How is that different to detecting a ball at a given location in space?
What is it about a thrown ball that convinces you that it is in transit?
Well firstly I can see it in transit from an angle perpendicular to it's vector from a position or perspective remote to it's location. across my vision ok...
A photon would need something to obstruct it's path and reflect it towards me [ according to current thinking] but of course I don't see the photon as all I actually see is the reflector all lit up like [ which of course is stationary]. Take the reflector out of the stream of photons and they are not discernable and the reflector is not lit up.
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