I could be bounded in a nutshell, and count myself a king of infinite space. Shakespeare , Hamlet, Act 2 Scene 2 Introduction As we saw in the last chapter, the received account of the relation between classical and quantum mechanics is a form of reductionism, where classical mechanics is supposed to emerge from quantum mechanics in the limit of some parameter. When we examine more closely the views of three of the key founders of quantum theory, however, we see that none of them took the relation between these theories to be adequately captured by such a reductionist limit. Indeed as we shall see presently, Werner Heisenberg's account of the relation between classical and quantum mechanics is actually a strong form of theoretical pluralism, quite similar to Nancy Cartwright's metaphysical nomological pluralism introduced in Section 1.3. Rather than viewing quantum mechanics as the fundamental theory that replaced classical mechanics, Heisenberg argues that both theories are required, each having its own proper domain of applicability and each being a perfectly accurate and final description of that domain. Throughout his career, Heisenberg held a highly original view in the philosophy of science, centered on his notion of a closed theory. Very briefly, a closed theory is a tightly knit system of axioms, definitions, and laws that provides a perfectly accurate and final description of a certain limited domain of phenomena. This notion has profound implications for Heisenberg's understanding of scientific methodology, theory change, intertheoretic relations, and realism.
I could be bounded in a nutshell, and count myself a king of infinite space. Shakespeare , Hamlet, Act 2 Scene 2 Introduction As we saw in the last chapter, the received account of the relation between classical and quantum mechanics is a form of reductionism, where classical mechanics is supposed to emerge from quantum mechanics in the limit of some parameter. When we examine more closely the views of three of the key founders of quantum theory, however, we see that none of them took the relation between these theories to be adequately captured by such a reductionist limit. Indeed as we shall see presently, Werner Heisenberg's account of the relation between classical and quantum mechanics is actually a strong form of theoretical pluralism, quite similar to Nancy Cartwright's metaphysical nomological pluralism introduced in Section 1.3. Rather than viewing quantum mechanics as the fundamental theory that replaced classical mechanics, Heisenberg argues that both theories are required, each having its own proper domain of applicability and each being a perfectly accurate and final description of that domain. Throughout his career, Heisenberg held a highly original view in the philosophy of science, centered on his notion of a closed theory. Very briefly, a closed theory is a tightly knit system of axioms, definitions, and laws that provides a perfectly accurate and final description of a certain limited domain of phenomena. This notion has profound implications for Heisenberg's understanding of scientific methodology, theory change, intertheoretic relations, and realism.
Today there is no agreement on which, if any, of the several known realist interpretations of quantum mechanics is the correct one, and disagreement on this matter is not merely verbal, but substantial. However, I will show that the interpretations share a common aim: to recover the classical world given that it is quantum. This aim responds to implicit and well-entrenched philosophical intuitions that can be phrased in terms of intertheory relations, traditionally involving theory reduction, in philosophy, and the quantum-classical limit, in the foundations of physics. However, not one of those notions is free from controversies, and many contest that there is a smooth transition from the quantum to the classical. Hence, the account of the relationship between quantum mechanics and classical mechanics is an unresolved problem, and the philosophical character of the underlying framework can be contested. This thesis will offer a critical analysis of current well-known realist interpretations and will also put forward an alternative framework. I will critically examine traditional views on intertheory relations and the recent view of interstructuralism. My main claim will be that the role of intertheory relations is overrated, because a more basic question has to be answered first: 'what is a quantum system?'. That will motivate my novel view. I will critically evaluate and defend an alternative view based on the philosophy of Werner Heisenberg. The view proposes that physical theories should be regarded as "closed" systems. This has immediate implications for how we should understand intertheory relations in general, as well as scientific realism in particular. My view will appear radical in comparison to traditional views of quantum mechanics. Yet, I will examine fruitful comparison with forms of realism such as perspectivism and metaphysical pluralism. I shall conclude with indications for future work.
There are many important questions that do not fall neatly into any one discipline; rather, their full investigation requires the integration of two or more distinct fields. This book is about just such a question – one that arises at the intersection of physics, philosophy, and history. The question can be simply stated as “What is the relation between classical and quantum mechanics?” The simplicity of the question, however, belies the complexity of the answer. Classical mechanics and quantum mechanics are two of the most successful scientific theories ever developed, and yet how these two very different theories can successfully describe one and the same world – the world we live in – is far from clear. One theory is deterministic, the other indeterministic; one theory describes a world in which chaotic behavior is pervasive, and the other a world in which it is almost entirely absent. Did quantum mechanics simply replace classical mechanics as the new universal theory? Do they each describe their own distinct domains of phenomena? Or is one theory really just a continuation of the other? In the philosophy literature, this sort of issue is known as the problem of intertheoretic relations. Currently, there are two accepted philosophical frameworks for thinking about intertheoric relations: the first is reductionism, and the second, pluralism. As we shall see, these labels each actually describe a family of related views.
