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.
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.
For over nine decades, quantum mechanics has profoundly shaped our understanding of nature, offering explanations for the stability of atoms, the formation of mole cules, the properties of materials, and phenomena such as light or radioactivity. It is essential to modern technologies—from microchips to lasers—and underpins the physics of elementary particles. Yet, despite its successes, it remains a deeply mysterious theory, confronting a central enigma: why does the quantum world behave so differently from everyday reality? Elements such as superposition and quantum entanglement—which allow particles to exist simultaneously in multiple states or remain interconnected regardless of distance—contradict classical world intuitions. This gap between microscopic and macroscopic behavior has given rise to what is known as the “measurement problem,” raising fundamental questions about the nature of reality. Diverging interpretations have led to two major schools of thought: anti-realism, promoted by Niels Bohr, which holds that reality depends on the observer and their interaction with measurement instruments; and realism, supported by Albert Einstein, which argues that quantum mechanics is incomplete and that eality exists independently of observation. Bohr’s complementary philosophy and Heisenberg’s uncertainty principle were central to the formulation of the “Copenhagen interpretation,” which became dominant in the 20th century. However, the persistent opposition of scientists like Einstein and Schrödinger inspired generations of physicists to seek a unification between quantum mechanics and relativity, culminating in new theories such as loop quantum gravity and string theory. Thus, the debate between realism and anti-realism remains alive, and philosophy continues to play a crucial role in exploring the new foundations of physics.
On the Limits of “Undecidability”: Quantum Physics, Deconstruction, and Anti-realism Christopher Norris (bio) I Philosophers of science have responded in various ways to the conceptual and interpretative problems thrown up by quantum mechanics. These problems emerged a century ago from Planck’s researches into black-body radiation and have scarcely been resolved—rather, if anything, deepened and complicated—by the intensive debate that has surrounded them since that time.1 For some theorists, the resultant dilemmas (of observer “interference,” wave/particle dualism, quantum superposition, nonlocal causality, superluminal [faster-than-light] propagation, etc.) are such as to entail drastic revisions to our very idea of the physical world as existing and exerting its causal powers quite apart from our current best theories or investigative methods.2 For others again, quantum mechanics just is the best theory currently available, whatever the problems that it happens to create for our normal habits of logical thought or consistent reasoning on the evidence. Thus logic itself may have to be revised—right down to putative “laws of thought” such as noncontradiction and excluded middle—if these turn out to conflict with the results of quantum-mechanical theory or experiment.3 This is the view taken by Hilary Putnam in his writings on quantum logic and also by others, von Neumann among them, for whom the working rule in any such trade-off is to keep the physics as simple as possible even if the result is to complicate logic by introducing values other than those of determinate (bivalent) truth or falsehood.4 Very often it consorts with the argument that if quantum mechanics is right—at any rate on the standard Copenhagen interpretation—then we had best give up any hope of retaining a “classical” Einsteinian ontology, that is to say, a Lorentz-invariant account of space-time coordinates where the speed of light is the limiting value for assignments of position, velocity, and causal propagation.5 Hence Einstein’s famous series of debates with Niels Bohr when he devised a whole range of increasingly elaborate thought-experiments designed to prove that the quantum-mechnical description of reality had to be in some way “incomplete,” or not to have reckoned with some crucial factor that would bring it into line with logical reasoning and a causal-realist ontology. For on Einstein’s view there was simply no room in science for a theory—such as Bohr’s—that involved either the suspension of classical truth/falsehood [End Page 407] values or the idea of some “spooky action-at-a-distance” which contravened both commonsense realism and the requirements of Special Relativity.6 However it is Bohr who is generally thought to have carried the day in these debates. In which case—so it is argued—we are left with a choice between three possible “solutions.” These are (1) the hypothesis that quantum mechanics is “incomplete” or open to an alternative (“hidden-variables”) interpretation;7 (2) the adoption of an alternative (many-valued or non-bivalent) quantum logic that effectively conjures such problems away;8 or (3) the conclusion that realism may have to be abandoned in favour of some radically different ontology or worldview which counts this a price worth paying in order to conserve the predictive power of the standard quantum formalisms.9 On option (3) there is a further choice of interpretative views according to the theorist’s preferred choice between the various models (or possible-world scenarios) currently on offer. Thus the model may be one that embraces nonlocal simultaneous particle interaction, or which gives up space-time covariance (relative to the speed of light) as required by Einstein’s Special Theory. Or again it may be one that somehow envisions—strangest of all—the splitting-off of multiple coexistent but non-interacting “worlds” whenever the wave-packet collapses or whenever an act of measurement is performed upon any such quantum-system whose properties must be thought of as strictly indeterminate until that moment.10 For, according to its partisans, this theory is the most economical—i.e., involves least conflict with the standard quantum formalisms—despite its baroque proliferation of alternative worlds and its well-nigh unthinkable implications when applied...
