SERTARUL CU GANDURI

07/09/2014

„Stephen Hawking. A Life in Science” – Fragmente 3


Din cartea: „Stephen Hawking. A Life in Science” – Michael White and John Gribbin. John Henry Press.2002.

Since his undergraduate days Hawking has been a keen follower of the philosopher Karl Popper. The main thrust of Popper’s philosophy of science is that the traditional approach to the subject, “the scientific method” as originally espoused by the likes of Newton and Galileo, is in fact inadequate.

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Popper stands this process on its head and suggests the following approach. Take a problem. Propose a solution or a theory to explain what is happening. Work out what testable propositions you can deduce from your theory. Carry out tests or experiments on these deductions in order not to prove them but to refute them. The refutations, combined with the original theory, will yield a better one.

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In Popper’s system, the scientist tries to disprove the theory in an attempt to find a better one.

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The science writer Dennis Overbye once asked him how his mind worked. In reply, Hawking said: Sometimes I make a conjecture and then try to prove it. Many times, in trying to prove it, I find a counter-example, then I have to change my conjecture. Sometimes it is something that other people have made attempts on. I find that many papers are obscure and I simply don’t understand them. So, I have to try to translate them into my own way of thinking. Many times I have an idea and start working on a paper and then I will realize halfway through that there’s a lot more to it. I work very much on intuition, thinking that, well, a certain idea ought to be right. Then I try to prove it. Sometimes I find I’m wrong. Sometimes I find that the original idea was wrong, but that leads to new ideas. I find it a great help to discuss my ideas with other people. Even if they don’t contribute anything, just having to explain it to someone else helps me sort it out for myself.

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– Page 133: The first pulsars were discovered by a research student, Jocelyn Bell, while testing a new radio telescope. The astonishing thing about these radio sources is that they flick on and off several times

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– Page 134: This is so much like an artificial signal, a kind of cosmic metronome, that, only half-jokingly, the first pulsars discovered were labeled “LGM 1” and “LGM 2”—the initials “LGM” stood for “Little Green Man.”

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– Page 137: We now know that the Universe is indeed filled with a weak hiss of microwave background radiation, with wavelengths of around 1 millimeter, corresponding to a temperature of 2.73 K.

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– Page 138: Before 1965, cosmology was a quiet backwater of science, almost a little ghetto where a few mathematicians could play with their models without annoying anybody else. Today, a quarter of a century later, the study of the Big Bang is at the center of mainstream physics,

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Stephen Hawking

Stephen Hawking

– Page 141: Hawking had begun puzzling over the singularity at the beginning of time in the early 1960s but had soon been deflected, as we have seen, by the diagnosis of his illness, temporarily giving up his work. But by 1965 things were looking up. He had decided that he wasn’t going to die quite so quickly as the doctors had predicted, after all; he had met and married Jane; and he was back at work with a vengeance. He was one of the few people, at that time, to take seriously the more extreme predictions of the general theory of relativity.

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– Page 142: One of the few other people who did take the notion of black holes seriously was a young mathematician, Roger Penrose, working at Birkbeck College in London. It was Penrose who showed that every black hole must contain a singularity and that there is no way for material particles to slide past each other in the middle of the hole. Not just matter, but space-time itself simply disappears at the  singularity.

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– Page 142: Penrose proposed a “cosmic censorship” hypothesis, suggesting that all singularities must be hidden in this way and that “nature abhors a naked singularity.” In other words, observers outside the horizon of the black hole are always protected from any consequences of the breakdown of the laws of physics at the singularity.

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– Page 143: After all, when space shrinks to zero volume, there is literally no room left for particles to slip past one another. In other words, the expansion of the Universe away from the singularity in the beginning really is the exact opposite of the collapse of matter (and space-time) into a singularity inside a black hole. The cosmic censor has slipped up, and there is at least one naked singularity in the Universe that we are exposed to, even if it is separated from us by 15 billion years of time.

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– Page 144: While Hawking and Penrose were working all this out, the discovery of the background radiation was announced; pulsars were discovered; and Wagoner, Fowler, and Hoyle were explaining how helium had been made in the Big Bang. By the time the Hawking-Penrose theorems were published, John Wheeler had given astronomers the term “black hole,” and newspaper stories were being written about the phenomenon. What had started out as an esoteric (but erudite) piece of mathematical research had evolved by the end of the 1960s into a major contribution to one of the hottest topics in science at the time.

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– Page 144: The 1960s ended with Hawking being forced to make a concession to his physical condition. After a great deal of persuasion from Jane and a number of close friends, he decided to abandon his crutches and take to a wheelchair. To those who had watched his gradual physical decline, this was seen as a major step and viewed with sadness. Hawking, however, refused to let it get him down. Although the acceptance of a wheelchair was a physical acknowledgment of his affliction, at the same time he gave it not the slightest emotional or mental endorsement.

