What Is the Double Slit Experiment?

Imagine you are throwing baseballs at two vertical slits cut into a fence. If the balls go straight through like bullets, they hit the back wall in two distinct lines.

Now imagine those baseballs were actually ghosts. Instead of going through one slit or the other, each ghost goes through both at the same time. When thousands of ghosts throw themselves, they create a striped pattern on the wall, like ripples in a pond overlapping.

Here is the weird part. If you put a camera to watch which slit the ghost uses, it acts like a solid baseball again! It picks one path and stops making stripes. It seems like the act of watching forces the ghost to choose a single reality. This shows us that at a tiny level, things are not fixed until we look.