The Quantum Dissidents: Rebuilding the Foundations of Quantum Mechanics (1950-1990)

By Olival Freire Junior

This book tells the fascinating story of the people and events behind the turbulent changes in attitudes to quantum theory in the second half of the 20th century. The huge success of quantum mechanics as a predictive theory has been accompanied, from the very beginning, by doubts and controversy about its foundations and interpretation. This book looks in detail at how research on foundations evolved after WWII, when it was revived, until the mid 1990s, when most of this research merged into the technological promise of quantum information. It is the story of the quantum dissidents, the scientists who brought this subject from the margins of physics into its mainstream. It is also a history of concepts, experiments, and techniques, and of the relationships between physics and the world at large, touching on themes such as the Cold War, McCarthyism, Zhdanovism, and the unrest of the late 1960s.

• Language: English
• Publisher: Springer
• Release date: Dec 26, 2014
• ISBN: 9783662446621

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Olival Freire Junior

The Quantum DissidentsRebuilding the Foundations of Quantum Mechanics (1950-1990)

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Olival Freire Junior

Instituto de Física – UFBa Campus de Ondina, Salvador, Brazil

ISBN 978-3-662-44661-4e-ISBN 978-3-662-44662-1

DOI 10.1007/978-3-662-44662-1

Springer Heidelberg New York Dordrecht London

Library of Congress Control Number: 2014955612

© Springer-Verlag Berlin Heidelberg 2015

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To Olival and Antonieta, my parents, in memory.

To Vitor, Fátima, Inês, and Silvana, with love.

Preface

Olival Freire’s The quantum dissidents – Rebuilding the foundations of quantum mechanics 1950-1990 is a compelling, important book. It is also a remarkable book. At one level it is a richly documented history of how the foundations of quantum mechanics were formulated and variously interpreted from 1925 until the 1990s. Special emphasis is given to the developments from the 1950s on, and two threads are initially followed that eventually combine. The first has as its point of departure, the interpretation of the mathematical formalism of quantum mechanics that David Bohm and Hugh Everett formulated in the early 1950s. Bohm’s was a deterministic interpretation in contrast to the conventional probabilistic one, and Everett’s became known as a many world formulation of quantum mechanics. Their interpretations differed radically from those by the founding fathers, in particular the ones formulated by Werner Heisenberg, by Wolfgang Pauli, and by Niels Bohr, that became amalgamated and loosely referred to as the Copenhagen interpretation. Freire begins the second thread with Eugene Wigner’s post-World War II critical analysis of John von Neumann’s formulation of the measurement process as framed in his Mathematische Grundlagen der Quantenmechanik in 1932. The two threads became intertwined as foundational issues assumed greater legitimacy in the late 1950s. A new phase opened in the early 1960s when John Bell showed how to quantitatively address the quantum weirdness exhibited by entanglement and non-locality, and John Clauser and Abner Shimony indicated how to translate these insights into executable experiments. Alain Aspect’s definitive experiments in the early 1980s confirmed the validity of quantum mechanics and corroborated what John Archibald Wheeler had said regarding delayed choice experiments, namely that no phenomenon is a phenomenon until it is an observed phenomenon. Research on the foundations of quantum mechanics became highly regarded by the community after Aspect’s experiments. The subsequent refinements of these experiments made them critically relevant to computer science and helped establish the field of quantum information, one of whose aims is to revolutionize computing, and another is to make the transmission of information absolutely secure and thereby revolutionizing cryptography. All these developments are beautifully expounded by Freire.

If The quantum dissidents contained only its detailed, internalist, presentation of the history of how the foundations of quantum mechanics became differently interpreted, this would already be a most impressive accomplishment by virtue of the command and synthesis of the huge amount of materials Freire had gathered and made use of: personal interviews, the American Physical Society’s Center for the History of Physics’ as well as other interviews, biographies, documents from numerous archives, correspondences, published articles and books, unpublished notes and papers, annotations to papers, …. And equally impressive is the fact that Freire explains all the physics he presents in a readily accessible, accurate, clear, succinct fashion. For example, we learn what the measurement problem is, how it became a foundational issue, and why by virtue of the extreme fineness of the level structure of a macroscopic body when described quantum mechanically, its interactions with its surrounding can never be neglected and that it can never be considered a closed system. This is the basis of the decoherence mechanism that Dieter Zeh, Wojciech Zurek, and others have introduced in order to explain how definitive pointer readings come about in the quantum mechanical description of the measurement process. Today, by virtue of these advances a complete quantum mechanical description of the measurement process is almost at hand.

But Freire wanted his presentation to be more than a longue durée internalist narration of the history of the changes in the conceptualization of the foundations of quantum mechanics brought about by the investigations of various theorists who dissented from the orthodox view. He wanted to understand why investigating foundational questions regarding quantum mechanics was actively discouraged until the 1960s. And in addition to answers to questions such as: What were the factors that led these dissenters to choose issues from the foundations of quantum mechanics as research themes? What issues did each one of them come to grips with? What were the favorable factors, and what were the obstacles to their activities? And to what extent did they succeed in their endeavor? Freire wanted to know in what ways the political and cultural contexts made the change possible, and in what ways these contexts—as well as ideology and metaphysics—were reflected in the interpretations given.

Considering the founding fathers of quantum mechanics—Heisenberg, Dirac, Pauli, Schrödinger, Bohr—as being off-scale was part of a creation myth and contributed to the belief that all foundational problems had been answered by the Copenhagen interpretation. Similarly, von Neumann, whose axiomatization of quantum mechanics made rigorous mathematical statements regarding the formalism possible, was deemed off-scale among the then off-scale mathematicians. His proof of the impossibility of introducing hidden variables was assumed flawless and went unchallenged until Bell—who was trying to understand the consistency of Bohm’s deterministic interpretation of quantum mechanics with a particle’s position and momentum considered hidden variables—discovered an invalid assumption in von Neumann’s proof. Interestingly, the mistake had been detected in the mid-1930s by Grete Hermann, but because she was primarily a mathematician interested in philosophical problems and perhaps because she was a woman, her finding went unnoticed by the physics community. In any case, physicists during the 1930s were fully occupied successfully extending the boundaries of the applicability of quantum mechanics to solid state and nuclear physics, and exploring its validity at ever smaller distances.

