Book contents
- Frontmatter
- Contents
- List of illustrations
- Preface
- Part I Perspectives on the 1927 Solvay conference
- Part II Quantum foundations and the 1927 Solvay conference
- 5 Quantum theory and the measurement problem
- 6 Interference, superposition and wave packet collapse
- 7 Locality and incompleteness
- 8 Time, determinism and the spacetime framework
- 9 Guiding fields in 3-space
- 10 Scattering and measurement in de Broglie's pilot-wave theory
- 11 Pilot-wave theory in retrospect
- 12 Beyond the Bohr–Einstein debate
- Part III The proceedings of the 1927 Solvay conference
- Appendix
- Bibliography
- Index
7 - Locality and incompleteness
Published online by Cambridge University Press: 05 March 2013
- Frontmatter
- Contents
- List of illustrations
- Preface
- Part I Perspectives on the 1927 Solvay conference
- Part II Quantum foundations and the 1927 Solvay conference
- 5 Quantum theory and the measurement problem
- 6 Interference, superposition and wave packet collapse
- 7 Locality and incompleteness
- 8 Time, determinism and the spacetime framework
- 9 Guiding fields in 3-space
- 10 Scattering and measurement in de Broglie's pilot-wave theory
- 11 Pilot-wave theory in retrospect
- 12 Beyond the Bohr–Einstein debate
- Part III The proceedings of the 1927 Solvay conference
- Appendix
- Bibliography
- Index
Summary
Einstein's 1927 argument for incompleteness
A huge literature arose out of the famous ‘EPR’ paper by Einstein, Podolsky and Rosen (1935), entitled ‘Can quantum-mechanical description of physical reality be considered complete?’. The EPR paper argued, on the basis of (among other things) the absence of action at a distance, that quantum theory must be incomplete. It is less well-known that a much simpler argument, leading to the same conclusion, was presented by Einstein eight years earlier in the general discussion at the fifth Solvay conference (pp. 440ff.).
Einstein compares and contrasts two views about the nature of the wave function ψ, for the specific case of a single electron. According to view I, ψ represents an ensemble (or ‘cloud’) of electrons, while according to view II, ψ is a complete description of an individual electron. Einstein argues that view II is incompatible with locality, and that to avoid this, in addition to ψ there should exist a localised particle (along the lines of de Broglie's theory). Thus, according to this reasoning, if one assumes locality, then quantum theory (as normally understood today) is incomplete.
The conclusion of Einstein's argument in 1927 is the same as that of EPR in 1935, even if the form of the argument is rather different. Einstein considers electrons striking a screen with a small hole that diffracts the electron wave, which on the far side of the screen spreads out uniformly in all directions and strikes a photographic film in the shape of a hemisphere with large radius (see Einstein's figure, p. 440).
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- Quantum Theory at the CrossroadsReconsidering the 1927 Solvay Conference, pp. 175 - 183Publisher: Cambridge University PressPrint publication year: 2009