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Cabinet grants ‘in-principle’ approval to the LIGO-India mega science proposal

The Union Cabinet chaired by the Prime Minister Shri Narendra Modi has given its ‘in principle’ approval to the LIGO-India mega science proposal for research on gravitational waves. The proposal, known as LIGO-India project (Laser Interferometer Gravitational-wave Observatory in India) is piloted by Department of Atomic Energy and Department of Science and Technology (DST). The approval coincides with the historic detection of gravitational waves a few days ago that opened up of a new window on the universe to unravel some of its greatest mysteries.

The LIGO-India project will establish a state-of-the-art gravitational wave observatory in India in collaboration with the LIGO Laboratory in the U.S. run by Caltech and MIT.

The project will bring unprecedented opportunities for scientists and engineers to dig deeper into the realm of gravitational wave and take global leadership in this new astronomical frontier.

LIGO-India will also bring considerable opportunities in cutting edge technology for the Indian industry which will be engaged in the construction of eight kilometre long beam tube at ultra-high vacuum on a levelled terrain.

The project will motivate Indian students and young scientists to explore newer frontiers of knowledge, and will add further impetus to scientific research in the country.

Cabinet has granted ‘in-principle’ approval to the LIGO-India mega science proposal for research on gravitational waves. — PMO India (@PMOIndia) February 17, 2016

The approval coincides with the historic detection of gravitational waves a few days ago. — PMO India (@PMOIndia) February 17, 2016

LIGO-India project will establish a state-of-the-art gravitational wave observatory in collaboration with LIGO Laboratory run by Caltech&MIT — PMO India (@PMOIndia) February 17, 2016

Project will bring opportunities to dig deeper into realm of gravitational wave & take global leadership in this new astronomical frontier. — PMO India (@PMOIndia) February 17, 2016

LIGO-India will also bring considerable opportunities in cutting edge technology for the Indian industry. — PMO India (@PMOIndia) February 17, 2016

The project will motivate Indian students & scientists to explore newer frontiers of knowledge & will add impetus to scientific research. — PMO India (@PMOIndia) February 17, 2016

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Explained: What Is The LIGO-India Project And How Will It Benefit The Country

After seven years of in-principle approval, the government approved the construction of the laser interferometer gravitational-wave observatory (ligo) project..

After seven years of in-principle approval, the government approved the construction of the Laser Interferometer Gravitational-Wave Observatory (LIGO) project. It will be built by a collaboration between multiple departments and research institutions, including the Department of Atomic Energy, the Department of Science and Technology, and the U.S. National Science Foundation, along with several national and international research institutions.

The project is expected to significantly advance research in the field of gravitational-wave astronomy and help understand the universe better.

What is LIGO?

LIGO is a network of laboratories, spread around the world, designed to detect gravitational waves. These waves are incredibly weak, making their detection very challenging. The LIGO detectors are sensitive to distance changes that are several orders of magnitude smaller than the length of a proton.

In 2015, LIGO made history by detecting gravitational waves for the first time. These waves were produced by the merger of two black holes that were 29 and 36 times the mass of the Sun, 1.3 billion years ago. This achievement earned the scientists involved in the project the Nobel Prize in Physics in 2017.

Three operational observatories in the world

Currently, there are three operational gravitational wave observatories around the world - two in the United States (Hanford and Livingston), one in Italy (Virgo), and one in Japan (Kagra). For accurate detection, four comparable detectors need to be operational simultaneously across the globe.

The LIGO detectors consist of two 4-km-long vacuum chambers, arranged at right angles to each other, with mirrors at the end. The experiment works by releasing light rays simultaneously in both chambers.

Normally, the light should return at the same time in both chambers. However, if a gravitational wave passes through, one chamber gets elongated while the other gets squished, resulting in a phase difference in the returning light rays. Detecting this phase difference confirms the presence of a gravitational wave.

What is the LIGO-India project?

The LIGO-India project is an initiative aimed at detecting gravitational waves from the universe. It involves the construction of two vacuum chambers that are perpendicular to each other and 4 kilometres long each, making them the most sensitive interferometers in the world.

The project is expected to commence scientific runs from 2030 and will be located in the Hingoli district of Maharashtra, approximately 450 km east of Mumbai.

Significance of the LIGO-India project

The LIGO-India project is significant as it will be the fifth node of the planned network, thereby bringing India into a prestigious international scientific experiment.

This project will make India a unique platform that combines the frontiers of science and technology of the quantum and the cosmos.

It has the potential to provide unprecedented insights into the mysteries of the universe, including the nature of black holes, neutron stars, and other celestial phenomena, reports the Indian Express.

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The Indian role

Significant indian contributions to theoretical source modelling and data analysis made the ligo discovery of september 2015 possible..

Published : Mar 02, 2016 12:30 IST

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Some of the members of the Indian gravitational-wave research community, which comes under the umbrella of the Indian Initiative in Gravitational-wave Observations (IndIGO).

ON September 14, 2015, around 3:20 p.m. Indian Standard Time, ripples in space-time caused by the merger of two black holes hit the two Laser Interferometer Gravitational-wave Observatory (LIGO) centres in the United States. The signal was so strong that just by looking at the data one could “see” the signal. Yet, it took the collaborating scientific groups several weeks of analysis to confirm the detection and to extract the astrophysical information contained in the observed signal. In addition to confirming Einstein’s century-old prediction of the existence of gravitational waves (GWs), this detection marked the beginning of a new era in astronomy. The LIGO discovery was made possible by significant Indian contributions to theoretical source modelling and data analysis.

Indian scientists have made major contributions to GW physics over the past 25 years. In the late 1980s and early 1990s, Bala Iyer’s group at the Raman Research Institute (RRI), Bengaluru, in collaboration with a group of French scientists, pioneered the mathematical calculations used to model the GW signals expected from orbiting black holes and neutron stars. These calculations, using the so-called post-Newtonian methods, form the basis for computing the theoretical “templates” of the expected signals employed in GW detection.

Around the same period, in parallel, 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. The present Indian GW research community has essentially grown out of research programmes these two groups carried out. Several researchers belonging to the next generations, including Sukanta Bose, A. Gopakumar, Sanjit Mitra, Rajesh Nayak, Archana Pai, B.S. Sathyaprakash, Anand Sengupta and the authors of this article, trained under these groups.

Mergers of binaries A big discovery does not happen overnight and requires decades of preparation. A unique feature of GW astronomy is the rich interplay it demands between experiment, theory and data analysis. Historically, scientists had realised that mergers of binaries consisting of black holes or neutron stars were the best bet for the first detection of GWs. (A binary system is a system of two stellar objects—brown dwarfs, planets, neutron stars, black holes, galaxies or asteroids—which are close enough that their mutual gravitational interaction causes them to orbit each other around their common centre of mass.)

Experimental advances in the field were positively influenced by the theoretical progress made in solving the Einstein field equations for such systems to accurately compute the expected signal shapes, or “waveforms”. It was realised early on that if one could calculate the expected signal shapes, a powerful data analysis method called “matched filtering” could be employed for detection. This method involves comparing the data with theoretical templates of the expected signals making use of the mathematical operation called cross-correlation.

Immediately after the LIGO project was funded in the U.S., Kip Thorne at Caltech, California, convened an international meeting of experts in January 1994 to brainstorm the theoretical challenges the experiment posed. Bala Iyer was one of the participants at that meeting as was Dhurandhar and the French theoretical physicist Luc Blanchet. “During the meeting, Blanchet felt that the ‘post-Newtonian formalism’ he was developing with Thibault Damour could be generalised to the second post-Newtonian order and higher,” recalled Iyer.(Post-Newtonian expansions in general relativity are used to find an approximate solution to the Einstein field equations. The approximations are expanded in terms of a small parameter, v / c (where v is the velocity of the astrophysical object and c is the speed of light), which express orders of deviations from Newton’s law of universal gravitation. Higher order terms can be added to increase accuracy. In the limit, when the small parameters approach zero, the post-Newtonian expansion reduces to Newton’s equations.)

Together with Blanchet, Damour and a few young colleagues, Iyer was involved in extending the theoretical formalism, now called the Blanchet-Damour-Iyer formalism, to higher orders, enabling the computation of theoretical waveforms to a very high accuracy. These waveforms constitute the theoretical inputs on which the present data analysis strategies rely.

The signal waveforms from binaries of black holes or neutron stars depend on the properties of these objects. For example, two neutron stars with masses comparable to that of the sun will orbit each other at very close separations (and hence high orbital frequencies) before they merge. Thus, they produce GW signals of very high frequencies (around 2,000 hertz) during the merger. On the other hand, heavy mass black holes such as the ones LIGO observed will merge at large orbital separations and hence low orbital frequencies (see Figure 1). Hence, their GW signals span only low frequencies (around 20-200 Hz), which are in the human audio frequency range.

