If you take the normal double slit experiment but shine light on one of the slits so that it's possible to tell which slit each electron went through (by detecting scattered photons) then the "fringes" disappear amd you get constant light. If before the scattered photons hit the photon detector -but after the electrons hit the screen- the information they hold is destroyed (but passing them through a lense for example) then the fringes "should" reappear because now there's no way to tell which slit they passed through but there's no visible (or measurable) difference because there're now two fringe patterens (where one is shifted a little from the other) which can no longer be tild apart. (Is that right so far) My question is, why are there two fringe patterens? I understand why there's one in the middle (by middle I mean one who has a fringe in in the middle of the screen which is the kind of pattern you see in the standerd experiment) by where did the shifted one come from? Thanks.