Realism, operationalism, and quantum mechanics

Hans Primas

Frank Arntzenius

This chapter discusses which quantities one should take to be fundamental in quantum mechanics. Five views are discussed: ‘configuration space realism’, ‘wave-function amplitude realism’, ‘density operator realism’, ‘Heisenberg operator realism’, and ‘flash-realism’. Arguments are given in favour of ‘Heisenberg operator realism’ which, contrary to perceived wisdom, makes quantum mechanics an entirely separable and local theory.

G. C. Ghirardi

Martin Däumer, Detlef Dürr, Sheldon Goldstein +1 more

A source of much difficulty and confusion in the interpretation of quantum mechanics is a ``naive realism about operators.'' By this we refer to various ways of taking too seriously the notion of operator-as-observable, and in particular to the all too casual talk about ``measuring operators'' that occurs when the subject is quantum mechanics. Without a specification of what should be meant by ``measuring'' a quantum observable, such an expression can have no clear meaning. A definite specification is provided by Bohmian mechanics, a theory that emerges from Schrodinger's equation for a system of particles when we merely insist that ``particles'' means particles. Bohmian mechanics clarifies the status and the role of operators as observables in quantum mechanics by providing the operational details absent from standard quantum mechanics. It thereby allows us to readily dismiss all the radical claims traditionally enveloping the transition from the classical to the quantum realm---for example, that we must abandon classical logic or classical probability. The moral is rather simple: Beware naive realism, especially about operators!

D. M. Fucci, R. M. Angelo

The distinctive features of quantum mechanics, which set it apart from other physical theories, challenge our notions of realism. Recovering realism from purely philosophical grounds, a quantitative and operational criterion was proposed in the past, but solely for the context of quantum mechanics. We use a framework of generalized probabilistic theories to expand the notion of realism for a theory-independent context, providing a criterion uniquely based on the probabilities assigned to measurement outcomes. More so, using robustness and the Kullback-Leibler divergence, we propose quantifiers for the realism of arbitrary physical properties given a particular state of a generic physical theory. These theory-independent quantifiers are then employed in quantum mechanics and we investigate their relation with another well-established irrealism measure.

Peter Kosso