ELI5: Explain Like I'm 5

Tree-graded space

Imagine you are trying to climb a really big tree. The tree has lots of branches, some higher up and some lower down. You might start at the bottom and climb up the branches, but you can only move up or down one branch at a time. Some branches might be really close together, while others might be far apart.

Now imagine that instead of a physical tree, you have a "tree-graded space". This is a fancy term for a type of mathematical object that looks like a tree. Just like the branches on a tree, the space is made up of different "levels" or "layers". Each level contains a bunch of points that are all the same "distance" from the base of the tree (the bottom). But the distance here means something a little different from what we normally think of. It's actually a way to measure how different two points are.

At the bottom of the tree, all the points are really close together (they're all "equivalent" to each other). But as you move up the tree, the points become more and more different from each other (they're not equivalent anymore). This happens because the distance between points on different levels is usually greater than the distance between points on the same level. It's like climbing up branches that are further and further apart.

Why is this useful? Well, tree-graded spaces come up in lots of different areas of math and science. For example, they can be used to study the relationships between different shapes or objects. They can also help us understand how things change over time (for instance, if we're measuring something that evolves in a certain way, like the population of a species of animal). So while they might sound a little complicated at first, tree-graded spaces are actually a really cool tool that help us make sense of all sorts of things in the world around us.