After World War II, the plethora of new precision instruments that became off-shelf equipment in the laboratory, the success of the renormalization program in quantum electrodynamics, masers, lasers, transistors, and PDP computers opened up new worlds in table-top physics. And ever more powerful accelerators did the same in high energy physics. In the United States, the one country whose home grounds had not been devastated by the war, worrying about the foundations of quantum mechanics—when the latter had been responsible for successfully designing an atomic bomb during the war—seemed misguided given all the concrete problems that were being successfully addressed using the conventional interpretation of quantum mechanics to get measurable numbers out. Furthermore, philosophizing had always been looked at askance in the United States and positivistic pragmatism flourished there after it was introduced by Charles Sanders Pierce and William James in the last third of the nineteenth century.

But two new factors altered the postwar political and social contexts of the physics community in the United States. One was the Cold War and the concomitant McCarthyism; the other was the large increase of its physics community—from some 3,000 before the war to over 8,000 after the war— the number of theorists among them and the new status accorded to them. Freire sensitively conveys the consequences of the Cold War and of McCarthyism in his narration of how and why David Bohm formulated his particular interpretation of quantum mechanics. Likewise, the paternalism that bound the physics community and the power it had vested in Bohr and his apostle, Leon Rosenfeld, are clearly described when Freire tells the story of Hugh Everett and of the reception of his relative state formulation of quantum mechanics. Similarly, the crucial importance of the political and cultural contexts is convincingly rendered when Freire analyzes the ways the civil rights movement, the Vietnam war, and the student upheavals transformed what had been deemed good physics and helped bring center stage foundational issues in quantum mechanics in the early 1970s.

One of the outstanding features of the book is its weaving together of professional, cultural, and political contexts with the personal and individual. We thus get short, incisive biographies of the principal actors, their family background, the institutions they were educated in, their mentors and thesis advisors, the universities they became associated with, the resources they could draw on, the encouragement and support they received from colleagues at their home institution, and from the wider physics community. And these presentations are supplemented by sociological insights gleaned from various sources: Pierre Bourdieu on habitus and various forms of capital, the strong program of the sociology of scientific knowledge, Timothy Lenoir, David Kaiser,… In the final chapter of the book, Freire makes use of prosopography to characterize the two dozen or so courageous physicists who were primarily responsible for effecting the dramatic changes in the conceptualization of quantum mechanics, the ones he calls the quantum dissidents. They belonged to different generations, but they all had integrity, were self-confident, and they all shared the belief that issues in foundations of quantum mechanics were worthy enough to be pursued as part of a professional career in physics, and that denying this was a dogmatic attitude. This was the main feature of their dissidence, as most physicists at the time disagreed with this. One other feature stands out as a result of Freire’s analysis. The decisive changes came about by virtue of what a few in that group had done: Bell, Shimony, Clauser, Aspect. The changes were engendered by the actions of individuals making use of the resources of the collectivity they were part of. The seminal paper of John Bell, John Clauser, Abner Shimony, Michael Horne, and Richard Holt seems to be the exception. But it turns out to have resulted from pooling together into one paper the conclusions Bell, Clauser, and Shimony had reached independently. They did so in order to maximize its impact.

Commendations similar to the above can be made regarding Freire’s discussion of philosophical issues. One of the central concerns of the book is explaining how come the same mathematical structure can support so many different physical interpretations. When explaining why this is so, Freire introduces the reader to the Quine-Duhem thesis regarding the under-determination of theories, to concerns with realism, to the equivalence of various mathematical formulations, to what constitutes deterministic or probabilistic explanations, to when are explanations causal, and much else. And Freire always does so simply, concisely and without ostentation.

I would characterize the book as exemplifying what the successful synthesis of the history, sociology, and philosophy of science can accomplish. I can give The quantum dissidents – Rebuilding the foundations of quantum mechanics 1950-1990 no higher compliment than to say that anyone aspiring to become a physicist would become a better one by reading it.

Silvan S. Schweber

Waltham, MA

Archives and Abbreviations

Aage Bohr Papers, Niels Bohr Archive, Copenhagen—ABP

Abner Shimony Papers, ASP.2009.02, Archives of Scientific Philosophy, Special Collections Department, University of Pittsburgh—ASP

Archives for the History of Quantum Physics, American Philosophical Society, Philadelphia, PA—AHQP

Archives of the Italian Physical Society, Bologna—ASIF

Archivio Occhialini, Università degli studi, Milan—AO

Arquivos do CNPq, Museu de Astronomia, Rio de Janeiro—AC

Bohr Scientific Correspondence (BSC–AHQP)

Costas Papaliolios Papers—[Accession 14811], Harvard University Archives—CPP

Guido Beck Papers, Centro Brasileiro de Pesquisas Físicas, Rio de Janeiro—GBP

David Bohm Papers, Birkbeck College, University of London—BP

Eugene Wigner Papers, Manuscripts Division, Department of Rare Books and Special Collections, Princeton University Library—WigP

Everett Papers—American Institute of Physics, College Park, MD—EP

Everett Papers in possession of Mark Everett, available at http://​hdl.​handle.​net/​10575/​1060—ME

Henry Margenau Papers, Manuscripts and Archives, Yale University Library—MP

John Clauser Papers. Clauser’s Personal Archive—JCP

Klaus S. Tausk Personal Archive, São Paulo—KST

Lancelot L. Whyte Papers, Department of Special Collections, Boston University, Boston—LWP

