [299] [300] In 1999, Hawking was awarded the Julius Edgar Lilienfeld Prize of the American Physical Society. [301]

In August 2012, Hawking narrated the "Enlightenment" segment of the 2012 Summer Paralympics opening ceremony in London. [302] In 2013, the biographical documentary film Hawking, in which Hawking himself is featured, was released. [303] In September 2013, he expressed support for the legalisation of assisted suicide for the terminally ill. [304] In August 2014, Hawking accepted the Ice Bucket Challenge to promote ALS/MND awareness and raise contributions for research. As he had pneumonia in 2013, he was advised not to have ice poured over him, but his children volunteered to accept the challenge on his behalf. [305]

Plans for a trip to space

In late 2006, Hawking revealed in a BBC interview that one of his greatest unfulfilled desires was to travel to space [306] on hearing this, Richard Branson offered a free flight into space with Virgin Galactic, which Hawking immediately accepted. Besides personal ambition, he was motivated by the desire to increase public interest in spaceflight and to show the potential of people with disabilities. [307] On 26 April 2007, Hawking flew aboard a specially-modified Boeing 727-200 jet operated by Zero-G Corp off the coast of Florida to experience weightlessness. [308] Fears that the manoeuvres would cause him undue discomfort proved groundless, and the flight was extended to eight parabolic arcs. [306] It was described as a successful test to see if he could withstand the g-forces involved in space flight. [309] At the time, the date of Hawking's trip to space was projected to be as early as 2009, but commercial flights to space did not commence before his death. [310]

Hawking died at his home in Cambridge on 14 March 2018, at the age of 76. [311] [312] [313] His family stated that he "died peacefully". [314] [315] He was eulogised by figures in science, entertainment, politics, and other areas. [316] [317] [318] [319] The Gonville and Caius College flag flew at half-mast and a book of condolences was signed by students and visitors. [320] [321] [322] A tribute was made to Hawking in the closing speech by IPC President Andrew Parsons at the closing ceremony of the 2018 Paralympic Winter Games in Pyeongchang, South Korea. [323]

His private funeral took place on 31 March 2018, [324] at Great St Mary's Church, Cambridge. [324] [325] Guests at the funeral included The Theory of Everything actors Eddie Redmayne and Felicity Jones, Queen guitarist and astrophysicist Brian May, and model Lily Cole. [326] [327] In addition, actor Benedict Cumberbatch, who played Stephen Hawking in Hawking, astronaut Tim Peake, Astronomer Royal Martin Rees and physicist Kip Thorne provided readings at the service. [328] Although Hawking was an atheist, the funeral took place with a traditional Anglican service. [329] [330] Following the cremation, a service of thanksgiving was held at Westminster Abbey on 15 June 2018, after which his ashes were interred in the Abbey's nave, between the graves of Sir Isaac Newton and Charles Darwin. [1] [326] [331] [332]

Inscribed on his memorial stone are the words "Here lies what was mortal of Stephen Hawking 1942–2018" and his most famed equation. [333] He directed, at least fifteen years before his death, that the Bekenstein–Hawking entropy equation be his epitaph. [334] [335] [note 1] In June 2018, it was announced that Hawking's words, set to music by Greek composer Vangelis, would be beamed into space from a European space agency satellite dish in Spain with the aim of reaching the nearest black hole, 1A 0620-00. [340]

Hawking's final broadcast interview, about the detection of gravitational waves resulting from the collision of two neutron stars, occurred in October 2017. [341] His final words to the world appeared posthumously, in April 2018, in the form of a Smithsonian TV Channel documentary entitled, Leaving Earth: Or How to Colonize a Planet. [342] [343] One of his final research studies, entitled A smooth exit from eternal inflation?, about the origin of the universe, was published in the Journal of High Energy Physics in May 2018. [344] [345] [346] [347] Later, in October 2018, another of his final research studies, entitled Black Hole Entropy and Soft Hair, [348] was published, and dealt with the "mystery of what happens to the information held by objects once they disappear into a black hole". [349] [350] Also in October 2018, Hawking's last book, Brief Answers to the Big Questions, a popular science book presenting his final comments on the most important questions facing humankind, was published. [351] [352] [353]

On 8 November 2018, an auction of 22 personal possessions of Stephen Hawking, including his doctoral thesis ("Properties of Expanding Universes", PhD thesis, Cambridge University, 1965) and wheelchair, took place, and fetched about £1.8 m. [354] [355] Proceeds from the auction sale of the wheelchair went to two charities, the Motor Neurone Disease Association and the Stephen Hawking Foundation [356] proceeds from Hawking's other items went to his estate. [355]

In March 2019, it was announced that the Royal Mint issued a commemorative 50 pence coin in honour of Hawking. [357] The same month, it was reported that Hawking's nurse, Patricia Dowdy, had been handed an interim suspension in 2016 for "failures over his care and financial misconduct." [358]

Future of humanity

In 2006, Hawking posed an open question on the Internet: "In a world that is in chaos politically, socially and environmentally, how can the human race sustain another 100 years?", later clarifying: "I don't know the answer. That is why I asked the question, to get people to think about it, and to be aware of the dangers we now face." [359]

