What is a physical object according to the theory of quantum mechanics? The first answer to be considered is that given by Bohr in terms of the concept of complementarity. This interpretation is illustrated by way of an example, the two slit experiment, which highlights some of the associated problems of ontology. One such problem is the so-called problem of measurement or observation. Various interpretations of measurement in Quantum Theory, including those of Heisenberg, von Neumann, Everett and Bohr, are compared and contrasted. A second problem concerns whether or not QT can be considered complete and therefore satisfactory as a basis for physics. Various attempts to complete QT by means of the addition of ‘hidden variables’ to the quantum mechanical state function are considered and their aims and achievements assessed. Finally, we investigate some of the characteristic ontological problems for the orthodox interpretation of Relativistic Quantum Theory.
What is a physical object according to the theory of quantum mechanics? The first answer to be considered is that given by Bohr in terms of the concept of complementarity. This interpretation is illustrated by way of an example, the two slit experiment, which highlights some of the associated problems of ontology. One such problem is the so-called problem of measurement or observation. Various interpretations of measurement in Quantum Theory, including those of Heisenberg, von Neumann, Everett and Bohr, are compared and contrasted. A second problem concerns whether or not QT can be considered complete and therefore satisfactory as a basis for physics. Various attempts to complete QT by means of the addition of ‘hidden variables’ to the quantum mechanical state function are considered and their aims and achievements assessed. Finally, we investigate some of the characteristic ontological problems for the orthodox interpretation of Relativistic Quantum Theory.
For Bohr quantum mechanics is complete. It expresses all that can be said about the atomic world, which he regards as a newly discovered and separate ontological component of reality, operating at the Planck scale, and describable only with a separate physics, namely, quantum mechanics. The classical world, in contrast, represents its binary and symbiotic counterpart, which is also ontologically substantive, but operates according to 'classical concepts'. The different physics of each component indicates a different ontology, the classical one is accessible to us, as we are classical objects, where the Planck scale does not apply, while the other is not. The measurement problem cannot therefore be solved through the discovery of hidden variables as these are classical in nature and therefore ineffective in explaining the quantum world. The measurement problem is therefore not due to epistemological limitations but emerges directly from a 'two worlds' dualism. Bohr's Copenhagen interpretation has therefore been erroneously misunderstood as a positivist retreat rather than as a view of reality proposing an ontological structure which is dualistic. l then propose similarities between Bohr and a ‘two worlds’ view of Kant, where noumena is an ontology which is inherently unknowable as it is devoid of a priori agents, much as the quantum world is unknowable as it is devoid of Bohr's classical concepts. However, just as classical concepts in Bohr are crucial in constituting classical reality, a priori intuitions and concepts in Kant are crucial in constituting phenomena, which are real ontological objects and not just appearances. The noumenal and quantum realms are therefore both substantive, but impossible to investigate. The phenomenal and classical worlds are also substantive. They are where objects and therefore meaning condenses. They are therefore open to our investigations.
We begin by discussing ``What exists?'', i.e. ontology, in Classical Physics which provided a description of physical phenomena at the macroscopic level. The microworld however necessitates a introduction of Quantum ideas for its understanding. It is almost certain that the world is quantum mechanical at both microscopic as well as at macroscopic level. The problem of ontology of a Quantum world is a difficult one. It also depends on which interpretation is used. We first discuss some interpretations in which Quantum Mechanics does not provide a complete framework but has to be supplemented by extra ingredients e.g. (i) Copenhagen group of interpretations associated with the names of Niels Bohr, Heisenberg, von-Neumann, and (ii) de-Broglie-Bohm interpretations. We then look at some interpretations in which Quantum mechanics is supposed to provide the entire framework such as (i) Everett-deWitt many world, (ii) quantum histories interpretations. We conclude with some remarks on the rigidity of the formalism of quantum mechanics, which is sharp contrast to it's ontological fluidity.
The field of interpretation of quantum mechanics emerged in an attempt to solve the measurement problem. This turned on the perception that Niels Bohr avoided addressing the measurement problem by taking an instrumentalist view of quantum mechanics. I argue that this view is mistaken and Bohr's interpretation of quantum mechanics is realist. Moreover, Bohr's interpretation, which is different from textbook quantum mechanics (which is due more to Von Neumann and Paul Dirac), succeeds in solving the measurement problem. While the claim that Bohr dissolves the measurement problem within the limits of the epistemological framework he assumes has been made by a few authors, rarely has the case been made that Bohr's project unambiguously and completely overcomes the measurement problem. I make the strong case that Bohr eliminated the measurement problem altogether. For this, I put forward two new postulates through which to make sense of Bohr's interpretation. The article thus seeks to single out Bohr's interpretation from the various views that go together under the umbrella of orthodox quantum mechanics, and which have been traditionally considered susceptible to the measurement problem. It shows that Bohr's interpretation should be classified along with those like hidden variable theories, collapse models, modal interpretations etc., which offer a solution to the measurement problem and are committed to a realist ontology.
We present a historical-epistemological analysis of the foundations of quantum mechanics, highlighting the relationships between quantum mechanics and scientific realism, as well as the influence of the neo-positivist philosophy of the first decades of the 20th century. The great significance of the measurement process in the context of quantum mechanics is underlined as an essential element in providing a coherent description of reality, moving from micro to macrocosm, as well as the role that the measurement apparatus and the consciousness of the observer assume during the act of measurement, the related ontological problems, the question of the objectification of the wave function, and that of the definition of discernibility. We consider also an overview of the most important alternative proposals to the standard interpretation of quantum mechanics (Copenhagen interpretation), with particular reference to hidden variable theories and other alternatives to standard quantum mechanics philosophical approach, that are modifying the vision of reality, such as the Everett’s many-worlds theory, the QBism and unified holistic approaches, such as the Primordial Dynamic Space.
This work presents a historical-epistemological analysis of the foundations of quantum mechanics. From a philosophical point of view, the relationships between quantum mechanics and scientific realism are highlighted, as well as the influence of the neo-positivist philosophy of the first decades of the 20th century. The great significance of measurement in the context of quantum mechanics is underlined, as an essential element in providing a coherent description of reality moving from the microcosm to the macrocosm, as well as the role that the measurement apparatus and the consciousness of the observer assume during the act of measurement, the ontological problem, the problem of the objectification of the wave function and the problem of the definition of discernibility. This is followed by an overview of the most important alternative proposals to the standard interpretation (Copenhagen interpretation), with particular reference to hidden variable theories, and other alternatives to standard quantum mechanics that profoundly modify the vision of reality, such as the Everett’s many-worlds theory, the QBism, the unified holistic approach.
This thesis is an examination of the measurement problem from within the Copenhagen interpretation of quantum mechanics where I take issue with von Neumann’s theory of measurement which argues for the subjective collapse of the wave function by a conscious observer. I argue that von Neumann’s postulate of collapse has led to several intractable philosophical and conceptual problems in its account of quantum measurement. I argue that these problems arise from von Neumann’s misreading of Bohr’s complementarity regarding the relationship between subject and object as distinct metaphysical entities. Instead, I offer a new way of defining the subject-object relation based on Don Howard’s reading of Bohr’s complementarity as subject-object nonseparability (SON). I argue that the SON principle has the potential of placing Copenhagen on more solid philosophical footing by viewing the subject-object relationship not as a causal relation, but as a relation of ontological dependence to avoid the idea of collapse altogether.