What Is Reality, Anyway?

Imagine you're playing with a ball. You see it, feel it, but what if someone told you that the ball is just your brain's way of understanding something even smaller? To a little kid, reality might be everything they can touch and see right now. But when scientists start asking questions like 'What if we're just dreaming?' or 'Are we all made of atoms?', then reality starts to feel like it has layers.