Advanced LIGO, the newest iteration of the LIGO experiment has finally turned on. LIGO is a gravitational wave observatory using extremely high precision interferometers to look for signatures of gravitational waves hitting Earth. Advanced LIGO is meant to finally have enough sensitivity to have a decent likelihood of finding gravitational waves within a reasonable amount of time.
Finding direct evidence of gravitational waves would be a huge discovery, as that would confirm an important prediction of the theory of general relativity, which states that mass warps the shape of spacetime. Events such as black hole mergers are thought to generate measurable gravitational waves due to the huge gravitational forces governing their dynamics.