The Argument for Complementarity
Bohr presented his entire argument in six paragraphs which comprise the first
section of his Como papers. He begins by calling attention to the "peculiar"
difficulties which result from the quantum postulate:
The quantum theory is characterized by the acknowledgment of a fundamental
limitation in the classical physical ideas when applied to atomic phenomena.
The situation thus created is of a peculiar nature, since our interpretation
of the experimental material rests essentially on the classical concepts.
Notwithstanding the difficulties which, hence, are involved in the formulation
of the quantum theory, it seems, as we shall see, that its essence may be
expressed in the so-called quantum postulate, which attributes to any atomic
process an essential discontinuity, or rather individuality, completely
foreign to the classical theories and symbolized by Planck's quantum of
action. The Philosophy of Niels Bohr Page 109
In this opening statement several important ideas are already noted. First,
Bohr is clearly looking for a "fundamental limitation" which would restrict
the application of "the classical physical ideas when applied to atomic
phenomena". Once he realized that wave-particle dualism was inescapable, he
concentrated not on over-throwing these paradoxical representations, but
rather on removing the paradox by limiting their use. Second, Bohr claims
these classical concepts MUST be retained because without them, it would be
impossible to provide what he calls an "interpretation of the experimental
This has deep philosophical ramifications that I am not sure Bohr was
completely aware of, otherwise he would have certainly stressed it more. In
essence, what Bohr is telling us in this paragraph is that this "peculiar
nature" is a fundamental way in which we conceive of our everyday classical
reality. Complementarity does not spring from classical mechanics, but rather
it is classical mechanics that spring from complementarity.
Bohr's reference to this discontinuity as an "individuality" is his way of
expressing that because it has been discovered that it is necessary to
describe interactions involving atomic systems with a theoretical formalism
which represents them as taking place discontinuously, within that formalism
it is impossible to define separately the classical state of each of the
systems that interact. A state for the interacting whole system as an
"individual" can be defined, but not for its separate components. Thus the
acceptance of the quantum postulate implies the impossibility of describing
the observations in a way which subdivides the whole phenomenon of interaction
into a process taking place between systems for which classical mechanical
states can be precisely defined throughout the interaction.
Here Bohr is identifying not only an individualistic atomic state, but
also our individualist state of awareness, as the observers are indeed included
in the framework of complementarity as essential components of the observation.
Complementarity shifts the burden of proof away from an "independent" reality
into a proof provided by unambiguous communication, in other words, our
agreements (see Pragmatism, Precession and the Metaphysics of Quality) become
all-important. This feature of "individuality" has major philosophical
ramifications that cannot be stressed enough, something Bohr, in my opinion,
failed to do time and again.
In the next paragraph, Bohr considers the consequences of this
"individuality" on the use of the classical concepts in the description of such
a discontinuous interaction:
This postulate implies a renunciation as regards the causal space-time
co-ordination of atomic processes. Indeed, our usual description of physical
phenomena is based on the idea that the phenomena may be observed without
disturbing them appreciably. This appears, for example, clearly in the theory
of relativity, which has been so fruitful for the elucidation of classical
theories. As emphasized by Einstein, every observation or measurement
ultimately rests on the coincidence of two independent events at the same
space-time point. Just these coincidences will not be affected by any
differences which the space-time co-ordination of different observers
otherwise may exhibit. Now, the quantum postulate implies that any observation
of atomic phenomena will involve an interaction with the agency of observation
not to be neglected. Accordingly, an independent reality in the ordinary
physical sense can neither be ascribed to the phenomena nor to the agencies of
observation. The Philosophy of Niels Bohr Page 110
Disturbing the Phenomena
In this early presentation of complementarity, Bohr is still confusing the
observation as "disturbing" the observed phenomena. The fact that an
observation requires a physical interaction between the observed object and
the observing system implies that it "disturbs" it. This is already the case
in classical mechanics. However, in that context, the presupposition that the
observed and the observing system change state continuously in the interaction
allows one to determine theoretically the nature and extent of the
disturbance. Thus classically it was possible on the basis of an observation
to define the state of the closed system isolated from interaction by
correcting for the disturbance produced by observing it. In Bohr's words, "the
interaction is controllable".
