A girl observes one of two vacuum chambers measuring four kilometers in length during a public tour of the Laser Interferometer Gravitational-Wave Observatory (LIGO) at the Hanford Site in Richland, Washington, U.S., on Saturday, Feb. 13, 2016. Scientists have discovered the existence of gravitational waves, tiny ripples in the fabric of space-time, which have long been predicted but never before been seen or measured. Photographer: David Ryder/Bloomberg via Getty Images

A girl observes one of two vacuum chambers measuring four kilometers in length during a public tour of the Laser Interferometer Gravitational-Wave Observatory (LIGO) at the Hanford Site in Richland, Washington, U.S., on Saturday, Feb. 13, 2016. Scientists have discovered the existence of gravitational waves, tiny ripples in the fabric of space-time, which have long been predicted but never before been seen or measured. Photographer: David Ryder/Bloomberg via Getty Images