Why all this excitement? The existence of gravitational waves is the last big prediction of Einstein’s theory of general relativity. General relativity is a theory of gravity that works amazingly well at the large scales of the universe, but has troubles blending with the other most successful physics theory of the 20th century, quantum mechanics, which instead explains amazingly well the realm of ’very small things’. Now, where is that general relativity and quantum mechanics don’t get along? For example on the edges of black holes. And what can produce gravitational waves? Well, indeed the merger of two black holes. Interestingly, this is what the rumors say LIGO has detected [Update: They did it!]. In general, gravitational waves can open a new window for astronomers to observe distant, dramatic events like the coalescence of neutron stars and certain supernovae explosions. Some of these events, like the merger of two black holes, would be otherwise completely invisible. Very exciting times ahead!