Gravitational Waves Discovered

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At a press conference on Feb. 11, 2016 we learned that researchers detected gravitational waves, predicted a century ago by Albert Einstein’s theory of General Relativity.  In the early 1600’s Johannes Kepler worked out the mathematics of the motions of the planets, showing that they orbit the Sun in nearly circular ellipses.  Though Kepler’s laws could predict the motions of the planets, Kepler had no idea why the planets move in ellipses.  In the 1660’s Isaac Newton formulated his principles of motion and of gravity, but could not explain why gravity exists or what it is.  The theory of General Relativity fills those gaps.  Here’s the beginning of a New Yorker article on the discovery of gravitational waves:


Gravitational Waves Exist: The Inside Story of How Scientists Finally Found Them
By
Just over a billion years ago, many millions of galaxies from here, a pair of black holes collided.  They had been circling each other for aeons, in a sort of mating dance, gathering pace with each orbit, hurtling closer and closer.  By the time they were a few hundred miles apart, they were whipping around at nearly the speed of light, releasing great shudders of gravitational energy.  Space and time became distorted, like water at a rolling boil.  In the fraction of a second that it took for the black holes to finally merge, they radiated a hundred times more energy than all the stars in the universe combined.   They formed a new black hole, sixty-two times as heavy as our sun and almost as wide across as the state of Maine.  As it smoothed itself out, assuming the shape of a slightly flattened sphere, a few last quivers of energy escaped.

Then space and time became silent again.  The waves rippled outward in every direction, weakening as they went.  On Earth, dinosaurs arose, evolved, and went extinct.  The waves kept going.  About fifty thousand years ago, they entered our own Milky Way galaxy, just as Homo sapiens were beginning to replace our Neanderthal cousins as the planet’s dominant species of ape.  A hundred years ago, Albert Einstein, one of the more advanced members of the species, predicted the waves’ existence, inspiring decades of speculation and fruitless searching.  Twenty-two years ago, construction began on an enormous detector, the Laser Interferometer Gravitational-Wave Observatory (LIGO).  Then, on September 14, 2015, at just before eleven in the morning, Central European Time, the waves reached Earth.  Marco Drago, a thirty-two-year-old Italian postdoctoral student and a member of the LIGO Scientific Collaboration, was the first person to notice them.  He was sitting in front of his computer at the Albert Einstein Institute, in Hannover, Germany, viewing the LIGO data remotely.  The waves appeared on his screen as a compressed squiggle, but the most exquisite ears in the universe, attuned to vibrations of less than a trillionth of an inch, would have heard what astronomers call a chirp—a faint whooping from low to high.  This morning, in a press conference in Washington, D.C., the LIGO team announced that the signal constitutes the first direct observation of gravitational waves.

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