WERNER HEISENBERG AND THE SEMANTICS OF QUANTUM MECHANICS
BOOK IV - Page 3
Bohr's "Forms of Perception" and Neo-Kantianism
Having based his doctrine of closed-off theories on Bohr’s philosophy of observation, Heisenberg attempted to relate Bohr’s philosophy to the history of philosophy, and specifically to Kantianism. Heisenberg’s statements are found in his “Recent Changes in the Foundations of Exact Science” (1934) in Philosophical Problems of Quantum Physics, in his “The Development of Philosophical Ideas Since Descartes in Comparison with the New Situation in Quantum Theory” in Physics and Philosophy, in his “Quantum Physics and Kantian Philosophy (1930-1932)” in Physics and Beyond, and in his “Planck’s Discovery and the Philosophical Problems of Atomic Theory” in Across the Frontiers. Like Einstein, Heisenberg rejects the positivist phenomenalism and advocates realism; he was never a metaphysical Idealist, Kantian or otherwise. In “Planck’s Discovery” he states that quantum theory does not consider sense impressions to be the primary given, and that if anything is the primary given in quantum theory, it is the reality described with the concepts of classical physics. And in “Development of Philosophical Ideas Since Descartes” he describes his realistic variation on Kant’s views with the phrase “practical realism”, since in Heisenberg’s view things rather than perceptions are the given for the human mind.
But while Heisenberg is opposed to positivism as much as Einstein, his referencing the philosophy of Kant is not motivated by his antipositivism. Heisenberg is interested merely in relating Kantianism to the philosophy of observation he took from Bohr and incorporated in his doctrine of closed-off theories. In “Recent Changes in the Foundations of Exact Science” he says that in the field of philosophy of perception, Kant’s philosophy has been put into a new light as a result of the critique of absolute time and Euclidian space by relativity theory and by the critique of the law of causality by quantum theory, and that the question of the priority of the forms of perception and of the categories of the understanding must be reconsidered. He states that there are two apparently contradictory propositions that must be reconciled: On the one hand relativity theory and quantum theory have shown that our space-time forms of perception and the category of causality are not independent of all experience in the sense that they must for all time remain essential constituents of every physical theory. On the other hand, as Bohr taught, the applicability of the classical (i.e., Kantian) forms of perception and the law of causality are the premises of every objective experience even for modern physics. The physicist can only communicate the course of an experiment and the result of a measurement by describing the necessary manual operations and instrument readings as objective events taking place in the space and time known to our intuition. And he could not infer the properties of the observed object from the result of measurement, unless the law of causality guaranteed an unambiguous connection between measurement and object. Heisenberg resolves the contradiction between the two statements as follows: Physical theories can have a structure differing from classical physics, only when their aims are no longer those of immediate sense perception; that is to say, only when they leave the field of common experience dominated by classical physics.
In “Quantum Physics and Kantian Philosophy” Heisenberg views Kant’s philosophy of perception as a closed-off theory, as he elsewhere describes closed-off theories in physics. He compares the validity of Kant’s philosophy to the validity of Archimedes’ theory of the lever, and he states that Kant’s theory is eternally true, just as Archimedes’ theory is eternally true. Kant’s analysis of perception represents true knowledge that applies wherever thinking beings enter into the kind of contact with their environment called “experience”. Relativity theory and quantum theory have defined the limits of the a priori in the exact sciences in ways that could not have been known to Kant. The a priori has not been eliminated from physics, and Kant’s analysis of how we come by our experiences is essentially correct. But the a priori has become “relativised” in the sense that classical concepts are a priori conditions for relativity and quantum theory, since classical concepts are necessary for experiments. Remarkably Heisenberg says that the progress of science has changed the structure of human thought, and has taught us the meaning of “understanding”. In the closing paragraph of his “Quantum Physics and Kantian Philosophy” Heisenberg states that he has described the relationship between Kant’s philosophy and modern physics from the perspective of Bohr’s teachings.
