Niels Bohr’s Argument for the Irreducibility of Biology to Physics


Even in his youth, Bohr was familiar with those difficult and controversial questions surrounding the relationship of the phenomena of life to those of inanimate nature, or in other words, the relationship of biology to physics and chemistry. (See e.g., APHK, 96; Folse, 1985, 45–46; and 1990a, 212; Holton, 1970, 142–143, 151; Kay, 1985a, 490; Meyer-Abich, 1965, 180; Petersen, 1985, 307; and Röseberg, 1985, 15–18, 195–196.) Are the phenomena of life in any sense fundamentally different from the processes of inanimate nature, or aren’t they? Bohr became more intensely preoccupied with this question once the stormy development of quantum mechanics had more or less wound down.

  1. Meyer-Abich comes to the same conclusion in (1965), 181.Google Scholar
  2. See the “Preface” to ATDN on the dates of composition for the “Introductory Survey” and its “Addendum”.Google Scholar
  3. For a detailed presentation of the institutional circumstances of Delbrück’s career, see Kay (1985b).Google Scholar
  4. For an account of the circumstances of this discovery from Watson’s perspective, see his wellknown book The Double Helix, Watson (1968). See the contributions to Stent (1980) for commentaries on this book. For further literature, see e.g. Winkler (1985).Google Scholar
  5. Footnote to English and German versions.Google Scholar
  6. In the discussion which follows, I shall treat Bohr’s (1937a) and (1957), which deal with the same issues as “Light and Life”, only in passing, since they do not substantively go beyond “Light and Life;” q.v. APHK, 74–76; and 91–92, and Essays, 20–21. For Pascual Jordan’s reception of Bohr’s argument, see Jordan (1932) and (1934), and for the discussion this precipitated in the Vienna Circle, see Bünning (1935), Frank (1935), Neurath (1935), Reichenbach (1935), Schlick (1935), and Zilsel (1935). See Heitler (1976) for a contemporary attempt at a revival of Bohr’s argument. Hoyningen-Huene (1991a), (1991b), and (1992) contain earlier, substantially shorter analyses of Bohr’s argument. The focus of these papers is on a “theory of antireduct ion ist argume nts”, and on the role Bohr’s arg ument might play in such a theory.Google Scholar
  7. In his (1929), Bohr cites “the freedom and power of adaptation of the organism in its reaction to external stimuli” as examples of “more profound biological problems” (ATDN, 118). In that portion of the “Introductory Survey” composed in 1929, Bohr claims that “living individuals are first of all characterized by the sharp separation of the individuals from the outside world and their great ability to react to external stimuli” (ATDN, 20–21). While I do not know what moved Bohr to change his choice of examples for what is characteristic of life, this issue is of only subordinate importance here.Google Scholar
  8. A similar claim is made in Bohr (1937a), where he states that quantum mechanics has offered “a complete explanation of the remarkable relationships between the physical and chemical properties of the elements, as expressed in the famous periodic table of Mendeleev” (Bohr, (1937a), APHK, 18).Google Scholar
  9. Similar passages with the same tone may be found in Bohr (1932), on 359, 363, 366, 368, and 373. Folse even claims that, for Bohr, the reduction of chemistry to physics is the whole purpose of atomic physics; “Bohr understood the fundamental task of atomic physics to be accounting for the properties of the chemical elements in terms of atomic structures” (Folse, 1985, 57). Also compare Kragh (1985a) (especially 50–51) and Kragh (1985b). — That the conviction, as widespread among physicists today as it was then, that chemistry must, at least in principle, be reducible without remainder to physics, is not only not self-evidently true, but perhaps even false, has recently been noted, especially by Hans Primas. See Primas (1981), (1985a), and (1985b).Google Scholar
  10. In his (1974), Popper argues that many apparently successful reductions in the history of science are incomplete in this sense.Google Scholar
  11. Many passages in Bohr’s work support this reading. See e.g. Bohr (1925), 847; (1932), 355, 356, 357, 377.Google Scholar
  12. Two assumptions or consequences of Bohr’s 1913 atomic model, in particular, are incompatible with classical physics. The first is the existence of so-called stationary states, in which a charge, despite undergoing what, in mechanical terms, is accelerated motion, doesn’t radiate. The second, “perhaps the greatest and most original of Bohr’s breaks with existing tradition” (Heilbron and Kuhn, 1969, 266), though less well-known than the first, consists in Bohr’s separation of the mechanical oscillation frequencies of charges from the frequencies of electromagnetic radiation.Google Scholar
  13. See e.g. Folse (1985), 61–64, 184; and Rosenfeld (1967), 118. See Heilbron and Kuhn (1969) and Hoyer (1974) for the historical details.Google Scholar
  14. That such contradiction is a central, hence indispensible element of complementarity has been emphasized, most notably, by Drieschner (1979), 152; q.v. Röseberg (1984), especially 237f.Google Scholar
  15. At any rate, this reading has had some appeal to contemporary philosophers of science; see e.g. Scheibe (1988), 169–170.Google Scholar
  16. See Feyerabend (1962), 88; and (1976), Ch. 3. See also Krajewski (1984), 11–12, and Hoyningen-Huene (1985), 275–276.Google Scholar
  17. Compare section 2.1, point 2.Google Scholar
  18. It seems to me that Bohr only arrived at the view that, despite quantum physics, classical concepts are indispensible, after 1925; His 1925 essay “Atomic Theory and Mechanics” still argues for the complete abandonment of classical concepts and spatio-temporal notions. Unfortunately, limited space prevents me from presenting in detail the textual evidence for this view, which diverges, for example, from that of Folse (1985), 99–101 and Murdoch (1987), 31–33.Google Scholar
  19. See Feyerabend (1958), 81–89, for a critique of this assumption of Bohr’s.Google Scholar
  20. For attempts to differentiate the notion of complementarity aimed at separating out distinct notions (only some of which are relevant to physics), see Drieschner (1979), 152; Folse (1985), 269–270; Honner (1987), 58–59; Hyland and Kirsch (1988); MacKay (1958); Murdoch (1987), 58–61; Redhead (1987), 170–171; and von Weizsäcker (1955), 284–297; and (1957).Google Scholar
  21. Bohr had already noted both the possibility and necessity of subjecting certain aspects of biological phenomena to physical explanation in his (1929), ATDN, 117–118 and ATDN, 21.Google Scholar
  22. In his (1937a), Bohr supplements this argument with the following remark: “The incessant exchange of matter which is inseparably connected with life will even imply the impossibility of regarding an organism as a well-defined system of material particles like the systems considered in any account of the ordinary physical and chemical properties of matter” (Bohr, 1937a, in APHK, 20–21).Google Scholar
  23. For a different approach to the critique of Bohr’s argument, see Folse (1985), 183–193.Google Scholar
  24. Although Bohr’s statements in his (1962), Essays, 26, aren’t entirely unequivocal. For Stent, the case is closed with the discovery of the structure and function of DNA; “Bohr’s conjecture that one needs to kill an organism in order to study it at the atomic level and that this is bound to hide the ultimate secrets of life from us turned out to be wrong” (Stent, 1989, 13).Google Scholar
  25. Theoretically, there are two conceivable ways in which this circularity might be avoided. First, one might attempt to show that the second feature of complementarity is implied by the first. However, this appears not to be the case. One might also attempt to find a criterion of complementarity which doesn’t invoke the irreducibility of the aspects involved. No such criterion is currently known, and it is highly doubtful that there even is one.Google Scholar
  26. I am very grateful to Alexander Levine, who translated this essay from the German.Google Scholar

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