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)

“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)

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)

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)

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)