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– Page 153: Meanwhile Hawking was finding the mathematics of the work increasingly difficult to deal with. The equations for interpreting the physics of black holes are amazingly complex,

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– Page 154: Hawking is not unique in having this talent. In 1983 he dazzled students at a Caltech (California Institute of Technology) seminar when he dictated a forty-term version of an important equation from memory. As his assistant finished writing the last term, his colleague, Nobel laureate Murray Gell-Mann, who happened to be sitting in on the talk, stood up and declared that Hawking had omitted a term. Gell-Mann was also working from memory.

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– Page 159: Working on the equations in his head was difficult enough, but after months of intense work Hawking kept coming up with completely nonsensical results. According to the equations, black holes appeared to be emitting radiation. He, and everyone else at the time, believed this to be impossible. He was still convinced that he was really on to something but took the conscious decision not to discuss the problem with anyone until he had settled the matter one way or another.

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– Page 159: Finally, in January 1974 he took the plunge and confided in Dennis Sciama, who was organizing a conference at the time. To Hawking’s surprise, Sciama was very excited by the idea and, with Hawking’s permission, set about spreading the word.

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– Page 160: Going against all current ideas about black holes, by the power of mathematical reasoning, Hawking had been forced to the unarguable conclusion that not only did tiny black holes emit radiation, but under certain conditions they could actually explode. By late January one of his colleagues and friends from postgraduate days, Martin Rees, was convinced that Hawking had made a great discovery.

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– Page 160: He had a hunch, now supported by a number of his respected colleagues and peers, that he was on to something very big. At last he was wheeled to the front of the lecture theater, and his illustrations were projected on to the back wall while he delivered his talk in the almost unintelligible tones to which his colleagues had become accustomed. His final line was delivered. A stunned hush fell over the entire room. You could hear a pin drop as the audience of scientists tried to absorb the astonishing news. Then the backlash began.

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– Page 161: A month after the meeting outside Oxford, Hawking published in Nature his own paper describing the newly discovered phenomena. Within weeks, physicists all over the world were discussing his work, and it became the hot topic of conversation in every physics laboratory from Sydney to South Carolina. Some physicists went so far as to say that the new findings constituted the most significant development in theoretical physics for years. Dennis Sciama described Hawking’s paper as “one of the most beautiful in the history of physics.” The radiation that he had discovered could be emitted by certain black holes was from then on known as Hawking Radiation.

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– Page 164: Hawking’s achievements had been noticed by the scientific establishment. In March 1974, within weeks of the announcement of Hawking Radiation, he received one of the greatest honors in any scientist’s career. At the tender age of thirty-two, he was invited to become a fellow of the Royal Society, one of the youngest scientists in the society’s long history to be given such an honor.

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– Page 169: Hawking, whose career has been founded on the study of black holes, made a bet with Kip Thorne of Caltech, that Cygnus X-1 does not contain a black hole. The form of the bet was that, if it were ever proved that the source is a black hole, Hawking would give Thorne a year’s subscription to Penthouse; but if it were ever proved that Cygnus X-1 is not a black hole, Thorne would give Hawking a four-year subscription to the satirical magazine Private Eye. In June 1990 Hawking decided that the evidence was now overwhelming, and paid up—although, being Hawking, he did so in a typically mischievous fashion, enlisting the aid of a colleague to break into Thorne’s office at Caltech. They extracted the document recording the bet and officially “signed” his admission of defeat with a thumbprint before returning the paper to the files for Thorne to discover later. Over the following months, Thorne duly received the promised issues of Penthouse.

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– Page 171: This basic truth about black holes was established in 1967, by the Canadian-born researcher Werner Israel. When he first developed the equations, Israel himself thought that because black holes had to be spherical, what the equations were telling him was that only a perfectly spherical object could collapse to form a black hole. But Roger Penrose and John Wheeler found that an object collapsing to form a black hole would radiate away energy in the form of gravitational waves—ripples in the fabric of space-time itself. The more irregular the shape of the object, the more rapidly it would radiate energy, and the effect of this radiation would be to smooth out the irregularities.

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– Page 171: So it was established by the early 1970s that a black hole could rotate, but it could not pulsate (Hawking played a small part in this work, too). The size and shape of a black hole depend only on its mass and the speed at which it rotates; the horizon, all that we can see from the outside Universe, carries no identifying features that can tell us what the hole was made of. Physicists call this lack of identifying features the “no hair” theorem. A black hole has no “hair” in the sense that it has no identifying features, and because all we can ever know about it is its mass and its rate of rotation, this makes the mathematical study of black holes much simpler than scientists had feared it would be.

