LIGO co-founders Kip Thorne speaks about the discovery that scientists have observed the ripples in the fabric of spacetime called gravitational waves for the first time, confirming a prediction of Albert Einstein's theory of relativity, during a press conference at the National Press Club in Washington, DC, February 11, 2016. The machines that gave scientists their first-ever glimpse at gravitational waves are the most advanced detectors ever built for sensing tiny vibrations in the universe.The two US-based underground detectors are known as the Laser Interferometer Gravitational-wave Observatory, or LIGO for short. / AFP / SAUL LOEB (Photo credit should read SAUL LOEB/AFP via Getty Images)