ELI5: Explain Like I'm 5

Brill–Noether theory

Brill–Noether theory is like a game of collectible cards where certain rules determine how many cards you can collect and what kind of cards you can collect. In this game, a "curve" is like a deck of cards, and the "cards" are called "line bundles." Each line bundle is like a fancy sleeve that you put on your deck of cards, and it determines which cards you can add to your deck.

Now, the rules of the game (or the theory) say that not every deck can have all types of sleeves. Depending on the number of cards in your deck and the type of sleeves you choose, sometimes you can't add any more cards. This is what is called a "Brill–Noether curve." It's like having a deck that is already so powerful, that you can't add any more fancy sleeves to it.

But why is this important, you might ask? Well, mathematicians use this theory to study curves, and curves show up in lots of places - computer graphics, physics, and more! By understanding how to play this game of collectible cards with curves (and using the rules of Brill–Noether theory), mathematicians can discover hidden patterns and properties of these curves, which can in turn help them understand the world better.