We got a light source and the light comes through a slit in a plate. A photon passes through the slit and ends up somewhere on a screen not in the straight direction due to diffraction. The question is, in quantum physics, does the plate feel the reaction of the photon deflection (1) at the time it passes through the hole or (2) at the time it reaches the screen? (1)If the reaction happens at time the photon passes through the hole, then, we could, with a very light plate, measure the reaction force to an arbitrary precision. And we know the error in position, it's the same as the slit width. What will stop us from measuring the reaction to a high precision, so that heisenberg uncertainity principle is obeyed? (2)If the reaction happens when the photon reaches the screen, then, by having two screens, we can open one sometimes so that the light goes further, to the second. And when it's closed, it'll go closer distance. So then, we can send information at a speed greater than the speed of light from the screens back to the plate by measuring it's reaction.