Introduction It is not exaggeration to claim that one of the major divides in the foundations of non-relativistic quantum mechanics derives from the way physicists and philosophers understand the status of the wave function. On the instrumentalist side of the camp, the wave function is regarded as a mere instrument to calculate probabilities that have been established by previous measurement outcomes. On the other “realistic” camp, the wave function is regarded as a new physical entity or a physical field of some sort. While both sides agree about the existence of quantum “particles” (the so-called theoretical entities), and therefore reject the radical agnosticism about them preached by van Fraassen (1980), the various “realistic” (and consequently, instrumentalist) philosophies of quantum mechanics are typically formulated in different, logically independent ways, so their implications need to be further investigated. For instance, on the one hand it seems plausible to claim that a realistic stance about the wave function is not the only way to defend “realism” about quantum theory. One can support a “flash” or a “density-of-stuff ” ontology (two variants of GRW), or an ontology of particles with well-defined positions (as in Bohmian mechanics), as primitive ontologies for observer-independent formulations of quantum mechanics (Allori, Goldstein, Tumulka and Zanghí, 2008). “Primitive ontologies”, as here are understood, are not only a fundamental ground for other ontological posits, but also entail a commitment to something concretely existing in spacetime (see also Allori, 2013). On the other hand, however, it is still debated whether such primitive ontologies can be autonomous from some form of realism about the wave function (Albert, 1996). In order to discuss this problem, we begin with a preliminary clarification of the meaning of “realism” and “instrumentalism” in physics, which are often subject to ideological and abstract discussions that often have little to do with the practice of physics (Section 9.2).
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.
ABSTRACT The paper aims to bridge the history of quantum theory with its philosophical implications. The focus is not only on the scientific underpinnings of quantum mechanics (these theories emerged as ‘ad hoc’ responses to experimental anomalies) but also on the philosophical ramifications of its probabilistic nature and indeterminacy, which differ from classical realism. The paper examines Dirac's, Bell's, and modern views, focusing on how quantum mechanics (QM) challenges traditional notions of causality, objectivity, and truth while embracing epistemological and metaphysical perspectives. Debates over collapse theories and hidden variables are discussed, as well as Putnam's philosophical outlook, which includes his trenchant involvement with realism, logic, and the measurement problem. Finally, the paper proposes that QM represents a philosophical revolution that renews our understanding of reality, knowledge, and scientific explanation, rather than simply serving as a physical theory for assessing the prospects of quantum philosophy by connecting it to broader aspects such as relativity, causality, and scientific realism.
While philosophy of science is the study of problems of knowledge concerning science in general, there also exists - or should exist - a '' philosophy in science'' directed at finding out in what ways our actual scientific knowledge may validly contribute to the basic philosophical quest. Contrary to philosophy of science, which is a subject for philosophers, philosophy in science calls on the services of physicists. When, in its spirit, quantum theory and Bell's theorem are used as touchstones, the two main traditional philosophical approaches, realism and idealism, are found wanting. A more suitable conception seems to be an intermediate one, in which the mere postulated existence of a holistic and hardly knowable Mind-Independent Reality is found to have an explaining power. Some corrections to comments by Schins of a previous work on the same subject are incorporated.