Since one does not have prior knowledge of the properties of the signal that is buried in the data, each data segment has to be compared with signal waveforms corresponding to different values of the source parameters, such as the masses of the black holes. This calls for a clever optimisation: the “template bank” should contain a signal waveform that is close to the signal buried in the data; at the same time, the total number of templates in the bank has to be limited so that the data analysis is computationally tractable.

Matched filtering technique The IUCAA scientists Dhurandhar and B.S. Sathyaprakash (who later went on to set up a leading research group at Cardiff University, Wales), along with a few young collaborators, laid the foundations for a method that makes use of a sophisticated geometric approach to tackle this problem. In the 1990s, the IUCAA became a major hub of activity in the then nascent field of GW data analysis. Dhurandhar and Sathyaprakash were among the first ones to think of using the matched filtering technique for GW data analysis and to implement it in a full-blown computer code.

A particularly intriguing contribution of Dhurandhar’s is the use of a mathematical technique called “stationary phase approximation” to compute the “Fourier transform” of the expected GW signals from binary systems. (The Fourier transform decomposes a signal into the frequencies that make it up, similar to how a musical chord can be expressed as the amplitude (or loudness) of its constituent notes—Wikipedia.) In private conversations, Dhurandhar confesses that this idea occurred to him in a rare moment of inspiration while he was jogging in a park in Cardiff. People in the field acknowledge this as Dhurandhar’s original contribution, though he never published a paper on it. Story has it that a reputed journal rejected his paper describing this method for the first time. However, this method was to become an essential tool for GW data analysis in the coming years.

Over the past decade, the Indian GW community has expanded to a number of educational and research institutions. Major contributions of Indian scientists include the development of techniques to “coherently” combine and analyse the data from multiple observatories, development of “hierarchical” search methods that allow them to progressively dig into the data, techniques to make “sky maps” of stochastic GWs similar to the sky maps of the cosmic microwave background, formulating methods to accurately test Einstein’s theory of general relativity using GW observations, modelling GW signals by combining post-Newtonian calculations with large-scale supercomputer simulations, and cross-correlation-based techniques to detect continuous GWs from spinning neutron stars.

The Indian participation in the LIGO experiment, under the umbrella of the Indian Initiative in Gravitational-wave Observations (IndIGO), as part of the worldwide LIGO Scientific Collaboration involves 61 scientists from nine institutions (see table). The IUCAA and the Bengaluru-based International Centre for Theoretical Sciences (ICTS) of the Tata Institute of Fundamental Research (TIFR), Mumbai, host LIGO Tier-3 grid computing centres. At the TIFR, a prototype detector is being built for training and research.

Indian groups have also contributed to the understanding of the response of the detector to the signals and terrestrial influences, to the method used to detect the signal, bounding the orbital eccentricity, to estimating the mass and spin of the final black hole and the energy and power radiated during merger, to confirming that the observed signal agrees with Einstein’s theory, and to the search for a possible electromagnetic counterpart using optical telescopes.

The shape of the observed signal allows scientists to identify the properties of its distant astrophysical source, such as the mass of the orbiting black holes and how fast they spin. In spite of having been formed only in 2013, the ICTS-TIFR group has already made significant contributions to the analysis of the data from the GW detection of September 2015. Making use of results from already available supercomputer simulations, this work has led to the accurate estimation of the mass and spin of the final black hole. The September 14 event has produced a new black hole that is approximately 62 times more massive than the sun and spinning at 67 per cent of the maximum possible spin rate for black holes according to the theory of general relativity (Figure 2). This is the most massive black hole in the stellar-mass range discovered so far, and one of the most accurate astronomical measurements of its kind.

100 times more powerful Black hole mergers are the most powerful astronomical events in the universe after the Big Bang. Although simple analytical calculations provide order-of-magnitude estimates of the energy and power radiated during the merger, a faithful treatment of the systematic and statistical errors requires results from supercomputer simulations of the merger. In the September 14 event, scientists (with major contributions from the same Indian group) have estimated the peak power of the gravitational radiation to be as high as 3.6 × 10 49 watts. This makes this event at least 100 times more powerful than the brightest “gamma ray burst”, the most powerful astronomical phenomenon discovered so far. The peak power emission in this event (in the form of GWs) is larger than the average power emission from all the stars in the universe put together.

These powerful astronomical events allow scientists to test Einstein’s theory of general relativity in a hitherto unexplored regime. A new way of testing general relativity emerged out of a collaboration between the RRI group and other scientists, notably Sathyaprakash. They proposed a way of measuring the coefficients of the post-Newtonian expansion from the observed signal to see whether these agreed with the values predicted by the theory.

This test was performed on the recent LIGO observation, with contributions from groups at the Chennai Mathematical Institute, the Indian Institute of Science Education and Research (IISER) Thiruvananthapuram, and IISER Kolkata.

Yet another test proposed and implemented by the ICTS-TIFR group involved measuring the mass and spin of the final black hole from the “inspiral” part of the signal (produced by the motion of the black holes before they merge) and checking their consistency with the same parameters measured from the “post-merger” signal. Analyses performed on the September 14 event have revealed that the observations are fully consistent with the theory’s prediction within measurement uncertainties. These are some of the first tests of Einstein’s theory in the regime of extreme gravity and velocities.

At this point, it is important to mention the seminal work of C.V. Vishveshwara from the 1970s. Vishveshwara worked in Maryland, U.S., but later moved to the RRI. His study of how a black hole responds to an external perturbation led to the prediction of characteristic oscillation modes of black holes, called “quasi-normal modes”. It was later realised that a “perturbed” black hole formed by the merger of two black holes will settle into a stationary black hole by radiating the same type of quasi-normal modes. In the LIGO observation, the last part of the observed signal (referred to as the “ring down” of the black hole) is consistent with the presence of a quasi-normal mode inferred from theory.

The Indian involvement in experimental GW physics started only relatively recently, with the formation of the IndIGO consortium (see table), but the Indian scientific community has the relevant expertise in various aspects of the science of precision measurement. With the prospect of LIGO-India being established, the community aspires to play a leading role in this emerging research frontier.

P. Ajith is a physicist at the International Centre for Theoretical Sciences (ICTS) of the Tata Institute of Fundamental Research. K.G. Arun is a physicist at the Chennai Mathematical Institute.

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India Approves Construction of Its Own LIGO

The Indian government has granted the final approvals necessary for construction to begin on LIGO-India, a nearly identical version of the twin LIGO (Laser Interferometer Gravitational-Wave Observatory) facilities that made history after making the first direct detection of ripples in space and time known as gravitational waves in 2015. The Indian government will spend about $320 million to build LIGO-India, with first observations expected by the end of the decade.

"We've worked very hard over the past few years to bring a LIGO detector to India," says David Reitze, the executive director of the LIGO Laboratory at Caltech. "Receiving the green light from the Indian government is a very welcome development that will benefit not only India but the entire international gravitational-wave community."

"As the newest gravitational-wave detector, LIGO-India will have all of our latest and best techniques incorporated from the get-go," says Rana Adhikari, a professor of physics at Caltech who helps lead the development of LIGO-India along with Reitze and others on the LIGO team, in collaboration with Indian scientists.

LIGO-India is a collaboration between the LIGO Laboratory —operated by Caltech and MIT and funded by the National Science Foundation (NSF)—and India's Raja Ramanna Center for Advanced Technology (RRCAT), Institute for Plasma Research (IPR), Inter-University Centre for Astronomy and Astrophysics (IUCAA), and the Department of Atomic Energy Directorate of Construction Services and Estate Management (DCSEM). The planned facility—which, like the LIGO observatories in Hanford, Washington, and Livingston, Louisiana, will include an L-shaped interferometer with 4-kilometer-long arms—will be built near the town of Aundha in the Indian state of Maharashtra.

When LIGO-India is completed, it will join a global network of gravitational-wave observatories that includes Virgo in Italy and KAGRA in Japan. With its advanced gravitational-wave-sensing technology, LIGO-India will greatly improve the ability of scientists to pinpoint the sky locations of the sources of gravitational waves. Because of its location on Earth with respect to LIGO, Virgo, and KAGRA, it will also fill in blind spots in the current gravitational-wave network.

"LIGO-India will increase the precision with which we can localize the gravitational-wave events by an order of magnitude," says Adhikari. "This will greatly enhance our ability to answer fundamental questions about the universe, including how black holes form and the expansion rate of our universe, as well as to more rigorously test Einstein's general theory of relativity."

