Gravitational waves from merging black holes were directly detected in 2015.

For a century, ripples in the fabric of spacetime were just a theory. Then, the LIGO detectors felt a tiny tremor. Two black holes, millions of light-years away, spiraled into each other and merged. The collision shook the very fabric of the cosmos. It converted three times the mass of our Sun directly into pure gravitational energy, sending out waves we could finally measure on Earth.