Hawking expressed concern that life on Earth is at risk from a sudden nuclear war, a genetically engineered virus, global warming, or other dangers humans have not yet thought of. [307] [360] Hawking stated: "I regard it as almost inevitable that either a nuclear confrontation or environmental catastrophe will cripple the Earth at some point in the next 1,000 years", and considered an "asteroid collision" to be the biggest threat to the planet. [351] Such a planet-wide disaster need not result in human extinction if the human race were to be able to colonise additional planets before the disaster. [360] Hawking viewed spaceflight and the colonisation of space as necessary for the future of humanity. [307] [361]

Hawking stated that, given the vastness of the universe, aliens likely exist, but that contact with them should be avoided. [362] [363] He warned that aliens might pillage Earth for resources. In 2010 he said, "If aliens visit us, the outcome would be much as when Columbus landed in America, which didn't turn out well for the Native Americans." [363]

Hawking warned that superintelligent artificial intelligence could be pivotal in steering humanity's fate, stating that "the potential benefits are huge. Success in creating AI would be the biggest event in human history. It might also be the last, unless we learn how to avoid the risks." [364] [365] However, he argued that we should be more frightened of capitalism exacerbating economic inequality than robots. [366]

Hawking was concerned about the future emergence of a race of "superhumans" that would be able to design their own evolution [351] and, as well, argued that computer viruses in today's world should be considered a new form of life, stating that "maybe it says something about human nature, that the only form of life we have created so far is purely destructive. Talk about creating life in our own image." [367]

Science vs. philosophy

At Google's Zeitgeist Conference in 2011, Hawking said that "philosophy is dead". He believed that philosophers "have not kept up with modern developments in science" and that scientists "have become the bearers of the torch of discovery in our quest for knowledge". He said that philosophical problems can be answered by science, particularly new scientific theories which "lead us to a new and very different picture of the universe and our place in it". [368]

Religion and atheism

Hawking was an atheist. [369] [370] In an interview published in The Guardian, Hawking regarded "the brain as a computer which will stop working when its components fail", and the concept of an afterlife as a "fairy story for people afraid of the dark". [312] [143] In 2011, narrating the first episode of the American television series Curiosity on the Discovery Channel, Hawking declared:

We are each free to believe what we want and it is my view that the simplest explanation is there is no God. No one created the universe and no one directs our fate. This leads me to a profound realisation. There is probably no heaven, and no afterlife either. We have this one life to appreciate the grand design of the universe, and for that, I am extremely grateful. [371] [372]

Hawking's association with atheism and freethinking was in evidence from his university years onwards, when he had been a member of Oxford University's humanist group. He was later scheduled to appear as the keynote speaker at a 2017 Humanists UK conference. [373] In an interview with El Mundo, he said:

Before we understand science, it is natural to believe that God created the universe. But now science offers a more convincing explanation. What I meant by 'we would know the mind of God' is, we would know everything that God would know, if there were a God, which there isn't. I'm an atheist. [369]

In addition, Hawking stated:

If you like, you can call the laws of science 'God', but it wouldn't be a personal God that you would meet and put questions to. [351]

Politics

Hawking was a longstanding Labour Party supporter. [374] [375] He recorded a tribute for the 2000 Democratic presidential candidate Al Gore, [376] called the 2003 invasion of Iraq a "war crime", [375] [377] supported the academic boycott of Israel, [378] [379] campaigned for nuclear disarmament, [374] [375] and supported stem cell research, [375] [380] universal health care, [381] and action to prevent climate change. [382] In August 2014, Hawking was one of 200 public figures who were signatories to a letter to The Guardian expressing their hope that Scotland would vote to remain part of the United Kingdom in September's referendum on that issue. [383] Hawking believed a United Kingdom withdrawal from the European Union (Brexit) would damage the UK's contribution to science as modern research needs international collaboration, and that free movement of people in Europe encourages the spread of ideas. [384] Hawking was disappointed by Brexit and warned against envy and isolationism. [385]

Hawking was greatly concerned over health care, and maintained that without the UK National Health Service, he could not have survived into his 70s. [386]

Hawking feared privatisation. He stated, "The more profit is extracted from the system, the more private monopolies grow and the more expensive healthcare becomes. The NHS must be preserved from commercial interests and protected from those who want to privatise it." [387] Hawking alleged ministers damaged the NHS, he blamed the Conservatives for cutting funding, weakening the NHS by privatisation, lowering staff morale through holding pay back and reducing social care. [388] Hawking accused Jeremy Hunt of cherry picking evidence which Hawking maintained debased science. [386] Hawking also stated, "There is overwhelming evidence that NHS funding and the numbers of doctors and nurses are inadequate, and it is getting worse." [389] In June 2017, Hawking endorsed the Labour Party in the 2017 UK general election, citing the Conservatives' proposed cuts to the NHS. But he was also critical of Labour leader Jeremy Corbyn, expressing scepticism over whether the party could win a general election under him. [390]

