Gravitational Waves

Alexander Zhang, Larry Wang

One hundred years ago, Albert Einstein predicted the existence of gravitational waves. Recently, scientists have proved their existence. But what exactly are gravitational waves? Gravitational waves are, as suggested by the name, waves of gravity that distort space-time, like ripples on a pond. They are a time machine, formed billions of years ago, giving us information about the cosmos long before humans, or even mammals, existed.
Albert Einstein predicted the existence of gravitational waves in 1916, 100 years before it was discovered. It was part of his ground-breaking theory of general relativity. The confirmation of gravitational waves took place at the Laser Interferometer Gravitational-wave Observatory (LIGO). Scientists had to measure a distance that was equal to 1/1000th the width of a proton, in the order of magnitude of 11018 meters.

There were two detectors, one located in Livingston, Louisiana, and one in Hanford, Washington used to detect gravitational waves. Each detector is ‘L’ - shaped, two 4-kilometer-long legs. A laser is shined from the crux (intersection of two arms) to the end of each arm’s mirror, with the laser reflected back to the crux. Usually, the laser beams arrive at the same time. If the two laser beams arrive at different times, gravitational waves are present. Gravitational waves distort the fabric of space-time. A gravitational wave would compress one arm of LIGO slightly, so the laser in the compressed arm arrives first. According to David Reitze of the California Institute of Technology (Caltech),

“LIGO is the most precise measuring device ever built.” It was crucial in the discovery of gravitational waves. 1.3 billion years ago, two medium-sized black holes came into contact with each other. Gravitational waves were generated by this collision. LIGO's two huge detectors picked up the signal of gravitational waves on September 14, 2015, nearly one-hundred years after Einstein predicted the existence of gravitational waves.
There are many concepts of Einstein’s theory of General Relativity, one of which is the concept of gravitational waves. Gravitational waves are when one celestial object orbits another celestial object.

When one celestial object orbits another celestial object, the movement causes ripples in space. We now know these types of ripples as gravitational waves. All gravitational waves are invisible, and are incredibly fast, being at the speed of light. Gravitational waves have the potential of stretching and squeezing anything in their path. These waves do not have to be caused by just orbiting celestial objects. In fact, whenever an object accelerates, it can cause gravitational waves.

Many times, the gravitational waves created are incredibly weak, and are extremely hard to detect. The strength of a gravitational wave mostly depends on the mass of the object producing the gravitational wave. An example of this is two black holes colliding creating strong gravitational waves. It is easiest to detect gravitational waves when two extremely massive objects collide.
As you now know, gravitational waves are created by the acceleration of a celestial body, whether it is orbiting another celestial body or colliding with another celestial body. Yet, this is not all of the ways gravitational waves are produced. Inflation is another way gravitational waves are produced. Gravitational waves affect the polarisation (the way the wave moves back and forth) of the cosmic microwave background, which is essentially some electromagnetic radiation left behind from the earlier stage of the universe after the Big Bang. Incredibly sensitive instruments can measure the strength of the polarisation produced by the waves. The results give a figure of the amount of energy involved at the time of inflation and help determine when the inflation occurred, thus determining when the gravitational waves occurred.

Gravitational waves give us another way to observe space. For example, waves from the Big Bang would tell us a little more about how the universe formed. Waves also form when black holes collide, supernovae explode, and massive neutron stars wobble. So detecting these waves would give us a new insight into the cosmic events that produced them. Gravitational waves could also help physicists understand the fundamental laws of the universe.
Gravitational waves do not have a huge impact on our daily lives, but they do tell us about the past. Physicists use them to learn the history of the universe. Einstein was able to predict the existence of something 100 years before its discovery. Gravitational waves may be a key in figuring out the creation of the universe.


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