A brief history of the evolution of the
“complementarity” meme in quantum physics
Christopher B. Germann (2019)
It was a pivotal turning point for physics when Nils Bohr first introduced his formulation of
the idea of complementarity to his numerous colleagues. This historical event took place at the
International Congress of Physics in September 1927 in Como, Italy and the world’s most em-
inent physicists were in the audience: Max Born, Enrico Fermi, John von Neumann, Wolfgang
Pauli, Max Planck, Werner Heisenberg, Eugene Wigner, Louis de Broglie, to name just a few.
However, Albert Einstein was noticeably absent for some unbeknown reason (Holton, 1970).
The idea of complementarity fundamentally transformed physics. One of the crucial points
Bohr emphasised concerned the impossibility of any sharp separation between the behaviour
of atomic objects and the interaction with the measuring instruments which serve to define the
conditions under which the phenomena appear” (Bohr, 1961).
In a theme issue of the journal DIALECTICA edited by Wolfgang Pauli and published in 1948
compiles various seminal papers on complementarity by eminent physicists. Bohr also contrib-
uted an article to this special issue entitled “On the notions of causality and complementarity
(Bohr, 1948) in which he discusses the dialectic complementarity mode of description and the
impossibility to objectively separate between behaviour of the atomic objects and their inter-
action with the measuring instruments defining the conditions under which the phenomena
(Bohr, 1948, p.312).
Interestingly, Bohr was a cousin of the famous Danish psychologist Edgar Rubin who is famous
for his eponymous Rubin’s Vase (Rubin, 1915), see Figure 3. This ambiguous visual stimulus
is today still widely used in research on bistable perception in psychology and neuroscience
(e.g., Hasson, Hendler, Bashat, & Malach, 2001; Qiu et al., 2009; Wang et al., 2017). Interest-
ingly from a history of science point of view, it was Rubin who introduced Bohr to the concept
of complementarity. Both were members of the club “Ekliptika” (see Figure 4). Rubin in turn
adopted the idea from the writings of the late William James who wrote about complementarity
in Chapter 8 in his timeless classic “Principles of Psychology” (James, 1890). While Rubin
focused on perceptual complementarity, Bohr was primarily concerned with epistemological
complementarity (Pind, 2014) and much of his later writings were concerned with this topic.
Hence, from this historical vantage point, the quantum cognition paradigm is bringing the
meme of complementarity (which originated in psychology and spread to change the funda-
mentals of physics) back to its roots.
Figure 1. Rubin’s Vase: A bistable percept as a visual example of complementarity-coupling
between foreground and background.
In an interview
with Thomas Kuhn
which took place in 1962, Bohr stated:
I was a close friend of Rubin, and, therefore, I read actually the work of William
James. William James is really wonderful in the way that he makes it clearI think I read the
book, or a paragraph, called . No, what is that called?It is called ‘‘The Stream of
Thoughts,’’ where he in a most clear manner shows that it is quite impossible to analyse things
in terms ofI don’t know what one calls them, not atoms. I mean simply, if you have some
things…they are so connected that if you try to separate them from each other, it just has noth-
ing to do with the actual situation. I think that we shall really go into these things, and I know
something about William James. That is coming first up now. And that was because I spoke to
people about other things, and then Rubin advised me to read something of William James,
and I thought he was most wonderful.”
The significance of complementarity beyond the domain of physics has been discussed in
greater detail by Atmanspacher, Römer, & Walach (2002). The complementarity principle is
closely related to the concepts of entanglement, superposition, noncommutativity, and the stip-
ulated collapse of the wave-function. In fact, “quantum noncommutativity can be regarded as
a mathematical expression of the complementarity principle(Plotnitsky, 2016).
