8. Back to the Future: Marty’s parents’ bad memory - Even though Marty is only in 1955 for a week, he plays a pretty pivotal role in his future parents’ lives. It stands to reason, then, that they would remember him pretty well, don’t you think? Now, I’m not George McFly, but most men would probably have a few questions if one of their children grew up to look exactly like a friend from high school that their wife dated briefly.
2. The Empire Strikes Back: Time dilation - Luke and R2D2 leave Hoth to go to Dagobah at the same time Han, Leia, Chewbacca, and C3PO leave to go… well, they never really say what their initial destination is. Anyway, on Dagobah, Luke embarks on an intensive Jedi training course with Yoda — it’s never stated, but it’s heavily implied that this takes a long time... So, at the same time that Luke finishes this months-long training and runs off to Cloud City, his friends have clearly just gotten there a short time before. Yet all they did on the way was flee from a Star Destroyer and fly down the gullet of a giant space worm. That must have taken hours, not months. So was the Millennium Falcon flying at close to the speed of light (but not at light speed) for a while and thus experiencing time dilation? Yeah, that’s the ticket.
--Matt Blum, Wired, on temporal problems in sci-fi