What’s the most beautiful thing created by a human being that helps the world?
As a single thing, I think I would vote for Kurt Goedel’s Incompleteness Theorem.
It proves logically that even in a fully deterministic realm, and given all the rules and all the starting conditions, there will be statements that are true about the system that cannot be proven.
For those who are truly addicted to logic, it forces consideration of uncertainty at a whole new level.
To me, the beauty of this level of recursion is sublime at the highest level of logic.