Source: Post to the Bohm Dialogue Mailing List

ON THE FAILURE OF COMMUNICATION BETWEEN BOHR AND EINSTEIN
D.Bohm and D.L.Schumacher
Birkbeck College, University of London, 1969

The most relevant point concerning the discussions between
Bohr and Einstein is that they did not communicate, in spite of serious
efforts to do so. It is even now difficult to face the simple fact of their
failure to communicate in a similar serious fashion, without prejudgement
concerning the truth of either position. Although in some superficial sense
Einstein may have admitted the consistency of Bohr’s arguments, it is clear
that he did not understand the novel implications of what Bohr was trying to
say. Likewise, it seems evident that for this reason Bohr did not fully
understand what made it impossible for Einstein to see the full meaning of
his novel contribution to scientific discourse. It would therefore not be
relevant to suppose, for example, that Bohr was clear and Einstein confused
(or vice versa) and that the confusion of one or the other of these men
brought about his failure to grasp the content of what the other man said.
Rather, the essential point in this situation was a mutual kind of
confusion in which each failed to see what was relevant to the other; thus
both contributed to the failure of communication which was not a property of
either person. The fact of a failure of communication in this situation was
much more significant than the content of what was to be communicated. It
led physics to split into mutually irrelevant fragmentary parts which tended
to develop fixed forms, rather than to engage in a genuine dialogue in which
each would change, permitting something new to emerge.

The first point of confusion in the argument was Einstein’s use of the word
disturbance” in connection with the quantum context. Einstein’s whole
argument depended on the statement that two distant atoms do not “interact”
(so by “observing the spin of one of them”, one knows that of the other,
without any “disturbance” at all). But the word “interaction” has meaning
only in a classical context, in which one atom exerts a “force” on another,
this effect being described in terms of Newton’s law applied to well-defined
orbits. On the other hand, if one looks at the many-body wave function , one
sees that to bring in words like “potential energy or interaction” to the
description is even from a purely formal point of view a rather
inappropriate metaphor. Formally, what we have in the quantum context is an
abstract “potential function” which enters the equation for a 3N dimensional
wave, in which description there is no place relevantly to discuss localized
entities (such as particles), or localized events (such as measurements), or
anything else to which the word “interaction” could meaningfully be applied.

Now what Bohr did was to say all this only implicitly, in terms of his
notion of the wholeness of the experimental conditions and the experimental
results. But Einstein could not see the relevance of Bohr’s arguments,
because in them, tacitly and informally, Bohr gave a central place to the
term “observing apparatus”. Of course, Bohr did not mean by this to accept
the positivist notion that measurements or observations are the most
essential aspects of physics. Nevertheless, informally he could not avoid
communicating to Einstein the implication that he regarded observation to
have a fundamental relevance in the content of physics.The key point was, of
course, that the terms “observing apparatus” and “object” were being tacitly
taken by Bohr to be informal forms of discourse, whereas Einstein supposed
that he was taken them to be the aspect of essential content of discourse.
However, by so heavily emphasizing these forms in his answers to Einstein,
Bohr was informally strengthening Einstein’s feeling that Bohr was taking
the observing instrument as part of the basic content of physics. Thus, Bohr
s response to Einstein was not relevant, in that it did not properly meet
Einstein’s tacit, informal and unstated objections and reservations, and
instead tended to strengthen these rather than answer them. Further, the
notion of wholeness became confused as it tended to become a content of
discourse referring to the impossibility of separating the “apparatus” from
the “object”. Rather, it is the form of the experimental conditions and the
content of the experimental outcome which are a whole in the sense of Bohr’s
quantum description.

In order to reach Einstein, Bohr should perhaps have begun immediately, and
without complicated arguments, to question the relevance of the term
interaction” in the quantum context. Since the word “interaction” has no
meaning in this context (even though physicists use it continually in their
work with quantum theory), it follows that the notion of “no interaction”
also has no meaning. Thus, Einstein’s conclusion that the properties of an
atom could be measured without “disturbing” that atom or some other atom
depended on the use of irrelevant descriptive language. Without this
conclusion, Einstein’s inference that there are separately existent
elements of reality” corresponding to each atom is untenable.”

