Heisenberg and radical theoretic change

  • Patrick A. Heelan


Heisenberg, in constructing quantum mechanics, explicitly followed certain principles exemplified, as he believed, in Einstein's construction of the special theory of relativity which for him was the paradigm for radical theoretic change in physics. These were the principles of (i) scientific realism, (ii) stability of background knowledge, (iii) E-observability, (iv) contextual re-interpretation, (v) pragmatic continuity, (vi) model continuity, (vii) simplicity. Fifty years later, in retrospect, Heisenberg added the following two: (viii) a principle of non-proliferation of competing theories — scientific revolutions are not a legitimate goal of physics — and (ix) a principle of tenacity — existing theories are to be conserved as far as possible. The conservative as well as the revolutionary potential of these principles is then discussed. A more penetrating philosophical criticism of these principles is postponed.


Quantum Mechanic Model Continuity Background Knowledge Special Theory Scientific Realism 


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  1. 1.
    The term “Received View”, coined by H. Putnam, has gained considerable circulation for the tradition of the philosophy of science inspired by the Vienna Circle and Reichenbach's Berlin School. For an excellent summary of criticisms of the Received View and for the existing available alternatives, see the introduction by F. Suppe, in F. Suppe (ed.).The Structure of Scientific Theories, pp. 3–243 (Urbana, Ill., University of Illinois Press, 1974).Google Scholar
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    Published and unpublished sources will be used in this study. The unpublished sources are in theArchive for the History of Quantum Physics (hereafter referred to as AHQP) compiled and maintained by a Joint Committee of theAmerican Physical Society and theAmerican Philosophical Society, Philadelphia, on the History of Theoretical Physics in the Twentieth Century. TheArchive is deposited, in original or duplicate form, at the Library of the American Philosophical Society, Philadelphia, at the Bancroft Library of the University of California, Berkeley, at the Niels Bohr Library, American Institute of Physics, New York, and at the Universitets Institut for Teoretisk Fysik, Copenhagen, Denmark. The Archive contains documents on the history of quantum physics and taped interviews conducted by T. S. Kuhn, J. L. Heilbron and others with Heisenberg, Niels Bohr and other quantum physicists. All the interviews cited or referred to were with T. S. Kuhn. Reference and citation will be by date of interview. The writer was enabled to consult this material by permission of the Joint Committee referred to above through the courtesy of Dr. Charles Weiner, formerly Director of theCenter for the History and Philosophy of Physics, a division of the AIP, New York, and Mrs Joan Warnow, presently Acting Director of theCenter. Permission to quote from the unpublished material was kindly given by Professor Werner Heisenberg and the Joint Committee. The principal published sources for the biographical material are W. Heisenberg, “Erinnerungen an die Zeit der Entwicklung der Quantum Mechanik”, inTheoretical Physics in the Twentieth Century: Memorial Volume to Wolfgang Pauli, ed. by M. Fierz and J. F. Weisskopf (New York, Interscience, 1960), pp. 40–7; “The Development of the Interpretation of Physics”, inNiels Bvhr and the Development of Physics, ed. by W. Pauli (New York, McGraw-Hill, 1955), pp. 12–29;Physics and Philosophy (New York, Harper and Row, World Perspectives Series, vol. 19, 1958) — hereafter referred to as PP;Physics and Beyond, (Harper and Row, World Perspectives Series, vol. 42, 1971) — hereafter referred to as PB;Across the Frontiers, trans., from the German by Peter Heath (Harper und Row, World Perspectives, Series, vol. 48, 1974) — hereafter referred to as AF.Google Scholar
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    An object comes to be known when two conditions are fulfilled: (1) when it is conceptually categorized (or becomes subject to clear semantical description); (2) when it is recognized by particular observers in particular instances. An objectifiable object then is one which has a two fold independence from observers: (i) alogical (orsemantical) independence, and (ii) a real independence. An object islogically (orsemantically) independent of observers if its notion does not logically involve any set of observers (whether these be instrumental contexts or human perceivers) or if its descriptive framework does not refer to a class of observers or speakers (instrumental or perceptual). Absolute position and velocity would fulfil this condition (but not relative position and velocity); also properties invariant for all observers, such as for example, rest mass or the velocity of light. An object isreally independent of observers if it does not depend for the fact of its existence on the activity, for example, of measuring