Time travelling eh? It's a tricky business. And it's a subject that movies have long been pretty well obsessed with, despite the logistical minefield.
Even the characters in Rian Johnson's brilliant new film Looper (which opens here next week), find it causes chaos.
"This time-travel crap fries your brain like an egg," says Jeff Daniels' crime boss character Abe - and he's from the future.
The thing is, Looper pulls it off beautifully, in no small part because of the engrossing plot line and some great turns by Joseph Gordon-Levitt, Emily Blunt, and Bruce Willis. Despite the blurry lines and confusion, Johnson also manages to make it deeply affecting - and that ultimate question of whether you can change events or whether history has already been set, is nicely toyed with for the audience.
But there are plenty of past examples where the time travel doesn't quite work, which begs the questions: what makes it entertain and engage; and what makes it distracting and confusing?