Making Perspectives Physical

My first talk left out physical details of key ideas in a pragmatist sketch of quantum theory. This talk is about what needs to be done to complete the picture.

Relational Quantum Mechanics (RQM), QBism, and my pragmatist view (DP) all take a quantum state to relate a system to something else, but they disagree about what that is. DP takes it to be a physical situation, but of just what kind? The second key idea was environmental decoherence. This is needed to say what the Born rule assigns probabilities to, and to make sense of relative facts such as measurement outcomes in a EWFS. Rapid and permanent diagonalization of a subsystem density operator is only a very good approximation: and it does not say what happens to the subsystem if its quantum state represents none of its properties. So how can we say when a system acquires a property, or when even a relative fact emerges as a result of environmental decoherence? And can quantum Darwinism help explain why we all observe the same outcome of a quantum measurement?