WERNER HEISENBERG AND THE SEMANTICS OF QUANTUM MECHANICS
BOOK IV - Page 4
Comment and Conclusion
In “Bohm and the ‘Inevitability’ of Acausality” in Bohmian Mechanics and Quantum Theory: An Appraisal (1996) Mara Beler takes a cynical perspective to Heisenberg’s inconsistency, arguing that he had neither belief nor commitment, but only a selective and opportunistic use of Bohrian doctrine for the finality of the Copenhagen orthodoxy. Such might be the appearances, but Heisenberg was not cynical. A new philosophy does not spring forth as from the brow of Zeus – coherent, complete, and finally formed. It struggles to emerge from the confusion produced by the inevitable conflict between new seminal insights and old conventional concepts. It is not surprising, therefore, that there should exist an inconsistency between the seminal insights in Heisenberg’s philosophical reflections described in his autobiographical accounts, and the conventional concepts in his systematic philosophy of science described in his doctrine of closed-off theories.
Naturalistic vs Artifactual Semantics for Observation Language
There is indeed an inconsistency in Heisenberg’s philosophy, and it is due to the conflicting influences of Bohr and Einstein. The conflict has its basis in two fundamentally different philosophies of the semantics of language; particularly where the relevant language is the vocabulary used to conceptualize the sense stimuli delivered in observations. The philosophy of language in contemporary pragmatist philosophy of science is the artifactual thesis of semantics, and the traditional philosophy is the naturalistic thesis. Bohr’s naturalistic philosophy of language is that the semantics of language is the natural product of perception, such that concepts used for observation are what in Atomic Theory and the Description of Nature he calls the “customary forms of perception”, which have their information content determined by nature and the natural processes of perception, and which therefore relegate the mathematical quantum theory to instrumentalist status. Einstein’s artifactual philosophy of language on the other hand is that the semantics of language is an artifact, a “free convention”, a cultural product instead of a natural product, such that concepts and categories used for observation in physics do not have their information content specifically determined by the natural processes of perception, and are therefore changeable.
It was evident to Heisenberg as well as to every other physicist at the time that revolutionary revisions had been made in twentieth-century physics. Heisenberg wanted to explain how such developments in the history of science could produce correspondingly revolutionary revisions in the semantics of the language of physical theory. Heisenberg’s response was his doctrine of closed-off theories, and the philosophy of language that he used for this semantical theory was due to the influence of Niels Bohr. This doctrine restricts semantical revision to the description of phenomena that lie beyond ordinary perception, and thereby retains semantical permanence for the description of phenomena accessible to ordinary observation and described by the language and concepts of Newtonian physics. According to Heisenberg’s doctrine of closed-off theories Newtonian physics is permanently valid and serves as the observation language for physics, because it is necessary for reporting experimental measurements and other observations.
Thus Heisenberg believed that all observation must be with concepts supplied by either classical physics or “everyday” language. In his mature version of his doctrine of closed-off theories these concepts are not the same. The everyday concepts have a “lack of precision” or vagueness, while the concepts of classical physics have their semantics rigidly and precisely defined by the context consisting of the laws of Newtonian physics. The concepts of quantum physics also have their content fixed by the context consisting of the laws of quantum physics. What is significant is that the laws of classical and quantum physics are mutually inconsistent. And most notably in Heisenberg’s view the quantum concepts are not merely alternative resolutions of the vagueness in everyday concepts, but they cannot be used for observation. The fact that classical and quantum concepts occur in mutually inconsistent laws implies that, when these concepts are associated with the same descriptive term or variable, they are alternative meanings making that common term equivocal.
