Quantum Reality

by Jim Baggott

  I’m not alone. Although we probably shouldn’t read too much into the results, a poll of 33 scientists taken during a conference on the foundations of quantum mechanics held in Traunkirchen, Austria, in 2011, suggested a strong bias towards anti-realist interpretations (see Figure 17).3 For sure, this is not a statistically significant number of respondents, nor is the sample completely unbiased—the conference was organized by Anton Zeilinger, which may explain the fairly strong preference for information-theoretic interpretations and the absence of votes for de Broglie–Bohm theory and consistent histories. And the leading proponents of the many-worlds interpretation listed in Chapter 10 were notable by their absence. Nevertheless, the results are quite striking.

  Figure 17 Results of a multiple-choice questionnaire distributed to 35 attendees of the conference ‘Quantum Physics and the Nature of Reality’ organized by Anton Zeilinger and held at the International Academy, Traunkirchen, Austria, in July 2011. This graphic shows the results obtained from 33 respondents to the question ‘What is your favourite interpretation of quantum mechanics?’ I have excluded respondents checking ‘Other’ (12%) and ‘I have no preferred interpretation’ (12%). There were no votes for some interpretations I have not considered in this book, such as John Cramer’s transactional interpretation.

  Perhaps, just as Odysseus himself reasoned, it is better to risk a few crew members by sailing too close to Scylla than risk losing the whole Ship of Science in the whirlpool of metaphysical nonsense that is Charybdis. If we are to learn something new, speculations about our representation of reality must connect with the empirical facts of the things-as-they-appear. After all, this is what it means for something to be scientific. I cannot accept an interpretation based on pure metaphysics, no matter how ‘parsimonious’ this might appear. Just as Dennett argued that accepting Cartesian dualism is giving up, so in my view is accepting many worlds.

  There may yet be another way out. I’m pretty confident that quantum mechanics is not the end. Despite its unparalleled success, we know it doesn’t incorporate space and time in the right way. This is why I don’t think closer inspection of a realistically interpreted wavefunction necessarily makes for a good route to an answer, since this tends to drag the baggage of absolute space and time around with it. Unfortunately, we can’t look to contemporary efforts to develop a quantum theory of gravity to save us, as these appear to rely too heavily on the existing quantum formalism and don’t provide an obvious way to transcend it.

  Now it may well be that any theory that transcends quantum mechanics will still be rife with conceptual problems and philosophical conundrums. But it would be nice to discover that, despite appearances to the contrary, there was indeed something more to see here.

  Appendix

  Realist Propositions and the Axioms of Quantum Mechanics

  Realist Propositions (Chapters 2 and 3)

  Realist Proposition #1: The Moon is still there when nobody looks at it (or thinks about it). There is such a thing as objective reality.

  Realist Proposition #2: If you can spray them, then they are real. Invisible entities such as photons and electrons really do exist.

  Realist Proposition #3: The base concepts appearing in scientific theories represent the real properties and behaviours of real physical things. In quantum mechanics, the ‘base concept’ is the wavefunction.

  Realist Proposition #4: Scientific theories provide insight and understanding, enabling us to do some things that we might otherwise not have considered or thought possible. This is the ‘active’ proposition. When deciding whether a theory or interpretation is realist or anti-realist, we ask ourselves what it encourages us to do.

  The Axioms of Quantum Mechanics (Chapter 4)

  Axiom #1: The state of a quantum mechanical system is completely defined by its wavefunction. This is the ‘nothing to see here’ axiom. The wavefunction has everything you need so don’t bother to look for some deeper level of reality that lies beneath it.

  Axiom #2: Observables are represented in quantum theory by a specific class of mathematical operators. This is the ‘right set of keys’ axiom. To get at the observables, such as momentum and energy, we need to unlock the box represented by the wavefunction. Different observables require different keys drawn from the right set.

  Axiom #3: The average value of an observable is given by the expectation value of its corresponding operator. This is the ‘open the box’ axiom. It is the recipe we use to combine the operators and the wavefunction to calculate the values of the observables.

  Axiom #4: The probability that a measurement will yield a particular outcome is derived from the square of the corresponding wavefunction. This is the Born rule, or the ‘What might we get?’ axiom. Applying the Born rule to a superposition doesn’t tell us what we will get from the next measurement.

