  Traditional geometry employs idealized concepts like that of a point or a
curve, the operational definition of which relies on the availability of
classical point particles as probes. Real, physical objects are quantum in
nature though, leading us to consider the implications of using realistic
probes in defining an effective spacetime geometry. As an example, we consider
de Sitter spacetime and employ the centroid of various composite probes to
obtain its effective sectional curvature, which is found to depend on the
probe's internal energy, spatial extension, and spin. Possible refinements of
our approach are pointed out and remarks are made on the relevance of our
results to the quest for a quantum theory of gravity.
