Quantum Science 101

What are Gravitational Waves?

Image Credit: Posteriori | Shutterstock.com

In his 1915 Theory of Relativity, Albert Einstein proposes how the force of gravity is directly related to the geometrical curvature of space and time. This theory provided possible explanations for the expansion of the universe, the presence of black holes within the galaxy, and what is often referred to as gravitational waves.

Einstein also 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 space-time 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.1

'Ripples' Within the Universe

According to his theory of general relativity, 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.2

These waves are simply the mechanism by which changes in gravity are causally communicated from a dynamic source to distant observers.3

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.4

The determination of gravitational waves therefore is particularly important in helping scientists understand the complex nature of the early universe, as they illustrate how mass in the Universe distorts space-time.

While devoid of the stars and galaxies, gravitational waves are their own entity, which arise from what has been described by the Laser Interferometer Gravitational-Wave Observatory (LIGO) as the “most violent and energetic processes in the Universe.”

Massive accelerating objects, such as neutron stars or black holes orbiting each other, can disrupt space-time in such a way that gravitational waves of this distorted space radiate from their source.

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.5

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 second5.

Inflation is especially important in the determination of gravitational waves, as a process as intense as cosmic inflation was able to amplify gravitational waves for current attempts at their detection.

The Strongest Detectable Gravitational Waves

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.

Of particular interest for identification purposes is the collision of two black holes, which is expected to emit a burst of gravitational waves that may be detectable by instruments currently available on Earth.

On September 14, 2015, LIGO laser interferometers in Hanford, Washington and Livingston, Louisiana allowed researchers to “listen to” 7 milliseconds of what LIGO claimed to be the sounds of a powerful black-hole collision that occurred 1.3 billion years ago.6

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

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.7

Professor Karsten Danzmann, Leibniz University

The Importance of Gravitational Waves

What is the importance of being able to detect these gravitational waves, and how can this new discovery prove useful to scientists in future endeavors?

Not only are scientists now able to investigate black holes and other extraordinary objects within the universe, such as neutron stars, but it is also proposed that scientists will now be able to look much deeper into the universe than ever before.

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.7

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
 

References and Further Reading

  1. Spacetime, Relativity, and Quantum Physics
  2. General Relativity: Gravitational Waves
  3. Gravitational Wave Astronomy and Cosmology
  4. What Are Gravitational Waves?
  5. Cosmic Inflation - The Big Bang and the Big Crunch - The Physics of the Universe
  6. We've Detected Gravitational Waves, So What? : DNews
  7. Einstein's Gravitational Waves 'seen' from Black Holes - BBC News

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