“Gravitational waves are distortions or ‘ripples’ in the fabric of space-time, caused by some of the most violent and energetic processes in the Universe.”
In 1916, Einstein proposed his theory of gravitational waves in his general theory of relativity.
Einstein’s General Theory of Relativity basically states that gravity is a result of the ‘curvature’ of spacetime; and that matter and/or energy can “stretch or warp” these curvatures.
Evidence for the existence of gravitational waves first arrived in 1974 when two astronomers at the Arecibo Radio Observatory in Puerto Rico discovered two very dense & heavy stars in orbit around each other.
After 8 years of observation, they found that the stars got closer to each other at the rate proposed by the general relativity theory.
They have since observed the system for 40 years and the changes in orbit still correspond to the general relativity theory.
On September 18, the scientists at LIGO received a signal from their detector in Louisiana & a second signal from their Washington detector a few milliseconds later.
The scientists determined after analyzing the data with a few equations that it had been two black holes that caused the signal.
Basically, we now have visual & audible evidence for what Einstein predicted 100 years ago!