Through Two Doors at Once: The Elegant Experiment That Captures the Enigma of Our Quantum Reality

by Ananthaswamy, Anil

  “Now, ladies and gentlemen” : Ibid.

  a decade-old paper by John Bell : J.S. Bell, “On the Einstein Podolsky Rosen paradox,” Physics Physique Fizika 1, no. 2 (Nov 1, 1964): 195–200.

  Taylor used something called a coincidence detector : William M. Honig, David W. Kraft, and Emilio Panarella, eds., Quantum Uncertainties: Recent and Future Experiments and Interpretations (New York: Plenum Press, 1987), 339.

  A rough-and-ready calculation : The calculation appears in Giancarlo Ghirardi, Sneaking a Look at God’s Cards: Unraveling the Mysteries of Quantum Mechanics (Princeton: Princeton University Press, 2005), 16.

  “This experiment has never been done” : Richard P. Feynman, Robert B. Leighton, and Matthew Sands, The Feynman Lectures on Physics, vol. 1, New Millennium Edition (New York: Basic Books, 2011), 37–5.

  Möllenstedt noticed that when the tungsten : Edgar Völkl, Lawrence F. Allard, and David C. Joy, eds., Introduction to Electron Holography (New York: Springer Science, 1999), 3.

  “kept a collection of spiders” : Robert Crease, The Prism and the Pendulum: The Ten Most Beautiful Experiments in Science (New York: Random House, 2004), 197.

  the team did not see any fringes at first : Völkl, Allard, and Joy, eds., Introduction to Electron Holography , 5.

  “Thomas Young had produced” : Ibid.

  “It was . . . a great pleasure to see” : Ibid., 7.

  In 1974, Italian physicists : Pier Giorgio Merli, GianFranco Missiroli, and Giulio Pozzi, “On the Statistical Aspect of Electron Interference Phenomena,” American Journal of Physics 44, no. 306 (1976): 306–7.

  the movie even won an award : https://www.bo.imm.cnr.it/users/lulli/downintel/electroninterfea.html .

  In 1989, Akira Tonomura and colleagues : A. Tonomura et al. “Demonstration of Single Electron Buildup of an Interference Pattern,” American Journal of Physics 57, no. 117 (1989): 117–20.

  “We believe that we carried out” : Letter to editor, “The Double-Slit Experiment with Single Electrons,” Physics World (May 2003): 20.

  Such an excited atom falls back : Alain Aspect, Philippe Grangier, and Gérard Roger, “Experimental Tests of Realistic Local Theories via Bell’s Theorem,” Physical Review Letters 47, no. 7 (Aug 17, 1981): 460–63.

  “just a name for something” : David Albert, Quantum Mechanics and Experience (Cambridge, MA: Harvard University Press, 1994), 11.

  “the most unsettling story perhaps” : Ibid., 1.

  Einstein imagined some gunpowder : Arthur Fine, The Shaky Game: Einstein, Realism and the Quantum Theory (Chicago: University of Chicago Press, 1986), 78.

  “Through no art of interpretation” : Ibid.

  “I am long past the stage” : Ibid., 82.

  “A cat is shut up in a steel chamber” : Moore, Schrödinger , 308.

  a particle interferes with itself : Paul Dirac, The Principles of Quantum Mechanics (Oxford: OUP, 1958), 9.

  “great smoky dragon” : Warner A. Miller and John A. Wheeler, “Delayed-Choice Experiments and Bohr’s Elementary Quantum Phenomenon,” S. Kamefuchi et al., eds., Proceedings of the International Symposium on Foundations of Quantum Mechanics (Tokyo: Physical Society of Japan 1984), 140–52.

  “What the dragon does” : Ibid.

  “One decides whether the photon” : John Wheeler and Wojciech Zurek, eds., Quantum Theory and Measurement (Princeton: Princeton University Press, 1983), 183.

  an interferometer with arm lengths of 48 meters : Vincent Jacques et al., “Experimental Realization of Wheeler’s Delayed-Choice Gedanken Experiment,” Science 315, no. 5814 (Feb 16, 2007): 966–68.

