Why scientists are excited about gravitational waves
Scientists are rejoicing over a new discovery announced on January 11. They have observed ripples in the fabric of space-time called gravitational waves for the first time since Albert Einstein made the prediction in the General Theory of Relativity a century ago. The discovery will open up a new window into the understanding of the universe. The gravitational waves were detected on September 14, 2015 but the discovery has been announced in a research paper in journal Physical Review Letters. An international consortium of scientists including from India was behind this major experiment.
What are gravitational waves?
Gravitational waves are "ripples" in the fabric of space-time caused by some of the most powerful processes in the universe - colliding black holes, exploding stars, and even the birth of the universe itself. Albert Einstein predicted the existence of gravitational waves in 1916, derived from his General Theory of Relativity. Einstein's mathematics showed that massive accelerating objects (such as neutron stars or black holes orbiting each other) would disrupt space-time in such a way that waves of distorted space would radiate from the source. These ripples travel at the speed of light through the universe, carrying information about their origins, as well as clues to the nature of gravity itself.
What is the significance of gravitational waves?
Detecting and analysing the information carried by gravitational waves will allow us to observe universe in a way like never before. This will open up a new window on the universe.
Historically, scientists have relied primarily on observations with electromagnetic radiation (visible light, X-rays, radio waves, microwaves, etc) to learn about and understand phenomena in the universe. In recent years, subatomic particles called neutrinos have also been used to study aspects of the heavens. Each of these kinds of sources of information gives scientists a different and complementary view of the universe, with each new window bringing exciting new discoveries.
What is LIGO?
LIGO (Laser Interferometre Gravitational Wave Observatory) is the world's largest gravitational wave observatory and one of the world's most sophisticated physics experiments. LIGO consists of two laser interferometres located thousands of kilometres apart, one in Livingston Louisiana and the other in Hanford Washington State. LIGO uses the physical properties of light and of space itself to detect gravitational waves. It was funded by the US National Science Foundation, and it is managed by Caltech and MIT. Hundreds of scientists in the LIGO Scientific Collaboration, in many countries, contribute to the astrophysical and instrument science of LIGO.
How does LIGO detect gravitation waves?
An interferometre like LIGO consists of two perpendicular "arms" (in LIGO's case each one is 4km long!) along which a laser beam is shone and reflected by mirrors at each end. When a gravitational wave passes by, the stretching and squashing of space causes the arms of the interferometre alternately to lengthen and shorten, one getting longer while the other gets shorter and then vice-versa. As the interferometres' arms change lengths, the laser beams travelling through the arms travel different distances - which means that the two beams are no longer "in step" and what we call an interference pattern is produced. (This is why we call the LIGO instruments "interferometres".) The effect of this change in arm length is very small, but LIGO's interferometres are so sensitive that they can measure even tiny amounts.
What is India's participation in LIGO?
Indian participation in the experiment was significant. Indian scientists were part of the LIGO Scientific Collaboration (LSC), under the umbrella of the Indian Initiative in Gravitational-Wave Observations (IndIGO). In all 61 scientists from nine Indian institutions such as Tata Institute of Fundamental Research, Inter-University Centre for Astronomy and Astrophysics, Chennai Mathematical Institute, Institute for Plasma Research. Indian groups contributed to understanding the response of the detector to signals and terrestrial influences, to the method used for detecting the signal, bounding the orbital eccentricity, estimating the mass and spin of the final black hole and the energy and power radiated during merger, confirming that the observed signal agrees with Einstein's General Theory of Relativity.
(Compiled from LIGO and IndIGO websites.)