As you head East along the I-12 out of Baton Rouge, the state capital of Louisiana, you’ll be greeted by many sights: enormous outdoors shops which sell everything from boots to guns to boats; dozens of billboards advertising the legal services of the local accident lawyers; and some days you’ll even be overtaken by a house on the back of a lorry, migrating along the old West Florida Republic Parkway. If you’re (un)lucky, and are driving through the swamp after a rain storm you might get a sampling of the strong smell of swamp gas a few miles outside the city too.

As you drive further out of the city you’ll eventually see signs for a town named Livingston. The freeway exit takes you through the edge of a pine forest, and as you drive over the bridge which spans the interstate you get your first glimpse of a town which has earned a line in the history of science. Livingston’s not a big place. It’s a fraction of a size of its Scottish namesake, an unprepossessing place by most accounts. You’ll eventually reach the end of the road, and find yourself turning left, following the direction on a small green sign next to an advertisment offering a solution to “Bee problems”. Taking a right turn at the old abandoned firework shop, and crossing the railroad tracks will put you on course for a winding journey through a thick pine forest. On either side of the road there are wooden houses, and there’s a scrapyard.

A few miles further down the road there’s a left turning, and the first indication of the goliath which lies in these woods. A sign stands by the turning avertising “LIGO Livingston Observatory”. You cross a cattle-grid in the road before driving down LIGO Road for a mile or so, until you reach a straight section of road which has traffic cones on either side, and down the middle. “Slow: Experiment in Progress” the signs warn; “10 MPH SPEED LIMIT” reads another. The end of the road is barricaded; you need to press a button to enter.

“Control room!”, the voice will say, “The gate’s opening, come on in. But keep it slow, we’re observing”, they might continue, if you’ve been granted access. You’ve arrived at the epicentre of an event which shook the scientific world in 2016. You’ve arrived at the observatory which detected gravitational waves. As you drive into the parking lot you’ll catch a glimpse of a structure which extends off into the distance, cutting the forest in two.

LIGO is where the story I want to tell you starts, but it’s a fairly long story, and you might have heard bits of it before. It’s also a story which hasn’t ended, though I’ve got to a point where I think I can make it pretty interesting. You see, I arrived in Baton Rouge three months ago to spend some time working at LIGO, and my time there has now come to an end. It’s been an experience I’ll never forget. But why was I here?

A story 100 years in the making

To really understand why there’s an observatory deep in rural Louisiana I need to talk a bit about physics, specifically about one of the great achievements of 20th century physics: the General Theory of Relativity. By 1915 Albert Einstein had already risen to fame within the physics community as a result of his 1905 formulation of a “Special” Theory of Relativity, a theory so called as it was only valid under special circumstances. It took him a decade to develop this into a theory which was generally valid. Today that theory is the basis for our entire theoretical understanding of gravity. It’s a theory which has been tested time and time again, and withstood those tests. By 1916 Einstein had spotted a consequence of his work, which was probably inspired by the work of the Scottish scientist James Clerk Maxwell (whose work had already been a major motivation for the development of Special Relativity). A few decades before Maxwell had developed a theory which explained how light propagates through the vacuum of space as a wave-like excitation of electrical and magnetic fields at a fixed, constant speed. Einstein noticed that the same mathematical structures existed in his General Theory of Relativity; a suggestion that a wave could travel through a gravitational field.

In the end Einstein persuaded himself that this phenomenon was actually a mathematical curiosity, and would be undetectable (there are both mathematical and physical reasons which make this a fairly reasonable line of logic on some level). The idea of “gravitational waves” would of out of fashion again for decades, until a meeting of physicists in North Carolina in 1957, where a young researcher, Felix Pirani, presented a paper which would lay the groundwork for a mathematical framework in which gravitational waves could not only be better understood than when Einstein first tackled the idea in 1916, but which would also provide convincing reasoning for their physical existence. Even persuaded of their existence, however, few physicists would be convinced that they could ever be detected.

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