Is there any reason to take such a picture seriously? Can we not regard the photon as simply having a 50 per cent probability that it is in one of the places and a 50 per cent probability that it is in the other? No, we cannot! No matter for how long it has travelled, there is always the possibility that the two parts of the photon’s beam may be reflected back so that they encounter one another, to achieve interference effects that could not result from a probability weighting for the two alternatives.
