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24-cell

math Maturity 7-9 Next article →

Imagine a shape that lives in four dimensions.

24-cell
24-cell

We call this shape the 24-cell. It is a very special type of object called a regular 4-polytope. This means all its parts are exactly the same. It is a shape that exists beyond the three dimensions we see every day.

Octahedron
Octahedron

The 24-cell is built from 24 smaller shapes called octahedral cells. An octahedron is a solid shape with eight triangular faces. In this four-dimensional shape, these octahedra join together in a very precise way. It is a beautiful example of how math creates order in high dimensions.

To understand how it works, we can look at its parts. The 24-cell has 24 vertices, which are its corners. It also has 96 edges and 96 triangular faces.

24-cell-6 ring edge center perspective
24-cell-6 ring edge center perspective

At every vertex, six octahedral cells meet together. At every edge, exactly three cells meet. This specific pattern makes the shape very balanced. It is also self-dual, which is a special math property. This means the shape can be turned into its own twin. This is similar to how a 5-cell works in four dimensions.

Mathematicians use special symbols to describe these complex shapes. The 24-cell has a symbol called {3,4,3}. It also goes by many other names like the icositetrachoron or the octaplex.

OctacCrop
OctacCrop

Some people call it the hyper-diamond or the polyoctahedron. It is the fourth shape in a sequence of six regular 4-polytopes. These shapes can be ordered by how much space they fill. The 24-cell is more complex than the tesseract. However, it is smaller and less complex than the 120-cell.

This shape has amazing connections to other parts of math. For example, its 24 vertices can represent something called root vectors.

F4 roots by 24-cell duals
F4 roots by 24-cell duals

These vectors belong to a group called F4. The 24-cell can even be used to build a honeycomb.

Icositetrachoronic tetracomb
Icositetrachoronic tetracomb

This is a way to tile four-dimensional space perfectly. In this honeycomb, each 24-cell has 24 neighbors. They fit together without leaving any gaps. This makes it a very important tool for studying space.

When the 24-cell rotates, it does something very strange.

24-cell-orig
24-cell-orig

It can perform a double rotation. This means it turns in two different directions at once. In one special kind of rotation, the shape seems to turn inside out. This is called an isoclinic rotation. It can even change its chirality, which is a fancy word for handedness. This is like how a mirror makes your right hand look like a left hand. It is a wonderful way to see how math works in four dimensions.

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🖼️ Images & Media (16)
File:Octahedron.png
Octahedron.png
File:F4 roots by 24-cell duals.svg
F4 roots by 24-cell duals.svg
File:Binary tetrahedral group elements.png
Binary tetrahedral group elements.png
File:Icositetrachoronic tetracomb.png
Icositetrachoronic tetracomb.png
File:24-cell.gif
24-cell.gif
File:24-cell-orig.gif
24-cell-orig.gif
File:Hopf band wikipedia.png
Hopf band wikipedia.png
File:Regular_star_figure_4(6,1).svg
Regular_star_figure_4(6,1).svg
File:Regular_star_figure_4(3,1).svg
Regular_star_figure_4(3,1).svg
File:Regular_star_figure_2(6,1).svg
Regular_star_figure_2(6,1).svg
File:Regular_polygon_24.svg
Regular_polygon_24.svg
File:Regular_star_figure_12(2,1).svg
Regular_star_figure_12(2,1).svg

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