RUSSELL HANSON, DAVID BOHM AND OTHERS ON THE SEMANTICS OF DISCOVERY
BOOK VII - Page 1
Norwood Russell Hanson (1924-1967), born in New Jersey, was a U.S. Marine Corps fighter pilot during the Second World War, who earned the rank of major, and was awarded the Distinguished Flying Cross and the Air Medal for flying combat missions over Japan. Afterward he studied at the University of Chicago, Columbia University, and Yale University in the United States, and then studied at both Oxford University and Cambridge University in England. He received a Ph.D. from Oxford in 1955 and a Ph.D. from Cambridge in 1956, and was afterward a fellow at the Institute for Advanced Study at Princeton. He accepted a faculty appointment at Indiana University in 1957, where he was founder and chairman of Indiana University's Department of History and Logic of Science from 1960 to 1963. He then accepted a professorship on the philosophy department faculty of Yale University, which he had at the time of his premature death at the age of forty three in a crash of his private airplane in 1967. His principal works are Patterns of Discovery (1958) and Concept of the Positron (1963). At the time of his death he left an uncompleted textbook in philosophy of science intended for first-year college students, which was edited by Willard C. Humphreys, a former student of Hanson, and then published as Perception and Discovery (1969). A year after his death a complete bibliography of his publications appeared in a memorial volume of Boston Studies in the Philosophy of Science, Volume III (1968).
David Bohm (1917-1992) was born in Wilkes-Barre, PA, and received his doctorate in physics from the University of California. He taught physics at Princeton, and eventually moved to England. He was professor of theoretical physics from 1961 at Birkbeck College, University of London, where he was professor emeritus from 1983 until his death in 1992. A brief biography may be found in the "General Introduction" in Quantum Implications (ed. B.J. Hiley and F. David Peat, 1987), and a three-hundred-fifty page biography by David Peat was later published under the title Infinite Potential: The Life and Times of David Bohm (1997). Bohm’s initial statement of his hidden-variable interpretation of quantum theory was published in 1952 in two articles in the Physical Review, in which he reports that the interpretation was originally stimulated by a discussion with Einstein in 1951. His principal statements of his hidden-variable interpretation of quantum theory are set forth in two of his books. The earlier is a brief monograph of only one-hundred-forty pages titled Causality and Chance in Modern Physics published in 1957, and the more recent is his more elaborate Undivided Universe co-authored with Basil Hiley and posthumously published in 1993. After publishing his seminal articles in 1952, he found that his interpretation had been anticipated in important respects in 1927 by Louis de Broglie (1892-1987). De Broglie's interpretation had been criticized severely, and he had consequently abandoned it, but Bohm had further developed the thesis enough that the fundamental objections confronting de Broglie had been answered. Bohm's interpretation was shown to be consistent with all the experimentally detectable effects then known about of the quantum phenomena, and additional suggestions were made by Vigier, a colleague of de Broglie. De Broglie then returned to his original proposals, since he believed that the decisive objections against them had been answered. Bohm and Vigier afterwards published a joint paper setting forth the interpretation in the Physical Review in 1954, and de Broglie wrote a "Foreword" to Bohm's 1957 book. Bohm was one of the physicists who recognized nonlocality (a.k.a. entanglement) in the quantum theory. Peat’s generally sympathetic biography shows how the idea of nonlocality led Bohm firstly to his wholistic ontology for physics, then to his process metaphysics, and finally to his mysticism of the implicate order, according to which mind and matter are indivisibly united. To the dismay and consternation of his friends and colleagues, this mysticism was encouraged by Bohm’s long-time association with an Indian guru, and also led Bohm to take seriously the mind-over-matter exhibitions of a stage magician.
Hanson takes very seriously issues about the interpretation of the modern quantum theory, and he truculently defends the Copenhagen interpretation. In “Appendix II” to his Patterns of Discovery he notes that while for most practical microphysical problems Born, who accepted the Copenhagen interpretation, and Schrödinger, who did not, would have made the same theoretical calculations. Nevertheless, their alternative interpretations organized their thinking differently, and consequently influenced their future research work in very different ways. After 1930 Born was led to work on collision behavior, on the statistical analysis of scattering matrices, while Schrödinger pursued investigation of the so-called ghost waves of the elementary particles. The interpretations, therefore, are important because each supplies an agenda that influences the direction of future research in physics.
