Einstein, Incompleteness, and the Epistemic View of Quantum States

Nicholas Harrigan, Robert W. Spekkens

Miguel Ferrero, David Cienfuegos Salgado, J. L. S�nchez-G�mez

Terry Rudolph

Joshua B. Ruebeck, Piers Lillystone, Joseph Emerson

ψ -epistemic interpretations of quantum theory maintain that quantum states only represent incomplete information about the physical states of the world. A major motivation for this view is the promise to provide a reasonable account of state update under measurement by asserting that it is simply a natural feature of updating incomplete statistical information. Here we demonstrate that all known ψ -epistemic ontological models of quantum theory in dimension d≥3 , including those designed to evade the conclusion of the PBR theorem, cannot represent state update correctly. Conversely, interpretations for which the wavefunction is real evade such restrictions despite remaining subject to long-standing criticism regarding physical discontinuity, indeterminism and the ambiguity of the Heisenberg cut. This revives the possibility of a no-go theorem with no additional assumptions, and demonstrates that what is usually thought of as a strength of epistemic interpretations may in fact be a weakness.

Euan J. Squires

Maria Beatrice Buonaguidi

The dilemma concerning the meaning of the wave function is perhaps one of the most controversial and overlooked in contemporary physics. There is widespread disagreement in the scientific community as to whether the wave function should be viewed as a representative of a real physical object or whether it corresponds to a state of incomplete knowledge about the underlying system, such as a probability density. These views are respectively called ψ-ontic and ψ-epistemic. This article aims to give a clear insight into the problem and features of both views. After some clarifying preliminaries, I will give an overview of how the question was perceived and interpreted by the pioneers of quantum theory, such as Bohr and Einstein, and then move on to more modern days with the likes of Bell, Kochen, and Specker. Then I will focus on the contemporary literature and try to give a comprehensive account of the pros and cons of each view. Finally, I will discuss some of the questions that the question of the wave function raises for us, such as our relationship to reality.