Léon Rosenfeld Papers, Niels Bohr Archive, Copenhagen—RP

John von Neumann Papers, Library of Congress, Washington, DC—JvNP

John Wheeler Papers, American Philosophical Society, Philadelphia, PA—WP

Niels Bohr Library & Archives, American Institute of Physics, College Park, MD, USA—AIP

Norbert Wiener Papers, MC022, Institute Archive, MIT, Cambridge, MA—NWP

Pipkin Papers [Accession 12802], Harvard University Archives—PP

Princeton University Library (Seeley G. Mudd Manuscript Library, Graduate Alumni Records)—GAR

Thomas Kuhn Papers, MC240, Institute Archive, MIT, Cambridge, MA—TKP

Contents

1 Dissidents and the Second Quantum Revolution 1

1.​1 The Dynamics of Change in Science 5

1.​2 Strategy and Historiographica​l Issues 9

References 14

2 Challenging the Monocracy of the Copenhagen School 17

2.​1 Interpretation of Quantum Theory Before David Bohm 17

2.​2 Bohm’s Causal Interpretation of Quantum Mechanics 21

2.​3 Backgrounds of Bohm’s Causal Interpretation 25

2.​3.​1 Trapped in the Cold War Storm 28

2.​3.​2 Bohm, de Broglie, and Pauli:​ Conceptual Issues and Disputes About Priorities 30

2.​3.​3 Exile in Brazil 32

2.​4 Critics and Supporters of the Causal Interpretation 35

2.​4.​1 Supporters 42

2.​4.​2 Mixed Reactions 44

2.​4.​3 The Old Guard 45

2.​4.​4 Bohm’s Proposal and Philosophers of Science 48

2.​5 Waning Causality and Disenchantment with Communism (Late 1950s–Early 1960s) 49

2.​5.​1 Break with Communism 49

2.​5.​2 Causality Relativized 52

2.​5.​3 Abandonment of the Causal Interpretation 54

2.​5.​4 Citizenship Lost, Dignity Preserved 55

2.​5.​5 New Acquaintances:​ Students and Collaborators 57

2.​6 New Perspectives:​ Wholeness and Implicate Order 59

2.​6.​1 Returning to the Quantum Potential 61

2.​7 On the Legacy of a Notable Quantum Dissident 63

2.​7.​1 Historiography on Bohm’s Interpretation 66

References 68

3 The Origin of the Everettian Heresy 75

3.​1 Introduction 75

3.​2 Historical Background:​ The Twilight of the Copenhagen Monocracy 77

3.​2.​1 General Attitude Towards the Foundational Issues in the US 77

3.​2.​2 Bohr and the Quantum Orthodoxy 79

3.​2.​3 The Revival of Dissidence and the Measurement Problem 83

3.​3 The Genesis of Everett’s Thesis 87

3.​3.​1 Everett at Princeton 87

3.​3.​2 The Steps Towards the Dissertation 91

3.​4 The Reasons for Everett’s Discontent 93

3.​4.​1 Standard Formulation 93

3.​4.​2 Dualistic Approach 95

3.​4.​3 Hidden Variables 98

3.​5 Everett’s Project 99

3.​5.​1 A Unitary Model of the World 99

3.​5.​2 Objective Description and Correlations 101

3.​5.​3 Subjective Experience and Probabilities 103

3.​6 Striving for Copenhagen’s Imprimatur 107

3.​7 The Issues at Stake in the Debate 115

3.​7.​1 Symbolism 115

3.​7.​2 Relativity 117

3.​7.​3 Irreversibility 119

3.​7.​4 Words 121

3.​7.​5 Observers 125

3.​8 Epilogue 129

Concluding Remarks 133

References 134

4 The Monocracy is Broken:​ Orthodoxy, Heterodoxy, and Wigner’s Case 141

4.​1 Introduction 141

4.​2 Measurement Problem Before Wigner 142

4.​3 Enter Wigner 149

4.​4 The Heated Dispute:​ Wigner Versus Rosenfeld and the Italians 156

4.​5 The Orthodoxy Splits 161

4.​6 Wigner’s Style of Intellectual Leadership 162

Epilogue and Conclusion:​ Orthodoxy Becomes Heterodoxy 166

References 170

5 The Tausk Controversy on the Foundations of Quantum Mechanics:​ Physics, Philosophy, and Politics 175

5.​1 Introduction 175

5.​2 Scientific Background 176

5.​3 Tausk in Trieste 179

5.​4 Loinger’s and Rosenfeld’s Attacks 181

5.​5 Bohm’s, Jauch’s, and Fonda’s Defenses of Tausk 183

5.​6 Further Developments 185

5.​7 Return to Brazil 187

5.​8 Tausk’s Preprint and the Rosenfeld-Wigner Dispute 188

Conclusions 190

Appendix:​ Summary of Tausk’s Arguments 192

References 193

6 From the Streets into Academia:​ Political Activism and the Reconfiguration of Physics Around 1970 197

6.​1 Introduction 197

6.​2 The Mesh of Science and Politics:​ The Varenna Summer Schools 201

6.​3 The Schools and Their Results 206

6.​3.​1 1970:​ Foundations of Quantum Mechanics 206

6.​3.​2 1972:​ History of Physics in the Twentieth Century 214

6.​4 Ongoing Political Activism and Its Later Fading 218

6.​5 On the Other Side of the Atlantic:​ The Schwartz Amendment 222

6.​6 Physics Today and the Second Life of Everett’s Quantum Proposal 225

Conclusion 228

References 230

7 Philosophy Enters the Optics Laboratory:​ Bell’s Theorem and Its First Experimental Tests (1965–1982) 235

7.​1 Introduction 235

7.​2 Bell’s Theorem, the Context of Its Production, and Its Initial Reception 239