The equivocal relation between classical and quantum concepts is illustrated in the cases of the terms “position” and “momentum”, which occur in both classical and quantum physics. The advocates of the Copenhagen interpretation of the quantum theory argue that in practice the concepts of classical physics must operate in descriptions of the macrophysical experimental apparatus and observation measurement. This classical semantics includes the idea that nature is fundamentally continuous, and the idea that in principle the measurements can be indefinitely accurate, notwithstanding the fact that in practice the degree of accuracy is always limited. They also argue that there are meanings for these terms that are distinctive of quantum physics, and this semantics, which is defined by the context supplied by the indeterminacy relations, includes the ideas that nature is fundamentally discontinuous and that the accuracy of the joint measurement of momentum and position is limited by Planck’s constant. Therefore, on Heisenberg’s philosophy of closed-off theories, in order for observation to be possible in quantum physics there must exist an equivocation for every term common to classical and quantum physics, such that for every quantum concept determined by the context of quantum physics there must be a corresponding classical concept for observation determined by the context of classical physics. Such is the unfortunately equivocal outcome of Heisenberg’s explicit and systematic philosophy of science.
Yet Heisenberg’s use of Einstein’s aphorism for describing the tracks in the Wilson cloud chamber, which led to his subsequent development of the indeterminacy relations, does not agree with the observation language required by his doctrine of closed-off theories. Einstein’s aphorism is the semantical thesis that the theory decides what the physicist can observe, and for microphysical experiments this thesis implies that the quantum theory contributes to defining the semantics for observational description.
The Contemporary Pragmatist Alternative
Contrary to Heisenberg’s semantical doctrine of closed-off theories, classical concepts are not necessary for observation, variables in the quantum laws are not equivocal, and all the concepts in the quantum theory are quantum concepts that are operative in observational description. It is possible with a metatheory of semantical description to follow through with Einstein’s aphorism and to say that theory decides what the physicist can observe, because the concepts used for observation are quantum concepts. Such a new semantical theory is needed, because like Bohr, Heisenberg had premised his doctrine of closed-off theories on the naturalistic philosophy of language. Attempts to preserve a permanent semantics for observation, while at the same time to explain the semantical revisions produced by the revolutionary developments in theory, result in a positivist philosophy of language that attributes equivocation to language that in practice physicists are routinely able to use unambiguously. The historic twentieth-century scientific revolutions have motivated post-positivist philosophers of science to reject the naturalistic philosophy of the semantics of language, and to accept the artifactual philosophy instead. It is necessary to consider further how to describe the semantics both of quantum theory and of experimental observation, in order to exhibit how concepts are culturally determined as linguistic artifacts instead of predetermined as products of nature, and to explain why semantical change occurs in observation reporting without involving complete equivocation.
False Assumptions in Closed-off Theories Doctrine
Heisenberg’s doctrine of closed-off theories contains certain basic assumptions that are in need of reconsideration. The first is the tacit assumption that all concepts are indivisible or simple wholes, that must be either completely different or completely the same, such that classical and quantum concepts are simply and wholly equivocal. The second is the explicit assumption that observation language must be exclusively associated with macroscopic phenomena. Both of these assumptions contain errors.
Firstly it is incorrect to assume that the meanings of terms in physics or in any other discourse are simple wholes that cannot be analyzed into component parts. Secondly it is necessary to reconsider the Copenhagen school’s basis for dividing the relevant language into statements of experiment and statements of theory. Specifically rejection of the naturalistic philosophy of language implies rejecting two mental associations that occur in Heisenberg’s doctrine of closed-off theories. The first is the classical-macroscopic-observation association, and the second is the quantum-microscopic-theoretical association. Consider firstly the pragmatist alternative to the wholistic view, and how it affects Heisenberg’s thesis of equivocation.
Semantical Wholism Rejected
Conventional habitual meanings of words are synthetically experienced wholistically. However reflection on the common occurrence of looking up words like a common noun in a unilingual dictionary reveals that the meanings of words are not simple wholes, but rather have component parts that are identified by the defining words occurring in the dictionary definition or lexical entry. Dictionary definitions that are not proper names give semantical descriptions of the meanings they define, and in order to function in this way they always must have the force of universally quantified statements accepted as true. Furthermore dictionary definitions are often viewed as describing the complete meaning of the term, but dictionary definitions are actually minimal statements, and by no means give complete meaning. Usually the understanding of the meaning of a univocal term, especially a technical term, requires a larger context consisting of a discourse having many statements containing the term. Today such larger context may be examined extensively with the aid of a key-word-in-context computer program.