  Axiom #5: In a closed system with no external influences, the wavefunction evolves in time according to the time-dependent Schrödinger equation. This is the ‘how it gets from here to there’ axiom. Note that there’s no place here for the kind of discontinuity we associate with the process of measurement. As von Neumann understood, accepting this axiom forces us to adopt a further (but related) axiom in which we assume that a wavefunction representing a superposition of many measurement possibilities collapses to give a single outcome.

  Acknowledgements

  I left academia many years ago, but after spending 13 years studying, teaching, and conducting research in five different universities across the world, I guess certain habits became ingrained and they really do die hard. Wherever I can, I try to get academic specialists to read my stuff and provide comments on it, to reassure me when I’ve got it right, and to chastise me when I’ve got it wrong.

  Consequently, I’m indebted once again to Carlo Rovelli at Aix-Marseille University for reading the draft manuscript, engaging in extensive correspondence on relational quantum mechanics via email, and for accepting some responsibility for undermining my faith in Einstein’s realism. I have also benefited from comments on consistent histories from Robert Griffiths at Carnegie Mellon University; on QBism from Christopher Fuchs at the University of Massachusetts Boston; on the philosophy of science (and my grand metaphor for scientific theorizing) from Massimo Pigliucci at the City College of New York and Michela Massimi at Edinburgh University; on the problem of the preferred basis in the many worlds interpretation from Michael Cuffaro at the University of Western Ontario; on the Everett interpretation from both Harvey Brown at Oxford University and David Wallace at the University of Southern California; and on naturalized metaphysics from James Ladyman at Bristol University. Please understand that my acknowledgement of debt here should not lead you to assume that these good folks agree with or are even sympathetic to anything I’ve written on these subjects in this book. Those errors of confusion and misinterpretation that remain are all my own work.

  And, of course, none of this would have been possible without Latha Menon, my long-suffering editor, Jenny Nugee, Lucia Perez, Charles Lauder, and the production team at Oxford University Press, Argentinian artist Eugenia Nobati, who provided the beautifully drawn versions of my metaphor for scientific theorizing (Figure 7) and Wheeler’s great smoky dragon (Figure 10), and my son Tim, who provided the pictograms. I will remain eternally grateful for all their efforts.

  Jim Baggott

  October 2019

  List of Figure Acknowledgements

  Figure 1 Reproduced from C. Christiansen, Lærebog i Physik (Gyldendal, Copenhagen, 1910).

  Figure 2 (b) Reproduced with permission from Veritasium, L'experience originale en double fente (2013). YouTube: https://www.youtube.com/watch?v=Iuv6hY6zsd0.

  Figure 3 (a) © Cloudylabs / Wikimedia Commons / CC-BY-SA-3.0. Reproduced under the terms of the Creative Commons Attribution-ShareAlike 3.0 Unported license. https://creativecommons.org/licenses/by-sa/3.0/deed.en. (b) Reproduced with permission from A. Tonomura, et al., Demonstration of single-electron buildup of an interference patt
ern. American Journal of Physics, 57 (2): 117–20. Copyright © 1989, AIP Publishing. https://doi.org/10.1119/1.16104.

  Figure 4 Reproduced with permission from A. Tonomura, et al., Demonstration of single-electron buildup of an interference pattern. American Journal of Physics, 57 (2): 117–20. Copyright © 1989, AIP Publishing. https://doi.org/10.1119/1.16104.

  Figure 8 Artepics / Alamy Stock Photo.

  Figure 9 Reproduced from Albert Einstein: Philosopher-scientist, Vol I, edited by Paul Arthur Schilpp. Open Court Publishing Company, a division of Carus Publishing Company, Chicago IL. Copyright © 1949 by the Library of Living Philosophers. Reproduced with permission.

  Figure 12 Reproduced with permission from J. S. Bell, Bertlmann’s socks and the nature of reality. J. Phys. Colloques, 42 (C2): C2-41-C2-62. Copyright © 1981, EDP Sciences. https://doi.org/10.1051/jphyscol:1981202.

  Figure 15 Adapted with permission from C. Philippidis et al. Quantum interference and the quantum potential. Nuovo Cimento, 52B: 15–28. Copyright © 1979, Società Italiana di Fisica.

  Figure 16 Adapted with permission from S. Hameroff. Quantum computation in brain microtubules? The Penrose–Hameroff ‘Orch OR’ model of consciousness. Philosophical Transactions of the Royal Society of London. Series A: Mathematical, Physical and Engineering Sciences, 356 (1743). http://doi.org/10.1098/rsta.1998.0254.