7.​3 Philosophy Enters the Labs:​ The First Experiments 249

7.​4 Settling the Tie and Turning the Page 265

7.​5 New Challenges:​ While the Photons Are in Flight 274

Conclusion 279

References 281

8 The 1980s and Early 1990s, Research on Foundations Takes Off 287

8.​1 Introduction 287

8.​2 The Fate of Bell’s Theorem 290

8.​2.​1 The Ongoing Experiments with Entanglement 297

8.​3 Theoretical and Experimental Breakthrough:​ Decoherence and the Quantum Classical Boundary 301

8.​3.​1 Work on Decoherence:​ Zeh, Leggett, Zurek, and Haroche 305

8.​4 New Techniques and New Experiments in Foundations of Quantum Physics 311

8.​4.​1 Techniques 312

8.​4.​2 Experiments 313

8.​4.​3 The Conspicuous Double Slit Experiment 314

8.​5 Interlude:​ Wheeler’s Perennial Concern with the Quantum 317

8.​6 The Proliferation of Interpretations 319

8.​7 Early Quantum Information Achievements 327

References 331

9 Coda:​ Quantum Dissidents - A Collective Biographical Profile 339

9.​1 Introduction 339

9.​2 Achievements 342

9.​3 Synopsis of the Quantum Controversy Dynamics 343

9.​4 Training, Professional Losses, Philosophical Trends, and Interpretations 344

9.​5 The Quantum Dissidents 346

References 348

Index351

© Springer-Verlag Berlin Heidelberg 2015

Olival Freire JuniorThe Quantum Dissidents10.1007/978-3-662-44662-1_1

1. Dissidents and the Second Quantum Revolution

Olival Freire Junior¹ 

(1)

Instituto de Física – UFBa Campus de Ondina, Salvador, Brazil

Abstract

The second quantum revolution, which may lead to a major technological breakthrough in science and technology with the creation of quantum computers, was the term coined by the French physicist Alain Aspect to describe changes in physics, the beginnings of which date back to the 1960s. To flesh out the new term he brought together two different threads. The first one embraced the emergence of the awareness of the importance of a new physical effect, entanglement. This refers to the quantum description of a composite system which is not reducible to the sum of its parts. It started a conceptual revolution, including the perspective of building quantum computers with calculation power exponentially greater than the best computers of today. The second thread derives from physicists’ ability to isolate, control, and observe single quantum systems such as electrons, photons, neutrons and atoms. Finally these threads merged into the creation of a new field of research entitled quantum information. In Aspect’s formulation, found in his introduction to John Bell’s papers (Speakable and unspeakable in quantum mechanics: collected papers on quantum philosophy. Cambridge University Press, 2004), he posited two quantum revolutions taking place in the twentieth century. The first one, in the first half of the century, created the scientific theory that describes the behavior of atoms, radiation, and their interactions. The second one occurred in the second half and is still evolving, as the promise of quantum computers remains unaccomplished. This book deals with the origins of this alleged second revolution—from the early 1950s to the mid-1990s—and is a historical account of the context and intellectual aspects that arose from the renewal of research on the foundations of quantum physics. It roughly covers the period from the 1950s, when this research gained momentum with the appearance of new interpretations for the mathematical formalism of this physical theory, to the early 1990s, when research on these foundations was established as a promising topic on the agenda of research in physics. As quantum information became a new field of research in the middle of the 1990s, this narrative ends when quantum information as a blossoming field of research starts. This book can thus be regarded as a prehistory of quantum information.

Quantum theory is an exemplary case in the history of physics in that the success of its predictions and explanations coexisted with profound doubts about the soundness of its foundations. However, analogous doubts had appeared with major physical theories such as Newtonian mechanics and thermodynamics. Devices such as lasers and transistors, which dramatically changed science, technology, and society in the second half of the twentieth century, were based on quantum theory. Strange as it may seem, the number of scientists who called for the need to scrutinize its foundations grew over the same period. This recalls the Pascalian view that a broad scope of knowledge leads to restricted certainty about its foundations. Thus, it is legitimate to ask questions such as, Does their instrumental effectiveness stand on the rock of secure concepts or the sand of unresolved fundamentals? (Briggs et al. 2013). Physicists were troubled at the existence of different interpretations for the theory’s mathematical formalism. Indeed, some of them thought that the theory’s foundations were insufficiently established for the next stage in the development of physics. John Bell, one of the most distinguished physicists to work on these issues, used to state that quantum mechanics is rotten, using Hamlet’s famous line in an oblique reference to the father of the standard interpretation of this theory, the Danish physicist Niels Bohr (Gottfried 1991). The doubts about the foundations of quantum theory have become one of the most compelling controversies in the history of science, comparable either to that which pitted Newtonians against Cartesians at the dawn of modern physics or the supporters of energeticism against those of atomism in the late nineteenth century. Since most of the research on the foundations of quantum physics in the second half of the twentieth century was intertwined with controversy that roiled about those foundations, our account focuses on both of these aspects, which we refer to as the quantum controversy.

The quantum controversy, therefore, drew a divide between those who thought that there was nothing further to be researched in the foundations of the theory after they were set by its founding fathers, such as Niels Bohr, Werner Heisenberg, Wolfgang Pauli, Max Born, Pascual Jordan, Paul Dirac, and John von Neumann, and those, mostly from a younger generation, who committed their professional careers to investigating such themes. Indeed, until the late 1970s, research on alternative interpretations of quantum mechanics was not considered real physics by many; even the existence of such a controversy was a controversial position. This is why Léon Rosenfeld, for example, objected to the use of the term Copenhagen interpretation because it could mean the validity of a diversity of interpretations (Ballentine 1987, p. 786; Freire Jr. 2005, p. 28). Let us now illustrate this view with two recent testimonies. The French physicist Franck Laloë published in 2001 a paper provocatively titled Do we really understand quantum mechanics? Strange correlations, paradoxes, and theorems. The good reception of the paper led him to enlarge it into a full book (Laloë 2012). Laloë (2001, p. 656) gives us the following account:

Until about 20 years ago, probably as a result of the famous discussions between Bohr, Einstein, Schrödinger, Heisenberg, Pauli, de Broglie, and others […], most physicists seemed to consider that Bohr was right and proved his opponents to be wrong, even if this was expressed with more nuance. In other words, the majority of physicists thought that the so-called Copenhagen interpretation had clearly emerged from the infancy of quantum mechanics as the only sensible attitude for good scientists.

