Sep 23, 2011 - nothing but spreading her hands in a gesture of impotence. âPositive⦠but, cara ... They had not bargained for the law of human chaos, though.
I - 23 September 2011 It was like Boxing Day, the first day of the winter sales. People were using their elbows to fight for a seat, while others had resigned themselves to sitting on the ground. On that Friday, 23 September 2011, in the lecture theatre at CERN, the speed of light had admitted defeat, the theory of relativity was in shreds. And all this because a well-known group of respected researchers was claiming that the neutrino, an unassuming nuclear particle, had taken the liberty of travelling faster than photons; effectively blasphemy, a very rash claim indeed. Nothing moves faster than the speed of light; this is the principle underlying Einstein’s theory of relativity. The whole of modern science, without exception, is posited on this foundation. It all began when Luisa Giacometti, a young researcher just turned twenty-five, intent on her doctoral work at the Gran Sasso National Laboratory, saw the unwelcome figure +60.7 ns flash up on her computer screen. “It’s not possible,” she told herself, as she fed the data into the computer for the third time and the processor, making the calculation with lightning speed, again came up with the answer +60.7 ns. She seemed to hear its synthetic voice saying: “Plus sixty point seven nanoseconds”. There must be an error somewhere. 3
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Her job was to use the data gathered by the OPERA particle detector to determine the velocity of the neutrino, an as yet little-known quantity. In practice, Luisa’s task was to measure the time taken by neutrinos produced at CERN in Geneva to travel the distance from CERN to the Gran Sasso, not far from Rome, and compare it with the time that light would take to cover the same distance. In this way, she could obtain the so-called “difference in time of flight between light and neutrino” and establish which of the two arrived first. This might seem a simple task, but technically it was anything but. When a neutrino arrived, the OPERA detector measured the exact time of the event to the nanosecond. What was known at the other end was the departure time of long bursts of neutrino-projectiles, or “packets”, separated by periods of “silence”: the departure time of the neutrino in question was therefore approximate. However, it was possible to deduce, by statistical calculation, an average time of flight, its degree of uncertainty diminishing as the number of events observed increased. For this reason, Luisa’s task was to study all the thousands of events that had occurred in the last three years, sixteen thousand in all; hardly a cushy job. Nor was it simply a matter of using the raw data. For each and every neutrino, she had to calculate the specific flight distance, i.e. the 730,534.61 metres (roughly 730 kilometres) from CERN to the reference point on the eastern side of OPERA, plus the distance to the exact position of the collision that had taken place in the detector, which was more than 20 metres in length. She also had to factor in a number of corrective parameters for events occurring during the first three months, during the next seven months, and so on, as changes had been made to the equipment between the time when they had begun to gather data, in mid-2008, and the present. Finally, all this work yielded only an approximate difference in time of flight, because various delays in the measurement line still needed to be subtracted, such as the 4
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time required for the signals to pass through the optical fibres and other connecting cables, values accurately calibrated beforehand and kept in the archives. Hers, then, was a task demanding the patience of Job: she had to catalogue and order the data for all the neutrinos observed since the start of the OPERA experiment, carefully correlate the dates on which observations were made with the correct experimental parameters, and so on. After months of this painstaking work, it all ended with that brief moment in which the computer performed its calculation, the few seconds in which it produced the result. Imagining she had made a mistake was the most obvious response and, when the electronic brain flashed up its +60.7 ns, she began the entire process again from scratch. Because the result must, must be zero. Neutrinos travel at the speed of light, according to the theory: full stop. It was impossible that there should be a difference in the flight time. Of course, if she had obtained a negative difference, a delay, indicating that neutrinos travelled slower than the speed of light, some rational explanation might be found. Some theoretical scientists had said that they would not be surprised. But a positive difference, an advance, like +60.7 ns, was just not possible and Luisa, after yet again checking the log books, the information sheets, the reports, the tables, the data fed into the computer, decided to ask her line manager for help. The person in question was Dr Danilo Morsini, operations supervisor for the experiment. He was crouched over his desk, intent on reading an article. At the same time, he was making notes in a notebook, repeatedly taking off and replacing his glasses, a nervous tic of his. Luisa saw him from the corridor, hesitated for a moment, then plucked up courage and passed through the open doorway. “Hi Danilo… look, I need help, I’ve a real problem.” 5
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He did not look up immediately, but finished writing the sentence he had started, then put down his pencil and, finally, glanced at her: “What is it, Luisa?” She placed the computer printout in front of him, the +60.7 ns circled with a fluorescent yellow highlighter, saying nothing but spreading her hands in a gesture of impotence. “Positive… but, cara mia, that’s just not possible, as you very well know,” said Morsini, accompanying his words with a shaking of the head. Such a possibility was inconceivable. “I’ve checked and it always comes up with the same result… positive.” “But look here, Luisa, it’s impossible,” repeated Morsini, this time with the hint of a sarcastic smile. “I’ve run out of ideas… I’ve checked everything ten or a dozen times,” she replied, with a touch of annoyance. Morsini often gave the impression that he did not have a very high opinion of her. His reply was a sigh: why was he always the one who had to deal with new members of staff and their problems? He sought clarification, asking abrupt, tactless questions, as he was wont to do when annoyed by other people’s incompetence and inexperience, which he regarded as one and the same. Luisa defended her position. Morsini was a difficult fellow, bearable only in his professional capacity. Morsini insinuated that she must have got into a “muddle” somewhere, making the already difficult situation worse, bringing her to the verge of tears, before finally accepting that he would have to get off his backside and deal with the matter in person. “OK… I’ll come and check myself,” he said, very irritated at the thought of having to waste his precious time. Because, from his point of view, it would be a waste of time: a difference in flight time between light and the neutrino, to the latter’s advantage, was an impossibility.
