I m new to quantum mechanics and read about how an observation causes the quantum object to change from wave to particle in the double slit experiment. How it's done is that whenever scientists put a measuring device to fing which path they went, they act like particles instead of waves if there are no measuring devices. It seems to show that the objects knows that they are watched. In the delayed choice experiment, the detectors are put after the slits and the quantum objects still acted like particles, which suggest that they somehow know that the detectors were there. What's really going on in here, can somebody please explain?