Intuitive

When we shoot balls onto a double slit, most balls will end up somewhere in the middle. If we open just one of the slits, we will find most balls somewhere directly behind the slit. The result with both slits open is simply the addition of the two results with one slit closed.

In contrast, if we send waves like they appear in water onto a double slit the result is remarkably different. While the results with one slit closed are the same as for the balls, we see something completely different if both slits are open at the same time: an interference pattern.

Now, if we send individual electrons onto a double slit we would naively expect the same result as for balls. However, in reality, we observe an interference pattern like we did for waves.

The double slit experiment, therefore, exemplifies that we need waves to describe particles.

• Surfing and the double-slit experiment by Brian Skinner

Concrete

• A great discussion can be found in Vol. 3 of the Feynman Lectures.

Abstract

Why is it interesting?

[The Double Slit Experiment] which is impossible, absolutely impossible, to explain in any classical way, has in it the heart of quantum physics

Richard Feynman

…the most (in)famous quantum mechanical experiment of all: the double-slit experiment.Surfing and the double-slit experiment by Brian Skinner