future lightcone

The future lightcone is a cone-shaped portion of spacetime containing all (future) locations at which light could arrive after having departed from a particular location within spacetime (the tip of the cone). Points inside the cone can be reached at the speed of light or slower and points on the surface only at the speed of light. Since nothing can travel faster than light, points outside the cone cannot in any way be affected by the tip. See light cone.