To demonstrate the direction in which Einstein’s descriptive
language was taking him, Bohr could have called Einstein’s attention to the
kind of non-linear field theories that Einstein felt to be capable of
providing a universal mode of description. In such theories, there can be no
question of a separately existent particle. Rather the word “particle” is
only a convenient name for a pattern or structure of fields that pervade all
space, but has a relatively localized pulse-like region of high intensity
(or perhaps even singularity). In such a description, each “atom” actually
interpenetrates all the others (including those comprising any “measuring
apparatus”). So, at least on the face of the matter, it would appear that
there was no reason for Einstein not to consider the long range coordination
of responses implied in the experiment of Einstein, Podolsky and Rosen as a
whole (similar, in certain ways, to what Bohr suggested). Certainly, in the
“non-relativistic” context to which they had restricted themselves (e à
infinity), it would not appear at all strange to have a description of this
kind, because in this case all “parts” of the universe would have to be in
immediate and direct contact.

Of course, Einstein would have objected at this point by
saying that to him, the relevant context for field theory was also that for
other relativistic notions, especially that of a signal, with a finite limit
of velocity of propagation. Since the EPR experiment, regarded in this way,
would imply the instantaneous transfer of a certain communicable content
(“information”), Einstein would never have regarded such a point of view to
be worthy of serious consideration, not even for a moment.

In this connection it is essential to recognize that for
Einstein, the notion of “signal” was so basic that he was probably not aware
of how deeply it pervaded his thinking in its role as a universally relevant
form which is the background of all his discourse. It is rather like water,
of which fishes may be unaware. Therefore, Bohr’s principle task in this
situation would have been to call Einstein’s attention to his tacit
relevance judgements which made it impossible for him seriously to consider
other informal language forms, e.g. Bohr’s, as at least potentially
reasonable points of view which could usefully be explored.

In doing this, Bohr would have been able to indicate that
Einstein was using “signal” as a form of discourse, rather than as a part of
the basic content of physics. In this form there is implicit a distinction
between a “signal” and its “significance”. That is, Einstein was making a
separation of form and its content in his communication. Evidently, these
are an unanalysable whole, (e.g. it is the “significance” that justifies
calling a set of events a “signal” rather than “noise”). So, Einstein
himself was using a purely formal distinction of “signal” and “significance”
as basic to his terms of description in the context of physics. Bohr could
then have pointed out that if “signal” had been mistakenly regarded as part
of the basic content of physical description, then one could have been led
to a view which would also have made “significance” (or “meaning”) an
essential part of this content. This would have put the conscious observer
who thinks about the meaning of his observations into a very central role
indeed. Thus Einstein’s theory of relativity is just as open to such
misinterpretation as is Bohr’s, in which one could similarly regard the
distinction between observing apparatus and observed system to be part of
the basic content of physics.

In this way, Bohr could probably have made it clear to Einstein that every
theory tacitly assumes the relevance of certain formal distinctions as basic
to its terms of discourse. Assuming the relevance of these distinctions does
not commit us to the assumption that they are a necessary part of the
content of physics (or that they are of any “ontological” significance). In
this way, Einstein’s feeling that Bohr was making the whole universe depend
on the observer (or on his measuring instruments) could have been shown to
be unfounded. Einstein then could have seriously entertained the notions
that Bohr was putting forth for consideration.

But then, Einstein would almost certainly have been led to
question certain features of Bohr’s presentation. For Bohr tacitly suggested
that his informal forms of discussion of the quantum context should have
universal relevance. To be sure, he emphasized that physical theory must
develop in novel ways. But it was generally implied that these new
developments could be assimilated as extensions of the “quantum” mode of
description, in the sense that the latter would remain relevant in such
novel contexts. Specifically, the paper on field measurements by Bohr and
Rosenfeld indicated that under certain assumptions the “quantum” mode of
description can be extended to the context of field theory, so that in
principle one could go on to discuss relativistic theories in such terms.