Classical mechanics and quantum mechanics are two of the most successful scientific theories ever discovered, and yet how they can describe the same world is far from clear: one theory is deterministic, the other indeterministic; one theory describes a world in which chaos is pervasive, the other a world in which chaos is absent. Focusing on the exciting field of 'quantum chaos', this book reveals that there is a subtle and complex relation between classical and quantum mechanics. It challenges the received view that classical and quantum mechanics are incommensurable, and revives another, largely forgotten tradition due to Niels Bohr and Paul Dirac. By artfully weaving together considerations from the history of science, philosophy of science, and contemporary physics, this book offers a new way of thinking about intertheory relations and scientific explanation. It will be of particular interest to historians and philosophers of science, philosophically-inclined physicists, and interested non-specialists.
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.
I distinguish two senses in which one can take a given physical theory to be `complete'. On the first, a complete physical theory is one that, in principle, completely describes physical reality. On the second, a complete physical theory is one that provides all of the conceptual resources one needs to describe any (in general probabilistic) physical phenomenon to any level of detail one likes, in principle. I argue that while the (neo-)Everettian approach to interpreting quantum mechanics aims to show that it is complete in the first sense, the (neo-)Bohrian approach begins from an understanding of quantum mechanics as being complete in the second sense. I then discuss some of the essential differences between how classical and quantum theory describe phenomena, and the way in which the quantum description can be thought of as a ``natural generalisation'' (to use Bohr's phrase) of the classical description. Finally, I elaborate upon the two visions of physics from which one can motivate the first and the second sense of completeness, respectively: \emph{metaphysical realism}, on the one hand, and what I will call \emph{methodological realism}, on the other -- and discuss what one can say about the significance of the differences between quantum and classical description from each of these points of view. I suggest that there is a sense in which the views of (neo-)Everett and the views of (neo-)Bohr can be understood to be mutually supporting positions, from their respective perspectives, even though they are diametrically opposed.
In PHYSICS AND PHILOSOPHY: The Revolution Modern Science, (1) Werner Heisenberg aims, in not too technical language, to clarify change concept of reality manifesting itself quantum theory. He means to contribute to an articulation of the (not only epistemology) that underlies quantum theory's modified logical patterns. (2) To highly unusual degree, Heisenberg is gripped by sense of responsibility of modern quantum physicist to convey, language immediately intelligible to thinking public, his most serious and far-reaching reflections on metaphysical implications of his scientific work. One may go so far as to say that there is substantial evidence, partly within Physics and Philosophy, that Heisenberg regards such reflections and their public communication as his most important task. Heisenberg is especially apt for this intensely self-conscious contribution to humanity's historical-cultural development because his stature as principal originating architect of quantum at its most fundamental level is complemented by his deployment of an unusually broad and deep erudition and lifelong preoccupation with philosophic and artistic ontology from Anaximander through Kant and Goethe to Heidegger. No thinker has yet appeared who possesses such an authoritative combination of decisively necessary learning quantum physics and historical development of philosophic ontology. Despite flurry of renewed scholarly interest development of Heisenberg's scientific work, (3) and his complex relation to dramatic unfolding of German cultural his time, (4) there has yet to be executed sustained and philosophically critical interpretative commentary on this book that is his crucial philosophical-ontological legacy. Given profound ontological puzzles that continue to attend quantum physics and its implications for humanity's past as well as present and future conception of reality, such critical exegesis of this text is overdue. In what follows I try to extricate central nerve of Heisenberg's sinuously unfolding, dialectical exposition, and process to elucidate its strengths but also its deep ambiguities and perplexities--which express, I believe, fundamental dilemmas that pervade contemporary ontology. I Heisenberg makes inviolability of principle of noncontradiction cornerstone of his discussion. Unlike Aristotle (5) Heisenberg does not wrestle with challenge posed by possible denial of principle. He understands nonmathematical articulation of quantum to escape what would otherwise be devastating contradictions--most obviously contradiction wave/particle character of basic entities described by theory--through Bohr's famous principle of complementarity (which Heisenberg closely associates with von Weizsacker's notion of coexistent states), combined with Heisenberg's own principle of potentia, potentiality, potentialities. (6) II After brief introduction, Heisenberg his second chapter sketches history of quantum theory and process begins to explain what he means by potentia. In 1924 Bohr and his colleagues tried to solve apparent contradiction between picture and particle picture by concept of wave. The electromagnetic were treated not as 'real' waves but as mathematical descriptions of probabilities, every point relevant space, for the absorption (or induced emission) of light quantum by an atom at this point. Later this idea of was applied more effectively to much more abstract mathematical in many-dimensional configuration space that was discovered through researches of Schrodinger. Heisenberg reinterprets this mathematical probability wave ontological tenus, as signaling tendency [Tendenz] for a definite happening [einem bestimmten Geschehen], thus introducing remarkable kind of physical reality, standing middle between possibility and actuality: a quantitative version of old concept of 'dunamis' or 'potentia' philosophy of Aristotle. …