While physicists have been talking about the possibility of gravitational waves being discovered by the Laser Interferometer Gravitational-Wave Observatory (LIGO), people like you and me are scratching our heads wondering what exactly these gravitational waves are! Gravitational waves are basically disturbances in the fabric of spacetime. Yes you heard it right ‘fabric’. According to Einstein’s general theory of relativity, spacetime isn’t a void, but rather a four-dimensional “fabric,” which can be pushed or pulled as objects move through it.
These distortions are the real cause of gravitational attraction. If you touch the surface of water in a still pool, ripples emanate from that point and waves follow in its path and spread outwards. According to Albert Einstein, the same thing happens when heavy objects move through spacetime.
You can understand this by using a very simple experiment. Take a taut rubber sheet and place a heavy object on it. That object will cause the sheet to sag around it. If you place a smaller object near the first one, it will fall toward the larger object. A star exerts a pull on planets and other celestial bodies in the same manner.This simple experiment just gives you an idea of how spacetime works. It makes one understand that what we think of as a void is actually a dynamic substance. Based on this, it can be deduced that any accelerating body should create ripples in this substance but there is a catch in it too. Only incredibly massive objects—such as neutron stars or black holes—will create gravitational waves that continue to spread all the way to Earth and small ripples would fade out comparatively quickly.
Can these waves be detected?
There are a few experiments going on around the world in different labs in order to detect the gravitational waves LIGO being the front runner. It is understood that as a wave passes by, it stretches space in one direction and shrinks it in a perpendicular direction. LIGO aims to detectthese changes using an instrument called an interferometer. This device splits a single laser beam into two and sends both beams shooting off perpendicularly to each other. If the beams travel equal distances, bounce off mirrors, and come back, the waves that make them up should still be in alignment when they return. But a passing gravitational wave can actually change the distance of each arm, which would change the distance that each beam travels relative to its sibling. When the beams return to their source, scientists would be able to detect this change. Though it has been a decade and LIGO hasn’t yet succeeded in finding or detecting a gravitational wave, the scientists are still hopeful. They have come up with an advance version of it called Advanced-LIGO which they believe would achieve what LIGO couldn’t.
Apart from LIGO, European Space Agency’s (ESA) Laser Interferometer Space Antenna, or LISA is also doing its bit in detecting these waves. The ESA launched the LISA pathfinder in December to test the technology that will eventually be deployed in future LISA missions.
The North American Nanohertz Observatory for Gravitational Waves or NANOGrav has their own way of detecting gravitational waves. They do it by looking at the bursts of radio waves emitted by the neutron stars calledpulsars. These radio wave pulses are normally strictly timed, so if they arrive early or late, it could be because a gravitational wave interfered with their journey to Earth.
Among other methods, programmes likeBackground Imaging of Cosmic Extragalactic Polarization(BICEP), Harvard’s series of experiments at the south pole, observe the leftover radiation in an attempt to find the telltale polarization patterns.
But why do we want to find these waves at all?
These waves will give us another new perspective to observe and understand the universe and the space around us. For example, waves from the Big Bang can reveal more secrets about how the universe formed. Waves also form when black holes collide, supernovae explode, and massive neutron stars wobble. Detecting these waves would give us a new insight into cosmic events like collision of black holes, supernova explosion, etc. which are characterized by formation of waves. And last but not the least; gravitational waves could also help physicists understand Einstein’s general theory of relativity. Finding them would prove if this theory is right and if not then where it goes wrong.
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Author: Technology Blog