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– Page 174: So Hawking’s dramatic realization, coming with such force that evening in November 1970, was to lead to the idea that the law which says that the area of a black hole can only stay the same or increase is equivalent to the law which says that the entropy of a closed system can only stay the same or increase. But even Hawking didn’t make that connection at first.

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– Page 175: But when a student at Princeton University, Jacob Bekenstein, suggested that the size of the horizon around the singularity might literally be a measure of the entropy of a black hole, he started an avalanche of  investigation which led Hawking to the discovery that black holes are not necessarily black after all—they explode.

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– Page 175: Hawking was annoyed by Bekenstein’s suggestion. Even a research student ought to have realized that there is a direct connection between entropy and temperature, so that if the area of a black hole were indeed a measure of entropy it would also be a measure of temperature. And if a black hole had a temperature, then heat would flow out of it, into the cold (–270°C) of the Universe. It would radiate energy, contradicting the most basic fact known about black holes,

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– Page 178: A black hole weighing about a billion tons, for example (the mass of a mountain here on Earth), would have a radius roughly the same as that of a proton. Less massive miniholes would be correspondingly smaller. And if you are dealing with objects as small as that, physicists knew, you have to use the quantum description of reality in order to understand what is going on.

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– Page 183: A hole smaller than a proton will not eat up much material from its surroundings, even if it happens to be inside a planet. To a hole that small, even solid matter is mostly empty space!

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– Page 186: In the second half of the 1970s he moved on to investigate the origin of the Universe itself, going back to the beginning of time.

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– Page 186: The 1970s were the years when he established himself as a world-class physicist, and they marked the beginning of two decades of startling success in the disparate worlds of arcane research and popular writing.

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– Page 189: …another physicist who was to play a significant role in collaborations and become one of Hawking’s lifelong friends—Don Page. Page, who was born in Alaska and graduated from a small college in Missouri, was working on his Ph.D. at the time of Hawking’s visit. The two of them immediately hit it off, and before Hawking’s year at Caltech was over they had written a black hole paper together.

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– Page 199: But she had a growing feeling that she was being ignored as a human being, as an intelligent woman who was academically successful in her own right. She was beginning to feel like nothing more than a sidekick to the great Stephen Hawking. As she has put it: Cambridge is a jolly difficult place to live if your only identity is as the mother of small children. The pressure is on you to make your own way academically.

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– Page 201: Jane was raised as a Christian and has very strong religious views. To one interviewer she has said: Without my faith in God, I wouldn’t have been able to live in this situation. I wouldn’t have been able to marry Stephen in the first place, because I wouldn’t have had the optimism to carry me through, and I wouldn’t be able to carry on with it.16 Hawking, for his part, is not an atheist; he simply finds the idea of faith something he cannot absorb into his view of the Universe. His outlook is not unlike that of Einstein, and he has been quoted as saying: We are such insignificant creatures on a minor planet of a very average star in the outer suburbs of one of a hundred thousand million galaxies. So it is difficult to believe in a God that would care about us or even notice our existence.17

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– Page 202: Equally, of course, there are a number of practicing scientists who have very strong Christian convictions, and some have claimed that Hawking is simply not qualified to make statements about religion because he knows nothing about it.

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– Page 203: His work deals with the origins and early life of the Universe. Could a subject be any more religious? He once stated: It is difficult to discuss the beginning of the Universe without mentioning the concept of God. My work on the origin of the Universe is on the borderline between science and religion, but I try to stay on the scientific side of the border. It is quite possible that God acts in ways that cannot be described by scientific laws. But in that case one would just have to go by personal belief.19

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– Page 203: When asked if there is any conflict between religion and science, Hawking tends to fall back on the same argument about personal belief and sees no real conflict. “If one took that attitude,” he replied, when asked whether he believed that science and religion were competing philosophies, “then Newton would not have discovered the law of gravity.”20 And what, in the light of Stephen’s and Jane’s dilemma, do we make of the famous last paragraph of A Brief History of Time?

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– Page 203: When asked if there is any conflict between religion and science, Hawking tends to fall back on the same argument about personal belief and sees no real conflict. “If one took that attitude,” he replied, when asked whether he believed that science and religion were competing philosophies, “then Newton would not have discovered the law of gravity.”20 And what, in the light of Stephen’s and Jane’s dilemma, do we make of the famous last paragraph of A Brief History of Time? However, if we do discover a complete theory, it should in time be understandable in broad principle by everyone, not just a few scientists. Then we shall all, philosophers, scientists, and just ordinary people, be able to take part in the discussion of the question of why it is that we and the Universe exist. If we find the answer to that, it would be the ultimate triumph of human reason—for then we would know the mind of God.21

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– Page 211: By March 1977, however, the university had decided to offer him a specially created chair of gravitational physics, which would be his for as long as he remained in Cambridge; the same year he was awarded the status of professorial fellow at Caius, a separate professorship bestowed by the college authorities.  

