This set up introduces 3 major problems into the film, before we even get to the love story. First, in the 5 minute breathy introduction to the movie by Sturgess, he sounds like a teenage girly girl who's having to present a science project to class, and that's not very attractive. Second, it's never a good idea to introduce something that's complete bunk the second we start watching the film. We've nothing invested in it, so why should we buy into it? Thirdly we're told that gravity only works on the things from a particular world. So up world attracts up things (like Dunst), while sh**y down world only attracts how things. That beggers the question, how is it possible to have "up world" strip mine you of your stuff? How in the world are they going to hold onto it, while they purify it?
The two do meet and fall in love, but by that stage, it all feels contrived, and so far beyond belief that you've stopped caring any more. There are analogies aplenty in this film, it's just by the end, you'd have wished they'd stopped trying to tell you a morality play, and just had fun with it all.