Since Quine rejected the analytic-synthetic distinction, all universal empirical or “synthetic” statements accepted as true may also be viewed as definitional or “analytic”. Thus if one were to make a list of logically consistent universally quantified affirmative categorical statements containing a univocal descriptive term as their common subject term with each statement accepted as true, then the predicates in each of the mutually consistent statements constituting the list describe part of the meaning of the common subject term, and the entire list as well as each statement in it may be called a “semantical description” of the univocal common subject term’s meaning. In summary a semantical description consists of the language context, in which a descriptive term’s meaning is determined and described by a set of universal affirmations believed to be true.
This contextual determination of the semantics of language is the essence of the artifactual thesis. Quine calls this context the “web of belief”. A term is equivocal if any of the universal affirmations in the semantical description are mutually inconsistent. This equivocation is made explicit, when the predicates of the inconsistent universal affirmations can be related to one another by universal negations accepted as true. The several different meanings in the equivocation each have separate semantical descriptions, which can be exhibited when the original list is subdivided into mutually exclusive subsets with each subset containing only mutually consistent universal affirmations. Then each subset is a semantical description of one of the several different meanings of the equivocal term instead of each subset functioning as a description of different parts of the one meaning of a univocal term.
The equivocations postulated by Heisenberg’s doctrine of closed-off theories as applied to microphysics are the result of the logical inconsistency between the theories of classical and quantum physics. Thus there exists equivocation with each theory context constituting a separate semantical description list for any term common to the two theories, terms such as “position” or “momentum”.
In addition to the properties of equivocation and univocation there is another aspect of language called vagueness. Equivocation and univocation are properties of terms, while vagueness and clarity are properties of meanings. Meanings are more or less clear or vague. Two concepts are clear in relation to one another, if they can be related to each other by universal affirmations or negations accepted as true, and they are vague in relation to each other if they cannot be so related by any universal statements. And adding any universal affirmations or negations believed to be true to a single univocal term’s semantical description list has the effect of reducing the vagueness in the concept associated with the term by explicitly adding or excluding meaning.
Every meaning is always vague and admits to further clarifying resolution, because potentially its semantical description can always be increased by additional universal statements believed to be true. This becomes evident when instances are encountered about which no decision had been made regarding the applicability of the term in question. Friedrich Waismann has called this inexhaustible residual vagueness the “open texture” of concepts. What Heisenberg calls “everyday language” is merely language which has a degree of vagueness or “lack of precision” that is greater than the degree of vagueness in Newtonian and quantum concepts due to the latter’s contexts consisting of their respective equations. However no terms that are part of a language including everyday terms can be utterly without any defining context such as is found in the term’s lexical entry in a dictionary.
Naturalistic “Observation” and “Theory” RejectedConsider next the relation between the language of observation and the language of theory, the second basic assumption in the doctrine of closed-off theories. Scientists and philosophers still conventionally use the word “theory” to refer to Newton’s “theory” of gravitation, to Einstein’s “theory” of relativity, and to the quantum “theory”, even though the physics profession had decided many years ago either to accept or to reject these expressions as physical laws and explanations. As Norwood Russell Hanson, Yale University pragmatist philosopher of science and advocate of the Copenhagen interpretation of quantum mechanics, notes in this conventional usage the term “theory” does not function as it did when these expressions were firstly advanced for testing as proposed explanations of problematic phenomena in research science. When they were firstly proposed, these expressions represented statements that had a much more hypothetical status in the judgment of the cognizant professions than they do today, and they were typically topics of controversy.