Stephen Hawking

Stephen Hawking

 

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– Page 217: The size of these uncertainties is determined by Planck’s constant, which gives us basic “quanta” known as the Planck length and the Planck time. Both are very small. The Planck length, for example, is 10–35 of a meter, far smaller than the nucleus of an atom. According to the quantum rules, not only is it impossible in principle ever to measure any length more accurately than this (we should be so lucky!), but also there is no meaning to the concept of a length shorter than the Planck length.

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– Page 217: So if an evaporating black hole were to shrink to the point where it was just one Planck length in diameter, it could not shrink any more. If it lost more energy, it could only disappear entirely. The quantum of time is, similarly, the smallest interval of time that has any meaning. This Planck time is a mere 10–43 of a second, and there is no such thing as a shorter interval of time.

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– Page 219: What Hawking has tried to do is to develop a sum over histories describing the entire evolution of the Universe. Now this is, of course, impossible. Just one history of this kind would involve working out the trajectory of every single particle through spacetime from the beginning of the Universe to the end, and there would be a huge number of such histories involved in the “integration.”

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– Page 226: In 1978 Hawking was awarded one the most prestigious prizes in physics, the Albert Einstein Award given by the Lewis and Rose Strauss Memorial Fund, which announced the winner at a gala event in Washington. The citation claimed that Hawking’s work could lead to a unified field theory, “much sought after by scientists,”1 as one Cambridge newspaper put it. The Albert Einstein Award is considered to be the prestigious equivalent of a Nobel Prize and was undoubtedly the most important award Hawking had received up until that time.

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– Page 226: However, there are two reasons why Hawking is unlikely ever to receive a Nobel Prize. First, a cursory glance at the list of winners since the first prizes in 1901 shows very few astronomers. The reason for this, according to one story, is that the chemist Alfred Nobel, who created the awards, decreed that astronomers should be ineligible. Rumor has it that their exclusion was because his wife had an affair with an astronomer, and he subsequently felt only hatred for the whole profession. Despite this, Martin Ryle and Antony Hewish shared the 1974 Nobel Prize for Physics for their work in radio astrophysics and Subrahmanyan Chandrasekhar won it in 1983 for his theoretical studies on the origin and evolution of stars. These were awarded a good seventy years after the founder’s death, so perhaps the academy now views astronomers with greater sympathy.

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-Page 227: One of the academy’s rules states that a candidate may be considered for a prize only if her discovery can be supported by verifiable experimental or observational evidence. Hawking’s work is, of course, unproved. Although the mathematics of his theories is considered beautiful and elegant, science is still unable even to prove the existence of black holes, let alone verify Hawking Radiation or any of his other theoretical proposals.

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-Page 228: Hawking is well aware of his place in the history of science. He is fascinated by the fact that he was born on the three-hundredth anniversary of Galileo’s death on January 8, 1642. That year Isaac Newton was born in Woolsthorpe, a little village in Lincolnshire, and it was Isaac Newton who was appointed Lucasian professor at Cambridge in 1669, three hundred and ten years before Hawking.

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-Page 229: The appointment as Lucasian Professor of Mathematics at Cambridge University was one of the highlights of Hawking’s career. To be professor at one of the oldest and most respected universities in the world is a huge achievement in itself, but to have accomplished such a feat by the age of thirty-seven is remarkable. Newton was Hawking’s junior by ten years when he gained the chair, but in the seventeenth century there were far fewer academics and very little competition for such positions. Newton did also happen to be the youngest ever to be appointed Lucasian Professor at Cambridge.

30/08/2014

„Stephen Hawking. A Life in Science” – Fragmente 2


Din cartea: „Stephen Hawking a Life in Science” – Michael White and John Gribbin. John Henry Press.2002.

Electrons and atoms are not like tiny snooker balls bouncing around in accordance with Newton’s laws.

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…in a small city in Hertfordshire a seventeen-year-old schoolboy named Stephen Hawking was getting ready for the Oxford entrance examination in a large, cluttered bedroom in his parents’ rambling Edwardian house.

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Stephen and his father settled on the first alternative, and he was entered for the examination toward the end of his final year at St. Albans School. The intention from the start was that he was going for a scholarship, the highest award offered by the university.