or observing, of any class of observers or speakers. There are two ways in which the fact of existence of an object can come to depend on the activity of an observer: first of all, when the object is the real product of that activity, as, for example, in participant-observer situations in the social sciences, or in the physical sciences, for such properties as are the product of an interaction with a standard set-up that acts simultaneously as a measurement frame. According to one (re-)interpretation,position is the product of a localizing (inter)action with (one of a class of) macroscopic instrumental reference frames; that is, in so far as it is relative, position is according to this (re-)interpretation not a merelynotional relation but areal relation founded on the action of the reference frame on it. A second kind of existential dependence on observers arises when the object has existence only in virtue of being recognized by the observer, such as, for example, warm-as-felt, or red-as-sensed, etc.; according to one interpretation of the reduction of the wave packet, quantum mechanical variables also belong to this class. Cf. for example, F. London and E. Bauer,La théorie de l'observation dans la physique quantique (Paris, Hermann, 1939), and Eugene Wigner, “Remarks on the Mind-Body Problem”, inThe Scientist Speculates, ed. by I. J. Good (London, 1962), pp. 284–301. The physical systems of classical physics are paradigm cases ofobjectifiable objects. Relativity and quantum mechanics were to change, not merely the kinds of objects admitted to be real, but also the nature of scientific objectivity.Google Scholar
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    Cf. Patrick Heelan,Quantum Mechanics and Objectivity: A Study of the Physical Philosophy of Werner Heisenberg (The Hague, Nijhoff, 1965) — hereafter referred to as QMO — pp. 64–71. In relativity theory, Einstein only went so far as to re-defineposition asconceptually relative to frames of reference. M. Sachs notes: “it was tacitly assumed that anoutside observer will always have at its disposal a set of measuring rods and clocks — to probe the properties of the universe (as closely as he pleases!) ... [but] these investigations did not attempt to explicitly incorporate the measuring processes”, p. 59 in “The Elementarity of Maesurement in Relativity”, inBoston Studies in the Philosophy of Science, Vol. iii, ed. by R. S. Cohen and M. Wartofsky (New York, Humanities Press, 1968), pp. 56–80. Cf. QMO, pp. 73, 76–111.Google Scholar
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    Heisenberg writes: “The concepts of classical physics will remain the basis of any exact and objective science. Because we demand of the results of science that they can be objectively proved (i.e., by measurements registered on suitable apparatus) we are forced to express these results in the language of classical physics ...; Thus while thelaws of classical physics ... appear only as limiting cases of more general and abstract connections the concepts associated with these laws remain an indispensable part of the language of science without which it would not be possible even to speak of scientific results”,Philosophic Problems of Nuclear Science (London, Faber and Faber, 1952), p. 45. The same idea is expressed in Heisenberg,Physical Principles of the Quantum Theory (New York, Dover), pp. 1–4, 11, 62–4 and passim, where it is supposed that the descriptive categories of classical physics are identical with those of everyday language; also in PP, pp. 44, 144; PB, pp. 64, 130. See also QMO, chap. iv.Google Scholar
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    The analysis of the subject-object cut especially in acts of observation, leads to an epistemology that permits the displacement of the S-O cut so that the measuring instrument becomes functionally part of the observing subject. Observational languages then are context-dependent: where the context of observation depends on the location of the S-O cut. Cf. the author's “Hermeneutics of Experimental Science in the Context of the Life-World”,Philosophia Mathematica, (1972), pp. 101–44 and the commentary by T. Kisiel inZeit. f. Allgem. Wissenschaftstheorie 5 (1974), pp. 124–134 where this topic is discussed.Google Scholar
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    For Heisenberg, the mathematical structure of a physical theory tells how nature really is: this he learned from Einstein. Language, however, is tied to everyday experience, since it is the product of conventions and historical process. At first (1925–6), he tried to force on the language of physics a semantical re-interpretation to make it conform to the quantum mechanical formalism; but Bohr convinced him (early 1927) that language need not be so re-interpreted; its old usages could be retained provided it was understood that the meaning of the old terms was sufficiently vague and imprecise. Besides language (or words), there wereintuitions orpictures, roughly intuitive classical models; language uses these pictures realistically, of the macroscopic everyday world, but in quantum mechanics, a variety of complementary pictures is used to adapt ordinary language to the purposes of scientific expression; the reality expressed, however, is isomorphic, not with the picture or the language, but with the mathematical schemes, (or meaning); cf. Heisenberg,Physical Principles, op. cit., p. 11, and notes 44, 61, 65 and 68 below.Google Scholar
