Figure 6

Figure 6: Fermi normal coordinates of a point x relative to a world line γ. The time coordinate t selects a particular point on the word line, and the disk represents the set of spacelike geodesics that intersect γ orthogonally at z(t). The unit vector ωa := ˆxa ∕s selects a particular geodesic among this set, and the spatial distance s selects a particular point on this geodesic.