Against (unitary) interpretation (of quantum mechanics): removing the metaphysical load

          @misc{ pirsa_PIRSA:25100177,
            doi = {10.48660/25100177},
            url = {https://pirsa.org/25100177},
            author = {Zukowski, Marek},
            keywords = {Quantum Foundations},
            language = {en},
            title = {Against (unitary) interpretation (of quantum mechanics): removing the metaphysical load},
            publisher = {Perimeter Institute},
            year = {2025},
            month = {oct},
            note = {PIRSA:25100177 see, \url{https://pirsa.org}}
          }
          

Abstract

In June 1925 Heisenberg arrived at Helgoland/Heligoland island to escape a fit of hay fever. He returned with a sketch of a strange theory of the micro-world, which we now call quantum mechanics. This essay attempts to present a look at this theory, which tries to return to the original insight of Heisenberg on what should be the essence of a theory of atomic realm: it must be a theory of the observable events, in which fundamentally unobservable quantities have no place. No ontological status is given to elements of the mathematical formulation of the theory. The theory is about our description of events in laboratories, probabilities of which are given by the Born rule. Following Bohr, these events involve macroscopic measuring apparatuses, and the accessible final events are classically describable and "the unambiguous account of proper quantum phenomena must, in principle, include a description of all relevant features of experimental arrangement". . Information about the events is cloneable, as it is of a classical nature, The modern quantum theory of classicality is the decoherence theory. It treats "the pointer variable" of measuring apparatus as an open system interacting with an environment consisting of all other "zillions" of degrees of freedom of the device, and anything coupled to it. Because such environment is uncontrollable we have no possibility to reverse measurements. The quantum mechanical measurement theory based on decoherence theory is reproducing the probabilistic predictions of Born rule. There is no “measurement problem” in quantum mechanics, as it is a theory giving probabilistic predictions. “The quantum state only describes our knowledge” (Zeilinger). Notwithstanding, possibility of reversing measurements and of application of Born rule in situations other than these which lead to macroscopically observable events are features of a modification of quantum mechanics which is called by its adherents "unitary quantum mechanics". As its predictions, which go beyond quantum mechanics, are not testable - we claim that unitary quantum mechanics in an interpretation of quantum mechanics. As such it is metaphysics. The talk is based on arXiv:2003.07464 (PRL) and arXiv:2508.19207 co authored with M. Markiewicz.