Gravitational Waves/LIGO

Gravitational Waves/LIGO

By Avinash Agarwal

UPSC GENERAL STUDIES: Paper III (Awareness in the field of Space)

Table of Contents

What do you understand by Gravitational waves?

How does the detection of gravitational waves influence our understanding of our universe?

What role did India play in Gravitational Wave Detection?

What benefits can accrue to India by participating in this initiative?

What lessons can be learnt from India’s successful participation in the LIGO project?

Miscellaneous Points that can be used in Essays

* Importance of Persistence

* Role played by Frugal Engineering

* Failures as a stepping stone towards success

An artist's impression of gravitational waves generated by binary neutron stars.

Q.) What do you understand by Gravitational waves?

It is simplest to visualise them using an analogy. One can think of the space-time continuum of general relativity as a malleable rubber sheet. It is bent by heavy bodies such as stars.

The heavier the body, the more is the space-time continuum bent, and the greater is its curvature. Black holes bend it maximally.

Now imagine two such bodies moving towards each other, and finally colliding. On a rubber sheet, two colliding heavy balls would send out ripples as they approach each other. The same thing happens in general relativity.

Gravitational waves are these ripples in the very geometry of space-time. The ripples are tiny when the bodies are far away but gain strength as the bodies approach one other. When they collide, the ripples can have cataclysmic strength. If the two bodies are black holes, space-time is shaken so violently that there is a veritable tsunami in the very fabric of space-time. In a tiny fraction of a second, more energy is emitted than one would obtain by “burning” a few suns, converting their entire mass into energy!

Q.) How does the detection of gravitational waves influence our understanding of our universe?

Ever since the human race started gazing at the night sky and pondering about the nature of heavenly bodies, all our information about the universe has come in the form of electromagnetic waves.

Until the middle of the last century, we only knew what was revealed to us in visible light. By and large, the universe appeared to be rather calm. But then we broadened the frequency bands and looked at the universe using radio waves, through infrared light, through X-rays and through gamma rays. The universe seen at these frequencies, we found, was dramatically different.

Brand new phenomena were seen to unfold. There were huge bursts of energy in the form of jets. There were radio bursts. We saw brand new processes heavenly bodies engage in that had not been even imagined before. As a result, our view of the universe today is very different from what it was half a century ago.

The novel and exotic phenomena are now part of the standard picture. They were always there. But we were blind to them in spite of centuries of careful observations simply because we did not have the appropriate detectors to receive the messengers that the cosmos has been sending.

Gravitational waves are a whole new genre of cosmic messengers, entirely different from our electromagnetic channels. Starting now, we will be blessed with novel, unforeseen opportunities. It is as if a curtain is being drawn back, exposing us to new aspects of the cosmos we inhabit.

We cannot see black hole collisions through any of the electromagnetic frequencies. The only messengers that can inform us of such phenomena are gravitational waves. Over the last quarter of a century, astronomers have pondered a great deal about black holes. But they have been unsure of whether our universe harbours black holes of tens of solar masses. The very first gravitational-wave signal has dispelled that doubt.

Gravitational waves have opened an entirely new branch of astronomy, with various frequency bands of its own. They will reveal to us an untold number of new phenomena. Over the next quarter of a century, our view of the universe is likely to change dramatically.

Q.) What role did India play in Gravitational Wave Detection?

Over several decades, Indian researchers at the Inter-University Centre for Astronomy and Astrophysics (IUCAA) in Pune and the Raman Research Institute in Bengaluru have been deeply involved in gravitational-wave science, making important theoretical contributions to diverse aspects of the problem, ranging from mathematical studies within general relativity to novel aspects of statistics and analysis of large data sets.

* Bala Iyer’s group at the Raman Research Institute (RRI), Bengaluru: pioneered the mathematical calculations used to model the GW signals expected from orbiting black holes and neutron stars.

* Sanjeev Dhurandhar’s group at the Inter-University Centre for Astronomy and Astrophysics (IUCAA), Pune: did foundational work on developing the data analysis techniques used to detect these weak signals buried deep in the detector noise.

Currently, under the umbrella of the IndIGO consortium, some 60 scientists from nine institutions are members of the LIGO Scientific Collaboration, and the paper reporting the first detection includes 35 authors from these institutions.

These researchers have proposed the creation of a Laser Interferometer Gravitational-wave Observatory in India itself, which will become an integral part of the international network of such observatories, including two in the U.S., one in Europe and one in Japan.

We heard recently that the Union Cabinet has now given its approval, clearing the way for the construction of this observatory. Through a bilateral agreement, the U.S. will provide an advanced detector valued approximately at $120 million and India will invest upwards of Rs.1,200 crore to create the observatory.

The present Indian GW research community has essentially grown out of research programmes these two groups carried out. Over the past decade, the Indian GW community has expanded to a number of educational and research institutions.