The full transcript of the interview is available on the homepage of the American Institute of Physics under the
following URL: https://www.aip.org/history-programs/niels-bohr-library/oral-histories/4517-5
Interestingly, Thomas Kuhn made use of ambiguous visual stimuli in his own work to demonstrate the percep-
tual change that accompanies a paradigm-shift. He used the “duck-rabbit” (a bistable figure created by the psy-
chophysicist Joseph Jastrow and popularised by Ludwig Wittgenstein), as a visual metaphor to illustrate that a
paradigm-shift can cause the cogniser to perceive the same information in a completely different way (see Ap-
pendix A7 for an example and a discussion). The complementarity principle was thus utilised in the context of
the perception of seemingly incompatible scientific paradigms. That is, it illustrates the Kuhnian concept of in-
commensurability which is of great relevance for the discussion of the perceived dichotomy between mind and
matter. Moreover, the inability to entertain multiple viewpoints simultaneously is of great pertinence for discus-
sion of interdisciplinarity, e.g., psychology and physics (mind/matter) can be regarded as complementary.
Figure 2. Photograph of Niels Bohr and Edgar Rubin as members of the club “Ekliptika” (Royal
Library of Denmark).
From left to right: Harald Bohr, Poul Nørlund, Edgar Rubin, Niels Bohr and Niels-Erik Nør-
lund (Royal Library, Copenhagen
When Bohr received the prestigious Danish Order of the Elephant(a distinction normally
reserved for royalty) he emphasised the importance of the complementarity principle. Bohr
choose to wear the ancient Chinese Yin & Yang symbol on his coat of arms together with
the Latin slogan “Contraria sunt complementa” (opposites are complementary), see Figure 5.
The resemblance between the Yin and Yang symbol and the ambiguous figures studied by
Rubin is remarkable. Moreover, various interdisciplinary scholars maintain that nonduality be-
tween mind and matter (psyche vs. physis, percipient vs. perceived, observer vs. observed,
inner vs. outer, etc. pp.) is a fundamental pillar of Advaita Vedānta, Mahayana/Madhyamaka
Buddhism, and Neo-Platonism (e.g., Plotinus), inter alia.
Associated URL of the file in the digital Royal Library of Denmark: http://www.kb.dk/im-
Figure 3. Escutcheon worn by Niels Bohr during the award of the “Order of the Elephant”.
In 1947 Bohr was awarded with the “Order of the Elephant” (Elefantordenen), Demarks
highest-ranked accolade. Bohr chose a “coat of arms” which was embroidered with the Bud-
dhistic Yin & Yang symbol on order to emphasise the centrality of nonduality and comple-
in his work on quantum physics. Chinese Buddhism is an offshoot of early Hindu-
ism, the womb of the ancient nondual philosophical school of Advaita Vedānta
which is
based on a highly sophisticated and extensive logic system (Gabbay & Guenthner, 2014;
Nicholson, 2007).
Interestingly from both a visual science and physics point of view, when light interacts with the eye the wave-
particle duality resolves, that is, observation collapses the superpositional state into a determinate eigenvalue. In
this context, Einstein wrote the following on the complementarity of physical descriptions: “It seems as though
we must use sometimes the one theory and sometimes the other, while at times we may use either. We are faced
with a new kind of difficulty. We have two contradictory pictures of reality; separately neither of them fully ex-
plains the phenomena of light, but together they do.” (Einstein & Infeld, 1938, p. 278)
According to Advaita Vedānta, consciousness and material reality do not exist in separation. This schism, is an
illusion or Māyā (Bhattacharji, 1970; Dabee, 2017). That is, the subject/object divide is also part of Māyā or
mere appearance”. Beyond the perceived duality is what quantum physicist John Hagelin calls “the unified
field” or “string field”pure abstract self-awareness which forms the nondual basis for all of existence, material
and immaterial (Hagelin & Hagelin, 1981).
Nils Bohr writes:
Altogether, the approach towards the problem of explanation that is embodied in the notion
of complementarity suggests itself in our position as conscious beings and recalls forcefully
the teaching of ancient thinkers that, in the search for a harmonious attitude towards life, it
must never be forgotten that we ourselves are both actors and spectators in the drama of
(Bohr, 1950, p.54).
Applied to the dichotomy between science and mysticism described by William James (see
introduction), the complementarity principle entails that that the seemingly polar oppiste “sci-
ence versus mysticismare not mutually exclusive but both necessary to complete the circle
of human understanding (Hofmann, 1994).
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