After giving a panoramic view of the " text-book " interpretation of the new quantum mechanics, as a sequel to the old quantum theory, the conceptual basis of quantum theory since the Copenhagen Interpretation is reviewed in the context of various proposals since Einstein and Niels Bohr, designed to throw light on possible new facets bearing on its foundations, the key issues to its inherent "incompleteness" being A) measurement, and B) quantum non-locality. A related item on measurement, namely Quantum Zeno (as well as anti-Zeno) effect is also reviewed briefly. The inputs for the new facets are from some key Indian experts : S.M. Roy, V. Singh ; D. Home; B. Misra; C.S. Unnikrishnan
After giving a panoramic view of the " text-book " interpretation of the new quantum mechanics, as a sequel to the old quantum theory, the conceptual basis of quantum theory since the Copenhagen Interpretation is reviewed in the context of various proposals since Einstein and Niels Bohr, designed to throw light on possible new facets bearing on its foundations, the key issues to its inherent "incompleteness" being A) measurement, and B) quantum non-locality. A related item on measurement, namely Quantum Zeno (as well as anti-Zeno) effect is also reviewed briefly. The inputs for the new facets are from some key Indian experts : S.M. Roy, V. Singh ; D. Home; B. Misra; C.S. Unnikrishnan
The foundations and meaning of quantum theory became a central issue to Albert Einstein and Niels Bohr since the onset of their impassioned debate in the 1920s, enriched by the contributions of many other distinguished scientists and philosophers.The questions are not settled down at all, despite the great achievements of the theory, its impressive accordance with experiment and predictive power.The fundamental and technological applications range from cosmology to biology, with the development of invaluable instruments and the design of new materials.Is quantum mechanics a complete or an incomplete theory?Is there an objective reality independent of the observer or is the reality created by the measurements?Are hidden-variable theories justifiable?Is there a quantum theory founded in a local-causal and non-linear approach that formally contains the orthodox linear theory as a special case?Can such a formulation unify classical and quantum physics?Are Heisenberg's uncertainty relations valid in all cases?Here, the subject is addressed as an adaptation of our contribution to the Colloquium "Quantal aspects in Chemistry and Physics.
This is not a review article on the conceptual foundations of quantum theory. Rather, it should be considered an “overview paper”, or better, as claimed in the title, a “map” whose aim is to help one in orienting through the subject. The material is organized as follows. After a brief exposition of the three classic paradoxes of quantum mechanics—the measurement, Zeno, and EPR paradoxes— the main interpretations of the theory, as well as the major alternative theories, are outlined. Some puzzling topics of conceptual interest are also presented and briefly discussed. Particular attention has been devoted to the preparation of the bibliography.
This article surveys a selection of key conceptual and interpretational developments in quantum mechanics, tracing the theory from its foundational postulates to contemporary discussions of measurement, nonlocality, and the emergence of classicality. Beginning with the structure of Hilbert space and the postulates governing state evolution and measurement, the epistemic stance of the Copenhagen interpretation and its modern reformulations are examined. The Einstein-Podolsky-Rosen argument, Bell's theorem, and Hardy's paradox are then discussed as probes of locality and realism, alongside the deterministic but explicitly nonlocal de Broglie-Bohm theory. The measurement problem and the implications of contextuality are analyzed in relation to objective collapse models, which introduce new physical dynamics to account for definite outcomes. Finally, the role of decoherence in the suppression of interference and the emergence of classical behavior is explored, together with the interpretational frameworks of many-worlds and consistent histories. This material aims to provide a coherent introductory overview of how several of the most prominent interpretations address the central concern of what quantum mechanics tells us about the nature of physical reality.
