Niels Bohr's overriding concerning in his writings from 1935 to his
death in 1962 was to bring the lessons of complementarity to fields other
than atomic physics. But Bohr's success in describing the atomic system
worked against him, in a way, and his point that complementarity teaches
a lesson about the use of concepts for describing all phenomena
was largely ignored.
Since all the sciences aspire to unambiguous communication of phenomena
based on observation, such a discovery as complementarity affects all the
sciences. In the classical framework, it was considered to be a criterion
of objective description that the properties ascribed to the object were
possessed by it quite apart from the observational interaction on which
the description was based. According to complementarity though, the individuality
of the interaction means the properties of the phenomenal object
exist only in relation to the specific agencies of observation that produced
the phenomena. The description is unambiguous (i.e., "objective")
only when it includes a full description of the agencies of observation
which produced the phenomenon.
Classically, one could make a determination of the state of a physically
isolated system the criterion of objective description only if such a description
could be regarded as pictures of the properties of an independent reality
existing apart from the observation. Such an ideal is only possible where
either the causal effect of the observation could be "controlled" or could
be considered negligible. By abandoning the classical point of view, complementarity
used two distinctive modes of observation, each pursuing a goal necessary
for the employment of the other.
Complementarity in Anthropology
Although the role of an anthropologist doing field research on a primitive
tribe is not how Bohr attempted to portray complementarity, it illustrates
his ideas very well. In the case of an anthropologist from an "advanced"
culture observing the behavior of a hitherto isolated tribe, his presence
may well affect the tribe in ways which are neither negligible nor can
be controlled. And if he describes just what he observes, his description
is ambiguous because another anthropologist coming under different circumstances
may well alter the tribe's behavior in a different way, which again will
be neither negligible nor controllable. Complementarity tells us that neither
description is a description of the "real" tribe as it exists apart from
these observations.
What both describe is the phenomenal tribe and its behavior patterns
under different specific observational circumstances. In order to apply
both descriptions to the tribe, the anthropologist must develop causal
principles to enable a determination of how such an outside influence affects
the tribe's behavior, and then by applying these causal principles, it
can be predicted just how the presence of the anthropologists effected
the behavior of the tribe as it was prior to their arrival.
The lesson of complementarity is that a well defined representation
of the tribe is not a picture of an independently existing tribe, but rather
an abstraction necessary for the unambiguous use of descriptions of that
tribe.
Complementarity in Psychology
Bohr never put his ideas in writing and his only account of them is
far from clear. In his university days his interest was aroused by the
problem of discussing human consciousness processes, particularly
when it touched upon freedom of the will. In his last interview, Bohr said:
At that time I really thought to write something about philosophy,
and that was about this analogy with multivalued functions. I felt that
the various problems in psychology - which were called the big philosophical
problems, of the free will and such things - that one could really reduce
them when one considered how one really went about them, and that was done
on the analogy to multivalued functions. [1]
His basic scheme seemed to be like this. When attempting to describe one's
own consciousness, i.e., the consciousness one experiences directly,
one must make a distinction between that consciousness as an object of
description and the subject consciousness that describes it. This is essentially
the same as Kant's distinction between empirical and transcendental egos.
All attempts to describe the experiencing subject in its experiencing activity
necessarily elude the grasp of the descriptive concepts. As soon as one
begins to describe that experience, it becomes the object of experience,
thereby shifting the distinction between experiencing subject and experienced
object.
The theory of complex functions is one area of mathematics where multivalued
functions arise. Each complex number can be represented unambiguously on
a two-dimensional plane, but the multivalued functions have potentially
an infinite number of values, each a complex number and each a complex
variable value. G.F.B. Riemann proposed mapping such functions as different
"branches" of a single curve, each on a different plane, and each one representing
the curve of a single value function. In this case, as long as the curve
is followed in the same plane, the function can be mapped continuously
without ambiguity arising in the point number relationship.