"I am very pleased to learn of the Indian Cabinet's approval of construction funding for a gravitational-wave observatory there," says NSF director Sethuraman Panchanathan. "Partnering with like-minded nations like India who share our values and aspirations will not only make possible fantastic discoveries but, more importantly, energize talent and unleash innovation everywhere. Utilizing high-tech interferometer components developed by the NSF-funded LIGO collaboration, LIGO-India will augment the existing network of gravitational-wave detectors—the two LIGO detectors in the U.S., Virgo in Italy, and KAGRA in Japan—to enable more precise identification of the location of gravitational-wave sources and more robust monitoring of their signals. This will give a big boost to researchers around the world who will combine observations from optical and radio telescopes with the information from the gravitational-wave network to make new discoveries about the universe."

So far, LIGO and Virgo have detected the massive rumblings of dozens of collisions between black holes. In 2017, the observatories also detected a collision between neutron stars that sent out not only gravitational waves but a powerful burst of light waves spanning the electromagnetic spectrum. Because all three gravitational-wave detectors (LIGO's twin facilities and Virgo) were observing the sky during the 2017 event, scientists were able to narrow down the region of sky where the event occurred. This proved to be a crucial factor in guiding the light-based telescopes to pinpoint the precise location of the spectacular blast. The light-based observations led to the discovery that heavy elements, such as gold, were forged in the cosmic explosion.

Since that event, one more collision involving neutron stars was confidently detected by the LIGO-Virgo network, although it was not seen with light-based telescopes. With LIGO-India's eyes on the sky, spotting these so-called multi-messenger events (where light and gravitational waves are the messengers) should become an easier task.

Some preconstruction activities for LIGO-India have already taken place, such as the design of the LIGO-India buildings, the construction of the roads that lead into the site, and the fabrication and testing of vacuum chambers. The facility will be built by Indian researchers working jointly with members of the LIGO team.

The international collaboration has already resulted in an exchange of ideas and new relationships between the two countries. For instance, dozens of Indian students have been chosen to work with the LIGO team as part of Caltech's Summer Undergraduate Research Fellowship (SURF) program. In addition, Caltech plans to invite several visiting scientists from India to work on LIGO at Caltech.

"Having a distant third LIGO observatory in the international network, which benefits from common instrument designs, commissioning knowledge, technical coordination, and sensitivity, will fulfill a longstanding LIGO goal," says Fred Raab, the former associate director for observatory operations at LIGO Hanford who has been working on the LIGO-India project for nearly a decade. "This will be a game-changer for science."

Written by Whitney Clavin

• Conferences
• Last updated February 17, 2017

World’s third LIGO project to be commissioned in India, ready by 2024

• Published on February 17, 2017
• by Richa Bhatia

India is all set to add another feather to its cap. The site for the proposed LIGO India project, an advanced gravitational wave observatory has been finalized. To be operational by 2024, India has the honour for setting up the world’s third LIGO observatory. Currently, USA houses two observatories – Hanford in Washington and the other in Livingston in Louisiana operated by CalTech and MIT.  The two sites identified for the project are Udaipur in Rajasthan and Hingoli in Maharashtra. With a budget of Rs 1,260 crore earmarked and a nod from Prime Minister Narendra Modi, the Indian LIGO project will open up avenues of research in space matter and energy by tracking cosmic gravitational waves.

For the uninitiated, Laser Interferometer Gravitational-Wave Observatory (LIGO) is a massive gravitational wave observatory consisting of two laser interferometers placed thousands of kilometers apart to make use of light and space to detect gravitational waves.

The ground-breaking LIGO- India project that will refine the “understanding of black holes and why they occur” will be carried out in collaboration with several international partners Australia, UK and Germany. The proposed LIGO project will also reportedly move one advanced LIGO detector from Hanford to India.

Astronaut Today lists down how the path-breaking scientific endeavor will impact Indian scientific community:

• This large scale physics experiment and observatory is a step in the direction of gravitational wave astronomy
• Lead to a new breed of young researchers in advanced physics, gravitational physics, cosmology, computational sciences, and mathematics and in engineering
• Spawn academic-industry partnerships and lead to more job opportunities
• The LIGO-India project will serve as a research facility for the international community

The Indian LIGO project will be a collaboration between California Institute of Technology (CalTech) and Massachusetts Institute of Technology (MIT) and three Indian universities Inter-University Centre for Astronomy and Astrophysics (IUCAA), Pune, Institute for Plasma Research (IPR), Gandhinagar, and Raja Ramanna Centre for Advanced Technology (RRCAT), Indore.

What goes into the making of LIGO?

Seismic isolation system is aimed at eliminating vibrations that fall under two categories – active and passive damping system.  Since LIGO is sensitive to the smallest motions and fleeting vibrations  such as the ones caused by speeding trucks on a nearby road, seismic isolation system is the defense system to remove these environmental noises. In a way, it works likes a noise-cancelling headphone.

Vaccum : LIGO comprises of one of the largest vacuums on earth with the atmospheric pressure that equals one-trillionth that of air pressure at sea level. The vaccum functions to eliminate any dust that will deflect on the laser. Another reason for building a high-quality vacuum is to remove any air in the path of laser that could potentially mask gravitational waves.

Optics System: The optic system comprises of a 200 watt laser beam that helps in detecting gravitational waves.

Mirrors: The pure fuse silica glass mirrors weighing up to 40 kg can absorb one in 3 million photons that hit them, which means they are able to reflect most of the light that hits them. The mirrors are used to refocus the laser so that it can travel without interruptions and maintains the stability of laser light.

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India Approves Construction of LIGO

• 11 Apr 2023
• GS Paper - 3
• Indigenization of Technology
• Scientific Innovations & Discoveries

For Prelims : Gravitational Waves, LIGO-India Project

For Mains: Significance and benefit of LIGO-India Project.

Why in News?

Recently, the government approved the construction of the Laser Interferometer Gravitational-Wave Observatory (LIGO) project after seven years of in-principle approval.

• It will be built by the Department of Atomic Energy and the Department of Science and Technology with the U.S. National Science Foundation and several national and international research institutions.

What is LIGO-India Project?

• The project aims to detect gravitational waves from the universe.
• The Indian LIGO would have two perpendicularly placed 4-km long vacuum chambers, that constitute the most sensitive interferometers in the world.
• It is expected to begin scientific runs from 2030.
• It will be located in the Hingoli district of Maharashtra , about 450 km east of Mumbai.
• It will be the fifth node of the planned network and will bring India into a prestigious international scientific experiment.
• It will make India a unique platform that brings together the frontiers of science and technology of the quantum and the cosmos.
• The LIGO-India project would have several spin-off benefits to Indian science, apart from making India an integral part of one of the most prestigious international scientific experiments.
• The observatory is expected to enable dramatic returns in astronomy and astrophysics, as well as leapfrog Indian science and technology in cutting-edge frontiers of great national relevance.

What are Gravitational Waves?

• Gravitational waves were first postulated (1916) in Albert Einstein's General Theory of Relativity, which explains how gravity works.
• These waves are produced by the movement of massive celestial bodies, such as black holes or neutron stars, and are the ripples in spacetime that propagate outward.

What is LIGO?

• LIGOs are designed to measure changes in distance that are several orders of magnitude smaller than the length of the proton.  Such high precision Instruments are needed because of the extremely low strength of gravitational waves that make their detection very difficult.
• These gravitational waves were produced by the merger of two black holes, which were about 29 and 36 times the mass of the Sun, 1.3 billion years ago.
• Black hole mergers are the source of some of the strongest gravitational waves.
• To detect gravitational waves, four comparable detectors need to be operating simultaneously around the globe.
• LIGO consists of two 4-km-long vacuum chambers, set up at right angles to each other, with mirrors at the end.
• When light rays are released simultaneously in both chambers, they should return at the same time.
• Detecting this phase difference confirms the presence of a gravitational wave.

UPSC Civil Services Examination, Previous Year Question (PYQ)

Q. Recently, scientists observed the merger of giant ‘blackholes’ billions of light-years away from the Earth. What is the significance of this observation? (2019)

(a) ‘Higgs boson particles’ were detected. (b) ‘Gravitational waves’ were detected. (c) Possibility of intergalactic space travel through ‘wormhole’ was confirmed. (d) It enabled the scientists to understand ‘singularity’

• Every few minutes a pair of black holes smash into each other. These cataclysms release ripples in the fabric of space time known as gravitational waves.
• Gravitational waves are ‘ripples’ in space-time caused by some of the most violent and energetic processes in the Universe.
• Albert Einstein predicted the existence of gravitational waves in 1916 in his General Theory of Relativity.
• The strongest gravitational waves are produced by catastrophic events such as colliding black holes, the collapse of supernovae, coalescing neutron stars or white dwarf stars, etc.
• Scientists have yet again detected gravitational waves produced by the merger of two light black holes about a billion light-years away from the Earth.
• It was recorded by Laser Interferometer Gravitational-Wave Observatory (LIGO).
• Therefore, option (b) is the correct answer.

