This figure illustrates the nonzero "vorticity" of the timelike congruence of world lines of "Langevin observers", who rotate about the axis r=0 in cylindrical coordinates with angular velocity ω. In the figure, the red curve represents the world line a fiducial Langevin observer, together with two gold light cones with three frame vectors (the fourth frame vector is inessential and has been suppressed). The blue dashed curves represent the world lines of neighboring Langevin observers, which twist about the red curve. The cyan curve shows that the spatial frame vectors are rotating to radial symmetry, so the Langevin frame is spinning as well as non-inertial. This figure was created by User:Hillman using eog to convert to png format a jpg image exported from a Maple session.