  Einstein’s most cited paper : Dennis Overbye, “Quantum Trickery: Testing Einstein’s Strangest Theory,” New York Times, December 27, 2005, http://www.nytimes.com/2005/12/27/science/quantum-trickery-testing-einsteins-strangest-theory.html .

  “Nonlocality forces us” : Nicolas Gisin, Quantum Chance: Nonlocality, Teleportation and Other Quantum Marvels (Cham, Switzerland: Springer, 2014), 32.

  “first apologized for not having” : Andrew Whitaker, Einstein, Bohr and the Quantum Dilemma: From Quantum Theory to Quantum Information (Cambridge: Cambridge University Press, 2006), 203.

  Einstein made the point that this localization : Ibid.

  EINSTEIN ATTACKS QUANTUM THEORY : Kelly Devine Thomas, “The Advent and Fallout of EPR,” IAS: The Institute Letter (Fall 2013): 13.

  “I deprecate advance publication” : Ibid.

  “If The New York Times is the secular press” : David Mermin, Oppenheimer Lecture, University of California, Berkeley, March 17, 2008, https://youtu.be/ta09WXiUqcQ?t=833 .

  elegant four-page-long paper : Albert Einstein, Boris Podolsky, and Nathan Rosen, “Can Quantum-Mechanical Description of Physical Reality Be Considered Complete?” Physical Review 47 (May 15, 1935): 777–80.

  teatime conversation between Einstein and Rosen : Thomas, “Advent and Fallout of EPR.”

  Sixteen years later, in 1951 : David Bohm, Quantum Theory (New York: Dover Publications, 1989), 611.

  “ If, without in any way” : Einstein, Podolsky, and Rosen, “Quantum-Mechanical Description.”

  “a piece of historical silliness” : Fine, Shaky Game, 57.

  “the first and only female doctoral student” : Elise Crull and Guido Bacciagaluppi, eds., Grete Hermann—Between Physics and Philosophy (Dordrecht: Springer, 2016), 4.

  “A thorough examination of the proof of von Neumann reveals” : Harald Atmanspacher and Christopher A. Fuchs, eds., The Pauli-Jung Conjecture: And Its Impact Today (Exeter, UK: Imprint Academic, 2014), ebook.

  “Why should we believe in that?” : Ibid.

  “would rather be a cobbler” : Isaacson, Einstein, 324.

  “If that had something to do with it” : Crull and Bacciagaluppi, Grete Hermann , 184.

  “In 1952, I saw the impossible done” : Olival Freire Jr., The Quantum Dissidents: Rebuilding the Foundations of Quantum Mechanics (1950–1990) (Heidelberg: Springer-Verlag, 2015), 66.

  “The von Neumann proof” : Charles Mann and Robert Crease, “John Bell,” Omni , May 1988, 88.

  “I cannot seriously believe” : Jürgen Audretsch, Entangled Systems: New Directions in Quantum Physics (Weinheim, Wiley-VCH, 2007), 130.

  “These experiments are a magnificent affront” : Brian Greene, The Fabric of the Cosmos: Space, Time, and the Texture of Reality (New York: Vintage Books, 2005), 199.

  recognized for their efforts in 2010 : “Where Credit is Due,” editorial in Nature Physics (Jun 1, 2010), https://www.nature.com/articles/nphys1705 .

  was housed in Schrödinger’s home : https://www.esi.ac.at/material/Evaluation2008.pdf .

  in 1913, he crossed the nearly 1,800-meter-high Maloja Pass : Alice Calaprice, Daniel Kennefick, and Robert Schulmann, An Einstein Encyclopedia (Princeton: Princeton University Press, 2015), 89.

  nature of reality and beef cattle production : “Physicist Designs Perfect Automotive Engine,” ScienceDaily (Feb 27, 2003), https://www.sciencedaily.com/releases/2003/02/030227071656.htm .

  “The mystery is not that I’m interested” : Vimal Patel, “Cows Meet Quantum, Lifelong Learning on the Banks of the Brazos,” Texas A&M University Science News , November 21, 2013, http://www.science.tamu.edu/news/story.php?story_ID=1141#.WTOOvO-0k7Y .

