 Observer event horizon

An observer's future event horizon bounds the events that can ever signal to its future-inextendible worldline. Its past event horizon bounds the events reachable by signals from its past-inextendible worldline. A complete inertial observer in Minkowski spacetime has neither. The uniformly accelerated worldline $t=a^{-1}\sinh (a\tau )$, $x=a^{-1}\cosh (a\tau )$ has $I^{-}(\gamma )=\{t-x<0\}$ and $I^{+}(\gamma )=\{t+x>0\}$. Their boundaries are its two Rindler horizons. This observer dependence is distinct from a black-hole horizon defined using future null infinity.