3.1.2. Background and influences

  Bohr never devoted any time to systematic study of philosophy. In his writings he does not refer to any of the great authorities. Still, much of his contribution to the development of modern physics was to strive to clarify the possibilities and limitations of our means to describe observations, a typical problem of philosophy usually referred to as epistemology. However, when late in life he was asked about his interest in the discipline he is reported to have answered: “It was, in a way, my life.” He, however complained that no philosopher ever understood his concept of complementarity.

  Early Bohr seems to have contemplated the possibilities of attaining meaning and the ways to avoid ambiguity. Already as a boy, he enjoyed the privilege of listening to advanced discussions about the meaning and significance of science. His father, the professor of physiology, collected his peers at home for discussions. Among these were Christian Christiansen, the professor of physics at the university, Harald Høffding, the professor of philosophy, and Vilhelm Thomsen, a famous linguist. The Bohr boys sat in on these discussions, and they were, no doubt, imbued with much of the cultural debate which flourished in Copenhagen in those days. Thus they became educated without attending lectures, instructed in dialectics without study, and used to logical argumentation without formal training. This situation, however, makes it difficult to ascertain when Niels learned about various ideas in philosophy.

  Two of the participants later served as Niels Bohr's teachers. Christiansen, as the single professor in physics at the university, taught him both experimental and theoretical physics, apparently both efficiently and successfully. As an undergraduate student, Bohr had to take a compulsory course introducing philosophy. Here he, no doubt, got acquainted with the classic names and ideas of the academic tradition in philosophy. He also learned to respect and admire the teacher, Høffding, for his clarity and openness of mind. The respect must have been mutual, because Høffding let Bohr read a manuscript of his textbook on logic while Bohr was still an undergraduate student. His possible role as Bohr's source of philosophical knowledge justifies a scrutiny of his intellectual position, which I will undertake below. Later Høffding was trying to understand Bohr's concept of complementarity, but without great success.

  (p.51) Niels Bohr's elder brother Harold became a mathematician. He, however, also was a member of the 1908 Danish Olympic soccer team. When he took the doctoral degree, this was announced on the sports page. Thus Niels early got to know the details of advanced mathematics.

  Harold Bohr came to Göttingen in 1909 to study with Hilbert. When Niels visited him, he had the opportunity to meet Hilbert and discuss modern mathematics as represented by the Göttingen school. Niels visited his brother frequently and informed Hilbert about the progress in contemporary physics. Thus Niels, no doubt, got some connections with the modern developments of mathematics, which must have helped him in grasping the more formal aspects of quantum physics.

  Niels Bohr seems to have had an uncanny ability to attach philosophical significance to formal machinery. This is a trend clearly exhibited by his discourse as a mature scientist, but already as a student, he was attracted by such relations. In mathematics, he learned about the way a complex function may acquire different values on different sheets of its definition. These are the well‐known Riemann sheets, which allow a function to present different results at seemingly identical points in the plane. The function itself is defined on the collection of all such sheets. Bohr saw in this an analogy with language: The use of words may carry different meaning depending on the setting of the discourse. The similarity with his later ideas about complementarity seems obvious.

  Another philosopher who appears to have been important for Bohr was the psychologist William James (1842‐1910). It is not clear to what extent Bohr had read the works of James nor when he may have done so. However, James consistently stresses that the description of mental concepts cannot remain unaffected by the methods of investigating them. The wording is close to that which reappears in quantum theory later. Also his concept of flow of consciousness versus external experience seemed to support Bohr's combination of phenomena from observational setting and microscopic atomic processes. Bohr introduced the novel concept of a phenomenon, as one consisting of both the observed object, the unambiguous result of the observation, and the full description of the conditions validating the result. This new concept was to form the foundation for the utilization of the approach of complementarity, and it is one of Bohr's essential contributions to philosophy. Later he was to apply this concept also outside its original setting as a description of quantum measurements.

  Bohr was clearly aware of the Viennese movement of logical positivism. He had met Otto Neurath already in 1934. Furthermore, in 1936 the “2. International Kongress für Einheit der Wissenschaft” took place in Copenhagen. This was organized by Otto Neurat and Jørgen Jørgensen, the latter being a Danish representative of the Viennese movement. In addition to these two, Bohr had contacts with Philipp Frank. Bohr exchanged letters with Neurath over the following couple of years, but it is difficult to judge how strongly the positivist aversion against metaphysics influenced Bohr's view of reality. He remained a realist concerning the objects of study in physics, but an instrumentalist concerning their observable attributes.

  (p.52) Bohr must at some time have devoted reading to getting acquainted with oriental philosophy:

  We must in fact turn to quite other branches of science, such as psychology, or even to that kind of epistemological problems with which such thinkers like Buddha and Lao‐Tse have been confronted.

  Significantly, when, in 1947, Bohr chose his coat of arms, he adopted the Chinese Yin‐Yang symbol and the device contraria sunt complementa. Do we here trace the origin of the concept complementarity to the logical relation of “contraries” which are not “contradictory”?

