Double-edged sword, Google. Basically? You're in another world. Think alternate dimension. Basically, this one had an apocalypse, there was a biblical Seal (like the lock) that got broken and fucked up the barriers between worlds, and now people get slipped through the cracks into this one.
I've a theory about other worlds leech through to others via the human subconscious and it gets put down as fiction, which is why some of us know each other as story characters.
It was a damn good movie, if that makes you feel any better.