Hawking feared Donald Trump's policies on global warming could endanger the planet and make global warming irreversible. He said, "Climate change is one of the great dangers we face, and it's one we can prevent if we act now. By denying the evidence for climate change, and pulling out of the Paris Agreement, Donald Trump will cause avoidable environmental damage to our beautiful planet, endangering the natural world, for us and our children." [391] Hawking further stated that this could lead Earth "to become like Venus, with a temperature of two hundred and fifty degrees, and raining sulphuric acid". [392]

Hawking was also a supporter of a universal basic income. [393]

In 1988, Hawking, Arthur C. Clarke and Carl Sagan were interviewed in God, the Universe and Everything Else. They discussed the Big Bang theory, God and the possibility of extraterrestrial life. [394]

At the release party for the home video version of the A Brief History of Time, Leonard Nimoy, who had played Spock on Star Trek, learned that Hawking was interested in appearing on the show. Nimoy made the necessary contact, and Hawking played a holographic simulation of himself in an episode of Star Trek: The Next Generation in 1993. [395] [396] The same year, his synthesiser voice was recorded for the Pink Floyd song "Keep Talking", [397] [180] and in 1999 for an appearance on The Simpsons. [398] Hawking appeared in documentaries titled The Real Stephen Hawking (2001), [300] Stephen Hawking: Profile (2002) [399] and Hawking (2013), and the documentary series Stephen Hawking, Master of the Universe (2008). [400] Hawking also guest-starred in Futurama [186] and had a recurring role in The Big Bang Theory. [401]

Hawking allowed the use of his copyrighted voice [402] [403] in the biographical 2014 film The Theory of Everything, in which he was portrayed by Eddie Redmayne in an Academy Award-winning role. [404] Hawking was featured at the Monty Python Live (Mostly) in 2014. He was shown to sing an extended version of the “Galaxy Song”, after running down Brian Cox with his wheelchair, in a pre-recorded video. [405] [406]

Hawking used his fame to advertise products, including a wheelchair, [300] National Savings, [407] British Telecom, Specsavers, Egg Banking, [408] and Go Compare. [409] In 2015, he applied to trademark his name. [410]

Broadcast in March 2018 just a week or two before his death, Hawking was the voice of The Book Mark II on The Hitchhiker's Guide to the Galaxy radio series, and he was the guest of Neil deGrasse Tyson on StarTalk. [411]

Hawking received numerous awards and honours. Already early in the list, in 1974 he was elected a Fellow of the Royal Society (FRS). [412] At that time, his nomination read:

Hawking has made major contributions to the field of general relativity. These derive from a deep understanding of what is relevant to physics and astronomy, and especially from a mastery of wholly new mathematical techniques. Following the pioneering work of Penrose he established, partly alone and partly in collaboration with Penrose, a series of successively stronger theorems establishing the fundamental result that all realistic cosmological models must possess singularities. Using similar techniques, Hawking has proved the basic theorems on the laws governing black holes: that stationary solutions of Einstein's equations with smooth event horizons must necessarily be axisymmetric and that in the evolution and interaction of black holes, the total surface area of the event horizons must increase. In collaboration with G. Ellis, Hawking is the author of an impressive and original treatise on "Space-time in the Large".

The citation continues, "Other important work by Hawking relates to the interpretation of cosmological observations and to the design of gravitational wave detectors." [413]

Hawking received the 2015 BBVA Foundation Frontiers of Knowledge Award in Basic Sciences shared with Viatcheslav Mukhanov for discovering that the galaxies were formed from quantum fluctuations in the early Universe. At the 2016 Pride of Britain Awards, Hawking received the lifetime achievement award "for his contribution to science and British culture". [414] After receiving the award from Prime Minister Theresa May, Hawking humorously requested that she not seek his help with Brexit. [414]

Medal for Science Communication

Hawking was a member of the Advisory Board of the Starmus Festival, and had a major role in acknowledging and promoting science communication. The Stephen Hawking Medal for Science Communication is an annual award initiated in 2016 to honour members of the arts community for contributions that help build awareness of science. [415] Recipients receive a medal bearing a portrait of Hawking by Alexei Leonov, and the other side represents an image of Leonov himself performing the first spacewalk along with an image of the "Red Special", the guitar of Queen musician and astrophysicist Brian May (with music being another major component of the Starmus Festival). [416]

The Starmus III Festival in 2016 was a tribute to Stephen Hawking and the book of all Starmus III lectures, "Beyond the Horizon", was also dedicated to him. The first recipients of the medals, which were awarded at the festival, were chosen by Hawking himself. They were composer Hans Zimmer, physicist Jim Al-Khalili, and the science documentary Particle Fever. [417]


My kind of town (Chicago is)

While Chicago isn't the most violent city in the country, it does have a treasure trove of data on reported crime, neighborhood pollution levels, weather, and other micro-geographical information that makes it an excellent choice for a study like this. By combining the information collected between 2001 and 2012, the authors were able to compare changes in the crime rate upwind and downwind of several major highways — namely I-90, I-94, I-290, I-55, and I-57 — on a day-by-day basis while controlling for other factors, such as temperature, that are also known to influence crime.

