ELI5: Explain Like I'm 5

120-cell

Okay kiddo, imagine you have a bunch of tiny balls that you can play with, like marbles or beads. Now, let's take 120 of these little balls and put them together in a very special way. We're going to connect them together so that they make a really cool shape called a 120-cell.

But here's the tricky part. The 120-cell isn't like a regular ball or sphere that you can hold in your hand. It's actually a four-dimensional shape! That means it has four dimensions instead of just three like the world we live in.

So, let's imagine that we live in a two-dimensional world, like a flat piece of paper. In that world, we can draw a square, a triangle, or a circle, right? Those are all two-dimensional shapes. But if we lived in a three-dimensional world, like the one we actually live in, we could also draw a cube or a sphere, which are three-dimensional shapes.

And in the same way, the 120-cell is a four-dimensional shape that we can't really imagine in our heads. But we can understand it by looking at a special kind of picture called a projection. This is like making a flat drawing of the shape that we can understand.

So imagine that we have a bunch of tiny balls arranged in a certain way. We can imagine that they're connected by lines, sort of like how we can draw lines between the corners of a square or a triangle. But because we're dealing with four-dimensional space, these lines have to be curved instead of straight.

When we connect all the balls together with these curved lines, we get a really complicated shape that looks like it has a bunch of bubbles inside it. It's called the 120-cell because it has 120 of these little balls, or vertices.

This shape is really important in math and geometry because it has a lot of really interesting properties. For example, it's what's called a regular polytope, which means that all of its faces are the same shape and size. It's also what's called a four-dimensional sphere, which is like a sphere in three-dimensional space but with another dimension added on.

So, in summary, the 120-cell is a really cool shape made up of 120 little balls connected together by curved lines in four-dimensional space. It's hard to imagine, but we can understand it by looking at special pictures called projections. And it's important in math and geometry because of its interesting properties, like being a regular polytope and a four-dimensional sphere.
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