This article examines the epistemological views of key quantum physicists of the Copenhagen circle (Niels Bohr, Werner Heisenberg and Léon Rosenfeld). The discussion begins with a presentation of their conception of measurement, indeterminacy and complementarity, and goes on to focus on their views regarding the nature of being and knowledge. The author identifies the basic areas of consensus in the Copenhagen circle as well as the disagreements and disputes that arose between its members. Three main points are argued: (1) The fundamental epistemological consensus in the group was that subject and object are inseparable; that the subject participates in the formation of images of reality, which are multiple and depend on how the subject is concretely constituted historically; the disagreements within the group did not arise with logical inevitability from the principles of quantum mechanics but largely stemmed from ideological clash in the Cold War context. (2) Being linked to specific configurations of the subjects, knowledge is always relative; but it does not follow that knowledge is illusory or inadequate; on the contrary, it is the pretension of attaining the ultimate nature of things “in themselves” that leads to devaluation of any concrete knowledge. (3) The world is something external, generally independent of our desires and will, but at the same time is constructed as concrete objects through the specific configuration of each concrete subject.
This article examines the epistemological views of key quantum physicists of the Copenhagen circle (Niels Bohr, Werner Heisenberg and Léon Rosenfeld). The discussion begins with a presentation of their conception of measurement, indeterminacy and complementarity, and goes on to focus on their views regarding the nature of being and knowledge. The author identifies the basic areas of consensus in the Copenhagen circle as well as the disagreements and disputes that arose between its members. Three main points are argued: (1) The fundamental epistemological consensus in the group was that subject and object are inseparable; that the subject participates in the formation of images of reality, which are multiple and depend on how the subject is concretely constituted historically; the disagreements within the group did not arise with logical inevitability from the principles of quantum mechanics but largely stemmed from ideological clash in the Cold War context. (2) Being linked to specific configurations of the subjects, knowledge is always relative; but it does not follow that knowledge is illusory or inadequate; on the contrary, it is the pretension of attaining the ultimate nature of things “in themselves” that leads to devaluation of any concrete knowledge. (3) The world is something external, generally independent of our desires and will, but at the same time is constructed as concrete objects through the specific configuration of each concrete subject.
This article deals with the Copenhagen interpretation of quantum mechanics and its epistemological discussion by Ernst Cassirer and Richard Hönigswald. The starting point is Cassirer's treatise Determinism and Indeterminism in Modern Physics, published in Stockholm. Both philosophers and several physicists were involved in the subsequent exchange of letters. From a physical point of view, the Copenhagen interpretation was particularly criticised by v. Laue and Einstein. Both demanded a revision of the foundations of quantum mechanics or a critical examination of essential physical concepts. The epistemological implications of the Copenhagen interpretation were rejected, in particular that the interactions between observation, the observed and the observer in quantum physics experiments should lead to a renunciation of the concept of causality or an objectively unambiguous description of natural processes. Cassirer argues here that quantum mechanics fulfils the epistemological requirement of transforming ontological “concepts of things” into epistemological concepts of relations and is therefore compatible with the neo-critical approach he advocates. At the same time, Hönigswald was working on two major treatises on the structure of physics and the concept of causality. Here he undertakes an epistemological foundation of physics as a whole. A transcendental foundation of the concept of experience and its specifications in principles such as contemplation, observation or experiment appears to be called for. Hönigswald therefore essentially rejects the Copenhagen interpretation, as it draws epistemological consequences by physical means and thus inadmissibly reverses the transcendentally necessary relations of justification. These arguments are examined and could be used for a current discussion on the epistemological foundations of quantum mechanics and physics as a whole. A post-Neo-Kantian, transcendental philosophical foundation of scientific knowledge, especially of modern physics, seems possible and necessary.
Far from regarding physical science as a universal model of human knowledge, Werner Heisenberg relativized the scientificity of natural science, situating this domain of knowledge in a wide range of our modes of experiencing the world. In this paper, with a focus on his critical analysis of the notion of objectivity in quantum theory and other fields, I survey Heisenberg’s view of the world as divided into six distinct areas of reality, including – but not centered on – physical science. I also seek to show how this conception of the structure of reality, specifically of the relation between different areas of reality, is mediated by his mis- or reinterpretation of Bohr’s idea of complementarity.
