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At a time when progress in science is being registered mostly through incremental advances, the detection of gravitational waves came as a fundamental discovery. The concept of gravitational waves is indeed one of the pillars of modern physics.
To be sure, the detection of gravitational waves by the US-based Ligo (Laser Interferometer Gravitational-Wave Observatory) detectors was only an experimental validation of an existing theory. Almost exactly 100 years before they were finally detected, Albert Einstein had postulated the existence of gravitational waves through his work on the general theory of relativity, and created the mathematical foundation for it. For a full century, physics progressed on the assumption that these waves did, indeed, exist. Although direct observation of these waves remained elusive, the various consequences flowing from their existence were evident in several experiments during this time. When they were finally detected, on September 14, 2015, it assured scientists that physics had, indeed, been developing on the right track all these years.
The concept of gravitational waves flowed from Einstein’s attempt to explain two inexplicable facets of an otherwise extremely successful and beautiful theory of gravitation proposed by Isaac Newton in the 17th century, one that every high school student is aware of. Though mathematically accurate — it continues to be so — Newton’s theory does not say why any two bodies in the universe feel an attractive force towards each other. Newton himself was aware of this shortcoming — and had acknowledged it while proposing the theory in 1687.
The second flaw became evident only after Einstein’s special theory of relativity was established in the first decade of the 20th century. Newton’s law of gravitation seemed to suggest that the attractive force was evident on the two bodies instantaneously, irrespective of the distance between them, while Einstein had shown that nothing, not even information, could travel faster than light
The discrepancies in Newton’s theory were resolved by Einstein’s proposal that massive objects actually bend space-time around them, just like a large ball, when placed on a rubber sheet, creates a depression around it. And, it is this curvature of space-time that forces smaller bodies to feel ‘attracted’ towards more massive objects
The consequence of this proposal was that when bodies move in space-time, they carry the curvature with them, creating ripples, or waves, just like a moving boat would in water. And that these gravitational waves, as they were named, indeed move with finite speed, so that the ‘attractive’ force would not be propagated instantaneously.
The detection of the gravitational waves was made possible by global scientific collaboration and incredible precision in recording unimaginably faint signals. The Ligo detectors at two sites in the US are among the most sophisticated scientific facilities in the world. The paper in which the results of the detection were published had more than 1,000 authors, 37 of them working in Indian scientific institutions. After the first one in September 2015, three more detections have been announced, the latest one just last week, in which the European detector Virgo, too, participated. Data collected from these detections have provided new insights into the working of the universe. Evidence of black holes, the size of which had so far not been directly observed, have now been found.
Much before the first detection was made, a proposal to set up a new Ligo-like detector in India had been awaiting government clearance. Within a week of the announcement of detection in February last year, the Indian government gave the go-ahead. The Indian Ligo, as it has come to be called, will be a replica of the two US observatories, and the three will together to form an array of Ligo facilities
The Indian Ligo is slated to begin scientific operations in 2024. Which means the facility has to be ready at least two years before that. A site for locating the facility has been finalised, even though it has not been made public. Various kinds of studies are being carried out at the site, and the process of land acquisition is under way. Funding of Rs 1,260 crore for the first phase of the project has been secured. The Pune-based Inter-University Centre for Astronomy and Astrophysics, which is leading the project, has begun recruiting scientists. Negotiations for selecting industry partners for a variety of collaborations are under way.
By the time the Indian facility comes online, it is expected that detection of gravitational waves would become a weekly, if not more frequent, affair. The novelty and excitement of first detection will no longer be there, but the data from every such instance would continue to be valuable. Scientists expect that very soon gravitational waves would become as common a tool as light and other electromagnetic waves are today in unveiling the secrets of the universe.