It is argued that while quantum mechanics contains nonlocal or entangled states, the instantaneous or nonlocal influences sometimes thought to be present due to violations of Bell inequalities in fact arise from mistaken attempts to apply classical concepts and introduce probabilities in a manner inconsistent with the Hilbert space structure of standard quantum mechanics. Instead, Einstein locality is a valid quantum principle: objective properties of individual quantum systems do not change when something is done to another noninteracting system. There is (...) no reason to suspect any conflict between quantum theory and special relativity. (shrink)

It is shown how all the major conceptual difficulties of standard (textbook) quantum mechanics, including the two measurement problems and the (supposed) nonlocality that conflicts with special relativity, are resolved in the consistent or decoherent histories interpretation of quantum mechanics by using a modified form of quantum logic to discuss quantum properties (subspaces of the quantum Hilbert space), and treating quantum time development as a stochastic process. The histories approach in turn gives rise to some conceptual difficulties, in particular the (...) correct choice of a framework (probabilistic sample space) or family of histories, and these are discussed. The central issue is that the principle of unicity, the idea that there is a unique single true description of the world, is incompatible with our current understanding of quantum mechanics. (shrink)

Stapp’s counterfactual argument for quantum nonlocality based upon a Hardy entangled state is shown to be flawed. While he has correctly analyzed a particular framework using the method of consistent histories, there are alternative frameworks which do not support his argument. The framework dependence of quantum counterfactual arguments, with analogs in classical counterfactuals, vitiates the claim that nonlocal (superluminal) influences exist in the quantum world. Instead it shows that counterfactual arguments are of limited use for analyzing these questions.

This article describes how an empirically supported theory of human behaviour, perceptual control theory, can be used to advance nursing practice and improve health outcomes for people who are accessing nursing care. Nursing often takes a pragmatic approach to the delivery of care, with an emphasis on doing what appears to work. This focus on pragmatism can sometimes take precedence over any consideration of the underlying theoretical assumptions that inform decisions to take one particular approach over another or the mechanisms (...) through which nursing interventions have their effects. For nursing to develop as a profession, there needs to be an increased focus on the core principles that underpin the delivery of care. In addition to understanding what works, nurses must develop their understanding of how and why particular approaches work or do not work. Understanding the fundamental principles that underpin nurses’ actions will lead to more efficient and effective approaches to the delivery of nursing care. It will also enable nurses to maximize those elements of their practice that are most beneficial for people and minimize other activities that either have little effect or actually lead to worse outcomes. In this article, we will propose that the phenomenon of control is fundamental to human health. Perceptual control theory provides a coherent theoretical framework that enables us to understand the phenomenon of control through a functional model of human behaviour. People are healthy when their neurochemical, physiological, biological, psychological and social states are all controlled satisfactorily. We will explain the implications of understanding health as control throughout the paper. From this perspective, we will argue that the aim of nurses and nursing should be to support people to maintain or recover control over those aspects of their lives that are important and meaningful to them. (shrink)

In this essay I will discuss and appraise two conflicting answers to the question of whether there was a crisis in Ptolemaic astronomy prior to the Copernican revolution. I will begin by giving a brief account of why anybody should be interested in this question. I will discuss the two conflicting answers of Kuhn (1962, 1970), who claims to present evidence which shows that Ptolemaic astronomy was anomaly-ridden at the time of Copernicus, and of Gingerich (1975), who claims that the (...) supposed anomalies, which have been passed down in the historical literature due to poor scholarship, are fictitious. Finally I will appraise Gingerich’s criticism of Kuhn, giving my own evaluation of Gingerich’s arguments. I conclude that Gingerich’s arguments against the existence of a technical crisis in Ptolemaic astronomy prior to Copernicus appear to be, either arguments against the efficacy of the Copernican system, or arguments based on definitions of complexity which are not directly attributable to Kuhn. (shrink)

This article is a response to various assertions made by B. d'Espagnat about the consistent history approach to quantum mechanics. It is argued that the consistent history interpretation allows for counterfactual definitions, does not imply that the future influences the past, is “realistic” according to d'Espagnat's own definition of that term, and provides a consistent substitute for classical logic in the quantum domain.

Any attempt to introduce probabilities into quantum mechanics faces difficulties due to the mathematical structure of Hilbert space, as reflected in Birkhoff and von Neumann's proposal for a quantum logic. The (consistent or decoherent) histories solution is provided by its single framework rule, an approach that includes conventional (Copenhagen) quantum theory as a special case. Mermin's Ithaca interpretation addresses the same problem by defining probabilities which make no reference to a sample space or event algebra (“correlations without correlata”). But this (...) leads to severe conceptual difficulties, which almost inevitably couple quantum theory to unresolved problems of human consciousness. Using histories allows a sharper quantum description than is possible with a density matrix, suggesting that the latter provides an ensemble rather than an irreducible single-system description as claimed by Mermin. The histories approach satisfies the first five of Mermin's desiderata for a good interpretation of quantum mechanics, including Einstein locality, but the Ithaca interpretation seems to have difficulty with the first (independence of observers) and the third (describing individual systems). (shrink)