Past Lightcone A cone-shaped portion of spacetime containing all (past) locations from which light could arrive at a particular location within spacetime (the tip of the cone). The tip can be reached from points inside the cone at

spacetime. Events in the past which can influence event O lie inside what is called the past lightcone of O. Events which O can influence in the future lie inside what is called the future lightcone of O. Events which can neither influence O