There is, therefore, an ambiguity between “theory” understood as an accepted or rejected explanation in what Hanson called “catalogue science”, and “theory” understood as a tentative proposal submitted for empirical testing in what he called “research science”. In the “Introduction” to his pioneering Patterns of Discovery: An Inquiry into the Conceptual Foundations of Science (1958), Hanson wrote that earlier philosophers of science had mistakenly regarded as paradigms of inquiry finished systems like planetary mechanics instead of the unsettled, dynamic research sciences like contemporary microphysics. He explains that the finished systems are no longer research sciences, although they were at one time. He therefore says that distinctions applying to the finished systems ought to be suspect when transferred to research disciplines, and that such distinctions afford an artificial account of the activities in which Kepler, Galileo and Newton were actually engaged. He thus maintains that ideas such as theory, hypothesis, law, causality and principle, if drawn from what he calls the finished “catalogue-sciences” found in undergraduate textbooks, will ill prepare one for understanding research-science.
Only the functional meanings as found in what Hanson calls “research science” are strategic in the contemporary pragmatist philosophy of science, even though the conventional or “almanac” meaning of “theory” occurs even in its own expository discourse such as herein. From this functional view theory language that has been tested and not falsified by a decisive test ceases to be a theory and has thereby been given the status of a law that can be used in an explanation. Due to empirical underdetermination there may nonetheless be multiple tested and nonfalsified former theories that address the same problem, and that therefore also have the status of explanations accepted by some scientists in the same profession. Some scientists are uncomfortable with this pluralism, but the contemporary pragmatist philosophers recognize such pluralism as historically characteristic of science.
In an empirical test of a theory the semantics of the vocabulary in all the relevant discourse is controlled by a strategic decision that is antecedent to the performance of the test. This is the functional decision as to what statements are presumed for testing and what statements are proposed for testing. The former language is the explicit statements of test design together with usually many tacit assumptions. The latter language is the explicit statements of the theory. This decision is entirely pragmatic, since it is not based on the syntactical or the semantical characteristics of language, but rather is based on the use or function of the language in basic research, namely empirical testing. The test-design statements are those that by prior decision and agreement among cognizant members of the profession have the status of definitions. These statements are presumed to be true regardless of the outcome of the test, and serve to identify the subject of investigation and to describe the test execution procedure throughout the test. The theory is the language that by prior decision and agreement among the cognizant members of the profession has the less certain status of a hypothesis. The hypothesis is believed to be true to the extent that it is considered worthy of testing, although the developer and his entourage of cheerleading advocates may be quite firmly convinced. But if the test outcome is a falsification, then by prior agreement among scientists who accept the test design, it is the statements of theory and not the statements of test design that are judged to have been falsified and in need of revision.
However, a falsification may lead some interested scientists, such as the theory’s developer and advocates, to reconsider the beliefs underlying the test design, even while admitting that the test was executed in accordance with its design. This is a rôle reversal between test design and theory, which may result in productive research. In such cases when the falsified theory is made a test-design statement characterizing the problematic phenomenon, the problem has become reconceptualized. As James Conant recognized to his dismay in his On Understanding Science: An Historical Approach, the history of science is replete with such prejudicial responses to scientific evidence that have nevertheless been productive and strategic to the advancement of basic science in historically important episodes.
The decision distinguishing test-design language and theory language made prior to the experiment may but need not result in identifying mathematical equations as the statements of theory and of identifying colloquial discourse as the statements of test design. The decision is not based on syntactical characteristics of the language, and the test-design statements often include mathematically expressed statements together with statements in colloquial language describing the measured phenomenon, the measurement procedures, and the design and operation of the measurement apparatus. Even more relevantly the decision is not based on semantical criteria, as advocates of the naturalistic philosophy of the semantics of language believe. Contrary to both Bohr and the positivists the decision is not based on any purportedly inherent distinction between observation and theory, whether or not, as in the case of quantum mechanics, the observation concepts are called “classical” or “macroscopic”, and the theoretical concepts are called “quantum” or “microscopic”. The distinction between statements of test design and statements of theory is neither syntactical nor semantical; it is distinctively and entirely pragmatic.
