With a bit more digging, I was able to find the information you were
asking about. Let me begin with a question:
"If a tree falls in the forest and nobody hears it, has it made a sound?"
This classic philosophical puzzler does a good job of linking together
some of the key issues that were at the heart of Niels Bohr's ideas
about the way the world works. There is an indelible link between an
event and an observer, and if we try too hard to distinguish the two
-- the event of the tree falling, and the observation of its crashing
to the ground -- then we wind up with contradictions within
Bohr, the eminent Danish physicist, was awarded something called the
Order of the Elephant in 1947 -- one of the highest honors that can be
bestowed on a Danish citizen. Ordinarily, the Order is awarded to
royalty, who emblazon it with their family coat of arms and their
family inscription. Bohr -- possessing neither a coat of arms or an
inscription -- designed his own. He chose the Yin-Yang symbol as the
coat of arms, and inscribed it "Contraria sunt complementa"
--opposites are complementary.
And therein hangs a tale.
Bohr and his colleagues, including Heisenberg, Einstein, and other
luminaries of 20th century physics -- grappled with the seeming
duality of physical quanta. Was light a wave or particle?
Heisenberg's uncertainty principle made matters even worse -- not only
do we not know if light is a wave or a particle, but we can't know
sure precisely where the wave/particle of light *is* or how fast it is
Bohr's approach to reconciling these contradictions is his philosophy
of complementarity, which served as a narrowly-focused approach to his
physics, as well as a broader approach (used by Bohr and others) to
viewing the larger issues of life. Complementarity is as much about
language and knowledge, as it is about physics, as it acknowledges the
imperfect nature of language for describing the physical world, but
recognizes it's the best tool we have just the same. As Bohr himself
"Washing dishes and language can in some respects be compared. We have
dirty dishwater and dirty towels and nevertheless finally succeed in
getting the plates and glasses clean. Likewise, we have unclear terms
and a logic limited in an unknown way in its field of application--
but nevertheless we succeed in using it to bring clearness to our
understanding of nature."
Rather than go off on my own description of Bohr's work (at profound
risk of mangling things greatly), I'll direct you to others who have
given the matters great thought and clear (as clear as one can, in
this muddled topic) explanation.
If you need additional information of anything presented here, just
let me know by posting a Request for Clarification, and I'll be glad
to assist you further.
A good, concise summary of Bohr's life and work can be found at this
site on Bohr posted by Danish Embassy:
I've excerpted some key passages on Complementarity:
During the 1920s it became clear that many phenomena in modern physics
could be viewed from two mutually conflicting viewpoints. For
instance, it turned out that light that had been acknowledged as a
wave propagation could also be regarded as particles, photons, and
this acknowledgment, which originated in Einstein's discoveries as
early as 1905, was supplemented by the acknowledgment that atomic
particles could, on the other hand, possess wave characteristics.
Generally, the conclusion was that waves can possess particle
characteristics and particles can possess wave characteristics.
This meant that a complete description required the use of two
mutually contradictory images and this Niels Bohr named
complementarity - the characteristics related to the two images are
complementary. He did this for the first time in a speech he held in
1927 which he referred to later saying among other things the
following: "It is of the greatest importance to realize that an
account of all experience - irrespective of how far the phenomena are
from the scope of classical physics - must be expressed by means of
classical concepts"... "This implied", continued Bohr, "the
impossibility of a sharp distinction between the behavior of atomic
objects and their interplay with the measuring instruments that serve
to define the conditions under which the phenomena occur". And:
"Experience gained under different experimental conditions cannot,
therefore, be combined in a single image, but must be regarded as
complementary in the sense that only together do the phenomena exhaust
the possibility of obtaining information on the objects".
...complementarity has become a permanent component of the conceptual
repertoire of modern physics, and Bohr also extended its use to other
branches of science, in particular psychology and biology, and he saw
this concept as an aid to obtaining greater mutual understanding
between cultures and between nations. Also the position of the
individual human being in society was in his opinion influenced by
complementarity, for instance when the two ideals of justice and mercy
were set up in opposition to each other. The Greek tragedians had
known and shown this....Again and again Bohr repeated: "Here we are
faced with complementary phenomena related to the human situation
which, in an unforgettable way, is expressed in ancient Chinese
philosophy which reminds us that in the great drama of life we are
both actors and audience".
...in 1947, he had received the Order of the Elephant, which is only
at many years' interval awarded to Danes who are not members of the
Royal family and thus he had received the highest honors that could be
obtained in Denmark. For the coat-of-arms which was to be placed among
coats-of-arms of other Knights of the Order of the Elephant in the
chapel at Frederiksborg Castle, Niels Bohr chose the Chinese symbol of
Yin and Yang, the two opposite elements that supplement each other,
and which together describe the whole world. As his device he chose
Contraria sunt complementa ... the opposites are complementary.