·    Chennai Mathematical Institute, the Indian Institute of Science Education and Research (IISER) Thiruvananthapuram, and IISER Kolkata; TIFR Mumbai.

Q.) What benefits can accrue to India by participating in this initiative?

LIGO-India has the potential to impact precision experiments and cutting-edge technology in the country. The project has interfaces with quantum metrology, laser physics and technology, vacuum technologies, optical engineering, sensor technologies, control systems, grid and cloud computing, to list a few. As Beverly Berger of the U.S. National Science Foundation said: “Every single technology they are touching they are pushing and there is a lot of technologies they are touching.”

This initiative represents a truly extraordinary opportunity for development of both fundamental science and technology. On the scientific front, the participating institutions will create human resources not only in physics and astronomy but also in statistics, computational science and data analysis. Through summer schools, workshops and visits to other institutions in the U.S. and Europe, young researchers will be trained in state-of-the-art techniques in all these areas. The opportunities to push forefront technology to new heights are truly immense.

The observatory will feature 4-km-long tunnels in which laser beams bounce back and forth between suspended mirrors. Through the vacuum systems employed in the 4-km-long tunnels, through the powerful lasers used in the interferometer, and through the novel methods that go in the building of the required mirrors and the suspension system that holds them, research and development efforts have already improved technologies used in vacuum systems, optics and material science by several orders of magnitude. It is a true blessing for young researchers to be able to put together, use, and further develop such fine instruments. Through this participation, they will remain at the very cusp of technology in these areas for years to come.

Q.) What lessons can be learnt from India’s successful participation in the LIGO project?

There are three unique aspects of the IndIGO Consortium that have possibly contributed to its success thus far:

* The consortium set goals that projected well ahead into the future, allowing time for a healthy next generation of young researchers to be established. It also allowed time to consolidate expertise scattered across different laboratories in India under a common umbrella. It has also gained international recognition as a channel for Indian researchers abroad to explore possibilities of returning and contributing to the national effort.

* The IndIGO Consortium was an informal collection of researchers devoid of any institutional affiliation. This allowed these researchers to take bold uninhibited steps driven solely by scientific and technological considerations rather than by existing funding and institutional structures. (The IndIGO Consortium enjoyed logistic support from IUCAA to carry out many of its activities and that was formalised recently in an MoU.) Despite being an informal body, the consortium was formally recognised in the global GW community with a membership in the GWIC. The consortium benefited immensely from the cooperative nature of GW endeavours.

* The open and non-institutional nature of the consortium encouraged an influx of experts from all forms of institutional settings, national and international, such as large research laboratories, IISERs, IITs, National Institutes of Technology (NITs), and from other related fields of experimentation and theory. On the other hand, the globally cooperative and collaborative nature of GW science has instilled among the members the spirit of working effectively in a large scientific collaboration.

Note: How the expertise and culture is spreading to other institutes in India: Over the last decade, the Indian GW community, mainly consisting of researchers trained at the research groups in the IUCAA and the RRI, have spread to take up faculty positions at a number of educational and research institutions in India.

Q.) Miscellaneous Points that can be used in Essays

Importance of Persistence:

THE recent detection of gravitational-waves (GWs) by the Laser Interferometer Gravitational-wave Observatory (LIGO), nearly 100 years after they were first recognised by Einstein as a consequence of his general theory of relativity, is the result of one of modern science’s longest campaigns. For more than 40 years, the theoretical world debated back and forth about whether what was predicted was a real phenomenon or just a mathematical artefact with no physical significance.

Role played by Frugal Engineering

Scaling the interferometer to multi-kilometre arm length includes engineering challenges as well. To achieve the required sensitivity, the laser beams must travel in ultra-high vacuum pipes, aligned to millimetre accuracy. While the techniques for building such a large vacuum system were available when LIGO was first proposed, they would have been too expensive for such an uncertain venture. LIGO scientists and engineers worked with commercial companies to develop lower-cost ways to fabricate and install the high vacuum tubes that carry the laser beams. This led to new fabrication techniques for high-vacuum systems, new treatments for the stainless steel used to fabricate them, and even one of the first demonstrations of the use of GPS for precision alignment over long baselines.

Failures as a stepping stone towards success

From the early days of LIGO, it was structured as a two-step programme: first, an initial set of LIGO detectors which would use the best technologies available in the late 1990s, to be followed by a set of advanced detectors incorporating technologies that needed more time for development.

* However the first generation detectors could not detect the GWs.

* But the experience with the first-generation detectors would be extremely valuable in refining the developments needed for the advanced detectors.

* From 2010 to 2015, the initial LIGO detectors were replaced with entirely new, advanced ones.

* These advanced detectors, in very early stage of commissioning, were able to detect the GWs, ending the 100 year old quest for their search.