Originally posted by humy
"Instead, retrocausality means that, when an experimenter chooses the measurement setting with which to measure a particle, that decision can influence the properties of that particle (or another particle) in the past, even before the experimenter made their choice."
Giving this some more thought.
The current state of the universe predicts or determines the past to a much greater accuracy than it predicts or determines the future.
So, once could argue that causality more accurately describes the reverse of the traditional timeline.
When an atom emits a photon, its direction is apparently random. But, when it is detected, we know which direction it went. Hence the detection causes the emission direction and NOT the reverse.
The confusion in the OP is that is sets up another event that puts the detector in a specific spot. So it says, if the detector were moved somewhere else, that would influence where the photon is detected and hence the emission direction. Then it adds the question of causality to the location of the detector ie if the detectors position is dependent on an event prior the experiment. I personally think that what at first looks paradoxical is not actually so. We just have multiple states of the universe in a series that are bound by certain laws of consistency across the states.
In one direction of time, fundamental events appear to be utterly random within the constraints of the laws. In the other direction, they are not so random, and lead to an inexplicable orderliness which is predictable hence our illusion of a fixed past and a less than fixed future.