A Cheat's Guide To Gravitational Waves

Scientists have finally detected gravitational wave 100 years after Einstein predicted them.

NASA

Scientists have announced that they have finally detected gravitational waves after all this time and everybody is going bonkers.

Just one thing: What on earth are gravitational waves?

What Are They?

Gravitational waves are a phenomenon predicted by Einstein's Theory of General Relativity.

They are ripples in spacetime caused by extremely violent events. Any object with mass will cause spacetime to curve around it, much like a bowling ball on a trampoline.

Accelerating masses will agitate spacetime so much that they will create ripples in spacetime that propagate out at the speed of light, much like ripples in a pond.

What's Happened?

realistic black hole
IOP Publishing Ltd

In this instance two black holes managed to get caught in each other's gravitational field and began to spiral in towards each other. This created the gravitational waves predicted by Einstein.

Scientists were able to detect these waves for the very first time using a piece of kit called LIGO (lie-go). This consists of two very long tunnels in the shape of an L. A laser is split between the two tunnels, bounced off a mirror at the other end and returned to the start point.

Usually, the two beams of light should arrive back at exactly the same time, and their wavelengths will cancel each other out. But, if a gravitational wave happens to pass through at the same time, then it will distort spacetime, essentially stretching or compressing the length of one of the tunnels and changing the distance that one of the beams of light has to travel.

If this happens, the two beams of light will arrive back at the starting point at different times, the wavelengths won't cancel each other out and the signal will be detected, which is exactly what happened.

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