Compatibility of implicit and explicit observers in quantum theory and beyond

          @misc{ pirsa_PIRSA:18040084,
            doi = {10.48660/18040084},
            url = {https://pirsa.org/18040084},
            author = {Galley, Thomas},
            keywords = {},
            language = {en},
            title = {Compatibility of implicit and explicit observers in quantum theory and beyond},
            publisher = {Perimeter Institute},
            year = {2018},
            month = {apr},
            note = {PIRSA:18040084 see, \url{https://pirsa.org}}
          }
          

Abstract

The observer is implicitly present in the measurement postulates of quantum theory. However the observer can also be modeled as a quantum system interacting with other quantum systems. A theory where every action implicitly undertaken by an agent (such as a measurement or preparation) can be explicitly modeled as non-classical systems interacting is called a universal theory. By modifying the measurement postulates of quantum theory (and preserving the other postulates) we create theories where the observer can still be explicitly modeled as a pure quantum state, but where the implicit observer is different. We argue that any modification of the measurement postulates of quantum theory gives a theory which is not universal. That is to say there are certain actions implicitly carried out by an agent which cannot be explicitly modeled.