Self-tying shoes Self-tying shoes Self-tying shoes (also known as "self-lacing" or "power laces") are designed to automatically tighten once the user puts them on. Such shoes were initially depicted in the 1989 science fiction film "Back to the Future II". In April 2009, Nike filed a patent for self-lacing shoes, with a design that bears a resemblance to those worn by Marty in the film "Back to the Future II", raising speculation among fans about a possible debut of self-lacing shoes. In 2014, Tinker Hatfield, the designer of the original Nike shoes as depicted in "Back to the Future II", indicated that
Time travel causal future of the world line is also in its causal past, a situation which is akin to time travel. Such a solution was first proposed by Kurt Gödel, a solution known as the Gödel metric, but his (and others') solution requires the universe to have physical characteristics that it does not appear to have, such as rotation and lack of Hubble expansion. Whether general relativity forbids closed time-like curves for all realistic conditions is still being researched. Wormholes are a hypothetical warped spacetime which are permitted by the Einstein field equations of general relativity. A proposed time-travel machine using