Nobel Prize 2017: Physics

Rainer Weiss, Barry C. Barish and Kip S. Thorne were awarded the 108th Nobel Prize in Physics “For their decisive contributions to the LIGO detector and the observation of gravitational waves”

Rainer Weiss, a professor of Massachusetts Institute of Technology was awarded the one half of the honor along with Barry Barish and Kip Thorne both from California Institute of Technology will share the other half of the honour for their discoveries of ripples in space-time known as gravitational waves which were predicted by Einstein a century ago but were never seen directly. While announcing the award, The Nobel Committee termed it as “Discovery that Shook The World!”

The first gravitational waves were detected in February 2016 when scientist and astronomers working at the Laser Interferometer Gravitational-wave Observatory (LIGO) and The LIGO Scientific Collaboration which includes 1000s of scientists announced that they had recorded gravitational waves emanating from the collisions of a pair of massive black holes billions of light years away!

What are gravitational waves?

Gravitational waves are the ripples in the fabric of space-time which are produced due to the collision of two ultra-dense neutron stars or merging black holes. These cosmic events are so powerful that they radiate gravitational waves which we can directly observe as distortions in space-time. Although, gravitational waves are washing over the earth all the time until very recently the experiments were never sensitive enough to detect them.

Einstein’s General Theory of Relativity in 1916 suggested that the universe was expanding from what we now call The Big Bang and it also predicted that the motions of massive objects like black holes or other dense remnants of dead stars would ripple space-time with gravitational waves! Einstein wasn’t totally convinced that he was right; over the next several decades, he continually waffled over the question of gravitational waves and occasionally published papers refuting his original idea.

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Source: National Geographic

Why are they so hard to detect?

By the time gravitational waves reach us from the distant events that triggered them they distort the space-time in a very minute. A gravitational wave which passes through the earth will alternately stretch and squeeze the earth in two axes (orthogonal directions). These distortions are very very small- one part in a billion trillion, less than the diameter of a proton!!! Measuring such minute changes in length is pretty much impossible for most instruments ever built!

How did they detect?

The technological odds were against them, when Dr. Weiss was explaining their concept to their funders everyone thought “They were out of their mind”.

They built a Laser Interferometer Gravitational-Wave Observatory (LIGO) funded by the National Science Foundation spending over 1 billion dollars in 40 years!

The LIGO Detectors in US consists of two identical L- Shaped detectors in Washington state and Louisiana, each of which employs lasers and mirrors to measure tiny changes in space-time made by passing gravitational radiation. It’s the most sensitive measuring device on the planet, with each arm of the L measuring roughly 2.5 miles end-to-end.

The gravitational waves are detected by change in distance between mirrors parked at each end of those perpendicular arms of the L-Shaped detectors.

One mirror is set at the tip of each L-arm, and there’s another at the point where the arms meet. As gravitational waves wash over Earth, they’ll first distort the distance between one pair of mirrors, and then distort the distance between the perpendicular pair. A laser bouncing back and forth between the mirrors keeps track of how far apart they are to an almost impossibly precise degree (the detectors are sensitive to such things as passing trucks, lightning strikes, ocean waves, and earthquakes). For a signal to be real, it should show up in both detectors. So far four such signals have been picked up by LIGO of which 3 are from colliding black holes.

Aside from the fact that they prove Einstein was right (Once Again!), Why is it important?

The direct detection of gravitational waves also opens a new vista on the “dark” side of the cosmos, to times and places from which no optical light escapes. This includes just fractions of a second after the Big Bang, 13.7 billion years ago, when scientists believe gravitational waves left a permanent imprint on the cosmos that may still be perceptible today. We also are now aware that black hole collisions occur more frequently than we thought.

 

 

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