When particles are shot at the plate/screen in the double slit experiment, why doesn't the particles interact with the screen? Shouldn't the plate act as an observer and "collapse" the wave function into one or the other slit? Why does it take a measuring apparatus to know which slit the particle went through? Here's a pic: The screen is a classical object so shouldn't the particles interact with the screen? The detector plate is classical. It's said Schrodinger's cat will end up in one state or the other because of decoherence. Why doesn't that apply to the screen/plate and the detector plate? So if you had the cat in the box, wouldn't it have to be in both states like the screen/plate until a measuring apparatus or human measured it? Let's replace the cat with a tennis ball. If the atom decays, the ball explodes but if it doesn't the ball is fine. Without a measuring device, doesn't the ball have to be in two states until a measurement occurs? The screen/plate isn't in a single state. It's not particle through left slit or particle through right slit until measured. So why would a cat be dead/alive or the tennis ball be exploded/not exploded until a measuring apparatus measured it? The wave function must contain both states of the cat/ball until it's measured. There may be a single cat/ball in the box but do they have an objective existence until a measurement occurs?