An Observer's Measure of De Sitter Entropy

Abstract

The two-point correlation function of a massive field $\langle\chi(\tau)\chi(0)\rangle$, measured along an observer's worldline in de Sitter (dS), decays exponentially as $\tau \to \infty$. Meanwhile, every dS observer is surrounded by a horizon and the holographic interpretation of the horizon entropy $S_{\rm dS}$ suggests that the correlation function should stop decaying, and start behaving erratically at late times. We find evidence for this expectation in Jackiw-Teitelboim gravity by finding a topologically nontrivial saddle, which is suppressed by $e^{-S_{\rm dS}}$, and which gives a constant contribution to $|\langle \chi(\tau)\chi(0)\rangle|^2$. This constant might have the interpretation of the late-time average of $|\langle \chi(\tau)\chi(0)\rangle|^2$ over all microscopic theories that have the same low-energy effective description.