Test Language Before Test Execution
With the above concepts in mind and at the expense of some repetition consider the language of an empirical test before the test is executed and its outcome is known. In order for the test-design statements to characterize evidence independently of the theory proposed for testing, the test-design statements and the theory statements must be logically independent; i.e., neither set of statements may be merely a logical or mathematical transformation of the other. The test-design statements, the language presumed for testing, may neither deductively imply nor contradict the theory or any of its alternatives. In the case of quantum mechanics this means that the test-design language for experiments cannot be from Newtonian physics, which postulates matter to be infinitely divisible and its physical laws to be deterministic. Test-design language must be silent about such claims, and must be given the status that Heisenberg called “everyday” language, which is silent, i.e., vague, about these Newtonian claims. Furthermore the statements of the quantum theory proposed for testing are too hypothetical to function as definitions except for the developer and other advocates of the theory, who may believe in the theory as strongly as they believe in the truth of the test-design statements.
But for all the critical researchers for whom the test is contingent and functions as a decision procedure, the semantical consequence of the logical independence and greater hypothetical status of a theory proposed for testing relative to the universal statements of test design, is that each of the terms common to both the test-design statements and theory statements have their semantics defined only in relation to the meanings of the other terms in the test-design statements, such that they characterize the subject matter of the experiment, but do not have their semantics defined in relation to the meanings of the terms in the theory proposed for testing. In other words by strategic decision for testing, the theory statements are not included in the same semantical description list as the test-design statements, even though both sets of statements are mutually consistent and contain the same common subject terms. The meaning of each term common to the test-design and theory statements is therefore vague with respect to the meanings of the other terms of the theory.
And on the artifactual thesis of the semantics of language the observation language in turn is merely the test-design statements with their logical quantification changed from universal to particular, to enable their application to describe the particular ongoing or historical experiment performance. The test-design statements similarly supply the vocabulary that describes the observed test outcome, especially if the outcome contradicts and thus falsifies the claims of the tested theory.
Test Language After Test Execution
Consider next the language of the empirical test after the test is executed and its outcome is known. When the test is executed, a falsifying test outcome produces no semantical change except for the developer and advocates of the tested theory, who had been convinced of the theory’s truth, and who decide to reconsider their belief in the theory due to the test outcome. The latter’s belief revision causes a semantical change. But a nonfalsifying outcome produces a semantical change, especially for the critics of the theory for whom the test is a decision procedure. After the test the theory no longer has the greater hypothetical status that it formerly had merely as a proposal, but assumes the status of a law that may operate in an explanation, which is neither more nor less contingent than other accepted universal empirical statements including the test-design statements. The semantical outcome is that both the test-design statements and the theory statements (now elevated to the status of a law) are semantical rules exhibiting the composition of the meanings of the univocal terms common to both sets of statements. Those component parts contributed by the test-design statements remain included. But the semantical descriptions for these terms now include not only the test-design statements but also the statements constituting the tested and nonfalsified former theory. These former theory statements are additional information learned from the successful test outcome that resolves some of the vagueness in the vocabulary terms common to both the theory and the test-design statements.
In summary: the descriptive terms common to both test-design and theory statements have part of their semantics defined by the test-design statements throughout the test, both before, during, and after the test is executed. And these common terms have their semantics augmented and thus defined by the statements of the tested and nonfalsified former theory added after the test, such that the test-design concepts have their vagueness resolved by the tested and nonfalsified former theory.