  Figure 17 The Picture Art Collection / Alamy Stock Photo.

  Symbols

  (http://www.onlinewebfonts.com, CC BY 3.0)

  (Premiumvectors / Shutterstock.com)

  (iStock.com / MrPlumo)

  Endnotes

  When referencing the primary scientific literature I’ve tried as far as possible to provide the original published article and the relevant preprint, posted on the online preprint archive managed by Cornell University. The preprints can be accessed free of charge from the arXiv home page—http://arxiv.org/—by typing the article identifier in the search window. Where they are given, direct quotes are typically derived from the preprint.

  Preamble

  1. I’ve been developing this metaphor for some time. It features in a short talk I gave in June 2017 on the nature of quantum reality—see https://www.youtube.com/watch?v=VGR68Zl1k8w&. It also features in my book Quantum Space: Loop Quantum Gravity and the Search for the Structure of Space, Time, and the Universe, published by Oxford University Press in 2018, and in Jim Baggott, ‘The Impossibly Stubborn Question at the Heart of Quantum Mechanics’, Prospect, 2 August 2018, https://www.prospectmagazine.co.uk/science-and-technology/the-impossibly-stubborn-question-at-the-heart-of-quantum-mechanics

  2. Albert Einstein, quoted in Maurice Solovine, Albert Einstein: Lettres à Maurice Solovine, Gauthier-Villars, Paris, 1956. This quote is reproduced in Arthur Fine, The Shaky Game: Einstein, Realism and the Quantum Theory, 2nd edition (University of Chicago Press, Chicago, 1986), p. 110.

  Prologue

  1. N. David Mermin, ‘A Bolt from the Blue: The E-P-R Paradox’, in A. P. French and P. J. Kennedy (eds), Niels Bohr: A Centenary Volume (Harvard University Press, Cambridge, MA, 1985), pp. 141–7.

  2. In The Character of Physical Law (MIT Press, Cambridge, MA, 1967) on p. 129 Richard Feynman famously wrote: ‘I think I can safely say that nobody understands quantum mechanics.’

  Chapter 1: The Complete Guide to Quantum Mechanics (Abridged)

  1. Quoted in Abraham Pais, Subtle is the Lord: The Science and the Life of Albert Einstein (Oxford University Press, Oxford, 1982), p. 382.

  2. For this demonstration, see https://youtu.be/Iuv6hY6zsd0?t=254

  3. Einstein wrote: ‘Quantum mechanics is very impressive. But an inner voice tells me that it is not yet the real thing. The theory produces a good deal but hardly brings us closer to the secret of the Old One. I am at all events convinced that He does not play dice.’ Letter to Max Born, 4 December 1926. Quoted in ibid., p. 443.

  4. ‘The Unreasonable Effectiveness of Mathematics in the Natural Sciences’ was the title of Eugene Wigner’s Richard Courant lecture in mathematical sciences delivered at New York University on 11 May 1959. It was published in Communications on Pure and Applied Mathematics, 13 (1960), 1–14.

  5. Erwin Schrödinger, quoted by Werner Heisenberg in Physics and Beyond: Memories of a Life in Science (George Allen & Unwin, London, 1971), p. 75.

  Chapter 2: Just What is This Thing Called ‘Reality’, Anyway?

  1. Steven Weinberg, Dreams of a Final Theory: The Search for the Fundamental Laws of Nature (Vintage, London, 1993), p. 133.

  2. Lee Smolin and Leonard Susskind, ‘Smolin vs. Susskind: The Anthropic Principle’, The Edge, 18 August 2004: http://www.edge.org/3rd_culture/smolin_susskind04/smolin_susskind.html

  3. Lawrence Krauss, presentation to the American Atheists 38th National Convention, 25 March 2012, https://www.youtube.com/watch?v=u9Fi-BqS_Fw. This comment appears around 2:33.

  4. And, in any case, as theorist Carlo Rovelli has argued: ‘Those who deny the utility of philosophy, are doing philosophy.’ See https://blogs.scientificamerican.com/observations/physics-needs-philosophy-philosophy-needs-physics/

  5. Larry and Andy Wachowski, The Matrix: The Shooting Script (Newmarket Press, New York, 2001), p. 38.

  6. Richard E. Cytowic and David M. Eagleman, Wednesday is Indigo Blue: Discovering the Brain of Synesthesia (MIT Press, Cambridge, MA, 2009).

