120-cell


120-cell
120-cell
Schlegel wireframe 120-cell.png
Schlegel diagram
(vertices and edges)
Type Convex regular 4-polytope
Schläfli symbol {5,3,3}
Coxeter-Dynkin diagram CDel node 1.pngCDel 5.pngCDel node.pngCDel 3.pngCDel node.pngCDel 3.pngCDel node.png
Cells 120 {5,3} Dodecahedron.png
Faces 720 {5} Regular pentagon.svg
Edges 1200
Vertices 600
Vertex figure 120-cell verf.png
tetrahedron
Petrie polygon 30-gon
Coxeter group H4, [3,3,5]
Dual 600-cell
Properties convex, isogonal, isotoxal, isohedral
Uniform index 32

In geometry, the 120-cell (or hecatonicosachoron) is the convex regular 4-polytope with Schläfli symbol {5,3,3}.

The boundary of the 120-cell is composed of 120 dodecahedral cells with 4 meeting at each vertex.

It can be thought of as the 4-dimensional analog of the dodecahedron and has been called a dodecaplex (short for "dodecahedral complex"), hyperdodecahedron, and polydodecahedron. Just as a dodecahedron can be built up as a model with 12 pentagons, 3 around each vertex, the dodecaplex can be built up from 120 dodecahedrons, with 3 around each edge.

The Davis 120-cell, introduced by Davis (1985), is a compact 4-dimensional hyperbolic manifold obtained by identifying opposite faces of the 120-cell, whose universal cover gives the regular honeycomb {5,3,3,5} of 4-dimensional hyperbolic space.

Contents

Elements

  • There are 120 cells, 720 pentagonal faces, 1200 edges, and 600 vertices.
  • There are 4 dodecahedra, 6 pentagons, and 4 edges meeting at every vertex.
  • There are 3 dodecahedra and 3 pentagons meeting every edge.

Cartesian coordinates

The 600 vertices of the 120-cell include all permutations of:[1]

(0, 0, ±2, ±2)
(±1, ±1, ±1, ±√5)
(±φ-2, ±φ, ±φ, ±φ)
(±φ-1, ±φ-1, ±φ-1, ±φ2)

and all even permutations of

(0, ±φ-2, ±1, ±φ2)
(0, ±φ-1, ±φ, ±√5)
(±φ-1, ±1, ±φ, ±2)

where φ (also called τ) is the golden ratio, (1+√5)/2.

Visualization

The 120-cell consists of 120 dodecahedral cells. For visualization purposes, it is convenient that the dodecahedron has opposing parallel faces (a trait it shares with the cells of the tesseract and the 24-cell). One can stack dodecahedrons face to face in a straight line bent in the 4th direction into a great circle with a circumference of 10 cells. Starting from this initial ten cell construct there are two common visualizations one can use: a layered stereographic projection, and a structure of intertwining rings.

Layered stereographic projection

The cell locations lend themselves to a hyperspherical description. Pick an arbitrary cell and label it the "North Pole". Twelve great circle meridians (four cells long) radiate out in 3 dimensions, converging at the 5th "South Pole" cell. This skeleton accounts for 50 of the 120 cells (2 + 4*12).

Starting at the North Pole, we can build up the 120-cell in 9 latitudinal layers, with allusions to terrestrial 2-sphere topography in the table below. With the exception of the poles, each layer represents a separate 2-sphere, with the equator being a great 2-sphere. The centroids of the 30 equatorial cells form the vertices of an icosidodecahedron, with the meridians (as described above) passing through the center of each pentagonal face. The cells labeled "interstitial" in the following table do not fall on meridian great circles.

Layer # Number of Cells Description Colatitude Region
1 1 cell North Pole Northern Hemisphere
2 12 cells First layer of meridian cells 36°
3 20 cells Non-meridian / interstitial / "Tropic of Cancer" 60°
4 12 cells Second layer of meridian cells 72°
5 30 cells Non-meridian / interstitial 90° Equator
6 12 cells Third layer of meridian cells 108° Southern Hemisphere
7 20 cells Non-meridian / interstitial / "Tropic of Capricorn" 120°
8 12 cells Fourth layer of meridian cells 144°
9 1 cell South Pole 180°
Total 120 cells

Layers 3 and 7's cells are located directly over the pole cell's vertices. Layer 5's cells are located over the pole cell's edges.

Intertwining rings

Two intertwining rings of the 120-cell.

