I emit photons in all directions, their paths in spacetime define what is
usually called the "lightcone" whose bottom lies at my present moment. Because of the limitation c imposes, the
worldlines for anyone moving past me, regardless of their speed, will lie
within this lightcone, and so will any and all the events which I can
influence. The region of spacetime
within my lightcone is called the causal future; the events which can
influence me lie within my causal past.
Events lying in the region between my causal future and causal past,
called my elsewhere, have no causal
relation to me.
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