“Positronium is the simplest atom composed of equal-mass constituents, and until it self-annihilates, it behaves as a neutral ...

Until recently, gravitational waves could have been a figment of Einstein’s imagination. Before they were detected, these ripples in spacetime existed only in the physicist’s general theory of ...

Two black holes spiraled into each other in a spectacular collision 1.3 billion years ago. The black holes in a galaxy far, far away then merged, vibrated and produced gravitational waves, a type of ...