Contemporary physics, especially quantum theory, has raised profound questions about the relationship between the methods of science and the reality these methods seek to investigate. D'Espagnat investigates these questions as well as how we should answer them. Part I examines the practices of contemporary physicists and addresses the criticism philosophers of science have made of these practices. The doctrine of physical realism, adopted by most physicists and many philosophers of science, comprises Part II. Part III explores the consequences of (...) physical realism for our understanding of what science can seek to know of reality, and concludes by outlining the position contemporary physics indicates we should take. (shrink)
Abstract. In the last decades, several rapprochements have been made between quantum physics and the Advaita Vedānta (AV) school of Hinduism. Theoretical issues such as the role of the observer in measurement and physical interconnectedness have been associated with tenets of AV, generating various critical responses. In this study, I propose to address this encounter in the light of recent works on philosophical implications of quantum physics by the physicist and philosopher of science Bernard d’Espagnat.
On Two Types of Realism in Quantum Theory. Current realist approaches to the foundations of quantum theory emphasize the dichotomy between (Copenhagen) positivism and ‘beable’-realism. Recently it was even attempted to turn this picture into two (equally possible) histories in order to legitimate Bohmian Mechanics as a viable alternative. This paper argues that this dichotomy is philosophically inadequate and historically questionable by embedding it into the philosophical discussion on positivism and realism that has taken place since the 1920s. Logical Empiricists (...) back then advocated empirical realism and contrasted it to absolutistic metaphysical realism. From this viewpoint David Bohm's ‘beable’-realism combines elements of Mach's sensualism with a pre-Kantian metaphysics. As Wesley Salmon's position shows, empirical realism can become quite pronounced without relapsing into Bohmian philosophy. Instead it arrives close to the GRWP-interpretation. Hence, when Bernard d'Espagnat binds both together as ‘ontological interpretations’, he blurs the borderline between empirical and metaphysical realism that his Veiled Reality has set out to draw, quite in concordance with Logical Empiricism. (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.
Should we doubt the exactness of the predictive quantum rules of calculation? Although this question is sometimes raised in connection with the one on how to physically understand quantum mechanics, these two questions should not be mixed up. It is recalled here that even the first one is stil an object of controversy, and it is shown (a) that in one specific case the arguments put forward in support of such doubts are hardly cogent but (b) that, nevertheless, at least (...) in one specific other context, the question is worth attention. This is the problem of repeated imperfect measurements. Relative to it, a theoretical possibility is shown of discriminating between the thesis that the quantum rules are exact and a powerful theory of which it is proved that it cannot be reconciled with the assumption. (shrink)
It is generally agreed that decoherence theory is, if not a complete answer, at least a great step forward towards a solution of the quantum measurement problem. It is shown here however that in the cases in which a sentient being is explicitly assumed to take cognizance of the outcome the reasons we have for judging this way are not totally consistent, so that the question has to be considered anew. It is pointed out that the way the Broglie–Bohm model (...) solves the riddle suggests a possible clue, consisting in assuming that even very simple systems may have some sort of a proto-consciousness, but that their “internal states of consciousness” are not predictive. It is, next, easily shown that if we imagine the systems get larger, in virtue of decoherence their internal states of consciousness progressively gain in predictive value. So that, for macro-systems, they may be identified (in practice) with the predictive states of consciousness on which we ground our observational predictions. The possibilities of carrying over this idea to standard quantum mechanics are then investigated. Conditions of conceptual consistency are considered and found rather strict, and, finally, two solutions emerge, differing conceptually very much from one another but in both of which the, possibly non-predictive, generalized internal states of consciousness play a crucial role. (shrink)
It is stressed that any theory of which it is claimed that it is compatible both with standard realism and with the experimental data is subject to severe constraints. One is that it must either incorporate superluminal influences or negate the free will of the experimentalist. The other one is that, in it. it is only at the price of accepting “backward causality” that a measurement can he interpreted as revealing the value the measured quantity had, just before, rather than (...) just after, the measurement look place. (shrink)
