A chirp reveals the origins of the world: LIGO proves existence of gravitational waves

Rewon Shimray, Staff Writer

The idea of a black hole is terrifying in and of itself.

But now, imagine two black holes colliding into one another at the speed of light. This collision would result in a larger black hole, sending ripples called gravitational waves through the spacetime fabric of the universe.

Einstein’s theory of gravitational waves is fundamental to the concept that the universe is made of spacetime, the web of space and time that hold the universe together. Gravitational waves ripple through spacetime, creating slight distortions in the speed at which things travel and are shaped. However, there was no evidence of the existence of gravitational waves at all until Sept. 14, 2015.

Gravitational waves are different from the typical waves learned about in science classes. Until a few months ago, modern scientists had only been able to observe electromagnetic waves (light, microwaves, radio waves, etc). Einstein observed the behaviors of these electromagnetic waves: how they become disturbed by stimuli and how some are visible while others aren’t.

Einstein concluded from these observations that gravity in itself is a wave–invisible to the human eye and with the ability to change form–but a wave nonetheless. Most importantly, gravitational waves could be observed not only on Earth’s surface, but throughout the entire universe.

Einstein’s theory of gravitational waves had no tangible proof until a century later. Infographic made by Rewon Shimray.
Einstein’s theory of gravitational waves had no tangible proof until a century later. Infographic made by Rewon Shimray.

Einstein created the theory of relativity, key to the idea of gravitational waves. This states that things can only be influenced by their immediate surroundings and therefore no influence can travel faster than the speed of light–any faster and the influence would have to be jumping across space.

Influences originate in places where large masses move (i.e. two large black holes colliding), which typically happens far, far away from Earth. This makes being able to trace gravitational waves very difficult. The ripples that gravitational waves make in spacetime are similar to those found on the surface of water, slowly fading out further away from the origin. By the time the influence of a gravitational waves reaches Earth, it is so insignificant that it’s hardly traceable at all.

It wasn’t until 1968 that MIT student Rainer Weiss conceived the design for a device that could detect gravitational waves (approval for such a large-scale project took decades). The Laser Interferometer Gravitational-Wave Observatory, better known as LIGO, set up two interferometers, one in Washington and the other in Louisiana. These detectors look like large X’s from a bird’s eye view.

LIGO has two interferometers, devices used to detect gravitational waves, stationed in separate areas of the Unites States. Diagram provided by LIGO.
LIGO has two interferometers, devices used to detect gravitational waves, stationed in separate areas of the Unites States. Diagram provided by LIGO.

The two main arms of the interferometers are 4 kilometers long. To put that in perspective, that’s about 2.5 miles. From a third end, a powerful laser is projected that splits into the two arms. At the end of each of the arms, there are massive mirrors made of pure glass that weigh 88 pounds. The laser light bounces off these mirrors and shoots back into the photodetector on the fourth end. The photodetector views the light as waves. When the lights recombine, their wave patterns should match. So, if one of the beams takes longer than the other to get back to the meeting point, that indicates a disturbance caused by gravitational waves.

The difference between the light waves, caused by gravitational wave activity, was translated into a sound. Scan the QR code to hear the resulting noise.
The difference between the light waves, caused by gravitational wave activity, was translated into a sound. Scan the QR code to hear the resulting noise.

On Sept. 14, 2015, LIGO detected the first trace of gravitational waves. The difference between waves was minuscule (only a shift of a few thousandths of the diameter of a proton), but it was enough to prove the existence of gravitational waves. The scientists at LIGO translated the unsynchronized light waves into a sound wave, and the result is a chirp-like noise.

The two LIGO observatories stationed in Washington and Louisiana worked in tandem to confirm and support one another’s research, and both picked up a similar signal. Nonetheless, several things can cause the difference between light signals, such as a distant earthquake which would shift the mirrors, simulating the same kind of change a gravitational wave would. A team of a thousand scientists immediately went to work to make sure that there was nothing that altered the data. On Feb. 11, 2016, LIGO released the news of their discovery, finding that the chances of the unsynced lasers not being a result of gravitational waves were less than one in 3.5 million.

In the future, scientists are looking forward to discovering a new unexplored dimension of the universe. Scientists now no longer limited to the realm of electromagnetic waves, can observe things such as black holes and neutron stars using gravitational waves. Plans for additional tracking devices are underway. The first is the Einstein telescope which will have three 10 kilometer-long arms in a triangle, and construction is expected to be completed by the late 2020s. The second, more ambitious project is the Evolved Laser Interferometer Space Antenna, nicknamed Elisa, which will be composed of three satellites with arms a million kilometers long in orbit around the sun to observe the gravitational waves surrounding it.

Ultimately, gravitational waves carry the record of momentous events in the universe. With LIGO’s interferometer, a chirp may be enough to prove the collision of the two black holes that created our world as we know it. So, the next time someone asks how you know how the world was created, say a little birdie told you.