LIGO Surpasses the Quantum Limit

In 2015, the Laser Interferometer Gravitational-Wave Observatory, or LIGO, made history when it made the first direct detection of gravitational waves, or ripples in space and time, produced by a pair of colliding black holes. Since then, the U.S. National Science Foundation (NSF)-funded LIGO and its sister detector in Europe, Virgo, have detected gravitational waves from dozens of mergers between black holes as well as from collisions between a related class of stellar remnants called neutron stars. At the heart of LIGO's success is its ability to measure the stretching and squeezing of the fabric of spacetime on scales 10 thousand trillion times smaller than a human hair.

As incomprehensibly small as these measurements are, LIGO's precision has continued to be limited by the laws of quantum physics. At very tiny, subatomic scales, empty space is filled with a faint crackling of quantum noise, which interferes with LIGO's measurements and restricts how sensitive the observatory can be. Now, writing in the journal Physical Review X , LIGO researchers report a significant advance in a quantum technology called "squeezing" that allows them to skirt around this limit and measure undulations in spacetime across the entire range of gravitational frequencies detected by LIGO.

This new "frequency-dependent squeezing" technology, in operation at LIGO since it turned back on in May of this year , means that the detectors can now probe a larger volume of the universe and are expected to detect about 60 percent more mergers than before. This greatly boosts LIGO's ability to study the exotic events that shake space and time.

"We can't control nature, but we can control our detectors," says Lisa Barsotti, a senior research scientist at MIT who oversaw the development of the new LIGO technology, a project that originally involved research experiments at MIT led by Professor of Physics Matt Evans (PhD '02) and Professor of Astrophysics Nergis Mavalvala. The effort now includes dozens of scientists and engineers based at MIT, Caltech, and the twin LIGO observatories in Hanford, Washington, and Livingston, Louisiana.

"A project of this scale requires multiple people, from facilities to engineering and optics—basically the full extent of the LIGO Lab with important contributions from the LIGO Scientific Collaboration. It was a grand effort made even more challenging by the pandemic," Barsotti says.

"Now that we have surpassed this quantum limit, we can do a lot more astronomy," explains Lee McCuller, assistant professor of physics at Caltech and one of the leaders of the new study. "LIGO uses lasers and large mirrors to make its observations, but we are working at a level of sensitivity that means the device is affected by the quantum realm."

The results also have ramifications for future quantum technologies such as quantum computers and other microelectronics as well as for fundamental physics experiments. "We can take what we have learned from LIGO and apply it to problems that require measuring subatomic-scale distances with incredible accuracy," McCuller says.

"When NSF first invested in building the twin LIGO detectors in the late 1990s, we were enthusiastic about the potential to observe gravitational waves," says NSF Director Sethuraman Panchanathan. "Not only did these detectors make possible groundbreaking discoveries, they also unleashed the design and development of novel technologies. This is truly exemplar of the DNA of NSF—curiosity-driven explorations coupled with use-inspired innovations. Through decades of continuing investments and expansion of international partnerships, LIGO is further poised to advance rich discoveries and technological progress."

The laws of quantum physics dictate that particles, including photons, will randomly pop in and out of empty space, creating a background hiss of quantum noise that brings a level of uncertainty to LIGO's laser-based measurements. Quantum squeezing, which has roots in the late 1970s, is a method for hushing quantum noise or, more specifically, for pushing the noise from one place to another with the goal of making more precise measurements.

The term squeezing refers to the fact that light can be manipulated like a balloon animal. To make a dog or giraffe, one might pinch one section of a long balloon into a small precisely located joint. But then the other side of the balloon will swell out to a larger, less precise size. Light can similarly be squeezed to be more precise in one trait, such as its frequency, but the result is that it becomes more uncertain in another trait, such as its power. This limitation is based on a fundamental law of quantum mechanics called the uncertainty principle , which states that you cannot know both the position and momentum of objects (or the frequency and power of light) at the same time.

Since 2019, LIGO's twin detectors have been squeezing light in such a way as to improve their sensitivity to the upper frequency range of gravitational waves they detect. But, in the same way that squeezing one side of a balloon results in the expansion of the other side, squeezing light has a price. By making LIGO's measurements more precise at the high frequencies, the measurements became less precise at the lower frequencies.

"At some point, if you do more squeezing, you aren't going to gain much. We needed to prepare for what was to come next in our ability to detect gravitational waves," Barsotti explains.

Now, LIGO's new frequency-dependent optical cavities—long tubes about the length of three football fields—allow the team to squeeze light in different ways depending on the frequency of gravitational waves of interest, thereby reducing noise across the whole LIGO frequency range.

"Before, we had to choose where we wanted LIGO to be more precise," says LIGO team member Rana Adhikari, a professor of physics at Caltech. "Now we can eat our cake and have it too. We've known for a while how to write down the equations to make this work, but it was not clear that we could actually make it work until now. It's like science fiction."

Uncertainty in the Quantum Realm

Each LIGO facility is made up of two 4-kilometer-long arms connected to form an "L" shape. Laser beams travel down each arm, hit giant suspended mirrors, and then travel back to where they started. As gravitational waves sweep by Earth, they cause LIGO's arms to stretch and squeeze, pushing the laser beams out of sync . This causes the light in the two beams to interfere with each other in a specific way, revealing the presence of gravitational waves.

However, the quantum noise that lurks inside the vacuum tubes that encase LIGO's laser beams can alter the timing of the photons in the beams by minutely small amounts. McCuller likens this uncertainty in the laser light to a can of BBs. "Imagine dumping out a can full of BBs. They all hit the ground and click and clack independently. The BBs are randomly hitting the ground, and that creates a noise. The light photons are like the BBs and hit LIGO's mirrors at irregular times," he said in a Caltech interview .

The squeezing technologies that have been in place since 2019 make "the photons arrive more regularly, as if the photons are holding hands rather than traveling independently," McCuller said. The idea is to make the frequency, or timing, of the light more certain and the amplitude, or power, less certain as a way to tamp down the BB-like effects of the photons. This is accomplished with the help of specialized crystals that essentially turn one photon into a pair of two entangled , or connected, photons with lower energy. The crystals don't directly squeeze light in LIGO's laser beams; rather, they squeeze stray light in the vacuum of the LIGO tubes, and this light interacts with the laser beams to indirectly squeeze the laser light.

"The quantum nature of the light creates the problem, but quantum physics also gives us the solution," Barsotti says.

An Idea That Began Decades Ago

The concept for squeezing itself dates back to the late 1970s, beginning with theoretical studies by the late Russian physicist Vladimir Braginsky; Caltech's Kip Thorne, Richard P. Feynman Professor of Theoretical Physics, Emeritus; and Carlton Caves, a former Caltech research fellow now at the University of New Mexico. The researchers had been thinking about the limits of quantum-based measurements and communications, and this work inspired one of the first experimental demonstrations of squeezing in 1986 by H. Jeff Kimble, Caltech's William L. Valentine Professor of Physics, Emeritus. Kimble compared squeezed light to a cucumber; the certainty of the light measurements are pushed into only one direction, or feature, turning "quantum cabbages into quantum cucumbers," he wrote in an article in Caltech's Engineering & Science magazine in 1993 .

In 2002, researchers began thinking about how to squeeze light in the LIGO detectors, and, in 2008, the first experimental demonstration of the technique was achieved at the 40-meter test facility at Caltech. In 2010,MIT researchers developed a preliminary design for a LIGO squeezer, which they tested at LIGO's Hanford site. Parallel work done at the GEO600 detector in Germany also convinced researchers that squeezing would work. Nine years later, in 2019, after many trials and careful teamwork, LIGO began squeezing light for the first time .

"We went through a lot of troubleshooting," says Sheila Dwyer, who has been working on the project since 2008, first as a graduate student at MIT and then as a scientist at the LIGO Hanford Observatory beginning in 2013. "Squeezing was first thought of in the late 1970s, but it took decades to get it right."

Too Much of a Good Thing

However, as noted earlier, there is a tradeoff that comes with squeezing. By moving the quantum noise out of the timing, or frequency, of the laser light, the researchers put the noise into the amplitude, or power, of the laser light. The more powerful laser beams then push LIGO's heavy mirrors around causing a rumbling of unwanted noise corresponding to lower frequencies of gravitational waves. These rumbles mask the detectors' ability to sense low-frequency gravitational waves.

