by Prasad Ganti

Gravity waves have been in the news for the last two years or so. Firstly, when the hundred year old prediction of Albert Einstein came true. Gravity waves were discovered when two black holes collapsed into one, about a billion light years away. The feeble vibrations of space-time was heard by two well engineered and sensitive detectors called LIGO (Laser Interferometer Gravitational-Wave Observatory). Few more such observations have been made over the last two years. The most recent one resulting from a neutron star collapsing into a neutron star.

When a massive star, tens of times heavier than our Sun dies, it ends up as a neutron star and possibly a black hole. Being so dense and compact, both of them represent gravitational extremities. Neutron stars can be detected by radio and optical telescopes but black holes can only be detected indirectly.

Upon finding the evidence for a century old prediction by the all time great physicist Einstein, the Nobel prize for Physics in 2017 was awarded to Kip Thorne, Rainer Weiss and Barry Barish for their work on gravity waves. These waves were undetected for a century mainly because they are very very weak. They result from very violent cosmic events like merger of gravitationally intense objects like black holes and neutron stars. These events do not happen frequently in our galaxy. Certainly not in our neighborhood. If they did, we would not exist anymore. Happening at far away distances, the waves travel at the speed of light, and get attenuated on the way to almost the level of insignificance.

Lot of sensitivity in the instrumentation is required to detect such feeble signals. And the noise resulting from other sources needs to be subtracted. Rainer Weiss had analysed the possible sources of background noise that would disturb their measurements. He had also designed a detector, a laser-based interferometer, which would overcome this noise. Basically consisting of two arms in “L” shape running across several miles, with very precise mirrors in both the arms. And a laser beam bouncing back and forth. If there is any disturbance in space-time, the two beams would be out of sync, almost by a whisker. It was necessary to develop new laser technology and invent new materials, as well as construct gigantic vacuum tubes, seismic isolation and other vital technology far beyond what had previously been achieved. Two such detectors were constructed (One in Louisiana and another in Washington state) to eliminate any false alarms resulting from local incidents. Now a third detector in Italy joined the fray.

In 1994, when Barry Barish took over as leader for LIGO, he transformed the small research group of about 40 people into a large-scale international collaboration with more than a thousand participants. He searched for the necessary expertise and brought in numerous research groups from many countries. Thus, big science and sophisticated engineering came together. Reminds me very much of the LHC (Large Hadron Collider) in Geneva, Switzerland, which led to the discovery of Higgs Boson, another monumental discovery of this decade. This led to a Nobel prize in Physics to Peter Higgs and Francois Englert in 2013.

Kip Thorne was instrumental in setting up of LIGO. In addition, he was a consultant and an executive producer of the science fiction movie “Interstellar”. The special effects in the movie were pretty close to realty. The graphics team which created the special effects worked very closely with Thorne who worked out several equations to bring a sense of credibility to the imagination. I am glad that Throne won the Nobel prize. Though the prize is not for the movie.

The most recent detection of gravity waves resulted from the collision of two neutron stars. The difference this time being that as soon as the waves were detected, other telescopes and observatories were notified. There was detection of other signals from the same event. Gamma rays were detected by the Fermi observatory in space. Several telescopes detected optical and radio signals as well. It was the first time when multiple scientific devices were able to track a mega cosmic event and study its aftermath.

It is a watershed event in the history of science when such mega projects come together to witness a significant cosmic event, amplifying the human ability to study the cosmos in such detail and depth.