Interactive Double-Slit Experiment
Note on the Interpretation of the Experiment
In popular science literature, closing one of the two slits is frequently portrayed as the decisive moment when a quantum object sheds its "wave cloak" and suddenly behaves like a classical "particle". This is often seen as the core of the so-called wave-particle duality.
From a physical perspective, this interpretation is untenable. We have deliberately included this experiment here to demonstrate that even when passing through a single slit, the frequency distribution on the measuring screen is exactly described by classical single-slit wave diffraction. There is no sudden change in the nature of the object; rather, the experiment demonstrates the inadequacy of the intuitive categories of "wave" or "particle" for describing quantum objects.
In the theoretical derivation of the plane wave, we saw that the intensity distribution $I_{DS}(\alpha)$ at the double slit is not simply the addition of two independent slits. Coherent superposition at the state level yields the formula:
\begin{equation*} I_{DS}(\alpha) = 4 \cdot I_S(\alpha) \cdot \cos^2\Gamma_+ \end{equation*}In this interactive simulation, you can now continuously vary the parameters of the experiment. Pay special attention to the red dashed curve: it represents the envelope of the interference fringes. As mathematically required, this envelope corresponds exactly to 4 times the single-slit intensity (dotted gray), and not merely to the simple sum.