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Stephen insisted that he wanted to read mathematics and physics, a course then known as natural science. His father was unconvinced; he believed there were no jobs in mathematics apart from teaching. Stephen knew what he wanted to do and won the argument; medicine had little appeal for him. As he says himself: My father would have liked me to do medicine. However, I felt that biology was too descriptive, and not sufficiently fundamental. Maybe I would have felt differently if I had been aware of molecular biology, but that was not generally known about at the time.1

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The entrance examination was pretty tough. It was spread over two days and consisted of five papers in all, each of which was two and a half hours long. These included two physics and two mathematics papers, followed by a paper that tested candidates on their general knowledge and awareness of current affairs and world issues. A typical question would have been something like “Discuss the possible short-term global consequences of Fidel Castro’s takeover of Cuba.”

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Little did he know that he had scored around ninety-five percent in both his physics papers, with only slightly lower percentages in the others. A few days after the second interview the all-important letter fell on to the Hawkings’ doormat. University College was offering him a scholarship. He was invited to enroll at Oxford University the following October, the only condition being that he obtain two A Level passes in the summer.

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In the late fifties and early sixties, Oxford, as a microcosm of British society, was on the brink of great change. When Hawking arrived at the High on his first October Thursday as an undergraduate, the university had in many respects changed little since his father’s time or, indeed, for the past few hundred years. University discipline had relaxed somewhat since the end of the war. Before then, students had been forbidden to enter the city’s pubs and could, if caught, be expelled from them by the university police, known as the Bulldogs. Women were not allowed in male students’ rooms without written permission from the dean, who would specify strict time limitations and conditions in a letter sent to the head porter, who would then rigorously uphold the dean’s instructions. All this changed when servicemen returning from the war entered the university either as freshmen or to restart courses interrupted by the fighting.

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Most Oxford colleges are built in the form of a number of quads, each with a lawn at the center and paths around and across the grass. From the quads, staircases lead off into the buildings, and the students’ rooms are on a number of levels up to the top of each staircase.

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The intake at Oxford was still largely male and from the country’s private schools, and the majority of those were from the top ten, including  Eton, Harrow, Rugby, and Westminster.

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A simple point of reference illustrates the changes about to hit Oxford soon after Hawking went up, encapsulated by one of his contemporaries. “When we arrived in Oxford,” he said, “anybody who was anybody rowed and never wore jeans. When we left, anybody who was anybody never rowed and did wear jeans.”

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Despite its many charms, Hawking’s first year at Oxford was, by all accounts, a pretty miserable time for him. Very few of his school contemporaries and none of his close friends from St. Albans had gone up the same year.

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The prevailing attitude at Oxford at that time was very anti-work. You were supposed either to be brilliant without effort or to accept your limitations and get a fourth-class degree. To work hard to get a better class of degree was regarded as the mark of a gray man, the worst epithet in the Oxford vocabulary.2

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They were all or nothing, the focal point of the whole three years of study. Hawking once calculated that during the entire three years of his course at Oxford he had done something like 1,000 hours’ work, an average of one hour per day—hardly a foundation for the arduous finals. One friend remembers with amusement, “Towards the end he was working as much as three hours a day!”

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He had applied to Cambridge to begin Ph.D. studies in cosmology under the most distinguished British astronomer of the day, Fred Hoyle. The catch was that to be accepted for Cambridge he had to achieve a first-class honors degree, the highest possible qualification at Oxford.

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The chief examiner asked him to tell the board of his plans for the future. “If you award me a first,” he said, “I will go to Cambridge. If I receive a second, I shall stay in Oxford, so I expect you will give me a first.” They did.

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It has been said that Cambridge is the only true university town in England. Oxford is a much larger city and has, lying beyond the ring road, heavy industrial areas nestling next to one of Europe’s largest housing estates. Cambridge is altogether quainter and more thoroughly dominated by academia. Although evidence suggests that the University of Cambridge was established by defec-tors from Oxford, both seats of learning were created at around the same time in the twelfth century, using as their model the University of Paris. Like Oxford, Cambridge University is a collection of colleges under the umbrella of a central university authority. Like Oxford, it attracts the very best scholars from around the world and has a global reputation, paralleled only by its great rival and historical twin a mere eighty miles away. And, like Oxford, it is steeped in tradition, drama, and history.

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Stephen Hawking, B.A. (Hon.), arrived in Cambridge in October 1962, exchanging the scorched, barren landscape of the Middle East for autumnal wind and drizzle across the darkening fields of East Anglia.

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In the days leading up to his move to Cambridge, with the world outside looking set to tear itself apart, Stephen Hawking was gradually becoming aware of an inner personal crisis. Toward the end of his time at Oxford he had begun to find some difficulty in tying his shoelaces, he kept bumping into things, and a number of times he felt his legs give way from under him. Without a drink passing his lips he would, on occasion, find his speech slurring as though he were intoxicated. Not wanting to admit to himself that something was wrong, he said nothing and tried to get on with his life.

