The objective of this article is to demonstrate how the historical debate between materialism and idealism, in the field of Philosophy, extends, in new clothes, to the field of Quantum Physics characterized by realism and anti-realism. For this, we opted for a debate, also historical, between the realism of Albert Einstein, for whom reality exists regardless of the existence of the knowing subject, and Niels Bohr, for whom we do not have access to the ultimate reality of the matter, unless conditioning it to the existence of an observer endowed with rationality, position adopted in the Interpretation of Complementarity (1927) – posture that was expanded in 1935 when Bohr assumed a “relationalist” conception, according to which the quantum state is defined by the relationship between the quantum object and the entire measuring device. This is an extremely important debate, as it further consolidates the results of nascent Quantum Mechanics, guaranteeing Bohr the leadership of the orthodoxy based on the interpretation of complementarity. Here, when dealing with Quantum Theory, we will not make any distinction between the terms Quantum Physics, Quantum Theory or Quantum Mechanics. The entire discussion will be held under the name “Quantum Theory”. Theory that tries to analyze and describe the behavior of physical systems of reduced dimensions, close to the sizes of molecules, atoms and subatomic particles. We hope that the reader will appreciate the genius of these two titans in this field of Physics when they magnificently formulate the arguments that support the object of their defenses.
The objective of this article is to demonstrate how the historical debate between materialism and idealism, in the field of Philosophy, extends, in new clothes, to the field of Quantum Physics characterized by realism and anti-realism. For this, we opted for a debate, also historical, between the realism of Albert Einstein, for whom reality exists regardless of the existence of the knowing subject, and Niels Bohr, for whom we do not have access to the ultimate reality of the matter, unless conditioning it to the existence of an observer endowed with rationality, position adopted in the Interpretation of Complementarity (1927) – posture that was expanded in 1935 when Bohr assumed a “relationalist” conception, according to which the quantum state is defined by the relationship between the quantum object and the entire measuring device. This is an extremely important debate, as it further consolidates the results of nascent Quantum Mechanics, guaranteeing Bohr the leadership of the orthodoxy based on the interpretation of complementarity. Here, when dealing with Quantum Theory, we will not make any distinction between the terms Quantum Physics, Quantum Theory or Quantum Mechanics. The entire discussion will be held under the name “Quantum Theory”. Theory that tries to analyze and describe the behavior of physical systems of reduced dimensions, close to the sizes of molecules, atoms and subatomic particles. We hope that the reader will appreciate the genius of these two titans in this field of Physics when they magnificently formulate the arguments that support the object of their defenses.
The objective of this article is to demonstrate how the historical debate between materialism and idealism, in the field of Philosophy, extends, in new clothes, to the field of Quantum Physics characterized by realism and anti-realism. For this, we opted for a debate, also historical, between the realism of Albert Einstein, for whom reality exists regardless of the existence of the knowing subject, and Niels Bohr, for whom we do not have access to the ultimate reality of the matter, unless conditioning it to the existence of an observer endowed with rationality, position adopted in the Interpretation of Complementarity (1927) – posture that was expanded in 1935 when Bohr assumed a “relationalist” conception, according to which the quantum state is defined by the relationship between the quantum object and the entire measuring device. This is an extremely important debate, as it further consolidates the results of nascent Quantum Mechanics, guaranteeing Bohr the leadership of the orthodoxy based on the interpretation of complementarity. Here, when dealing with Quantum Theory, we will not make any distinction between the terms Quantum Physics, Quantum Theory or Quantum Mechanics. The entire discussion will be held under the name “Quantum Theory”. Theory that tries to analyze and describe the behavior of physical systems of reduced dimensions, close to the sizes of molecules, atoms and subatomic particles. We hope that the reader will appreciate the genius of these two titans in this field of Physics when they magnificently formulate the arguments that support the object of their defenses.
According to the orthodox interpretation of quantum mechanics (Bohr being its leading voice), the attributes of a physical object (position, momentum, spin, etc.) can be assigned only when they have been measured. Einstein advocated the local realist viewpoint that an object had definite attributes whether they had been measured or not. The Copenhagen school view that measurement actually produces an object’s property would imply that the measurement of one part of an entangled quantum state can instantaneously fix the value of another part, no matter how far the two parts have been separated. Einstein, Podolsky, and Rosen devised a thought experiment to shine a light on this “spooky action-at-a-distance” feature; its discussion and debate have illuminated the meaning of quantum mechanics (QM). It led later to Bell’s theorem showing that these seemingly philosophical questions can lead to observable results. The experimental vindication of the orthodox theory has sharpened our appreciation of the nonlocal features of quantum mechanics. Nevertheless, the counter-intuitive QM picture of objective reality still troubles many, leaving one to wonder whether quantum mechanics is ultimately a complete theory.
The historical debate between Niels Bohr and Albert Einstein is often presented as anirreducible metaphysical opposition between contextualism and realism. We argue that itshould instead be understood as a conflict between implicit ontological frameworks, eachrationally defensible within the descriptive space available at the time. The central thesisdefended here is independent of any specific physical theory: the Bohr–Einstein tension isnot principled, but structural. Extended descriptive frameworks are introduced solely inan illustrative capacity, to show that a conceptual resolution is logically possible withoutcontradicting the established results of quantum mechanics.
This article explores Bohr's argument, advanced under the heading of 'complementarity,' concerning quantum phenomena and quantum mechanics, and its physical and philosophical implications.In Bohr, the term complementarity designates both a particular concept and an overall interpretation of quantum phenomena and quantum mechanics, in part grounded in this concept.While the argument of this article is primarily philosophical, it will also address, historically, the development and transformations of Bohr's thinking, under the impact of the development of quantum theory and Bohr's confrontation with Einstein, especially their exchange concerning the EPR experiment, proposed by Einstein, Podolsky and Rosen in 1935.Bohr's interpretation was progressively characterized by a more radical epistemology, in its ultimate form, which was developed in the 1930s and with which I shall be especially concerned here, defined by his new concepts of phenomenon and atomicity.According to this epistemology, quantum objects are seen as indescribable and possibly even as inconceivable, and as manifesting their existence only in the effects of their interactions with measuring instruments upon those instruments, effects that define phenomena in Bohr's sense.The absence of causality is an automatic consequence of this epistemology.I shall also consider how probability and statistics work under these epistemological conditions.
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.
The framework of a simple opposition realism – anti-realism is not enough to analyze the views on the reality of unobservable objects of quantum theory. First, it is necessary to distinguish between realism in relation to the theory and realism in relation to the theory’s objects. Secondly, realism in relation to classical objects can be combined, both with realism and with anti-realism in relation to quantum objects. Third, the concept of “existence” and “to exist objectively” can have different meanings. To take into account these factors, the article describes three approaches: classical realism, quantum anti-realism, and quantum realism. I show that the debate around quantum reality has intensified in recent decades due to a series of new quantum experiments. The current stage of the debate is caused by the second quantum revolution relating to the transfer and processing of quantum information. Classical realism and old versions of quantum anti-realism have become insufficiently effective to explain the results of a series of experiments. Proponents of quantum realism, in turn, refer to the possibility of using the wave function to manipulate quantum objects before their measurement. In conclusion, I assume that not only theoretical discussions but also experiments and new technologies can have a major impact on the seemingly purely philosophical debate about reality.