What is the value of "delayed choice" experiments? Disclaimer: I do realize that nearly any experiment deserves to be performed even to make sure the QM theory predicts the results of such experiment right. So I have no objections to the work of people which implemented these sorts of experiments in their labs. The other problem bothers me. If we consider the original works of Wheerler and his thought experiments... I could really understand and appreciate if such works had appeared in 1920-1930ies, that was IMO the right time for these dilemmas, but not 1970ies when these thought experiments were actually proposed. Did anybody think or claim at this time that the electron of photon may "know" ahead the configuration of the experiment and behave accordingly? Was it still the time when people were concerned with wave-particle duality and thought that may be the photon behaves "like a particle" from the beginning if we just remove the 2nd wave spliter in M-Z interferometer? So, forgive me my polemic style above (I do realize I may have very wrong understanding of subtleties of QM and its history) but could somebody explain what was the way of thinking of people who designed and valued these experiments, Wheeler included? What did they try to prove or disprove which was not yet already well known in that time in QM? What is the value of these thought experiments for today? 2nd Disclaimer: my own understanding of these experiments is along the collapse interpretation, I think. I.e. until the particle is detected, it propagates like a wave, then on the detection/measurement the collapse happens according to the Born rule, so that the wave function of one particle (or of two entangled particles) is projected onto the eigenstates defined by measuring device(s). This, I think, gives rather full description (as full as QM currently may give) of what happens in delayed choice experiment of Wheeler with M-Z interferometer, "quantum eraser" of Walborn, "delayed choice quantum eraser" of Kim. Again, I understand, this my understanding may be in some parts wrong, I am just sharing it here so that you know what is in my head.