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He had originally chosen to go to Cambridge University because at the time Oxford could not offer cosmological research and, most important, he wanted to study under Fred Hoyle, who had a worldwide reputation as the most eminent scientist in the field.

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When Stephen returned to St. Albans for the Christmas vacation at the end of 1962, the whole of southern England was covered in a thick blanket of snow. In his own mind he must have known that something was wrong. The strange clumsiness he had been experiencing had occurred more frequently but had gone unobserved by anyone in Cambridge. Sciama remembered noticing early in the term that Hawking had a very slight speech impediment but had put it down to nothing more than that.

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He returned to Cambridge and awaited the results of the tests. A short time later he was diagnosed as having a rare and incurable disease called amyotrophic lateral sclerosis, or ALS, known in the United States as Lou Gehrig’s disease after the Yankee baseball player who died from the illness. In Britain it is usually called motor neuron disease.

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One of the amazing ironies of the situation was that Stephen Hawking just happened to be studying theoretical physics, one of the very few jobs for which his mind was the only real tool he needed. If he had been an experimental physicist, his career would have been over.

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In the twice-daily ritual, well established at the Cavendish and carried over to Silver Street, everyone would meet at 11 a.m. for coffee and 4 p.m. for tea to exchange their latest thoughts and ideas.

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During his first two years at Cambridge, the effects of the ALS disease rapidly worsened. He was beginning to experience enormous difficulty in walking and was compelled to use a stick in order to move just a few feet.

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Over the course of the talks at King’s, Roger Penrose had introduced his colleagues to the idea of a space-time singularity at the center of a black hole, and naturally the group from Cambridge was tremendously excited by this.

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Hawking peered through the window, watching the darkened fields stream past and the juxtaposition of his friends reflected in the glass. His colleagues were arguing over one of the finer mathematical points in Penrose’s discussion. Suddenly, an idea struck him, and he looked away from the window. Turning to Sciama sitting across from him, he said, “I wonder what would happen if you applied Roger’s singularity theory to the entire Universe.” In the event it was that single idea that saved Hawking’s Ph.D. and set him on the road to science superstardom.

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Applying singularity theory to the Universe was by no means an easy problem, and within months Sciama was beginning to realize that his young Ph.D. student was doing something truly exceptional. For Hawking this was the first time he had really applied himself to anything. As he says: I . . . started working hard for the first time in my life. To my surprise, I found I liked it. Maybe it is not really fair to call it work. Someone once said, “Scientists and prostitutes get paid for doing what they enjoy.”11

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The final chapter of Hawking’s thesis was a brilliant piece of work and made all the difference to the awarding of the Ph.D. Doctors and Doctorates 73 work was judged by an internal examiner, Dennis Sciama, and an expert external referee. As well as being passed or failed, a Ph.D. can be deferred, which means that the student has to resubmit the thesis at a later date, usually after another year. Thanks to his final chapter, Hawking was saved this humiliation and the examiners awarded him the degree. From then on the twenty-three-year-old physicist could call himself Dr. Stephen Hawking.

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Obviously, since it could emit no light, such an object would be black, which is why the American relativist John Wheeler dubbed them “black holes” in 1969. But although it was well known that the general theory made this prediction, at the time Hawking was completing his undergraduate studies and moving on to research no one took the notion of black holes seriously. The reason is that there are very many known stars that have more than three times the mass of our Sun.

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But quantum theory said that there is a way to make a star denser than a white dwarf. If the star were squeezed even more by gravity, the electrons could be forced to combine with protons to make more neutrons. The result would be a star made entirely of neutrons, and these could be packed together as closely as the protons and neutrons in an atomic nucleus. This would be a neutron star.

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The density of the matter in a neutron star, in grams per cubic centimeter, would be 1014—that is, 1 followed by 14 zeros, or one hundred thousand billion. Even an object this dense would not be a black hole, though, for light could still escape from its surface into the Universe at large.

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The quantum equations said, in fact, that there was no way that even neutrons could hold up the weight of a dead star of 3 solar masses or more and that, if any such object were left over from the explosive death throes of a massive star, it would collapse inward completely, shrinking to a mathematical point called a singularity. Long before the collapsing star could reach this state of zero volume and infinite density, it would have wrapped space-time around itself, cutting off the collapsar from the outside Universe.

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if it were possible to squeeze our own Sun down into a sphere with a radius of about 3 kilometers, it would become a black hole. So would the Earth, if it were squeezed down to about a centimeter. In each case, once the object had been squeezed down to the critical size, gravity would take over, closing space-time around the object while it continued to shrink away into the infinite density singularity inside the black hole.

