Hydroelectric power – during a drought

FEW PEOPLE HAD HEARD

of the Laser Interferometer Gravitational-wave Observatory before it shared news in February that it had confirmed the existence of gravitational waves, a phenomenon Albert Einstein predicted back in 1916. But that doesn’t mean it wasn’t there. LIGO, which is actually two enormous L-shaped scientific instruments called laser interferometers – one in Hanford, Washington and another in Livingston, Louisiana – first opened in 1999 and ran for years before upgrading in 2007.

That initial run was sort of an experiment. No one had ever tried to find gravitational waves before. The ripples in space-time are caused by events like stars collapsing and black holes colliding. The only way to know if one has passed is to detect a tiny signal, the result of microscopic stretching and compression of the Earth, on two identical laser interferometers, set many kilometres apart. The interferometers work by splitting a beam of light in half and sending it down both arms of the L simultaneously. Each beam hits a mirror at the end of its arm, which sends the beam back to a photodetector. When the beams reach the detector, they cancel each other out. The sensor sees nothing until a gravitational wave bounces through, stretching space so that the arms themselves lengthen and shorten by a distance as small as one ten-thousandth the diameter of a proton and some light waves make it to the sensor. In those first eight years, scientists found nothing. But they did learn how to increase potential signal and decrease noise from things like earthquakes. So they closed the facilities down and built an even better version.

When the new, improved LIGO opened in 2015, just months before it detected its first wave, the lasers were 20 times more powerful, the mirrors were more reflective and it had a souped-up vibrationisolation system – a four-stage hanging set-up that passively reduces shaking by a factor of a trillion and a two-stage seismicreduction platform that actively counteracts the motion of the Earth. “The analogy I like to give is that the first interferometer was a family sedan, but the new one is a Ferrari,” says LIGO executive director David Reitze. And now it even has a bunch of awards on the dash.