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On
Scientific Revolutions
Heisenberg considers the development of modern
quantum theory to be one of the two great scientific
revolutions of twentieth century physics; the other in
his view is relativity theory.
Few would disagree. The complete title of his
1958 book is Physics
and Philosophy: The Revolution in Modern Science.
But by the 1960's the term "revolution" as
used in connection with the development of science had
become what Heisenberg calls a "vogue word"
due to some similarities between scientific
revolutions and social revolutions.
Possibly the vogue status of the term is due to
the popular monograph,
Structure of Scientific Revolutions, written by
Thomas Kuhn in the United States in 1962, but
Heisenberg never references Kuhn, and their views
are not the same.
Heisenberg discusses his idea of revolution in
science in a lecture delivered to the Association of
German Scientists in Munich in 1969, which was
published in English in 1974 as "Changes of
Thought Pattern in the Progress of Science" in
his Across the
Frontiers.
Heisenberg recognizes the operation of
sociological forces in the scientific professions,
but his views are different from those of Kuhn.
Heisenberg defines a "revolution" in
science as a change in thought pattern, which is to
say a semantical change.
He states that a change in thought pattern
becomes apparent, when words acquire meanings that are
different from those they had formerly, and when new
questions are asked.
He does not reference his semantical thesis of
closed-off theories in this context, although the
episodes in the history of post-Newtonian physics that
he cites as examples of scientific revolutions are the
same as those that he also says resulted in new
closed-off theories in the history of physics.
And the semantical change that occurs in the
transition to a new axiomatic theory and the closing
off of the old one, is the change involved in the
transition to a new thought pattern.
The central question that Heisenberg brings to
the phenomenon of revolution in science understood as
a change in thought pattern, is how the revolution is
able to come about.
The occurrence of the revolution is problematic
due to resistance to the change in thought pattern
offered by the cognizant profession.
Heisenberg also expresses the question in
more sociological terms, when he asks how a small
group of physicists are able to "constrain"
other physicists to make the change in thought pattern
in spite of the latter's resistance to do so.
Firstly he discusses the reasons for
resistance.
Then he discusses various proposed explanations
about how the resistance is overcome.
In his discussion of the reasons for resistance
he states that there have always arisen strong
resistances to every change in the pattern of thought.
The progress of science proceeds as a rule
without much resistance or dispute; the scientist has
by training been put in readiness to fill his mind
with new ideas.
But the case is altered when new groups of
phenomena compel changes in the pattern of thought.
Here even the most eminent of physicists find
immense difficulties, because a demand for change in
thought pattern may create the perception that the
ground is to be pulled from under one's feet.
A researcher who has achieved great success in
his science with a pattern of thinking he has accepted
from his young days, cannot be ready to change this
pattern simply on the basis of a few novel
experiments.
Heisenberg states that once one has observed
the desperation with which clever and conciliatory men
of science react to the demand for a change in the
pattern of thought, one can only be amazed that such
revolutions in science have actually been possible at
all.
Undoubtedly the case in Heisenberg's experience
is the desperation that he saw in Schrödinger's and
especially Einstein's opposition to the new thought
pattern represented by the Copenhagen interpretation
of the quantum mechanics.
He then considers several possible answers to
the question of how scientific revolutions can come
about in spite of the resistances, of how the
resistances are overcome.
One answer that he rejects is that the
revolution is due to a strong revolutionary
personality.
He maintains that no such strong personality
could overcome the profession's resistance.
Another answer that he rejects might be described
as a variation on the conspiracy thesis, the view that
a small group of physicists intended from the outset
to overthrow the existing state of the science.
He states that never in its history has there
ever been a desire for any radical reconstruction of
the edifice of physics; this is because at the onset
of a revolution there is a very special, narrowly
restricted problem, which can find no solution
within the traditional framework.
The revolution is brought about by researchers
who are genuinely trying to resolve the special
problem, but who otherwise wish to change as little as
possible in the previously existing physics.
It is precisely the wish to change things as
little as possible, which demonstrates in Heisenberg's
opinion, that the introduction of novelty is a matter
of being compelled by the facts.
The change of thought pattern is enforced by
the phenomena.
He concludes therefore that the way to make a
scientific revolution is to try to change as little as
possible: it is an error to demand the overthrow of
everything existing due to the risk of attempting a
change that nature makes impossible.
Small changes on the other hand show what is
compelled by the facts, and in the course of years or
decades enforce a change in thought pattern and shift
the foundation of the science.
