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If, according to relativity, time doesnt pass for a photon and everything is instantaneous (or if the world is so compressed in the direction of travel that it becomes almost 2 dimentional), then the quantum delayed choice experiment (QDCE) makes much more sense because a photon knows no past or future. If that's the right explanation then the QDCE should not work for other particles. Should it ?

M. Enns
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Manu de Hanoi
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    "According to relativity, time doesn't pass for a photon" is a phrase of debatable meaningfulness, cf. https://physics.stackexchange.com/q/29082/50583. Many would say that a photon doesn't have a notion of time - time is not "frozen" for it, the notion simply does not make any sense. – ACuriousMind Aug 19 '17 at 23:43

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I agree: If that were the correct explanation, the delayed choice experiments work only for photons. However, de Broglis idea that particles can behave wavelike, turned out to be very fruitful and many matter (electrons, atoms, neutrons) double slit experiments have verified this. So a distinction between massless photons and massive particles is somewhat prehistoric.

Here a part from the summary from this paper: It is a general feature of delayed-choice experiments that quantum effects can mimic an influence of future actions on past events. However, there never emerges any paradox if the quantum state is viewed only as "catalogue of our knowledge" (Schroedinger, 1935) without any underlying hidden variable description. Then the state is a probability list for all possible measurement outcomes and not a real physical object. The relative temporal order of measurement events is not relevant, and no physical interactions or signals, let alone into the past, are necessary to explain the experimental results. To interpret quantum experiments, any attempt in explaining what happens in an individual observation of one system has to include the whole experimental configuration and also the complete quantum state, potentially describing joint properties with other systems. According to Bohr and Wheeler, no elementary phenomenon is a phenomenon until it is a registered phenomenon (Bohr, 1949; Wheeler, 1984). In light of quantum erasure and entanglement swapping, one might like to even say that some registered phenomena do not have a meaning unless they are put in relationship with other registered phenomena (Ma et al., 2012).

Semoi
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