“Everettian worlds are the same way. We don’t need to keep track of the entire wave function to make useful predictions, just what happens in an individual world. To a good approximation we can treat what happens in each world using classical mechanics, with just the occasional quantum intervention when we entangle with microscopic systems in superposition. That’s why Newton’s laws of gravitation and motion are sufficient to fly rockets to the moon without knowing the complete quantum state of the universe; our individual branch of the wave function describes an emergent almost-classical world.”