In this largely nontechnical book, eminent physicists and philosophers address the philosophical impact of recent advances in quantum physics. These are shown to shed new light on profound questions about realism, determinism, causality or locality. The participants contribute in the spirit of an open and honest discussion, reminiscent of the time when science and philosophy were inseparable. After the editors' introduction, the next chapter reveals the strangeness of quantum mechanics and the subsequent discussions examine our notion of reality. The spotlight (...) is then turned to the topic of decoherence. Bohm's theory is critically examined in two chapters, and the relational interpretation of quantum mechanics is likewise described and discussed. The penultimate chapter presents a proposal for resolving the measurement problem, and finally the topic of loop quantum gravity is presented by one of its founding fathers, Carlo Rovelli. The original presentations and discussions on which this volume is based took place under the auspices of the French "Académie des Sciences Morales et Politiques". The book will appeal to everybody interested in knowing how our description of the world is impacted by the results of the most powerful and successful theory that physicists have ever built. (shrink)

t. 1. Le chaos, le temps, le principe anthropique -- t. 2. Les interprétations de la physique quantique -- t. 3. Complexité, vie, conscience.

Conceptual Foundations of Quantum Mechanics provides a detailed view of the conceptual foundations and problems of quantum physics, and a clear and comprehensive account of the fundamental physical implications of the quantum formalism. This book deals with nonseparability, hidden variable theories, measurement theories and several related problems. Mathematical arguments are presented with an emphasis on simple but adequately representative cases. The conclusion incorporates a description of a set of relationships and concepts that could compose a legitimate view of the world.

By questioning the validity of some of our basic concepts, such as space, object, and causality, quantum physics contributes quite decisively to the dramatic changes now taking place in our world picture. Veiled Reality provides a detailed view of the reasons why such a questioning arises, a survey of the corresponding conceptual and theoretical problems, and a comprehensive, up-to-date account, useful to scientists and epistemologists alike, of the various ways present-day physicists tackle these problems.The book deals with the E.P.R. reality (...) criterion, local causality, and quantum measurement including relativistic quantum collapse, decoherence theories, consistent histories approaches, and ontologically interpretable theories. Questions bearing on the connection between counterfactuality and realism, intersubjective agreement, and limits of the bearing of the verbs “to have” and “to be,” follow naturally from the analysis and are thoroughly examined. Finally, distinguishing between empirical reality and a veiled independent reality whose only knowable features are structural yields a clue to a plausible interpretation of current physics.Accessible to readers with only very elementary background in modern physics, Veiled Reality offers nonspecialists, including students in physics and philosophy, easy access to basic problems in the foundation of physics. (shrink)

Among the great ironies of quantum mechanics is not only that its conceptual foundations seem strange even to the physicists who use it, but that philosophers have largely ignored it. Here, Bernard d'Espagnat argues that quantum physics--by casting doubts on once hallowed concepts such as space, material objects, and causality-demands serious reconsideration of most of traditional philosophy. On Physics and Philosophy is an accessible, mathematics-free reflection on the philosophical meaning of the quantum revolution, by one of the world's (...) leading authorities on the subject. D'Espagnat presents an objective account of the main guiding principles of contemporary physics-in particular, quantum mechanics-followed by a look at just what consequences these should imply for philosophical thinking. The author begins by describing recent discoveries in quantum physics such as nonseparability, and explicating the significance of contemporary developments such as decoherence. Then he proceeds to set various philosophical theories of knowledge--such as materialism, realism, Kantism, and neo-Kantism--against the conceptual problems quantum theory raises. His overall conclusion is that while the physical implications of quantum theory suggest that scientific knowledge will never truly describe mind-independent reality, the notion of such an ultimate reality--one we can never access directly or rationally and which he calls "veiled reality"--remains conceptually necessary nonetheless. (shrink)

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)

“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)

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)

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)

ResumeLes avancées que la physique a effectuées au cours de notre siècle rendent intertables beaucoup des vues de la philosophie réaliste traditionnelle. Mais ce n'est pas à dire que la position réaliste, conçue au sens large, doive, ou même puisse, être abandonée. Le texte vise à montrer qu'il n'en est rien. Plus précisément il cherche àétablir que l'idée ? une réalité dont l'existence ne relève pas de l'esprit humain demeure une idée nécessaire, qu'il est même légitime de concevoir une telle (...) réalité comme entrevue gräce aux activités noétiques de l'homme, mais que cependant il semble aujourd'hui hautement présomptueux de concevoir les choses observées comme des éléments de la ≫réalité≫ dont il s'agit. Les phénomènes, qui sont l'objet de la physique, constituent cependant eux‐mêmes une réalité en un autre sens, puisqu'ils forment un ensemble doué? une forte structuration et ? une relative mais large autonomic par rapport à nous. La distinction proposée entre ≫réalité indépendante≪ ‐ dont ľ'existence ne reléve pas de l'homme ‐ et ≫réalité empirique≪ ‐ ou ensemble des phénoménes ‐ paraît done maintenant être une bonne clé pour l'intelligence du donné.SummaryThe advances of physics in this century have made a number of views of traditional realist philosophy untenable. But this is not to say that the ‘realist position, in the broad sense', must or even can be abandoned ‐ as it is the aim of this work to show. More specifically, the aim is to establish that the idea of ‘reality, the existence of which does not depend of the human mind', remains necessary, that one may even consider that the noetic activities of men let them catch a glimpse of the reality in question, but that today, however, it seems highly presumptuous to consider observed things as elements of the “reality” that we are concerned with here. Phenomena, which are the subject of physics, do however constitute a reality in another sense, since they form a whole endowed with structure and with a relative but extensive autonomy in relation to us. The proposed distinction between “independent reality” ‐ the existence of which does not depend on man ‐ and “empirical reality” ‐ or all phenomena taken together ‐ would therefore appear to be a good key to the understanding of raw data. (shrink)

Cet ouvrage reprend l'essentiel des discours prononces et des communications presentees lors du colloque qui s'est tenu le 16 novembre 2001 a l'Institut Superieur de Philosophie en l'honneur des 80 ans de Jean Ladriere. On y trouve, outre les discours de Marcel Crochet, Gilbert Gerard et Michel Molitor, une contribution importante de Jean Ladriere et des communications de Stanislas Breton, Bernard d'Espagnat, Dominique Lambert, Jean-Francois Malherbe, James Pembrun, Andre Van de Putte et Philippe Van Parijs. Toutes les interventions (...) portent sur la problematique de la rationalite - un theme central et unificateur de l'oeuvre philosophique de Jean Ladriere - dans les domaines de l'histoire de la philosophie, la philosophie sociale et politique, la philosophie du langage, la philosophie des sciences et la theologie. L'ouvrage se termine par une interview de Jean Ladriere par Philippe Van Parijs.". (shrink)

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)

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.