"Even though we are using squeezing to put order into our system, reducing the chaos, it doesn't mean we are winning everywhere," says Dhruva Ganapathy, a graduate student at MIT and one of four co-lead authors of the new study. "We are still bound by the laws of physics." The other three lead authors of the study are MIT graduate student Wenxuan Jia, LIGO Livingston postdoctoral scholar Masayuki Nakano, and MIT postdoctoral scholar Victoria Xu.

Unfortunately, this troublesome rumbling becomes even more of a problem when the LIGO team turns up the power on its lasers. "Both squeezing and the act of turning up the power improve our quantum-sensing precision to the point where we are impacted by quantum uncertainty," McCuller says. "Both cause more pushing of photons, which leads to the rumbling of the mirrors. Laser power simply adds more photons, while squeezing makes them more clumpy and thus rumbly."

The solution is to squeeze light in one way for high frequencies of gravitational waves and another way for low frequencies. It's like going back and forth between squeezing a balloon from the top and bottom and from the sides.

This is accomplished by LIGO's new frequency-dependent squeezing cavity, which controls the relative phases of the light waves in such a way that the researchers can selectively move the quantum noise into different features of light (phase or amplitude) depending on the frequency range of gravitational waves.

"It is true that we are doing this really cool quantum thing, but the real reason for this is that it's the simplest way to improve LIGO's sensitivity," Ganapathy says. "Otherwise, we would have to turn up the laser, which has its own problems, or we would have to greatly increase the sizes of the mirrors, which would be expensive."

LIGO's partner observatory, Virgo, will likely also use frequency-dependent squeezing technology within the current run, which will continue until roughly the end of 2024. Next-generation larger gravitational-wave detectors, such as the planned ground-based Cosmic Explorer , will also reap the benefits of squeezed light.

With its new frequency-dependent squeezing cavity, LIGO can now detect even more black hole and neutron star collisions. Ganapathy says he's most excited about catching more neutron star smashups. "With more detections, we can watch the neutron stars rip each other apart and learn more about what's inside."

"We are finally taking advantage of our gravitational universe," Barsotti says. "In the future, we can improve our sensitivity even more. I would like to see how far we can push it."

The Physical Review X study is titled " Broadband quantum enhancement of the LIGO detectors with frequency-dependent squeezing ." Many additional researchers contributed to the development of the squeezing and frequency-dependent squeezing work, including Mike Zucker of MIT and GariLynn Billingsley of Caltech, the leads of the "Advanced LIGO Plus" upgrades that includes the frequency-dependent squeezing cavity; Daniel Sigg of LIGO Hanford Observatory; Adam Mullavey of LIGO Livingston Laboratory; and David McClelland's group from the Australian National University.

The LIGO–Virgo–KAGRA Collaboration operates a network of gravitational-wave detectors in the United States, Italy, and Japan. LIGO Laboratory is operated by Caltech and MIT, and is funded by the NSF with contributions to the Advanced LIGO detectors from Germany (Max Planck Society), the U.K. (Science and Technology Facilities Council), and Australia (Australian Research Council). Virgo is managed by the European Gravitational Observatory (EGO) and is funded by the Centre national de la recherche scientifique (CNRS) in France, the Istituto Nazionale di Fisica Nucleare (INFN) in Italy, and the National Institute for Subatomic Physics (Nikhef) in the Netherlands. KAGRA is hosted by the Institute for Cosmic Ray Research (ICRR) at the University of Tokyo and co-hosted by the National Astronomical Observatory of Japan (NAOJ) and the High Energy Accelerator Research Organization (KEK).

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First LIGO lab outside U.S. may come up in Maharashtra’s Hingoli

On february 17, the union cabinet gave in principle approval to the proposal for research on gravitational waves.

Updated - September 22, 2016 05:55 pm IST

Published - September 08, 2016 05:39 pm IST - New Delhi

An aerial view of the LIGO Hanford laboratory site near Hanford, Washington.

The Laser Interferometer Gravitational-wave Observatory (LIGO) project that was given the in-principle approval by the Union Cabinet may come up in Maharashtra’s Hingoli district.

A senior scientist with the Department of Science and Technology (DST) said to PTI, “Aundh in Hingoli district is a preferred site for the Ligo project. We’ve begun work on it, which includes setting up committees to start the preliminary work.”

According to the official, a strip of four km on both sides of a 150-metre wide area was needed to carry out experiments. “So we would not be needing much land,” he said to PTI.

“We needed a flat site to carry out the experiments, the four km strips that would require an unhindered straight and flat site for studying the lasers. The Aundh site fits the bill,” said a senior Department of Atomic Energy (DAE) official, according to the PTI report.

When contacted, Dr. Tarun Souradeep, official spokesperson for the project said Aundh is one of the likely choices for a site. “Recommendations have been made and the site has been reviewed by LIGO labs. Our team has visited the site but we are yet to make a final announcement,” he said.

LIGO-India will bring considerable opportunities for Indian scientists in instrumentation and development also, as they along with industry members will be engaged in the construction of the eight km-long beam tube at ultra-high vacuum on a levelled terrain.

(with inputs from PTI)

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science and technology / Maharashtra

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The 2017 Nobel Prize in Physics has been awarded to LIGO co-founders. (Medal image: Wikipedia. Collage: LIGO Lab)

2017 Nobel Prize in Physics Awarded to LIGO Founders

Caltech Press Release | MIT Press Release

Caltech Press Release

Caltech scientists awarded 2017 nobel prize in physics.

The 2017 Nobel Prize in Physics has been awarded to three key players in the development and ultimate success of the Laser Interferometer Gravitational-wave Observatory (LIGO). One half of the prize was awarded jointly to Caltech's Barry C. Barish, the Ronald and Maxine Linde Professor of Physics, Emeritus and Kip S. Thorne (BS '62), the Richard P. Feynman Professor of Theoretical Physics, Emeritus; and the other half was awarded to MIT's Rainer Weiss, professor of physics, emeritus.

On September 14, 2015, the National Science Foundation (NSF)-funded LIGO made the first-ever direct observation of gravitational waves—ripples in the fabric of space and time predicted by Albert Einstein 100 years earlier. The public announcement took place on February 11, 2016, in Washington, D.C. Each of the twin LIGO observatories—one in Hanford, Washington, and the other in Livingston, Louisiana—picked up the feeble signal of gravitational waves generated 1.3 billion years ago when two black holes spiraled together and collided. Two additional detections of gravitational waves, once again from merging black-hole pairs, were made on December 26, 2015 , and January 4, 2017 , and, on August 14, 2017 , a fourth event was detected by LIGO and the European Virgo gravitational-wave detector.

The detections ushered in a new era of gravitational-wave astronomy. LIGO and Virgo provided astronomers with an entirely new set of tools with which to probe the cosmos. Previously, all astronomy observations have relied on light—which includes X-rays, radio waves, and other types of electromagnetic radiation emanating from objects in space—or on very-high-energy particles called neutrinos and cosmic rays. Now, astronomers can learn about cosmic objects through the quivers they make in space and time.

The Nobel Prize recognizes Weiss, Barish, and Thorne for their "decisive contributions to the LIGO detector and the observation of gravitational waves."

"I am delighted and honored to congratulate Kip and Barry, as well as Rai Weiss of MIT, on the award this morning of the 2017 Nobel Prize in Physics," says Caltech president Thomas F. Rosenbaum, the Sonja and William Davidow Presidential Chair and professor of physics. "The first direct observation of gravitational waves by LIGO is an extraordinary demonstration of scientific vision and persistence. Through four decades of development of exquisitely sensitive instrumentation—pushing the capacity of our imaginations—we are now able to glimpse cosmic processes that were previously undetectable. It is truly the start of a new era in astrophysics."

Thorne received the call from the Nobel committee this morning at 2:15 a.m. Pacific Daylight Time.

"The prize rightfully belongs to the hundreds of LIGO scientists and engineers who built and perfected our complex gravitational-wave interferometers, and the hundreds of LIGO and Virgo scientists who found the gravitational-wave signals in LIGO's noisy data and extracted the waves' information," Thorne says. "It is unfortunate that, due to the statutes of the Nobel Foundation, the prize has to go to no more than three people, when our marvelous discovery is the work of more than a thousand."

Barish received the call from the Nobel committee this morning at 2:45 a.m. Pacific Daylight Time.

"I am humbled and honored to receive this award," says Barish. "The detection of gravitational waves is truly a triumph of modern large-scale experimental physics. Over several decades, our teams at Caltech and MIT developed LIGO into the incredibly sensitive device that made the discovery. When the signal reached LIGO from a collision of two stellar black holes that occurred 1.3 billion years ago, the 1,000-scientist-strong LIGO Scientific Collaboration was able to both identify the candidate event within minutes and perform the detailed analysis that convincingly demonstrated that gravitational waves exist."

