We apply the distinction between parameter independence and outcome independence to the linear and nonlinear models of a recent nonrelativistic theory of continuous state vector reduction. We show that in the nonlinear model there is a set of realizations of the stochastic process that drives the state vector reduction for which parameter independence is violated for parallel spin components in the EPR-Bohm setup. Such a set has an appreciable probability of occurrence (≈ 1/2). On the other hand, the linear model (...) exhibits only extremely small parameter dependence effects. We investigate some specific features of the models and we recall that, as has been pointed out recently, if one wants to be able to speak of definite outcomes (or equivalently of possessed objective elements of reality) at finite times, one has to slightly change the criteria for their attribution to physical systems. The concluding section is devoted to a detailed discussion of the difficulties which one meets when one tries to take, as a starting point for the formulation of a relativistic theory, a nonrelativistic scheme which exhibits parameter dependence. Here we derive a theorem which identifies the precise sense in which the occurrence of parameter dependence forbids a genuinely relativistic generalization. Finally we show how the appreciable parameter dependence of the nonlinear model gives rise to problems with relativity, while the extremely weak parameter dependence of the linear model does not give rise to any difficulty, provided one takes into account the appropriate criteria for the attribution of definite outcomes. (shrink)

With reference to recently proposed theoretical models accounting for reduction in terms of a unified dynamics governing all physical processes, we analyze the problem of working out a worldview accommodating our knowledge about natural phenomena. We stress the relevant conceptual differences between the considered models and standard quantum mechanics. In spite of the fact that both theories describe systems within a genuine Hilbert space framework, the peculiar features of the spontaneous reduction models limit drastically the states which are dynamically stable. (...) This fact by itself allows one to work out an interpretation of the formalism which makes it possible to give a satisfactory description of the world in terms of the values taken by an appropriately defined mass density function in ordinary configuration space. A topology based on this function and which is radically different from the one characterizing the Hilbert space is introduced, and in terms of it the idea of similarity of macroscopic situations is precisely defined. Finally, the formalism and the interpretation are shown to yield a natural criterion for establishing the psychophysical parallelism. The conclusion is that, within the considered theories and at the nonrelativistic level, one can satisfy all sensible requirements for a completely satisfactory macro-objective description of reality. (shrink)

Presents a guide to the basics of quantum mechanics and measurement.

This book comprises all of John Bell's published and unpublished papers in the field of quantum mechanics, including two papers that appeared after the first edition was published. It also contains a preface written for the first edition, and an introduction by Alain Aspect that puts into context Bell's great contribution to the quantum philosophy debate. One of the leading expositors and interpreters of modern quantum theory, John Bell played a major role in the development of our current understanding of (...) the profound nature of quantum concepts. First edition Hb (1987): 0-521-33495-0 First edition Pb (1988): 0-521-36869-3. (shrink)

The GRW theory is a recent attempt to solve the measurement problem in quantum mechanics, and the tails problem is a well-known and potentially fatal criticism of the GRW theory. The first half of the paper is an exposition of the measurement problem, the GRW theory, and the tails problem. In the remainder of the paper, two methods of dealing with the tails problem are considered: first, altering the GRW theory so as to avoid the tails problem; and second, denying (...) that the tails problem is more than a novel aspect of a universal vagueness in the way scientific theories relate to everyday language. (shrink)

The continuous spontaneous localization (CSL) model modifies Schrödinger's equation so that the collapse of the state vector is described as a physical process (a special interaction of particles with a universal fluctuating field). A consequence of the model is that an electron in an atom should occasionally get “spontaneously” knocked out of the atom. The CSL ionization rate for the 1s electrons in the Ge atom is calculated and compared with an experimental upper limit for the rate of “spontaneously” generated (...) x-ray pulses in Ge. This gives, for the first time, an experimental constraint on the parameters which characterize this model (the GRW parameters and the relative collapse rate of electrons and nucleons). It is concluded that the values assigned to the GRW parameters by GRW may be maintained only if the coupling of electrons to the fluctuating field is 0.35% or less than the coupling of nucleons, suggestive of a mass-proportional (and therefore gravitational) collapse mechanism. For other allowed values of the GRW parameters, it is still argued that nucleons should collapse more rapidly than electrons. (shrink)

We discuss two recent attempts two solve Schrodinger's cat paradox. One is the modal interpretation developed by Kochen, Healey, Dieks, and van Fraassen. It allows for an observable which pertains to a system to possess a value even when the system is not in an eigenstate of that observable. The other is a recent theory of the collapse of the wave function due to Ghirardi, Rimini, and Weber. It posits a dynamics which has the effect of collapsing the state of (...) macroscopic systems. We argue that the modal interpretation cannot account for non-accurate measurements and that both accounts have the consequence that in ordinary measurement situations the observables that ends up well defined are not quite the ones that we want to be well defined. (shrink)