On Scientific Revolutions
Heisenberg considers the development of modern quantum theory to be one of the two great scientific revolutions in twentieth century physics; the other in his view is relativity theory. Few would disagree. The complete title of his 1958 book is Physics and Philosophy: The Revolution in Modern Science. But by the 1960’s the term “revolution” as used in connection with the development of science had become what Heisenberg calls a “vogue word” due to some similarities between scientific revolutions and social revolutions. Possibly the vogue status of the term is due in part to the popular monograph, Structure of Scientific Revolutions, written by Thomas Kuhn in the United States in 1962, but Heisenberg never references Kuhn, and their views are not the same. Heisenberg discusses his idea of revolution in science in a lecture delivered to the Association of German Scientists in Munich in 1969, which was published in English in 1974 as “Changes of Thought Pattern in the Progress of Science” in his Across the Frontiers. Heisenberg recognizes the operation of sociological forces in the scientific professions, but his views are different from those of Kuhn.
Heisenberg defines a “revolution” in science as a change in thought pattern, which is to say a semantical change. He states that a change in thought pattern becomes apparent, when words acquire meanings that are different from those they had formerly, and when new questions are asked. He does not reference his semantical thesis of closed-off theories in this context, although the episodes in the history of post-Newtonian physics that he cites as examples of scientific revolutions are the same as those that he also says resulted in new closed-off theories in the history of physics. And the semantical change that occurs in the transition to a new axiomatic theory and the closing off of the old one, is the change involved in the transition to a new thought pattern. The central question that Heisenberg brings to the phenomenon of revolution in science understood as a change in thought pattern, is how the revolution is able to come about. The occurrence of the revolution is problematic due to resistance to the change in thought pattern offered by the cognizant profession. Heisenberg also expresses the question in more sociological terms, when he asks how a small group of physicists are able to “constrain” other physicists to make the change in thought pattern in spite of the latter’s resistance to do so. Firstly he discusses the reasons for resistance. Then he discusses various proposed explanations about how the resistance is overcome.
In his discussion of the reasons for resistance he states that there have always arisen strong resistances to every change in the pattern of thought. The progress of science proceeds as a rule without much resistance or dispute; the scientist has by training been put in readiness to fill his mind with new ideas. But the case is altered when new groups of phenomena compel changes in the pattern of thought. Here even the most eminent of physicists find immense difficulties, because a demand for change in thought pattern may create the perception that the ground is to be pulled from under one’s feet. A researcher who has achieved great success in his science with a pattern of thinking he has accepted from his young days, cannot be ready to change this pattern simply on the basis of a few novel experiments. Heisenberg states that once one has observed the desperation with which clever and conciliatory men of science react to the demand for a change in the pattern of thought, one can only be amazed that such revolutions in science have actually been possible at all. Undoubtedly the case in Heisenberg’s experience is the desperation that he saw in Schrödinger’s and especially Einstein’s opposition to the new thought pattern represented by the Copenhagen interpretation of the quantum mechanics.
He then considers several possible answers to the question of how scientific revolutions can come about in spite of the resistances, of how the resistances are overcome. One answer that he rejects is that the revolution is due to a strong revolutionary personality. He maintains that no such strong personality could overcome the profession’s resistance. Another answer that he rejects might be described as a variation on the conspiracy thesis, the view that a small group of physicists intended from the outset to overthrow the existing state of the science. He states that never in its history has there ever been a desire for any radical reconstruction of the edifice of physics; this is because at the onset of a revolution there is a very special, narrowly restricted problem, which can find no solution within the traditional framework. The revolution is brought about by researchers who are genuinely trying to resolve the special problem, but who otherwise wish to change as little as possible in the previously existing physics. It is precisely the wish to change things as little as possible, which demonstrates in Heisenberg’s opinion that the introduction of novelty is a matter of being compelled by the facts. The change of thought pattern is imposed by the phenomena. He concludes therefore that the way to make a scientific revolution is to try to change as little as possible: it is an error to demand the overthrow of everything existing due to the risk of attempting a change that nature makes impossible. Small changes on the other hand show what is compelled by the facts, and in the course of years or decades enforce a change in thought pattern and shift the foundation of the science. The relevant example of such a small change is Planck’s quantum of action, which years later resulted in the modern quantum theory.
