The third Chris Fields lecture of "Physics as Information Processing" course:
https://www.youtube.com/live/TOZp_XNYijQ

Session 3: introduce the ideas of quantum reference frames (QRFs) and their representation using hierarchies of binary classifiers. These formal structures provide a semantics for measurements, and hence provide the basis for a theory of meaning for interacting agents. The language of QRFs allows a particularly straightforward and intuitive definition of variational free energy, and so allows a fully-general, quantum formulation of the FEP. We will see that the FEP is a classical limit of the principle of Unitarity, the fundamental principle of quantum theory.

Course syllabus

Discussions at AII Discord server