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    Heisenberg emphatically believes that physics, though necessarily expressed in terms of mathematical structures, depends in an important way on physical intuitions into possible experiments. He criticizes Born, Wightman, Symanski and others for being too mathematically oriented. “First solve the physics”, he says echoing Bohr, “and then find the mathematical tools”. (AHQP, 22 February 1963). “Such terms as ‘the stability of the atom’ or ‘the quantum condition’ give a different style to physics ... more difficult ...; forgetting about mathematical schemes, one comes to a kind of substance of things which one is inclined to forget if one works in the mathematics alone ... [However] it is difficult to describe physics without having the logical connection [of mathematics]. Still by doing so, one is forced to think very carefully about what will happen in ... experiments”. (AHQP, 28 February 1965).Google Scholar
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    Heisenberg reports that Einstein held that the valid applicability of the old physics is a necessary condition for the observation of facts in the new physics; PB, pp. 63–4.Google Scholar
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    AHQP, 17 February 1963: Heisenberg said, “Quantum theory ... certainly includes Newtonian physics in some way ... The concepts for quantum mechanics can only be explained by already knowing the Newtonian concepts; ... I would say thatNewtonian mechanics is a kind of a priori for quantum theory ... in that sense that it is that language which enables us to say what we observe. If we have not the language of classical physics, I don't know how we should speak about our experiences” (italics inserted). See note 18 for other references.Google Scholar
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    Heisenberg's belief in the unrevisable cumulative character of scientific knowledge is expressed in his notion ofclosed theory orabgeschlossene Theorie. For an explicit analysis of this notion, see his “Recent Changes in the Foundation of Exact Science”, (1934),Philosophic Problems, op. cit., pp. 11–26; “The Notion of ‘Closed Theory’ in Modern Science” (1948), in AF, pp. 39–46. The notion is adumbrated inZeit. f. Physik, xviii (1927), p. 172. In thePhysicist's Conception of Nature (London, Hutchinson, 1958), he writes that a closed theory “is valid for the entire cosmos and cannot be changed or improved” (pp. 27–8). Closed theories are unrevisable because, as he says, they are “idealizations” of reality (AF, pp. 184–191.) The evolution of physics, for Heisenberg, takes place through the dialectic of “idealization” (or formalization making a “closed theory”) and research into “domains of applicability” of theories that are “closed”. The domain of a closed theory is always to some extent indefinite. New research discovers areas of inapplicability of the old theory; this necessitates a new “idealization” (subject to principles of growth and continuity) and so on; cf.Physical Principles, op. cit., pp. 1–4. About the domain of applicability of a closed theory, he says, “When you axiomatize a theory, as for instance, Newton [did] ... then from this moment on you do not know whether this whole scheme has anything at all to do with nature because then it is closed. You may be lucky and it may actually fit to nature in a very large number of observations: all right, but you never can say how much it fits. I mean in some way, you have lost contact with nature”. (AHQP, 5 July, 1963).Google Scholar
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    As Heisenberg wrote to W. Pauli on 24 June, 1925, “Grundsatz ist bei der Berechnung von irgenwelchen Größen, wie Energie, Frequenz, usw., dürfen wir nur Beziehungen zwischen prinzipiell beobachtbaren Größen vorkommen”, cited in Heisenberg, “Erinnerungen”,op. cit.; see also QMO, pp. 30–2 and passim.Google Scholar
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    In practice then, Heisenberg's Principle of Observability functioned negatively, much like falsification in Karl Popper's philosophy of science; cf. K. Popper,The Logic of Scientific Discovery (London, Hutchinson, 1959),Conjectures and Refutations (London, Routledge and Kegan Paul, 1963),Objective Knowledge (New York, Oxford Univ. Press 1972).Google Scholar
