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Norwood Russell Hanson (1924-1967), born in New
Jersey, was a U.S. Marine Corps fighter pilot during
the Second World War, who earned the rank of major,
and was awarded the Distinguished Flying Cross and
the Air Medal for flying combat missions over Japan.
Afterward he studied at the University of
Chicago, Columbia University, and Yale University in
the United States, and then studied at both Oxford
University and Cambridge University in England.
He received a Ph.D. from Oxford in 1955 and a
Ph.D. from Cambridge in 1956, and was afterward a
fellow at the Institute for Advanced Study at
Princeton.
He accepted a faculty appointment at Indiana
University in 1957, where he was founder and
chairman of Indiana University's Department of
History and Logic of Science from 1960 to 1963.
He then accepted a professorship on the
philosophy department faculty of Yale University,
which he had at the time of his premature death at
the age of forty three in a crash of his private
airplane in 1967.
His principal works are Patterns
of Discovery (1958) and Concept
of the Positron (1963).
At the time of his death he left an
uncompleted textbook in philosophy of science
intended for first-year college students, which was
edited by Willard C. Humphreys, a former student of
Hanson, and then published as Perception
and Discovery (1969).
A year after his death a complete
bibliography of his publications appeared in a
memorial volume of Boston
Studies in the Philosophy of Science, Volume III
(1968).
David Bohm (1917-1992) was born in
Wilkes-Barre, PA, and received his doctorate in
physics from the University of California.
He taught physics at Princeton, and
eventually moved to England.
He was professor of theoretical physics from
1961 at Birkbeck College, University of London,
where he was professor emeritus from 1983 until his
death in 1992.
A brief biography may be found in the
"General Introduction" in Quantum
Implications (ed. B.J. Hiley and F. David Peat,
1987), and a three-hundred-fifty page biography by
Peat was published under the title Infinite
Potential: The Life and Times of David Bohm
(1997).
Bohm’s initial statement of his
interpretation was published in 1952 in two articles
in the Physical
Review, in which he reports that the
interpretation was originally stimulated by a
discussion with Einstein in 1951.
His principal statements of his
hidden-variable interpretation of quantum theory are
set forth in two of his books.
The earlier is a brief monograph of only
one-hundred-forty pages titled Causality and Chance in Modern Physics published in 1957, and the
more recent is his more elaborate Undivided
Universe co-authored with Basil Hiley and
posthumously published in 1993. After publishing his
seminal articles in 1952, he found that his
interpretation had been anticipated in important
respects in 1927 by Louis de Broglie (1892-1987).
De Broglie's interpretation had been
criticized severely, and he had consequently
abandoned it, but Bohm had further developed the
thesis enough that the fundamental objections
confronting de Broglie had been answered.
Bohm's interpretation was shown to be
consistent with all the essential characteristics of
the quantum theory, and additional suggestions were
made by Vigier, a colleague of de Broglie.
De Broglie then returned to his original
proposals, since he believed that the decisive
objections against them had been answered.
Bohm and Vigier then published a joint paper
setting forth the interpretation in the Physical
Review in 1954, and de Broglie wrote a
"Foreword" to Bohm's 1957 book.
Bohm was one of the physicists who recognized
nonlocality in the quantum theory.
Peat’s generally sympathetic biography
shows how the idea of nonlocality led Bohm firstly
to his wholistic ontology for physics, then to his
process metaphysics, and finally to his mysticism of
the implicate order, according to which mind and
matter are indivisibly united.
To the dismay and consternation of his
friends and colleagues, this mysticism was
encouraged by Bohm’s long-time association with an
Indian guru, and also led Bohm to take seriously the
mind-over-matter exhibitions of a stage magician.
Hanson takes very seriously the question of
the interpretation of the modern quantum theory, and
he truculently defends the Copenhagen
interpretation.
In “Appendix II” to his
Patterns of Discovery he notes that while for
most practical microphysical problems Born, who
accepted the Copenhagen interpretation, and Schrödinger,
who did not, would have made the same theoretical
calculations.
Nevertheless, their alternative
interpretations organized their thinking
differently, and consequently influenced their
future research work in very different ways: after
1930 Born was led to work on collision behavior, on
the statistical analysis of scattering matrices,
while Schrödinger pursued investigation of the
so-called ghost waves of the elementary particles.
The interpretations, therefore, are important
because each supplies an agenda that influences the
direction of future research in physics.
Hanson does not view all interpretations as
equally worthy of consideration, and he considers
particularly unfortunate is the
"hidden-variable" interpretation developed
by David Bohm.
