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14. Bohr’s Response to the Einstein- Podolsky- Rosen Argument

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From Data to Quanta
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14: bohr’s response to the einstein- podolsky- rosen argumentI know that no living person has looked so deeply into the actual abysses of quantum theory as the two of you, and that nobody else sees how necessary are completely radical new conceptions.— Paul Ehrenfest, commenting on Albert Einstein and Niels Bohr 1A perceived paradox at the heart of the newly established quantum me-chanics was advocated in the famous paper by Einstein, Boris Podolsky, and Nathan Rosen in 1935. The usual brief textbook summary of the ar-gument (e.g., Howard 2007; Norton 2018) states that since particles must have defi nite observable properties, such as spin, even before any measure-ment is performed on them, quantum mechanics cannot be complete, as it does not account for hidden properties. This leads to the correlation of the spins of two particles— for example, two atoms leaving the molecules because of electrostatic force (the force that does not disturb their spins). Quantum mechanics gives us possible values of the property (of spin) that we choose when performing the measurement, but it cannot give us a full description of the system. The two particles are really separated and, in principle, the measurements can be performed on each particle indepen-dently. What quantum mechanics offers us is just a statistical account of particle ensembles, not of individual states and their properties which lie hidden in the fabric of physical reality and wait to be discovered by a new and better complete theory. As Bohr correctly summarized it: “Einstein here argues that the quantum- mechanical description is to be considered merely as a means of accounting for the average behaviour of a large num-ber of atomic systems and his attitude to the belief that it should offer an exhaustive description of the individual phenomena” (Bohr 1949, 235).As is well known, Bell’s argument (1964), and subsequent experimental tests of it (Aspect, Grangier, and Roger 1982), demonstrated that if quan-tum mechanics correctly predicted the outcomes of measurements, then there was no set of hidden properties of the type that Einstein assumed to exist, that would be consistent with the set of such outcomes.A striking aspect of the Einstein- Podolsky- Rosen (EPR) paper is its
© 2021 University of Chicago Press

14: bohr’s response to the einstein- podolsky- rosen argumentI know that no living person has looked so deeply into the actual abysses of quantum theory as the two of you, and that nobody else sees how necessary are completely radical new conceptions.— Paul Ehrenfest, commenting on Albert Einstein and Niels Bohr 1A perceived paradox at the heart of the newly established quantum me-chanics was advocated in the famous paper by Einstein, Boris Podolsky, and Nathan Rosen in 1935. The usual brief textbook summary of the ar-gument (e.g., Howard 2007; Norton 2018) states that since particles must have defi nite observable properties, such as spin, even before any measure-ment is performed on them, quantum mechanics cannot be complete, as it does not account for hidden properties. This leads to the correlation of the spins of two particles— for example, two atoms leaving the molecules because of electrostatic force (the force that does not disturb their spins). Quantum mechanics gives us possible values of the property (of spin) that we choose when performing the measurement, but it cannot give us a full description of the system. The two particles are really separated and, in principle, the measurements can be performed on each particle indepen-dently. What quantum mechanics offers us is just a statistical account of particle ensembles, not of individual states and their properties which lie hidden in the fabric of physical reality and wait to be discovered by a new and better complete theory. As Bohr correctly summarized it: “Einstein here argues that the quantum- mechanical description is to be considered merely as a means of accounting for the average behaviour of a large num-ber of atomic systems and his attitude to the belief that it should offer an exhaustive description of the individual phenomena” (Bohr 1949, 235).As is well known, Bell’s argument (1964), and subsequent experimental tests of it (Aspect, Grangier, and Roger 1982), demonstrated that if quan-tum mechanics correctly predicted the outcomes of measurements, then there was no set of hidden properties of the type that Einstein assumed to exist, that would be consistent with the set of such outcomes.A striking aspect of the Einstein- Podolsky- Rosen (EPR) paper is its
© 2021 University of Chicago Press

Chapters in this book

  1. Frontmatter i
  2. Contents v
  3. 1. Introduction 1
  4. Part 1. Preliminaries
  5. 2. From Laboratory to Theory 25
  6. 3. From Classical Experiments to Quantum Theory 33
  7. Part 2. Bohr’s Vision in Practice: The Old Quantum Theory
  8. 4. Spectral Lines, Quantum States, and a Master Model of the Atom 59
  9. 5. The Correspondence Principle as an Intermediary Hypothesis 87
  10. 6. Reception 97
  11. 7. The Scientific Moderator 103
  12. Part 3. Toward Quantum Mechanics
  13. 8. Quantum Corpuscles, Quantum Waves, and the Experiments 113
  14. 9. The Uncertainty Principle as an Intermediary Hypothesis 133
  15. 10. Metaphysical Principles and Heuristic Rules 139
  16. 11. New Formalisms and Bohr’s Atom 151
  17. 12. Complementarity Established and Applied 165
  18. Part 4. Aftermath
  19. 13. Bohr and the “Copenhagen Orthodoxy” 179
  20. 14. Bohr’s Response to the Einstein- Podolsky- Rosen Argument 185
  21. 15. The Mature Bohr and the Rise of Slick Theory and Theoreticians 195
  22. Acknowledgments 205
  23. Notes 207
  24. Bibliography 221
  25. Index 239
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https://doi.org/10.7208/chicago/9780226798479-014

Chapters in this book

  1. Frontmatter i
  2. Contents v
  3. 1. Introduction 1
  4. Part 1. Preliminaries
  5. 2. From Laboratory to Theory 25
  6. 3. From Classical Experiments to Quantum Theory 33
  7. Part 2. Bohr’s Vision in Practice: The Old Quantum Theory
  8. 4. Spectral Lines, Quantum States, and a Master Model of the Atom 59
  9. 5. The Correspondence Principle as an Intermediary Hypothesis 87
  10. 6. Reception 97
  11. 7. The Scientific Moderator 103
  12. Part 3. Toward Quantum Mechanics
  13. 8. Quantum Corpuscles, Quantum Waves, and the Experiments 113
  14. 9. The Uncertainty Principle as an Intermediary Hypothesis 133
  15. 10. Metaphysical Principles and Heuristic Rules 139
  16. 11. New Formalisms and Bohr’s Atom 151
  17. 12. Complementarity Established and Applied 165
  18. Part 4. Aftermath
  19. 13. Bohr and the “Copenhagen Orthodoxy” 179
  20. 14. Bohr’s Response to the Einstein- Podolsky- Rosen Argument 185
  21. 15. The Mature Bohr and the Rise of Slick Theory and Theoreticians 195
  22. Acknowledgments 205
  23. Notes 207
  24. Bibliography 221
  25. Index 239
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