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If a detector is kept at the two slits the fringes disappear. But, when the detectors are removes do the fringes come up immediately without any significant time lag?
Can there be a way to switch on and off the detector so fast that it all happens within the time required for the light to reach the screen form the source? What would be the result if it is possible?
The time lag is the amount of time it takes for the light that has not been detected to reach the screen. That is, the distance from the slits to the screen divided by the speed of light.
If you turn the detector on and off, then the screen will show a flickering of fringes/no-fringes.