It is not likely that Einstein would have been satisfied
with this view of the harmonizing of relativity and quantum theory. Firstly,
in the Bohr-Rosenfeld paper there appeared informal notions (such as
particles of effectively infinite charge and mass), which do not seem to be
relevant to the atomic constitution of matter as accepted by the authors.
Surely, it is significant here that as yet there is not even a consistent
formal theory of elementary particles that is “relativistic”. In view of the
persistent difficulty of producing such a theory over a period of forty
years or, one may reasonably wonder whether it is in fact possible to do
this at all. And without such a theory, Einstein (and probably a large
number of other physicists as well) would feel that the formal treatment of
measurability of field is too abstract to be relevant to the serious
situation of physics. To this once could add that, just as Bohr emphasizes,
the consistency of the whole mode of description depends critically on the
smallness of e2/(ch). This might tend to suggest that it is only when
“relativistic” considerations are unimportant that Bohr’s mode of
description can be considered relevant. And it need hardly be added in the
present context that Bohr’s mode of description was also his mode of
communication.

In addition to the more or less technical questions,
Einstein would almost certainly have criticized Bohr’s way of describing the
experimental context solely in terms of the language of classical physics
(with words like “position” and “momentum”). Einstein’s point of view
implied that ultimately one would cease to use words like “the position and
momentum of a particle” or “the value of a field quantity at a given point”
as basic terms for description of the experimental conditions and the
experimental results. Rather, in terms of non-linear field theory, one can
only talk about various aspects of the whole field. The words “momentum” and
“particle”, etc., and the phrase “field at a given point” can best be
regarded as abstractions, relevant in the general context of this whole,
just as words like “window” and “doorway” are abstractions relevant in the
context of a house. So, as we would not feel obliged to describe a house as
an interacting aggregate of rooms, windows, doorways, etc. each with its own
position and momentum, we would similarly not feel it necessary to discuss
cloud chamber photographs and Geiger counter clicks in terms of “paths of
particles”. Rather, we would say that these furnish indications that are
relevant to the condition of the whole field, so that descriptions like “the
value of a field quantity at a given point” would also have little or no
relevance.

Without necessarily adopting Einstein’s particular way of
approaching this question, one can say that he also had certain insights
which are relevant for physics. For implicitly at least, he was pointing out
that new kinds of theories implied a new informal language of description of
the experimental results that is in harmony with the formal language. On the
other hand, by adopting “classical” terms for the informal language of
physics, and an entirely different set of “quantum” terms for its formal
language, Bohr was introducing a certain further kind of disharmony into the
whole situation of the mode of description and communication in physics. In
this sense one can say implicitly at least, Bohr was subscribing to the
current usage in which the formal terms of the quantum theory, such as
“operator”, “commutator”, “Hilbert space”, etc. are sharply contrasted with
informal terms, such as “the curvature of a track”, “the click of a Geiger
counter”, etc.

When one first learns quantum theory, one is forcefully
struck by the almost fantastic difference between these two kinds of terms.
Of course, Bohr emphasized that they are related in the sense that the
“noncommutation” of the two operators” correspond to the mutual
exclusiveness of the experimental conditions needed to measure them. But
just emphasizing such a point in the language adopted merely continues his
sort of disjunction of the language forms with a relationship of
correspondence between them; this is not the same as wholeness, which in
this case would be a harmony of the formal with the informal.

Even if in conversation Bohr called attention to the wholeness of formal and
informal languages, the fact is that in his writing he gives the distinct
impression, tacitly and informally, of accepting the current disjunction of
these languages in physics to be natural and unavoidable. Surely Bohr would
be the first to admit that informal implications of what he writes after
careful and due deliberation are at least as significant as what he says
informally, and in many ways, even more so, otherwise he would not have
taken the trouble to revise his manuscripts many times. If there is a lack
of harmony between the implications of the form of the writings and the
content of what is expressed informally, this would suggest that Bohr did
not manage to reach clarity on this point. And this is very probably one of
the reasons why communication between Bohr and Einstein broke down.