Having rejected the view that scientific revolution occurs due to a conspiracy either with or without a strong revolutionary personality, Heisenberg then considers the answer that the resistances to revolution are overcome simply because there is a “right” and a “wrong” in physics, and the new theory is right while the old theory is wrong. It is noteworthy that Heisenberg does not reject the thesis that there is a right and a wrong in the sense of a correct and an incorrect, and in view of his thesis of closed-off theories, it would be remarkable if he did. Furthermore he had explicitly rejected historical relativism in his “Quantum Physics and Kantian Philosophy”. Still he finds that there is a problem with this answer as an explanation for overcoming resistances, namely that historically the right theory has not always prevailed. He cites as an example the dominance of the geocentric theory of Ptolemy over the heliocentric theory of Aristarchus, who lived in the third century BC.
Therefore, while there are absolute standards for criticism of scientific theories, there still remains the question of why some correct theories succeed in gaining acceptance over the strong forces of resistance, while others do not, even though the rejected theories may be correct. Heisenberg then proposes his own answer. Scientists perceive that with the new pattern of thought, they can achieve greater success in their science than with the old; the new system proves to be more fruitful. Heisenberg states that once anyone has decided to be a scientist, he wants above all to get ahead, to be on hand when the new roads open up; it does not satisfy him merely to repeat what is old and has often been said before. Consequently the scientist will be interested in the kind of problems where there is something to be done, where he has the prospect of successful work. That is how relativity theory and quantum theory came to prevail according to Heisenberg. He describes this as a “pragmatic criterion of value”, and he states that while one cannot always be certain that the right theory will always prevail, nevertheless these are forces that are strong enough to overcome the resistances to a change in thought pattern.
Since Heisenberg is a principal participant in one of the great scientific revolutions in modern physics, his views based on his personal experience deserve singular consideration. He was undoubtedly impressed by the resistances offered to the Copenhagen interpretation by Schrödinger and especially by Einstein. While few contemporary philosophers of science accept Heisenberg’s doctrine of closed-off theories with its naturalistic view of observation, which he uses to interpret his experience of scientific revolution, they recognize the operation of sociological forces including the thrust of opportunistic careerism. And they also recognize that semantical change occurs in scientific revolutions, and that the adjustment it imposes on the affected profession operates as a cause of resistance within it, even though they do not accept Heisenberg’s theory of semantical change and permanence. Unlike others such as Kuhn, Heisenberg does not identify the institutionalized criteria for scientific criticism with the existing thought pattern, and he does not maintain that the revolution is a change with no institutional framework controlling it. Heisenberg avoids the historical relativism found by many in Kuhn’s thesis, and which is explicitly embraced by Feyerabend. And one would not expect the proponent of the doctrine of closed-off theories and the advocate of Bohr’s theory of observation to find the process of scientific criticism very problematic. The scientist is simply compelled by the facts, and the semantics of the statements of fact are not a problematic matter. Failure of the correct theory to overcome the forces of resistance, and indeed the very existence of those resistances, is due to the professional failure of those who cannot adjust to new thought patterns when the facts compel, and not to any inherently problematic character in the process of scientific criticism itself.
One can only wonder what Heisenberg might have said, were he to have followed through with Einstein’s thesis that it is the theory that decides what the physicist can observe; how he would have addressed the consequent problem that the concepts used to describe the facts are supplied by the choice of thought patterns expressed in the new theory.
Heisenberg’s Philosophy of Science
Heisenberg’s rich and extensive philosophical writings can be related to the four functions performed in basic-scientific research:
Aim of Science
The aim of science has a special importance in Heisenberg’s philosophy, because it was explicitly developed to defend the Copenhagen interpretation of quantum theory against Einstein’s explicitly formulated programmatic aim of all physics. Heisenberg’s views are expressed in his “Notion of ‘Closed Theory’ in Modern Science” and in his “On the Unity of the Scientific Outlook on Nature” (1941) in Philosophical Problems of Quantum Physics. Einstein used his programmatic aim of physics to claim that the statistical quantum theory is “incomplete” in the sense that it does not represent an adequate explanation for the problem that it addresses, and that further research work is still needed. The reason he said it is still incomplete is that it is not consistent with the ontology of field physics, which describes physical reality as continuous in four dimensions and deterministic.
