Quantum Theory: a Pragmatist Approach

While its applications have made quantum theory arguably the most successful theory in physics, its interpretation continues to be the subject of lively debate within the community of physicists and philosophers concerned with conceptual foundations. This situation poses a problem for a pragmatist for whom meaning derives from use. While disputes about how to use quantum theory have arisen from time to time, they have typically been quickly resolved, and consensus reached, within the relevant scientific sub-community. Yet rival accounts of the meaning of quantum theory continue to proliferate . In this article I offer a diagnosis of this situation and outline a pragmatist solution to the problem it poses, leaving further details for subsequent articles

Observation and Quantum Objectivity

The paradox of Wigner's friend challenges the objectivity of description in quantum theory. A pragmatist interpretation can meet this challenge by judicious appeal to decoherence. On this interpretation, quantum theory provides situated agents with resources for predicting and explaining what happens in the physical world---not conscious observations of it. Even in Wigner's friend scenarios, differently situated agents agree on the objective content of statements about the values of physical magnitudes. In more realistic circumstances quantum Darwinism also permits differently situated agents equal observational access to evaluate their truth. In this view, quantum theory has nothing to say about consciousness or conscious experiences of observers. But it does prompt us to reexamine the significance even of everyday claims about the physical world

Quantum decoherence in a pragmatist view: Resolving the measurement problem

This paper aims to show how adoption of a pragmatist interpretation permits a satisfactory resolution of the quantum measurement problem. The classic measurement problem dissolves once one recognizes that it is not the function of the quantum state to describe or represent the behavior of a quantum system. The residual problem of when, and to what, to apply the Born Rule may then be resolved by judicious appeal to decoherence. This can give sense to talk of measurements of photons and other particles even though quantum field theory does not describe particles

Quantum decoherence in a pragmatist view: Part I

The quantum theory of decoherence plays an important role in a pragmatist interpretation of quantum theory. It governs the descriptive content of claims about values of physical magnitudes and offers advice on when to use quantum probabilities as a guide to their truth. The content of a claim is to be understood in terms of its role in inferences. This promises a better treatment of meaning than that of Bohr. Quantum theory models physical systems with no mention of measurement: it is decoherence, not measurement, that licenses application of Born's probability rule. So quantum theory also offers advice on its own application. I show how this works in a simple model of decoherence, and then in applications to both laboratory experiments and natural systems. Applications to quantum field theory and the measurement problem will be discussed elsewhere

Case study: embedding 'A vision of Britain through time' as a resource for academic research and learning

As part of the 'JISC e-Content and Digitisation Programmes: Impact and Embedding of Digitised Resources,' this case study explores the impacts of the A Vision of Britain Through Time website (http://www.visionofbritain.org.uk/) on academic research and learning. It is complemented by 'Impact Report on ‘A Vision of Britain through Time’ 2004-10: Investigating the current use and impact of a popular digital resource for local history research.

Pragmatist Quantum Realism

Realism comes in many varieties, in science and elsewhere. Van Fraassen's influential formulation took scientific realism to include the view that science aims to give us, in its theories, a literally true story of what the world is like. So understood, a quantum realist takes quantum theory to aim at correctly representing the world: many would add that its success justifies believing this representation is more or less correct. But quantum realism has been understood both more narrowly and more broadly. A pragmatist considers use prior to representation and this has prompted some to dub pragmatist views anti-realist, including the view of quantum theory I have been developing recently. But whether a pragmatist view of quantum theory should be labeled anti-realist depends not only on its ingredients but also on how that label should be applied. Pragmatism offers a healthy diet of quantum realism

A pragmatist view of the metaphysics of entanglement

Quantum entanglement is widely believed to be a feature of physical reality with undoubted (though debated) metaphysical implications. But Schrödinger introduced entanglement as a theoretical relation between representatives of the quantum states of two systems. Entanglement represents a physical relation only if quantum states are elements of physical reality. So arguments for metaphysical holism or nonseparability from entanglement rest on a questionable view of quantum theory. Assignment of entangled quantum states predicts experimentally confirmed violation of Bell inequalities. Can one use these experimental results to argue directly for metaphysical conclusions? No. Quantum theory itself gives us our best explanation of violations of Bell inequalities, with no superluminal causal influences and no metaphysical holism or nonseparability—but only if quantum states are understood as objective and relational, though prescriptive rather than ontic. Correct quantum state assignments are backed by true physical magnitude claims: but backing is not grounding. Quantum theory supports no general metaphysical holism or nonseparability; though a claim about a compound physical system may be significant and true while similar claims about its components are neither. Entanglement may well have have few, if any, first-order metaphysical implications. But the quantum theory of entanglement has much to teach the metaphysician about the roles of chance, causation, modality and explanation in the epistemic and practical concerns of a physically situated agent