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Gravitational Waves Detected, What Are They and How Are They Detected?

The collision and then merging of two black holes apparently released gravitational waves. 
(Image: LIGO via via Wikimedia Commons)
The collision and then merging of two black holes apparently released gravitational waves. (Image: LIGO via via Wikimedia Commons)

The recent discovery of “gravitational waves” has gone viral on the Internet, and is being reported by most news-media around the world. The phenomenon scientists have been trying to prove for many decades has finally taken place recently in a far away system, where two black holes collided, causing what media are repeatedly calling “ripples in space and time.”

A game changer for astronomy is how scientists, such as Prof. Steven Hawkins, frame the discovery.

According to Cliff Burges, theoretical physicist at McMaster University in Ontario, what makes the confirmation of gravitational waves so exciting is the prospect of using it to peer into the depths of the universe, farther than what was possible before.

Burges told Vox Science & Health in an interview:

The observation was made by the Laser Interferometer Gravitational Wave Observatory (LIGO), which announced its discovery last week. LIGO has two gravity wave detectors, one in Hanford, Washington, and one in Livingston, Louisiana, according to Astronomy Magazine.

Good news travels far and fast

There is lots of excitement among researchers, with some — like the renowned “star astronomer” Prof. Stephen Hawkins — predicting that this latest discovery may “revolutionize astronomy.”

The Guardian reported Hawkings said:

The research and observation of gravitational waves was a joint effort among groups of scientists around the world.

Japan is in the process of completing the construction of a facility to measure and observe gravitational waves.

The head of the University of Tokyo’s Institute for Cosmic Ray Research and a Nobel laureate, Takaaki Kajita, said his group hopes to “complete the construction, achieve high (measurement) sensitivity, and join the international gravitational wave (observation) network as soon as possible,” according to The Japan Times.

Ok, everything sounds like really “good news,” up until here (pun intended). Two certain questions are itching the minds of many readers, and what was mostly left unanswered was:

“What the heck are gravitational waves and what do they do?”

We shall attempt to dissect the “elephant in the room,” and synthesize an answer in the plainest terms possible.

Einstein: the general of relativity

To understand the importance of gravitational waves we first need to bounce the medicine ball called “spacetime.”

According to Einstein in his General Theory of Relativity, spacetime is like a fabric or a mesh. What we understand as gravity is apparently the warping or the dent left in this mesh of spacetime, by the mass of a heavy object, or a star for example. Accordingly, a planet caught in this warped space will orbit that star. “Like a ball spinning around a roulette wheel.”

Wrapping his mind around this idea, Einstein was led to the prediction that if two massive objects where to collide, this would cause a so-called “ripple in the fabric of spacetime.” According to Einstein, with this ripple in space, time would manifest as “gravity waves,” through the ripple in space, time would also be technically detectable.

With this in mind, it becomes easier to understand what all the recent articles meant when they spoke about a “ripple in spacetime” or the discovery of “gravitational waves,” and the confirmation of Einstein’s General Theory of Relativity.

The path light takes in a interferometer from it's source to the photon detector. This method is also used for the detection of gravitational waves. (Image: Hermann Rohr)

The path light takes in a interferometer, from its source to the photon detector. This method is also used for the detection of gravitational waves. (Image: Hermann Rohr)

Tuning into the fabric of space

Ok, once the background and motivation that drove scientists for decades in their search for gravitational waves is established, one might wonder how these mystical “distortions in time and space” might be detected.

It’s quite simple actually, according to the inventor of the gravitational wave detector, Rainer (Rei) Weiss. A gravity wave distorts the fabric of space, a part of “space” permeated by a gravitational wave would collapse up and down, and stretch sideways, according to Weiss.

To measure this stretching and squeezing Weiss came up with an ingenious idea. A laser would create a light beam that would be split into two beams of equal length. Next, each light beam would bounce off a mirror at the end of the arm. Both light beams would meet at a third mirror (simultaneously) where they would be joined and reflected into a measuring device where the actual “magic” would happen.

“The beams come back in such a way that they cancel each other out.” In normal conditions the measured amplitude of the waves (frequency of the photons emitted by the laser) would cancel each other out, resulting in a “zero” reading.

However, if a gravitational wave was to pass through one of the arms, the resulting “warp of space” would cause one of the arms to become minutely longer or shorter than the other, resulting in a different reading in the detector. The two beams would not travel simultaneously anymore, and would go out of sync.

This process is called interferometry; this was not invented by Weiss, but by Albert Abraham Michelson. Weiss was just the clever mind to come up with the idea of how to use interferometry to detect gravitational waves.

Knowing this should also allow us to shrink the monstrosity called “Laser Interferometer Gravitational — waver Observatory” (LIGO) into a format that any layman could wrap their brains around.

In the end that’s all the hype is about.

Summary a.k.a plot

Two black holes meet and they collide, sending shockwaves through “time space,” which also happen to be called “gravitational waves.” LIGO, which was patiently waiting, was affected by these gravitational waves, causing the “twin laser interferometer” to give of a reading that was out of the ordinary.

LIGO announces the detection of the waves, which were also predicted by Albert Einstein almost a century ago, and wham! The supernova of a media buzz about super complicated terms packed in super interesting reporting.

But, just in case this article was just as super complicated, watch this video that explains and illustrates what gravitational waves are, and how they are detected:

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