NPR cosmos & culture: Can We Change The Past?
“An important detail is that the switching over of detecting apparatus must be faster than the time the photon has to travel to the detectors. This way, there is no way the photon could “know” what to do. (If a photon knows anything, anyway.) Experiments presented in October extended the range of the photon’s trip to about 2,200 miles, and still the photon seems to always choose the path consistent with the delayed choice. It is as if — Mike McRae wrote in this Science Alert piece — “that even after the horse has bolted 2,200 miles out of the gate, it can still wait until the finish line to decide which race it ran.” That is, which path to the finish line it took.”