But Hanson does not view all interpretations as equally worthy of consideration, and he considers particularly unfortunate is the "hidden-variable" interpretation developed by David Bohm. In contrast to the Copenhagen interpretation with its duality thesis that the wave and particle are two manifestations of the same physical entity, Bohm’s alternative interpretation is that the wave and particle are different physical entities, even though they are never found separately. Furthermore it says that the wave oscillates in an as yet experimentally undetected and therefore hidden subquantum field. In the context of the topic of scientific discovery Bohm’s views are interesting, because they illustrate the semantical approach to scientific discovery and to the development of theory in physics. His views illustrate the use of linguistic figures of speech as a technique for theory development based on certain postulated basic similarities between the macrophysical and microphysical orders of magnitude, similarities that are denied by advocates of the Copenhagen interpretation. But firstly consider Bohm’s early advocacy of the Copenhagen interpretation, and then turn to his later agenda for future physics including his hidden-variable alternative to the Copenhagen interpretation for quantum theory.
Bohm's Early Copenhagen Views
The hidden-variable thesis is Bohm’s more mature view. He started out as an advocate of the Copenhagen interpretation, which he also calls the “usual” interpretation, and then changed his mind after the talk with Einstein in 1951, the year in which his textbook titled Quantum Theory was published setting forth his earlier view. There are at least two noteworthy features of this early book. The first is Bohm’s distorted understanding of Bohr’s philosophy of quantum theory. The second is his ontology for quantum theory, the ontology of potentialities, which anticipated Heisenberg’s similar ontology of potentia by seven years.
In the “Preface” to his Quantum Theory Bohm says that as a result of the work of Neils Bohr, it has become possible to express the results of quantum theory in terms of comparatively qualitative and imaginative concepts, which are totally different from those appearing in the classical theory. He rejects the view that the quantum properties of matter imply the renunciation of the possibility of these properties being understood in the customary imaginative sense, and that they imply the sufficiency of only a self-consistent mathematical formalism which can in some mysterious way correctly predict the numerical results of experiments. The eighth chapter of the book is titled “An Attempt to Build a Physical Picture of the Quantum Nature of Matter”, and Bohm writes in a footnote that many of the ideas appearing in the chapter are an elaboration of material in Bohr’s Atomic Theory and the Description of Matter. However, Bohm’s understanding of Bohr is distorted. Bohr maintained an instrumentalist view of the equations of quantum theory, which rejects any semantics or ontology for quantum theory, and he repeatedly denied explicitly that quantum phenomena are pictureable. From Bohm’s statement in his 1952 articles that his hidden-variables thesis was the result of a talk with Einstein in 1951, it is reasonable to speculate that Einstein had read Bohm’s book, had recognized that Bohm was ripe for disillusionment with the views in Bohr’s philosophy, and had concluded that Bohm was ready for induction into the ranks of Bohr’s critics. In any event whatever may have been Einstein’s unreported comments to Bohm in their private conversation, the ultimate outcome after forty years was Bohm’s Undivided Universe: An Ontological Interpretation of Quantum Theory (1973), a book in which Bohm explicitly says he is supplying an ontology to replace the epistemological interpretation he thought he had found in Bohr’s writings.
The ontology for quantum theory that Bohm described in 1951 is a wholistic ontology of potentialities, in which the world is an indivisible unit where quanta have no component parts describable by hidden variables, and are not even separate objects, but are only a way of talking about indivisible transitions. This metaphysics is also called monism. At the quantum-mechanical level the properties of a given object do not exist separately in the quantum object alone, but rather are potentialities which are realized in a way that depends on the systems with which the object interacts. Thus the electron has the potentiality for developing either its particle-like or its wave-like form, depending on whether it interacts with an apparatus that measures either its position or momentum. Bohm’s views are also realist; he does not maintain that the quantum phenomenon has its properties because it is being measured. He says that a quantum-mechanical system can produce classically describable effects not only in a measuring apparatus, but also in all kinds of systems that are not actually being used for the purpose of making measurements. Throughout the process of measurement the potentialities of the electron change in a continuous way, while the forms in which these potentialities can be realized are discrete. The continuously changing potentialities and the discontinuous forms in which the potentialities may be realized are complementary properties of the electron.
