>>In special relativity, a light cone (or null cone) is the pattern describing the temporal evolution of a flash of light in Minkowski spacetime. This can be visualized in 3-space if the two horizontal axes are chosen to be spatial dimensions, while the vertical axis is time.
The light cone is constructed as follows. Taking as event p a flash of light (light pulse) at time t0, all events that can be reached by this pulse from p form the future light cone of p, whilst those events that can send a light pulse to p form the past light cone of p.
Given an event E, the light cone classifies all events in spacetime into 5 distinct categories:
* Events on the future light cone of E.
* Events on the past light cone of E.
* Events inside the future light cone of E are those which are affected by a material particle emitted at E.
* Events inside the past light cone of E are those which can emit a material particle and affect what is happening at E.
* All other events are in the (absolute) elsewhere of E and are those that will never affect and can never be affected by E.