One could say that Bohr first admit classical language as a basic informal
mode of description, and then in some way denies its universal relevance by
saying that the content of a description which makes relevant such
experimental conditions which would allow measuring the momentum is not
compatible with the content of a description which makes relevant those
experimental conditions which allow measuring the position. (For Bohr would
not speak of the experimental conditions as content of the description.)
This is a form of discourse that is not in complete harmony with Bohr’s
intention of wholeness. Such disharmony is similar to that which arises in
the use of words like “inseparable”. This word depends for its meaning in
first asserting the notion of “separation” and then denying it. However,
such a procedure still makes the notion of “separation” relevant. So to
assert “inseparable wholeness” is a form of confusion, because “wholeness”
implies the irrelevance of “separation”; putting the two words together in
this way implies their mutual relevance (e.g. one could relevantly imagine
the possibility of separating the whole into parts, but that as a matter of
contingent fact it is not actually possible to carry out such a separation.)
Similarly, Bohr appears to assert the concepts of classical dynamics and
then to deny their universal relevance, so that there must apparently be
such a denial depending on the contingent fact of the applicability of the
quantum algorithm. A harmonious description would require that one does not
begin with a language form implying the relevance of “disjunction into
dynamic components” and then try to deny the relevance of this disjunction
in the same context in which such relevance is necessarily implied in a
tacit and informal way.

It is here that Einstein’s insights are significant although
they are confused by much that is irrelevant. They indicated especially that
formal and informal terms of description need not be sharply contrasted and
implicitly contradictory.

If Bohr could have understood the deeper meanings in
Einstein’s views, at least to the extent outlined above, then he could also
have admitted the need to take seriously the possibility that the “quantum”
mode of description may have limited relevance. For reasons given here
already (as well as for other reasons) he could have seen that the quantum
mode of description may not be relevant in any context which makes relevant
the informal “relativity” language of Einstein, e.g. the context of the
“non-relativistic” descriptions. Similarly, Einstein could have seen that
the notion of a “signal” cannot be relevant in the “quantum” context,
because the “significance” of such a signal implies a pattern of order of
events, which can be present only in the limit where many “quanta” are
involved. It has been said, for example, that in a very sensitive condition,
the human eye can respond to two “quanta”. But clearly this response could
not have enough “significance” to make it relevant to call these “quanta” by
the name “signal”.

It is therefore extremely easy to regard “signal” as a form of disjunction
and to regard “wholeness” as a form of union, in the context of these
remarks. Rather “signal” stands for a verbal form which implies in this
context the analytic content of disjunction and union (in the formal
languages of dynamics, geometry, and logical inference), whereas form and
content are a whole, e.g. the form of the experimental conditions and
content of the experimental results, (which is not the object of relevant
discourse). It might be added that “individual effects” and “(quantum)
ensembles” are another expression of this whole. Of course, if these remarks
are interpreted in a way which assumes a distinction between form and
content, a certain kind of irrelevant discourse could accrue, as does, for
example, when there is an implicit separation between a “theory” and “what
it asserts”. The “separation of subject and object” is a separation of form
and content, and thus even a phrase like “expression of wholeness” could
lead to a continuation of such discourse.
Communication between Einstein and Bohr could have been opened up if each
had become aware of his implicit judgements of relevance, and if both had,
thus, gone out to explore new contexts in which neither relativity nor
quantum theory would be considered to be basically relevant. Such
communication would have been creative, rather than merely a means of
conveying each point of view to the other. In such a communication one is
not talking “about” quantum theory or “about” relativity. Such talking
“about” has a very limited relevance; when it is carried beyond a limited
context it can for example present essentially unresolvable “problems”, or
it can create opposing “sides” which cannot meet.

Similarly, just in writing these remarks it is not the main intention to
talk “about” Bohr’s view or “about” Einstein’s view as if these were objects
of discourse. (E.g. it is not the intention “to explain Bohr more clearly”.)
Rather, the “intention” is to say something essentially new (which is not
really an “intention” at all, since it implies “interpretation”, or a
separation of form and content.) This has so far not been said because all
those who discussed these matters tended to continue the breakdown of
communication between Bohr and Einstein.

So in the present work it is not an intention to “talk about our own views”,
or to “criticize others”. The main relevant point which can be summarized
briefly is that physicists have not been in full communication; if each of
those concerned can be aware of implicit judgements, his own and those of
others, then full communication can begin.

Copyright 1969 Sarah Bohm