Spacetime fabric. Mass tells spacetime how to curve, and spacetime tells matter how to move. The woven sheet is spacetime: black holes sink into it, specks of stardust roll across it and spiral into the wells, and when two black holes merge they shake the whole weave with gravitational waves, the ripples first heard by LIGO in 2015. Drag a black hole to move it · drag the fabric to turn it · click to drop a new one.
Spacetime fabric
In general relativity, gravity is not a force: it is the shape of spacetime itself.
How it works
A sheet that curves. Here spacetime is drawn as a woven sheet. Each black hole sinks into it, and the stardust rolls along the slopes, orbiting and spiralling down into the wells.
Black holes merge. When two black holes come close they lose energy by radiating gravitational waves, so they spiral in faster and faster until they become one. The waves spread out as a ripple through the whole fabric. LIGO first heard such a merger on 14 September 2015, from 1.3 billion light years away.
What is real and what is not. The rising chirp, the quadrupole pattern of the ripples and the ringing of the final black hole follow the physics; the size and speed of everything are stretched so that the eye can follow them.