ABSTRACT
As Professor Victor F. Weisskopf recounts in these interesting movies, Niels Bohr enjoyed reasoning on thought experiments. And he was very careful to draw all the details of the apparatus, specially the screws. More specifically, Einstein's interpretation of the photoelectric effect is often considered a proof of the necessity of describing the light as composed of photons. Wave particle duality for the photon is considered a typical example of quantum behaviour. It is a widely spread belief that all the famous historical "single photon interference experiments" are a definite experimental evidence for the wave-particle duality of light. The quantum theory of light predicts a perfect anticorrelation for detections on both sides of the beam splitter. For a classical-wave description of the light, the intensity is divided on the beam splitter into a reflected and a transmitted part. There is no doubt that these experiments have shown interferences, even with very weak light, evidencing the wave-like behaviour.
