Quantum Non-Locality and Relativity: Metaphysical Intimations of Modern Physics

Description

The impetus for a third edition of Quantum Non-Locality and Relativity arises from several different circumstances. The most important is the development of a fully relativistic, precise physical theory that can produce violations of Bell’s inequality for experiments at space-like separation. This theory, called flashy Relativistic GRW, was discovered by Roderich Tumulka, and is described in the new chapter 10. Tumulka’s theory settles the logical question about the possibility of fully reconciling quantum theory and Relativity. But as the reader will see, the theory also suggests that the consummation was perhaps not so devoutly to be wished. That is, there is a price of plausibility to be paid by this theory, a price so high that it is unlikely to gain converts. One nice thing about flashy GRW is that it forces us to confront deep issues about what exactly makes for a plausible physical theory. Interest in Bell’s inequality has been on the rise in recent years for other unrelated reasons. John Conway and Simon Kochen produced the so-called “Free Will Theorem,” whose title alone is enough to raise eyebrows. The theorem utilizes a situation in which there is a violation of Bell’s inequality, and Conway and Kochen have made some rather astonishing claims about its significance. This theorem is also discussed in the new chapter. More generally, interest in Bell’s theorem has been reinvigorated by the rise of quantum information theory and the experimental verification of such quantum effects as the teleportation of quantum states. The information- theoretic analysis of quantum theory has had the entirely salubrious effect of focusing attention on the key aspect of quantum theory called entanglement. The entanglement of distant systems is what produces violations of Bell’s inequality in quantum theory, and physicists have come to routinely accept this entanglement as a quantifiable, exploitable physical resource. There is little dispute any more that the entanglement of distant systems is somehow physically real. The reason that this development is so cheering is that it deflects attention from other less important aspects of quantum theory. For example, it has been repeated ad nauseam that Einstein’s main objection to quantum theory was its lack of determinism: Einstein could not abide a God who plays dice. But what annoyed Einstein was not lack of determinism, it was the apparent failure of locality in the theory on account of entanglement. Einstein recognized that, given the predictions of quantum theory, only a deterministic theory could eliminate this non-locality, and so he realized that a local theory must be deterministic. But it was the locality that mattered to him, not the determinism. We now understand, due to the work of Bell, that Einstein’s quest for a local theory was bound to fail. Schrödinger, in his famous “cat” paper, remarked on the “entanglement of our knowledge of […] two bodies” (1935, p. 161) found in the quantummechanical formalism, but denied, as Einstein did, that this could reflect any real physical connection between separated systems: “Measurements on separated systems cannot directly influence each other – that would be magic” (ibid., p. 164). Bell’s work has shown that the magic is real, and physicists who study entanglement have accepted the non-locality that Einstein and Schrödinger could not abide. I have briefly adverted to recent work on the information-theoretic implications of quantum theory in chapter 6 of this new edition. When I first wrote Quantum Non-Locality and Relativity, I tried to keep discussion of the foundations of quantum theory to a minimum. All that is relevant to Bell’s theorem are the predictions of quantum theory, not how the theory itself is understood. Separating these issues was especially important at the time because discussions of quantum theory per se contained a wealth of distractions and confusion. Perhaps the time is at last ripe to open up the dialog again, and to recover an understanding of Einstein’s and Schrödinger’s real concerns through the lens of Bell’s theorem. I hope that chapter 10 provides a small step in the direction of a clearer understanding of what a comprehensible presentation of any physical theory (and hence a comprehensible presentation of quantum theory) demands. Preface to First Edition vi Preface to Second Edition x Preface to Third Edition xii Introduction 1 1 Bell’s Theorem: The Price of Locality 6 Appendix A: The GHZ Scheme 24 2 Relativity and Space-time Structure 27 3 Finger Exercise: Superluminal Matter Transport 55 4 Controlling the Connection: Signals 74 Appendix B: Bohmian Mechanics 106 5 Causation 114 6 Secret Messages 148 7 Points of View 173 8 Life in Elastic Space-time 205 9 Morals 221 10 New Discoveries and Deeper Insights: The View from 2010 224 An Overview of Quantum Mechanics 260 References 284 Index 290