Abstract
Harrigan and Spekkens (Found Phys 40:125–157, 2010) provided a categorization of quantum ontological models classifying them as psi-ontic or psi-epistemic if the quantum state psi describes respectively either a physical reality or mere observers’ knowledge. Moreover, they claimed that Einstein—who was a supporter of the statistical interpretation of quantum mechanics—endorsed an epistemic view of psi . In this essay we critically assess such a classification and some of its consequences by proposing a twofold argumentation. Firstly, we show that Harrigan and Spekkens’ categorization implicitly assumes that a complete description of a quantum system (its ontic state, lambda) only concerns single, individual systems instantiating absolute, intrinsic properties. Secondly, we argue that such assumptions conflict with some current interpretations of quantum mechanics, which employ different ontic states as a complete description of quantum systems. In particular, we will show that, since in the statistical interpretation ontic states describe ensembles rather than individuals, such a view cannot be considered psi-epistemic. As a consequence, the authors misinterpreted Einstein’s view concerning the nature of the quantum state. Next, we will focus on relational quantum mechanics and perspectival quantum mechanics, which in virtue of their relational and perspectival metaphysics employ ontic states lambda dealing with relational properties. We conclude that Harrigan and Spekkens’ categorization is too narrow and entails an inadequate classification of the mentioned interpretations of quantum theory. Hence, any satisfactory classification of quantum ontological models ought to take into account the variations of lambda across different interpretations of quantum mechanics.
Highlights
The question concerning what is the correct interpretation of quantum mechanics (QM) and how it represents the microphysical world arose since the first formulations of the theory in the twenties
In the previous section we argued that the assumption that applies to individual systems cannot capture the basic tenets of the statistical interpretation of quantum mechanics
For PQM, it is clear that any fair description of an irreducibly relational world must be given by relational quantum states, which by definition include the possibility of ascribing different states to the same physical system
Summary
The question concerning what is the correct interpretation of quantum mechanics (QM) and how it represents the microphysical world arose since the first formulations of the theory in the twenties. It is worth noting that one of the principal aims of the authors is to argue that Einstein showed that quantum theory is incomplete, and that the quantum state represents merely observers’ knowledge, endorsing a -epistemic view Given that he supported a statistical view of QM, Harrigan and Spekkens conclude that such an interpretation must be considered -epistemic. A statistical ontological model poses a different sort of with respect to that employed in Harrigan and Spekkens [26] This fact, in turn, is conceptually relevant since it implies that the statistical interpretation should not be considered a -incomplete and -epistemic model—as in Harrigan and Spekkens’ classification— but -complete and, thereby, -ontic.
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