the discovery told by Carlo Rovelli
Milan , February 11, 2016 – 23:22
the the world of physics was in for weeks fibrillation. The rules of the game, which serve to reduce the risk of false alarms, imposed secrecy until the official announcement, and colleagues kept tight-lipped. But the glitter of their eyes betrayed them. At the bottom is a virtually certain Nobel. Yesterday, in an emotional press conference followed live on the web in the whole world, the official announcement came: detected gravitational waves. For physicists is an ecstatic moment. Until the day before, the only fundamental waves were observed by man electromagnetic waves, those of which are made radio signals and light. Yesterday was observed another type of wave. It is as if we were to rewrite Genesis, replacing “Fiat lux” with “Fiat lux et gravitatis fluctus”. Waves are a bit ‘like electromagnetic ones, but also something different and strange are the space oscillations. The space ripples and fluctuates as the surface of a lake.
we already knew the very existence before seeing
the most spectacular aspect of this history is not the strangeness of nature, nor the skill of the scientists who built the antenna capable of detecting the space waves. What’s extraordinary is that we knew about the existence of these waves long before they see them: their existence is predicted by Albert Einstein’s general relativity, which we have just celebrated the centenary. If the benign Nature wanted to honor Einstein one hundred years after his theory, he has found the most elegant way. Hard to imagine a clearer indication of the strength of a thought, leaning on evidence and reason, it is able to see that far; so much so that eyes and hands need another century to follow. To get there, it is a large international collaboration was needed, where the Italians have – once again – a greater role. We were convinced that these waves exist. But one thing is to be convinced that there are lions. Another is to look for a real lion and look into his eyes. The difference is what we call “science.”
They were produced by the crashing of two blacks holes
the existence of these “gravity waves” is a consequence of the fact that nothing goes faster than light. The light takes eight minutes to get from the sun to us. If the Sun were wiped out now, maybe a neutron star that madness for the Galaxy (unlikely event), that would happen in the next eight minutes on Earth? Answer: nothing. Because here there is no way to know that the sun is gone, no message has had time to arrive. But the gravity of the Sun holds the Earth in its orbit, so for eight minutes the Earth would still attracted by the Sun, although the Sun is no more! During these eight minutes, something has to travel into space, carrying information that the Sun is no more, and the attraction of the Sun should go off. That something is a gravitational wave: the rapid spread of a petite space deformation. The observed order now from Ligo (Laser interferometer gravitational-waves observatory: observatory of gravitational waves in laser interferometry) were produced from a disaster: the sinking of two blacks holes in each other. Were each weighing several tens of times the Sun, and their spiraling crashing on each other radiated into space an amount of energy equal to three full “Suns” vaporized within moments. The event violence has produced waves as a galactic tsunami have traveled millions of years in interstellar space and time have come to lapping, weakened, on our antennas.
The role of the Italian physicists
An antenna to watch this space deformation is simple in principle. Just take two objects, two balls hanging by a thread, and accurately measure the distance between them. a gravitational wave is change, swing, distance, because space stretches and pulls like a wire for hanging swinging in the wind. The problem is that the change is small, and detect it requires highly advanced engineering. Ligo measure the distance between two large masses suspended at a distance of some kilometers, by means of a laser that bounces between the two and makes interference with a second laser that bounces between two masses arranged at ninety degrees. Why the antennas are buildings with two long perpendicular arms. The slight offset between the two arms is what you measure. In Italy there is a similar antenna at Pisa, called Virgo, an integral part of the extensive collaboration that has led to the result yesterday. Virgo also has two long arms several kilometers. Is one visit show. Virgo was not on when there was a celestial event seen by LIGO, but the Italian physicists who built Virgo played a vital role. Italy is in the front row in the world and the search for gravitational waves is a long tradition with us – goes back to the vision of Edoardo Amaldi, a student of Enrico Fermi, the noble father of the Italian post-war physical and the Department of Physics in Rome – and it was conducted on many fronts. Remember, a student at Trent, craft and brilliant explorations of Cerdonio Massimo and Stefano Vitale who, perhaps too ahead of their time, they tried to use the superconductor as small antennas to detect the waves of space … An ounce of bitterness that they were not the first to “see,” but also for physicists Italian gravitational waves is the moment of triumph: Virgo is, as LIGO, an amazing car which now becomes a fantastic telescope for observing the universe. Because that yesterday is not a point of arrival, it is a starting point: we have opened new telescopes on the universe. We are at the point where Galileo, having perfected his telescope, was able to use it to see the sky. What we will see, once again, we will surprise us.
That dinner with Isaacson in the nineties
the construction of these antennas have attended dozens of physicists, technicians, engineers, and hordes of students. For decades. In the early nineties I was a young professor in America, and Richard Isaacson had come to Pittsburgh, where I was teaching. Richard was responsible for the physics of gravitation of the National science foundation, the American agency that assigns funds for scientific research. He had just decided, in person, how do you use in America, to invest substantial funds for LIGO. The goal was to detect the waves in five years. I had expressed concerns. He, passing from Pittsburgh, wanted to understand why. We ate dinner together at a small table in one of those nice ethnic restaurants that dot the American university areas. He asked me if I had doubts about the existence of gravitational waves. “Practically none.” Criticisms of the principle of the measure? “No,” everything clear. Then? The waves are weak, I remember I answered, and before the technology arrives to see them, pass time. I asked him what gave him the belief that one could get. The answer was clear: trust in Kip Thorne. Kip is one of the great relativists. He worked at Caltech. It’s the same Kip Thorne who participated in the writing of the film Interstellar : thanks to him that even today the man in the street has become convinced that we can meet again with their daughter, older self. A few years later, having met him at a conference, I asked him what had given security to convince Isaacson of the feasibility of the measure. Kip has waited a long time before answering, looking into my eyes. Then he asked me: “Do you think we should not try?”. It’s been twenty five years. I finally understood: Kip had reason. Today we saw the gravitational waves.
Faith in reason
It is a triumph for science, yet another triumph for Einstein, a triumph for Thorne and Isaacson, and their poker bet. It is a triumph for a small community of stubborn researchers, in America as in Italy, who has spent his life building the machines great with funding much smaller than those of CERN, chasing a dream: to see completely new types of waves, which no one had ever seen before. A dream based on a strange faith, faith that scientific functions right: that the logical deductions of Einstein and his mathematics is reliable. Only that faith in reason is a peculiar faith: a faith that you do not really believe in it, it always asks you to control. We checked. There are. It’s a great day for science. Fortunately Isaacson has spared my doubts.
February 11, 2016 (edited February 12, 2016 | 08:35)
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