Most physicists here requires clarification. The question was not the existence of a majority of physicists consciously adopting the complementarity view or von Neumann’s presentation. Indeed, complementarity itself never was part of the training of physicists, being absent from most textbooks (Kragh 1999, p. 211). However, the received view among physicists was that foundational issues were already solved by the founding fathers of quantum physics and one did not need to spend time reading the papers where such problems were already solved. References to this tacit knowledge will appear many times through this book. The second testimony to illustrate this view is given by Christopher Gerry and Kimberley Bruno, who wrote The Quantum Divide, intended for a wider audience than professional physicists. They told us the following anecdote (Gerry and Bruno 2013, p. 172):

Some years ago, the senior author of this book (CCG) gave a talk about Bell’s inequalities, and in the audience was a retired professor who had once been a post-doctoral research associate at Bohr’s institute. After the talk he informed the audience that there was nothing of importance in the Bell inequalities, and that Bohr had already solved all the problems of quantum mechanics.

This all foundational issues are solved approach to the foundations of quantum physics was, however, challenged by other physicists who thought that these issues were worth pursuing as part of a professional career in physics. By doing so, the latter were questioning the very definition of what good physics was and challenging the established distribution of scientific capital, to use Bourdieu’s notion of scientific fields (Bourdieu 1975). I have called them, in this sense, quantum dissidents, a borrowing from the notion of dissidence in politics and religion. They include David Bohm, Jean-Pierre Vigier, Hugh Everett, John Bell, John Clauser, Abner Shimony, Heinz Dieter Zeh, Bernard d’Espagnat, Anthony Leggett, Franco Selleri, GianCarlos Ghirardi, Anton Zeilinger, and Alain Aspect, along with some physicists from the old guard of quantum mechanics, such as Louis de Broglie and Eugene Wigner.

In the early stages of this controversy the debate was restricted to theoretical arguments. Bohm, Everett, and de Broglie in the early 1950s, as well as Wigner and Shimony in the early 1960s, could not have imagined how to move the debate into the laboratory. The absence of experiments led a physicist, Albert Messiah, to say in his influential textbook that the controversy has finally reached a point where it can no longer be decided by any further experimental observations; it henceforth belongs to the philosophy of science, rather than to the domain of physical science proper (Messiah 1961, p. 48). Such a conclusion had clear-cut professional implications; it meant the controversy was not a professional matter for physicists, particularly for those new to the profession. The perception that the beginnings of the quantum controversy was a philosophical controversy survived in later accounts by the new protagonists of this research. In 1974, the historian Max Jammer wrote a comprehensive book on the history of interpretations of quantum mechanics entitled The Philosophy of Quantum Mechanics (Jammer 1974). As late as 1999, the physicist Anton Zeilinger recalled: most work on the foundations of quantum physics was initially motivated by curiosity and even by philosophical considerations (Zeilinger 1999, p. S295).

In the late 1960s the scene changed dramatically. In addition to the wide cultural trends that influenced the controversy, a trio composed of Bell, Clauser, and Shimony was able to connect this controversy and its philosophical connotations with the lab benches. A theorem formulated by Bell and developed by Clauser, Shimony, Michael Horne, and Richard Holt was put to experimental test. This theorem contrasted plain quantum mechanics with any physical theory with hidden variables which had locality as an assumption. Hidden variables were variables additional to those used by standard quantum physics which are introduced to assert that quantum systems have well-defined properties independent of their measurements. In short, hidden variables were a strategy to preserve physical realism in this new domain. Locality, a widely accepted premise among physicists, voiced by Einstein in 1935 in a paper co-authored with Boris Podolsky and Nathan Rosen, states that measuring one system should not affect another far away. Bell’s theorem could then pit quantum predictions against local realism. Thus, the history of this also sheds light on the different ways that theory and experiments intertwine in physical sciences. However, even during the first experiments on Bell’s theorem in the 1970s the subject was still regarded with suspicion by many. After Alain Aspect’s experiments in the early 1980s, research on foundations of quantum mechanics became good physics, plain and simple, as Aspect received wide recognition for his works. In the late 1980s and early 1990s these experiments were resumed, gathering since then an impressive number of physicists devoted to such experiments. The experiments confirmed the predictions of quantum mechanics and physicists resurrected an old term, coined by Erwin Schrödinger, to describe the new physical effect: entanglement. Since then, physical systems that first interact and later separate should be considered as just one system, described as a single quantum state. Some of the quantum dissidents had hoped to invalidate quantum theory but their hopes remained unfulfilled. Despite this frustration, the controversy over local realism was fruitful for physics and we now understand quantum theory better than its founding fathers. In this sense, this is an interesting case for analyzing the workings of scientific controversies, a theme which has claimed the attention of scholars.

In the early 1990s, new events brought the foundations of quantum mechanics into mainstream physics. It did not come on its own, but blended with computer science in a burgeoning field then called quantum information. The new field brought the technological promise of revolutionizing computing and cryptography. It was thus no surprise that it became one of the areas most funded by the military, corporations, and funding agencies interested in its possible applications.¹ Key concepts emerged from the research on foundations of quantum mechanics, such as entanglement, decoherence, and quantum cryptography. There is an exciting interaction between theory and experiment, with experiments with mesoscopic systems that have been compared to Schrödinger’s cat, which will be explained in later chapters, now being performed in labs, while other experiments on Bell’s theorem have reached new peaks. In 2012 a team led by Anton Zeilinger announced that they had managed to do quantum teleportation, reproduction of a quantum state from a system far away, over a distance of 144 km (Ma et al. 2012). Thus this story demonstrates how a subject was brought from the margins of physics, considered by some a subject for philosophers alone, into the mainstream of science through the complex and subtle ways in which science works.

