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LIGO Confirms the Existence of Gravitational Waves!

Everybody do the wave—the gravitational wave!

Today, the Laser Interferometer Gravitational Wave Observatory, or LIGO, has confirmed that they directly detected the existence of gravitational waves on September 14, 2015. In a paper accepted by Physical Review Letters, physicists at LIGO say that they detected gravitational waves produced by the merger of two black holes over 400 megaparsecs—or 1.3 billion lightyears—from Earth.

The direct confirmation of gravitational waves by LIGO’s detectors in Livingston, Louisiana, and Hanford, Washington, comes nearly 100 years after Einstein’s General Theory of Relativity predicted their existence. And while there’s been indirect evidence of their existence, up until now, they had never been directly detected.

For those unfamiliar with gravitational waves, they are ripples in the fabric of spacetime caused by the acceleration of massive objects, which in this case, are two colliding black holes: one about 36 times the mass of our Sun, the other about 29 times as massive.

As Einstein discovered with his General Theory of Relativity, everything in our universe takes place in the cosmic stage known as spacetime. Spacetime can essentially be thought of as a sheet of rubber, which bends as objects with mass are placed upon it (in this example the spacetime rubber is 2-D, when in fact spacetime is 3-D, but it still works as an example). I.e. if you were to place a bowling ball on this sheet of spacetime rubber, it would bend thanks to the bowling ball’s mass, effectively causing the spacetime rubber to curve. This is the reason Earth, as well as all of the other planets in the solar system, revolve around the Sun; it’s not because the planets are “attracted” to the Sun, but because they follow the warping of spacetime caused by the mass of the Sun; imagine a marble rolling around the dip in the rubber sheet caused by the bowling ball. The proportions (Earth/Sun, marble/bowling ball) are way off, but that’s essentially the concept.


Earth, like the Sun, or any other object with mass, curves spacetime.

Gravitational waves—as far as we can possibly detect—are caused by massive objects accelerating in spacetime, therefore causing it to ripple. Imagine the rippled caused by dropping the bowling ball onto the rubber sheet of spacetime, or, say, if that bowling ball exploded:


Ripples in the fabric of spacetime, a.k.a. gravitational waves.

Scientists at LIGO were able to detect these gravitational waves thanks to laser measurements. Essentially, the only way to observe a gravitational wave is to measure it with light. If we imagine two points in spacetime, point A and point B, and then allow a wave to ripple through spacetime from point A to point B, the spacetime between the two points will expand and contract. But if we were to try and measure this expansion and contraction with a standard measuring tool—say, a super accurate ruler—we wouldn’t be able to detect the waves, because just as spacetime expands and contracts because of the wave, so too would the ruler.

But light, which is constant, will take more time to travel from point A to point B when space expands, and less time when it contracts. The scientists at LIGO, by noting the changes in the amount of time light took to get from one of their detectors to the other, were able to definitively say that there had been a ripple in spacetime. The laser measurements also had to be extraordinarily sensitive, detecting a spacial change that is equivalent to detecting a change in the distance from Earth to the Moon of about 1/100th the diameter of a human hair.

But why all the hubbub? What is so important about detecting gravitational waves?

The reason the direct detection of gravitational waves is such a huge deal is because it essentially gives us a whole new way of observing the universe. It’s like developed a new sense. Just as we can determine myriad important details about the source of a given light based on the light’s wavelength (whether its source is moving away or toward us, the chemical composition of the source, etc.), detecting gravitational waves can give us clues as to what constitutes their sources; For example, by measuring gravitational waves, we can figure out if they came from a binary neutron star system or a supernova—or in this case, the collision of two black holes. In other words, with the ability to detect gravitational waves, we have a new method, a new sense we can use, to figure out and discover the makeup of our universe.

So, we can now add the direct detection of gravitational waves—alongside the discovery of water on Mars, as well as the Higgs boson—to the list of impressive advancements of the past few years. Which means the 21st century is shaping up to be pretty spectacular in terms of scientific discovery. The only question is, what’s next? Quantum teleportation? A theory of everything? Diet soda that tastes just as great as regular soda?! Who knows. But we gotta ride this wave as long as we can.

What do you think about LIGO’s confirmation of gravitational waves? Let us know in the comments section below!

Images: NASA, Johnstone/NASA, Superborsuk
Video: PBS Space Time

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