I will tell you what I think I have learned, said Galileo. I have learned that information only exists if there is a difference that makes a difference. For how would anything exist, if nothing can make a difference to it? How could it exist, if it has no choice—an element with only one possible state? I have learned that information and causation are one and the same thing, and that is all there is: what exists must be a difference that makes a difference, a choice that’s causal.