The timeline of this book runs until the mid-1990s when the term quantum information became commonplace and there was a boom in physics research into this new field. Two historical stories coincide here. The first is that what began as research without experimental bearings ended in a field with the technological perspective of changing the landscape of computers. The second is that the times of the almost-total dominance of the complementarity and of the all problems were solved views were over. Gone were the days when physicists such as Léon Rosenfeld and Richard Feynman thought that physicists who doubted the foundations and interpretations of quantum mechanics simply did not understand it.² From the late 1990s on, hard supporters of complementarity live with and take advantage of the controversy over the quantum interpretation. One of the most-skilled current experimenters and supporters of the complementarity view, Anton Zeilinger, both defends complementarity and values the controversy (Zeilinger 1999, pp. S291–S296; Briggs et al. 2013; Schlosshauer et al. 2013).

1.1 The Dynamics of Change in Science

To a certain extent then both the history of the quantum controversy and of the research on foundations of quantum theory in the second half of the twentieth century are success stories. Eventually a subject once considered too philosophical and marginal in physics became a hot topic for physics research and even contributed to the appearance of the blossoming field of quantum information. Thus it is a history whose dynamics deserve some explanation. What were the factors shaping such changes? We already have an answer given by those who first explored this new territory, the physicists who work on the research related to the foundations of quantum physics. They attribute the change to the improvements in technical procedures enabling real lab experiments which had hitherto only been idealized experiments (Gedankenexperiments). Thanks to the recent advancement in technology, it becomes now feasible to perform many experiments which could only be conceived in theoreticians’ brain before and [this conference] was organized […] for the purpose of reviewing fundamental concepts of quantum mechanics with the aid of experimental means made available by recent technological advancements. These were the opening words at the International Symposia on Foundations of Quantum Mechanics in the Light of New Technology held in Tokyo in 1983 and 1986 (Nakajima 1983, 1987). Similar ideas were expressed by American and European physicists leading research on these topics (Greenberger 1986; Haroche 2004). Historian Joan Bromberg has exploited this answer furthermore. After noticing that historiography so far had been focusing on themes such as Marxism and alternatives to the Copenhagen interpretation, David Bohm’s causal interpretation, and the inception of Bell’s theorem, she emphasized one lead that historians have yet to pursue is constant reference that working physicists make to the role of new instrumentation (Bromberg 2008, p. 327).³ This kind of explanation tends to be the received view on the subject not only due to the bulk of materials concerning Bell’s inequalities and experiments on them in the last two decades but also for the impressive technical improvements, particularly from the 1980s on, which enabled the manipulation of single quantum systems. Furthermore, this view is akin to the description of changes in physical sciences in which only theory and experiments could play a role. It explains the changes in the quantum controversy mainly as a consequence of the role played by experiments in physics. It may be a kind of experimental determinism, heir to technological determinism. However, is it the only or even the most interesting explanation?

This book explores an alternative perspective about the changes in the research on foundations of quantum mechanics from the 1950s on. There was a slowly developing change in the perceptions of the physicists concerning the foundations of physics, both as a controversial subject and a field of research. New institutional and professional opportunities related to the subject were created, even before the first experiments on Bell’s theorem had taken place. This change happened during the 1950s and 1960s, and it can explain the elaboration and the positive reception the Bell’s theorem experiments obtained. Experiments on Bell’s theorem certainly increased the speed of that change and later other factors played their role. However, and this is crucial to our point, even after the first experiments on Bell’s theorem began to be carried out, professional stigma against the physicists who were working on these experiments remained, as demonstrated by John Clauser’s case and John Bell and Alain Aspect’s concerns throughout the 1970s. Explaining changes in physics based only on theory and experiment as driving factors does not harmonize with the survival of professional stigma against a topic of research despite the performance of successful experiments. It begs for a wider kind of explanation. Indeed, it is not enough to have experiments for work to be considered good physics; it is necessary that many other physicists consider such experiments to be relevant. It is certainly true that the existence of technical improvements and real experiments were influential in the emergence and consolidation of the research on the foundations of quantum physics. It was an effective driver if you restrict your analysis to the 1980s, but it is a particularly limited explanation if one considers the whole transformation happening since the early 1950s. In addition, as we will see, even in the 1980s traces can be found of professional and cultural prejudice against research on these topics. Indeed, diverse factors may have played their roles in the evolving controversy over the foundations of this theory. Among these factors, it is worth considering philosophical and ideological issues, professional biases, generational and cultural changes, and the diversity of the social and professional environments in which physics was practiced throughout the century. In addition to this, there were conceptual and theoretical breakthroughs, technical innovations, Gedankenexperiments and factual experimental feats as well as technological expectations.

Let us illustrate the diversity of factors driving the change in the intellectual and professional landscape of the foundations of quantum theory after World War II. While the first round of experiments were concerned with Bell’s theorem in the early 1970s, other theoretical issues were pressing physicists, both before and during the surge of interest on Bell’s theorem. In the 1950s alternative interpretations of quantum physics were formulated by David Bohm and Hugh Everett. Bohm conjectured about different predictions at what he called the subquantum level but none of them at that time consistently considered the experimental implications of their proposals. While Bohm’s interpretation was influential in motivating John Bell for his later work and its experimental implications, Everett’s proposal never had and possibly never will have experimental predictions other than those of usual quantum physics. And yet it has been influential for its heuristic capabilities. Furthermore, after a decade without attracting the attention of experts, Everett’s approach was revived by Bryce DeWitt. He was motivated by the problem of the marriage between quantum physics and general relativity, a domain which even today is far from experimental or observational concerns but has increasingly been attractive to physicists. Another pressing theoretical issue was the analysis of the quantum measurement processes, which led Eugene Wigner to diagnose the existence of a quantum measurement problem in the early 1960s. When discussions on the measurement problem became acute, pitting Wigner against Léon Rosenfeld, there was no perspective of experiments to enlighten the debate. Finally, when a problem related to the measurement problem—the transition from the quantum to the classical behavior—gained momentum among physicists in the early 1980s, it was not immediately driven by possible experiments, although a little later it did enter the lab. From this we can conclude that there was an agenda of theoretical problems in the foundations of quantum mechanics driving research after World War II. This agenda did not have any immediate bearing on experiments as these came later. In addition, there was the increasing philosophical discomfort with the instrumentalistic overtones related to the standard views of quantum mechanics.

