What ontology does realism about the quantum state suggest? The main extant view in contemporary philosophy of physics is wave-function realism. We elaborate the sense in which wave-function realism does provide an ontological picture; and defend it from certain objections that have been raised against it. However, there are good reasons to be dissatisfied with wave-function realism, as we go on to elaborate. This motivates the development of an opposing picture: what we call spacetime state realism; a view which takes the states associated to spacetime regions as fundamental. This approach enjoys a number of beneficial features, although, unlike wave-function realism, it involves non-separability at the level of fundamental ontology. We investigate the pros and cons of this non-separability, arguing that it is a quite acceptable feature; even one which proves fruitful in the context of relativistic covariance. A companion paper discusses the prospects for combining a spacetime-based ontology with separability, along lines suggested by Deutsch and Hayden
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This is a preliminary version of a chapter in the
Ashgate Companion to the New Philosophy of Physics. In it, I aim to
review, in a way accessible to foundationally interested physicists as well as
physics-informed philosophers, just where we have got to in the quest for
a solution to the measurement problem. I don’t advocate any particular
approach to the measurement problem (not here, at any rate!) but I do
focus on the importance of decoherence theory to modern attempts to
solve the measurement problem, and I am fairly sharply critical of some
aspects of the "traditional" formulation of the problem.
(PDF) (PostScript)
Deutsch and Hayden have proposed an alternative formulation of quantum mechanics which is completely local. We argue that their proposal must be understood as having a form of `gauge freedom' according to which mathematically distinct states are physically equivalent. Once this gauge freedom is taken into account, their formulation is no longer local.
NOTE: So good they published it twice! For some reason, Foundations of Physics also published the paper in the next issue of the journal, one month later.
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(Preprint PDF)
(Preprint PostScript)
The quantum theory of de Broglie and Bohm solves the measurement problem, but
the hypothetical corpuscles play no role in the argument. The solution finds a
more natural home in the Everett interpretation.
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(Preprint PDF)
(Preprint PostScript)