The experiments considered in this lesson can also be viewed from the point of view of wave-particle duality.
Experiment 3.6 can be understood as a contradiction to the idea that photons behave according to the wave model inside the interferometer. According to wave theory, the intensity of the incident beam would be divided equally between the two arms of the interferometer at the semi-transparent mirror. One would then expect the two detectors to register the same intensity at every instant, albeit reduced compared with the incident beam. This is not what happens in the experiment. The detectors in fact never both register a non-zero intensity at the same time. The prediction of wave theory is not confirmed by the experiment.
The experimental result, on the other hand, agrees with the particle model. The fact that only one of the two detectors ever responds means that photons are always detected undivided, as a whole. Their entire energy is absorbed by the detector at a particular place and at a particular time. This corresponds to a particle-like picture.
Experiments 3.4 and 3.5 with polarization filters, by contrast, strongly indicated that no path can be assigned to a photon. They thus contradict the particle model. Taken together, the experiments show once again that the wave and particle models are individually insufficient to describe the observed phenomena.