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 a flash of light (light pulse) at time , all events that can be reached by this pulse from form the future light cone of , whilst those events that can send a light pulse to form the past light cone of .
Given an event , the light cone classifies all events in spacetime into 5 distinct categories:
- Events on the future light cone of .
- Events on the past light cone of .
- Events inside the future light cone of are those which are affected by a material particle emitted at .
- Events inside the past light cone of are those which can emit a material particle and affect what is happening at .
- Events in the absolute elsewhere of are those that can never be affected by .
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.
See also
[edit]External link
[edit]- The Einstein-Minkowski Spacetime: Introducing the Light Cone
- The Paradox of Special Relativity