In his 1907 paper, while describing his infamous theory of general relativity, Albert Einstein proposed that gravity was in fact a resultant of a bend in space-time caused by the existence of a mass. This mass would result in emergence of ripples in space-time and the distortion of the space around it. A straightforward example of this which can be observed on a smaller scale is the orbit of the Earth and other planets in the Solar System around the Sun due to the ripples formed by to the Sun’s colossal mass. Similarly, the production of gravitational waves is a result of the change in the distortion in space-time caused by the acceleration of masses. In simpler terms, anything with merely mass and energy can cause the formation of gravitational waves. However, a tremendous mass is required to form waves that would even be discoverable and therefore, gravitational waves are only observed due to the activities of celestial bodies.
The Nobel Prize in Physics laureates who are credited with discovering the existence of gravitaional waves through their LIGO experiment
With no concrete evidence to back this claim, this theory was considered to be a mere rumour until just recently, when on 11th February, 2016, the Laser Interferometer Gravitational-Wave Observatory (LIGO) announced the groundbreaking discovery of gravitational waves which had been caused by the merging of two black holes with masses of 29 and 36 solar masses 1.3 billion light years away. The group of three Americans physicists who discovered the long-awaited marvel, sparked an ultimate approval of Einstein’s theory around the globe, successfully paving their way to winning the Nobel Prize in Physics.
The mass of the merged black hole amounted to 62 solar masses, thus revealing that 3 solar masses had been emitted in the form of gravitational waves. As gravitational waves travel at the speed of light, this meant that these waves were formed by the merger of black holes 1.3 billion years ago and were only just reaching the Earth.
An artist's depiction of gravitational waves generated by binary neutron stars. Picture credits:- www.nasa.gov
The factor which made the unearthing of gravitational waves extremely difficult were that they only lasted for an extremely short of time, within which objects would stretch or compress due to the gravitational waves (depending on the angle at which the waves strike) and return to their original position. Furthermore, as every object in the vicinity would also stretch or compress proportionally, it would seem as if there had been no change whatsoever. Therefore, in order to combat this problem, light was used to come to a concrete conclusion on whether or not gravitational waves had actually struck in their experiment. This was done on the basis that if the distance between two points increases, light would take a longer time to travel back and forth and vice versa. This theory was practically put into place by installing two 4km long rods perpendicular to each other and the constant provision of a laser at 1, and exactly 1, wavelength as a change in the wavelength itself would cause interference of the laser, defeating the entire purpose of the interferometer to detect gravitational waves through interferences in the laser. The reason for having the arms perpendicular to each other is that as earlier stated, the angle at which the gravitational wave strikes would result in one of the arms to shrink and the other to expand simultaneously and the interference of the laser can be used to measure whether the space in between has increased or decreased. However, these measurements need to be extremely precise as gravitational waves only cause the arms to expand and shrink by, at most, 1x10-18 metres.
The detection of gravitational waves is one of the most significant discoveries in Physics in recent times as it can open doors to a wide range of other breakthroughs with regards to the vast Universe, only a fraction of which we have been successful in uncovering. What makes this discovery so vital in the larger scheme is that it allows us to observe phenomena that do not emit light such as black holes due to its ability to pass through matter and come out the other side unchanged. Moreover, this discovery would go a long way in solving physics’ greatest mysteries such as those relating to the formation of black holes and whether or not the theory of general relativity is an accurate description of gravity and ultimately allowing us to understand the origin of our beloved cosmos even better.