Do I Misunderstand The Double Slit Experiment

[Borodog]

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so ... what happens if we set up the cameras to watch the slits, and we bring two people into the room.

Person A does not know the cameras are set up and can see the screen. What does he see?

Person B knows the cameras are set up, but can't see the screen. Afterwards, he takes the camera, falls down and the film is destroyed. He returns to the screen, what does he see?

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Do A and B ever communicate with each other?

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At this point in time, Person A returns, does what he see differ than what he saw earlier?

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I didn't know A ever left? What difference would that make? The screen cannot magically change from what he has previously seen.