My first post is inspired by the physicist and blogger Scott Aaronson, who recently blogged his criticisms about a theory I’ve been working on, called causal emergence. To see the simple nature of his error, skip down to Isn’t causal emergence just an issue of normalization?, although this does assume you are familiar with some of the theory's terminology. Since Scott's criticisms reflected a lack of understanding of the theory, it prompted me to do this generalized explainer. Please note this explainer is purposefully designed to not be technical, formalized, or comprehensive. Its goal is to give interested parties a conceptual grasp on the theory, using relatively basic notions of causation and information.
What’s causal emergence?
It’s when the higher scale of a system has more information associated with its causal structure than the underlying lower scale. Causal structure just refers to a set of causal relationships between some variables, such as states or mechanisms. Measuring causal emergence is like you're looking at the causal structure of a system with a camera (the theory) and as you focus the camera (look at different scales) the causal structure snaps into focus. Notably, it doesn’t have to be “in focus" at the lowest possible scale, the microscale. Why is this? In something approaching plain English: macrostates can be strongly coupled even while their underlying microstates are only weakly coupled. The goal of the theory is to search across scales until the scale at which variables (like elements or states) are most strongly causally coupled pops out.