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    AHQP, 5 July 1963: Heisenberg narrated how late in 1926 as he ran in Faelled Park near Bohr's Institute in Copenhagen, the insight came to him, “Why not simply say that only those things occur in nature which fit our mathematical scheme!” This thought, clearly inspired by Einstein, led him to consider the gamma-ray microscope, etc. The problem of expressing in language what occurred in nature as revealed by quantum mechanics was a real one: on the one hand, Bohr held that language was a given, consecrated by historical process, convention, everyday usage and the “customary forms of perception”; on the other hand, Heisenberg believed that the experience of relativity showed the flexibility of language to contextual re-interpretation forced by changes in the mathematical formalism. Heisenberg eventually came to accept the view (Bohr's) that it was not necessary to re-interpret the language of physics (classical language), but that the old language could remain provided limitations were imposed on its use in quantum mechanics, principally a certain vagueness of meaning; cf. note 68.Google Scholar
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    As I have shown in QMO, chap. ii, Heisenberg's original intention was to re-interpret the kinematical variables within the context of the measuring process. The title of his revolutionary paper proclaims this intention, “Über quantentheoretische Umdeutung kinematischer und mechanischer Beziehungen”, (“On quantum theoretical re-interpretation of kinematic and mechanical relations”),Zeit. f. Physik, 33 (1925), pp. 879–893. Bohr was more cautious, as we have seen (note 44). Heisenberg came to accept complementarity in March 1927, as he told Kuhn (AHQP, 25 February 1963). Heisenberg's explicit adoption of Bohr's philosophy is announced in the Preface to hisPhysical Principles, op. cit., but internal evidence in the text shows a considerable difference of viewpoint; cf. QMO, chaps. ii and iii. See below, especially note 68, for further comments on the differences between Bohr and Heisenberg.Google Scholar
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    In PB, Heisenberg speaks of the goals of science: “‘Understanding’ in Modern Physics (1920–22)”, pp. 27–42, “Atomic Physics and Pragmatism (1929)”, pp. 93–102, “Positivism, Metaphysics and Religion (1952)”, pp. 205–17. Predictive ability, he says, is not enough, because even Ptolemy could achieve this (pp. 31, 212). Exact science moves towards more and more comprehensive theoretical syntheses, expressed by simple mathematical formulae (p. 99). The beauty and simplicity of these formulae witness to their truth as expressing the real course of nature (p. 212; also AF, p. 172).Google Scholar
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    See for example, Heisenberg,Physical Principles, op. cit. pp. 66, 105, 107;Philosophic Problems, op. cit., p. 24, where pragmatic continuity is implied. In noting the variety of formalisms developed for the quantum theory — by Schrödinger, Dirac and himself — and the variety of interpretations of the formalisms — by Bohr, Schrödinger, Born and himself — he consoles himself with the thought that, after all, they all give pragmatically the same experimental results; cf., PB, p. 77. In AF, he writes, that the success and fruitfulness of a new theory is reason why scientists come to accept it; this he calls a “pragmatic criterion of value” (p. 163).Google Scholar
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    AHQP, 27 February 1963: Heisenberg said, “When you have a number of axioms as Newton had in ...Principia Mathematica, then the words are not only defined by the customary use of the language, but they aredefined by their connections ... That is, you cannot change one word without ruining the whole thing”. (italics inserted).Google Scholar
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    AF, pp. 187, 189. Enough has been said to prove that for Einstein and Heisenberg the mathematical formulae contained the relationships essential to a scientific understanding of phenomena. Both demanded model continuity as one passed beyond the domain of applicability of a Closed Theory to the more extended domain of the new theory. It does not follow, of course, that model continuity was in fact achieved; in the case of quantum mechanics, it was not achieved as Bohr and Heisenberg knew well. It is not always the case that h → 0 and/or masses or quantum numbers become very large, that the classical formula is obtained. Cf. QMO, pp. 114–5. The same point is made by P. Feyerabend in “Problems of Empiricism II” p. 296–300 inNature and Function of Scientific Theories, ed by R. G. Colodny (Univ. of Pittsburgh Press, 1970).Google Scholar
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    AF, chap. 12, “Changes of Thought Patterns in the Progress of Science”, pp. 154–65. The citations are on pp. 163–5. This paper was given during the student unrest of the late ‘60's and perhaps its rhetorical form was influenced by Heisenberg's rejection of what he took to be the use of political means to transform the disciplines. He does admit, however, that there are social components to a scientific revolution, for, as he says, echoing Wolfflin, not everything is possible in every epoch (p. 158).Google Scholar
