LIGO (the Laser Interferometer Gravitational-Wave Observatory) has just announced the first ever direct detection of gravitational waves. These are ripples in spacetime itself, propagating at the speed of light, and are a prediction of Einstein’s 1915 General Theory of Relativity. They should be produced copiously in many astrophysical processes, but they are so difficult to detect that only waves produced in extremely energetic processes are detectable. The signal seen by LIGO, for example, is from the collision of two black holes, of mass 29 and 36 times the mass of our sun, and resulting in about 3 solar masses being converted into gravity wave energy in a fraction of a second. The peak power was about 50 times that of the entire visible universe!
This is a major discovery, not only for the confirmation of a long-standing prediction of general relativity, but because it opens a new window on the structure of the universe. The era of gravity wave astronomy has dawned!