School of Physics Colloquium

Abstract: Recent developments [1] have shown that the collapse hypothesis is self-inconsistent and is no longer a viable theory. (The collapse hypothesis in quantum mechanics is that the state of a system is collapsed by a measurement, by some process of unknown character.) Based on earlier work by Ballentine [2] on the Ensemble Interpretation (in spite of the familiar-sounding name, this is almost entirely unknown), more recent work [3] has filled it out and demonstrated clearly that it provides a simple and natural resolution to the problem of measurement in quantum mechanics. We discuss the Ensemble Interpretation and recent developments, measurement theory in quantum mechanics (correcting many common misconceptions), and the resolutions of Schrödinger Cat, Wigner’s Friend, and Extended Wigner’s Friend experiments. Given that almost all current QM textbooks are based on the now defunct collapse hypothesis [4], we propose switching to textbooks based on the Ensemble Interpretation [5] as a means of restoring consistency to QM. [1] D. Frauchiger & R. Renner, “Quantum theory cannot consistently describe the use of itself”, Nature Comm [2018] [2] L. Ballentine, “The statistical interpretation of quantum mechanics”, Rev Mod Phys [1970] [3] A. Rizzi, “How the natural interpretation of QM avoids the recent no-go theorem” Foundations of Physics [2020] and “A simple approach to measurement in quantum mechanics” arXiv [2020] [4] Two common examples include Griffiths and Morrison. Even though both discuss the use of ensembles, the statistical understanding is undermined completely by use of the collapse hypothesis in discussing measurements. [5] See L. Ballentine, “Quantum Mechanics” and A. Rizzi, “Physics for Realists: Quantum Mechanics”.