2019 is nature's 150th birthday. To mark this anniversary, nature is publishing a series of reviews

that take a look at the past, present and future of science. One of these reviews looks at the

first direct detection of gravitational waves, a momentous event for science that happened back in 2015.

The detection was the climax of a cosmic dance between two black holes.

After spending an eternity spiraling closer and closer to each other, eventually these black holes merged.

A cataclysmic event that sent ripples in spacetime across the universe that were detected by the Lago facilities in the US.

This detection was the culmination of a story that began over a hundred years ago,

when a certain Albert Einstein predicted that gravitational waves might exist.

Cole Miller, from the University of Maryland in the U.S., co-author of this year's review,

explains how this story got off to a bit of a bumpy start.

Einstein came up with the final version of his general theory of relativity in 1915.

Just the next year, he came up with the thought about whether there could be waves related

to gravity. Remarkably, though, Einstein made some significant mathematical errors

in that first paper, and even a corrected version in 1918 had errors, and then he had

conceptual problems with it one way or the other. He published papers saying that the gravitational

waves don't exist, and they published papers saying they do exist.

So it was really only in the 1950s where people really accepted the gravitational waves were real things, but detecting them was another story.

According to Einstein's general theory of relativity, each time two objects orbit each other, the system

loses a fraction of its energy, which radiates out as gravitational waves. Removing energy like

this brings the objects a tiny bit closer together and makes their orbit a tiny bit faster.

As gravitational waves only deforms space-time a tiny amount, they're difficult to

directly detect. The first indication of their existence actually came indirectly via the discovery

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