An example of such a small change is Planck's
quantum of action, which years later resulted in the
modern quantum theory.
Having rejected the view that scientific
revolution occurs due to a conspiracy either with or
without a strong revolutionary personality, Heisenberg
then considers the answer that the resistances to
revolution are overcome simply because there is a
"right" and a "wrong" in physics,
and the new theory is right while the old theory is
wrong.
It is noteworthy that Heisenberg does not
reject the thesis that there is a right and a wrong in
the sense of a correct and an incorrect, and in view
of his thesis of closed-off theories, it would be
remarkable if he did.
Furthermore he had explicitly rejected
historical relativism in his "Quantum Physics
and Kantian Philosophy".
Still he finds that there is a problem with
this answer as an explanation for overcoming
resistances, namely that historically the right theory
has not always prevailed.
He cites as an example the dominance of the
geocentric theory of Ptolemy over the heliocentric theory
of Aristarchus.
Therefore, while there are absolute standards
for criticism of scientific theories, there still
remains the question of why some correct theories
succeed in gaining acceptance over the strong forces
of resistance, while others do not, even though the
rejected theories may be correct.
Heisenberg then proposes his own answer.
Scientists perceive that with the new pattern
of thought, they can achieve greater success in their
science than with the old; the new system proves to be
more fruitful.
Heisenberg states that once anyone has decided
to be a scientist, he wants above all to get ahead, to
be on hand when the new roads open up; it does not
satisfy him merely to repeat what is old and has often
been said before.
Consequently the scientist will be interested
in the kind of problems where there is something to be
done, where he has the prospect of successful work.
That is how relativity theory and quantum
theory came to prevail according to Heisenberg.
He describes this as a "pragmatic
criterion of value", and he states that while one
cannot always be certain that the right theory will
always prevail, nevertheless these are forces that are
strong enough to overcome the resistances to a change
in thought pattern.
Since Heisenberg is a principal participant in
one of the great scientific revolutions in modern
physics, his views based on his personal experience
deserve singular consideration.
He was undoubtedly impressed by the resistances
offered to the Copenhagen interpretation by Schrödinger
and especially by Einstein.
While few contemporary philosophers of
science accept Heisenberg’s doctrine of closed-off
theories with its naturalistic view of observation,
which he uses to interpret his experience of
scientific revolution, they recognize the operation of
sociological forces including the thrust of
opportunistic careerism.
And they also recognize that semantical change
occurs in scientific revolutions, and that the
adjustment it imposes on the affected profession
operates as a cause of resistance within it, even
though they do not accept Heisenberg's theory of
semantical change and permanence.
Unlike others such as Kuhn, Heisenberg does not
identify the institutionalized criteria for scientific
criticism with the existing thought pattern, and he
does not maintain that the revolution is a change with
no institutional framework controlling it.
Heisenberg avoids the historical relativism
found by many in Kuhn's thesis, and which is
explicitly embraced by Feyerabend.
And one would not expect the proponent of the
doctrine of closed-off theories and the advocate of
Bohr's theory of observation to find the process of
scientific criticism very problematic.
The scientist is simply compelled by the
facts, and the semantics of the statements of fact are
not a problematic matter.
Failure of the correct theory to overcome the
forces of resistance, and indeed the very existence of
those resistances, is due to the professional
failure of those who cannot adjust to new thought
patterns when the facts compel, and not to any
inherently problematic character in the process of
scientific criticism itself.
The contemporary Pragmatist philosopher of
science can only wonder what Heisenberg might have
said, were he to have followed through with Einstein's
thesis that it is the theory that decides what the
physicist can observe; how he would have addressed the
consequent problem that the concepts used to describe
the facts are supplied by the choice of thought
patterns expressed in the theory.
Yet the semantics of the statement of fact is
not unproblematic, as Hanson attempted to demonstrate
in his Patterns
of Discovery (1958), where he considers at length
the interpreted nature of the observations relevant in
the choice between the geocentric and the heliocentric
theories of the planetary motions.
If what Heisenberg calls "the pragmatic
criterion of value" determines the choice between
the old and the new theories, and each theory
determines the facts, then a problem arises as to how
facts can have any independently compelling force.
Heisenberg’s
Philosophy of Science
Heisenberg's rich and extensive philosophical
writings can be related to the four basic questions
addressed by contemporary professional philosophers
of science.
