Cambridge University Press eBooks

Speakable and unspeakable, past and future

Aephraim M. Steinberg

Published Apr 22, 2004• 2 citations

Abstract

Introduction A volume in honor of a visionary thinker such as John Archibald Wheeler is a rare license to exercise in the kind of speculation and exploration for which Wheeler is famous, but which most of the rest of us usually feel we had better keep to ourselves. We have all – even those of us who never had the fortune to work directly with him – been inspired and motivated by Wheeler's creativity and open-mindedness. For all of our apparent understanding of quantum mechanics, our ability to calculate remarkable things using this theory, and the regularity with which experiment has borne out these predictions, at the turn of the twenty-first century it seems there are as many puzzles on the road to a true understanding of quantum theory as there were at the start of the previous century. Then, at least, one could hope to be guided by the mysteries of unexplained experiment. Now, by contrast, we may seem to have lost our way, as even though our experiments are all “explained” (in some narrow sense which can only be deemed satisfactory out of fear to leap beyond the comfortable realm of formalism), the theory itself is mysterious. Further explorations, without the anchor of experiment, certainly run the risk of becoming mere flights of metaphysical fancy, giving rise to factions characterized less by intellectual rigor than by fundamentalist zeal. Yet it would be premature to give up the journey before at least trying to establish a foothold on the terrain ahead.

DOI: 10.1017/cbo9780511814990.015

Related papers

Quantum Mechanics

Peter E. Hodgson

The difﬁculties of the old quantum theory were largely dispelled by the development of quantum mechanics in the 1920s. First Heisenberg (1925) developed the rather abstract matrix mechanics and soon after Schro¨dinger (1926; see also Eckart, 1926) developed the physically more appealing wave mechanics. Subsequently he showed them to be mathematically equivalent. The physicists were greatly relieved; now they had once again a mathematical formalism that enabled the results of experiments to be calculated. It was possible to move forward. It is certainly a very elegant and indeed beautiful formalism, and does enable the results of many physical measurements to be calculated with great accuracy. It is used daily by atomic and nuclear physicists; there is no other way to make calculations. From the earliest days there has been intense debate about the interpretation of quantum mechanics, and it shows no signs of being settled; if anything it is becoming more intense over the years. As Penrose has remarked, no one understands quantum mechanics. Feynman (1967; see also Sykes, 1994) also admitted that ‘nobody understands quantum mechanics’, and Einstein once remarked: ‘I have thought a hundred times as much about the quantum problems as I have about general relativity theory’ (Pais, 1994, p. 57). It should therefore be evident that the most that can be done here is to try to show where the real difﬁculties lie, and how the failure to recognize that quantum mechanics is an essentially statistical theory has led to a series of confusing quantum paradoxes. It is just these paradoxes that have often been used to support theological speculations. It is useful to ask what ‘understanding quantum mechanics’ actually means. Certainly it means being able to calculate the results of many measurements. The same applies to Newton’s theory of gravitation, which we understand in the sense that we can use it as a basis of calculation, although we do not really understand the gravitational force itself. Very often, especially in modern physics, the mathematical formalism does not give us the sort of intuitive physical feeling for what is going on that we often obtain from classical mechanics. Perhaps we can never achieve more than this for quantum mechanics. In classical mechanics we can assume that a property that is measured objectively exists prior to the interaction of the measuring apparatus with the observed system. Quantum mechanics, however, ‘is incompatible with the proposition that measurement discovers some unknown but pre-existing property’ (Peres, 1997, p. 14). There is an important distinction between mysteries and absurdities. We may be forced to live with mysteries, but there is no reason why we should put up with absurdities such as the wave-particle duality, tunnelling through potential barriers, acausal events and the collapse of the wave function. These are the quantum paradoxes that will be discussed later on. They arise within the Copenhagen interpretation of quantum mechanics and are solved by other interpretations. These alternative interpretations enable us to make conjectures about what is going on, even though we cannot understand it in detail. This is acceptable and a stimulus to further research. It is certainly difﬁcult enough to understand quantum mechanics, but there is no need to try to visualize logical absurdities in the effort to do so. Quantum mechanics is a mathematical formalism that makes it possible to calculate the results of some experiments. Anything more than this, such as questions about the interpretation of what is measured and whether it tells us what is actually going on in the system being studied, belongs to philosophy. Thus we are concerned here with what is essentially a philosophical debate; if it were just a matter of physics the debate would have been settled long ago. One of the difﬁculties is that it invokes the results of experiments and uses the language of quantum mechanics. Inevitably this language uses philosophical terms and then it is easy to give the impression that the philosophical propositions are in some way entailed by the physical results. These in turn can inﬂuence theological thinking. In order to be quite clear which arguments are justiﬁed and which are not, it is essential to separate the three levels of discourse: physical, philosophical and theological. Our task is to relate these together, and this immediately raises the traditional problems of the philosophy of science, including the relation of experiment to theory, and of theory to explanation. We begin by discussing experiments, distinguishing between those that are real and those that are imaginary.

