Abacus9900. Your description of the 'delayed choice quantum eraser experiment' is the best I have seen. If you are not already an author of PS books, perhaps you should consider that. "Hitch-hikers" like me need clear explanations.
Thank you Bill S., but it took me a while to really get my head around it and I'm still not sure I have fully grasped it! I only wished I had the talent to write books!
Lost here! In the case of a single photon, does the device generate a second photon which is then entangled with the first? If this is the case, how does the second photon, which did not exist when the first photon passed through the slit(s) "know" which slit(s) the first photon came through?
Well, I do not claim to be an expert by any stretch of the imagination, but I think the basic explanation is that when a photon is 'split' into two entangled photons they still act as one system (whatever that means). I think they share the energy of the original photon. I don't think anyone really knows how two entangled photons are able to be aware of what happens to each one. What puzzles me is how can something as simple as a photon 'know' what a complicated piece of apparatus as used in the experiment we have been discussing is measuring? On top of that it seems to be aware of what the experimenter is doing at a later time!
It kind of makes you wonder whether our simplistic understanding of our four dimensional spacetime universe needs radical revision in order to account for all these strange events. David Deutsch could be right!