Aim
of Science
The question of the aim of science has a
special importance in Heisenberg's philosophy, because
it was explicitly developed to defend the Copenhagen
interpretation of quantum theory against Einstein's
explicitly formulated programmatic aim of all
physics.
Heisenberg's views are expressed in his
"Notion of 'Closed Theory' in Modern
Science" and in his "On the Unity of the
Scientific Outlook on Nature" (1941) in Philosophical Problems of Quantum Physics.
Einstein used his programmatic aim of physics
to claim that the statistical quantum theory is
"incomplete" in the sense that it does not
represent an adequate explanation for the problem that
it addresses, and that further research work is still
needed.
The reason it is still incomplete is that it is
not consistent with the ontology of field physics,
which describes physical reality as continuous in four
dimensions and deterministic.
Heisenberg denied Einstein's thesis that the
microphysical theory must employ the same ontological
concepts as those used in macrophysical field theory,
and his doctrine of closed-off theories was motivated
in part by his desire to show how multiple ontologies
can co-exist in physics.
This is Heisenberg's thesis of pluralism in
science.
The Copenhagen interpretation of quantum
theory is complete in Heisenberg's view, because it is
a closed-off theory, and like all closed-off theories
it is not only a complete solution to the problem that
it addresses, but it is also a permanently true
solution.
In Heisenberg's philosophy of science the aim
of science is to progress through a sequence of
closed-off theories, and it is not, as Einstein
maintained, to progress toward a single and
all-inclusive ontology.
The result of physics pursuing its aim as
Heisenberg views it, has been the architectonic scheme
for physics, a scheme of closed-off theories which he
delineates in his "Relation of Quantum Theory to
Other Parts of Natural Science" in Physics
and Philosophy.
Discovery
In Heisenberg's treatment of the question of
scientific discovery, two aspects may be
distinguished: One is the syntactical or structural
aspect, and the other is the semantical or the
interpretative aspect, which also includes ontological
considerations.
The structural aspect pertains to the
development of the new formal axiomatic system, the
new mathematical theory.
These new formal structures are the result of
repeated failures of the conservative attempts by the
researchers to extend a currently acceptable theory
to explain phenomena in a new domain of experience,
and eventually may result in a revolutionary
development.
Closely related to the first aspect is the
second, the interpretative problem.
When extension of Newtonian physics could not
solve the problem of microphysics, and after the
matrix mechanics was eventually developed by
Heisenberg, the interpretation of the new matrix
mechanics still remained problematic.
Using Einstein's thesis that the theory decides
what the physicist observes, Heisenberg reinterpreted
the relevant observations in the Wilson cloud chamber
experiment, and developed the uncertainty relation and
its nondeterministic ontology. The new interpretation
was accomplished by taking the new quantum theory
realistically, as a description of the ontology of the
microphysical world.
When Einstein attacked the statistical quantum
theory, he attacked only the second aspect, the
Copenhagen interpretation with its nondeterministic
ontological claim; he rejected the indeterminacy claim
as a true description of the real world.
Explanation
Heisenberg's views on the question of
scientific explanation are implicit in his position
against Einstein's objections to the Copenhagen
interpretation.
Einstein's objection to the Copenhagen
interpretation is that it is incomplete as a
scientific explanation.
This objection is a very traditional type of
objection, because historically the concept of
scientific explanation has been defined in terms of
one or another ontology, and Einstein demanded
conformity to the ontology defined by the concepts of
field physics.
Bohr placed himself and his Copenhagen
colleagues at a disadvantage, when he employed the
vocabulary of their critics by referring to the
statistical quantum theory as "noncausal";
he accepted the definition of causality in terms of
the ontology of classical physics and field theory.
But Heisenberg also maintained that the
revolutionary developments in physics consisted in
part of interpreting the new mathematical formalism
realistically, such as accepting the field as a
reality, accepting relativistic time as real time,
abandoning the concept of absolute time, and most
notably accepting the uncertainty relation as
describing the real microphysical world as
nondeterministic.
This amounts to separating the concept of
scientific explanation from any preconceived ontology,
a view of scientific explanation that was quite
radical in its time, even though it is now the common
property of the contemporary Pragmatist philosophers
of science.
Criticism
In striking contrast to his radical concept of
scientific explanation, Heisenberg's treatment of the
fourth question, the question of scientific criticism,
is very conservative: he believed that his doctrine of
closed-off theories enables him to explain how
scientific theories can be permanently true.