This site includes includes excerpts from many interviews and articles about Bohr:
and has this to say about Bohr's "AHA!" moment:
Your physical aha-experience?
"Contraria sunt complementa -- opposites are complementary."
In 1913, Bohr was told that the "wavelengths of a complete series of
spectral lines in the hydrogen spectrum can be expressed with the aid
of integers. This information, he [Bohr] said, left an indelible
impression on him."
A further discussion of Complementarity at this University of Virginia
site shows how Bohr dealt with the inherent contradiction of atomic
energy as both threat and opportunity:
Niels Bohr exercised this sort of moral imagination when he foresaw
the two sides of the atomic bomb. Bohr's coat of arms bore the
inscription "Contraria Sunt Complementa"(Holton, 1973). He had argued
that there were two, complementary ways of looking at light; depending
on how one set up an experiment, it behaved as a wave or as a
particle. It could not be reduced further--physicists would have to
accept light's complementary nature.
Similarly, he saw the atom bomb as both threat and opportunity: a
monstrous weapon that threatened mass-destruction and an opportunity
to make war--and even nation-states--obsolete... Bohr felt that the
development of atomic weapons meant that, "We are in a completely new
situation that cannot be resolved by war"... Bohr tried to communicate
these views in various ways to Roosevelt and Churchill, emphasizing
the need for international cooperation in dealing with this threat and
opportunity after the war--cooperation that would of necessity involve
the Soviets. Churchill would have none of it--he thought of atomic
weapons as bigger bombs, not qualitatively different weapons, and he
also thought that the U.S.-British monopoly on this new technology
could be preserved, at least for a time. Roosevelt was initially more
sympathetic to Bohr, but was persuaded by Churchill to adopt the Prime
Minister's view that this whole effort of Bohr's was subversive and
dangerous. What Bohr advocated was the kind of open sharing of
information that was characterisitic of science, but not of relations
between nations. Once everyone clearly understood the danger
represented by fission and fusion weapons, then there would have to be
And at this site devoted to symbols and numbers, there is as good a
chart as I've seen that integrates the traditional opposites of yin
and yang with some of the more contemporary contradictory notions that
are integral to modern physics:
At this University of Toronto site on Complementarity, there is some
additional perspective on the overlap between western physics, eastern
philosophy, contradiction and integration. I particularly like Bohr's
story about the blind man, at the end of the excerpts here:
A nice analogy is Figure-Ground studies such as the one shown to the
right [NOTE: visit the site to see the figure]. Looked at one way, it
is a drawing of a vase; looked at another way it is two faces.
We can switch back and forth between the two viewpoints. But we can
not see both at once. But the figure is both at once.
Similarly, we can think of an electron as a wave or we can think of an
electron as a particle, but we can not think of it as both at once.
But in some sense the electron is both at once. Being able to think of
these two viewpoints at once is in some sense being able to understand
In 1947 Bohr was awarded the Order of the Elephant from the Danish
government. For a proud Dane like Bohr, this was a very big deal, and
Bohr is the only person to be awarded it who was not royalty and/or a
famous general. As part of the award, the winner's family coat of arms
is carved into a sort of wall of fame. Bohr's family, though, did not
have a coat of arms, so Bohr got to design one himself. The figure to
the right is what he designed.
You will notice that he choose the ancient Chinese symbol for the Tao,
the "Yin-Yang Symbol," for the centerpiece. He did not do this
lightly. The inscription reads CONTRARI SUNT COMPLEMENTA or Opposites
Are Complements. Thus he chose to represent his Principle of
Complementarity as the centrepiece of his coat of arms.
...the first two of the following quotations are famous to Taoists,
while the last is not nearly as well-known:
"The ten thousand things carry yin and embrace yang.
They achieve harmony by combining these forces."
-- Lao Tsu, Tao Te Ching
"The Tao that can be told is not the true Tao."
-- Tao Te Ching
"The electron that can be told is not the true electron."
-- David Harrison
At the risk of pushing the illustration of Western physics by means of
Eastern ideas too far, you may wish to consider the following:
"[In 1961] I had occasion to discuss Bohr's ideas with the great
Japanese physicist [Yukawa], whose conception of the meson with its
complementary aspects of elementary particle and field of nuclear
force is one of the most striking illustrations of the fruitfulness of
the new way of looking at things that we owe to Neils Bohr. I asked
Yukawa whether the Japanese physicists had the same difficulty as
their Western colleagues in assimilating the idea of complementarity
... He answered `No, Bohr's argumentation has always appeared quite
evident to us; ... you see, we in Japan have not been corrupted by
Aristotle." -- Rosenfeld, Physics Today 16, (Oct 1963), pg. 47.
