“Sliding Doors.” Or “Bridget Jones’ Chaos Theory,” merging a Cool Britannia women’s sitcom and the Philosophy Lite of parallel realities. Paltrow, an unemployed London publicist, takes the tube home to catch her novelist boyfriend shagging an American harpy, then dumps him, gets a fab hairdo, starts her own PR firm, and hooks up with a new duplicitous guy. And she also misses the train, gets mugged, then sullenly waits tables, a morally conflicted boyfriend still surreptitiously shagging throughout. The story is hackneyed, and the gimmick only doubles the dullardry. On the other hand, a small sadistic joy adheres to watching patrician Paltrow’s downtrodden flack treated like a doormat.