Grice on the ontology of quantum theory

T. Hickey in online study

http://www.philsci.com/pdf/BOOKVII.pdf

[Bohm's] ontology for quantum theory, the ontology of potentialities, which anticipated Heisenberg’s similar ontology of potentia by seven years.

"Bohr maintains an instrumentalist view of the equations of quantum theory, which rejects any semantics or ontology for quantum theory."

"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."

"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 realist."

"Bohm 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."

"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 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."

"Hence there are both deterministic and indeterministic varieties of mechanism."

"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’s hidden-variable interpretation is both an alternative interpretation of quantum theory motivated by this prior ontological commitment."

"Bohm 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."

"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."

"Bohm uses figures of speech, which he calls analogies."

"In his Causality and Chance Bohm uses an analogy with Brownian movements of particles in a gravitational field, and illustrates what Heisenberg’s indeterminacy principle would mean in terms of a subquantum-mechanical field."

"Bohm maintains that Heisenberg's indeterminacy principle should not be regarded as expressing the impossibility of making measurements of unlimited precision. Rather it should be regarded as expressing the incomplete degree of self-determination characteristic only of entities that can be defined in the quantum-mechanical level."

"Quite notably Bohm says the fact that the action of the quantum potential upon the particle depends only on its form and not on its magnitude, implies the possibility of a strong nonlocal connection of distant particles and a strong dependence of the particle on its general environmental context."

"Bohm believes that in expounding his doctrine of potentia Heisenberg states that whereas possibilities can exist outside the human mind, physical actuality can only exist when someone perceives it."


To assess Bohm’s criticism, it is necessary firstly to examine Heisenberg’s own statements about the role of subjectivism in quantum theory.

"[For Heisenberg] [t]he statement of fact is a statement about possibilities or tendencies, and he references Aristotle’s concept of potentia."

"The potentia or potential is completely objective and does not depend on any observer."

"The realization of the potential, the transition from the possible to the actual, takes place during the act of observation, as soon as the of object interacts with the measuring device."

"These comments would suggest that Heisenberg wishes to preclude any metaphysical idealism such as Berkeley’s esse est percipi."


"[T]he probability function is an object language statement with a semantics describing the potentia ontology and the ontology of indeterminism."

"On the subjective interpretation the probability function is a statement in a metalanguage for physics with a semantics describing the physicist’s state of knowledge or ignorance expressed by the object language, and it consists of statements making statistical estimates of measurement error."

"The modern quantum theory brought down the Positivist philosophy by occasioning the rejection of the naturalistic thesis of the semantics of descriptive language including notably those terms that the Positivists called observation terms."

"Bohm maintains that semantic incommensurability can be overcome with metaphor. He furthermore says that revolution occurs when a new metaphor is developed, and normal science is the creative unfolding of that new metaphor."

"The term “unpack” in connection with semantical analysis is a phrase used by the early Pragmatist philosopher William James, although Hanson does not reference James."

"[T]he concepts of wave and particle had undergone semantical change with the advance of physical experiment and theory."


"The only way the Copenhagen wave-particle duality thesis can be affirmed consistently is to let the equations control the semantics of the terms "wave" and "particle", as these terms relate to the descriptive variables in the mathematically consistent formalism."

"Letting the consistent mathematical formalism of the theory control its semantics and thus the ontology its semantics describes, enables the new theory to supply a new semantics and ontology. But recognition of semantical change does not resolve the central ontological issues associated with the quantum theory. In fact there is no compelling evidence either from experiment or from the formalism of the quantum theory for the Copenhagen ontology. Whether the wave and particle are two alternative manifestations of the same entity, as Bohr and Heisenberg say, or whether they are copresent but separate entities, as de Broglie and Bohm say, or whether the particle is the only real entity, as Lande says, or whether the wave is the only real entity, as Schrödinger says - are all different ontological commitments that cannot be decided by reference to the mathematical syntax, because mathematics does not reference entities, or in Carnap’s phraseology it is not a “thing language”."

"The mathematical syntax does not express instantiation in things or entities like the syntax of the Aristotelian categorical logic, the Russellian predicate calculus, or ordinary language."

"[I}n the Russellian predicate calculus quantified (or bound) variables also reference entities, although in the Russellian predicate calculus ontology and quantification are commingled so that the syntax implies nominalist ontology, such that one may blithely ignore such subtleties as simple or personal supposition, and say with Quine that in the Russellian predicate calculus to be is to be the value of a variable."


"Thus each ontological interpretation for quantum theory can be construed as realist, but only to the extent that the theories are empirically warranted. Thus scientific realism does not resolve issues of ontology."

"Due to ontological relativity the empirical under-determination of language carries over into ontology, and the unresolved ontological issues in quantum theory result from the empirical underdetermination of the theory and its associated test design language."

"In a conventional generic sense the term “analogy” might include metaphor and simile, because they are all figures of speech expressing similarity. But in its more restrictive sense based on the idea of a grammatical form, it is a compound sentence having two independent clauses connected with the conjunction “as”. The typical form is “A is to B as C is to D.” For example: “The electron is to the atomic nucleus as a planet is to the sun.”"

And so on.