...The fact that the interaction cannot be reduced beyond a minimum
amount, the interchange of a single photon, is the heart of the
Heisenberg Uncertainty Principle. However, Bohr realised that it means
even more than this. At this level we can not divide the quantum of
energy into a contribution from the apparatus and a contribution from
the system: the process is inseparable. Thus it is holistic.
This in turn means that at this level it is not meaningful to talk
about the system at all separate from the apparatus observing it...An
example by Bohr may clarify:
We customarily think of the outside world as separate from ourselves,
and the boundary between the two is the surface of our skin. However,
think of a blind person who gets around with the assistance of a cane.
In time that person will probably treat the cane as part of his or her
body, and will think of the outside world as beginning just at the tip
of the cane. Now imagine the blind man's sense of touch extending out
of the tip of the cane and into the roadway itself. Imagine it
extending further, down the block, into the countryside, to the whole
world. There is no point where the blind man ends and the world
begins. Similarly, we can not say which is the system and which is us
Finally, here is an even broader discussion of complementarity as one
person applies it human experience in general:
"Contraria sunt complementa", that is, opposites are complementarity.
There is, however, a distinction between two sorts of truth:
trivialities, where the opposites are obviously absurd, and profound
truths, recognised by the fact that the opposite is also a profound
The complimentarity approach allows the possibility of accommodating
widely divergent human experiences in an underlying harmony, and
bringing to light newer prospects and ethical views for the
exploration and mitigation of human suffering. If we adopt the
complementary approach to problems of life we may discover to our
pleasant surprise that seemingly irreconcilable points of view need
not be contradictory. These, on deeper understanding may be found to
be mutually illuminating; the two apparently opposing views being
partial views of a ?totality? seen from different planes. It is well
known that the electron is a particle. It is equally well known that
the electron is also a wave. The wave and particle natures are
flagrantly opposite because a certain thing cannot at the same time be
a particle (that is, substance confined to a very small volume) and a
wave (that is a field spread out over a large space), but the electron
exhibits both, though not simultaneously as the two natures are
mutually exclusive. The wave-particle duality of electron presents a
most familiar example of complementarity of opposites in the domain of
physics. In fact, the Principle of Complementarity formulated by the
Danish physicist Niels Bohr, has emerged from quantum physics. There
is now a growing interest in exploring this Principle which links
astonishingly well Western Science and Eastern Wisdom.
The theme of the complementarity approach is that the apparently
paradoxical, contradictory accounts of events should not divert out
attention from the essential wholeness. We should attempt not to
reconcile the dichotomies but rather to realise the complementarity of
representation of events in two quite different languages. The
separateness of the descriptions only confirms the fact that in the
normal language that we human beings have developed for communicating
the results of our experiments, we can express the wholeness of nature
only through a complementary mode of description. Bohr?s favorite
aphorism was Schiller?s: "Nur die Fülle führt zur Klarheit" (Only
wholeness leads to clarity).
The language of complementarity is a language of respect for others?
views, which promises to be the language of the future. With the
miraculous achievements in the communication system of the world it
will be a lot easier and quicker for us to approach any part of the
globe, and understand and appreciate others? cultural and ethical
norms and ways of life as complementary modes of living. Such a
cross-cultural intercourse would provide us with a holistic picture of
Truth which in Schiller?s world ?lies in the abyss?. I have given
earlier only the first line of Schiller?s couplet reported to have
been one of the favourite sayings of Niels Bohr. After the line: "Only
wholeness leads to clarity, and Truth lies in the abyss" (Nur die
Fülle führt zur Klarheit, Und im Abgrund wohnt die Wahrheit).
The motto ?Contraria sunt complementa?inspires people following
different norms and ways of life to respect others? views even if
those are opposite to theirs?. Nobody need be victimised because he or
she holds the opposite view, as the same too may be a profound truth.
The same truth when perceived from different angels may give rise to
contradictory visions, but in reality all these visions are
complementary. Light is particulate, light is also wavy. The wave and
particle natures are totally opposite to each other but these are
complementary characteristics of the same photon.
I hope this information provides you some of the insight and
perspective you were looking for. As I mentioned above, if you would
like any additional information or explanation, just let me know, and
I'll be happy to assist you further.
And remember...what IS the sound of one hand clapping...?
search strategy -- Google searches on:
bohr (Contradicta OR Complementa)
"Contraria sunt complementa"