Watching Looper last night I became exasperated with film makers for not getting time travel right. The model of time travel that they use suffers from the grandfather paradox. After the film I tried to explain time (with diagrams!!) to my friends, but everyone left immediately. I'm going to try again via the medium of the internet.
In my childhood I spent lots of happy hours playing Monopoly with my brother. He usually won. Anyway, when you look at a game of Monopoly you can vaguely tell how far through the game you are. If there aren't any properties bought, and everyone's still in the game, you know you're at the beginning. If there are just two players left and there are hotels everywhere you know you're probably nearing the end.
Monopoly is like the multiverse. The state of the game is like a universe. In the real world if you take a sequence of photos, say of an ice cube melting, if the order of the photos get muddled up you can easily put them back in order.
Similarly, with Monopoly if you took a sequences of photos of the game and then muddled them up, someone could probably put them back in order.
The thing is that in Monopoly you can sometimes go back in time. A common example is getting the 'Go Back To The Old Kent Road!' card. In this case the person putting the muddled photos back in order might get it slightly wrong.
Or everyone could actually decide to go back in time by selling houses, hotels and properties. If they did that, they could make it really difficult for someone to reconstruct the order of the photos. This is time travel, and you can see that there it doesn't suffer from the grandfather paradox, or any other problems.
So film makers, could you use the Monopoly model of time travel in all future films please?