The history of the quantum controversy may provide a window on the relationships between physics and its broader contexts. In the early 1950s, for example, Cold War tensions inevitably framed this debate both in the East and in the West. McCarthyism was a major factor shaping the career of Bohm and made him perhaps the most notable American scientist to choose exile in the last century. As philosophical themes such as determinism and realism were at stake, it comes as no surprise that ideological trends, such as the Soviet Zhdanovism, were influential in raising criticism against the standard interpretation of quantum theory. Thus as early as 1974 the historian of physics Max Jammer suggested the extent to which this process [decline of influence of the complementarity interpretation] was fomented and supported by social-cultural movements and political factors such as the growing interest in Marxist ideology in the West deserves to be investigated (Jammer 1974, p. 250). As we have argued elsewhere (Freire Jr. 2011b), Marxist criticisms contributed to the decline in the influence of the complementarity interpretation, even though there were Marxist physicists on both sides of the dispute, both pro and contra the complementarity view, as we will see throughout this book, particularly in Chaps. 2, 4, and 5. This tension was diluted in the late 1950s, but we can find traces of it later in the 1960s, as we will see in Chaps. 5 and 6. Resonance between physics practice and wider cultural trends were not limited to the ideological issues concerning Marxism. The surge of interest in foundations of quantum physics around 1970 was not out of tune with wider political and cultural changes that marked the times. Opposition to the Vietnam War and the cultural and political unrest of the late 1960s echoed in the decision of the Italian Physical Society to dedicate the 1970 issue of its traditional Varenna Summer School to the foundations of quantum mechanics and its 1972 issue to the history of physics in the twentieth century and its social implications. The former was the first major scientific gathering entirely dedicated to the foundations of quantum physics after World War II. Echoes from that unrest may also be found in John Clauser’s shift from high precision measurements in astrophysics towards foundations as well as in the opening of the magazine Physics Today to the debates on the diverse interpretations of quantum physics. In the same vein, historian David Kaiser in his book How the Hippies Saved Physics (Kaiser 2012) has convincingly argued that cultural trends inspired by the counter culture and based on the West Coast of the U.S. were influential in supporting some research on the foundational issues and provoking the physics establishment to produce one of the key results related to quantum information, the no-cloning theorem.

Last but not least, the threads of this story are also intertwined with technical developments such as lasers, photo-detectors, optical fibers, and computers; scientific breakthroughs such as the manipulation of quantum single systems, particularly photons; the flourishing of new disciplines, such as quantum optics; theoretical breakthroughs, such as the concepts of entanglement and decoherence; and the trade of skills between applied and foundational research. Thus the challenge for historians dealing with research on the quantum foundations is integrating such a diversity of factors into a single narrative. Indeed, bringing together the diversity of factors shaping science is the ultimate goal of historians of science. However, not all factors prevail at the same time; in fact, in each diachronic slice of this history the workings of only a few can be found. The job of the historian is therefore to disentangle the roles played by each factor in each local and temporal context. That is what we have tried to do throughout this book. In the final chapter I present a synopsis of the diverse factors which have played a role in each context.

1.2 Strategy and Historiographical Issues

My strategy to build a narrative on the research on foundations of quantum mechanics after 1950 was to follow people, issues, and their relevant contexts. It was a choice inspired in the dictum of the historian Marc Bloch: the historian is like the ogre of fairy tales, he knows that wherever he catches the scent of human flesh, there his quarry lies (Bloch 1953, p. 28). In doing this I deal with figures who attracted public attention well beyond physics, such as David Bohm, Hugh Everett and John Bell. However, this is not a story of great men. Bohm and Everett were not considered such by their fellow physicists at the time; their reputations developed later. Alongside great physicists, many of our characters are ordinary physicists who collaborated to develop research on foundations and in some cases also suffered professional prejudice. Some of these rank-and-file physicists can also be classified as anti-heroes, bearing the burden of the prejudices of the times, as was the case of Klaus Tausk, mentioned in Chap. 5. In addition to physicists, some characters in the quantum controversy were well-known philosophers, such as Karl Popper, Thomas Kuhn and Paul Feyerabend. Since I only became fascinated by this topic in the late 1980s when it had already become a regular field for research in physics, and the field of quantum information was beginning to blossom, it was important to avoid the sins of anachronism or the Whig interpretation of history (Kragh 1987, pp. 89–107). This choice of strategy was an antidote to these temptations. Another strategy was to ask the same questions to different people in order to allow me to build a collective biography of the scholars who worked on a theme they thought worthy of research. In doing this I was inspired in the historiographical method of prosopography (Stone 1971; Kragh 1987, pp. 174–181), although I did not follow this method strictly as I only used the biographical data in a qualitative manner. Chapter 9 represents my attempt to synthesize the collective biography. Thus, archival sources, oral histories, published papers, dynamics of science citations, and dialogue with the secondary literature relevant to the subject were the tools used throughout the research.