  “A dumb kid from Wyoming” : Interview of Marlan Scully by Joan Bromberg, July 15 and 16, 2004, Niels Bohr Library & Archives, American Institute of Physics, College Park, MD, www.aip.org/history-programs/niels-bohr-library/oral-histories/32147 .

  “When the province of physical theory” : Wheeler and Zurek, Quantum Theory and Measurement , 169.

  But by 1970, Wigner changed his mind : Art Hobson, Tales of the Quantum: Understanding Physics’ Most Fundamental Theory (New York: Oxford University Press, 2017), 201.

  “We propose and analyze an experiment” : Marlan O. Scully and Kai Drühl, “Quantum Eraser: A Proposed Photon Correlation Experiment Concerning Observation and ‘Delayed Choice’ in Quantum Mechan
ics,” Physical Review A 25, no. 4 (Apr 1982): 2208–13.

  Zeilinger and colleagues : Thomas J. Herzog et al., “Complementarity and the Quantum Eraser,” Physical Review Letters 75, no. 17 (Oct 23, 1995): 3034–37.

  Scully eventually joined hands : Yoon-Ho Kim et al., “Delayed ‘Choice’ Quantum Eraser,” Physical Review Letters 84, no. 1 (Jan 3, 2000): 1–5.

  “Although we listened to hundreds” : Freire, The Quantum Dissidents , 20.

  “It looks strange” : Wheeler and Zurek, Quantum Theory and Measurement , 185.

  “The final story of the relation” : Alwyn Van der Merwe, Wojciech Hubert Zurek, and Warner Allen Miller, eds., Between Quantum and Cosmos: Studies and Essays in Honor of John Archibald Wheeler (Princeton: Princeton University Press, 2017), 10.

  German physicist Mauritius Renninger : A. Cardoso, J. L. Cordovil, and J. R. Croca, “Interaction-Free Measurements: A Complex Nonlinear Explanation,” Journal of Advanced Physics 4, no. 3 (Sep 2015): 267–71.

  The paper did see the light of day : Avshalom Elitzur and Lev Vaidman, “Quantum Mechanical Interaction-Free Measurements,” Foundations of Physics 23, no. 7 (Jul 1993): 987–97.

  “Surely . . . it can be no sin to fail ” : Roger Penrose, Shadows of the Mind: A Search for the Missing Science of Consciousness (Oxford: Oxford University Press, 1996), 269.

  A nearly exact replica of this experiment : William Irvine, Juan Hodelin, Christoph Simon, and Dirk Bouwmeester, “Realization of Hardy’s Thought Experiment with Photons,” Physical Review Letters 95 (Jul 15, 2005): 030401–4.

  His paper : Lucien Hardy, “Quantum Mechanics, Local Realistic Theories, and Lorentz-Invariant Realistic Theories,” Physical Review Letters 68, no. 20 (May 18, 1992): 2981–4.

  “simpler and more compelling” : David Mermin, “Quantum Mysteries Refined,” American Journal of Physics 62, no. 10 (Oct 1994): 880–7.

  “stands in its pristine simplicity” : Ibid.

  “There’s an entirely different way” : David Albert, Quantum Mechanics and Experience , 134.

  He founded the first school of theoretical physics : Robert Sanders, “Conference, Exhibits Probe Science and Personality of J. Robert Oppenheimer, Father of the Atomic Bomb,” UC Berkeley News , April 13, 2004, https://www.berkeley.edu/news/media/releases/2004/04/13_oppen.shtml .

  “Bohr was God and Oppie was his Prophet” : Freire, The Quantum Dissidents , 26.

  Oppenheimer reassured UC Berkeley : Ibid.

  “probably Oppenheimer’s best student at Berkeley” : Ibid.

  Princeton suspended him : Ibid., 28.

  “Until we find some real evidence” : Bohm, Quantum Theory , 115.

  “only orthodox in the Copenhagen” : Karl Popper, Quantum Theory and the Schism in Physics: From the Postscript to the Logic of Scientific Discovery (New York: Routledge, 2013), 36.

  “general conceptual framework of the quantum theory” : Bohm, Quantum Theory , 115.

