In the Copenhagen interpretation, what that measurement does is a magical rearrangement of the whole universe, faster than light. In quantum mechanics however, a thing can be in multiple states, and amazingly enough, you can still have the same kind of correlation. Their collision (and mutual measurement) has collapsed the state of the opposite ball (from the perspective of both balls). Just for fun, a very outside perspective: Say you’re in another star system, and you can’t get any real information about what’s going on. But, from your very outside perspective, Bob’s many states are searching for the ball’s many states.