  Nobody can fathom exactly where Bohr acquired his information about philosophy. He read, but not extensively; he wrote only slowly and with difficulty. His manuscripts were rewritten and reworked numerous times, and the final product was often so contorted that its message is hard to extract even today when the quantum theory is firmly established. Bohr also wanted to work mainly orally. He needed young knowledgeable disciples to explain the issues, and he used to produce his texts by dictating to an assistant. When he understood an issue, his grasp was full and deep, but the formal expression of his vision was often beyond the capacity of the verbal tools at our disposal.

  3.1.3. References relating to Bohr

  There is a multitude of writings dedicated to the ideas and opinions of Niels Bohr. Here I only want to direct the reader to those sources on which my present summary is based. They cover the more philosophically oriented aspects of his thinking; for the physical analyses other sources must be consulted.

  A summary of Bohr's argument is given by Honner [29], where also a historical review is offered. Honner stresses the transcendental character of Bohr's concept of empirical activity of physics. Murdoch [30] analyzes the same material and concludes that Bohr's attitude is strongly similar to that of “pragmatism”. Folse [31] summarizes the received view of the s.c. Copenhagen school. Pais [32] inserts Bohr's achievements into a wider cultural perspective. Faye [33] goes through Bohr's background and its relation to philosophy. Here the details of Høffding's philosophy are presented. A more recent text by Plotnitsky [34] tends to stress the anti‐realist interpretation of Bohr's work.

  Bohr's own writings on philosophy and epistemology are collected in four booklets [35] to [38]. The impact and essential importance of Niels Bohr can be obtained from the published conference [39].

  3.1.4. The life and opinions of Høffding

  Biographical résumé

  Harald Høffding was born on March 11, 1843 as the son of a well‐to‐do merchant. The family home was situated in the very center of Copenhagen. The home of the Kierkegaard family was not far away.

  (p.53) Høffding was born in the same year as the famous Copenhagen Tivoli was opened. This was originally situated outside the city gates, but the growth of the city and its various activities made Tivoli a central part of the emerging modern city. When Høffding died in 1931, Copenhagen had essentially achieved its present status.

  Høffding entered university in 1861 and started his studies in theology and philosophy. Following the tradition that talented students entered the clergy, he aimed at the theological degree which he took in 1865. However, his logical and psychological studies under F. C. Sibbern had opened his eyes to philosophy. His favorite authors here became Spencer and Comte. An even more influential factor in his decision to devote himself to philosophy was the contact with the writings of Kierkegaard. He attended lectures on Kierkegaard's writings, but also read his works.

  The critical attitude towards religion displayed by Kierkegaard made it impossible for Høffding to seek a living as a priest. Especially the text Concluding Unscientific Postscript awoke Høffding's interest to the relation of personally centered subjectivity and truth.

  During the years 1868 to 1869, Høffding lived in Paris and studied French and English philosophy. Here he got his firm ground in positivism and empiricism even if he never became merely a disciple. He formed a strong personal view of philosophy, which led him to contribute to a multitude of questions during his long life. He, however, never took much interest in formal logic, where his understanding was not at the highest level.

  In 1870 Høffding married Emma Pape, who, however, died in 1877. At the age of 81, he married Greta Ellstam,—Fifty‐seven, year his junior who died in 1930, one year before Høffding himself.

  Høffding became a university professor in 1883 and retired in 1915. He was president of the university 1875–82. During the First World War, he worked devotedly for the Danish Red Cross, and even in retirement he remained active and produced written documents up to his death. He treated many philosophical questions related both to theological and moral issues. His last interest was in epistemology and the theory of knowledge, which was strongly related to his contacts with Niels Bohr. As a curiosity, it may be mentioned that, upon retirement, Høffding became the first honorary inhabitant in the apartment provided by the brewery Carlsberg to house eminent Danish scientists. After Høffding's stay, Niels Bohr became his successor in the very same apartment.

  Høffding's intellectual influence on youth was significant. He was here competing with the widely known radical littérateur Georg Brandes. Brandes's position at the university had been a drawn‐out struggle between his supporters and representatives of the conservative establishment. Denmark was in dire need of having a Nobel Laureate in literature, but Brandes was too controversial. Thus Høffding was nominated a few times in 1911–16. The powerful Carl David af Wirsén represented a highly conservative attitude in the Swedish Academy, and the “modern” approach by Høffding could not be accepted. The (p.54) situation was not improved by Høffding's reputation as a writer of formalistic and difficult prose.

  Høffding's philosophy

  The cultural atmosphere in Copenhagen was strongly dominated by N. F. S. Grundtvig (1783–1872). He accepted the contemporary German criticism of the origin of religious canon. He advocated a personal approach to faith, but regarded the Lutheran challenge to the individual to be too much influenced by papal thinking. By stressing the importance of personal religious experience, he managed to convey a strong religious feeling to the common people of Denmark.

  Combining religious thinking with a powerful emphasis on national identity he managed to unify two trends in the contemporary intellectual debate. He singlehandedly seems to have created the concept of the Danish people. His influence on his country represents a unique case history in Europe.

