ELI5: Explain Like I'm 5

Wonderful compactification

Have you ever tried to pack too many toys into a small box and had trouble closing the lid? That's kind of like the problem mathematicians have when they try to understand spaces that go on forever. But they came up with a clever solution called wonderful compactification!

Imagine you have a really big room with lots of doors and windows. If you look inside the room, you might see a table or a couch or a lamp. But if you look outside the room from one of the doors or windows, you might see a tree or a car or a person. The room is part of a bigger space that includes everything inside and outside it.

Now, let's say you want to understand that big space better, but you're having trouble because it goes on forever. What you could do is imagine closing up all the doors and windows and making the room a little bit smaller, so everything inside it is closer together. You might lose some of the things you could see outside the room, but what you have left is a nice, compact space that's easier to understand.

That's kind of like what wonderful compactification does. It takes a really big space with lots of weird, complicated parts, and it squishes it down into a smaller space with fewer parts. But it does it in a really clever way that makes it easy for mathematicians to study the space and figure out all kinds of interesting things about it.