  “one of the most fundamental” : Ibid. , 623.

  “no theory of . . . hidden variables” : Ibid.

  because it was too long : Freire, The Quantum Dissidents , 31.

  “If I write a paper” : Ibid.

  “All of the objections” : David Bohm, “A Suggested Interpretation of the Quantum Theory in Terms of ‘Hidden’ Variables,” Physical Review 85, no. 2 (Jan 15, 1952): 166–79.

  “If one man finds a diamond” : Freire, The Quantum Dissidents , 32.

  The impetus came from : Yves Couder and Emmanuel Fort, “Single-Particle Diffraction and Interference at a Macroscopic Scale,” Physical Review Letters 97 (Oct 13, 2006): 154101–4.

  “Our results do not close the door” : Giuseppe Pucci, Daniel Harris, Luiz Faria, and John Bush, “Walking Droplets Interacting with Single and Double Slits,” Journal of Fluid Mechanics 835 (Jan 25, 2018): 1136–56.

  The trio published a paper showing the trajectories : Chris Philippidis, Chris Dewdney, and Basil Hiley, “Quantum Interference and the Quantum Potential,” Il Nuovo Cimento B 52, no. 1 (Jul 1979): 15–28.

  In 1988, Yakir Aharonov : Yakir Aharonov, David Albert, and Lev Vaidman, “How the Result of a Measurement of a Component of the Spin of a Spin-1/2 Particle Can Turn Out to Be 100,” Physical Review Letters 60 (Apr 4, 1988): 1351–54.

  “It must be emphasized” : Howard Wiseman, “Grounding Bohmian Mechanics in Weak Values and Bayesianism,” New Journal of Physics 9 (Jun 2007): 165.

  “The team is the first to track” : Hamish Johnston, “Physics World Reveals Its Top 10 Breakthroughs for 2011,” Physics World (Dec 16, 2011), http://physicsworld.com/cws/article/news/2011/dec/16/physics-world-reveals-its-top-10-breakthroughs-for-2011 .

  “Tersely: Bohm trajectories are not realistic” : Berthold-Georg Englert, Marlan Scully, Georg Süssmann, and Herbert Walther, “Surrealistic Bohm Trajectories,” Zeitschrift für Naturforschung A 47, no. 12 (1992), 1175–86.

  It required a small but significant : Dylan Mahler et al., “Experimental Nonlocal and Surreal Bohmian Trajectories,” Science Advances 2, no. 2 ( Feb 19, 2016): e1501466.

  “inspired by the modern realization” : Louis Sass, Madness and Modernism: Insanity in the Light of Modern Art, Literature, and Thought (Cambridge, MA: Harvard University Press, 1994), 31.

  “A university student attending lectures” : Carlo Rovelli, Reality Is Not What It Seems: The Journey to Quantum Gravity (New York: Riverhead Books, 2017), 148.

  Penrose imagines a photon : Roger Penrose, Fashion, Faith, and Fantasy in the New Physics of the Universe (Princeton: Princeton University Press, 2016), 162.

  “shifty split” : John Bell, “Against ‘Measurement,’” Physics World 3, no. 8 (Aug 1990): 33.

  the Hungarian physicist : Lajos Diósi, “A Universal Master Equation for the Gravitational Violation of Quantum Mechanics,” Physics Letters A 120, no. 8 (Mar 16, 1987): 377–81.

  three physicists : Giancarlo Ghirardi, Alberto Rimini, and Tullio Weber, “Unified Dynamics for Microscopic and Macroscopic Systems,” Physical Review D 34, no. 2 (Jul 15, 1986): 470–91.

  “Any embarrassing macroscopic ambiguity” : John Bell, Speakable and Unspeakable in Quantum Mechanics (Cambridge: Cambridge University Press, 1989), 204.

  “have a certain kind of goodness” : John Bell quoted in Giancarlo Ghirardi, Sneaking a Look at God’s Cards: Unraveling the Mysteries of Quantum Mechanics (Princeton: Princeton University Press, 2005), 415.

  “They are honest attempts” : Ibid.

