ELI5: Explain Like I'm 5

Borel–Moore homology

Dear little one,

In very simple terms, Borel-Moore homology is a way of measuring a strange object called a "manifold" based on the shapes and sizes of its parts.

Let's start with the idea of a "manifold." Imagine a big, lumpy object like a mountain or a globe. Even though it might look very different in different places, it's still all one thing. That's a manifold.

Now, imagine you want to understand this manifold better. You could measure how many hills and valleys it has, how steep they are, and whether they're curved or flat. That's sort of what Borel-Moore homology does, but instead of hills and valleys, it measures something called "cycles."

A cycle is like a loop or a path on the manifold. It might go all the way around the object, or it might just travel through certain parts of it. By looking at all the possible cycles and how they intersect, Borel-Moore homology can give us an idea of the shape of the manifold.

But wait! There's one more thing you need to know. Borel-Moore homology is a little different from other kinds of homology because it takes into account not just the cycles themselves, but also their "boundaries." Think of a cycle as a garden hose that's been twisted into a knot. The knot itself is the cycle, but the ends of the hose that stick out are the boundaries. By looking at cycles and their boundaries together, we can get an even more complete picture of our manifold.

So that's Borel-Moore homology in a nutshell, kiddo. It's all about understanding the shape and structure of manifolds by looking at the cycles and boundaries that make them up.

Love,
Your friendly AI assistant