Bohm anticipated Heisenberg’s idea of potentiality, which Heisenberg did not propose until his Physics and Philosophy in 1958, the only place in Heisenberg’s literary corpus where the idea is mentioned. But there are differences in their ideas of potentiality, because unlike Bohm’s, Heisenberg’s is not a wholistic version. In the 1951 book Bohm said that potentiality makes quantum theory inconsistent with the hidden-variables thesis, because the hidden-variables view is based on the incorrect assumption that there are separately existing and precisely defined elements of reality. The idea of potentiality is much more integral to Bohm’s earlier interpretation than to Heisenberg’s, and it had distinctive implications for Bohm. One implication is Bohm’s thesis that mathematics is inadequate for physics. He says that the interpretation of the properties of the electron as incompletely defined potentialities finds its mathematical reflection in the fact that the wave function does not completely determine its own interpretation until it interacts with the measuring device, and that the wave function is not in one-to-one correspondence with the actual behavior of matter, but is merely an abstraction reflecting only certain aspects of reality. He believes that to obtain a description of all aspects of the world, one must supplement the mathematical description with a physical interpretation in terms of the incompletely defined potentialities.
Shortly afterwards he accepted the hidden-variables idea, and in the second chapter of his Undivided Universe, where he mentions in a footnote his anticipation of Heisenberg’s idea of potentiality, he rejects altogether the potentiality thesis that the particle itself is created by the measurement process. In Bohm’s hidden-variables view, the particle is not a wave-packet or otherwise created out of the wave; the particle is in reality distinct from the wave. His later view is not wave or particle, but wave and particle. That is, the wave and particle are not two alternative aspects of the same entity, but are different and separate entities.
Bohm's Agenda for Future Microphysics
Bohm's hidden-variable interpretation is an agenda for future microphysics, and his Causality and Chance (1957) sets forth three related objectives in this agenda. His first objective is the relatively modest one of demonstrating that an alternative to the Copenhagen interpretation is possible, in the sense that it is not the only one that is consistent with the formalism and measurements of quantum theory. He states this objective not only because he has another interpretation in mind, but also because he maintains that the development of alternative views is important for the advancement of science, while advocates of the Copenhagen interpretation deny that any alternative view including one involving a subquantum order of magnitude is conceivable. For example in his "Questions of Principle in Modern Physics" (1935) in Philosophical Problems of Quantum Physics Heisenberg states that the indeterminacy principle must be taken as a question of principle making other formulations into false and meaningless questions, just as in relativity theory it is supposed that it is in principle impossible to transmit signals at speeds greater than the velocity of light. But Bohm maintains that without alternatives the physicist is constrained to work along accepted lines of thought in the hope that either new experimental developments or new theoretical insights will eventually lead to a new theory. Bohm maintains that one of the functions of criticism in physics is to suggest alternative lines of research that are likely to lead in a productive direction. He thus sees criticism with alternatives to be integral to scientific discovery. This objective is particularly attractive to the philosopher of science Paul Feyerabend, once an advocate of Bohm's interpretation, who to the end of his life maintained that creating alternatives is necessary for advancement.
Bohm's second objective is to propose an interpretation of the history of physics, which shows successful precedents for the research strategy represented by his hidden-variable interpretation of quantum theory. The paradigmatic precedent he invokes is the atomic theory of matter, which postulated the existence of atoms unobservable at the time the theory was proposed. Analogously Bohm’s strategy consists of postulating that there exists an order of physical magnitude below the quantum order of magnitude containing the quantum of action represented by Planck's constant. Bohm postulates that this subquantum order contains qualitatively different types of phenomena governed by more deterministic laws than do those known to exist at the quantum order of magnitude. The existence of this postulated subquantum order of microphysical phenomena is denied by the Copenhagen interpretation advocates, and since there was no experimental detection of any such subquantum phenomena, the theory that postulates them is said to have “hidden variables”.
Bohm opposes his historical interpretation to another that he calls “mechanistic”, a term that is unfortunately ambiguous in both philosophical and scientific usage, but which has a specific and somewhat elaborate meaning in Bohm’s book. According to the objectionable mechanistic philosophy opposed by Bohm the qualitative diversity of things in the world can be reduced completely, without approximation, and in every possible domain of science to nothing more than the effects of some definite and limited general framework of quantitative laws, which are regarded as absolute and final. Prior to the development of quantum theory these quantitative laws were assumed to be deterministic; then later with the development of the Copenhagen interpretation of quantum theory these laws were assumed to be nondeterministic. Hence there are both deterministic and nondeterministic varieties of mechanism. In the former variety causal laws are thought to be fundamental, while in the latter probability laws are thought to be fundamental. Nondeterministic mechanism prevails today, because physicists have accepted Heisenberg's thesis that the indeterminacy principle represents an absolute and final limitation on our ability ever to define the state of things by measurement.
