ELI5: Explain Like I'm 5

Fiber-homotopy equivalence

Imagine you have a toy castle and a toy knight. The castle has two different ways to get from the entrance to the courtyard - you can either walk straight through the main gate or take a secret tunnel that goes under the castle walls.

Now, let's say you want to prove that these two paths are basically the same. To do this, you take your toy knight and start at the entrance of the castle. You walk straight through the main gate and end up in the courtyard. Then you take the secret tunnel and come out again in the courtyard. You notice that no matter which path you took, you ended up in the same place - the courtyard.

In the world of math, we call this a fiber-homotopy equivalence. A fiber is basically like a path or route, and homotopy means that two different fibers or paths are basically the same. So when we say something is fiber-homotopy equivalent, it means that there are two different routes or paths that get you to the same place.

But why is fiber-homotopy equivalence important? Well, in math, we often use something called a topological space, which is basically just a bunch of points and how they're related to each other - like your toy castle and the different paths you can take. When we have a fiber-homotopy equivalence between two topological spaces, it tells us that even though they might look different, they're actually the same in some important way.

So just like how your toy knight can take two different paths to get to the same place in the castle, in math we can have two different topological spaces that are basically the same because they have a fiber-homotopy equivalence between them.