Semantics and Quantum Theory Tests
In Heisenberg’s doctrine of closed-off theories the naturalistic philosophy of language requires retention of the Newtonian concepts for observation in any quantum-theory experiments. But the resulting equivocation is unnecessary. Newtonian concepts are never involved, since the Newtonian theory is a falsified microphysical theory or at least an alternative to the quantum theory. Before the test outcome is known it is sufficient to use a vaguer or less precise vocabulary that Heisenberg calls “everyday” words used by physicists, in order to describe the experimental set up, which is a macrophysical phenomenon. The meanings of these “everyday” concepts are vague, because they do not describe the fundamental constitution of matter. After the test outcome is known, the tested and nonfalsified quantum theory is recognized as empirically adequate, and the vagueness in these everyday concepts is resolved by the equations constituting the quantum theory. The quantum mechanics is the tested and nonfalsified former theory, which after the test as a law became a semantical rule contributing meaning parts to the complex meanings of the univocal terms used to describe the experimental set up such as the Stern-Gerlach or two-slit apparatuses. This effectively makes the meanings quantum concepts, whether or not quantum effects are empirically detectable or operative in the description of the macroscopic features of the experimental set up.
Even if some Newtonian laws are employable for their now known lesser truth, in order for this resolution of vagueness to occur in the terms used for description of the macroscopic features of the experimental set up, it is not necessary for the Newtonian macrophysical laws to be made logical extensions of quantum mechanics by logical reduction procedures, because the Newtonian theory is falsified as a microphysical theory. Nor is it necessary for the Newtonian macrophysical laws to be replaced by macrophysical laws that are an extension of the quantum laws. The univocal quantum semantics neither implies nor requires any logical reductionist or extensional development of macrophysical quantum mechanics, i.e., a macrophysical theory that is deductively or reductively a logical extension of the microphysical quantum mechanics. It is sufficient merely that the scientist realize that the nonfalsifying test outcome has made quantum mechanics and not classical mechanics an empirically warranted microphysical theory.
Heisenberg’s doctrine of closed-off theories is incorrect, and Einstein’s semantical thesis expressed in his aphorism to Heisenberg is correct, because the vocabulary used for macroscopic observation after quantum mechanics’ acceptance is a univocal vocabulary with meaning parts contributed by quantum mechanics. The descriptive terms in the equations of the quantum mechanics contribute to, and thereby resolve some of the vagueness in the meaning complex associated with the descriptive terms used for observation. Thus as Heisenberg maintained, quantum mechanics decides what the scientist observes in the Wilson cloud chamber. The macrophysical description is not antilogous to the microphysical quantum mechanics including the indeterminacy relations. In summary the quantum semantic values are included in the univocal meaning complexes associated with the observation description, and the Newtonian concepts were never included, because the macrophysical description never affirmed a Newtonian microphysical theory.
Heisenberg’s Last Statements on Semantics
In his “Remarks on the Origin of the Relations of Uncertainty” in a memorial volume dedicated to him titled The Uncertainty Principle and Foundations of Quantum Mechanics (1977), which was in press at the time of his death in 1976, Heisenberg says in this brief four-page article that there have been attempts to replace the traditional language with its classical concepts by a new language which would be better adapted to the mathematical formalism of quantum theory. But he adds that during the preceding fifty years, physicists have preferred to use the traditional language in describing their experiments with the precaution that the limitations given by the indeterminacy relations should “always be kept in mind”. He concludes that a “more precise” language has not been developed and in fact it is not needed, since there seems to be general agreement about the conclusions and predictions drawn from any given experiment in the field. In other words the semantics of terms like “momentum” and “position”, “wave” and “particle” have evolved much like the semantics of the term “atom” has evolved in the history of physics, even as the vocabulary has been retained.
Regrettably Heisenberg never repudiated his doctrine of closed-off theories. But contrary to his doctrine of closed-off theories, Heisenberg’s statement that the contemporary physicist must keep quantum effects “in mind” when the physicist is describing macrophysical objects, even while not explicitly accounting for quantum effects that are experimentally undetectable in the circumstances, is ipso facto a semantical change in the univocal vocabulary used to describe experiments due to the development of quantum mechanics. In other words a language in which the limitations given by the indeterminacy relations are “always be kept in mind”, means that a “more precise” language with a less vague semantics has in fact been evolved. This semantical evolution consists in the fact that the concepts employed for observational description contain component parts, i.e., semantic values, contributed from quantum mechanics. That is how the limitations of the indeterminacy relations are “always kept in mind”: they have become built into the semantics of those terms, even when those terms are used to describe macrophysical observations including but not limited to cloud chamber tracks.
