Figure 28: Instantaneous wave fronts in
the spacetime of a transparent string of finite radius with and . The picture is related to
Figure 25 as Figure 27 is
related to Figure 24. Instantaneous wave
fronts that have passed through the string have a caustic,
consisting of two cusp ridges that
meet in a swallow-tail point. This caustic is stable (see
Section 2.2). The caustic of the light cone in Figure 25 is the
union of the caustics of its instantaneous wave fronts. It consists
of two fold surfaces that meet in a
cusp ridge, like in the third picture of Figure 2.
|