Figure 6

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