Heisenberg’s semantical theory of equivocation in his and Bohr’s philosophy of observation language is the result of the acceptance of the naturalistic philosophy of the semantics together with the assumption that meanings are simple, indivisible wholes. However, all such views are untenable, because they imply what can only be called “double think”. The equivocation thesis demands that the modern physicist indulge in a contrived cognitive duplicity with himself, a pretense at simultaneously both knowing and not knowing the modern quantum theory. But concepts are not known like physical objects to which one may simply close one’s eyes; they are knowledge. Scientists never did in practice carry on the kind of cognitive duplicity that the equivocation semantical theses require, and since the ascendancy of the contemporary pragmatism, philosophers no longer expect that they should.
Heisenberg might have obtained greater utility from his insightful idea of “everyday” concepts, had he rejected Bohr’s philosophy of observation language, and realized that neither these “everyday” concepts nor the Newtonian concepts nor any other concepts are inherently observational. Heisenberg’s term “everyday” is admittedly awkward, because the everyday man in the street does not perform quantum experiments. But in the pragmatist perspective Heisenberg’s “everyday” concepts are distinctive only because they are vague in a very strategic fashion: they are the concepts used in test-design statements, and are vague relative to the concepts in the theories proposed for testing prior to execution of the test and prior to the production of a nonfalsifying test outcome. More specifically, in the case of the quantum-mechanics experiments, everyday test-design concepts are vague because they are not defined by either the Newtonian or the quantum theories or of any other proposed microphysical theory prior to the execution of the tests. After execution of the test and after production of a nonfalsifying test outcome, the vagueness of the “everyday” concepts is resolved with respect to microphysical phenomena and become quantum concepts, such as Heisenberg used for observing the electron tracks in the cloud chamber.
In “On the Methods of Theoretical Physics” in Ideas and Opinions (1933) Einstein said that if you want to find out anything from the theoretical physicists about the methods they use, stick closely to one principle: don’t listen to their words, but rather fix your attention on their deeds. This is good advice for anyone attempting to understand Heisenberg’s writings in philosophy of science. The philosophy of language that was instrumental to Heisenberg’s “deeds”, i.e., his development of his indeterminacy relations as a result of Einstein’s influence and that is chronicled in his autobiographical works, is historically more important and more revealing than the “words” he expounded as a result of Bohr’s influence and set forth as his doctrine of closed-off theories, because pragmatism is the philosophy of language that Heisenberg practiced.
Quantum physicists are like the Biblical characters who had been driven out of the Garden of Eden. They have eaten from the forbidden fruit of the tree of quantum knowledge, the fruit forbidden by Newtonian physics. They have consumed such findings as uncertainty, duality, and nonlocality, so that today they simply know too much to return to the their former state of blissful nineteenth-century innocence, in which Newtonian concepts had been used for the semantics for observational reporting. Now the semantics they must use in their conceptualization of the sense stimuli that produce their observational reporting language, is penetrated, permeated and suffused with semantic values from quantum theory.
A New Language Developed
Roland Omnès is presently Professor Emeritus of Theoretical Physics in the Faculté des sciences at Orsay at the Université Paris. In his Understanding Quantum Mechanics (1999) Omnès writes that since the 1980’s there has been a renewal in both experiments and theory due to a transition from a period when Bell’s ideas and the hidden variables issues were dominant, to the current period when the interpretation of Copenhagen quantum mechanics has become the dominant interest.