An Idea That Began Decades Ago

Einstein predicted in 1916 that gravitational waves would exist, but thought them too weak to ever be detected. By the 1960s, technological advances such as the laser and new insights into possible astrophysics sources made it conceivable that Einstein was wrong and that gravitational waves might actually be detectable.

The first person to build a gravitational-wave detector was Joseph Weber of the University of Maryland. Weber's detectors, built in the 1960s, used large aluminum cylinders, or bars, that would be driven to vibrate by passing gravitational waves. Other researchers elsewhere, including the late Ronald W. P. Drever at the University of Glasgow in Scotland—later a professor of physics at Caltech—soon followed Weber's lead.

When those experiments proved unsuccessful, the focus of the field began shifting to a different type of detector called a gravitational-wave interferometer, invented independently by Weiss at MIT and, in rudimentary form, by several others. In this instrument, gravitational waves stretch and squeeze space by an infinitesimal amount while widely separated mirrors hanging by wires "ride" the oscillations, moving apart and together ever so slightly. This mirror motion is measured with laser light using a technique called interferometry.

In the late 1960s, Weiss began laying conceptual foundations for these interferometers. In parallel, Thorne, along with his students and postdocs at Caltech, worked to improve the theory of gravitational waves, and estimated the details, strengths, and frequencies of the waves that would be produced by objects in our universe such as black holes, neutron stars, and supernovas.

In 1972, Thorne, with his student Bill Press (MS '71, PhD '73), published the first of many articles that would appear over the next three decades, summarizing what was known about the gravitational-wave sources and formulating a vision for gravitational-wave astronomy.

"LIGO would not exist without Kip's vision for the scientific potential of gravitational waves and his amazing gift for sharing that vision with other scientists," says Stan Whitcomb (BS '73), the chief scientist for the LIGO Laboratory at Caltech, who began working on the project in 1980.

Also in 1972, Weiss published a detailed analysis of his interferometers. He identified all of the major obstacles that could prevent the instruments from detecting gravitational waves, such as vibrations of the earth and of the mirrors, and he invented techniques to deal with each obstacle. At this stage, it became evident that large interferometers, several kilometers or more in size, might possibly prove successful—as, indeed, they ultimately did with LIGO and its 4-kilometer-long arms. Also evident was the fact that perfecting the interferometers would be exceedingly difficult: a passing gravitational wave would induce mirror motions 1,000 times smaller than a proton, and these infinitesimal changes would have to be measured. That's 100 million times smaller than an atom, and a trillion times smaller than the wavelength of the light being used in the measurement.

Triggered by Weiss's work, Drever's research group in Glasgow switched from bars to interferometers, as did a research group in Garching, Germany, led by Heinz Billing. By 1975, there were three prototype interferometers under development at MIT, Glasgow, and Garching.

A Fateful Hotel Room Discussion

At first Thorne was skeptical of Weiss's interferometer idea. "I even wrote, in a textbook, that it was not very promising," he says. But that changed when Thorne studied, in depth, Weiss's 1972 analysis. Thorne came to call it a "tour de force" and a "blueprint for the future."

In 1975, Weiss invited Thorne to speak at a NASA committee meeting in Washington, D.C., about cosmology and gravitation experiments in space. Hotel rooms that summer were fully booked, so the two shared a room, where they stayed up all night talking. Thorne came away so excited by the experimental prospects that he went home and proposed creating an experimental gravity group at Caltech to work on interferometers in parallel with MIT, Glasgow, and Garching. Caltech then brought Drever on board in 1979 to lead the new experimental effort, because, as Thorne says, they knew his inventiveness would prove crucial to LIGO's success. Soon thereafter, in 1980, Caltech hired a young Chicago astrophysicist, Whitcomb, to assist in the leadership.

"What a pleasure it was to have this brilliant, budding experimental group working alongside my theory group at Caltech," says Thorne. "Those were heady days."

Together, Drever and Whitcomb led the design and construction of a 40-meter interferometer at Caltech—a prototype to test and perfect the ideas of Weiss, Drever, and others, including the teams at Glasgow and Garching.

Meanwhile, Thorne and his theory students—in collaboration with the late Vladimir Braginsky of Moscow State University, a regular Caltech visitor over three decades—were analyzing various sources of noise that the big interferometers would face, especially "quantum noise," or random fluctuations of the mirrors' positions predicted by quantum theory. They were coming up with ways to deal with those fluctuations.

In 1984, all of this parallel work came together. Caltech and MIT, with encouragement from the NSF, formed a collaboration to design and build LIGO. Rochus E. (Robbie) Vogt , Caltech's R. Stanton Avery Distinguished Service Professor and Professor of Physics, Emeritus, was recruited in 1987 as LIGO's first director. Vogt led the merging of the Caltech and MIT experimental groups; the early planning for LIGO; the writing of a proposal to NSF to fund the project; and the education of Congress about this high-risk project with a potentially exceedingly high payoff. In 1992, Congress allocated the first major funding. "NSF and Congress have backed LIGO unwaveringly ever since," says Thorne.

Scaling up LIGO

Building LIGO was a tremendous challenge—logistically and technically. To meet this challenge, Caltech and MIT later recruited, as LIGO's second director, Barry Barish­­­­, who at that time had been the leader of several very large high-energy physics projects. Barish developed the first high-energy neutrino beam experiment at Fermilab near Chicago and was one of the leaders of a large international collaboration that performed a search for magnetic monopoles—magnetic analogs of single electric charges that, if found, would help confirm the Grand Unified Theory that seeks to unify the electromagnetic, weak, and strong forces. The experiment, called MACRO (Monopole, Astrophysics and Cosmic Ray Observatory), did not find magnetic monopoles but set the most stringent limits on their existence. Barish then led the design of one of the two detectors planned for another big science project, the Superconducting Super Collider—a particle accelerator to be built in Waxahachie, Texas. The accelerator was canceled during construction in 1993, after which Barish took on the challenge of LIGO, becoming its principal investigator in 1994, and then its director in 1997.

"I always wanted to be an experimental physicist and was attracted to the idea of using continuing advances in technology to carry out fundamental science experiments that could not be done otherwise," says Barish. "LIGO is a prime example of what couldn't be done before. Although it was a very large-scale project, the challenges were very different from the way we build a bridge or carry out other large engineering projects. For LIGO, the challenge was and is how to develop and design advanced instrumentation on a large scale, even as the project evolves."

"Barish, in my opinion, is the most brilliant leader of large science projects that physics has ever seen," says Thorne.

Barish ushered LIGO through its final design stages and secured funding through NSF's National Science Board. He oversaw construction of the two LIGO facilities from 1994 to 1999, and then the installation and commissioning of the initial LIGO interferometers from 1999 to 2005. The scaling up from Caltech's 40-meter prototype to LIGO's 4-kilometer interferometers was such a huge undertaking that it was carried out in two steps. First, the team built initial interferometers, which operated from 2002 to 2010, at a sensitivity that Barish characterized as being at a level where detections were "possible." This first step demonstrated the observatory's basic concepts and solved many technical obstacles. The development and approval of the next phase of LIGO, called Advanced LIGO, was also led by Barish and then-LIGO Laboratory deputy director Gary Sanders, and was designed to be sensitive to a level at which detections were "probable." Advanced LIGO was commissioned and built between 2010 and 2015. Though Barish left LIGO in 2006 to become director of the Global Design Effort for the International Linear Collider, he would rejoin the LIGO team in 2012, in time for the project's historic discovery in 2015. After Barish left, LIGO was led by Jay Marx of Caltech, followed by current executive director, Caltech's David H. Reitze .

"LIGO had to make the change from tabletop science to a real science facility," says Whitcomb. "Barry understood what was needed, and he guided that transformation without ever losing sight of the scientific goals."

Under Barish's leadership, several key technologies were developed that ultimately led to the detection of gravitational waves. For the first phase of LIGO, now referred to as Initial LIGO, he chose to use solid-state lasers rather than the gas lasers that were more commonly in use at that time. These solid-state lasers were the basis of more powerful versions developed for Advanced LIGO. He also oversaw the development of technologies for reducing unwanted movements in LIGO's mirrors, caused by earthquakes, passing trucks, and other ground vibrations.

"In the initial phase of LIGO, in order to isolate the detectors from the earth's motion, we used a suspension system that consisted of test-mass mirrors hung by piano wire and used a multiple-stage set of passive shock absorbers, similar to those in your car. We knew this probably would not be good enough to detect gravitational waves, so we, in the LIGO Laboratory, developed an ambitious program for Advanced LIGO that incorporated a new suspension system to stabilize the mirrors and an active seismic isolation system to sense and correct for ground motions," says Barish.

