The question of realism in physics is addressed by following the path laid out by Einstein and Bell. After an exposition of the problem of the completeness of quantum mechanics and a discussion of some aspects of the debate between Einstein and Bohr, we outline what are the requirements of a formulation of quantum mechanics that is not based on such vague and imprecise notions as “ measurement” or “ observer.” Finally , we show that a physical theory that describes “stuff” in the space that evolves over time makes transparent the relationship between theory and empirical reality. The conclusion has a Kantian flavor.
The question of realism in physics is addressed by following the path laid out by Einstein and Bell. After an exposition of the problem of the completeness of quantum mechanics and a discussion of some aspects of the debate between Einstein and Bohr, we outline what are the requirements of a formulation of quantum mechanics that is not based on such vague and imprecise notions as “ measurement” or “ observer.” Finally , we show that a physical theory that describes “stuff” in the space that evolves over time makes transparent the relationship between theory and empirical reality. The conclusion has a Kantian flavor.
The Bohr-Einstein debate on the interpretation of quantum mechanics may be viewed as a discussion on the epistemological status of knowledge gained by physics. It is shown that in fact the advent of quantum theory has led, in a new context, to an old philosophical controversy between epistemological realism (held by Einstein) and phenomenalism (held by Bohr). An inquiry into this controversy, taking into account the contemporary understanding of quantum mechanics based on the axiomatic study of its foundations, leads to the conclusion that contrary to widespread opinion, it is perfectly possible to formulate quantum mechanics in an entirely realistic manner according to the postulate of Einstein. We demonstrate that Bohr's episteme-logy, in which the role of experimental arrangements in the physical description is taken as a starting point, does not necessarily imply phenomenlism, but may be justifiably considered as a complementary standpoint to the realistic epistemology of Einstein, which is based on the notion of a mental construction which pictures reality.
RESUMENLos resultados empíricos y los análisis teóricos en física cuántica ni apoyan ni refutan concluyentemente el realismo. Aunque se mostrara que la interpretación de Copenhague era la única viable de entre todas las posibles, todavía quedaría por probar que con eso se había conculcado cualquier tipo de realismo. Bohr mismo aceptaba un realismo con tintes kantianos y mostraba desagrado hacia el instrumentalismo de Heisenberg. Pero además de la interpretación de Copenhague existen interpretaciones rivales que, a pesar de no estar tan desarrolladas como aquélla, dejan abierto el camino al realismo en la física cuántica. En particular la interpretación de David Bohm.PALABRAS CLAVEREALISMO CIENTIFICO – TEORIA CUANTICA – LOCALIDADABSTRACTThe empirical achievements and theoretical analyses in quantum physics neither support nor refute conclusively realism. Even if it were shown that Copenhagen Interpretation is the only feasible one between all the possible interpretations in quantum mechanics, it would remain to prove that it forbids every kind of realism. In fact, Bohr himself accepted a realism with Kantian aspects and disagreed whith Heisenberg’s instrumentalism. But there are interpretations, rival to Copenhagen’s, which in spite of not being son developped, smooth the way for realism in quantum physics. Particularly David Bohm’s interpretation.KEYWORDSSCIENTIFIC REALISM – QUANTUM THEORY – LOCALITY
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 foundations and meaning of quantum theory became a central issue to Albert Einstein and Niels Bohr since the onset of their impassioned debate in the 1920s, enriched by the contributions of many other distinguished scientists and philosophers.The questions are not settled down at all, despite the great achievements of the theory, its impressive accordance with experiment and predictive power.The fundamental and technological applications range from cosmology to biology, with the development of invaluable instruments and the design of new materials.Is quantum mechanics a complete or an incomplete theory?Is there an objective reality independent of the observer or is the reality created by the measurements?Are hidden-variable theories justifiable?Is there a quantum theory founded in a local-causal and non-linear approach that formally contains the orthodox linear theory as a special case?Can such a formulation unify classical and quantum physics?Are Heisenberg's uncertainty relations valid in all cases?Here, the subject is addressed as an adaptation of our contribution to the Colloquium "Quantal aspects in Chemistry and Physics.
The measurement problem in quantum mechanics first cropped up during the 1930s during a famous series of debates between Einstein and Bohr concerning the physical adequacy – or ‘completeness’ – of the orthodox (Copenhagen) theory.1 As we have seen, it is a topic central to Hanson’s thinking not only with regard to quantum mechanics but also for its wider bearing on the scope and limits of scientific knowledge, the theory-laden character of observations, and the underdetermination of theory by evidence.2 Thus it is frequently adduced in support of his proto-Kuhnian claim that scientists working within different paradigms must be thought of as observing different things or inhabiting ‘different worlds’.3 What I propose to do now is look in more detail at the arguments surrounding this topic and, especially, at various proposals – from Einstein down – for a realist construal of the quantum data (i.e., the empirical measurement-results) that would offer an alternative to Hanson’s idea of the uncertainty principle as placing an absolute limit on our knowledge of objects and events in the microphysical domain. Having set out his arguments already in chapters 4 and 5, I shall not make any further detailed reference to Hanson’s work but assume that the reader who has come this far will have them clearly in mind. Thus my purpose in the remainder of this book is to raise the question: what becomes of the paradigm-relativist approach to issues in the history and philosophy of science if it derives so much of its suasive force from an interpretation of quantum mechanics that has proved increasingly open to challenge?
‘Sprache und Wirklichkeit in der modernen Physik’ is the title of a lecture Heisenberg gave in 1960 at the Bayerische Akademie der Schönen Künste. The polemics that had accompanied the establishment of quantum mechanics were over by then and the so-called problems of its foundations had lost much of their initial interest. Einstein had been dead for some years. Right up to the end he had expressed his profound dissatisfaction with a theory which, in his opinion, had something unreasonable about it. With the volume dedicated to him by the community of physicists and philosophers, the long debate between Bohr and Einstein had come to an end. It had been a disappointing conclusion, marked by the reaffirmation of the respective viewpoints of two scientists who by now found great difficulty even in defining a common code of communication. As though seeking to narrow the gap between them, Heisenberg took the opportunity to underline the existence of a common feature in their contributions to 20th century physics. Their discoveries had in fact made it possible to recognize that ‘even the fundamental and most elementary concepts of science, such as space, time, place, velocity, have become problematic and must be re-examined’. The conceptual and cognitive implications of relativity and of quantum mechanics were obviously different but Heisenberg maintained that both theories asked the same question: ‘Does the language we use when we speak of experiments correspond to the artificial language of mathematics which, as we know, describes real relationships correctly; or has it become separated from it so that we must be content with imprecise linguistic formulations and only return to the artificial language of mathematics when we are forced to express ourselves with precision?’.