The renewal involves three theoretical ideas: the decoherence effect, the emergence of classical physics from quantum theory, and the constitution of a universal language of “interpretation” by means of consistent histories. The decoherence effect, which was recently observed, explains the absence of macrophysical interference and solves the Schrödinger’s cat problem. The emergence of classical physics from quantum theory using the Hilbertian framework explains the relation between quantum and classical physics, and reconciles determinism with probabilism. The constitution of a universal language of “interpretation” by the method of consistent histories provides a logical structure for quantum and classical physics, and it supplies the universal language of “interpretation” initially sought by the members of Bohr’s Copenhagen Institute for Physics, but which Bohr’s complementarity cannot supply. Omnès has been instrumental in developing the consistent histories and quantum decoherence approaches. He writes that when these three ideas are combined, they provide a genuine theory of interpretation, in which everything is derived directly from four basic principles using the Hilbert-space framework to deduce theorems including the rules of measurement theory, and he sets forth a set of axioms.
It may be said that Omnès’ deductive system not only resolves the relatively vague semantics of Heisenberg’s “everyday” language, but because it is deductive, it further resolves the vagueness in the semantics of the vocabulary in both macrophysics and microphysics. Omnès’ logical integration of physical theory may satisfy long-standing psychological yearnings for intellectual coherence expressed by both physicists and philosophers. But while Omnès reports that it depends on recent experimental results, he does not report any new testable proposals much less new empirical findings. Yale University’s Norwood Russell Hanson would likely have dismissed Omnès and his ilk as mere “axiomitizers”. Only time will tell whether or not Omnès’ tour de force yields any new testable proposals or new empirical findings.
Heisenberg’s Practice of Ontological Relativity
Unlike Bohr, Heisenberg effectively practiced what Quine called “ontological relativity”, when he reported that he interpreted the quantum mechanics equations realistically by replicating Einstein’s realist interpretation for special relativity. Heisenberg said the “decisive step” in the development of special relativity was Einstein’s rejecting the distinction between apparent time and actual time in the interpretation of the Lorentz transformation equation, taking Lorentz’s apparent time to be physically real time, and rejecting the Newtonian absolute time as real time. Heisenberg said he took the same kind of decisive step, when he inverted the question of how to pass from an experimentally given situation to its mathematical representation by affirming that only those states represented as vectors in Hilbert space can occur in nature and be realized experimentally. Heisenberg’s indeterminacy principle says that no quantum-mechanical state can be dispersion free for every variable. He thus believed that his decisive step affirms that microphysical reality is nondeterministic. He likewise maintains that Young’s two-slit experiment affirms the duality thesis of quantum mechanics, and that wave and particle are manifestations of the same entity that is indeterminate until subject to a measurement action.
Hanson and Heisenberg
In his Patterns of Discovery (1958) Norwood Russell Hanson (1924-1967) dismissed what he called Bohr’s “naïve epistemology”, and like Einstein he believed that observation is what Hanson called “theory laden”. It may be said that Hanson’s philosophy of quantum theory is what Heisenberg could have formulated, had Heisenberg rejected Bohr’s naturalistic semantics, which Heisenberg used for his doctrine of closed-off theories, and instead followed through on Einstein’s aphorism that theory decides what the physicist can observe.
Hanson defended the Copenhagen duality thesis by reference to the mathematical transformation theory developed in 1928 by Paul A. Dirac (1902-1984), who was a theoretical physicist at Cambridge University, and who shared the Nobel Memorial Prize for physics in 1933 with Schrödinger. Hanson had interviewed Dirac at Cambridge for writing his Concept of the Positron (1963). Dirac’s transformation theory enables physicists to exhibit the wave-particle duality by mathematically transforming the wave description into the quantum description and vice versa. Hanson thus says that in the formalisms for modern quantum physics there is a logicolinguistic obstacle to any attempt to describe with precision the total state of an elementary particle, such that quantum mechanics makes the dualistic ontology the only conceivable one. This thesis of Hanson echoes Heisenberg’s thesis of false questions set forth in his paper “Questions of Principle” (1935), in which he says that the system of mathematical axioms of quantum mechanics entitles the physicist to regard the question the simultaneous determination of position and impulse values as a false problem, just as Einstein’s relativity theory makes the question of absolute time a false question in the sense that they are devoid of meaning.
Hanson’s philosophy is discussed in BOOK VII below.