The American observatory LIGO detected a gravitational wave: the confirmation fell Thursday, February 11, 2016. Explanation of the operation of this interferometer, which could be found in the list of Nobel 2017.
INTERFEROMETER. A revolution in the history of science. The LIGO scientific site captured the characteristic signal of a gravitational wave. The information was confirmed Thursday, February 11, 2016, during a joint intervention to Paris researchers at LIGO and VIRGO their counterparts, almost identical facility in Italy and whose CNRS is a founding member: it is the 1st detection of the “space-time vibration” predicted by Albert Einstein. The latter asserts that any mass displacement – in a non-symmetrical way – in a point of the universe must create a wave that propagates through the cosmos, including the Solar System and the Earth. As this gravitational wave passes, a portion of the space expands and then contracts before returning to its original form. And it is the trace of this passage through the Earth that was detected.
With the confirmation of this information, it is the consecration for the American scientific observatory which, after a technical improvement in September 2015, now explores a volume of Universe ten times larger than before. LIGO extends to two sites at both ends of the United States, one in Hanford, Washington – west of the country – the other in Livingstone, Louisiana, in the southeast. The Franco-Italian Virgo Observatory near Pisa (Italy), which was launched at the beginning of the year, but later, was also initiated. Both use an interferometer. Its principle: a laser beam is sent on a mirror that separates it into two beams. Each of them traverses one of the multi-kilometer arms at the end of which a mirror returns the beam. After several round trips to increase the precision, the beam leaves the arm to cross the other beam with which it is recomposed. If the two beams have traveled the same distance, they return at the same time at the intersection: if one subtracts the shape of one beam from the other, the result is zero. On the other hand, if a gravitational wave has shortened or lengthened one of the arms, one of the beams comes out a little before or after the other. This phase shift ensures that the result of the subtraction of the two beams will not be zero. We then conclude that a gravitational wave has passed. This, therefore, has detected “vibration”.