  In dynamic spacetimes in which asymmetric gravitational collapse/expansion is
taking place, the timelike geodesic equation appears to exhibit an interesting
property: Relative to the collapsing configuration, free test particles undergo
gravitational "acceleration" and form a double-jet configuration parallel to
the axis of collapse. We illustrate this aspect of peculiar motion in simple
spatially homogeneous cosmological models such as the Kasner spacetime. To
estimate the effect of spatial inhomogeneities on cosmic jets, timelike
geodesics in the Ricci-flat double-Kasner spacetime are studied in detail.
While spatial inhomogeneities can significantly modify the structure of cosmic
jets, we find that under favorable conditions the double-jet pattern can
initially persist over a finite period of time for sufficiently small
inhomogeneities.
