Tachyonic chaos and causality in the open universe

The chaoticity of classical world lines in extended Robertson-Walker cosmologies is pointed out and related to the fractal limit set of the covering group of the spacelike slices. We investigate the possible existence of tachyons (faster-than-light particles) in this context. The cosmic time and the 3-space co-ordinates comoving with the galactic background provide a distinguished frame of reference. With respect to this comoving frame the causality of tachyonic events can be unambiguously defined, contrary to Minkowski space. We study the dynamics of tachyons and show that tachyonic world-lines are chaotic in the center of the spacelike slices.