The study omitted areas near multiple interstates, including downtown, and the extremities of the city such as O'Hare International Airport to avoid data that was too noisy to use. Data from days when the wind was not within sixty degrees of the line orthogonal to the interstate were also excluded. Importantly, the number of major roadways considered means that the data includes areas containing all socioeconomic levels.

The authors provide the example of taking measurements for neighborhoods near I-290, an east-west roadway connecting downtown with the suburb of Oak Park:

"To causally estimate the effect of pollution on crime, we compare crimes along the north side of I-290 to the south side of I-290 on days when the wind is blowing orthogonally to the interstate. On a day when the wind is blowing from the south, the pollution impacts the north side of I-290 and vice-versa. In essence, the side of the interstate from which the wind is blowing acts as a control for unobservable daily variation in side-invariant criminal activity, driven by, for example, weather."

In total, the effect of the wind-driven pollution amounted to roughly a two percent increase in violent crimes (homicide, assault, etc.) on the downwind side of the interstates.

There was no consistent effect on property crimes like theft or burglary. Areas further from the roadways, and thus with less pollution, saw reduced effects. The effect was also most notable when the weather was nice enough to be outside, possibly prompting people to go out, which in turn exposed them to more air pollution.

Possible long-term effects were not investigated by the authors, in part because the crime rate and pollution levels in Chicago went down over the time period considered in the study.


Astro 101: Black Holes

What is a black hole? Do they really exist? How do they form? How are they related to stars? What would happen if you fell into one? How do you see a black hole if they emit no light? What’s the difference between a black hole and a really dark star? Could a particle accelerator create a black hole? Can a black hole also be a worm hole or a time machine? In Astro 101: Black Holes, you will explore the concepts behind black holes. Using the theme of black holes, you will learn the basic ideas of astronomy, relativity, and quantum physics. After completing this course, you will be able to: • Describe the essential properties of black holes. • Explain recent black hole research using plain language and appropriate analogies. • Compare black holes in popular culture to modern physics to distinguish science fact from science fiction. • Describe the application of fundamental physical concepts including gravity, special and general relativity, and quantum mechanics to reported scientific observations. • Recognize different types of stars and distinguish which stars can potentially become black holes. • Differentiate types of black holes and classify each type as observed or theoretical. • Characterize formation theories associated with each type of black hole. • Identify different ways of detecting black holes, and appropriate technologies associated with each detection method. • Summarize the puzzles facing black hole researchers in modern science.

Получаемые навыки

Gravitation, Theory Of Relativity, Physics, Astronomy, Black Hole

Рецензии

Takes time to finish, yet totally interesting, and surely worth it. If you're a space enthusiast, this will surely leave you craving for more knowledge. Not boring at all. Kudos to the instructors.

An excellent point for amateur astronomers to gain insight into the underlying astrophysics without going too much into the technicalities and wonderful references to keep you glued to the course.

What is in a black hole? This module will start to explore the theoretical side of black hole physics. You will receive a basic introduction to relevant topics of Quantum Mechanics and thermodynamics with the aim of understanding current black hole debates among the giants of the field.