  7. Thanks to Michela Massimi for spelling this out for me in a personal communication dated 20 March 2019.

  8. Philip K. Dick, from the 1978 essay ‘How to Build a Universe that Doesn’t Fall Apart Two Days Later’, included in the anthology I Hope I Shall Arrive Soon, edited by Mark Hurst and Paul Williams (Grafton Books, London, 1988). This quote appears on p. 10.

  9. Bernard d’Espagnat, Reality and the Physicist: Knowledge, Duration and the Quantum World (Cambridge University Press, Cambridge, UK, 1989), p. 115.

  10. Karl Popper, quoted in John Horgan, The End of Science: Facing the Limits of Knowledge in the Twilight of the Scientific Age (Abacus, London, 1998), p. 35.

  11. Werner Heisenberg, Physics and Philosophy: The Revolution in Modern Science (Penguin, London, 1989; first published 1958), p. 46.

  12. Albert Einstein, quoted in Maurice Solovine, Albert Einstein: Lettres à Maurice Solovine (Gauthier-Villars, Paris, 1956). This quote is reproduced in Arthur Fine, The Shaky Game: Einstein, Realism and the Quantum Theory, 2nd edition (University of Chicago Press, Chicago, 1986), p. 110.

  13. Ian Hacking, Representing and Intervening: Introductory Topics in the Philosophy of Natural Science (Cambridge University Press, Cambridge, UK, 1983), p. 23.

  14. And I have to confess that I first heard about logical positivism from the infamous Australian ‘Bruces’ sketch, which appeared in an episode of Monty Python’s Flying Circus first broadcast in November 1970 (I was 13). This is set in the Philosophy Department of the University of Woolamaloo, in which all the faculty members are called Bruce. ‘Now, Bruce teaches classical philosophy, Bruce teaches Hegelian philosophy, and Bruce here teaches logical positivism and is also in charge of the sheep dip.’ From Monty Python’s Flying Circus: Just the Words, volume 1 (Mandarin Paperbacks, London, 1990), p. 295.

  15. Einstein was forever indebted to Mach for his approach to physics, but not his aggressively empiricist approach to philosophy. Einstein once commented that ‘Mach was as good at mechanics as he was wretched at philosophy.’ Quoted in Abraham Pais, Subtle is the Lord: The Science and the Life of Albert Einstein (Oxford University Press, Oxford, 1982). This quote appears on p. 283.

  16. For a much more detailed discussion of this aspect of the use of mathematics in physics, I strongly recommend Giovanni Vignale, The Beautiful Invisible: Creativity, Imagination, and Theoretical Physics (Oxford University Press, Oxford, 2011).

  17. For an example of a scientist arguing for the acceptance of absolute spacetime see Brian Greene, The Fabric of the Cosmos: Space, Time and the Texture of Reality (Allen Lane, London, 2004), p. 75 (where he writes: ‘spacetime is a so
mething’).

  18. Thomas Huxley, ‘Biogenesis and Abiogenesis’, Presidential Address to the British Association for the Advancement of Science, 1870, Collected Essays: Discourses Biological and Geological, volume 8, p. 229. See: https://mathcs.clarku.edu/huxley/CE8/B-Ab.html. ‘Harsh’, ‘brutal’, and ‘ugly’—I’m clearly not the first to think that Empirical Reality is a pretty mean-spirited place.

  19. Pierre Duhem, The Aim and Structure of Physical Theory, English translation of the second French edition of 1914 by Philip P. Wiener (Princeton University Press, Princeton, NJ, 1954), p. 145.

  Chapter 3: Sailing on the Sea of Representation

  1. Carl Zimmer, ‘In Science, It’s Never “Just a Theory” ’, New York Times, 8 April 2016. Available at http://www.nytimes.com/2016/04/09/science/in-science-its-never-just-a-theory.html?_r=0

  2. Bertrand Russell, The Problems of Philosophy (Oxford University Press, Oxford, 1912), p. 35.

  3. For an overview of the philosophical programme of naturalized metaphysics, see James Ladyman and Don Ross, with David Spurrett and John Collier, Every Thing Must Go: Metaphysics Naturalized (Oxford University Press, Oxford, 2007).

  4. Michela Massimi, personal communication, 25 March 2019.