According to Einstein, whenever massive objects interact, they produce gravitational waves -- distortions in the very fabric of space and time -- that ripple outward across the universe at the speed of light.
While astronomers have found indirect evidence of these disturbances, the waves have so far eluded direct detection. Ground-based observatories designed to find them are on the verge of achieving greater sensitivities, and many scientists think that this discovery is just a few years away.