Unfortunately, Bohr's way of phrasing this tended to confuse his
audiences into thinking he was claiming that in fact the systems described by
quantum theory do exist in classical mechanical states while in an
observational interaction, but because the observation "disturbs" those states
it is impossible to determine empirically precisely what they are. In this
interpretation, Bohr's talk of a "limitation" on the classical descriptive
concepts would appear to be a limitation on knowledge of the classical
mechanical state. This is clearly NOT what Bohr intended, seen by the fact
that this is inconsistent with Bohr's primary conclusion, expressed in the last
There he concludes that we cannot describe an observation in a way that
treats the observed object and the observing instrument as having "an
independent reality in the ordinary physical sense." If the objects described
by quantum mechanics, such as waves and particles, did in fact have
"independent reality in the ordinary physical sense" it would be possible to
define classical mechanical states for them.
Since by the quantum theory this is not possible, if the theory provides a
complete description, these objects cannot be regarded as existing in classical
mechanical states whether or not it would be possible for us to determine these
states. If Bohr had believed that the observed object does indeed exist in a
well-defined mechanical state, though we cannot determine it because of the
disturbance, there would be no reason why we could not continue to regard the
observed object as having "independent reality in the ordinary physical sense".
But the fact that we can no longer regard the observed object as really
"existing" represents the most dramatic break with the classical framework.
The disturbance language Bohr uses at the beginning of the second
paragraph tends to lead the reader away from this important conclusion.
However, the second line of argument derived from the "individuality" of the
observational interaction does not lend itself to this misinterpretation. This
argument is more apparent in later essays and is evident in the following
sentences that were appended to the second paragraph only in later versions:
After all, the concept of observation is in so far arbitrary as it depends
upon which objects are included in the system to be observed. Ultimately,
every observation can, of course, be reduced to our sense perceptions. The
circumstance, however, that in interpreting observations use has always to be
made of theoretical notions entails that for every particular case it is a
question of convenience at which point the concept of observation involving
the quantum postulate with its inherent "irrationality" is brought in. The
Philosophy of Niels Bohr Page 112
This passage presents a way of regarding the observational interaction
not liable to be misunderstood involving the "disturbance" interpretation.
Bohr explicitly repudiated the "disturbance" way of speaking. He emphasized
even more the fact that the process of interaction could not be non arbitrarily
subdivided. Because of the individuality of the interaction described as an
observation, any distinction between observed object and agency of observation
is arbitrary. Since it is arbitrary in any interaction which we wish to
consider an object and an observation system, it is merely a question of
convenience at which point we wish to make the discontinuity of change of state
required by the quantum postulate.
Interpreting the Observation
Bohr's talk of "interpreting observations" refers to the need to describe the
observation as an interaction between physical systems. Hence, such an
"interpretation" must make use of "theoretical notions". Since the
discontinuity in change of state occurs in the description of the interaction
between observed object and the observing system, where ever we decide to
make that distinction in the whole interaction is the point at which the
discontinuity will enter the picture.
In no case did Bohr mean that "reason" was to be abandoned in describing
quantum processes, as has been frequently misunderstood. In the third
paragraph, Bohr turns to consider the consequence of this individuality of
quantum processes on the classical ideal of description: This situation has
far-reaching consequences. On the one hand, the definition of the state of a
physical system, as ordinarily understood, claims the elimination of all
external disturbances. But in this case, according to the quantum postulate,
any observation will be impossible, and above all, the concepts of space and
time will lose their immediate sense. On the other hand, if in order to make
an observation possible we permit certain interactions with suitable agencies
of measurement, not belonging to the system, an unambiguous definition of the
state of the system is naturally no longer possible, and there can be no
question of causality in the ordinary sense of the word. The Philosophy of
Niels Bohr Page 112
Here Bohr uses "definition" to refer to the classical goal of defining
the state of an isolated system from which all "external disturbances" and been
"eliminated". He points out that this goal, necessary for applying the
conservation principles to determine the causal development of the state of the
system is impossible to achieve simultaneously with giving the space and time
concepts empirical reference ("immediate sense") in an observation.