But Heisenberg denied Einstein’s contention that the microphysical theory must employ the same ontological concepts as those used in macrophysical field theory, and his doctrine of closed-off theories was motivated by his desire to show how multiple ontologies can co-exist in physics. This is Heisenberg’s thesis of pluralism in science. The Copenhagen interpretation of quantum theory is complete in Heisenberg’s view, because it is a closed-off theory. And like all closed-off theories it is not only a complete solution to the problem that it addresses, but it is also a permanently true solution. In Heisenberg’s philosophy the aim of science is to progress through a sequence of closed-off theories, and it is not, as Einstein maintained, to progress toward a single and all-inclusive ontology. The result of physics pursuing its aim as Heisenberg views it, has been his architectonic scheme for physics, a scheme of closed-off theories which he delineates in his “Relation of Quantum Theory to Other Parts of Natural Science” in Physics and Philosophy.
In Heisenberg’s treatment of scientific discovery two aspects may be distinguished: One is the syntactical or structural aspect, and the other is the semantical or the interpretative aspect that also implies ontological considerations. The structural aspect pertains to the development of the new mathematical theory. The new quantum theory formal structure was the result of repeated failures of conservative attempts by the researchers to extend the classical theory, in order to explain phenomena at the microphysical order of magnitude. But eventually research resulted in the revolutionary development that is quantum mechanics.
Closely related to the first aspect is the second, the interpretative problem. When extension of Newtonian physics could not solve the problem of microphysics, and after Heisenberg eventually developed the matrix mechanics, the semantical and ontological interpretation of the new matrix mechanics still remained problematic. Using Einstein’s thesis that the theory decides what the physicist can observe, Heisenberg reinterpreted the observed tracks in the Wilson cloud chamber experiment, and developed the indeterminacy relation with its nondeterministic and duality ontology. The new interpretation was accomplished by taking the new quantum theory realistically, as a description of the ontology of the microphysical world. When Einstein attacked the statistical quantum theory, he attacked only the second aspect, the Copenhagen interpretation with its nondeterministic ontological claim; he rejected indeterminacy as a valid ontological claim.
Heisenberg’s views on the issue of scientific explanation are implicit in his position against Einstein’s objections to the Copenhagen interpretation. Einstein’s objection to the Copenhagen interpretation is that it is incomplete as a scientific explanation. This objection is a very traditional type of objection, because historically the concept of scientific explanation has been defined in terms of one or another ontology, and Einstein demanded conformity to the ontology defined by the concepts in Newtonian and field physics. Bohr placed himself and his Copenhagen colleagues at a disadvantage, when he employed the vocabulary of their critics by referring to the statistical quantum theory as “noncausal”, because he accepted the definition of causality in terms of the deterministic ontology of classical physics and field theory.
But Heisenberg also maintained that the revolutionary developments in physics include interpreting the new mathematical formalism realistically. He saw this in Einstein who accepted the field as real, accepted relativistic time as real time, and abandoned the concept of absolute time. Invoking Einstein’s practice as his precedent, Heisenberg likewise accepted his indeterminacy relation as describing the real microphysical world as nondeterministic. This amounts to separating the concept of scientific explanation from any preconceived ontology. Such separation had occurred previously in the history of physics, but its recognition was quite radical in microphysics after the lengthy domination of Newtonian physics, even though it is now the common property of the contemporary pragmatist philosophers of science in their thesis of ontological relativity.
In striking contrast to his radical concept of scientific explanation, Heisenberg’s treatment of the question of scientific criticism is very conservative. Actually it is anachronistic, because he believed that his doctrine of closed-off theories enables him to explain how scientific theories can be permanently true. His views of explanation and of criticism represent a very unusual combination of views. Historically philosophers and scientists have maintained that scientific explanations are permanently true, because as explanations they purport to describe correctly the one and only true ontology. Heisenberg’s philosophy of scientific criticism includes a semantical thesis, which is a thesis of both semantical change and semantical permanence. Whether or not this semantical thesis is a sustainable one is certainly questionable, particularly when it depends on such curious processes as the semantics of words becoming “detached” from the variables occurring in the closed-off axiomatic theories, when the theories encounter the limits of their applicability.
A philosopher of science such as Popper would dismiss such a thesis as a “content-decreasing” stratagem. If when a theory is criticized by an experimental test, the words expressing the test outcome describe something contrary to what the theory had predicted, then a later attempt to save its truth claim by equivocation, by the “detachment” of the meanings describing the experimental outcome from the terms in the theory, only makes the theory tautological. In other words Heisenberg’s doctrine in effect says a theory is true where it is true, and that where it is not true, it is not falsified, because it becomes silent, detached and inapplicable