Recent discussions in the physical literature, designed to clarify the logical position of modern physical theory, have brought to light an amazing divergence of fundamental attitudes which may well bewilder the careful student of physics as well as philosophy. Quantum mechanics, representing an abstract formalism, should be capable of having its logical structure analyzed with great precision like any other mathematical discipline. Its consequences in all problems to which its method can be applied are so unambiguous, consistent, and successful in (...) predicting physical experience as to disperse immediately all thoughts of possible discrepancies in its fundamental texture. Yet it must be said that even the founders of quantum theory are not in harmony in their various expositions of the bases of that theory. However, while this situation seems disquieting on the face of it, there is no cause for serious brow raising, for it is a fact that there exists agreement with regard to the central axioms of the theory, and that the ambiguities affect only their philosophical interpretation, a field in which differences of opinion may at present be honestly entertained. (shrink)

In this sequence of philosophical essays about natural science, the author argues that fundamental explanatory laws, the deepest and most admired successes of modern physics, do not in fact describe regularities that exist in nature. Cartwright draws from many real-life examples to propound a novel distinction: that theoretical entities, and the complex and localized laws that describe them, can be interpreted realistically, but the simple unifying laws of basic theory cannot.

Many of the experiments that produced the empirical basis of quantum mechanics relied on classical assumptions that contradicted quantum mechanics. Historically this did not cause practical problems, as classical mechanics was used mostly when it did not happen to diverge too much from quantum mechanics in the quantitative sense. That fortunate circumstances, however, did not alleviate the conceptual problems involved in understanding the classical experimental reasoning in quantum-mechanical terms. In general, this type of difficulty can be expected when a coherent (...) scientific tradition undergoes a theoretical upheaval. The problem may be circumvented through the use of phenomenological theory in experimentation during the period of theoretical instability. (shrink)

The direct use of a physical law for the purpose of measurement creates a problem of circularity: the law needs to be empirically tested in order to ensure the reliability of measurement, but the testing requires that we already know the value of the quantity to be measured. This problem is discussed through some detailed examples of energy measurements in quantum physics; three major methods are analyzed in their interrelation, with a focus on the method of “material retardation.” It seems (...) that the only reasonable solution is to establish the law needed for the measurement by relying on an alternate method of measurement. This solution is also circular, since it amounts to letting different measurement methods justify each other. However, this circularity can be fruitful for the process of concept building; meaning can be created in a web of interconnected measurement methods. (shrink)

Murdoch describes the historical background of the physics from which Bohr's ideas grew; he traces the origins of his idea of complementarity and discusses its meaning and significance. Special emphasis is placed on the contrasting views of Einstein, and the great debate between Bohr and Einstein is thoroughly examined. Bohr's philosophy is revealed as being much more subtle, and more interesting than is generally acknowledged.

This article explains why Bohr does not need to discuss the projection postulate or the "problem of measurement". Beginning with a thumbnail sketch of Bohr 's general views, it is argued that Bohr interprets the state function as giving a statistical summary of experimental outcomes. Against the objection that Bohr was too much a microrealist to endorse such an instrumentalist statistical interpretation it is suggested that he rejected the issue of microrealism as not well formed. It is shown that on (...) his statistical interpretation Bohr does not need the projection postulate or face the usual problem of measurement. (shrink)

If we take the state function of quantum mechanics to describe belief states, arguments by Stairs and Friedman-Putnam show that the projection postulate may be justified as a kind of minimal change. But if the state function takes on a physical interpretation, it provides no more than what I call a fortuitous approximation of physical measurement processes, that is, an unsystematic form of approximation which should not be taken to correspond to some one univocal "measurement process" in nature. This fact (...) suggests that the projection postulate does not provide a proper locus for interpretive investigation. Readers will also find section 3's analysis of fortuitous approximations of independent interest and presented without the perils of quantum mechanics. (shrink)