User:Mpatel/sandbox/Light cone

In special relativity, a light 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 $$t_0$$, 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 $$E$$.


 * Events in the absolute elsewhere of $$E$$ are those that can never be affected by $$E$$.

If space is measured in light-seconds and time is measured in seconds, the cone will obviously have a slope of 45°, because light travels a distance of one light-second in a vacuum during one second. Since special relativity requires the speed of light to be equal in every inertial frame, all observers must arrive at the same angle of 45° for their light cones. This is ensured by the Lorentz transformation.

In general relativity, the future light cone is the boundary of the causal future of a point and the past light cone is the boundary of its causal past.

External link

 * The Einstein-Minkowski Spacetime: Introducing the Light Cone
 * The Paradox of Special Relativity

Con de llum Category:Astrophysics Category:Relativity