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Physics World

Problems with “measurement”

Walter Whitham

Published May 1, 1991• 0 citations
Publisher

Abstract

Bohr is said to have remarked that anybody who is not shocked by quantum theory has not understood it. No physicist, however, challenges its practical usefulness in predicting experimental results and providing an explanatory framework for an enormous range of study. Nevertheless, more thoughtful physicists have been astonished and disturbed by what is implied when attempts are made to interpret its meaning. As a result a variety of ingenious, and sometimes bizarre, schemes have been devised since its inception in order to make these implications more acceptable to the scientific mind. Some of these schemes have resulted in proposals which appear stranger than the problems they have been designed to resolve. After some sixty years there is no consensus of opinion upon the solution of the epistemological problems posed. Indeed the debate keeps on resurfacing in the scientific literature and continues to generate library shelves of books. Some progress, however, has been made and the late John Bell himself and the experimental work of Alain Aspect have demonstrated that some epistemological positions cannot be sustained.

DOI
10.1088/2058-7058/4/5/14

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Bohr is said to have remarked that anybody who is not shocked by quantum theory has not understood it. No physicist, however, challenges its practical usefulness in predicting experimental results and providing an explanatory framework for an enormous range of study. Nevertheless, more thoughtful physicists have been astonished and disturbed by what is implied when attempts are made to interpret its meaning. As a result a variety of ingenious, and sometimes bizarre, schemes have been devised since its inception in order to make these implications more acceptable to the scientific mind. Some of these schemes have resulted in proposals which appear stranger than the problems they have been designed to resolve. After some sixty years there is no consensus of opinion upon the solution of the epistemological problems posed. Indeed the debate keeps on resurfacing in the scientific literature and continues to generate library shelves of books. Some progress, however, has been made and the late John Bell himself and the experimental work of Alain Aspect have demonstrated that some epistemological positions cannot be sustained.
Surely, after 62 years, we should have an exact formulation of some serious part of quantum mechanics? By ‘exact’ I do not of course mean ‘exactly true’. I mean only that the theory should be fully formulated in mathematical terms, with nothing left to the discretion of the theoretical physicist...until workable approximations are needed in applications. By ‘serious’ I mean that some substantial fragment of physics should be covered. Nonrelativistic ‘particle’ quantum mechanics, perhaps with the inclusion of the electromagnetic field and cut-off interaction, is serious enough. For it covers ‘a large part of physics and the whole of chemistry’ (P A M Dirac 1929 Proc. R. Soc.A 123 714). I mean too, by ‘serious’, that ‘apparatus’ should not be separated off from the rest of the world into black boxes, as if it were not made of atoms and not ruled by quantum mechanics.
Quantum mechanics is our most successful physical theory. It underlies our very detailed understanding of atomic physics, chemistry, and nuclear physics, and the many technologies to which physical systems in these regimes give rise. Additionally, relativistic quantum mechanics is the basis for the standard model of elementary particles, which very successfully gives a partial unification of the forces operating at the atomic, nuclear, and subnuclear levels. However, from its inception the probabilistic nature of quantum mechanics, and the fact that “quantum measurements” in the orthodox formulation appear to require the intervention of non-quantum mechanical “classical systems,” have led to speculations by many physicists, mathematicians, and philosophers of science that quantum mechanics may be incomplete. Among the Founding Fathers of quantum theory, Einstein and Schrödinger were both of the opinion that quantum mechanics is in some way unsatisfactory, and this view has been amplified in more recent profound work of John Bell, among others. In an opposing camp, many others in the physics, mathematics, and philosophy communities have attempted to provide an interpretational foundation in which quantum mechanics remains a complete and self-contained system. Among the Founding Fathers, Bohr, Born, and Heisenberg maintained that quantum mechanics is a complete system, and a number of recent proposals have been made to improve upon or to provide alternatives to their “Copenhagen Interpretation.” The debate continues, and has spawned an enormous literature.
While there is general agreement that quantum theory poses a fundamental challenge to the classical worldview, there is none on what worldview should replace it. This lack of clear positive implications is the heart of the interpretation problem in quantum theory, or understanding what the world must be like assuming the theory is true. The difficulty is twofold. First, if the theory is correct and complete then there seems to be no way to adjudicate empirically among its interpretations, forcing us to rely on metaphysics instead. Second, the classical metaphysics upon which human beings have relied in the past to interpret new theories is now itself problematic, leaving us without an interpretive backstop to anchor our thinking. Bell is surely right in expecting whatever picture of reality eventually emerges from quantum theory to “astonish us,” but by the same token it is very hard to see what that picture should be. In this chapter I address the debate about the positive worldview implications of quantum theory. Of all the chapters in this book it is the farthest removed from the concerns of social scientists. However, it plays an important dialectical function in my argument, which is to introduce and help justify the panpsychist interpretation of quantum theory that I will embrace and discuss at more length in Chapter 6. By ‘justify’ I do not mean that I will defend this interpretation as superior to others. My purpose is more modest, which is simply to show why, despite what might seem to be its bizarre and counter-intuitive nature, panpsychism is taken quite seriously by philosophers of physics as a way to interpret quantum theory. That's because (a) there are strong analogies between quantum systems and the human mind, and (b) the alternatives are equally bizarre and counter-intuitive. If readers are prepared to accept that panpsychism is a valid approach to the mind–body problem, then this chapter may be skipped – which I have made less costly by deferring until Chapter 6 a discussion of time-symmetric approaches like the Transactional Interpretation, which will play an important role later in the book.
Abstract While its applications have made quantum theory arguably the most successful theory in physics, its interpretation continues to be the subject of lively debate within the community of physicists and philosophers concerned with conceptual foundations. This situation poses a problem for a pragmatist for whom meaning derives from use. While disputes about how to use quantum theory have arisen from time to time, they have typically been quickly resolved, and consensus reached, within the relevant scientific sub-community. Yet rival accounts of the meaning of quantum theory continue to proliferate. This essay offers a diagnosis of this situation and outlines a pragmatist solution to the problem it poses, leaving further details for subsequent essays.