If a photon does not experience time and exists in its full trajectory at a given instant, how does it “perceive” a body moving to cut its path?

Question

OK maybe ELI12 would do.

In: Physics

Answer 1

If we are talking about something moving at “the speed of light” (or the local invariant speed), then either the thing hits the body or doesn’t. If it hits the body, that is because it was already there. If it doesn’t, the body was never there, but always to the side.

Or to put it another way, the object either is instantaneously absorbed by the body if it hits it, or it doesn’t need to “perceive” it because the body is out of its path.

Disclaimer: the rules for SR don’t apply to things travelling at the invariant speed. Also photons don’t always travel at this speed, for given definitions of “photon”, “travel” and “this speed.”