In contrast to the Copenhagen interpretation
with its duality thesis that the wave and particle
are two manifestations of the same physical entity,
Bohm’s alternative interpretation is that the wave
and particle are different physical entities, even
though they are never found separately, and that the
wave oscillates in an as yet experimentally
undetected and therefore hidden subquantum field. In
the context of the topic of scientific discovery
Bohm’s views are interesting, because they
illustrate the semantical approach to scientific
discovery and theory development in physics.
They illustrate the use of figures of speech
as a technique for theory development based on
certain postulated basic similarities between the
macrophysical and microphysical orders of magnitude,
similarities that are denied by advocates of the
Copenhagen interpretation.
Consider firstly Bohm’s early advocacy of
the Copenhagen interpretation, and then his later
agenda for future physics including his
hidden-variable interpretation for quantum theory.
Bohm's
Early Copenhagen Views
The hidden-variable thesis is Bohm’s more
mature view.
He started out as an advocate of the
Copenhagen interpretation, which he also calls the
usual interpretation, and then changed his mind
after the talk with Einstein in 1951, the year in
which his textbook titled Quantum
Theory was published setting forth his earlier
view. There are at least two noteworthy features of
this early book.
The first is Bohm’s distorted understanding
of Bohr’s philosophy of quantum theory.
The second is his ontology for quantum
theory, the ontology of potentialities, which
anticipated Heisenberg’s similar ontology of potentia
by seven years.
In the “Preface” to his Quantum
Theory Bohm says that as a result of the work of
Neils Bohr, it has become possible to express the
results of quantum theory in terms of comparatively
qualitative and imaginative concepts, which are
totally different from those appearing in the
classical theory.
He rejects the view that the quantum
properties of matter imply the renunciation of the
possibility of their being understood in the
customary imaginative sense, and that they imply the
sufficiency of only a self-consistent mathematical
formalism which can in some mysterious way correctly
predict the numerical results of experiments.
The eighth chapter of the book is titled
“An Attempt to Build a Physical Picture of the
Quantum Nature of Matter”, and Bohm writes in a
footnote that many of the ideas appearing in the
chapter are an elaboration of material in Bohr’s Atomic
Theory and the Description of Matter.
However, Bohm’s understanding of Bohr is
distorted.
Bohr maintained an instrumentalist view of
the equations of quantum theory, which rejects any
semantics or ontology for quantum theory, and he
repeatedly denied explicitly that quantum phenomena
are pictureable. From Bohm’s statement in his 1952
articles that his hidden-variables thesis was the
result of a talk with Einstein in 1951, it is
reasonable to speculate that Einstein had read
Bohm’s book, had recognized that Bohm was ripe for
disillusionment with the views in Bohr’s
philosophy, and had concluded that Bohm was ready
for induction into the ranks of Bohr’s critics.
In any event whatever may have been
Einstein’s unreported comments to Bohm in their
private conversation, the ultimate outcome after
forty years was Bohm’s Undivided Universe: An Ontological Interpretation of Quantum Theory
(1973), a book in which Bohm explicitly says he is
supplying an ontology to replace Bohr’s
epistemological interpretation.
The ontology for quantum theory that Bohm
described in 1951 is a wholistic ontology of
potentialities, in which the world is an indivisible
unit where quanta have no component parts
describable by hidden variables, and are not even
separate objects, but are only a way of talking
about indivisible transitions.
This metaphysics is also called monism.
At the quantum-mechanical level the
properties of a given object do not exist separately
in the quantum object alone, but rather are
potentialities which are realized in a way that
depends on the systems with which the object
interacts.
Thus the electron has the potentiality for
developing either its particle-like or its wave-like
form, depending on whether it interacts with an
apparatus that measures either its position or
momentum.
Bohm’s views are also realist; he does not
maintain that the quantum phenomenon has its
properties because it is being measured.
He says that a quantum-mechanical system can
produce classically describable effects not only in
a measuring apparatus, but also in all kinds of
systems that are not actually being used for the
purpose of making measurements.
Throughout the process of measurement the
potentialities of the electron change in a
continuous way, while the forms in which these
potentialities can be realized are discrete.
The continuously changing potentialities and
the discontinuous forms in which the potentialities
may be realized are complementary properties of the
electron.
Bohm anticipated Heisenberg’s idea of
potentiality, which Heisenberg did not propose until
his Physics and Philosophy in 1958, the only place in Heisenberg’s
literary corpus where the idea is mentioned. But
there are differences in their ideas of
potentiality, because unlike Bohm’s,
Heisenberg’s is not a wholistic version.
