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Light coneIn 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 3space if the two horizontal axes are chosen to be spatial dimensions, while the vertical axis is time. Additional recommended knowledgeThe 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:
If space is measured in lightseconds and time is measured in seconds, the cone will have a slope of 45°, because light travels a distance of one lightsecond in 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. Elsewhere, an integral part of light cones, is the region of spacetime outside the light cone at a given event (a point in spacetime). Events that are elsewhere from each other are mutually unobservable, and cannot be causally connected. Lightcones in general relativityIn 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. In a curved spacetime, the lightcones cannot all be tilted so that they are 'parallel'; this reflects the fact that the spacetime is curved and is essentially different from Minkowski space. In vacuum regions (those points of spacetime free of matter), this inability to tilt all the lightcones so that they are all parallel is reflected in the nonvanishing of the Weyl tensor. See also

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Light_cone". A list of authors is available in Wikipedia. 