A nice video by minutephysics analysing different forms of time travel in fiction.

… an explanation of how time travel functions in different popular movies, books, & shows – not how it works “under the hood”, but how it causally affects the perspective of characters’ timelines (who has free will? can you change things by going back to the past or forwards into the future?). In particular, I explain Ender’s Game, Planet of the Apes, Harry Potter and the Prisoner of Azkaban, Primer, Bill & Ted’s Excellent Adventure, Back to the Future, Groundhog Day, Looper, the video game “Braid”, and Lifeline.