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The mid-sixties turned out to be one of the most important times in Stephen Hawking’s life. Having become engaged to Jane, he realized that he would need to find a job very quickly if they were to be married. After obtaining a doctorate, the next stage in the career of any academic is usually to secure a fellowship, accompanied by a grant, in order to continue research.

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Fellowship is considered a great honor and a means by which academics may continue with their research and be paid for it. In return, a college gains prestige if one of its fellows turns out to be highly successful.

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The couple was married in July 1965 in the chapel of Hawking’s postgraduate college, Trinity Hall. It was not a typical “academic” wedding, but neither was it, by any means, a society occasion. Both sets of parents were ordinary, middle-class people.

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Of course they both knew, as did all the others on that day, that Stephen might die within a short time. In fact, according to the medical predictions he was already living on borrowed time.

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At the DAMTP and in Cambridge academic circles, Hawking was beginning to cultivate a “difficult genius” image, and his reputation as successor to Einstein, although embryonic, was already beginning to follow him around. People who knew him in those days remember him as a friendly and cheerful character, but already his natural brashness, coupled with his physical disabilities, was beginning to create communication difficulties with many of those around him.

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Both Jane and Stephen knew that they should not waste any time in starting a family once they were married, and their first child, a boy they named Robert, was born in 1967.

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Hawking was working harder than he had ever worked before, and it was paying dividends. In 1966 he won the Adams Prize for an essay entitled “Singularities and the Geometry of Spacetime.”

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He spent most of this time in collaboration with Roger Penrose, who was by then professor of applied mathematics at Birkbeck College in London. One of the major difficulties the two of them faced was that they had to devise new mathematical techniques in order to carry out the calculations necessary to verify their theories—to make them empirically sound and not just ideas. Einstein had experienced a similar problem fifty years earlier with the mathematics of general relativity. He, like Hawking, was not a particularly brilliant mathematician. Fortunately for Hawking, however, Penrose was. In fact, he was fundamentally a mathematician rather than a physicist, but at the deep level at which the two subjects become almost indistin-guishable.

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Hawking’s way of working is largely intuitive—he just knows if an idea is correct or not. He has an amazing feel for the subject, a bit like a musician playing by ear. Penrose thinks and works in a different way, more like a concert pianist following a musical score. The two approaches meshed perfectly and soon began to produce some very interesting results on the nature of the early Universe.

20/07/2014

„Stephen Hawking. A Life in Science” – Fragmente 1


Din cartea:” Stephen Hawking a Life in Science” (Michael White and John Gribbin), John Henry Press.2002.

At the age of twenty-one Hawking discovered that he had the wasting disease ALS, also called motor neuron disease, and he has spent much of his life confined to a wheelchair.

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She asks the professor if he believes that there is a God who created the Universe and guides His creation. He smiles momentarily, and the machine voice says, “No.”

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He has been made a CBE—commander of the British empire—and then companion of honour by Queen Elizabeth II and has written a popular science book, A Brief History of Time, which stayed on the best-seller list for five years from 1988 to 1993 and has to date sold over ten million copies worldwide.

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It is perhaps one of those oddities of serendipity that January 8, 1942 was both the three-hundredth anniversary of the death of one of history’s greatest intellectual figures, the Italian scientist Galileo Galilei, and the day Stephen William Hawking was born into a world torn apart by war and global strife. But as Hawking himself points out, around two hundred thousand other babies were born that day, so maybe it is after all not such an amazing coincidence.

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Stephen’s mother, Isobel, had arrived in Oxford only a short time before the baby was due. She lived with her husband Frank in Highgate, a northern suburb of London, but they had decided that she should move to Oxford to give birth.

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When he was two weeks old, Isobel Hawking took Stephen back to London and the raids. They almost lost their lives when he was two, when a V2 rocket hit a neighbor’s house.

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Hawking was eight when the family arrived there. Frank Hawking had a strong desire to send Stephen to a private school. He had always believed that a private school education was an essential ingredient for a successful career. There was plenty of evidence to support this view: in the 1950s, the vast majority of members of Parliament had enjoyed a privileged education, and most senior figures in institutions such as the BBC, the armed forces, and the country’s universities had been to private schools.

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Stephen, he decided, would be sent to Westminster, one of the best schools in the country.

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When he was ten, the boy was entered for the Westminster School scholarship examination. Although his father was doing well in medical research, a scientist’s salary could never hope to cover the school fees at Westminster—such things were reserved for the likes of admirals, politicians, and captains of industry. Stephen had to be accepted into the school on his own academic merit; he would then have his fees paid, at least in part, by the scholarship.