  In 1991, Jürgen Mlynek and colleagues : O. Carnal and J. Mlynek, “Young’s Double-Slit Experiment with Atoms: A Simple Atom Interferometer,” Physical Review Letters 66, no. 21 (May 27, 1991): 2689.

  atoms could be diffracted at gratings : Philip Moskowitz, Phillip Gould, Susan Atlas, and David Pritchard, “Diffraction of an Atomic Beam by Standing-Wave Radiation,” Physical Review Letters 51, no. 5 (Aug 1, 1983): 370.

  a double-slit experiment done with neon atoms : Fujio Shimizu, Kazuko Shimizu, and Hiroshi Takuma, “Double-Slit Interference with Ultracold Metastable Neon Atoms,” Physical Review A 46, no. 1 (Jul 1, 1992): R17.

  In 1999, Zeilinger, Arndt, and their team : Markus Arndt et al., “Wave–Particle Duality of C 60 Molecules,” Nature 401 (Oct 14, 1999): 680–82.

  it’s a bespoke molecule : Sandra Eibenberger et al., “Matter–Wave Interference of Particles Selected from a Molecular Library with Masses Exceeding 10,000 amu,” Physical Chemistry Chemical Physics 15 (Jul 8, 2013): 14696-700.

  There’s a 146-meter-high tower in Bremen : https://www.zarm.uni-bremen.de/en/drop-tower/general-information.html .

  Penrose had plans : Roger Penrose, “Wavefunction Collapse as a Real Gravitational Effect,” in Mathematical Physics 2000 , ed. A. Fokas, A. Grigoryan, T. Kibble, and B. Zegarlinski (London: Imperial College Press, 2000), 266–82.

  He knew people at NASA : https://youtu.be/mvHg5PcXb6k?t=45 .

  When they wrote their paper : William Marshall, Christoph Simon, Roger Penrose, and Dirk Bouwmeester, “Towards Quant
um Superpositions of a Mirror,” Physical Review Letters 91, no. 13 (Sep 23, 2003): 130401.

  “The collapse [of the wavefunction]” : Simon Saunders, Jonathan Barrett, Adrian Kent, and David Wallace, eds., Many Worlds?: Everett, Quantum Theory, and Reality (Oxford: Oxford University Press, 2010), 582.

  “He was rather upset when I met him” : Dirk Bouwmeester speaking at the Institute for Quantum Computing in Waterloo, Ontario, Canada, May 2013, https://youtu.be/g7RqLbqDr4U?t=387 .

  “Actualities seem to float” : William James, The Will to Believe: And Other Essays in Popular Philosophy (New York: Longmans Green and Co, 1907), 151.

  Wheeler’s attitude likely rubbed : Transcript of conversation between Hugh Everett and Charles Misner, in Hugh Everett III, The Everett Interpretation of Quantum Mechanics: Collected Works 1955–1980 with Commentary , ed. Jeffrey A. Barrett and Peter Byrne (Princeton: Princeton University Press, 2012), 309.

  “What actually does happen” : Everett, The Everett Interpretation , 65.

  “In other words, the observer” : Ibid., 67.

  “for almost all of the” : Ibid., 69.

  “can lay claim to a certain” : Ibid.

  “One can imagine an intelligent” : Ibid., 69–70.

  “I am frankly bashful” : Ibid., 71.

  “We do not believe” : Ibid., 153.

  “objectionable” dualism : Ibid.

  An American physicist, Alexander Stern : Ibid., 214.

  “lack meaningful content” : Ibid., 215.

  “matter of theology” : Ibid., 217.

  “I would not have imposed” : Ibid., 219.

  “this very fine and able” : Ibid.

  “javelin proof” : Ibid., 212.

  “I was stunned, I was shocked” : Interview of Bryce DeWitt and Cecile DeWitt-Morette by Kenneth W. Ford, February 28, 1995, Niels Bohr Library & Archives, American Institute of Physics, Oral Histories, https://www.aip.org/history-programs/niels-bohr-library/oral-histories/23199 .

  “I can testify to this” : Everett, The Everett Interpretation , 246.

  “hopelessly incomplete” : Ibid., 255.

  “a philosophic monstrosity” : Ibid.