Преподаватели

Sharon Morsink

Текст видео

[SOUND] So far quantum mechanics seems pretty weird, okay? Niels Bohr responsible for planetary model of the hydrogen atom once said, anyone who is not shocked by quantum theory has not understood it. Well that may be the case, another famous physicist Richard Feynman once said, I think I can safely say that nobody understands quantum mechanics. Now, Feynman didn't mean that quantum mechanics is a useless theory, but that the quantum world behaved so strangely compared to our macroscopic world that our human intuitions cannot be relied upon to predict what will happen. Quantum tunnelling is just one such example of how strange quantum mechanics can be. How can tiny particles vanish on one side of a wall only to appear on the other side? Well, if we recall from our last lesson, we don’t know exactly where particles are as a result to the uncertainty principle. If we don’t know exactly where something is, how could a wall know either? That’s the basic principle behind quantum tunnelling. That indeterminacy or uncertainty can lead to a whole host of outcomes. But quantum tunnelling is related to a process within black holes called Hawking radiation. So we need to understand that in order to continue. As we saw previously, one of the fundamental relations of quantum mechanics is the Heisenberg Uncertainty Principle. In a practical sense, it states that no matter how accurate our instrumentation, the experiments we conduct will always be limited in the accuracy of their results by at least h bar / 2. But it's not just our instruments, the entire universe obeys this uncertainty principle. The uncertainty principle has an important implication when we think about the vacuum. Normally, youɽ think of the vacuum as a void, space that is completely devoid of material, matter, and energy of any kind. In the context of quantum mechanics, that simply cannot be true. Because if there is absolutely nothing, that would imply certainty, certainty about the fact that there is no energy or mass in the vacuum. If you are certain that there's no energy in the vacuum, then you are saying that the uncertainty in the energy delta e is 0. However, the energy time version of the Heisenberg uncertainty principle states that delta E times delta t is greater than or equal to h bar divided by 2. In essence, you can never be totally certain that you have a true vacuum, since delta E has to be larger than 0. The uncertainty principle tells us that what we think is a vacuum actually has, for brief moments of time delta t, particles appearing and disappearing. This quantum view of the vacuum is sometimes called the quantum foam. In general, the uncertainty principle is meaningless in everyday life. We never measure things so precisely that we run into such a limit. But what if instead we zoom down into the quantum world, what do you suspect weɽ see? Let's shrink down in spatial dimensions to about the size of an atom and in the time dimension so that we are living through nanoseconds as if they were seconds. Already you can see that spacetime itself is strange at the quantum scale. Scientists call this mess the quantum foam. This is an artist's illustration of the quantum foam. And as you can see, the foam appears to be frothing with activity. What's going on down here? Since we've shrunk ourselves down in space and in time, we're living in the cold reality of what the uncertainty principle enforces on the universe, for lack of a better term, uncertainty. Down here, the foam can essentially be anything, a proton antiproton pair here, an electron muon neutrino entanglement there. The quantum foam might even generate tiny wormholes. As long as these species last for only a short time, they can have lots of energy. Physicists call particles born in the quantum foam, virtual particles. Because for all intents and purposes, they exist for such a short period of time that we in classical world barely measure their existence. We can borrow energy from the universe as long as we pay it back very quickly. So now a question we might ask is, what happens if we put a black hole nearby and zoom in on the quantum world at the boundary of the event horizon? Do virtual particles get pulled across the event horizon? Classically, weɽ say no. For one, the quantum foam is not a result of classical theories like general relativity. But given its existence anyway, we generally thing that virtual particles don't last long enough to fall in. However, we also have to consider where a particle is because in this universe, we obey the laws of quantum mechanics. So here we are among virtual particles in the quantum foam, and this black region is the event horizon of our black hole. Let's see if we can pin down an electron and its antiparticle, the positron, when they emerge from the quantum foam. This particle pair is called positronium because it exists, albeit temporarily, as a quasi-atom until the universe decides its time is up. And it vanishes back into the quantum foam. But the diagram here doesn't show a complete picture because the electron and positron in the image have definite positions. If we were to truly draw this properly, each would have a much larger probability density, which is to say, regions within which the particles are likely to exist. Probability densities characterized by something called the wave function are places where there are probably particles. So for example, positronium, there's a 100% chance that weɽ find them inside this boundary. But look, the way we've drawn this, there's a good chance that we could find the blue particle not just on the boundary of the event horizon but within it entirely. That's a bit goofy, you might think. The particle, antiparticle pair have come into to existence. And before they can repay their energy to the universe, one of them vanished into the black hole. So now we're in a pickle. We needed that blue particle to annihilate the red one. But instead, now we just have a red one left with no companion. And it doesn't want to stick around. Essentially, what you've just witnessed is Hawking radiation, the process by which particles can kind of escape from a black hole. When a particle, antiparticle pair pop out of the quantum foam, right on the boundary of a black hole, the outgoing particle actually steals energy from the black hole system. It doesn't have to pay the universe back for that energy, instead the black hole had to pay for that part of the equation. Not only does that mean that particles appear to come from the event horizon, but also that quantum mechanics allows black holes to evaporate slowly. So it's pretty obvious that quantum mechanics can do some pretty strange stuff. They can whittle away at a massive black hole until nothing remains. In the next lessons, we'll develop a further understanding of this concept by examining a black hole's temperature, its entropy, and eventually, we'll determine how long a black hole has to live in the face of quantum mechanics.


Stephen Hawking, 1942–2018

By: Monica Young March 14, 2018 14

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Stephen Hawking, renowned physicist, famed science communicator, and all-around inspiration, has passed away at the age of 76.

Stephen Hawking speaks to a crowd at Northeastern University in 1991.
S&T: Kelly Beatty

Professor Stephen William Hawking passed away on the morning of March 14, 2018, in the comfort of his home in Cambridge, UK. He was 76.

The physicist-become-international-icon spent decades defying expectations after his 1963 diagnosis with Lou Gehrig’s disease. He lived a remarkably full life, with a brilliant career in physics and science communication, and is survived by three children, Robert, Lucy, and Timothy, and three grandchildren.

Hawking was born on January 8, 1942, in Oxford, England. Though he exhibited natural intelligence (his schoolfriends nicknamed him “Einstein”), he didn’t apply himself in his early years, generally ranking at the lower end of his classes. But science intrigued him and left him with a hunger to understand the universe. That early interest served as the inspiration that led to him receiving a scholarship at the University College Oxford, where he studied physics and graduated with honors. He went on to graduate school at the University of Cambridge, where he studied cosmology and in 1966 published a thesis titled, “Properties of Expanding Universes.” Hawking became a research fellow at Cambridge after graduation and remained a fellow for the rest of his life.

Yet it was during this time period, in 1963, when at age 21 Hawking was diagnosed with amyotrophic lateral sclerosis (ALS, also known as Lou Gehrig’s disease). ALS is a motor neurone diseases, a group of disorders that affect the nerves in the brain and spinal cord. As the body’s muscles stop receiving messages from the brain, they weaken and waste away.

