Cosmic strings are hypothetical defects resulting from the creation of the universe. They are believed to have been formed when ancient forcefields were frozen in the fabric of spacetime due to collision or the inflation of superstrings. If you think of a black hole as one infinitely small point in the spacetime continuum, a cosmic string would be a 2 dimensional infinitely thin line.
If such strings exist, and one could maneuver 2 of them close together, it is possible in theory to create a closed time-like curve, on which one could travel to any place in time.
If such strings exist, and one could maneuver 2 of them close together, it is possible in theory to create a closed time-like curve, on which one could travel to any place in time.