If an observation is made, the observed system is in an interaction and in the
quantum representation the individuality of this interaction means that any
division made between observing system and observed object is an arbitrary one
made within the description of that interaction. Thus it is impossible to
formulate an "unambiguous" definition of the system's classical mechanical
state. Without such a definition of the closed system's state, it is
impossible to apply the conservation principles (the claim of causality) to the
state of the isolated system to provide a causal description of the temporal
development of that state.
Modes of Space and Time
The modes of space and time are necessary to describe what is determined by
an observation, and it has also been empirically determined that conservation
principles DO apply to each atomic process. Hence, although the two classical
modes of description cannot be applied at the same time, neither can they be
abandoned. In the fourth paragraph, Bohr concludes that space-time
co-ordination and causal description are "complementary":
The very nature of quantum theory thus forces us to regard the
space-time co-ordination and the claim of causality, the union of which
characterizes the classical theories, as complementary but exclusive features,
of the description, symbolizing the idealization of observation and definition
respectively. Just as the relativity theory has taught us that the convenience
of distinguishing sharply between space and time rests solely on the smallness
of the velocities ordinarily met with compared to the velocity of light, we
learn from the quantum theory that the appropriateness of our usual space-time
descriptions depends entirely on the small value of the quantum of action
compared to the actions involved in ordinary sense perceptions. Indeed, in the
description of atomic phenomena, the quantum postulate presents us with the
task of developing a "complementarity" theory the consistency of which can only
be judged by weighing the possibilities of definition and observation. The
Philosophy of Niels Bohr Page 114
The complementary relationship holds between space-time co-ordination and
the claim of causality, both of which were combined in the classical
framework. Only later does Bohr speak of complementarity between wave and
particle "pictures". Bohr's initial concern is to explain why these two
modes of description could have been united classically and why they no
longer can be so combined when describing atomic systems. The reason he
gives is because the processes in the classical framework normally can be
described using "ordinary sense perceptions", which require interactions so
huge relative to that measured by Planck's quantum constant, that for all
practical purposes the discontinuity in the interaction could be ignored.
This reasoning is an instance of Bohr's correspondence principle at work. It
provides his reasoning for regarding the classical framework as a special
case of which complementarity is a generalization.
In the next paragraph, Bohr calls to mind both the phenomena that
requires wave description and those which require particle descriptions:
This situation would seem clearly to indicate the impossibility of a causal
space-time description of the light phenomena. On the one hand, in attempting
to trace the laws of the time-spatial propagation of light according to the
quantum postulate, we are confined to statistical considerations. On the other
hand, the fulfillment of the claim of causality for the individual light
processes, characterized by the quantum of action, entails a renunciation as
regards space-time description. Of course, there can be no question of a quite
independent application of the ideas of space-time and causality. The two
views of the nature of light are rather to be considered as different attempts
at an interpretation of the experimental evidence in which the limitation of
the classical concepts is expressed in complementary ways. The Philosophy
of Niels Bohr Page 115
Bohr argues that "we are confined to statistical considerations" when
attempting a space-time description of light propagation because the
quantum formalism does not permit determining the state of the observed
radiation in an observational interaction with any greater precision than
that expressed by Heisenberg's uncertainty principle. If an observation of
a phenomenon which is interpreted by representing radiation as a photon at
a precise point in space and time, the energy of that photon cannot be
defined, for it requires determining the frequency of the radiation and
that in turn requires a wave description which represents the radiation as
spread out through a region of space.
