ELI5: Explain Like I'm 5

Spherical 3-manifold

Okay kiddo, so imagine you're playing with a ball, a really big ball that's so big you can walk inside it. Now imagine the surface of the ball is your whole world and you can't go outside of it.

Now let's pretend that you live on this ball and you want to explore all of it. But no matter how far you walk, you always end up where you started. This is because the ball is a sphere, which means it's round and has no corners or edges, so the surface loops back on itself.

This is kind of like what a 3-manifold is, but instead of a ball, we're talking about a three-dimensional space that's curved like a sphere. It's like you're living in a universe that's shaped like a ball and you can never leave it because no matter which direction you go, you'll eventually end up where you started.

But it's not just any ball, it's a special type of ball called a spherical 3-manifold. This means that the universe inside this ball is curved in a very specific way that's different from other types of 3-manifolds.

Now, why do mathematicians care about this? Well, it turns out that these types of shapes and spaces have some really interesting properties. They can help us better understand things like geometry, topology, and even the universe itself. Plus, it's just really cool to think about living in a world that's shaped like a giant ball!