The subject of the book also required a dialogue with some theoretical issues, in addition to those presented in the previous paragraph. Our narrative is a story of disciplinary change and power distribution in an established scientific field, physics in this case. Issues at stake included the value of the research on foundational issues and to what extent quantum mechanics could be applied to other areas in physics. If these issues were addressed by the physics community there would be a rearrangement in terms of professional recognition. Thus it almost naturally invites contributions from Pierre Bourdieu, as already mentioned. Let us use two quotations from Bourdieu’s seminal paper on scientific capital as a form of symbolic capital. For the French sociologist, the ‘pure’ universe of even the ‘purest’ science is a social field like any other, with its distribution of power and its monopolies, its struggles and strategies, interests and profits, but it is a field in which all these invariants take on specific forms (Bourdieu 1975, p. 19). Most of the quantum controversy may be read as a story of struggles for power and monopolies, as will be evident throughout the book. Bourdieu also noted that in the struggle in which every agent must engage in order to force recognition of the value of his products and his own authority […], what is at stake is in fact the power to impose the definition of science (i.e. the delimitation of the field of the problems, methods and theories that may be regarded as scientific) (Bourdieu 1975, p. 23). Bohm and Everett fought to maintain that they were doing good physics instead of metaphysics, philosophy, or, as some critics saw it, just pointless reasoning. We will see that some American physicists doubted if what Clauser was doing was real physics. Bourdieusian lenses are fruitful not only in these cases but also in a number of other episodes in our narrative.

Bourdieu’s distinction between two kinds of professional strategies, either succession or subversion, a choice young scientists in particular need to make when they enter into the profession, may be helpful for our analysis. According to his words (Bourdieu 1975, pp. 30–31),

Depending on the position they occupy in the structure of the field (and also, no doubt, on secondary variables such as their social trajectory, which governs their assessment of their chances), the ‘new entrants’ may find themselves orientated either towards the risk-free investments of succession strategies, which are guaranteed to bring them, at the end of a predictable career the profits awaiting those who realise the official ideal of scientific excellence through limited innovations within authorised limits; or towards subversion strategies, infinitely more costly and more hazardous investments which will not bring them the profits accruing to the holders of the monopoly of scientific legitimacy unless they can achieve a complete redefinition of the principles legitimating domination.

Many of the physicists who appear in our story chose the subversion strategy. The sociologist Trevor Pinch was the first to look for Bourdieu’s contributions while analyzing the dispute between Bohm and von Neumann around the validity of von Neumann’s proof against the possibility of existence of hidden variables compatible with quantum mechanics (Pinch 1977). I exploited Pinch’s suggestion further. Everett’s case, with his attempt to provide a new interpretation of quantum theory that should be the natural presentation of its mathematical formalism, thus displacing both Bohr’s and von Neumann’s views, fits in the subversion strategy. While he had meaningful capital to bid this game—a doctoral thesis at Princeton under John Wheeler—he did not succeed, at least in the short term, as he did not achieve a complete redefinition of the principles legitimating which was considered the right interpretation of quantum physics. Short term may be too much time for a singular career. Everett chose to leave physics and academia for a profession using mathematics in the U.S. defense system.

My narrative also made use of a number of other contributions and readings from sociology, history, and philosophy. Timothy Lenoir’s book on the cultural production of scientific disciplines was influential due to the diversity of factors he mobilized to discuss how disciplines are created and how they evolve (Lenoir 1997). He also used Bourdieu’s conceptual framework to make sense of the dynamics of the birth and change of disciplines. Lenoir (1997, p. 12) argues that one of the objectives of disciplinary struggles is to rechart the boundaries of the field, to legitimate and consecrate new combinations of assets with cultural prestige and authority, to revalue a form of capital previously considered ‘impure,’ and to secure that valuation through an institutionalized structure. Among the examples Lenoir used to illustrate his point are current efforts to legitimate computational mathematics as a field of mathematics on a par with traditional mathematical disciplines, and the consecration of science fiction as a literary genre admissible within academic departments of literature. The move of the foundations of quantum physics from a fringe position to the mainstream of physics seems to me another illustration of the disciplinary shifts Lenoir has studied. Furthermore, for Lenoir (1997, p. 19), ideology has a crucial role to play in this process. It is not negatively valued in [his] account. Quantum controversy is a case where the scientific disputes are loaded with philosophical and ideological commitments, and this has not been an obstacle to its cognitive development.

The controversy over the interpretation and foundations of quantum physics is thus an exemplary case of science as a cultural production, which demands that understanding science as a cultural activity…means learning to identify and to interpret the complicated and particular collection of shared actions, values, signs, beliefs and practices by which groups of scientists make sense of their daily lives and work (Galison and Warwick 1998). While I have studied each case or episode as rooted in its local contexts, thus attentive to study the history of science as the study of science at work, as a practice, the whole story presented in this book had to deal with a diversity of local settings in order to make this narrative intelligible. Some of the places featured are Princeton, São Paulo, Copenhagen, London, Paris, Boston, Berkeley, Heidelberg, Moscow, Geneva, Varenna, Vienna, College Park, and Bari, making the story truly international. I also had to appeal to history, tout court, and not only the history of science in order to make sense of backgrounds such as the Cold War, McCarthyism, Zhdanovism, Marxism, and the cultural and political unrest of the late 1960s.⁴ As philosophical themes popped up from time to time I could not, nor did I want to, be insensitive to the literature of the philosophy of science. Readings from Michel Paty (1989, 1999, 2000), Abner Shimony (1993), and Ian Hacking (1983) have been most influential in my own work as I coped with the philosophical dimension of the quantum controversy and in particular with the constraints that the very practice of physics in the twentieth century forced upon realism in science.

Finally, insofar as this history is also a history of a scientific controversy, I benefited from the attention science studies scholars have dedicated to controversies (McMullin 1987; Collins and Pinch 1993, 1998a, b).⁵ Bruno Latour emphasized this interest to the point of basing his first rule of method on them: We study science in action and not ready made science or technology; to do so, we either arrive before the facts and machines are blackboxed or we follow the controversies that reopen them (Latour 1987, p. 258). However, I must admit that I was attracted to the controversy over the quantum at a time when I