There is a vast literature near the topic of this post, much of which has developed specialized vocabularies and concepts. And I can’t be bothered to master enough of it to make this post match it well. So please try to treat my words here as if their meanings came from other less specialized literatures.

Consider three kinds of systems: Experience - Seen from the inside, a mind is aware of, can reason about, and might even “feel” a structure of experiences across time. These experiences are differentiated in many ways, and have many relations to each other. Brain - In brains, signals pass from nodes to nodes, and each node collects input signals, transform those according to patterns, changes its internal state, and then sends signals out.

A standard reduction view, which is also my view, is that each experience system is made of some part (perhaps all) of a particular brain system, which is then made of a some part of a physical world system. When system A is “made of” system B, then A descriptions drop detail from and abstract from details of B systems, but add almost nothing that isn’t implicit in B. A complete description of B could in principle be used to calculate an almost complete description of A.

I know of two claimed exceptions to this physics view. The first claimed exception is that some physical worlds are “actual” while others are just “possible”. The second claimed exception is that some experience systems are said to “actually” feel their experiences, while other similar systems with similar POS do not actually feel, but are instead “zombies” that only mimic real feelings.