The Other Half of Quantum Geometry: A First Glimpse

We point out that a proper treatment of quantum gravity ought to take into account the quantum nature of the probes used to unravel spacetime geometry. As a first step in this direction, we use extended classical probes in the study of the geometry of a classical manifold. We comment on a limitation of the standard Dixon-Beiglbock center-of-mass prescription, adopt in its place that of the centroid, appropriately generalized to curved spacetimes, and calculate explicitly the effective sectional curvature of de Sitter spacetime using a two-point-particle probe.