In the 1951 book Bohm said that potentiality
makes quantum theory inconsistent with the
hidden-variables thesis, because the
hidden-variables view is based on the incorrect
assumption that there are separately existing and
precisely defined elements of reality.
The idea of potentiality is much more
integral to Bohm’s earlier interpretation than to
Heisenberg’s, and it had distinctive implications
for Bohm.
One implication is Bohm’s thesis that
mathematics is inadequate for physics.
He says that the interpretation of the
properties of the electron as incompletely defined
potentialities finds its mathematical reflection in
the fact that the wave function does not completely
determine its own interpretation until it interacts
with the measuring device, and that the wave
function is not in one-to-one correspondence with
the actual behavior of matter, but is merely an
abstraction reflecting only certain aspects of
reality.
He believes that to obtain a description of
all aspects of the world, one must supplement the
mathematical description with a physical
interpretation in terms of the incompletely defined
potentialities.
Shortly afterwards he accepted the
hidden-variables idea, and in the second chapter of
his Undivided Universe, where he mentions in a footnote his anticipation
of Heisenberg’s idea of potentiality, he rejects
altogether the potentiality thesis that the particle
itself is created by the measurement process.
In Bohm’s hidden-variables view, the
particle is not a wave-packet or otherwise created
out of the wave; the particle is in reality distinct
from the wave.
His later view is not wave or
particle, but wave and
particle.
That is, the wave and particle are not two
alternative aspects of the same entity, but are
different and separate entities.
Bohm's
Agenda for Future Microphysics
Bohm's hidden-variable interpretation is an
agenda for future microphysics, and his Causality and Chance (1957) sets forth three related objectives in
this agenda.
His first objective is the relatively modest
one of demonstrating that an alternative to the
Copenhagen interpretation is possible, in the sense
that it is not the only one that is consistent with
the formalism and measurements of modern quantum
theory.
He states this objective not only because he
has another interpretation in mind, but also because
he maintains that the development of alternative
views is important for the advancement of science,
while advocates of the Copenhagen interpretation
deny that any alternative view including one
involving a subquantum level of magnitude is
conceivable.
For example in his "Questions of
Principle in Modern Physics" (1935) in Philosophical
Problems of Quantum Physics Heisenberg states
that the uncertainty principle must be taken as a
question of principle making other formulations into
false and meaningless questions, just as in
relativity theory it is supposed that it is in
principle impossible to transmit signals at speeds
greater than the velocity of light.
But Bohm maintains that without alternatives
the physicist is constrained to work along accepted
lines of thought in the hope that either new
experimental developments or lucky and brilliantly
new theoretical insights eventually will lead to a
new theory.
In contrast Bohm maintains that one of the
functions of criticism in physics is to suggest
alternative lines of research that are likely to
lead in a productive direction.
He thus sees criticism with alternatives to
be integral to scientific discovery.
This objective is particularly attractive to
the philosopher of science Paul Feyerabend, once an
advocate of Bohm's interpretation, who to the end of
his life maintained that creating alternatives is
necessary for the advancement of science.
Bohm's second objective is to propose an
interpretation of the history of physics, which
shows successful precedents for the research
strategy represented by his hidden-variable
interpretation of quantum theory.
The paradigmatic historical precedent he
invokes is the atomic theory of matter, which
postulated the existence of atoms unobservable at
the time the theory was proposed.
Analogously Bohm’s strategy consists of
postulating that there exists an order of physical
magnitude below the quantum order of magnitude
containing the quantum of action represented by
Planck's constant.
Bohm postulates that this subquantum order
contains new types of qualitative phenomena
governed by more deterministic laws than do those
known to exist at the quantum level of magnitude.
The existence of this postulated subquantum
level of microphysical phenomena is denied by the
Copenhagen interpretation advocates, and since there
is as yet no experimental detection of any such
subquantum phenomena, the theory that postulates
them is said to have hidden variables.
Bohm opposes his historical interpretation to
another that he calls mechanistic, a term that is
unfortunately ambiguous in both philosophical and
scientific usage, but which has a specific and
somewhat elaborate meaning in Bohm’s book.
According to the objectionable mechanistic
philosophy opposed by Bohm the qualitative diversity
of things in the world can be reduced completely,
without approximation, and in every possible domain
of science to nothing more than the effects of some
definite and limited general framework of
quantitative laws, which are regarded as absolute
and final.
Prior to the development of quantum theory
these quantitative laws were assumed to be
deterministic; then with the development of the
Copenhagen interpretation of quantum theory these
laws were assumed to be indeterministic.
