Unformatted text preview: and timelike if It is said to be lightlike if Points on the light cone described above are lightlike separated from the origin. To be precise, the points corresponding to an outgoing shell of light from a flash at the origin at t = 0 form the forward light cone . Since the equation depends only on t 2 , there is a solution with t negative, the “backward light cone”, just the reflection of the forward light cone in the plane t = 0. Possible causal connections are as follows: an event at the origin (0, 0, 0, 0) could cause an event in the forward light cone: so that is the “future”, as seen from the origin. Events in the backward light cone—the “past”—could cause an event at the origin. There can be no causal link between an event at the origin and an event outside the light cones, since the separation is spacelike: outside the light cones is “elsewhere” as viewed from the origin....
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 Fall '10
 DavidJudd
 Physics, Light, Spacetime, light cone, forward light cone

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