I've always been fascinated with how physics helps to define the physical reality around us. It's interesting that just a few simple rules and relationships can produce immense complexity. The four fundamental forces are at the heart of the matter, but even though we know a lot about the effects of these forces, we still don't know everything about how they actually work.
That's a fertile question for science, the answer to that question might just answer a lot of questions about the nature of reality.