In this essay, I'll present an example of counterfactual physical phenomena. More precisely, counterfactual definiteness and interaction-free measurements in quantum mechanics. The example used will be the Elitzur-Vaidman bomb testing experiment, which shows how we can probe the properties of objects, even when they have not been measured, i. e., counterfactual measurements. This type of physical phenomenon seems to operate by the same laws of causality as counterfactual reasoning in decision-making. After all, how can something that doesn't happen affect the (...) real world? I suggest that some mathematical tools used in quantum mechanics may be of interest to those who wish to better model counterfactual possibilities in the decision process or philosophers interested in better understanding the metaphysical implications of quantum mechanics. (shrink)

Robert Griffiths has recently addressed, within the framework of a ‘consistent quantum theory’ that he has developed, the issue of whether, as is often claimed, quantum mechanics entails a need for faster-than-light transfers of information over long distances. He argues that the putative proofs of this property that involve hidden variables include in their premises some essentially classical-physics-type assumptions that are not entailed by the precepts of quantum mechanics. Thus whatever is proved is not a feature of quantum mechanics, but (...) is a property of a theory that tries to combine quantum theory with quasi-classical features that go beyond what is entailed by quantum theory itself. One cannot logically prove properties of a system by establishing, instead, properties of a system modified by adding properties alien to the original system. Hence Griffiths’ rejection of hidden-variable-based proofs is logically warranted. Griffiths mentions the existence of a certain alternative proof that does not involve hidden variables, and that uses only macroscopically described observable properties. He notes that he had examined in his book proofs of this general kind, and concluded that they provide no evidence for nonlocal influences. But he did not examine the particular proof that he cites. An examination of that particular proof by the method specified by his ‘consistent quantum theory’ shows that the cited proof is valid within that restrictive version of quantum theory. An added section responds to Griffiths’ reply, which cites general possibilities of ambiguities that might make what is to be proved ill-defined, and hence render the pertinent ‘consistent framework’ ill defined. But the vagaries that he cites do not upset the proof in question, which, both by its physical formulation and by explicit identification, specify the framework to be used. Griffiths confirms the validity of the proof insofar as that pertinent framework is used. The section also shows, in response to Griffiths’ challenge, why a putative proof of locality that he has described is flawed. (shrink)

In a recent paper Griffiths [38] has argued, based on the consistent histories interpretation, that Hilbert space quantum mechanics is noncontextual. According to Griffiths the problem of contextuality disappears if the apparatus is “designed and operated by a competent experimentalist” and we accept the Single Framework Rule. We will argue from a representational realist stance that the conclusion is incorrect due to the misleading understanding provided by Griffiths to the meaning of quantum contextuality and its relation to physical reality and (...) measurements. We will discuss how the quite general incomprehension of contextuality has its origin in the ''objective-subjective omelette'' created by Heisenberg and Bohr. We will argue that in order to unscramble the omelette we need to disentangle, firstly, representational realism from naive realism, secondly, ontology from epistemology, and thirdly, the different interpretational problems of QM. In this respect, we will analyze what should be considered as Meaningful Physical Statements within a theory and will argue that Counterfactual Reasoning -considered by Griffiths as ''tricky''- must be accepted as a necessary condition for any representational realist interpretation of QM. Finally we discuss what should be considered as a problem in QM from a representational realist perspective. (shrink)