The diagnosis was devastating, as Hawking was told at the time that he would have one, maybe two years to live after the onset of symptoms. Decades later, doctors are realizing that the disease appears to progress differently in younger patients. Nevertheless, Hawking continued to surprise the medical community til the end: “I am not aware of anyone else who has survived with [ALS] as long,” Nigel Leigh, a professor of clinical neurology at King's College London, told the British Medical Journal in 2002.

Yet rather than slowing him down, the diagnosis only spurred him on. Hawking focused on his research more than ever before. In his best-selling A Brief History of Time, Hawking noted that in 1965, “…two years had gone by and I was not that much worse. In fact, things were going rather well for me . . .”

Indeed, that year Hawking was engaged to be married to a “very nice girl” named Jane Wilde, whom he had met at a college party in 1962. Needing a job, and hence first a PhD, he was casting about for a thesis idea when he came across the work of Roger Penrose (then at Birkbeck College in London). Penrose had used mathematical formulas to show that a star collapsing under its own gravity must become a singularity in spacetime. It didn’t take long for Hawking to cast these equations backward in time, proving that the expanding universe must have originated in a Big Bang singularity.

Black Holes: Not So Black

Hawking’s interest in singularities naturally led him to black holes. Even as ALS put him in a wheelchair by 1969, Hawking was piecing together the ideas behind the idea that earned him fame: Hawking radiation.

Hawking happened across the idea of not-so-black black holes as he was arguing against an idea posed by Jacob Bekenstein, a student at Princeton. The second law of thermodynamics tells us that the disorder of any closed system increases over time. The equations of general relativity also tell us that a black hole’s event horizon, the radius that measures the “point of no return” around the singularity, only grows as a black hole feeds on matter. So Bekenstein proposed that a black hole’s event horizon was a measure of its entropy, as both grow over time. In 1972 Hawking argued this relation couldn’t be true, as black holes don’t radiate. As he notes in A Brief History of Time, “…in writing this paper I was motivated partly by irritation with Bekenstein.”

Only, Hawking soon realized, black holes do radiate, and in a way that’s exactly in line with the second law of thermodynamics. In 1974 Hawking formalized this understanding by relating the singularities of general relativity to the peculiar notion in quantum mechanics that a vacuum isn’t empty. Rather, what appears to be empty space is, thanks to quantum uncertainty, actually a bath of virtual particles that exist for a fraction of a second. Particles can’t come from nothing, so these virtual particles come in pairs, one with positive energy and one with negative energy.

What Hawking realized was that in the presence of a black hole, the immense gravitational field will lend these vacuum particles energy, making them real. If one falls into the black hole, its partner can escape. To a distant observer, the once-virtual particle will appear to emanate from the black hole itself. And the black hole itself would appear to lose a tiny bit of mass.

Hawking radiation occurs when two virtual particles pop into existence near a black hole's event horizon. The black hole's tidal gravity pulls the pair apart, boosting their energy such that they become real, long-lived particles. If one particle falls into the black hole, the other may escape, carrying away some of the black hole's energy/mass.
S&T: Gregg Dindermann

Weirdly, this Hawking radiation depends on the black hole’s mass in the opposite way that you’d think: a stellar-mass black hole would take 10 66 years to evaporate, just a tad bit longer than the age of the universe (which is 10 10 years, roughly speaking). Only microscopic, perhaps primordial black holes could be spotted by their Hawking radiation — theoretically, anyway, as it hasn’t been done yet.

But Hawking radiation wasn’t important so much for practical observations as for what it meant for physics in general. Black holes can feed on any kind matter — gas, stars, the kitchen sink — so they hold an incredible amount of information. As Hawking told me during the inauguration of Harvard University’s Black Hole Initative in April 2016, “[Black holes] are the most efficient hard drives in the universe. All the information in Google databanks would be stored in a black hole smaller than a millionth of a millionth of an inch. Exactly how they are able to store so much information is one of the great mysteries of the universe that we are now working very hard to unravel.” Yet, if Hawking radiation is real, then all of that data is eventually sent away in a sea of informationless particles. In other words, black holes can destroy information itself. This idea, which Hawking published in 1981, led to far more controversy than the idea of Hawking radiation. Even now, physicists are still struggling to understand the implications, not just for black holes but also for the basic precepts behind quantum mechanics and general relativity.

Fame and the Future

In 1985 Hawking suffered an infection that led to a tracheotomy, a procedure that saved his life but cost him the ability to speak. He became fully reliant on a computerized voice system, first controlled by his fingers and in 2008, when the nerve that allowed his thumbs to move degraded, a muscle in his cheek.

These setbacks didn’t set him back — in 1988, he published A Brief History of Time, a survey of the complexities of general relativity, quantum mechanics, and the origin and structure of the universe. It stayed on the Sunday Times best-sellers list for 237 weeks, and is estimated to have sold 10 million copies in more than 40 languages. The clear, often witty descriptions of fundamental concepts granted him international fame, and he later made guest appearances in Star Trek: The Next Generation in 1993 and The Big Bang Theory in 2012, in addition to appearing in the Opening Ceremony of the London 2012 Paralympics.

