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Phoenix666 [soylentnews.org] writes:

If we can walk backwards and forwards in space, why not in time [npr.org]?

Scientists, especially theoretical physicists, like to play such games — controlling time with pencil and paper. Going forward in time, traveling to the future, is actually OK, according to the Theory of Relativity. All we need is a super-fast spaceship, traveling close to the speed of light. A technological, and not a conceptual obstacle.

Going back in time is more complicated. Much more. Remarkably, closed-time loops are not just the stuff of sci-fi stories. (Why a closed-time loop? Most people don't want to go back in time and be stuck there. A short visit to the past should suffice.) In 1949, the brilliant Austrian mathematician Kurt Gödel found a solution of Albert Einstein's equations of general relativity where it is possible, at least theoretically, to travel in a circle in time as we can in space, returning back to the starting point. The movie brilliantly plays with this notion, not least since 13.7's own Adam Frank worked as a scientific consultant [npr.org].

In practice, Gödel's solution and any of its modern versions are a very, very long shot. There are issues with how to keep such spacetimes from collapsing upon themselves, not to mention weird time paradoxes like the Grandfather Paradox [uoregon.edu]: If you travel back in time and kill your grandfather before he marries, would you exist? However, in a Marvel universe it is possible. When Dr. Strange discovers that he has this power, we see a disturbingly beautiful image of an apple being eaten and reassembled again and again, a small patch of space where a closed-time loop is possible.

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