  At the beginning of the nineteenth century, the philosophical tradition in Copenhagen was thus strongly dominated by religious issues. This tendency lingers on in the development of the debate created by Kierkegaard's writings. The resulting development in philosophy then led to an increasing emphasis on psychology. This is not surprising, because psychology emerged as a separate academic discipline of study only towards the end of the century. However, in Denmark this orientation became a bulwark against the strong influence from Hegel. Its concentration on the individual also prevented the Romantic philosophical tradition from gaining strong support.

  The dominating influence in Copenhagen derived from F. C. Sibbern (1785– 1872). Becoming professor of philosophy in 1813, he remained at the position for fifty‐seven years. Having started under the influence of the Romantic philosophy represented by Schelling, he developed into an early forerunner of the existentialist philosophy. His influence on Kierkegaard and Høffding was decisive. Both rejected the adoption of great systems and founded the view of the world on personal experience. Sibbern seems to have created the term “the individual” (“den enskilde”) as later to be used by Kierkegaard. In the debate about “belief and knowledge”, Kierkegaard came to stress the paradoxical in faith which necessitates the “leap of faith”.

  Sibbern's philosophical colleague at the university was Poul Møller (1794– 1838), who wrote little on philosophy, but whose work on the Danish student exerted a decisive influence on Niels Bohr. The existentially and subjectively oriented philosophy of personality advocated by Møller and Sibbern opposed the influence of Hegel and formed the platform for the extensive and influential work by Kierkegaard. In contrast to the absolute picture presented by Hegel, the philosophy of the individual offers a view of continuous development harmonious with the progress of the individual in the world. There was an attempt to reconcile Hegel's approach with religion by J. L. Heiberg and H. L. Martensen. These attempts were strongly opposed by Kierkegaard, who regarded their (p.55) dogmatism as incompatible with the subjectivity dominating the philosophy in Denmark.

  Høffding and Bohr

  After his initial interest in moral and faith, Høffding turned to more scientific issues later. In 1875 he started his study of psychology which resulted in a book in 1882. Here he related the theoretical discourse to experiments and foreshadowed the emergence of Gestaltpsychology. Following his conviction of personal subjectivity Høffding does not consider knowledge as accumulated experience but insight into the interrelationships between experiences.

  Høffding kept in contact with William James, who shared many of his opinions. In 1902 he published a book on Problems of Philosophy, which was issued in English in 1905 including a preface by James. The book Høffding published in 1904 on modern philosophy includes the ideas of Mach, Hertz, and Ostwald, showing his interest in modern physical science.

  Høffding's interest in epistemology is documented in the work Human Thought: Its Form and Its Tasks published in 1910. These issues were the topics of informal meetings organized in the home of Niels Bohr's father. Here the young Niels acquired many of the philosophical attitudes that came to shape the formulation of quantum physics. The interdisciplinary character of the meetings was guaranteed by the combination of the participants:

  • Christian Bohr (physiologist)

  • Harald Høffding (philosopher)

  • Wilhelm Thomsen (linguist)

  • Christian Christiansen (physicist and Niels's teacher).

  The discussion group used to meet after the Academy meetings up to the death of Bohr senior in 1911. Following his father's example, Niels entered in 1905 a discussion group EKLIPTIKA after starting at the University in 1903. This group, of slightly varying composition, discussed Høffding's lectures, and hence we may conclude that Niels had attended them by then. Some members of the group may have met as late as in 1916.

  Edgar Rubin was the driving force of the EKLIPTIKA. He later founded a “Copenhagen school” of psychology. This went beyond the Gestalt approach looking at the mind as an integrated totality. He presumably drew Niels's attention to the work by William James. The interest of the group thus seems to be strongly under the influence of Høffding.

  It is slightly unclear when Niels Bohr read James. In old age, he claims to have read about “the stream on consciousness” already as a student. Rosenfeld suggests that this happened only in 1932. These statements are not necessarily contradictory; Bohr may have learned about James as a student but read him more carefully only later. He also benefitted from Høffding's lectures on Kierkegaard. It seems clear, that Bohr read only little original philosophy, but he got acquainted with its main ideas from lectures and discussions.

  (p.56) Kierkegaard seems to have had an essential influence on Bohr; this was hard to avoid in Denmark at that time. According to Kierkegaard, we may create a system of ideas but not of reality. The personal approach is here confronted with the Hegelian approach. The concept of a “leap” utilized by Kierkegaard implies that the state changes in a moment; what happens in the transition cannot be described. According to Høffding such discontinuities play a role in the scientific description of reality. He explicitly refers to radioactive decay and mutations. According to him this introduces an element of “irrationality” into the description. These features may have been discussed with Bohr as a part of the “subject—object” discourse carried out by Høffding.

  When Bohr later presented his concept of “complementarity”, first in the Como lectures, his choice of language seems strongly influenced by Høffding. After Bohr had explained his complementary view of physics, he was told that “you said the same 20 years ago” by a collaborator (this story is referred either to Kalcker or to Heisenberg?).

 

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