A remarkable recent development in physics is the discovery of gravitational waves that were predicted by Einstein about a century ago. Astronomers announced the detection of primordial ‘gravitational waves’ that originated 380,000 years after the Big Bang that occurred 13.8 billion years ago.
The gravitational waves that originated after Big Bang are still resonating throughout the universe. The waves were, however, too feeble to measure directly till now. However, they can now be detected in the ‘cosmic microwave background’ radiation from the imprint that they have left in the broth of elementary particles. This background radiation can be detected using radiotelescopes. The detection of these waves are a confirmation of a key theory of the standard picture of cosmology called ‘inflation’, which envisages that during the first moments of its existence after the big bang, the Universe underwent a brief period of exponential expansion.
The announcement of the discovery of gravitational waves was made by David Reitze, executive director of the Laser Interferometer Gravitational-Wave Observatory (Ligo), at a press conference in Washington. Scientists have been struggling for the last 50 years to establish if gravitational waves existed. As the signals of such waves would be extremely weak, scientists and engineers have been trying to build instruments for the last 25 years that are sensitive enough to detect them.
How small these ripples are can be judged by the fact that they cause a distortion of a size about one-thousandth of the diameter of an atomic nucleus, across a 4km strip of laser beam and mirror! The only gravitational waves that we may be able to directly measure would be those from cataclysmic events such as stars exploding or two black holes colliding and fusing into one.
The Antarctic was selected for such studies as the atmosphere there is dry. Water vapour in the atmosphere tends to block microwave radiations making such detections difficult. The Amundsen–Scott South Pole Station where the studies were carried out is located on the Antarctic ice sheet about 2,800 meters where the air is relatively thin, and the area is uninhabited so that there is no interference from mobile phones, televisions and other electronic gadgets.
Until the beginning of the 20th century, space and time were believed to be independent of one another, space being defined by the three spatial dimensions, length, width and height, while time being a fourth independent temporal dimension. Later Einstein postulated that they were connected as a part of the same grid, and the concept of ‘space-time’ emerged as a single interwoven continuum. Thus events taking place could be pinpointed not only by where they occurred but also by when they took place. This was later proved to be correct, as it was shown that time slows at higher speeds.
Thus if you have an atomic clock on earth and compare the passage of time in it against an identical atomic clock in a space shuttle travelling fast around the earth, the atomic clock in the space shuttle would appear to be slightly slower than that on earth. In other words, the passage of time would be dependent on the velocity. Not only is the passage of time dependent on the velocity but also on the strength of the gravitational field for an observer outside such a field.
According to Einstein’s general theory of relativity, gravity from mass can deform the shape of space-time. The fabric of space-time will become curved near any massive body, and this deformation in the form of gravitational waves will, according to Einstein, propagate throughout the Universe, travelling through space at the speed of light. If you were able to watch such a gravitational wave travelling towards you head on, it would appear to be alternately stretching and compressing space, in the up-down and left-right directions.
Professor Kip Thorne of the California Institute of Technology says that astronomers had, till now, considered the universe as a calm sea. That has now changed. “The colliding black holes that produced these gravitational waves created a violent storm in the fabric of space and time, a storm in which time speeded up and slowed down, and speeded up again, a storm in which the shape of space was bent in this way and that way”.
According to Prof Alberto Vecchio, a senior researcher and from the University of Birmingham: “We have observed the universe through light so far. But we can only see part of what happens in the universe. Gravitational waves carry completely different information about phenomena in the universe. So we have opened a new way of listening to a broadcasting channel which will allow us to discover phenomena we have never seen before”.
“This observation is truly incredible science and marks three milestones for physics: the direct detection of gravitational waves, the first detection of a binary black hole, and the most convincing evidence to date that nature’s black holes are the objects predicted by Einstein’s theory.”
The discovery made is truly amazing since the scientists detected the fusion of black holes and the resulting cataclysmic event using an instrument that is so sensitive that it could detect a tiny change in the distance between the solar system and the nearest star four light years away with an accuracy corresponding to the thickness of a human hair.
So what we now have are the tools that will allow us to observe the events that occurred soon after the Big Bang. One huge unexplained mystery is that the galaxies – including all the stars, planets, and black holes – account for only about five percent of the total mass of the visible universe. Gravitational waves may allow us one day to understand why most of the mass of the universe is accounted for by some unseen mysterious forces that we call ‘dark energy’ and ‘dark mass’.