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    AF, p. 189. The theory of elementary particles that will unify the existing domains of physics will be a Closed Theory, but it will not close physics; this must grow in the direction of biology and other disciplines, where new concepts, such aslife, appear that do not appear in physics.Google Scholar
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    The method used can be compared with Husserlian eidetic intuition into the sense of a given (in this case of the givenness of scientific observables): one aims, by a type of eidetic phenomenological reduction, at the intuitive essence of what the theory says (should or could say) about the World; of the author's “Hermeneutics of Experimental Science”,op. cit. For eidetic phenomenological reduction, see Edmund Husserl,Ideen zu einer reinen Phänomenologie und phänomenologischen Philosophie, I, II and III. Husserliana, vols. I, III, IV and V (1952) (The Hague, Nijhoff). Vol. I trans. by W. R. Boyce Gibson asIdeas (London, Allen and Unwin, 1931).Google Scholar
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    Heisenberg's interesting account of the debate between himself and Bohr on one side and Schrödinger on the other is found in PB, pp. 70–76. Schrödinger said of quantum mechanics that it was, “von abschreckender ja abstoßender Unanschaulichkeit und Abstraktheit” (quoted by Heisenberg inZeit. f. Physik, xliii, 1927, p. 195, note).Google Scholar
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    About Heisenberg's disagreements with Bohr, see PB, pp. 76–81, and AHQP, 11, 13, 15, 19, 25 and 27 February and 5 July 1963. About Bohr, Heisenberg said, “I have really in this whole period (1925–27) been in real disagreement with Bohr and the most serious disagreement was at the time of the Uncertainty Relations”, (15 February 1963). Bohr wanted to start with “intuitions of how nature was and worked”, he asserted, “Bohr was not a mathematically-minded man ... he was Faraday but not Maxwell”. Bohr insisted on the experimental inadequacies of matrix mechanics; Heisenberg was less worried about these, trusting in the consistency of the mathematical formalism (25 February 1963). Bohr wanted to use both wave and particle pictures jointly to give intuitive sense of how nature is and works; Heisenberg wanted to use the mathematical formalism as guide to what nature is really like (27 February 1963, cf. also note 68).Google Scholar
  63. 65.
    About Bohr's philosophy, see Age Petersen'sQuantum Physics and the Philosophical Tradition (M. I. T. Press, Camb. Mass., 1968): QMO, pp. 44–56 and the author's “Complementarity, Context-dependence and Quantum Logic”,Foundations of Physics 1 (1970), particularly, pp. 108–9. Bohr's philosophy has been described both by Heisenberg and Petersen as a preoccupation with the possibilities of unambiguous communication through language. Bohr saw quantum mechanics as revealing certain limitations on the possibilities of human discourse arising out of (i) the inseparability of objective content and the observing subject and (ii) the fact that the partition between the actor and the audience can be moved at will so that what was part of the audience becomes in a new context part of what is being observed on the stage. The reason, he says is the “coupling between the phenomena and the agency by which it is observed”. This condition “forces us to adopt a new method of description designated ascomplementary in the sense that any given application of classical concepts precludes the simultaneous use of the classical concepts which in a different connection are equally necessary for the elucidation of the phenomena”,Atomic Theory and the Description of Nature (Cambridge Univ. Press, London, 1934), pp. 10–11. Bohr held that all communicable knowledge about the world is necessarily expressed in terms of the “customary forms of perception” of which the categories of classical physics are a clear and precise expression; cf.ibid., pp. 1, 5, 15–9, 22, 90–3, 103, 111; and “Discussions with Einstein on Epistemological Problems in Atomic Theory”, inAlbert Einstein: Philosopher-Scientist, op. cit., p. 209. As was pointed out above (note 28), Heisenberg uses the distinction betweenlanguage, picture, andmathematical scheme (ormeaning) in describing Bohr's philosophy, “Bohr was from his youth interested in our ways of expression, the limitations of word, the problem of talking about things where one knows that the words do not really get hold of the things... Bohr tried to keep the picture while at the same time omitting classical mechanics. He tried to keep the words and the pictures without keeping the meaning of the words and pictures”, So what do you do? he asks. He rejects Sommerfeld's “escape into mathematics” and endorses Bohr's perception that there was a philosophical problem to solve (AHQP, 11 February 1963).Google Scholar
  64. 66.
