Light Cone

Each point in space-time has both a past (-) and future (+) light cone corresponding to the two poles of the Feynman propagator in the momentum-energy hologram of space-time.

The principle of “retarded causality” is that signals can only propagate either inside or on the forward light cone.

Each point in space-time has both a past (-) and future (+) light cone corresponding to the two poles of the Feynman propagator in the momentum-energy hologram of space-time.