转: Being 1.3 billion light years away means that these black holes collided 1.3 billion years ago. The gravitational waves have been travelling through space for 1.3 billion years. When they arrived at Earth on 12 Sept. 2015, they caused the LIGO machinery to move by 1/1000 of the width of a proton particle. LIGO detected it. Amazing. _(:з」∠)_