Routledge eBooksSep 8, 20170 citations

Editors' preface

John David Barrow, P. C. W. Davies, Charles L. Harper

This book project began as part of a special program, Science and Ultimate Reality , developed in honor of the ninetieth birthday of renowned theoretical physicist John Archibald Wheeler. Having long yearned for a comprehensive, integrated understanding of the nature of the universe, Wheeler has blended scientific rigor with an unusually adventurous approach to research in physics and cosmology over a career spanning almost 70 years. Known for investigating many of the most fundamental and challenging issues in physics, Wheeler has often worked at the frontiers of knowledge where science and philosophy meet, probing the deep nature of physical reality. His vision, shaped in part by his influential mentor Niels Bohr, still flourishes today amid ongoing research activities pursued by several generations of those he has influenced over the course of much of the twentieth century. With Wheeler as its inspiration, the Science and Ultimate Reality program was developed with a focus on the future. It brought together a carefully selected group of outstanding contemporary research leaders in the physics community to explore the frontiers of knowledge in areas of interest to Wheeler and to map out major domains and possibilities for far-reaching future exploration. Its two principal components – (1) this book and (2) a previously held symposium – were developed to take Wheeler's vision forward into a new century of expanding discovery.

Cambridge University Press eBooksApr 22, 20040 citations

Why the quantum? “It” from “bit”? A participatory universe? Three far-reaching challenges from John Archibald Wheeler and their relation to experiment

Anton Zeilinger

Introduction First a word of thanks. When I first came across the papers of John Archibald Wheeler on the foundations of quantum mechanics, most of them reprinted in Wheeler and Zurek (1983), I could not believe what I read. Finally here was a colleague of worldwide reputation, given his many contributions to theoretical physics, who was not afraid to discuss openly the conceptual problems of quantum mechanics. The outstanding feature of Professor Wheeler's viewpoint is his realization that the implications of quantum mechanics are so far-reaching that they require a completely novel approach in our view of reality and in the way we see our role in the universe. This distinguishes him from many others who in one way or another tried to save pre-quantum viewpoints, particularly the obviously wrong notion of a reality independent of us. Particularly remarkable is Professor Wheeler's austerity in thinking. He tries to use as few concepts as possible and to build on this the whole of physics. A fascinating case in point is the title of one of his papers “Law without law,” the attempt to arrive at the laws of nature without assuming any law a priori. For me personally his work on fundamental issues in quantum mechanics has been particularly inspiring. The questions he raises are exceptionally far-reaching and some of his concepts in the foundations of physics are so radical that calling them revolutionary would not do them justice.

Cambridge University Press eBooksApr 22, 200458 citations

Introduction

Hans Halvorson

No scientific theory has caused more puzzlement and confusion than quantum theory. Beginning in 1900, the theory developed in fits and starts and found a consistent mathematical framing only when John von Neumann published his Mathematische Grundlagen der Quantenmechanik in 1932 [12]. But even today, we struggle to understand the world as pictured by quantum theory. Physics is supposed to help us to understand the world, and yet quantum theory makes it seem a very strange place. One might be tempted to push aside our puzzlement as the result of our clinging to a primitive worldview. But our puzzlement is not merely a psychological obstacle; it is also an obstacle to the development of physics itself. This obstacle is encountered primarily in our attempts to unify quantum theory and the general theory of relativity. As argued persuasively by Chris Isham (who is represented in this volume), Lee Smolin [10], and others, the primary obstacle between us and future physics is our own failure to understand the conceptual foundations of current physical theories. How, then, are we to make conceptual progress? What is the process by which we find a new perspective, a perspective in which previously puzzling phenomena find a place in an intelligible—and perhaps beautiful—structure? I do not wish to make prescriptions or to claim that conceptual progress can be achieved in only one way. But this book begins with the Ansatz that conceptual progress might be achieved through free creations of the human intellect.

Cambridge University Press eBooksApr 18, 20110 citations

Overview

Richard A. Healey

No interpretation of quantum mechanics can be wholly comprehended or validated before carefully investigating all of its details. I begin such an investigation of the present interpretation in the next chapter. But some of these details will prove rather intricate. The reader may need help in seeing the forest formed by the trees, and the skeptical reader may require encouragement before he or she agrees to enter its thickets. In this first chapter I therefore present a preliminary account of the basic ideas of the interpretation to be given, which may serve as a guide to what is to follow. Just as parts of a travel guide may seem puzzling before one actually visits the region described, so also parts of this chapter will likely seem much clearer when they are reread in the light of the rest of the book. There is another reason for beginning with a general overview. The present interpretation arose as what seemed to be the most promising way of implementing a certain general approach to quantum theory. But, though I am confident of the worth of this approach, the present interpretation may well come to be regarded as only a fruitful first attempt at its detailed implementation, requiring more or less extensive technical revision if it is to prove ultimately satisfactory. If so, this overview may continue to be useful as a guide to an interpretation whose technical framework differs more or less radically from that underlying the present interpretation.

Cambridge University Press eBooksNov 24, 19890 citations

Quantum theory and reality

Roger Penrose

Abstract In the previous chapter, we have been trying to come to terms with the puzzling Z-mysteries of quantum theory. Although not all of these phenomena have been experimentally tested—such as quantum entanglement over distances of several light years—there is already enough experimental support for effects of this kind to tell us that Z-mysteries are indeed things that we must take seriously as true aspects of the behaviour of the constituents of the world in which we live.

Aug 22, 19967 citations