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As Prof Ermiti answered the telephone, one fine March morning when the trees outside his office window were showing the first signs of spring, he could not have imagined what awaited him. Angelo Ermiti, professor of high-energy physics at the University of Bern, was director of the “OPERA collaboration”: a hundred-and-sixty physicists divided into thirty or so groups around the world, all involved with the imposing particle detector of the same name hidden away in the caverns of the Gran Sasso National Laboratory. “Angelo, I’ve not been able to sleep all night… we’ve obtained an incredible result, the difference in flight time is positive, the advance is around sixty nanoseconds with a margin of error of less than seven nanoseconds… the neutrino travels faster than the speed of light, I’m sure of it,” announced Morsini, his voice shaking with emotion. “Positive?… don’t be ridiculous!” At the other end of the line, Ermiti’s face expressed shock, half horrified half fearful, as he looked for the right words to calm his friend – above all to keep him from sounding off about it. If you were to tell people that a particle, sub-atomic or of any other kind, could travel faster than the speed of light, you were bound to get egg on your face. But six months later, around mid-September, a sea change had taken place. The OPERA collaboration physicists were convinced that they had eliminated every possibility of experimental error and decided to cross the Rubicon: to announce the discovery of “superluminal” neutrons, as they had been christened, to the scientific community. The “coming-out ceremony” was set for the morning of 23 September 2011, in the main lecture theatre at CERN. To tell the truth, things did not go exactly to plan. Everyone in the collaboration was well aware that a new development of this kind would arouse international interest. With this in mind, they had arranged to proceed with caution, 7
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not to make too much fuss about it, to speak of an “anomaly”, stressing that this was only a “provisional” result, still requiring independent confirmation. By keeping a low profile, they said, it would be possible to manage the impact on the media. Ermiti and Morsini arranged that the article giving the results would not be made public until the Thursday evening, when it would be posted on the arXiv.org server – the electronic pre-print archive used by the scientists. And to prevent leaks, a strict embargo would be maintained in the run-up to Friday morning’s seminar. They had not bargained for the law of human chaos, though. In Thursday’s edition of Il Giorno there appeared, out of the blue, a full-page interview with a famous colleague, which really let the cat out of the bag. It contained statements that could not pass unnoticed: “Superluminal neutrons may have slipped out through unknown dimensions of spacetime”, the stuff of science fiction, and there was even mention of the possibility of “travelling back and forwards in time” – a disastrous article, the beginning of an unstoppable chain reaction. The Italian press, the scientific editors of Nature, Science and every periodical of any importance were on the telephone to Ermiti, to Morsini, to the heads of particle-physics research, to the directors of the Gran Sasso Laboratory, of CERN, in a crescendo of agitation, fearing to be the last to report the news in their on-line pages. By Thursday evening, when Ermiti’s computer flashed up the automatic message: “Measurement of the neutrino velocity with the OPERA detector, arXiv:1109.4897, 22 September 2011 17:59:33 GMT” – confirmation that the article had been made available as planned – the tumult was already completely out of control. It was no surprise, then, that when the doors opened for the planned seminar at CERN, as if for the autumn sales, a surging tide of physicists, journalists, students and nosy parkers, all in a state of euphoria, elbowed their way to the 8
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best seats, and that the late-comers sat on the steps, leaned against the walls or hunkered down on the floor. ∞
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The speaker was Dr Morsini. His eyes switched back and forth between his watch and the audience; he kept putting his hand in his trouser pocket and removing it again, as if searching for something; when he had finished with his pocket, he began the familiar ritual with his glasses. Angelo Ermiti, on the other hand, showed no signs of nervousness, exchanging a few words with those who came to greet him, or turning round to bestow a winning smile on the many whose eyes were upon him. Dark-blue jacket, light-blue shirt, dark tie: he embodied the elegance one would expect of Italian science at its best. Luisa Giacometti, the official author of the discovery, was sitting beside Ermiti, in the front row. She sparkled with joy, like a young pupil who has got full marks in a test and has been rewarded with a smiley face in her homework diary. The large glasses that adorned her long, almost childish face could not conceal her sense of satisfaction. At eleven o’clock on the dot, Danilo Morsini cleared his throat. He started in a very matter-of-fact way, but who could blame him? “Good morning, everyone.” He could have begun self-importantly, chin up and a serious expression on his face, to stress the historic importance of the occasion: “On this day in September 2011, I have the honour of presenting, in all modesty, on behalf of the OPERA collaboration, one of the most significant discoveries in scientific history”. Or he might have adopted an ironical tone, very British, in the face of his attentive audience: “Well, I think I know why you have all come here today”. Instead, he continued in subdued fashion. “I am grateful for this opportunity to present our work.” 9