However, for each function the origin point is a "singular point" resulting
in the consequence that when a closed curve is traced around the origin,
such that it returns to the same value of the independent variable, the
value of the function now differs by a constant factor. For this reason,
each time a singular point is orbited, the value of the function must be
represented in another plane. Turning this into an analogy of the description
of consciousness, Bohr writes:
The analogy is this, that you say that the idea of yourself
is a singular in our consciousness. Then you find - now it is really a
formal way - that if you bring this idea (i.e., the idea of the
experiencing subject) in, then you leave a definite level of objectivity
or subjectivity. For instance, when you have to do with the logarithm,
then you can go around; you can change it by 2(pi) when you go one time
around a singular point. But then you can surely, in order to have it properly
and be able to draw conclusions from it, will have to go all the way back
again in order to be sure that the point is what you started on. Now I'm
saying it a little badly, but I will go on. That is then the general scheme,
and I felt so strongly that it was illuminating for the question of free
will, because if you go round, you speak about something else, unless you
really go back again [the way you came]. That was the general scheme you
see. [2]
The details are lacking, but Bohr seems to have intended to correlate the
relationship between the independent complex variable and the different
values of a multivalued function with a descriptive term and the different
references the term could have. Riemann had proposed eliminating this mathematical
ambiguity of a point on a single plane representing many possible values
of a complex function by turning the multivalued function into a series
of single valued functions represented on different planes. So Bohr proposed
that the different references of a term refer to different "planes of objectivity",
each analogized to a different meaning imparted to the "object" of the
experience as a consequence of different ways of drawing the distinction
between experiencing subject and experienced object. The chance for ambiguity
arises if we fail to note that when we trace a closed circle around a singular
point of the origin, we must move to a different plane.
Bohr intended to say that the attempt to describe the self is like drawing
a closed curve around a singular point. The concept of self is then analogized
to a multivalued function, which may take on different meanings. Bohr felt
that in attempting to describe the subject self (transcendental ego), we
must "map" that meaning onto one plane of objectivity, but in doing so
we make that subject self the object and thus effectively shift the subject/object
distinction. When we return to the subject self, it is not the same self
as was the subject before we began to describe it. We must recognize that
the reference of the term "self" has moved to another plane of objectivity.
Any description unheedful of this fact runs the risk of having its terms
slip from one plane to another, thereby producing ambiguity.
Bohr explored this line of thought well before he conceived of complementarity,
yet his early approach falls perfectly in line with his epistemological
lesson of complementarity, and he concluded his Como paper like this:
I hope, however, that the idea of complementarity is suited
to characterize the situation, which bears a deep-going analogy to the
general difficulty in the formation of human ideas, inherent in the distinction
between subject and object. [3]
And in the first paper he wrote after Como, he begins by referring
to the last sentence of his Como paper and then continues with probably
his most revealing description of complementarity as a general epistemological
lesson:
...For describing our mental activity, we require, on one hand,
an objectively given content to be placed in opposition to a perceiving
subject, while, on the other hand, as is already implied in such an assertion,
no sharp separation between subject and object can be maintained, since
the perceiving subject also belongs to our mental content. From these circumstances
follows not only the relative meaning of every concept, or rather of every
word, the meaning depending upon our arbitrary choice of viewpoint, but
also that we must, in general, be prepared to accept the fact that a complete
elucidation of one and the same object may require diverse points of view
which defy a unique description...The necessity of taking recourse to a
complementary, or reciprocal, mode of description is perhaps most familiar
to us from psychological problems. [4]
Bohr draws an analogy between "the unity of our consciousness" and
the "physical consequences of the quantum of action" which makes for the
individuality of the atomic system. Using the term "emotion" to refer to
the immediate subjective feeling of freedom, and "volition" to refer to
that which is objectively described in the act of willing, he points to
the "suggestive analogy" between these concepts as employed in the two
different modes of describing the act of willing in psychology, and the
two modes necessary for describing an object in physics. Just as the incautious
use of concepts as classically understood causes a misunderstanding of
the problem of wave-particle dualism, so too, the "problem of free will"
is created by assuming that "one and the same" object is being described.