    In the preface to thePhysical Principles of the Quantum Theory, op. cit., Heisenberg identifies himself with theKopenhagener Geist der Quantentheorie. Later (in 1955), he wrote “What was born in Copenhagen in 1927 was not only an unambiguous prescription for the interpretation of experiments, but also a language in which one spoke about Nature on the atomic scale and in so far a part of philosophy”, p. 16 in “The Development of the Interpretation of the Quantum Theory”, inNiels Bohr and the Development of Physics, op. cit. Google Scholar
  65. 68.
    AHQP, Heisenberg said that at the time he wrote the paper on the Uncertainty Relations, he did not realize that the words “position”, etc. could still be used in the old sense, but with limitations: Bohr made him realize this a few months later (27 February 1963). In fact, referring to his original intention, he said that he learnt from Bohr that “the thing I in some way attempted could not be done ... one has to talk about, e.g., the diffraction pattern (as a wave phenomenon) while holding the indivisible character of the electron (as a particle phenomenon) ... [for this] one needs a language ... taken from the historical process [which in our case] is a classical language [LN] ... thus one cannot avoid the tension between classical precise language and its limits (17 February 1963). Never-theless, the experience of relativity showed that his original intention was viable. Comparing the quantum mechanical and the relativistic revolutions: in relativity, he said, actual language has adjusted to the mathematical scheme ... In quantum theory, language has never adjusted to it... The mathematicians have shown that it could adjust to it by changing the Aristotelian logic... So far nobody has been willing to pay that price. Now that was not clear at that time. But still it was clear that probably the only sensible thing to do was to use the old words and always remember their limitations“ (27 February 1963). Various non-Aristotelian logics have been proposed, starting with the paper of G. Birkhoff and J. von Neumann, “The Logic of Quantum Mechanics”,Ann. of Math., 37 (1961), pp. 155–184; of the author's “Classical Logic and Quantum Logic: Their Respective Roles”,Synthese, 21 (1970), pp. 2–33.Google Scholar
  66. 69.
    The relative invisibility of eidetic methods in modern physics arises from the fact that there seems to be no systematic place for it or for the kind of evidence it produces in the “received” views, both empiricist and rationalist, of scientific inquiry. Some results in elementary particle physics, as, e.g., those obtained by Kosta Gavroglu in “Semiweak interactions and the non-leptonic weak decays”,Nuovo Cimento 16 A (1973), p. 61, were produced by the use of eidetic methods, according to a verbal report given to the author by Gavroglu. Gavroglu is now engaged in a study of these methods in physics, particularly as applied to elementary particle and quantum gravitational theory. Gavroglu is at SUNY at Stony Brook.CrossRefGoogle Scholar
  67. 70.
    For Heisenberg's work on unified field theory, see for example, his „Entwicklung der einheitlichen Feldtheorie der Elementarteilchen“,Naturwissen., 50 (1963), pp. 3–7, and hisUnified Theory of Elementary Particles (London, Interscience, 1966).Google Scholar
  68. 71.
    AF, p. 164.Google Scholar
  69. 72.

Copyright information

© Franz Steiner Verlag GmbH 1975

Authors and Affiliations

  • Patrick A. Heelan
    • 1
  1. 1.Department of PhilosophyState University of New York at Stony BrookStony BrookUSA

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