Wave and Particle "Pictures"
Thus Bohr concludes the sixth paragraph with the important claim that while
the use of wave and particle pictures to represent the quantum mechanical
object apart from the observational system is necessary for a theoretical
representation, these pictures refer to "abstractions":
In the discussions of these questions, it must be kept in mind that,
according to the view taken above, radiation in free space as well as
isolated material particles are abstractions, their properties on the
quantum theory being definable and observable only through their
interactions with other systems. Nevertheless, these abstractions are, as
we shall see, indispensable for a description of experience in connection
with our ordinary space-time view. The Philosophy of Niels Bohr Page 117
Using wave and particle "pictures" we can formulate theoretical
representations of the objects of quantum mechanical descriptions as
independent from an observational interaction, i.e., as "radiation in free
space" or as "isolated material particles. Bohr makes it clear that a
"description of experience", i.e., interpreting an observational event,
makes such a representation indispensable. And the apparent contradiction
of using wave representations in some situations and particle
representations in others is dispelled once it is understood they are both
abstractions or idealizations, and not the actual property of
independently existing entities.
This conclusion is the very core of the difference between how the
description of nature is understood within the classical framework and how
it is understood within complementarity. This is clearly one of the
reasons Bohr refuses to speculate in any manner as to where the
observation being focused on originated. This marks a break with classical
epistemology and our normal way of thinking, and seems to have deep
philosophical ramifications on what it is that we are capable of knowing
[The Quantum] postulate implies a renunciation as regards the causal
space-time co-ordination of atomic processes.
PDR (Doug Renselle)
I.e., there is no y = f(t) analytic function which can describe space-time
coordination of atomic processes.
This is what bothered Einstein about complementarity and triggered his famous
saying 'God doesn't play dice with the universe', or words to that effect.
The quantum postulate implies that observation of atomic phenomena will involve
an interaction with the agency of observation not to be neglected.
PDR (Doug Renselle)
The quantum postulate implies that any observation of atomic phenomena will
involve an interaction with the agency of observation not to be neglected.
Accordingly, an independent reality in the ordinary physical sense can neither
be ascribed to the phenomena nor to the agencies of observation.
Nor can there be an independent observer apart from the observed phenomenon.
Classically it was possible on the basis of an observation to define the state
of the closed system isolated from interaction by correcting for the
disturbance produced by observing it. In Bohr's words, "the interaction is
PDR (Doug Renselle)
PDR believes this hints at the concept of local context. PDR believes all
Quantonic interrelationships experience different levels of (statistical or
stochastic) stability which may be measured in terms of their latch duration.
The Quantonic interrelationships for any Quality Event may be ordered by
stability, and for quasi-classical observations measurement may converge
(adaptively) on selectable stable interrelationships. Imagine, for example,
the integral of selected nodes of the 'ket.'
I think part of the misunderstanding revolving around complementarity involves
the term "controllable interaction", by which Bohr seemed to mean that by
which we communicate unambiguously, and thereby turn into a local context that
our awareness can then deal with. Bohr's insistence on the need for using
classical concepts arose from this conviction that complementarity is
fundamental to how we perceive reality.
The very nature of quantum theory thus forces us to regard the space-time
co-ordination and the claim of causality, the union of which characterizes the
classical theories, as complementary but exclusive features, of the
description, symbolizing the idealization of observation and definition
PDR (Doug Renselle)
Given Stein's work and my comments above, I think Bohr is mistaken here.
Classically space and time were different concepts until Einstein's theories
of relativity united them. Now we know space-time is an identity, not a
complementary interrelationship. Causality is produce of analyticity,
determinism, and inductivism, all of which are well-refuted in any physical
realm (all seem perfectly acceptable in any pure conceptual realm of
mathematics -- which I see as a blissfully ignorant but pedagogic path of SOM
philosophy). See Pirsig, Stein, Popper, et al.
