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WARNIG: Contrafactual question

It is commonly known that Einstein was not fond of quantum mechanics -- formulated in the famous quote "God does not play dice with the universe".

This quote comes from the time when the Copenhagen interpretation of quantum mechanics was the dominant one, and one of the main point was the idea of wave functions collapse.

In the modern treatment of quantum mechanics, we don't really need wave function collapse, since we have the mechanism of decoherence. In this picture there in no real randomness, but randomness emerges due to the interplay of lots microscopic degrees of freedom.

Now for the question: If the ideas of decoherence would have been around a few decades earlier, is it possible that Einstein would have been won over of the quantum mechanics camp after all - given that the randomness he was so opposed of isn't really a problem.

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  • $\begingroup$ Decoherence does not eliminate the necessity of collapse, or apparent collapse. What decoherence does is selects a preferred basis and evolves coherent states into mixtures in it. Collapse still has to pick an eigenstate from the mixture "randomly". So decoherence does nothing for Einstein's concerns about God not playing dice, see Why did Einstein oppose quantum uncertainity? $\endgroup$
    – Conifold
    Jun 16, 2017 at 2:31
  • $\begingroup$ @Conifold Here I beg to differ. Decoherence (or interaction with an external environment if you like) entangles the local degrees of freedom with that of the environment - in a perfecly determinisitic manner. How a particular outcomme then gets choosen is to long to write in a comment ;) $\endgroup$
    – Mikael Fremling
    Jul 12, 2017 at 14:35

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The ideas of decoherence cannot avoid the "spukhafte Fernwirkungen" as demonstrated in the Bell-type experiments and save the local realist view of causality that was advocated by Einstein, Podolsky, and Rosen. The problem is not randomness but the predictable behaviour of entangled particles and their violating Bell's inequalities. Entangled photons from a 0 to 0 transition show with certainty 100 % correlation of spins when measured with polarizers under 90° or 0°. This cannot be explained in a local realist model. Therefore the answer is no.

Remark: This seems to be more a speculative and less a historic question.

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  • $\begingroup$ Isn't spukhafte Fernwirkungen distinct from the issue of quantum indeterminacy? (I ask partly per the framing of the question with "God does not play dice" quote, and partly because I'm intensely interested in this aspect of quantum mechanics:) $\endgroup$
    – DukeZhou
    Jun 15, 2017 at 22:01
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    $\begingroup$ @spukhafte Fernwirkungen, i.e., action over a distance with superluminal velocity generates determinacy. When neglecting experimental errors then the polarization of the entangled photons turn out to be always perpendicular to each other. Both pass the crossed polarizers or both are reflected. This cannot be simulated by Malus's law or any law based upon probabilistic local interaction. See also Conifold's comment above. $\endgroup$
    – Franz Kurz
    Jun 16, 2017 at 13:12
  • $\begingroup$ Thank you for the clarification. (I don't pretend to understand it, but it's an incredibly interesting subject!) $\endgroup$
    – DukeZhou
    Jun 16, 2017 at 16:09
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    $\begingroup$ I am aware that quantum mechanics is not a local, realistic, deterministic theory, which is what EPR was looking for. I agree however with @DukeZhou that 'spooky action at a distance' is a different problem than the quantum indeterminacy. The indeterminate (or de-coherence) decides what happens to the first spin, the 'spooky action at a distance' (or entanglement) determines what happens with the second. $\endgroup$
    – Mikael Fremling
    Jul 12, 2017 at 14:22

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