His personal life became tumultuous following his fame: he separated from Jane, his wife of 25 years in 1990, and they divorced in 1995. He married his one-time nurse, Elaine Mason, the same year, but they divorced in 2006. Nevertheless, Jane and Stephen Hawking maintained a good working relationship. Jane’s autobiography, titled Travelling to Infinity: My Life with Stephen, resulted in the 2014 movie celebrating Hawking’s life, The Theory of Everything. Eddie Redmayne won an Oscar for his role as Hawking.

Fame may have brought some turbulence to Hawking’s life, but it also brought its perks. On April 26, 2007, Hawking had the opportunity to fly NASA’s KC-135, a modified jet fondly called the Vomit Comet, to achieve four minutes of weightlessness.

“The chance to float free in zero-g will be wonderful,” Hawking said during a pre-flight news conference. “I want to demonstrate to the public that anybody can participate in this type of weightless experience.”

Stephen Hawking enjoyed zero gravity during a flight aboard a modified Boeing 707 aircraft known as KC-135, or more popularly, the Vomit Comet.
NASA

In fact, in his later years, Stephen Hawking began advocating that humanity move to the stars, largely because of his concerns over global warming, overpopulation, and epidemics, not to mention the rise of “artificial intelligence.” As part of his advocacy, Hawking helped launch Breakthrough Initiatives in 2015 and was a member of the board of Breakthrough Starshot, a project founded in 2016 with designs on visiting the nearest star system, Alpha Centauri.

At the launch of Breakthrough Starshot, Hawking spoke of transcending limits, saying “Nature pins us to the ground. But I just flew to America. Nature forbids me from speaking. [Pause.] But here I am.”

Friends and colleagues have paid tribute to Stephen Hawking today. Neil de Grasse Tyson said on Twitter, “His passing has left an intellectual vacuum in his wake. But it's not empty. Think of it as a kind of vacuum energy permeating the fabric of spacetime that defies measure. Stephen Hawking, RIP 1942-2018.”

NASA’s acting administrator Robert Lightfoot also issued a statement, saying “Today, the world lost a giant among men, whose impact cannot be overstated. . . . His loss is felt around the world by all he inspired with his work and his personal story of perseverance.”

But we are perhaps best left with the words of Hawking himself, a passionate advocate for understanding the universal laws that govern us all.

“I want to share my excitement and enthusiasm about this quest. So remember to look up at the stars and not down at your feet. Try to make sense of what you see and wonder about what makes the universe exist. Be curious, and however difficult life may seem, there is always something you can do, and succeed at. It matters that you don’t just give up.”


Professor Stephen Hawking 1942-2018

Friends and colleagues from the University of Cambridge have paid tribute to Professor Stephen Hawking, who died on 14 March 2018 at the age of 76.

Widely regarded as one of the world’s most brilliant minds, he was known throughout the world for his contributions to science, his books, his television appearances, his lectures and through biographical films. He leaves three children and three grandchildren.

Professor Hawking broke new ground on the basic laws which govern the universe, including the revelation that black holes have a temperature and produce radiation, now known as Hawking radiation. At the same time, he also sought to explain many of these complex scientific ideas to a wider audience through popular books, most notably his bestseller A Brief History of Time.

He was awarded the CBE in 1982, was made a Companion of Honour in 1989, and was awarded the US Presidential Medal of Freedom in 2009. He was the recipient of numerous awards, medals and prizes, including the Copley Medal of the Royal Society, the Albert Einstein Award, the Gold Medal of the Royal Astronomical Society, the Fundamental Physics Prize, and the BBVA Foundation Frontiers of Knowledge Award for Basic Sciences. He was a Fellow of The Royal Society, a Member of the Pontifical Academy of Sciences, and a Member of the US National Academy of Sciences.

He achieved all this despite a decades-long battle motor neurone disease, with which he was diagnosed while a student, and eventually led to him being confined to a wheelchair and to communicating via his instantly recognisable computerised voice. His determination in battling with his condition made him a champion for those with a disability around the world.

Professor Hawking came to Cambridge in 1962 as a PhD student and rose to become the Lucasian Professor of Mathematics, a position once held by Isaac Newton, in 1979. In 2009, he retired from this position and was the Dennis Stanton Avery and Sally Tsui Wong-Avery Director of Research in the Department of Applied Mathematics and Theoretical Physics until his death - he was also a member of the University's Centre for Theoretical Cosmology, which he founded in 2007. He was active scientifically and in the media until the end of his life.

Professor Stephen Toope, Vice-Chancellor of the University of Cambridge, paid tribute, saying, “Professor Hawking was a unique individual who will be remembered with warmth and affection not only in Cambridge but all over the world. His exceptional contributions to scientific knowledge and the popularisation of science and mathematics have left an indelible legacy. His character was an inspiration to millions. He will be much missed.”

Stephen William Hawking was born on January 8, 1942 in Oxford although his family was living in north London at the time. In 1959, the family moved to St Albans where he attended St Albans School. Despite the fact that he was always ranked at the lower end of his class by teachers, his school friends nicknamed him ‘Einstein’ and seemed to have encouraged his interest in science. In his own words, “physics and astronomy offered the hope of understanding where we came from and why we are here. I wanted to fathom the depths of the Universe.”

