Gravitational waves: another prediction of Einstein’s confirmed! – Point

At first, it was just a wild rumor. A message posted on Twitter on January 11 by the cosmologist Lawrence Krauss of Arizona State University: “My latest information about Ligo have been confirmed by independent sources. Stay tuned! Perhaps it was discovered gravitational waves !! Exciting. “Retweeted more than 1900 times, the tweet of the cosmologist has toured the world science, earning a volley of skeptical reactions as the news was hardly believable. But now, the discovery is almost official: physicists were able to detect gravitational waves. “If the information is confirmed, it is one of the most important scientific discoveries of our time. In my view, even more important than the Higgs boson! explains to the Point Catherine Bréchignac, perpetual secretary of the Academy of Sciences. The evidence that we now have a device capable of understanding the infinitely large. We will not be content to watch the stars, but see inside them, because these waves penetrate the material to the threshold which light stops. “

The story begins gravitational waves there are a hundred years with Albert Einstein who sets out to understand how the gravitational field spreads in the new theory of gravity that just built the theory of general relativity. But the article that the physicist wrote in 1916 contains a significant error, and it was not until 1918, in a second paper, he gives good description. Gravitational waves, “OG” in their pet name, form one of the key elements of the theory of general relativity: the propagation waves, the light speed of gravitation. General relativity predicts indeed that every body that moves creates a deformation of the structure of space-time, ie, change the distance and time, and this deformation spreads through successive waves into the cosmos in the manner of a wave on the surface of the water. Only extremely violent events generate OG, cosmic cataclysms, such as the formation of a star into a black hole, the explosion of a supernova or the collision of two neutron stars. But so far, no one had been able to detect these distortions of space-time that spread in the universe at 300,000 km / s, the speed of light.

” Courage “

For thirty years though scientists actively hunt down. On the one hand, Virgo, a detection antenna built in Pisa under the CNRS and the Italian National Institute for Nuclear Physics (INFN), which involves six French teams (APC, LAL, LAPP, LMA, LKB, OCA). On the other, Ligo from the National Science Foundation with its two interferometers in the United States. In 2014, given the magnitude of the challenge, Virgo and Ligo signed an agreement to share their data. In September 2015, two US interferometers who finally captured signals, ephemeral – they lasted only a small fraction of a second – from the orbital motion and the merger of two giant black holes, each of a mass equal to 30 suns, located about a billion light-years from Earth. This observation thus has been confirmed after verification of data.

For a long time doubted the existence of these waves. “The first mathematical proof has been provided in 1952 by Yvonne Choquet-Bruhat, specialist of relativity. Then, in the late 50′s, another pioneer, Joseph Weber, had the courage to believe that it was necessary to build sufficiently sensitive detectors to detect OG “says Thibault Damour (1), a professor at the Institute high scientific studies, which included providing network Ligo / Virgo unprecedented method to describe the signal from the merger of two black holes and thus facilitate its detection.

“Courage”, the word is not too much if one questions the researchers who have spent all or part of their careers in search of gravitational waves. “From the Virgo construction beginning there were many conservative voices are raised: it’s too risky, too expensive, it would be better to invest in other areas. Fortunately, CNRS held firm; this is the main advantage of national research organizations, their perseverance on long-term scientific targets, “recalls Stavros Katsanevas, Associate Scientific Director of the Institute of Nuclear Physics and Particle Physics (IN2P3) and President of the European Monitoring Centre for gravitational waves (EGO / VIRGO) from 2002 to 2012. “that said, the construction of Virgo began three years later than Ligo. Virgo colleagues have made remarkable efforts, and the delay was reduced to a few months. Both collaborations are working hand in hand and crucial contributions in the analysis of these events were made by European teams, such as the Astroparticle and Cosmology Laboratory IN2P3 / Paris-Diderot / CeA / Obs of Paris. “

Dizzying

Since the announcement of the detection, it is as if the world of physics had undergone a gravitational wave, and those who had not conspicuously enthusiasm now are jockeying to be in the photo. It is true that the feat of Virgo / Ligo gives nothing less than creating a new astronomy. Four hundred years after Galileo launched by optical astronomy when he pointed his telescope to the sky. “The first telescopes were then paved the way for radio astronomy, satellites launched astronomy X-ray, then the gamma rays, etc. Astronomies of all based on electromagnetic waves until the first detectors of cosmic neutrinos inaugurate neutron astronomy. The detection of gravitational waves, a different type of signal, therefore, gives us new glasses to see new things in the universe, “says Thibault Damour

In fact, the prospects are dizzying.: to probe dark energy, this strange force that would explain the expansion of our Universe, better explore the cosmos and, why not, go back in time up to 14 billion years. Indeed, not only physicists captured the signal from gravitational waves, but they also observed, for the first time, the merger of two black holes. The proof of the existence of these ogres guzzling light, holding perhaps the secret of the birth of our universe. In the early 2000s, Jean-Pierre Luminet, an astrophysicist at the Observatoire de Paris-Meudon and director of research at CNRS, wrote: “The frontiers of science are always an odd mixture of new truth, a reasonable assumption and extravagant conjecture. “The feat that just completed the American, French and Italian physicists opens a window on the Universe in extravagant appearance invented by Einstein a century ago.

(1) The next course of Thibault Damour at IHES, on February 18 and 25, focuses on “gravitational waves and binary systems” WWW.IHES.FR