Wigner's Friends and Relations

          @misc{ pirsa_PIRSA:25100071,
            doi = {10.48660/25100071},
            url = {https://pirsa.org/25100071},
            author = {},
            keywords = {Quantum Foundations},
            language = {en},
            title = {Wigner{\textquoteright}s Friends and Relations},
            publisher = {Perimeter Institute},
            year = {2025},
            month = {oct},
            note = {PIRSA:25100071 see, \url{https://pirsa.org}}
          }
          

Abstract

"Wigner's Friend is a variant of the Schrödinger's cat experiment in which the cat is replaced by a Friend, the difference being that the Friend is unambiguously a conscious agent who experiences definite measurement outcomes. It has received renewed attention in recent years due to the development of several Extended Wigner's Friend (EWF) arguments, aimed at ruling out certain kinds of Copenhagenish interpretations. In this talk, I will discuss the origins of Wigner's Friend in von Neumann and Wigner's discussions of what we now call the Orthodox interpretation of quantum mechanics. I will then discuss how the argument was taken up by Everett and his followers, generalized by Deutsch, and then more recently brought into the Copenhagenish context. Along the way, I emphasize how each variant of the argument has different implications for the Orthodox, Everett and Copenhagenish interpretations, concluding that all three interpretations require a theory of quantum mechanical agents in order to be complete. I outline some first steps towards such a theory."