A discussion of the quantum mechanical use of superposition or entangled states shows that descriptions containing only statements about state vectors and experiments outputs are the most suitable for Quantum Mechanics. In particular, it is shown that statements about the undefined values of physical quantities before measurement can be dropped without changing the predictions of the theory. If we apply these ideas to EPR issues, we find that the concept of non-locality with its 'instantaneous action at a distance' evaporates. Finally, it is argued that usual treatments of philosophical realist positions end up in the construction of theories whose major role is that of being disproved by experiment. This confutation proves simply that the theories are wrong; no conclusion about realism (or any other philosophical position) can be drawn, since experiments deal always with theories and these are never logical consequences of philosophical positions.
A discussion of the quantum mechanical use of superposition or entangled states shows that descriptions containing only statements about state vectors and experiments outputs are the most suitable for Quantum Mechanics. In particular, it is shown that statements about the undefined values of physical quantities before measurement can be dropped without changing the predictions of the theory. If we apply these ideas to EPR issues, we find that the concept of non-locality with its 'instantaneous action at a distance' evaporates. Finally, it is argued that usual treatments of philosophical realist positions end up in the construction of theories whose major role is that of being disproved by experiment. This confutation proves simply that the theories are wrong; no conclusion about realism (or any other philosophical position) can be drawn, since experiments deal always with theories and these are never logical consequences of philosophical positions.
The article examines the controversial relation of scientific realism with quantum mechanics. To this end, two distinct discussions are invoked: the discussion about ‘realism’ in the context of quantum mechanics and the discussion about ‘scientific realism’ in the context of the general philosophy of science. The aim is to distinguish them in order, first, to argue that the former—revolving around ‘local realism’ and the theorems of Bell and Kochen–Specker—unjustifiably identifies realism with features of a particular worldview, and thereby fosters the impression that the failure of ‘local realism’ in quantum experiments constitutes a failure of scientific realism too; and, second, in light of the latter discussion, to claim that scientific realism and quantum mechanics can be compatible—there is ground for dealing with quantum measurement simply as a physical mind-independent interaction. Therefore, a realist approach to the theory is possible despite its notorious measurement problem, even if the issue of its interpretation is still disputed.
I s it possible to bring experiments to bear on metaphysical theses such as realism? In recent developments in quantum mechanics particularly associated with the late John Bell it has been claimed that a certain type of realism, what is known as local realism, has indeed been refuted by a series of experiments, culminating in those carried out by Alain Aspect and his collaborators in Paris in 1982. Crudely local realism means in this context that atomic and subatomic entities, the subject matter of quantum mechanics, possess definite sharp values for all their attributes at all times, and, in addition, these attributes cannot be affected instantaneously by operations such as measurements performed on other microentities at different spatial locations from the one whose attributes are in question. In other words, realism is supplemented with a denial of the possibility of instantaneous action-at-a-distance. Now relativity theory, the other great pillar of modern theoretical physics, is standardly understood as committed to such a denial. So an experimental refutation of local realism would force us to give up either locality (the no-instantaneous-action-at-a-distance principle) or the realist thesis itself. The first horn of this dilemma is closed off by appeal to relativity theory, and so the conclusion of the argument would appear to be the refutation of realism.
Quantum mechanics is widely believed to be inconsistent with local realism because J.S. Bell proved the contradiction between quantum mechanics and the hidden variable theories based on reality and locality of matter. As described herein, the relation between quantum mechanics and local realism is discussed. This paper presents the question of whether any version of local realism is contradicted by quantum mechanics. The answer is negative. An interpretation is proposed by which the contradiction is explained using physical variables of two types: (1) physical variables of the first type, such as positions and angles (i.e. coordinates), are realistic variables and always possess definite values independently of measurements; (2) those of the second type, such as momenta, angular momenta, and spins (i.e., conserved quantities), are non-realistic variables, which possess no value before measurement. Value definiteness of the first type provides a reliable basis to physical reality of matter, and non-reality of the second type might solve the problem of inconsistency between quantum mechanics and local realism.
Why is so shop-soiled a topic as scientific realism once again prominent in the philosophy of science? Realism fought a great battle when Copernican and Ptolemaic world views were at issue long ago. Towards the end of the nineteenth century worries about atomism strongly contributed to anti-realism among philosophers of science. Is there a comparable scientific issue today? Maybe. One way to understand quantum mechanics is to take an idealist line. Some people argue that human observation plays an integral role in the very nature of a physical system, so that the system changes simply when it is measured. Talk of ‘the measurement problem in quantum mechanics’, the ‘ignorance interpretation’, and ‘the collapse of the wave packet’ make it no accident that contributions to the philosophy of quantum mechanics play an important part in the writings of the more original figures in the realist debate. A number of the ideas of Hilary Putnam, Bas van Fraassen or Nancy Cartwright seem to result from taking quantum mechanics as the model of all science. Conversely, numerous physicists wax philosophical. Bernard d'Espagnat has made one of the most important recent contributions to a new realism. He is partly motivated by the dissolution, in some parts of modern physics, of old realist concepts such as matter and entity. He is especially driven by some recent results, that bear the general name of Bell's inequality, and which have been thought to call in question concepts as various as logic, the temporal order of causation, and action at a distance.
I feel compelled to respond to the frequent references to spooky action at a distance that often accompany reports of experiments investigating entangled quantum mechanical states. Most, but not all, of these articles have appeared in the popular press. As an experimentalist I have great admiration for such experiments and the concomitant advances in quantum information and quantum computing, but accompanying claims of action at a distance are quite simply nonsense. Some physicists and philosophers of science have bought into the story by promoting the nonlocal nature of quantum mechanics. In 1964, John Bell proved that classical hidden variable theories cannot reproduce the predictions of quantum mechanics unless they employ some type of action at a distance. I have no problem with this conclusion. Unfortunately, Bell later expanded his analysis and mistakenly deduced that quantum mechanics and by implication nature herself are nonlocal. In addition, some of these articles present Einstein in caricature, a tragic figure who neither understood quantum mechanics nor believed it to be an accurate theory of nature. Consequently, the current experiments have proven him wrong. This is also nonsense.
Despite its remarkable success in describing microscopic phenomena, quantum mechanics continues to pose unresolved foundational questions concerning measurement, nonlocality, wavefunction collapse, and the nature of physical reality. These issues were highlighted by the EPR paradox1-2, in which Einstein and his co-authors examined the measurement of entangled particles in space-like separation. Quantum mechanics predicts that measuring one particle’s observable instantaneously determines the state of the other, seemingly violating special relativity’s prohibition of faster-than-light influences and suggesting an incomplete description of physical reality. However, Bell’s theorem3-5, along with the Bell-Kochen-Specker theorem6-10 and subsequent experiments, has largely ruled out local hidden variable theories. In this work, I apply the quantum decoherence framework11-13, pioneered by Zeh, Zurek, Joos and Leggett et al. to analyze an EPR-like system using system-environment interactions as a measurement model. I demonstrate that measurement on one entangled particle does not instantaneously collapse the system's wavefunction. Instead, the local wavefunctions of the measured particle and its environment evolve dynamically, while the remote particle’s wavefunction remains unchanged. Environment-induced decoherence selects pointer states and rapidly suppresses quantum correlations through local interactions, giving rise to the appearance of wavefunction collapse. These findings suggest that quantum mechanics can be reconciled with local realism if the wavefunction is treated as an ontic entity, offering a potential path toward a locally realistic quantum theory in alignment with Einstein’s vision.