Contrary to classical physics, which was strongly objective i.e. could be interpreted as a description of mind-independent reality, standard quantum mechanics (SQM) is only weakly objective, that is to say, its statements, though intersubjectively valid, still merely refer to operations of the mind. Essentially, in fact, they are predictive of observations. On the view that SQM is universal conventional realism is thereby refuted. It is shown however that this does not rule out a broader form of realism, called here ‘open (...) realism’, restoring the notion of mind-independent reality. (shrink)
“To be” or “to be found”? Some contributions relative to this modern variant of Hamlet's question are presented here. They aim at better apprehending the differences between the points of view of the physicists who consider that present-day quantum measurement theories do reach their objective and those who deny they do. It is pointed out that these two groups have different interpretations of the verbs “to be” and “to have” and of the criterion for truth. These differences are made explicit. (...) A notion of “empirical reality” is constructed within the representation of which the physicists of the first named group can consistently uphold their claim. A detailed way of sharpening this definition so as to make empirical reality free of nonlocal actions at a distance is also described. (shrink)
In the context of stochastic hidden variable theories, Howard has argued that the role of separability—spatially separated systems possess distinct real states—has been underestimated. Howard claims that separability is equivalent to Jarrett‘s completeness: this equivalence should imply that the Bell theorem forces us to give up either separability or locality. Howard's claim, however, is shown to be ill founded since it is based on an implausible assumption. The necessity of sharply distinguishing separability and locality is emphasized: a quantitative formulation of (...) separability, due to D'Espagnat, is reviewed and found unsatisfactory, in that it basically conflates separability and locality in a single notion. Finally, the possibility of an ‘Einsteinian’ nonseparable realism, envisaged by Shimony, is reviewed and found also to be implausible. (shrink)
With regard to the notion of cause—or more generally of influence—the various methods of proof of Bell's theorem do not all have the same bearing. The differences between two of these methods are analyzed, with regard to both their conceptual basis and their conclusions. It is shown that both methods give valuable information but, not too surprisingly, the one that is based on the more detailed and specific definition of the concept of influences, and that makes use of the concept (...) of attribute, leads to conclusions that are also to some extent more specific than those following from the other method. (shrink)
The idea is discussed according to which, in the Heisenberg picture, the operators correspond to the dynamic properties while the density matrix corresponds to our knowledge. A simple, soluble model is made use of in order to determine in what way this idea needs to be refined and what it then tells us about the relationship of reality and physics.
Does physics describe anything that can meaningfully be called “independent reality,” or is it merely operational? Most physicists implicitly favor an intermediate standpoint, which takes quantum physics into account, but which nevertheless strongly holds fast to quite strictly realistic ideas about apparently “obvious facts” concerning the macro-objects. Part 1 of this article, which is a survey of recent measurement theories, shows that, when made explicit, the standpoint in question cannot be upheld. Part 2 brings forward a proposal for making minimal (...) changes to this standpoint in such a way as to remove such objections. The “empirical reality” thus constructed is a notion that, to some extent,does ultimately refer to the human means of apprehension and of data processing. It nevertheless cannot be said that it reduces to a mere name just labelling a “set of recipes that never fail.” It is shown that our usual notion of macroscopic causality must be endowed with similar features. (shrink)
Instead of the usual asymptotic passage from quantum mechanics to classical mechanics when a parameter tended to infinity, a sharp boundary is obtained for the domain of existence of classical reality. The last is treated as separable empirical reality following d'Espagnat, described by a mathematical superstructure over quantum dynamics for the universal wave function. Being empirical, this reality is constructed in terms of both fundamental notions and characteristics of observers. It is presupposed that considered observers perceive the world as (...) a system of collective degrees of freedom that are inherently dissipative because of interaction with thermal degrees of freedom. Relevant problems of foundation of statistical physics are considered. A feasible example is given of a macroscopic system not admitting such classical reality.The article contains a concise survey of some relevant domains: quantum and classical Bell-type inequalities; universal wave function; approaches to quantum description of macroscopic world, with emphasis on dissipation; spontaneous reduction models; experimental tests of the universal validity of the quantum theory. (shrink)