Bohr argued that this use of complementary terms for describing consciousness
is a feature of language where different contexts imply different ways
of drawing the distinction between subject and object. He writes:
Actually, ordinary language, by its use of such words as thoughts
and sentiments, admits [a] typical complementary relationship between conscious
experiences implying a different placing of the section line between the
observing subject and the object on which attention is focused. ...In fact,
the varying separation line between subject and object, characteristic
of different conscious experiences is the clue to the consistent logical
use of such contrasting notions as will, conscience and aspirations, each
referring to equally important aspects of the human personality. [5]
This "clue" should make it clear that Bohr regarded it as necessary to
combine the mode of description of introspective, rational psychology with
the mode of naturalistic, empirical psychology in order to present an unambiguous
description of all "equally important aspects of human personality". For
further reading, see The
Contributions of Humberto Maturana to the Sciences of Complexity and Psychology
by Alfredo B. Ruiz.
Bohr's references to such terms as "unity of consciousness" and "change
of tinge" suggests that his thoughts were influenced by the writings of
William James. Though the date of Bohr's reading of William James is disputed,
a familiarity with James' Principles of Psychology is apparent as
early as 1929. Bohr was anxious that his comments about the concept of
free will in describing consciousness were not understood as asserting
a dualistic view of a causal influence between a non material "mind" and
the physiological organism. For Bohr, complementarity was relevant only
in the descriptions of physical interactions and not presumed psycho-physical
interactions of a dualistic metaphysics impossible to describe physically.
He appropriated the term "mysticism" in referring to such dualistic metaphysical
doctrines. Bohr wrote:
...the linkage of the atomic phenomena and their observations,
elucidated by the quantum theory compel[s] us to exercise a caution in
the use of our means of expression similar to that necessary in psychological
problems where we continually come upon the difficulty of demarcating the
objective content. Hoping that I do not expose myself to the misunderstanding
that it is my intention to introduce a mysticism which is incompatible
with the spirit of natural science. I may perhaps in this connection remind
you of the peculiar parallelism between the renewed discussion of the principle
of causality and the discussion of a free will which has persisted from
earliest times. Just as freedom of the will is an experiential category
of our psychic life, causality may be considered as a mode of perception
by which we reduce our sense perceptions to order. At the same time, however,
we are concerned with idealizations whose natural limitations are open
to investigation and which depend upon one another in the sense that the
feeling of volition and the demand for causality are equally indispensable
elements in the relation between subject and object which forms the core
of the problem of knowledge. [6]
Bohr did not endorse the view of some physicists that the advent of indeterminacy
at the quantum level destroys the causal chain on which the arguments for
a bio-physical determinism rests. He constantly emphasized the indispensability
of a category of causality for the ordering of our psychic life, which
the insistence on absolute indeterminism would turn into chaos. Several
points in this application of complementarity to psychology are hallmarks
of complementarity analysis of empirical knowledge in general.
First, what has been understood as a problem of reality, are electrons
"really" particles or waves, is understood as a problem in the use of concepts
for describing different aspects of experience.
Second, two modes of description are needed. To make a description objective,
i.e.,
to describe the object unambiguously, the object is described as interaction
with the subject, but to make this unambiguous, a second mode of description
must be combined with the first, this one describing the object as isolated
from observing interaction. In describing these two modes, the descriptive
terms must be understood as abstractions and not pictures
of an independent reality.
Third, unambiguous descriptions must distinguish between the observing
agency and the observed object. This distinction may be drawn at any point,
making it possible to define the phenomena as a different description on
a different plane of objectivity. To avoid any ambiguity, the description
of each phenomenal object must specify how the distinction between observed
object and agency of observation has been drawn. Failing to do this renders
the observation ambiguous due to the implicit but illicit shift of the
subject/object distinction.
Fourth, a failure to be sensitive to such ambiguities will give rise
to the appearance of genuine metaphysical problems about the nature of
reality, which disappear once the complementaristic analysis is employed.
Problems such as particle/wave dualism are not metaphysical conflicts about
the nature of reality, but rather these problems are confusions created
by failure to realize that such different descriptions refer not to the
same object, but to complementary phenomena which only together provide
an unambiguous description of reality.
Fifth, the expansion of our understanding of reality made possible by
the framework of complementarity occurs not through the invention of newer,
more sophisticated concepts for describing experience, but rather through
the understanding the conditions required for unambiguous employment of
descriptive concepts.
