A long time effort to detect gravitational radiation has finally led to a triumphant conclusion – for the first time after about a century of extensive effort, scientists have finally succeeded to verify and detect it. The discovery of gravitational waves was carried out with the participation of over a 1000 physicists using Laser Interferometer Gravitational-Wave Observatory (LIGO) and will open a new era in our understanding of the structure and dynamics of the universe.
In 1917, Albert Einstein proposed his general theory of relativity to include gravity in his special theory of relativity. The theory was a complete departure from Newton’s classical theory of gravitation. According to the new theory, what was once perceived to be a classical force, was indeed the deformation of the 4D geometry of universe caused by any form of matter or energy, similar to the deformation of the surface of a mattress by a metal ball on it.
The three famous predictions of the theory, including bending of light beams passing by the sun, unresolved problem of the retrograding motion of the planet Mercury and finally the red shifting of light beams originating from the sun, were all proved to be correct. This not only boosted the reputation and credibility of the theory but also put the challenge of the discovery of gravitational waves, its most astonishing prediction, before the physicists.
Similar to Maxwell’s electromagnetic equations that predicted the existence of electromagnetic waves, the Einstein’s tensor equation predicted the existence of gravitational waves in the fabric of the universe’s space-time. Just like the electromagnetic waves are produced by accelerating charges, Einstein’s gravitational waves were predicted to originate from any cosmic event leading to the disturbance in the geometry of the universe similar to seismic waves radiating from an earthquake. At the cosmological scale, cosmic events such as the annihilation of stars or collision of black holes can lead to the gravitational waves.
The technical barriers of such an experiment were so tremendous that it took about a century of effort to overcome them. Gravity is by far the weakest field as compared to the other three existing fields in nature, i.e., strong interactions, weak interactions and electromagnetic interactions, making its discovery extremely difficult. Gravitational waves cause vibrations at a scale equal to a millionth of the size of an atom, so any gravitational wave detector should be capable of its distinction from other vibrations caused by such events as earthquakes, normal surface vibrations and even vibrations caused by natural oceanic waves. Also, compared to electromagnetic radiation, the wavelength of gravitational waves is of the range of hundreds of kilometer, and so any gravitational antenna should be capable of intercepting simultaneous vibrations of the same source at hundreds of kilometers far apart.
The LIGO discovery of gravitational waves
With its huge 4 km-long arms instrument located at Washington State and its similar installation in Louisiana, on Feb. 11, 2016, LIGO finally succeeded to register a train of gravitational waves passing through the earth. The waves were caused by the collision of two spiraling black holes about a million years ago that rippled the fabrics of its surrounding space to be observed a million years later by LIGO.
Indirect proof of gravitational waves was first reported by R. A. Hulse and J. H. Taylor in 1975 leading them to win the 1993 Nobel Prize in Physics; however, this is the first time that they are directly intercepted and detected by a gravitational wave detector.
A new tool to observe the universe
The general theory of relativity was a revolution for our understanding of the universe and gravity. It opened a new era for modern physics and astrophysics. Now, the long-awaited discovery of gravitational waves will accelerate our understanding of the creation and evolution of the universe and gravity.
The new discovery will provide scientists with a new tool that can unhide the unobservable part of the universe. Until now, our understanding of the world relied upon observation tools and telescopes which used electromagnetic rays at the different range of frequencies, including radio waves, infrared waves, visible light spectrum, X-rays and gamma rays.
Now with this new powerful tool, scientists can observe cosmic phenomena that have never been observed before such as new details about the formation and evolution of the black holes, galaxies and the whole universe. This new technique may also pave the way for the verification of new theories, such as the existence of parallel worlds and multiverses at the cosmological level and quantum gravity at the quantum level.