The heart of quantum mechanics – Counting photons

Each photon hitting the screen is counted with a ball, which drops at the corresponding position on the screen, and is picked up in a pipe. Although the individual hits occur in a purely random manner, a ball distribution gradually forms, which allows for discerning a pattern. This pattern corresponds to the intensity distribution of the electromagnetic wave discussed in the previous slide.

In the case of the double slit, we are likewise selecting a small number of photons. Again, the random distribution of the balls converges to the intensity distribution. In comparison to the single slit, we have considered only half the number of photons, so that the distribution maximum in the centre of the screen is equally high in the case of either the single slit or the double slit.