putting photon detectors on each slit causes the photon to behave as a particle as it passes through the double slit: the detectors force each photon to pass through only one slit, and thus not interfere with themselves, when before they were free to behave as waves and pass through both slits. But asking where the photon was before the measurement is meaningless: waves have no singular location. The property measured was created by the measurement itself, and to ask about its location beforehand is mere sophistry.
main