List of participants Preface Part I. Introduction: 1. The function of the colloquium - editorial 2. The conceptual problem of quantum theory from the experimentalist's point of view O. R. Frisch Part II. Niels Bohr and Complementarity: The Place of the Classical Language: 3. The Copenhagen interpretation C. F. von Weizsacker 4. On Bohr's views concerning the quantum theory D. Bohm Part III. The Measurement Problem: 5. Quantal observation in statistical interpretation H. J. Groenewold 6. Macroscopic physics, quantum mechanics and quantum theory of measurement G. M. Prosperi 7. Comment on the Daneri-Loinger-Prosperi quantum theory of measurement Jeffrey Bub 8. The phenomenology of observation and explanation in quantum theory J. H. M. Whiteman 9. Measurement theory and complex systems M. A. Garstens Part IV. New Directions within Quantum Theory: What does the Quantum Theoretical Formalism Really Tell Us?: 10. On the role of hidden variables in the fundamental structure of physics D. Bohm 11. Beyond what? Discussion: space-time order within existing quantum theory C. W. Kilmister 12. Definability and measurability in quantum theory Yakir Aharonov and Aage Petersen 13. The bootstrap idea and the foundations of quantum theory Geoffrey F. Chew Part V. A Fresh Start?: 14. Angular momentum: an approach to combinatorial space-time Roger Penrose 15. A note on discreteness, phase space and cohomology theory B. J. Hiley 16. Cohomology of observations R. H. Atkin 17. The origin of half-integral spin in a discrete physical space Ted Bastin Part VI. Philosophical Papers: 18. The unity of physics C. F. von Weizsacker 19. A philosophical obstacle to the rise of new theories in microphysics Mario Bunge 20. The incompleteness of quantum mechanics or the emperor's missing clothes H. R. Post 21. How does a particle get from A to B? Ted Bastin 22. Informational generalization of entropy in physics Jerome Rothstein 23. Can life explain quantum mechanics? H. H. Pattee 24. Discussion: phenomena and sense data in quantum theory D. S. Linney and C. F. von Weizsacker Index of persons Index of subjects.
This article surveys a selection of key conceptual and interpretational developments in quantum mechanics, tracing the theory from its foundational postulates to contemporary discussions of measurement, nonlocality, and the emergence of classicality. Beginning with the structure of Hilbert space and the postulates governing state evolution and measurement, the epistemic stance of the Copenhagen interpretation and its modern reformulations are examined. The Einstein–Podolsky–Rosen argument, Bell’s theorem, and Hardy’s paradox are then discussed as probes of locality and realism, alongside the deterministic but explicitly nonlocal de Broglie–Bohm theory. The measurement problem and the implications of contextuality are analyzed in relation to objective collapse models, which introduce new physical dynamics to account for definite outcomes. Finally, the role of decoherence in the suppression of interference and the emergence of classical behavior is explored, together with the interpretational frameworks of many-worlds and consistent histories. This material aims to provide a coherent introductory overview of how several of the most prominent interpretations address the central concern of what quantum mechanics tells us about the nature of physical reality.
Quantum mechanics is our most successful physical theory. It underlies our very detailed understanding of atomic physics, chemistry, and nuclear physics, and the many technologies to which physical systems in these regimes give rise. Additionally, relativistic quantum mechanics is the basis for the standard model of elementary particles, which very successfully gives a partial unification of the forces operating at the atomic, nuclear, and subnuclear levels. However, from its inception the probabilistic nature of quantum mechanics, and the fact that “quantum measurements” in the orthodox formulation appear to require the intervention of non-quantum mechanical “classical systems,” have led to speculations by many physicists, mathematicians, and philosophers of science that quantum mechanics may be incomplete. Among the Founding Fathers of quantum theory, Einstein and Schrödinger were both of the opinion that quantum mechanics is in some way unsatisfactory, and this view has been amplified in more recent profound work of John Bell, among others. In an opposing camp, many others in the physics, mathematics, and philosophy communities have attempted to provide an interpretational foundation in which quantum mechanics remains a complete and self-contained system. Among the Founding Fathers, Bohr, Born, and Heisenberg maintained that quantum mechanics is a complete system, and a number of recent proposals have been made to improve upon or to provide alternatives to their “Copenhagen Interpretation.” The debate continues, and has spawned an enormous literature.