What Are Gravitational Waves?

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The Universe is spacetime – it is made of 3 dimensions of space and 1 dimension of time. When matter, a part of the universe, moves in the spacetime, it creates a wave-form of energy called the Gravitational waves. It is infinitesimally small for us to feel it; it is less than the size of a proton! For massive matter on the astronomical scale (like the black holes or very large stars), these waves travel in the form of a ripple across the curvature of spacetime. The energy involved in the interaction tells us a story about the Universe.

In his general theory of relativity (1915), Albert Einstein proposes how the force of gravity is directly related to the geometrical curvature of space and time, explaining the presence of gravitational waves, among other phenomenon in the universe. Until 2015 (eventually in the 100th anniversary year), gravitational waves were not detected, experimentally proving Einstein’s theory.

Einstein applies this theory to the motion of the planets, in which he states that objects of matter, such as the Earth and the sun, are able to change in their geometry of spacetime in order to grow and evolve. This concept of “space-time” describes a single physical entity in which ‘space’, such as the room you are in, and ‘time’, exist together.

…we are bathed with gravitational waves from every bit of moving matter in the universe…stretching and squeezing us, slowing time for us or speeding it up…this effect is minute…

Dr Kelly-Holley Bockelman

Ripples Within the Universe

Einstein states that gravitational waves are “ripples” within the universe that can propagate across space, similar to the ripples that spread across the surface of a pond. These infinitesimal ripples in space itself has opened up a new window of science to understand the dawn of cosmos and many complex astrophysical phenomena so far not understood.

These waves are simply the mechanism by which changes in gravity are causally communicated from a dynamic source to distant observers.

Scott A. Hughes, Department of Physics, Massachusetts Institute of Technology (MIT)

Able to travel at the speed of light, these ripples also carry valuable information regarding their cataclysmic origins, as well as additional details on the nature of gravity itself.

Gravitational waves arise from the “most violent and energetic processes in the Universe” as described by the Laser Interferometer Gravitational-Wave Observatory (LIGO). Rainer Weiss, (Massachusetts Institute of Technology (MIT) in Cambridge), Kip Thorne, (California Institute of Technology (Caltech) in Pasadena), and Barry Barish, (Caltech) were the involved in the planning and the guiding of the construction of the LIGO to detect these waves. These scientists were awarded the Nobel Prize in Physics 2017 “for decisive contributions to the LIGO detector and the observation of gravitational waves.” The interferometers detect these gravitational waves as small in length as 1/10,000 the width of a proton. The National Science Foundation (NSF) fund LIGO, and Caltech and MIT built and operate them.

On September 14, 2015, at 5:51 a.m. both of the twin LIGO detectors, located in Livingston, Louisiana, and Hanford, Washington, USA, allowed researchers to “listen to” 7 milliseconds of the gravitational waves converted into sound waves. The waves were produced 1.3 billion years ago during the final fraction of a second of the merger of two black holes whirling into each other to produce a single massive spinning black hole, located in the direction of the southern hemisphere of the earth. The whirling black holes lose energy through the emission of gravitational waves. Massive accelerating objects, such as neutron stars or black holes orbiting each other, can disrupt space-time in such a way that gravitational waves radiate from their source. The strongest detectable gravitational waves can be produced by the collision of black holes, the collapse of supernovae (stellar cores), or the coalescing neutron stars or white dwarf stars, all of which are some of the most catastrophic events that can occur in the universe. After the initial observation in 2015, the gravitational waves have been repeatedly detected in the years 2016, 2017 and 2018, produced from events such as another pair of black holes whirled into each other, binary black hole merger, and collision of neutron stars.

We found a beautiful signature of the merger of two black holes and it agrees exactly – fantastically – with the numerical solutions to Einstein equations…it looked too beautiful to be true.

Professor Karsten Danzmann, Leibniz University

Cosmic Inflation

One way in which gravitational waves can be generated is through the proposed process of cosmic inflation. Cosmic inflation assumes that immediately after the Big Bang occurred, the early universe went through a period of accelerated and exponential expansion during the first 10-35 of a second, before reducing to the more sedate rate of expansion that is still occurring today.

This theory concludes that the universe in existence today originated in an extremely small, even microscopic, causally-connected region. Proposed by Alan Guth in 1980, the theory of inflation claims that the size of the universe increased by a factor of about 1026 in less than a trillionth of a second. Cosmic inflation explains how gravitational waves are amplified, leading to their detection by humans on earth.

The Importance of Gravitational Waves

Professor Karsten Danzmann of the Max Planck Institute for Gravitational Physics and Leibniz University in Hannover, Germany claim that the detection of these gravitational waves is one of the most important developments in science, comparable to the determination of the DNA structure by Watson and Crick.

Information carried by gravitational waves have the potential to offer scientists information on the unification of forces, which is one of the biggest problems in physics to date in linking quantum theory to gravity. In addition to understanding the black holes and neutron stars, scientists are looking deeper into the universe than ever before. Because gravitational waves cross through practically every aspect of the universe, they act as the perfect messengers in sharing knowledge of the innumerable structures and events that occur throughout this vast universe.


Video Credit: NASA | C. Henze

Sources and Further Reading

This article was updated on the 1st March 2019.

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