There are two broad opposing classes of attitudes to reality (realist vs idealist, material vs mental) with corresponding attitudes to knowledge (objective vs subjective, scientific vs romantic). I argue that these attitudes can be compatible, and that quantum theory requires us to adopt both of them.
Reality is a word that carries many meanings and subtlely nuanced concepts. In order to have some reliable understanding of what Einstein and Tagore could have meant when they talked about reality, it is necessary to glean their conceptions from a broad survey of their writings and utterances over many years. Tagore's view on reality was strongly epistemological in character. He was by no means an orthodox idealist, as he is often made out to be. The predominant view is that quantum reality is fundamentally different from classical reality. The uncontrollable effect of a measurement on a quantum system makes all observed phenomena intrinsically probabilistic in nature, and the distinction between the observer and the observed is blurred. The putative nonlocality of quantum mechanics is usually inferred from violations of Bell inequalities by entangled quantum states. However, there are many interpretations of quantum mechanics that do away with this controversial postulate, such as Everett's interpretation and its offspring.
The proper goal of science is a unified theory of all of nature, including our thoughts. An adequate theory of this kind will resolve the quantum measurement problem, which is to reconcile the nonclassical character of the quantum world with the classical character of our perceptions of it. A framework for such a theory is described. It weds the opposing views of Bohr and Einstein. Bohr held that quantum theory provides rules that relate aspects of our knowledge, while Einstein claimed that basic theory should describe what could be reality itself, not merely our knowledge of it.
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.
Now that my account of Bohr's philosophy of physics has been completed, it remains for me to give a general assessment of it. What value should we assign to Bohr's main ideas – the notions of correspondence and complementarity? How does his interpretation of quantum physics fare in comparison with some of its rivals? What should our assessment of the Bohr–Einstein debate be? I shall take up these questions in the reverse order. Einstein or Bohr? The final verdict The Bohr–Einstein debate is primarily a dispute about the philosophical foundations in terms of which the interpretation of quantum mechanics should be based: specifically it is a dispute about the intrinsic-properties theory, i.e. about the scope of a realist interpretation of quantum mechanics. Einstein wished to maintain the two realist theses, the intrinsic-properties theory and the objective-values theory, whereas Bohr wished to hold only the latter. My own philosophical leanings are in the direction of realism. To my mind the notion of a physical reality the existence and constitution of which are independent of human thought and perception is coherent and plausible: what physical objects there are, and what properties they have, is not determined by human thought or perception, or by human practical interests. I have sympathy, therefore, with Einstein's position concerning the indefinability thesis and the question of the completeness of quantum mechanics.
Arguably the most important scientific debate of the 20th Century was that which took place between Albert Einstein and Niels Bohr over the nature of reality. Bohr argued that reality was subjective in nature and therefore depended on the presence of an observer or observing process, while Einstein argued that reality had to be objective. The debate was never resolved, ending prematurely with Einstein's death in 1955. Having outlived Einstein, Bohr's ideas have come to dominate modern physics and Einstein has been somewhat sidelined. Perhaps now it is time to revisit the debate to see if Einstein was correct all along.