The Double-Slit Bombshell

Fire electrons one at a time at a wall with two thin slits. Behind the wall, place a detector. You would expect two clusters of hits — one behind each slit. Like throwing baseballs through two doorways.

This is what waves produce passing through two openings — overlapping, reinforcing in some spots, cancelling in others. But these are individual particles. Each electron somehow passes through both slits simultaneously and interferes with itself. The result shattered classical physics.