  Semiclassical gravity and the holographic description of the static patch of
de Sitter space appear to disagree about properties of correlation functions.
Certain holographic correlation functions are necessarily real whereas their
semiclassical counterparts have both real and imaginary parts. The resolution
of this apparent contradiction involves the fact that time-reversal is a gauge
symmetry in de Sitter space -- a point made by Harlow and Ooguri -- and the
need for an observer (or quantum reference frame) as advocated by
Chandrasekaran, Longo, Penington, and Witten.
