Foundations of Physics

, Volume 8, Issue 7–8, pp 615–628 | Cite as

Proof of a retroactive influence

  • C. W. Rietdijk


Quantum theory predicts that, e.g., in a Stern-Gerlach experiment with electrons the measured spin component\(S_Z = \pm \frac{1}{2}\) does not come about by an adjustment at the last moment, a forced “flipping” or “tilting” of the spin (vector), which would imply z-angular momentum exchange between particle and instrument, but will afterward appear to have had the value\(\frac{1}{2} or - \frac{1}{2}\) already before the measurement. Because an electron spin cannot have components\( \pm \frac{1}{2}\) in all directions at the same time, the measuring direction has a “privileged” status before the measurement, however we choose that direction, which implies a retroactive effect. A second proof of retroactivity is derived from a special case of the paradox of Einstein, Podolsky, and Rosen. It is strongly suggested by our result that, in essential respects, both Bohr and Einstein were right in their famous controversy about determinism and considering microprocesses “as a whole.”


Measuring Direction Rosen Quantum Theory Electron Spin Spin Component 
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Copyright information

© Plenum Publishing Corporation 1978

Authors and Affiliations

  • C. W. Rietdijk
    • 1
  1. 1.BloemendaalThe Netherlands

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