I have some questions about double slit experiment. 1) Sometimes photons or electrons should bounce off the initial barrier and nothing should be detected in the plate. ¿Is this correct? i find a video saying that NOTHING is detected in the barrier, only in the plate. 2) If we put 1 detector in one slit, then it is posible to KNOW the position of an electron passing trough the other slit without interact with it. There is no PHYSICAL INTERACTION but wave function collapses anyway, so we are not speaking of a material phenomena. ¿Is this correct? 3) In the delayed choice quantum eraser the photon is entangled before it hits the plate. The entangled photon follows a path that sometimes erases the "which path" information resulting in the well known retrocausal observations. My question is: if both photons follow a path that destroy the "Which-path" information then we will observe an interference pattern IN ALL DETECTORS. What will take place if the entangled photon travels trough space, then bounce off a mirror and returns 5 minutes later? The experimenter have had time to observe the interference pattern in the original plate and change the experiment configuration to preserve "which-path" information. ¿Is this possible?