Bohr’s theory of the atom is surely the theory most often labelled ‘inconsistent’ by philosophers of science. However, one does not find in the literature what would count as a rigorous treatment of the inconsistency: the derivation of a contradiction from a set of statements. And if the inconsistency is the obvious one between Bohr’s postulates and classical electrodynamics, then it remains unclear what makes ‘Bohr’s theory’—or ‘old quantum theory’—a paradigm case of an internally inconsistent theory. In this chapter the method presented in Chapter 2 is put to work: we look at five different inconsistency claims which have been made, and consider the significance of those claims given the assumptions which have to be in place to make them stick. In the end it is argued that the most significant, historically relevant inconsistency is one pertaining to the later theory, an inconsistency barely discussed in the philosophy of science literature.
Bohr’s theory of the atom is surely the theory most often labelled ‘inconsistent’ by philosophers of science. However, one does not find in the literature what would count as a rigorous treatment of the inconsistency: the derivation of a contradiction from a set of statements. And if the inconsistency is the obvious one between Bohr’s postulates and classical electrodynamics, then it remains unclear what makes ‘Bohr’s theory’—or ‘old quantum theory’—a paradigm case of an internally inconsistent theory. In this chapter the method presented in Chapter 2 is put to work: we look at five different inconsistency claims which have been made, and consider the significance of those claims given the assumptions which have to be in place to make them stick. In the end it is argued that the most significant, historically relevant inconsistency is one pertaining to the later theory, an inconsistency barely discussed in the philosophy of science literature.
Niels Bohr's philosophical view of quantum mechanics has been the subject of extensive scholarship for the better part of five decades. Yet Bohr’s writings have remained obscure, as evidenced by the variety of different scholarly interpretations of his work. In this chapter, I review the historiography of Bohr scholarship, arguing that his meaning has remained elusive because his central preoccupations lay not so much with an interpretation of the quantum-mechanical formalism, which many commentators see as the problem of quantum theory, but rather with the epistemological question of how we can acquire empirical knowledge of quantum objects by means of experiment. Bohr’s doctrine of classical concepts, I argue, is therefore best understood as a philosophy of experiment.
Something is rotten in the state of Denmark. Shakespeare , Hamlet, Act 1 Scene 4 The rise and fall of the old quantum theory The principles of the old quantum theory were first articulated by Niels Bohr in 1913 in a three-part paper titled “On the Constitution of Atoms and Molecules.” Bohr had adopted Ernest Rutherford's model of the atom, according to which the mass of the atom is concentrated in a small central nucleus, while the electrons orbit the nucleus in planetary trajectories. The key challenge facing Rutherford's model was that it was unstable: according to classical electrodynamics, the electron, which is a moving charged body, should radiate energy and so eventually collapse into the nucleus. Bohr's solution was to incorporate Max Planck's theory of radiation, according to which “the energy radiation from an atomic system does not take place in the continuous way assumed in ordinary electrodynamics, but that it, on the contrary, takes place in distinctly separated emissions” (Bohr 1913, p. 4; BCW 2, p. 164). In this early paper, and most subsequent accounts, Bohr summarized his quantum theory by means of two assumptions or postulates. According to the first postulate, electrons cannot travel in any path they like around the nucleus, rather atomic systems can only exist in a series of discrete “stationary states,” in which the electron is in a particular allowed stable periodic orbit and is not emitting radiation.
Bohr’s atomic model is one of the better known examples of empirically successful, albeit inconsistent, theoretical schemes in the history of physics. For this reason, many philosophers use this model to illustrate their position for the occurrence and the function of inconsistency in science. In this paper, I proceed to a critical comparison of the structure and the aims of Bohr’s research program – the starting point of which was the formulation of his model – with some of its contemporary philosophical readings. My study comes to conclude that the attempt of certain philosophers to accommodate Bohr’s model to a form of paraconsistent logic obliterates essential aspects of scientists' actual practice and reasoning.
“Bohr was primarily a philosopher, not a physicist, but he understood that natural philosophy ... carries weight only if its every detail can be subjected to the ... test of experiment” (Heisenberg in [59], p. 95). As a result his approach differed from that of theschool-philosopherswhom he regarded with a somewhat “sceptical attitude, to say the least” ([59], p. 129) and whose lack of interest in “the important viewpoint which had emerged during the development of atomic physics” he noticed with regret ([59], p. 183).But it also differed, and to a considerable degree, from the spirit of what Professor T. S. Kuhn has called a “normal science.” Looking at Bohr's method of research we see that technical problems, however remote, are always related to a philosophical point of view; they are never treated as “tiny puzzles” whose solution is valuable in itself, even if one has not the faintest idea what it means, and where it leads: “For me” Bohr writes to Sommerfeld in 1922 ([59], p. 71) “[the quantum theory] is not a matter for petty didactic details, but a serious attempt to reach ... an inner coherence.” Emphasis is put on matters of principle ([59], p. 36) and minor discrepancies, or “puzzles” in the sense of Kuhn, instead of being deemphasized, and assimilated to the older paradigm,are turned into fundamental difficultiesby looking at them from a new direction, and by testing their background “in its furthest consequences by exaggeration” ([59], p. 329). A noteworthy example of Bohr's “non-normal” and rather metaphysical approach to physics is his scepticism in the face of the success of his own atomic model.
Quantum theory has passed through three distinct stages during its evolution. The first is generally referred to as ‘old quantum theory’. During a period roughly between 1900 and 1925 Planck, Bohr and Einstein, among others, grappled with various experimental and theoretical crises by patching up classical mechanics with some new quantum ideas applied as band-aids. This is not to disparage the work; it was vitally important, and you can only do what is possible at the time. The quantum world is very different to the picture painted by classical physics. That being the case and given the extreme nature of some of these differences, we might question the wisdom of accepting the quantum view. Scientists can be quite disparaging about philosophy, sometimes while in the process of espousing, quite stridently, a philosophical position of their own. The chapter also presents an overview on the key concepts discussed in this book.
Niels Bohr and Philosophy of Physics: Twenty-First Century Perspectives examines the philosophical views, influences and legacy of the Nobel Prize physicist and philosophical spokesman of the quantum revolution, Niels Bohr. The sixteen contributions in this collection by some of the best contemporary philosophers and physicists writing on Bohr's philosophy today all carefully distinguish his subtle and unique interpretation of quantum mechanics from views often imputed to him under the banner of the “Copenhagen Interpretation.” With respect to philosophical influences on Bohr's outlook, the contributors analyse prominent similarities between his viewpoint and Kantian ways of thinking, the views of the Danish philosopher Harald Høffding, and themes characteristic of American pragmatism. In recognizing the importance of Bohr's epistemological naturalism they examine his defence of the indispensability of classical concepts from a variety of different perspectives. This collection shows us that Bohr's interpretation of quantum mechanics, now nearly a century old, still has the power to shed light on a variety of issues that have arisen only since his lifetime, as well as decoherence theory and other non-collapse interpretations. Balancing historical themes with contemporary discussions, Niels Bohr and the Philosophy of Physics establishes Bohr's on-going contribution to the philosophy of physics and examines his place in the history of philosophy.