File:Relativity Of Simultaneity.svg
Event B is simultaneous with A in the green reference frame, but it occurred before in the blue frame, and will occur later in the red frame.
The upper highlighted area is A's future cone, consisting of the events which will occur after A in any reference frame. The lower highlighted area is A's past cone, consisting of the events which occurred before A in any frame. The interior consists of the events from which a massive particle could have reached A, or which can be reached by a massive particle starting at A. The surface of the light cone: the events which can be reached by a light ray starting at A, or from which a light ray reaching A could have originated. The black areas outside the double cone consist of the events whose temporal ordering with respect to A depends on the frame of reference.
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