His views of explanation and of criticism
represent a very unusual combination of views; historically
philosophers and scientists have maintained that scientific
explanations are permanently true, because as
explanations, they describe correctly the one and only
true ontology.
Heisenberg's philosophy of scientific criticism
includes a semantical thesis, which is a thesis of
both semantical change and semantical permanence.
Whether or not this semantical thesis is a
sustainable one is certainly questionable,
particularly when it depends on such curious processes
as the semantics of words becoming
"detached" from the variables occurring in
the closed-off axiomatic theories, when the theories
encounter the limits of their applicability.
A philosopher of science such as Popper would
dismiss such a thesis as a
"content-decreasing" stratagem.
If when a theory is criticized by an experimental
test, the words expressing the test outcome describe
something contrary to what the theory had predicted,
then the attempt to save its truth claim by
equivocation, by the "detachment" of the
meanings describing the experimental outcome from the
terms in the theory, only makes the theory
tautological.
In other words Heisenberg's doctrine in effect
says a theory is true where it is true, and that where
it is not true, it is not falsified, because it
becomes silent, i.e. inapplicable.
Comment
and Conclusion
A new philosophy does not spring forth as from
the brow of Zeus -
coherent, complete, and fully formed.
It struggles to emerge from the confusion
produced by the inevitable conflict between new
seminal insights and old conventional concepts.
It is not surprising, therefore, that there
should exist an inconsistency between the seminal
insights in Heisenberg's philosophical reflections on
his pioneering findings described in his
autobiographical accounts and the conventional
concepts in his systematic philosophy of science set
forth as his doctrine of closed-off theories.
In “Bohm and the ‘Inevitability’ of
Acausality” in Bohmian
Mechanics and Quantum Theory: An Appraisal (1996)
Mara Beler takes a cynical perspective to
Heisenberg’s inconsistency, arguing that he had
neither belief nor commitment, but only a selective
and opportunistic use of Bohrian doctrine for the
finality of the Copenhagen orthodoxy.
Human motives are seldom unmixed, but there is
likely more to the story.
Clearly the principal source of this
inconsistency in Heisenberg’s philosophy is the
conflicting influences of Bohr and Einstein, and the
conflict has its basis in two fundamentally different
philosophies of the semantics of language,
particularly where the relevant language is the
vocabulary used to describe observations.
The emerging new philosophy of language in
philosophy of science is the artifactual thesis of
semantics and the prevailing old one is the
naturalistic thesis.
Bohr's philosophy of language is that the
semantics of language is the natural product of
perception, such that concepts used for observation
are what he calls the "forms of perception"
that have their information content determined by
nature and the natural processes of perception.
Einstein's philosophy of language on the other
hand is that the semantics of language is an artifact,
a "free convention", a cultural product
instead of a natural product, such that concepts and
categories used for observation in physics do not have
their information content specifically determined by
the natural processes of perception.
It was evident to Heisenberg as well as to
every other physicist at the time that revolutionary
revisions had been made in twentieth-century physics.
Heisenberg wanted to explain how such
developments in the history of science could produce
correspondingly revolutionary revisions in the
semantics of the language of physical theory.
Heisenberg's response was his doctrine of
closed-off theories, and the philosophy of language
that he used for his semantical theory was greatly
influenced by Bohr.
This doctrine restricts semantical revision to
the description of phenomena that lie beyond ordinary
perception, and thereby retains semantical permanence
for the description of phenomena accessible to
everyday observation and described by the language and
concepts of classical physics.
According to Heisenberg’s doctrine of
closed-off theories Newtonian physics is permanently
valid and serves as the observation language for
physics, because it is necessary for reporting
experimental measurements and other observations.
This is similar to the Positivist philosophy of
science, which also assumes a naturalistic philosophy
of the semantics of language and the semantical
permanence of observation language.
In Heisenberg's semantical theory all
observation must be with concepts either of classical
physics or of "everyday" language.
In his mature version of his doctrine of
closed-off theories these concepts are not the same.
The everyday concepts have a "lack of
precision" or vagueness, while the concepts of
classical physics have their content rigidly and
precisely fixed by their occurrence in the context
consisting of the laws constituting the axiom system
of Newtonian physics.
The concepts of quantum physics also have their
content fixed by their occurrence in the context
consisting of the laws constituting the axiom system
of quantum physics.
What is significant is not just that the laws
may be expressed in axiomatized systems, but that the
quantum concepts are contextually determined in
contexts that are alternative concepts relative to
classical concepts, because the laws of classical and
quantum physics are mutually inconsistent.