The active seismic isolation system developed for Advanced LIGO works in a similar fashion to noise-canceling headphones, except it can measure and cancel out ground vibrations coming from many directions. In conjunction with this system, a new "quieter" way to suspend LIGO's mirrors was developed with the help of the Glasgow group, which involved hanging the mirrors with a four-stage pendulum. The combination of these two advances gave LIGO a huge improvement in sensitivity to lower frequencies of gravitational waves, which was ultimately what was needed to detect the crashing of two black holes.

Barish also created the LIGO of today: a collaboration of approximately 1,200 scientists and engineers at about 100 institutions in 19 nations called the LIGO Scientific Collaboration (LSC).

"In addition to picking the right technologies and developing them, and securing funding, we needed to build a collaboration of the absolute best people possible for this almost impossible project," says Barish. "Forming an international collaboration, the LSC, enabled this. We attracted the best people from other universities and countries, creating an 'equal opportunity' collaboration, where there was no advantage to being at Caltech or MIT." The LSC conducted the scientific searches and analysis that led to the LIGO discovery.

While this experimental work was taking place, theorists outside Caltech, MIT, and the LIGO project were developing computer codes to simulate the massive collisions of black holes and other sources of gravitational waves that LIGO might detect. These simulations are essential to LIGO; by comparing the shapes of the waves that LIGO observes with the simulations' predicted wave shapes, LIGO scientists can figure out what produces the observed waves. In the early 2000s, Thorne became alarmed at the slow progress on simulations and so with then-Caltech physicist Lee Lindblom, he created a research group at Caltech in collaboration with a group at Cornell University led by his former student Saul Teukolsky (PhD '74), who is now jointly the Robinson Professor of Theoretical Astrophysics at Caltech and Hans A. Bethe Professor of Physics and Astrophysics at Cornell University. By 2015, this SXS (Simulating eXtreme Spacetimes) project was simulating the collisions of black holes with ease, as were several other research groups.

On September 14, 2015, just after the Advanced LIGO interferometers began their first search for gravitational waves, they captured a strong signal. Comparison with the SXS simulations revealed that the signal was from the collision of two hefty black holes 29 and 36 times more massive than the sun and located 1.3 billion light-years from Earth. The waves carried away as much energy as would be produced by annihilating three suns. After intense scrutiny of the results, the LIGO scientists announced this discovery to the world on February 11, 2016.

"I'm positively delighted that the Nobel Committee has recognized the LIGO discovery and its profound impact on the way we view the cosmos," says Reitze. "This prize rewards not just Kip, Barry, and Rai but also the large number of very smart and dedicated scientists and engineers who worked tirelessly over the past decades to make LIGO a reality."

"LIGO was a huge technical and scientific gamble," says Fiona Harrison, the Benjamin M. Rosen Professor of Physics and the Kent and Joyce Kresa Leadership Chair in Caltech's Division of Physics, Mathematics and Astronomy. "But it paid off in spades with one of the most dramatic discoveries in decades. The entire LIGO team should be celebrating today."

The 2017 Nobel Prize in Physics represents the 37th and 38th Nobel Prizes awarded to Caltech faculty and alumni. Current Caltech faculty with Nobel Prizes include: Robert Grubbs , winner of the 2005 Nobel Prize in Chemistry with Yves Chauvin and Richard R. Schrock; David Politzer , recipient of the 2004 Nobel Prize in Physics with David J. Gross and Frank Wilczek; Rudy Marcus , sole winner of the 1992 Nobel Prize in Chemistry; and David Baltimore , winner of the 1975 Nobel Prize in Physiology or Medicine, with Renato Dulbecco and Howard M. Temin.

In 2016, Drever, Thorne, and Weiss won the Kavli Prize in Astrophysics , the Shaw Prize in Astronomy , the Gruber Foundation Cosmology Prize , and the Special Breakthrough Prize in Fundamental Physics . In 2017, Barish, Thorne, and Weiss won the Princess of Asturias Award for Technical and Scientific Research and the European Physical Society's Giuseppe and Vanna Cocconi Prize.

Barish was born on January 27, 1936, in Omaha, Nebraska, and spent his childhood in Los Angeles. He received his BA in physics in 1957 and his PhD in experimental particle physics in 1962, both from UC Berkeley. In 1963, he joined Caltech as a research fellow. He became an assistant professor in 1966, an associate professor in 1969, and a professor of physics in 1972. He was named the Ronald and Maxine Linde Professor of Physics in 1991 and Linde Professor, Emeritus, in 2005. He is a member of the National Academy of Sciences, and a fellow of the American Academy of Arts and Sciences, the American Association for the Advancement of Science, and the American Physical Society, the latter of which he served as president. In 2002, he received the Klopsteg Memorial Lecture Award from the American Association of Physics Teachers and, in 2016, he received the Enrico Fermi Prize from the Italian Physical Society. He won the Henry Draper Medal in 2017 with Whitcomb. For a full biography, click here .

Thorne was born on June 1, 1940, in Logan, Utah. He received a bachelor's degree in physics from Caltech in 1962 and a PhD in physics from Princeton University in 1965. He joined Caltech as a research fellow in 1966, and joined the faculty in 1967 as an associate professor of theoretical physics. In 1970, he became a professor of theoretical physics. In 1991, he was named the Richard P. Feynman Professor of Theoretical Physics. He retired in 2009. Thorne has coauthored or authored several books, including Black Holes and Time Warps: Einstein's Outrageous Legacy , published in 1994. He served as an executive producer and science adviser for the 2014 film Interstellar . He is a member of the National Academy of Sciences, the American Physical Society, the American Academy of Arts and Sciences, and the American Philosophical Society. On October 11, 2017, Thorne will publish the textbook Modern Classical Physics , coauthored with Roger Blandford. For a full biography, click here .

More information about LIGO's many partners is online here .

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MIT Physicist Rainer Weiss Shares Nobel Prize in Physics

Rainer Weiss ’55, PhD ’62, professor emeritus of physics at MIT, has won the Nobel Prize in physics for 2017. Weiss wins half the prize, sharing the other half of the award with Kip S. Thorne, professor emeritus of theoretical physics at Caltech, and Barry C. Barish, professor emeritus of physics at Caltech.

The Nobel Foundation, in its announcement this morning, cited the physicists "for decisive contributions to the LIGO detector and the observation of gravitational waves.”

“We are immensely proud of Rai Weiss, and we also offer admiring best wishes to his chief collaborators and the entire LIGO team,” says MIT President L. Rafael Reif. “The creativity and rigor of the LIGO experiment constitute a scientific triumph; we are profoundly inspired by the decades of ingenuity, optimism, and perseverance that made it possible. It is especially sweet that Rai Weiss not only served on the MIT faculty for 37 years, but is also an MIT graduate. Today’s announcement reminds us, on a grand scale, of the value and power of fundamental scientific research and why it deserves society’s collective support.”

Listening for a wobble

On Sept. 14, 2015, at approximately 5:51 a.m. EDT, a gravitational wave — a ripple from a distant part of the universe — passed through the Earth, generating an almost imperceptible, fleeting wobble in the world that would have gone completely unnoticed save for two massive, identical instruments, designed to listen for such cosmic distortions.

The Laser Interferometer Gravitational-wave Observatory, or LIGO, consists of two L-shaped interferometers, each 4 kilometers in length, separated by 1,865 miles. On Sept. 14, 2015, scientists picked up a very faint wobble in the instruments and soon confirmed that the interferometers had been infinitesimally stretched — by just one-ten-thousandth the diameter of a proton — and that this miniscule distortion arose from a passing gravitational wave.

The LIGO Scientific Collaboration, with the Caltech-MIT LIGO Laboratory and more than 1,000 scientists at universities and observatories around the world, confirmed the signal as the first direct detection of a gravitational wave by an instrument on Earth. The scientists further decoded the signal to determine that the gravitational wave was the product of a violent collision between two massive black holes 1.3 billion years ago.

The momentous result confirmed the theory of general relativity proposed by Albert Einstein, who almost exactly 100 years earlier had predicted the existence of gravitational waves but assumed that they would be virtually impossible to detect from Earth. Since this first discovery, LIGO has detected three other gravitational wave signals, also generated by pairs of spiraling, colliding black holes; the most announced of a detection came just last week .

“We are incredibly proud of Rai and his colleagues for their vision and courage that led to this great achievement,” says Michael Sipser, the Donner Professor of Mathematics and dean of the School of Science at MIT. “It is a wonderful day for them, for MIT, for risk-taking and boldness, and for all of science.”