His ambition brought him a scholarship to University College Oxford to read Natural Science.There he studied physics and graduated with a first class honours degree.

He then moved to Trinity Hall Cambridge and was supervised by Dennis Sciama at the Department of Applied Mathematics and Theoretical Physics for his PhD his thesis was titled ‘Properties of Expanding Universes.’ In 2017, he made his PhD thesis freely available online via the University of Cambridge’s Open Access repository. There have been over a million attempts to download the thesis, demonstrating the enduring popularity of Professor Hawking and his academic legacy.

On completion of his PhD, he became a research fellow at Gonville and Caius College where he remained a fellow for the rest of his life. During his early years at Cambridge, he was influenced by Roger Penrose and developed the singularity theorems which show that the Universe began with the Big Bang.

An interest in singularities naturally led to an interest in black holes and his subsequent work in this area laid the foundations for the modern understanding of black holes. He proved that when black holes merge, the surface area of the final black hole must exceed the sum of the areas of the initial black holes, and he showed that this places limits on the amount of energy that can be carried away by gravitational waves in such a merger. He found that there were parallels to be drawn between the laws of thermodynamics and the behaviour of black holes. This eventually led, in 1974, to the revelation that black holes have a temperature and produce radiation, now known as Hawking radiation, a discovery which revolutionised theoretical physics.

He also realised that black holes must have an entropy – often described as a measure of how much disorder is present in a given system – equal to one quarter of the area of their event horizon: – the ‘point of no return’, where the gravitational pull of a black hole becomes so strong that escape is impossible. Some forty-odd years later, the precise nature of this entropy is still a puzzle. However, these discoveries led to Hawking formulating the ‘information paradox’ which illustrates a fundamental conflict between quantum mechanics and our understanding of gravitational physics. This is probably the greatest mystery facing theoretical physicists today.

To understand black holes and cosmology requires one to develop a theory of quantum gravity. Quantum gravity is an unfinished project which is attempting to unify general relativity, the theory of gravitation and of space and time with the ideas of quantum mechanics. Hawking’s work on black holes started a new chapter in this quest and most of his subsequent achievements centred on these ideas. Hawking recognised that quantum mechanical effects in the very early universe might provide the primordial gravitational seeds around which galaxies and other large-scale structures could later form. This theory of inflationary fluctuations, developed along with others in the early 1980’s, is now supported by strong experimental evidence from the COBE, WMAP and Planck satellite observations of the cosmic microwave sky. Another influential idea was Hawking’s ‘no boundary’ proposal which resulted from the application of quantum mechanics to the entire universe. This idea allows one to explain the creation of the universe in a way that is compatible with laws of physics as we currently understand them.

Professor Hawking’s influential books included The Large Scale Structure of Spacetime, with G F R Ellis General Relativity: an Einstein centenary survey, with W Israel Superspace and Supergravity, with M Rocek (1981) The Very Early Universe, with G Gibbons and S Siklos, and 300 Years of Gravitation, with W Israel.

However, it was his popular science books which took Professor Hawking beyond the academic world and made him a household name. The first of these, A Brief History of Time, was published in 1988 and became a surprise bestseller, remaining on the Sunday Times best-seller list for a record-breaking 237 weeks. Later popular books included Black Holes and Baby Universes, The Universe in a Nutshell, A Briefer History of Time, and My Brief History. He also collaborated with his daughter Lucy on a series of books for children about a character named George who has adventures in space.

In 2014, a film of his life, The Theory of Everything, was released. Based on the book by his first wife Jane, the film follows the story of their life together, from first meeting in Cambridge in 1964, with his subsequent academic successes and his increasing disability. The film was met with worldwide acclaim and Eddie Redmayne, who played Stephen Hawking, won the Academy Award for Best Actor at the 2015 ceremony.

Travel was one of Professor Hawking’s pastimes. One of his first adventures was to be caught up in the 7.1 magnitude Bou-in-Zahra earthquake in Iran in 1962. In 1997 he visited the Antarctic. He has plumbed the depths in a submarine and in 2007 he experienced weightlessness during a zero-gravity flight, routine training for astronauts. On his return, he quipped “Space, here I come.”

Writing years later on his website, Professor Hawking said: “I have had motor neurone disease for practically all my adult life. Yet it has not prevented me from having a very attractive family and being successful in my work. I have been lucky that my condition has progressed more slowly than is often the case. But it shows that one need not lose hope.”

At a conference In Cambridge held in celebration of his 75th birthday in 2017, Professor Hawking said “It has been a glorious time to be alive and doing research into theoretical physics. Our picture of the Universe has changed a great deal in the last 50 years, and I’m happy if I’ve made a small contribution.”

And he said he wanted others to feel the passion he has for understanding the universal laws that govern us all. “I want to share my excitement and enthusiasm about this quest. So remember to look up at the stars and not down at your feet. Try to make sense of what you see and wonder about what makes the universe exist. Be curious, and however difficult life may seem, there is always something you can do, and succeed at. It matters that you don’t just give up.”

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