And most notably in Heisenberg's view the
quantum concepts are not merely alternative
resolutions of the vagueness in everyday concepts,
because according to the doctrine of closed-off
theories the quantum concepts cannot be used for
observation.
The fact that classical and quantum concepts
occur in mutually inconsistent axiom systems of laws
implies that, when these concepts are associated with
the same descriptive term or variable, they are
alternative meanings making that common term
equivocal.
The equivocal relation between classical and
quantum concepts is illustrated in the cases of the
terms "position" and "momentum",
which occur in both classical and quantum physics. On
the one hand the advocates of the Copenhagen
interpretation of the quantum theory argue that in
practice the concepts of classical physics must
operate in descriptions of the macrophysical
experimental apparatus and observation measurement.
This classical semantics includes the idea that nature
is fundamentally continuous, and the idea that in
principle the measurements can be indefinitely accurate,
notwithstanding the fact that in practice the degree
of accuracy is limited.
On the other hand there are also meanings for
these terms that are distinctive of quantum physics,
and this semantics which is defined in the context of
the indeterminacy relations, includes the ideas that
nature is fundamentally discontinuous and that the
accuracy of the joint measurement of momentum and
position is limited by Planck's constant.
Therefore, in order for observation to be
possible in quantum physics there must exist an
equivocation for every term common to classical and
quantum physics, such that for every quantum concept
determined by the context of quantum laws there must
be a corresponding classical concept for observation
determined by the context of classical physics. Such
is Heisenberg’s doctrine of closed-off theories, his
explicit and systematic philosophy of science.
Yet Heisenberg's use of Einstein's admonition
for describing the tracks in the Wilson cloud chamber,
which led to his subsequent development of the
indeterminacy relations, does not agree with his
doctrine of closed-off theories.
Einstein's admonition consists of the
semantical thesis that it is the theory that decides
what the physicist can observe, and for microphysical
experiments this thesis implies that the quantum
theory supplies the concepts for observation.
Contrary to Heisenberg's semantical doctrine of
closed-off theories, classical concepts are not
necessary for observation, variables in the quantum
laws are not equivocal, and all the concepts in the
quantum theory are quantum concepts including the
concepts used for observation.
It is possible with a metatheory of semantical
description to follow through with Einstein's
admonition and to say that theory decides what the
physicist can observe, because the concepts used for
observation are quantum concepts.
Such a new semantical theory is needed, because
Heisenberg had premised his doctrine of closed-off
theories on the naturalistic philosophy of language.
Attempts to preserve a permanent semantics for
observation, while at the same time to explain the
semantical revisions produced by the revolutionary
developments in theory, results in attributing
equivocation to language that in practice physicists
are routinely able to use unambiguously.
The historic twentieth-century scientific
revolutions motivated post-Positivist professional
philosophers of science to reject the naturalistic
philosophy of language, and to accept the artifactual
philosophy of language.
It is necessary to consider further how to
describe the semantics both of quantum theory and of
experimental observation, in order to exhibit how
concepts are culturally determined as linguistic
artifacts instead of predetermined as products of
nature, and to explain why semantical change does not
involve complete equivocation.
Heisenberg’s doctrine of closed-off theories
contains certain basic assumptions that are in need of
reconsideration.
One is the tacit assumption that all concepts
are indivisible or simple wholes, that must be either
completely different or completely the same, such
that classical and quantum concepts are simply and
wholly equivocal.
The other basic assumption is that observation
language must be exclusively associated with
macroscopic phenomena.
Both of these basic ideas contain errors.
Firstly it is incorrect to assume that concepts
in physics or in any other discourse are simple wholes
that cannot be analyzed into component parts.
And secondly it is necessary to reconsider the
Copenhagen school's basis for dividing the relevant
language into statements of experiment and statements
of theory.
Specifically rejection of the naturalistic
philosophy of language implies rejecting two mental
associations that occur in the doctrine of closed-off
theories.
The first is the
classical-macroscopic-observation association, and the
second is the quantum-microscopic-theoretical
association.
Consider firstly an alternative to the
wholistic view, and how it affects Heisenberg’s
thesis of equivocation.
Reflection on the common occurrence of looking
up a word in a unilingual dictionary or thesaurus
reveals that the meanings of words are not simple
wholes, but rather have component parts that are
identified by the defining words occurring in the dictionary
definition or lexical entry.
These dictionary definitions give semantical
descriptions of the meanings they define, and in order
to function in this way they always must have the
force of universally quantified statements accepted as
true.