A gravitational blueprint

The detection was an especially long-awaited payoff for Weiss, who came up with the initial design for LIGO some 50 years ago. He has since been instrumental in shaping and championing the idea as it developed from a desktop prototype to LIGO’s final, observatory-scale form.

In 1967, Weiss, then an assistant professor of physics at MIT, was asked by his department to teach an introductory course in general relativity — a subject he knew little about. A few years earlier, the American physicist Joseph Weber had claimed to have made the first detection of gravitational waves, using resonant bars — long, aluminum cylinders that should ring at a certain frequency in response to a gravitational wave. When his students asked him to explain how these Weber bars worked, Weiss found that he couldn't.

No one in the scientific community had been able to replicate Weber’s results. Weiss had a very different idea for how to do it, and assigned the problem to his students, instructing them to design the simplest experiment they could to detect a gravitational wave. Weiss himself came up with a design: Build an L-shaped interferometer and shine a light down the length of each arm, at the end of which hangs a free-floating mirror. The lasers should bounce off the mirrors and head back along each arm, arriving where they started at the exact same time. If a gravitational wave passes through, it should “stretch” or displace the mirrors ever so slightly, and thus change the lasers’ arrival times.

Weiss refined the idea over a summer in MIT’s historic Building 20, a wooden structure built during World War II to develop radar technology. The building, meant to be temporary and known to many as the “Plywood Palace,” lived on to germinate and support innovative, high-risk projects. During that time, Weiss came to the conclusion that his design could indeed detect gravitational waves, if built to large enough dimensions. His design would serve as the essential blueprint for LIGO.

An observatory takes shape

To test his idea, Weiss initially built a 1.5-meter prototype. But to truly detect a gravitational wave, the instrument would have to be several thousand times longer: The longer the interferometer’s arms, the more sensitive its optics are to minute displacements.

To realize this audacious design, Weiss teamed up in 1976 with noted physicist Kip Thorne, who, based in part on conversations with Weiss, soon started a gravitational wave experiment group at Caltech. The two formed a collaboration between MIT and Caltech, and in 1979, Scottish physicist Ronald Drever, then of Glasgow University, joined the effort at Caltech. The three scientists — who became the co-founders of LIGO — worked to refine the dimensions and scientific requirements for an instrument sensitive enough to detect a gravitational wave.

Barry Barish soon joined the team as first a principal investigator, then director of the project, and was instrumental in securing funding for the audacious project, and bringing the detectors to completion.

After years of fits and starts in research and funding, the project finally received significant and enthusiastic backing from the National Science Foundation, and in the mid-1990s, LIGO broke ground, erecting its first interferometer in Hanford, Washington, and its second in Livingston, Louisiana.

Prior to making their seminal detection two years ago, LIGO’s detectors required years of fine-tuning to improve their sensitivity. During this time, Weiss not only advised on scientific quandaries but also stepped in to root out problems in the detectors themselves. Weiss is among the few to have walked the length of the interferometers’ tunnels in the space between LIGO’s laser beam tube and its encasement. Inspecting the detectors in this way, Weiss would often discover minute cracks, tiny shards of glass, and even infestations of wasps, mice, and black widow spiders, which he would promptly deal with.

A cosmic path

Weiss was born in 1932 in tumultuous Berlin. When his mother, Gertrude Loesner, was pregnant with Weiss, his father, neurologist Frederick Weiss, was abducted by the Nazis for testifying against a Nazi doctor. He was eventually released with the help of Loesner’s family. The young family fled to Prague and then emigrated to New York City, where Weiss grew up on Manhattan’s Upper West Side, cultivating a love for classical music and electronics, and making a hobby of repairing radios.

After graduating high school, he went to MIT to study electrical engineering, in hopes of finding a way to quiet the hiss heard in shellac records. He later switched to physics, but then dropped out of school in his junior year, only to return shortly after, taking a job as a technician in Building 20. There, Weiss met physicist Jerrold Zacharias, who is credited with developing the first atomic clock. Zacharias encouraged and supported Weiss in finishing his undergraduate degree in 1955 and his PhD in 1962.

Weiss spent some time at Princeton University as a postdoc, where he developed experiments to test gravity, before returning to MIT as an assistant professor in 1964. In the midst of his work in gravitational wave detection, Weiss also investigated and became a leading researcher in cosmic microwave background radiation — thermal radiation, found in the microwave band of the radio spectrum, that is thought to be a diffuse afterglow from the Big Bang.

In 1976, Weiss was appointed to oversee a scientific working group for NASA’s Cosmic Background Explorer (COBE) satellite, which launched in 1989 and went on to precisely measure microwave radiation and its tiny, quantum fluctuations. Weiss was co-founder and chair of the science working group for the mission, whose measurements helped support the Big Bang theory of the universe. COBE’s findings earned two of its principal investigators the Nobel Prize in physics in 2006.

Weiss has received numerous awards and honors, including the Medaille de l’ADION, the 2006 Gruber Prize in Cosmology, and the 2007 Einstein Prize of the American Physical Society. He is a fellow of the American Association for the Advancement of Science, the American Academy of Arts and Sciences, and the American Physical Society, as well as a member of the National Academy of Sciences. In 2016, Weiss received a Special Breakthrough Prize in Fundamental Physics, the Gruber Prize in Cosmology, the Shaw Prize in Astronomy, and the Kavli Prize in Astrophysics, all shared with Drever and Thorne. Most recently, Weiss shared the Princess of Asturias Award for Technical and Scientific Research with Thorne, Barry Barish of Caltech, and the LIGO Scientific Collaboration.

Written by Jennifer Chu, MIT News Office

RELATED LINKS

2017 Nobel Prize in Physics

Rainer Weiss

Video: LIGO Detects Gravitational Waves

Advanced LIGO Instrument

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Scientists make first detection of gravitational waves

Gravitational waves from a binary black hole merger observed by LIGO and Virgo

Q&A: Rainer Weiss on LIGO's origins

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How a 130-Year-Old Technology Led to a Nobel Prize

The LIGO instrument responsible for detecting gravitational waves grew out of an 1880s experiment.

In 1887, Albert Michelson built an experiment that he hoped would lead to the detection of luminiferous ether. At the time, physicists believed that the ether permeated the universe and served as the medium through which light waves moved, like the way waves traveled across the ocean. *

The experiment turned out to be a failure . The mystical ether didn’t exist. But the instrument that Michelson invented to conduct this research would detect, more than a century later, a very real, very significant astronomical phenomenon: gravitational waves, the ripples in the fabric of space and time, coming from a violent collision between two black holes.

Scientists at the Laser Interferometer Gravitational-Wave Observatory, or LIGO, used Michelson’s invention to make the first-ever direct observation of gravitational waves in September 2015. Albert Einstein predicted the existence of gravitational waves in 1916 as part of his general theory of relativity, but no one had detected them directly. Since their first find, the LIGO scientists have detected the waves three more times. On Tuesday, they were awarded the Nobel prize in physics for their efforts.

The instrument at the heart of Michelson’s research is called an interferometer, which manipulates light inside closed tubes to make tiny measurements of natural phenomena. At LIGO’s twin observatories in Washington state and Louisiana, scientists use laser light.

Each observatory has two steel tubes measuring four kilometers long and placed in an L shape. At the ends of each arm are mirrors. LIGO scientists aim laser light into the L-shaped tube and let it travel back and forth between the mirrors. When gravitational waves reach Earth, they ripple through the arms of the tube, stretching and shrinking the steel. The distortions change the distance that the light travels as it bounces around. The change is the size of about one-thousandth the width of a proton.

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Michelson’s L-shaped interferometer was much smaller than LIGO’s; each arm of in the instrument measured 11 meters long. While they’re more sophisticated, LIGO’s interferometers are essentially giant versions of Michelson’s interferometer from the 1880s.

It’s not the size of LIGO’s interferometer that makes the difference. A massive interferometer is still just an interferometer, which isn’t capable of detecting something as tiny as waves in space-time. LIGO scientists needed to make some tweaks to Michelson’s design so that the instrument could detect the tiniest of changes. They added, among other features, mirrors that would increase the number of times the laser beam was reflected as it traveled through the tubes. The extra technology extended LIGO’s interferometers arms to 1,120 kilometers, making the instrument 144,000 times bigger than the one Michelson used—and sensitive enough to detect gravitational waves.

Michelson and the LIGO scientists have something else in common: They’re now both Nobel laureates. Michelson won the prize in physics in 1907 for his study of the speed and properties of light, becoming the first American to win a Nobel in science. He may not have found luminiferous ether, but he pioneered the technique that found something much more elusive.

* This article originally stated that luminiferous ether involved sound waves. We regret the error.

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