  The idea of constructing a time machine is not new and even received a boost
thanks to the realization that a traversable wormhole could be converted to a
time machine. This also implied that it would be impossible to travel back in
time beyond the creation of the time machine. This paper addresses these
issues, as well as the concomitant causality violations, by starting with a
physically acceptable model, a spacetime that is anti-de Sitter due to an extra
time-like dimension, thereby allowing the existence of closed time-like curves.
By assuming that the extra dimension is independent of the radial coordinate,
the wormhole retains its basic geometric properties regardless of its location
and can therefore serve as a shortcut for any closed time-like curve, which, in
turn, can extend indefinitely into the past. The same independence of the
radial coordinate suggests that the wormhole could connect a region in the
present to a local region that (1) lies in the past and (2) does not contain
any closed time-like curves. Previous studies have suggested that if such a
region is sufficiently localized, it may be possible to avoid a causality
violation.
