Pseudo-Interference in a Single Slit Experiment
with Classical Bodies

The single-slit experiment with particles was one of the most important in the development of modern physics, since it proved the wave-particle duality theory. However, when you have such a critical experiment that opens the door to completely new non-classical conceptions, I think it is wise, before your reach any conclusions, to repeat the experiment with classical bodies so that you know which is your "base line". In this way, you will be able to see clearly any departure from what classical theory predicts, and you will know which "component" is due to non-classical phenomena. This is analogous to the control conditions in a controlled scientific experiment.

Using the applet on the right, we can perform a simple single slit experiment with classical bodies. The applet does not show the bodies, it shows the "corridors" or pathways that are created by this setup. I will explain immediately what I mean. Click here to start. This is the main beam, and the main "corridor" for anything we shoot through the "gun" situated at x = 10. Now, things look simple and innocuous enough.

Let's see however what happens if we increase the slit "length" (as well as its width to unclutter the picture) by clicking here. Now the slit walls have a substantial length, and this allows us to see the "corridors" that were not as clear previously. So in our experiment we will have a number of classical bodies that will hit the walls of the slit following these corridors. And after they hit the walls they will bounce off and they will hit the screen like this.

And now let's increase gradually the slit length even more, to see where can that lead us.

We can see the formation of a "pseudo-interference" pattern, that in fact is created by the bodies that are reflected off the walls of the slit. In this case, the "fringes" of the pseudo-interference are "images" of the slit walls that are "reflected" on the screen. (You can play with the position, the width and the length of the slit using the controls on the right, and see how the pattern changes.) You will notice that under these conditions there is no need for a simultaneous emission of the bodies. This pattern will form even if we send one body per year at the slit, because it just describes the possible paths for the bodies and where they end up.

So, am I proposing that there is no wave-particle duality? Not exactly. I am proposing that there should be a single-slit experiment with classical bodies that will allow us to study pseudo-interference so that we will know what to expect. And then a single-slit experiment with elementary particles that will take into account pseudo-interference and will "subtract" it from the screen pattern, so that we can see what remains. We may very well see a legitimate genuine interference pattern, but until these experiments are performed I would say that we may be on shaky ground.