= Observer horizons in two-dimensional de Sitter spacetime
{title2=$d(\chi,0)<\pi/2-T\quad\text{or}\quad d(\chi,0)<T+\pi/2$}
For the complete observer $\chi=0$ in <two-dimensional de Sitter spacetime>, let $d(\chi,0)\in[0,\pi]$ be shortest angular distance. An event can signal to the observer exactly when $d(\chi,0)<\pi/2-T$, and can receive its signals exactly when $d(\chi,0)<T+\pi/2$. Equality describes its future and past <observer event horizons>. Their intersection is the <static patch of de Sitter spacetime> containing the observer. These are observer-dependent cosmological horizons; constant-$T$ circles are <Cauchy hypersurfaces>, so there are no <Cauchy horizons> in the full spacetime.
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