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St. Albans School had 600 boys when Stephen arrived there in September 1952. Each year was streamed as A, B, or C according to academic ability. Each boy spent five years in senior school, progressing from the first form to the fifth, at the end of which period he would sit for Ordinary (O) Level exams in a broad spectrum of subjects, the brighter boys taking eight or nine examinations. Those who were successful at O

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He passed easily and, along with exactly ninety other boys, was accepted into the school on September 23, 1952. The fees were fifty-one guineas (£53.55) a term.

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St. Albans School proudly boasted a very high intellectual standard, a fact recognized and appreciated by the Hawkings very soon after Stephen started there. Before long, any nagging regrets that he had been unable to enter Westminster were forgotten. St. Albans School was the perfect environment for cultivating natural talent.

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Much remembered and highly thought of was a master fresh out of university named Finlay who, way ahead of his time, taped radio programs and used them as launch points for discussion classes with 3A. The subject matter ranged from nuclear disarmament to birth control and everything in between. By all accounts, he had a profound effect on the intellectual development of the thirteen-year-olds in his charge, and his lessons are still fondly remembered by the journalists, writers, doctors, and scientists they have become today.

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English schoolboys attending the private schools of the 1950s had little time for girls in their busy program, and parties were single-sex affairs until the age of fifteen or sixteen. It was only then that they would have the inclination and parental permission to hold sherry parties at their houses

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Frank Hawking kept meticulous accounts of everything he did in a collection of diaries maintained until the day he died. He also wrote fiction, completing several unpublished novels. One of his literary efforts was written from a woman’s viewpoint. Although Isobel respected his efforts when she read it, she believed that it was unsuccessful.

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Michael Church describes how he felt an indefinable intellectual presence when it came to discussing matters vaguely mystical or metaphysical with Stephen. Remembering one encounter, he says: I wasn’t a scientist and didn’t take him remotely seriously until one day when we were messing around in his cluttered, joke-inventor’s den. Our talk turned to the meaning of life—a topic I felt pretty hot on at the time—when suddenly I was arrested by an awful realization: he was encouraging me to make a fool of myself, and watching me as though from a great height. It was a profoundly unnerving moment.2

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In the spring of 1958, Hawking and his friends, including new recruits to the group, Barry Blott and Christopher Fletcher, built a computer called LUCE—Logical Uniselector Computing Engine. In the 1950s in Britain, only a few university departments and the Ministry of Defence had computers.

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Hawking and his friends received their first exposure to the press when the local newspaper, the Herts Advertiser, covered the story of the “schoolboy boffins” building their newfangled machine.

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When scientists refer to the “classical” ideas of physics, they are not referring back to the thoughts of the Ancient Greeks. Strictly speaking, classical physics is the physics of Isaac Newton, who laid the foundations of the scientific method for investigating the world back in the seventeenth century.

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two revolutions, the first sparked by Einstein’s general theory of relativity and the second by the quantum theory. The first is the best theory we have of how gravity works; the second explains how everything else in the material world works. Together, these two topics, relativity theory and quantum mechanics, formed the twin pillars of modern twentieth-century science. The Holy Grail of modern physics, sought by many, is a theory that will combine the two into one mathematical package.

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the discovery of pulsars, in 1967, the year Stephen Hawking celebrated his own twenty-fifth birthday. These objects are now known to be neutron stars, the collapsed cores of massive stars that have ended their lives in vast outbursts known as supernova explosions. It was the discovery of pulsars, collapsed objects on the verge of becoming black holes, that revived interest in the extreme implications of Einstein’s theory of gravity, and it was the study of black holes that led Hawking to achieve the first successful marriage between quantum theory and relativity.

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Hawking was already working on the theory of black holes at least two years before the discovery of pulsars, when only a few mathematicians bothered with such exotic implications of Einstein’s equations,

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But within ten years, observations made by Edwin Hubble with a new and powerful telescope on a mountaintop in California had shown that the Universe is expanding.

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One of the people instrumental in establishing this “wave-particle duality” of light was Einstein, who in 1905 showed how the way in which electrons are knocked out of the atoms in a metal surface by electromagnetic radiation (the photoelectric effect) can be explained neatly in terms of photons, not in terms of a pure wave of electromagnetic energy. (It was for this work, not his two theories of relativity, that Einstein received his Nobel Prize.)

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The German physicist Werner Heisenberg established in the 1920s that all observable quantities are subject, on the quantum scale, to random variations in their size, with the magnitude of these variations determined by Planck’s constant. This is Heisenberg’s famous “uncertainty principle.” It means that we can never make a precise determination of all the properties of an object like an electron: all we can do is assign probabilities, determined in a very accurate way from the equations of quantum mechanics, to the likelihood that, for example, the electron is in a certain place at a certain time.

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