This paper argues against the possibility of presenting a consistent version of the Copenhagen Interpretation of Quantum Physics, characterizing its founders' philosophical pronouncements including those on the realism-antirealism issue, as a contingent collection of local, often contradictory, moves in changing theoretical and sociopolitical circumstances. The paper analyzes the fundamental differences of opinion between Bohr and the mathematical physicists, Heisenberg and Born, concerning the foundational doctrine of the “indispensability of classical concepts”, and their related disagreements on “quantum reality.” The paper concludes with an explanation of how the appearance of consensus was achieved despite fundamental disagreements among the proponents. The paper undermines the adequacy of the notion of a general conceptual framework to describe the philosophical endeavors of working scientists.
On October 24th, 1927, the world's most important physicists met in Brussels for what is known as the fifth edition of the Solvay Conference. The focus of the discussion was the new Quantum Mechanics, to which most of the people present at the meeting had contributed but about which they had contrasting opinions. On the one hand, Niels Bohr and Werner Heisenberg claimed they had provided the new science with a definite structure, not subject to further modifications, while on the other, eminent figures such as Erwin Schrodinger and Albert Einstein believed that the theories put forward by the so called Copenhagen School, of which Bohr and Heisenberg were the most important exponents, were incorrect or at least incomplete.
The ideas in Heisenberg's paper on quantum mechanics in 1925 mark the beginning not only of a new phase in modern physics, but also of Heisenberg's own philosophical journey. This thesis examines that journey between 1925 and the late 1950s by situating Heisenberg's philosophy of quantum mechanics in the context of his encounters with his contemporaries as well as the context of various strands of thought in the German-speaking world at the time. Heisenberg's early philosophical critique of the 'classical' viewpoint between 1925 and 1927 bears the decisive influence of Einstein's theory of relativity, more specifically, the positivism he saw as underpinning Einstein's emancipation from Newtonian physics. The positivist influence on Heisenberg's early attitude to quantum mechanics is evident in three ways: (a) his invocation of an observability principle in 1925 to justify the renunciation of the concept of the electron orbit, (b) an instrumentalist conception of understanding, which characterised Heisenberg's response to Schrodinger's demand for classical visualisation in space and time in 1926-7, and (c) the introduction of an operational definition of concepts such as position and velocity in 1927, in an attempt to replace the concepts of classical physics. But after discussions with Bohr and Einstein in 1926-7, Heisenberg soon recognised what we might term his `empiricist' viewpoint was problematic. In 1927 Heisenberg's thought undergoes a shift away from the `empiricist' viewpoint that had underpinned his early philosophy of quantum mechanics. The nature and scope of this transformation, which forms the central theme in this thesis, has, up until now, been poorly understood and often completely neglected. Through his discussions with Bohr, Heisenberg came to the realisation that despite their limitations, classical concepts were conditions for the possibility of the description of all experience. This marked the abandonment of his earlier attempt to replace classical concepts with quantum concepts. The recognition of the primacy of classical language forms the point of departure for much of Heisenberg's later thought, which brought him into contact with the attempts in the German-speaking world in the 1920s to reconstruct Kantian epistemology. By the mid-1930s, Heisenberg advocated a 'pragmatic transformation' of Kantian philosophy, in which classical concepts were held to be a priori in the sense that they remained the conditions for the possibility of experience, but were no longer held to be necessary or universal in a strict Kantian sense. After 1940 Heisenberg saw the paradoxes of quantum mechanics under the aegis of what can be termed a 'transcendental conception of language', according to which language is not a mere tool, but actively shapes, gives form, and objectifies, our 'reality'. The limits of a classical 'description' in quantum mechanics therefore came to signify for Heisenberg, the limits of 'objective reality'. While Bohr exerted perhaps the most important philosophical influence on Heisenberg, their intellectual relationship was characterised by disagreement and misunderstanding. This is most strikingly displayed in their respective views on wave-particle duality and complementarily. While after 1927 Heisenberg accepted Bohr's basic insight that our knowledge of the quantum world is mediated through classical language, he did not share Rohr's interpretation of complementarity. While Heisenberg certainly used terms such as 'complementarity' and wave-particle duality' in his writings, a close reading reveals that these terms had very different meanings for the two physicists. This is particularly evident in the contrast between Heisenberg's notion of wave-particle equivalence and Bohr's idea of complementarity. In bringing to light these divergences between Bohr and Heisenberg, this thesis lends further weight to the view - already advocated by scholars such as John Hendry and Mara Beller - that the so-called Copenhagen interpretation of quantum mechanics should not be thought of as a unified philosophical position, but actually comprises a number of different strands.
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.