In this paper I consider the problem of interpreting quantum mechanics. I argue that this problem has evolved in part into the problem of selecting tenable interpretations from a set of available interpretations. We lack the means to make this selection. There is consensus that interpretations should be consistent and empirically adequate. But these conditions are not particularly discriminative. Other conditions may be discriminative but are not generally accepted. I propose two new conditions for selecting tenable interpretations, motivated by the use of quantum mechanics in technology. The first requires that interpretations ascribe the physical properties to technical artefacts that are entailed by the ascription of technical functions to those artefacts. The second requires that they ascribe the physical properties represented by engineering sketches of those artefacts. I consider the example of quantum teleportation in some detail. 1. Introduction 2. The problem of interpreting quantum mechanics 3. Technical functions 4. Decoders in quantum teleportation 5. Engineering sketches 6. Conclusions Appendix: Quantum teleportation
In this paper I consider the problem of interpreting quantum mechanics. I argue that this problem has evolved in part into the problem of selecting tenable interpretations from a set of available interpretations. We lack the means to make this selection. There is consensus that interpretations should be consistent and empirically adequate. But these conditions are not particularly discriminative. Other conditions may be discriminative but are not generally accepted. I propose two new conditions for selecting tenable interpretations, motivated by the use of quantum mechanics in technology. The first requires that interpretations ascribe the physical properties to technical artefacts that are entailed by the ascription of technical functions to those artefacts. The second requires that they ascribe the physical properties represented by engineering sketches of those artefacts. I consider the example of quantum teleportation in some detail. 1. Introduction 2. The problem of interpreting quantum mechanics 3. Technical functions 4. Decoders in quantum teleportation 5. Engineering sketches 6. Conclusions Appendix: Quantum teleportation
INTRODUCTION In 1965 Hilary Putnam published the standard work on the interpretation of quantum mechanics, a piece that all philosophers of quantum mechanics of the time had to come to terms with. He laid out one-by-one in a clear non-technical way each of the available approaches to the problem and explained, again non-technically but very exactly, what is wrong with them. In his own final words Putnam took ‘the modest but essential step of becoming clear on the nature and magnitude of the difficulties’ (1965, 158). In the almost forty years since there have been a variety of advances, technical developments and new points of view. But none of these is uncontroversial. In fact each suffers from some one or another of the very difficulties that Putnam summarised. Many of the newer approaches explain why the problem is not a problem after all; a few bury the problems in technical detail; and some make heroic assumptions, often metaphysical, that cause the problems to disappear. My conclusion surveying the contemporary literature is the same as Putnam's in 1965: ‘no satisfactory interpretation of quantum mechanics exists today’ (1965, 157). The time scale is amazing. Putnam's important piece was written forty years after the first formulations and successes of quantum mechanics. I am writing forty years later, and about a theory that has transformed our technology and our way of thinking about the world. Why does this theory still have ‘no satisfactory interpretation’?
Whereas the technological applications of quantum mechanics are extraordinarily abundant, its ontological implications are very controversial. Not only did several interpretations of the original quantum formalism develop throughout the last century, but modifications of the primitive formalism were also proposed, introducing new relevant theoretical elements, which gave rise to very different quantum ontologies. This article highlights that the diversity of quantum ontologies reveals the impossibility of establishing an exclusive inference from the empirical success of a theory and its ontological truth. Since scientific objectifications in general —and those of quantum mechanics in particular— have a limited cognitive scope, they don’t allow choosing a specific interpretation of the theory among the many possible ones, so that meta-scientific criteria are required.
In this contribution I consider the consequences of using quantum me- chanics in nanoscale technology. I argue that this use leads to a problem that poses a two-sided challenge for interpretations of quantum mechanics. Firstly I present the problem: engineers typically ascribe technical functions to artifacts; function ascrip- tions imply particular physical descriptions of artifacts, and quantum mechanics sometimes fails to reproduce these descriptions. This problem may be solved by adopting an interpretation of quantum mechanics. An interpretation turns quantum mechanics into a theory that gives richer physical descriptions and that may repro- duce the physical descriptions implied by function ascriptions. It can be shown, however, that not all interpretations fulfill this promise. Secondly I argue that these results amount to a two-sided challenge. It challenges philosophers of physics to provide an interpretation that gives nano-engineers rich enough quantum-mechanical descriptions to ascribe functions to artifacts. And it challenges engineers to help phi- losophers of physics with selecting tenable interpretations. Philosophers of physics are in need of tests for judging the different existing interpretations, and nano- engineers can provide such tests by requiring that interpretations should reproduce the function ascriptions to the artifacts they design. A nanoscale technology example I consider is quantum teleportation.
As a last step towards general conclusions, I collect and assess the more important results obtained in the previous chapters. In the next and final chapter I then consider the question of whether the modal descriptions of reality meet the demands of being well developed, empirically adequate and metaphysically tenable. Indefinite properties and inexact magnitudes The bi, spectral and atomic modal interpretations do manage to interpret quantum mechanics by providing a description of what reality could be like in terms of systems possessing properties. Moreover, if one accepts the full property ascription (5.12) as developed in Section 5.4, this description of reality satisfies a number of desirable conditions. However, these modal interpretations do not simultaneously ascribe all the possible properties to a system. Instead they select at each instant a specific subset of the properties pertaining to a system and ascribe only these. And the properties which are not selected are taken to be indefinite. This possibility that properties of systems are sometimes not definite is in itself not that problematic for in some cases it is perfectly understandable what this means. Consider again the example of a tossing coin. During the toss the properties ‘heads’ and ‘tails’ can be said to be indefinite and this can be understood as meaning that these two properties are applicable only to coins which lie on surfaces. However, in other cases it is less clear what is going on.
Abstract This chapter surveys various proposals to interpret—that is, make sense of—quantum mechanics. We could attempt to think of quantum mechanics in purely instrumentalist terms, as an algorithm to predict observed experimental results. But this fits badly with scientific practice and is probably not viable. We could attempt to modify quantum mechanics itself to resolve the paradoxes, and there are some simple models that attempt to do that: some are ‘hidden-variable’ theories that add extra properties to the theory, some are ‘dynamical-collapse’ theories that modify the theory’s equations. But none of these models succeed in reproducing quantum theory’s predictions outside a relatively narrow range of applications. Or we could try to take the apparent indefiniteness of quantum mechanics literally, and interpret it as a theory of many parallel worlds. The correct interpretation of quantum mechanics remains controversial, but the search for understanding and interpretation of the theory has led to very substantial scientific results and is likely to lead to more.
This paper deals with the problem of the interpretation of quantum mechanics, the nature of physical theory, and the future of physics. First, the question of why there are so many different interpretations of quantum mechanics proposed and accepted by outstanding quantum experts is treated. This requires a discussion of the relation between physics and philosophy and drawing a distinction between a physical formalism and a physical explanation. The Copenhagen interpretation is considered, criticized, and found to be unsatisfactory in some respects. Finally, an interpretation that contains ideas from previous interpretations but which may itself be new, is proposed. Hopefully, this is superior to the previous interpretations. It has, I believe, the advantage of logical clarity. In the process of doing this, I introduce a theory of levels of physical theory, according to which microscopic physical theory, as it develops in successive stages, becomes more and more adaptable to explaining—or at least taking cognizance of—fundamental biological or ultimately psychological phenomena.