Rockets can propel themselves through the nothingness of space because of two fundamental laws of physics: Newton’s Third Law and the Conservation of Linear Momentum. Both ideas are essential to understanding how nearly everything in the universe moves. When an ice skater takes off from a dead stop, she digs her blade into the ice and the ice pushes back with an equal and opposite force, sending her gliding across the rink. When a cannon is fired, the cannonball goes hurtling through the air while the cannon recoils backward in response. Both of these principles stem from the same general idea: that the universe likes to keep everything in balance.