Hence there are both deterministic and
indeterministic varieties of mechanism.
In the former variety causal laws are thought
to be fundamental, while in the latter probability
laws are thought to be fundamental.
Indeterministic mechanism prevails today,
because physicists have accepted Heisenberg's thesis
that the indeterminacy principle represents an
absolute and final limitation on our ability ever to
define the state of things by any kind of
measurement.
In Causality
and Chance Bohm maintains that both causality
and chance are fundamental and objective, and that
both determinism and indeterminism are merely
idealizations.
Thus he departs from Einstein's determinism.
He also rejects the subjective interpretation
of probability, which says that the appearance of
chance is a result of human ignorance.
And he rejects the idea common to both
deterministic and indeterministic varieties of
mechanism that there is only one general framework
of laws and a limited qualitative diversity.
Bohm maintains that there are different
levels of depth or orders of magnitude with each
level having its own laws and qualitative diversity.
In the history of physics revolutionary
developments have occurred when laws and qualities
at a higher level are explained by those of a lower
level.
Experiments may disclose a breakdown of an
entire scheme of laws by the appearance of chance
fluctuations not originating in anything at the
higher level, but instead originating in
qualitatively different kinds of factors at a lower
level.
For example in classical physics a particle
such as an electron follows the classical orbit only
approximately, while in a more accurate treatment it
is found to undergo random fluctuations in its
motions arising outside the context of the classical
level. Thus Bohm affirms by way of historical
analogy and on the basis of his nonmechanistic
interpretation of the history of science that there
is a still deeper level, a subquantum level, which
in turn explains the randomness that is detected at
the higher quantum level of magnitude.
Bohm’s hidden-variable interpretation is
both an alternative interpretation of quantum theory
motivated by this prior ontological commitment and
also a discovery heuristic for which there is
historical precedent. He maintains that new work is
considerably facilitated by his thesis of a hidden
subquantum order of magnitude, because the physicist
can imagine what is happening, and can thereby be
led to new ideas not only by looking directly for
new equations but also by a related procedure of
thinking in terms of concepts and models that will
help to suggest new equations, equations which would
not likely be suggested by mathematics alone.
And he uses his postulated subquantum
ontology as a basis for figures of speech such as
analogy, which are a central feature in his
discovery strategy.
These figures aid in formulating new
hypotheses for future physics both on the basis of
similarities between the macrophysical and
microphysical orders of magnitude and on the basis
of past developments in the history of physics,
which he believes justifies his hidden-variables
ontology.
Bohm's third objective is to use the
hidden-variable interpretation as a guide for future
research for a new microphysical theory that will
resolve what he sees as the current crisis in
quantum physics.
This crisis manifests itself in Dirac's
relativistic quantum theory, when the wave equation
is applied to the description of particle scattering
with very high energies and at short distances.
For the Schrödinger wave equation to be used
in such applications, an ad hoc mathematical adjustment called renormalization is necessary.
Furthermore the behavior of very high-energy
particles in experiments reveals that there exist
many new kinds of particles not previously known,
and that they are unstable, since they decay into
one another and create other particles.
Nothing like this is accounted for by current
quantum theory.
To Bohm these problems for the current
quantum theory suggest that elementary particles are
not really elementary. The concept of a subquantum
level justifies the physicist considering a whole
range of qualitatively new kinds of theories that
approach the currently accepted theory only as
approximations, which hold in limiting cases.
He believes that the current crisis in
quantum theory portends a revolution in
microphysics, and that the hidden-variable
interpretation offers a superior guide for research
that promises to resolve the crisis.
These three objectives of Bohm's agenda
represent successively more ambitious claims.
The first claim is merely that an alternative
to the Copenhagen semantical interpretation
describing a subquantum level of magnitude is
conceivable in the sense that it is consistent with
the data and formalism of the current quantum
theory.
The second claim states more ambitiously that
the history of physics reveals that postulating
lower levels of magnitude supplies an analogy, which
is a productive strategy to guide new research.
The third claim is still more ambitious; it
states that a new scientific revolution in
microphysics is at hand, and that the
hidden-variable semantical interpretation will
produce a new microphysical theory that will resolve
the current crisis in quantum theory.
As de Broglie said in the closing sentence of
his "Foreword" to Causality and Chance (1957), Bohm's book comes at exactly the right
time.
Thirty-five years later in his Undivided
Universe Bohm was still predicting this
impending revolution.
No such revolution has yet occurred, but more
recent experiments based on John Stuart Bell’s
inequality have occasioned reconsideration of the
merits of Bohmian mechanics.
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