I am as yet unconvinced that Bohr was mistaken, yet at the same time I am not
able to offer a convincing reason why.
Just as the relativity theory has taught us that the convenience of
distinguishing sharply between space and time rests solely on the smallness of
the velocities ordinarily met with compared to the velocity of light, we learn
from the quantum theory that the appropriateness of our usual space-time
descriptions depends entirely on the small value of the quantum of action
compared to the actions involved in ordinary sense perceptions
PDR (Doug Renselle)
It is important to understand what Bohr is saying about the complementarity
twixt space-time and causality. Classically, as you noted, separate space and
time concepts were analytic and causal. In other words classical science
unified both concepts of time and analyticity, and, in addition, both concepts
space and analyticity. In Einsteinian relativity space-time became unified and
classical analyticity of its unification retained. In quantum science
space-time has its own Steinian complement: nonspace-nontime, or what Stein
calls nonspace, and I call nonactuality. We can represent these: Reality =
quanton(nonactuality,actuality), or reality = quanton(nonspace,space). In
quantum reality, nonspace is analytic and space is stochastic because of
quantum reality's quantized and random nature of measurement events which
allows nonspace to create, change, and discreate space.
This provides Bohr's reasoning for regarding the classical framework as a
special case of which complementarity is a generalization. I tend to relate
this to Stein's work relating space and time as special conditions of non
space and imaginary time.
Of course, there can be no question of a quite independent application of the
ideas of space-time and causality.
PDR (Doug Renselle)
Absolutely! Stein's ontology approaches this idea. Pirsig's MoQ is a new
philosophy which parents the new science.
And that independent application of ideas must be accomplished through
unambiguous communication of these ideas.
In the discussions of these questions, it must be kept in mind that, according
to the view taken above, radiation in free space as well as isolated material
particles are abstractions, their properties on the quantum theory being
definable and observable only through their interactions with other systems.
Nevertheless, these abstractions are, as we shall see, indispensable for a
description of experience in connection with our ordinary space-time view.
PDR (Doug Renselle)
In the new ontology, my conjecture is flux will be our one, general
abstraction, and we will say Static Patterns of Value (both
particles/substance and subjective phenomena) represent latched flux
abstraction and all else represent unlatched flux abstraction. Flux-latched
and flux-unlatched metaphors are something like this fluxL: SQ, mixed state,
actuality, space, etc. And fluxU: DQ, pure state, nonactuality, nonspace, etc.
It is clear to me that both Bohr and Pirsig believe the subject and object
dichotomy to be composed of only concepts, abstractions. Pirsig said that the
intellect level was just such an abstraction and it appears that Bohr would
agree with him on that count.
Complementarity, as Bohr understood it, was much more than only a quantum
tool. Yet because he didn't really understand the philosophical significance
of what that meant, due in part to his lack of a philosophical education, he
discovered his framework of complementarity was too vague to be grasped, and
instead of expanding his concepts of complementarity, he found himself
embroiled in a life long battle to defend it.
This ends Part 2, The Argument for Complementarity.
The final paragraph in the first section the Como papers marks a transition to
the remainder of the paper in which Bohr turns his attention to showing how
the uncertainty relations express the complementary aspects of the
description. This will be explored further in part 4 of this review. But
first, Part 3 contains Comments on Complementarity. The reader is free to skip
directly to Part 4 now, or continue sequentially with this review. And thank
you for reading!
The Framework of Complementarity
Part 1 - Overview Early Years Bohr Formulates Complementarity
Part 2 - Argument for Complementarity
Part 3 - Comments on Complementarity
Part 4 - Complementarity and the Uncertainty Principle
Part 5 - Refinement of Complementarity
Part 6 - Extension of Complementarity
Part 7 - The Nature of Empirical Knowledge
Part 8 - Complementarity and the Metaphysics of Quality