ELI5: Explain Like I'm 5

Ultrametric space

Imagine you are a Lego builder and you have many Lego pieces of different sizes and shapes. You want to put them together to make a tower, but you can only connect them in a certain way. All Lego pieces have different colours, and you can only connect two pieces if they have the same colour.

Now, let's imagine these Lego pieces are points in a space, and instead of using colours, we measure distances between them. In a regular space, the distance between two points is simply the shortest distance we can travel between them. But in an ultrametric space, the shortest distance between two points might not be a straight line.

To understand ultrametric space, imagine you are at the top of a Christmas tree. From your point of view, every branch looks like it's the same distance away. You can travel from one branch to the other, no matter which branch you're on. This is how ultrametric space works. Every point is the same distance away from every other point, no matter which point you start from.

Now imagine you are climbing down the Christmas tree, and as you get closer to the ground, some branches are farther away than others. If you want to travel from one branch to another, you might have to go up and down a lot before you get there. This is what happens in a regular space. But in an ultrametric space, it doesn't matter where you are on the tree. To get from one point to another, you always have to go straight down the branches or straight up to the trunk.

To sum it up, an ultrametric space is like a Christmas tree, where every point is equidistant from every other point, and the shortest distance between two points might not be a straight line.