Gott loop

A Gott loop is a hypothetical structure, discovered in 1991 Princeton physicist J. Richard Gott, that is made from two cosmic strings – long filaments of compressed matter postulated by some theorists to have formed in the Big Bang. Gott found that two of these structures, arranged in parallel and moving in opposite directions, could serve as a time machine by warping spacetime and allowing travel into the past (but not the future). He later reworked the idea to involve a single cosmic-string loop.