In Causality and Chance Bohm maintains that causality and chance are both fundamental and objective, and that both determinism and nondeterminism are merely idealizations. Thus he rejects Einstein's determinism. He also rejects the subjective interpretation of probability, which says that the appearance of chance is a result of human ignorance. And he rejects the idea common to both deterministic and nondeterministic varieties of mechanism that there is only one general framework of laws and a limited qualitative diversity. Bohm maintains that there are different orders of magnitude with each level having its own laws and qualitative diversity. In the history of physics revolutionary developments have occurred when laws and qualities at a higher level are explained by those of a lower level. Experiments may disclose a breakdown of an entire scheme of laws by the appearance of chance fluctuations not originating in anything at the higher level, but instead originating in qualitatively different kinds of factors at a lower level. For example in classical physics a particle such as an electron follows the classical orbit only approximately, while in a more accurate treatment it is found to undergo random fluctuations in its motions arising outside the context of the classical level. Thus Bohm affirms by way of historical analogy and on the basis of his nonmechanistic interpretation of the history of science that there is a deeper subquantum order of magnitude, which in turn explains the randomness that is detected at the higher quantum order of magnitude.
Bohm’s hidden-variable interpretation is both an alternative interpretation of quantum theory motivated by this prior ontological commitment to a subquantum order and also by a discovery heuristic for which there is historical precedent. He maintains that new work is considerably facilitated by his thesis of a hidden subquantum order, because the physicist can imagine what is happening, and can thereby be led to new ideas not only by looking directly for new equations but also by a related procedure of thinking in terms of concepts and models that will help to suggest new equations that would not likely be suggested by mathematics alone. And he uses his postulated subquantum ontology as a basis for linguistic figures of speech such as analogy, which are a central feature in his discovery strategy. These figures of speech aid in formulating new hypotheses for future physics both on the basis of similarities between the macrophysical and microphysical orders of magnitude and on the basis of past developments in the history of physics, which he believes justifies his hidden-variables ontology.
Bohm's third objective is to use the hidden-variable interpretation as a guide for future research for a new microphysical theory that will resolve what he sees as the current crisis in quantum physics. This crisis manifests itself in Dirac's relativistic quantum theory, when the wave equation is applied to the description of particle scattering with very high energies and at short distances. For the Schrödinger wave equation to be used in such applications, an ad hoc mathematical adjustment called “renormalization” is necessary. Furthermore the behavior of very high-energy particles in experiments reveals that there exist many new kinds of particles not previously known, and that they are unstable, since they decay into one another and create other particles. Nothing like this is accounted for by current quantum theory. To Bohm these problems for the current quantum theory suggest that elementary particles are not really elementary. The concept of a subquantum level justifies the physicist considering a whole range of qualitatively new kinds of theories that approach the currently accepted theory only as approximations that hold in limiting cases. He believes that the current crisis in quantum theory portends a revolution in microphysics, and that his hidden-variable interpretation offers a superior guide for research that promises to resolve the crisis.
In summary these three objectives of Bohm's agenda represent successively more ambitious claims. The first claim is merely that an alternative to the Copenhagen semantical interpretation describing a subquantum level of magnitude is conceivable in the sense that it is consistent with the data and formalism of the current quantum theory. The second claim states more ambitiously that the history of physics reveals that postulating lower levels of magnitude supplies an analogy, which is a productive strategy to guide new research. The third claim is still more ambitious; it states that a new scientific revolution in microphysics is at hand, and that the hidden-variable semantical interpretation will produce a new microphysical theory that will resolve the current crisis in quantum theory. As de Broglie said in the closing sentence of his "Foreword" to Causality and Chance (1957), Bohm's book comes at exactly the right time. Thirty-five years later in his Undivided Universe Bohm was still predicting this impending revolution. More recent experiments based on John Stuart Bell’s inequality have occasioned reconsideration of the merits of Bohmian mechanics. But if there has been any revolution since those days, it has been the quite different string theory.