The highlight of Upside Down—a sci-fi romance set in a world with, per the film's lengthy prologue that vaguely recalls the intro to Lady Gaga's "Born This Way" video, twin planets "each with its own and opposite gravity"—is the moment Adam (Jim Sturgess) inadvertently pisses on the ceiling. The bright yellow stream of urine cuts through writer-director Juan Solanas's otherwise icy palette and lends at least a fleeting moment of levity to a film whose awe-inspiring CG visuals and well-intentioned lead performances are weighed down by the screenplay's clever but not-entirely-cogent premise—which, in short, involves the prosperous world "up top" siphoning oil from "down below," pink bee pollen that can make Aunt Becky's pancakes levitate, and the smuggling of "inverse matter" for home heating.
Adam lands a job at TransWorld, the giant corporation responsible for the death of his parents in a refinery explosion, in order to reunite with his long-lost childhood sweetheart, Eden (Kirsten Dunst). By definition, sci-fi requires at least a minimal suspension of disbelief, but it's difficult to become engaged in these star-crossed lovers' plight when the film possesses such a fundamental misunderstanding of the laws of gravity—the very thing that's supposedly holding the whole story together. Simply entering the opposite world doesn't mean one is suddenly subject to that world's physical laws, and inanimate objects from one world don't adhere to the other's rules either. It makes for a few exhilarating set pieces, like Adam's accidental foray into water sports and a scene in which he escapes the world "up top" by falling out of a river and into a body of water "down below." But it's mostly just distracting for anyone with even a cursory knowledge of basic physics.
More troubling, however, is the love story itself. Solanas's lack of interest in attempting to disguise his archetypes is refreshing (though naming his characters Adam and Eden—because, you know, Eve would have been too on the nose—makes James Cameron's recasting of Romeo and Juliet in Titanic seem subtle), but he unnecessarily muddies the already convoluted plot by giving Eden amnesia and—spoiler alert—tacking on a denouement in which she lazily reveals she can suddenly traverse both worlds without bursting into flames because she's pregnant...with twins, of course! If their happily ever after wasn't enough, Adam breathlessly adds via voiceover that their love "would forever alter the course of history."