There is now a theory for what caused the end of the world in This Is The End — it's a zombie invasion.
Emma Watson shows up in the comedian bunker looking dirty, disheveled, and exhausted. She bided her time in a drain pipe while zombies apparently roamed around. Jay Baruchel is unconvinced zombies were the cause of the end though, so we're still not quite sure how this apocalypse came about. But we'll find out on June 12, when This Is the End comes out. Until then, maybe we should all follow Watson's example and grab the nearest ax — just to be safe.