Proving Einstein Right: Direct Detection of Gravitational Waves

Source: MIT, Feb 2016

… with his theory of general relativity, Einstein correctly predicted the behavior of gravitational waves, space-time ripples that travel to us from places in the universe where gravity is immensely strong. Those rippling messages are imperceptibly faint; until now, they had defied direct observation. Because LIGO succeeded in detecting these faint messages – from two black holes that crashed together to form a still larger one – we have remarkable evidence that the system behaves exactly as Einstein foretold.

… human achievement. It begins with Einstein: an expansive human consciousness that could form a concept so far beyond the experimental capabilities of his day that inventing the tools to prove its validity took a hundred years.

That story extends to the scientific creativity and perseverance of Rai Weiss and his collaborators. Working for decades at the edge of what was technologically possible, against the odds Rai led a global collaboration to turn a brilliant thought experiment into a triumph of scientific discovery.

Related Resource: Columbia Spectator, Feb 2016

Imperceptible to all but the most powerful instruments, gravitational waves are created when the motion of massive objects like black holes distorts space. These waves emanate outward like ripples on the surface of a pond, passing invisibly through stars and planets and the void between galaxies.

… gravitational waves leave only infinitesimal traces to mark their passing.

To detect the waves, adLIGO uses a basic interferometer design: A laser is split into two beams that head off at 90 degree angles until they bounce off mirrors to recombine before entering a light detector. Because the beams are adjusted to be 180 degrees out of phase from one another, they normally cancel out destructively so that no light reaches the detector.

When a gravitational wave passes through adLIGO, an arm of the apparatus, which is four kilometers long, changes in length by a minute amount. This change in length would alter the amount of time it takes light from one arm to reach the detector, so that the beams would no longer perfectly cancel out. By measuring light received by the detector, scientists can observe and determine the characteristics of gravitational waves.

NY Times, Feb 2016

the National Science Foundation, which spent about $1.1 billion over more than 40 years to build a new hotline to nature

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