  At first glance, it seems possible to construct in general relativity theory
causality violating solutions. The most striking one is the Gott spacetime. Two
cosmic strings, approaching each other with high velocity, could produce closed
timelike curves. It was quickly recognized that this solution violates physical
boundary conditions. The effective one particle generator becomes hyperbolic,
so the center of mass is tachyonic. On a 5-dimensional warped spacetime, it
seems possible to get an elliptic generator, so no obstruction is encountered
and the velocity of the center of mass of the effective particle has an overlap
with the Gott region. So a CTC could, in principle, be constructed. However,
from the effective 4D field equations on the brane, which are influenced by the
projection of the bulk Weyl tensor on the brane, it follows that no asymptotic
conical space time is found, so no angle deficit as in the 4D counterpart
model. This could also explain why we do not observe cosmic strings.
