Einstein predicted ripples in spacetime in 1916. We didn't detect one until 2015.

On 14 September 2015, twin detectors in Louisiana and Washington State picked up a fleeting distortion in spacetime from two black holes colliding 1.3 billion light-years away. It matched Einstein's century-old prediction almost exactly and confirmed gravitational waves exist. Three of the project's founders won the 2017 Nobel Prize in Physics for it.

— LIGO Scientific Collaboration and Virgo Collaboration, Observation of Gravitational Waves from a Binary Black Hole Merger — Physical Review Letters, 2016