Complementarity in Biology
Bohr's father was deeply involved in the dispute between mechanism and
vitalism in biological descriptions, a burning issue in the late nineteenth
century. Bohr considered his own attempt to resolve this dispute to be
in some way a repayment of the intellectual gifts from his father, and
so he derived great satisfaction over this particular use of complementarity.
Of all his discussions of complementarity outside of atomic physics, the
application to biology was the most recurrent and the only one he worked
out in any detail.
Bohr was anxious to avoid supporting the version of vitalism which argued
that organic systems possess a "vital stuff", some sort of nonphysical
entity which inorganic objects do not possess. He warned sternly against
any metaphysical defense for finalistic descriptions in biology,
maintaining that organic objects are no more than complex physical systems.
...this view, often known as vitalism, scarcely finds it proper
expression in the old supposition that a peculiar vital force, quite unknown
in physics, governs all organic life. I think we all agree with Newton
that the real basis of science is the conviction that Nature under the
same conditions will always exhibit the same regularities. Therefore, were
we able to push the analysis of the mechanism of living organisms as far
as that of atomic phenomenon, we should scarcely expect to find any features
differing from the properties of inorganic matter. [7]
Bohr pointed out that the progress of atomic physics revealed "the unsuspected
discovery of an essential limitation of the mechanical description of natural
phenomena". The limitation here is not that of the uncertainty principle,
but rather that imposed by the need to accept the quantum postulate in
order to describe the atomic system. Bohr seemed to regard the atomic property
of stability, which is destroyed by observing the system, as analogous
to the organism's property of "life", which is destroyed by observations
necessary for a mechanical description of its internal processes.
On one hand, a description of an organ within an organism is possible,
but this requires that the organism be described as an isolated system.
However, such isolation precludes describing it as "living", for that concept
refers to the organism's interaction with its surroundings. On the other
hand, a description of a living organism is possible by describing the
interactions of the organism with its environment, including the observing
system. Since the observing system necessary for observation must now fall
on the object side of the observer/observed distinction, the object
described in the vitalistic mode of description is a different object
from the one describing the mechanical mode. Since the physical conditions
necessary for the two modes are exclusive, they cannot be simultaneously
employed, but they both must be used for a complete description
of a living organism.
Quantum effects do play a role in biochemical processes at the molecular
level, but this was not the basis of Bohr's application of complementarity
to biological descriptions. The feature of "individuality" at the inorganic
atomic level parallels that in biological systems as life at the
organic level. Bohr writes:
...it must be stressed that an account, exhaustive in the sense
of quantum physics, of all the continually exchanged atoms in the organism
not
only is infeasible but would obviously require observational conditions
incompatible with the display of life. However, the lesson with respect
to the role which the tools of observation play in defining the elementary
physical concepts gives a clue to the logical applications of notions like
purposiveness foreign to physics, but lending themselves so readily to
the description of organic phenomena. Indeed, on this background it is
evident that the attitudes termed mechanistic and finalistic do not present
contradictory views on biological problems, but rather stress the mutually
exhaustive observational conditions equally indispensable in our search
for an ever richer description of life. [8]
Bohr did not hold that a mechanistic description of the interaction between
the organism and its surrounding environment was impossible. Quite the
contrary, such an account is not only possible, it is necessary
for a complete description. His point was that in order to describe such
interactions unambiguously, the state of the interaction must be defined
in isolation. Attempts to do this arbitrarily cuts off the organism
from the systems necessary to support life, destroying the physical conditions
necessary for the display of the vital phenomena. And since the observing
system and the observed organism do not form an indivisible whole, as they
do in quantum interactions, it is possible to take into account the effects
of the observational interactions. He writes:
The basis for the complementary mode of description in biology
is not connected with the problems of controlling the interaction between
object and the measuring tool, already taken into account in the chemical
kinetics, but with the practically inexhaustible complexity of the organism.
[9]
What cannot be done, because of the "practically inexhaustible complexity
of the organism", is to define its state apart from its living environment.
Bohr saw progress in biology advancing on two distinct complementary fronts.
One front is the level of biochemical descriptions of the physical mechanisms
responsible for the various phenomena manifested at the sub-cellular level;
the other on the level of the organism as a whole and its interacting role
within larger systems essential to maintaining the organism's life.