Dictionary definitions are often viewed as
describing the complete meaning of the term, but
dictionary definitions are minimal statements, and by
no means give complete meaning.
Usually an understanding of the meaning of a
technical term requires a larger context consisting of
a discourse having many statements containing the
term.
Such larger context may be examined with the
aid if a key-word-in-context computer program.
Since Hempel rejected the separation of the
meaning-specification and descriptive functions in
analytic statements and since Quine rejected the
analytic-synthetic distinction, all universal
empirical or “synthetic” statements may be viewed
as also definitional or “analytic”.
Thus if one were to make a list of logically
consistent universally quantified affirmative
categorical statements containing the common term as
the subject term with each statement accepted as true,
then the predicates in each of the mutually consistent
statements constituting the list would describe part
of the meaning of the common subject term, and the
entire list as well as each statement in it may be
called a "semantical description" of the
common subject term's univocal meaning.
A semantical description consists of the
language context in which the descriptive term’s
meaning is determined and described by a set of
universal affirmations believed to be true.
This contextual determination of the semantics
of language is the essence of the artifactual thesis.
Quine calls this context the “web of
beliefs”.
A term is equivocal if any of the universal
affirmations in the semantical description are
mutually inconsistent.
This equivocation is made explicit if the
predicates of the inconsistent universal affirmations
can be related to one another by universal negations
accepted as true.
The two meanings in the equivocation have
separate semantical descriptions which can be
exhibited when the original list is subdivided into
mutually exclusive subsets with each containing only
mutually consistent universal affirmations, such that
each subset is a semantical description of one of the
two different meanings of the equivocal term instead
of each functioning as a description of different
parts of the one meaning of a univocal term.
The equivocations postulated by Heisenberg's
doctrine of closed-off theories applied to
microphysics are the result of the logical
inconsistency between the axiomatic systems of
classical and quantum physics.
Thus there exists equivocation with each
axiomatic system, a separate semantical description
list for any common subject terms such as
“position” or “momentum”.
In addition to the properties of equivocation
and univocation there is another aspect of language
called vagueness.
Equivocation and univocation are properties of
terms, while vagueness and clarity are properties of
meanings.
Thus terms are univocal or equivocal relative
to meaning, but meanings are clear or vague relative
to one another, and thus indirectly relative to the
extensions they reference.
Two concepts are clear in relation to one
another, if they can be related to each other by
universal affirmations or negations accepted as
true, and they are vague in relation to each other if
they cannot be so related by any universal statements.
Adding to a univocal term's semantical
description list any universal affirmations or
negations believed to be true has the effect of
resolving the vagueness in the concept associated with
the term by explicitly adding or excluding meaning.
Every meaning is vague and admits to further
resolution or clarification, because its semantical
description can always be increased by additional
universal statements believed to be true, although
responsible addition in science usually requires
additional research.
Waismann has called this inexhaustible residual
vagueness the "open texture" of concepts.
Some comments are in order about mathematics in
empirical science.
Firstly mathematics supplies the grammar for
much of the language of science, and it is a
distinctive language.
Just as statements in logic and ordinary
discourse may be said to constitute what Carnap called
the “thing language” and what Whorf called the
language of substantives, so too the equations and
inequalities constitute what may be called the
“measurement language”.
Statements in substantive language, which
describe the measured phenomenon, the measurement
procedures, and the design and operation of any
apparatus employed, must be used to relate substantive
language to measurement language.
The controversy about the interpretation of the
quantum theory equations, which are in measurement
language, is about statements in substantive language
that describes what is a real entity in the quantum
domain.
The Copenhagen physicists including Heisenberg
maintained that the wave and particle are two
alternative aspects of what is really one entity.
Lande said that only the particle is a real
physical entity, Schrödinger believed that only the
wave is physically real, and Bohm said that wave and
particle are both co-existing and separate real
entities.
These issues become very philosophical, when
they are about explicitly expressed criteria for
identifying an entity.
Heisenberg was not explicit in his criterion,
but Lande and Born had their different yet explicit
philosophical criteria.
Both brilliant physicists and bull-headed
philosophers have spent most of the twentieth century
arguing about this issue, and they continue to do so,
because even with the practice of scientific realism,
the language of mathematics is silent about the
ontological category of physical entity.
Any future resolution will be the result of new
and superior experimental and observational
techniques, but mathematics alone cannot express the
findings that will resolve the issue.
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