The 120-cell can be partitioned into 12 disjoint 10-cell great circle rings, forming a discrete/quantized Hopf fibration. Starting with one 10-cell ring, one can place another ring along side it that spirals around the original ring one complete revolution in ten cells. Five such 10-cell rings can be placed adjacent to the original 10-cell ring. Although the outer rings "spiral" around the inner ring (and each other), they actually have no helical torsion. They are all equivalent. The spiraling is a result of the 3-sphere curvature. The inner ring and the five outer rings now form a six ring, 60-cell solid torus. One can continue adding 10-cell rings adjacent to the previous ones, but it's more instructive to construct a second torus, disjoint from the one above, from the remaining 60 cells, that interlocks with the first. The 120-cell, like the 3-sphere, is the union of these two (Clifford) tori. If the center ring of the first torus is a meridian great circle as defined above, the center ring of the second torus is the equatorial great circle that is centered on the meridian circle. Also note that the spiraling shell of 50 cells around a center ring can be either left handed or right handed. It's just a matter of partitioning the cells in the shell differently, i.e. picking another set of disjoint great circles.

Other great circle constructs

There is another great circle path of interest that alternately passes through opposing cell vertices, then along an edge. This path consists of 6 cells and 6 edges. Both the above great circle paths have dual great circle paths in the 600-cell. The 10 cell face to face path above maps to a 10 vertices path solely traversing along edges in the 600-cell, forming a decagon. The alternating cell/edge path above maps to a path consisting of 12 tetrahedrons alternately meeting face to face then vertex to vertex in the 600-cell.

Projections

Orthogonal projections

Orthogonal projections of the 120-cell can be done in 2D by defining two orthonormal basis vectors for a specific view direction.

Orthographic projections by Coxeter planes
H4 - F4
120-cell graph H4.svg
[30]
120-cell t0 p20.svg
[20]
120-cell t0 F4.svg
[12]
H3 A2 / B3 / D4 A3 / B2
120-cell t0 H3.svg
[10]
120-cell t0 A2.svg
[6]
120-cell t0 A3.svg
[4]

3-dimensional orthogonal projections can also be made with three orthonormal basis vectors, and displayed as a 3d model, and then projecting a certain perspective in 3D for a 2d image.

3D orthographic projections
120Cell 3D.png
3D isometric projection

Animated 4D rotation

Perspective projections

These projections use perspective projection, from a specific view point in 4-dimensions, and projecting the model as a 3D shadow. Therefore faces and cells that look larger are merely closer to the 4D viewpoint. Schlegel diagrams use perspective to show 4 dimensional figures, choosing a point above a specific cell, thus making the cell as the envelope of the 3D model, and other cells are smaller seen inside it. Stereographic projection use the same approach, but are shown with curved edges, representing the polytope a tiling of a 3-sphere.

A comparison of perspective projections from 3D to 2D is shown in anology.

Comparison with regular dodecahedron
Projection Dodecahedron Dodecaplex
Schlegel diagram Dodecahedron schlegel diagram.png
12 pentagon faces in the plane
Schlegel wireframe 120-cell.png
120 dodecahedral cells in 3-space
Stereographic projection Dodecahedron stereographic projection.png Stereographic polytope 120cell faces.png
With transparent faces
Perspective projection
120-cell perspective-cell-first-02.png Cell-first perspective projection at 5 times the distance from the center to a vertex, with these enhancements applied:
  • Nearest dodecahedron to the 4D viewpoint rendered in yellow
  • The 12 dodecahedra immediately adjoining it rendered in cyan;
  • The remaining dodecahedra rendered in green;
  • Cells facing away from the 4D viewpoint (those lying on the "far side" of the 120-cell) culled to minimize clutter in the final image.
120-cell perspective-vertex-first-02.png Vertex-first perspective projection at 5 times the distance from center to a vertex, with these enhancements:
  • Four cells surrounding nearest vertex shown in 4 colors
  • Nearest vertex shown in white (center of image where 4 cells meet)
  • Remaining cells shown in transparent green
  • Cells facing away from 4D viewpoint culled for clarity
120-cell.gif A 3D projection of a 120-cell performing a simple rotation.
120-cell-inner.gif A 3D projection of a 120-cell performing a simple rotation (from the inside).
Animated 4D rotation

See also

Notes

References

  • H. S. M. Coxeter, Regular Polytopes, 3rd. ed., Dover Publications, 1973. ISBN 0-486-61480-8.
  • Kaleidoscopes: Selected Writings of H.S.M. Coxeter, editied by F. Arthur Sherk, Peter McMullen, Anthony C. Thompson, Asia Ivic Weiss, Wiley-Interscience Publication, 1995, ISBN 978-0-471-01003-6 [1]
    • (Paper 22) H.S.M. Coxeter, Regular and Semi-Regular Polytopes I, [Math. Zeit. 46 (1940) 380-407, MR 2,10]
    • (Paper 23) H.S.M. Coxeter, Regular and Semi-Regular Polytopes II, [Math. Zeit. 188 (1985) 559-591]
    • (Paper 24) H.S.M. Coxeter, Regular and Semi-Regular Polytopes III, [Math. Zeit. 200 (1988) 3-45]
  • J.H. Conway and M.J.T. Guy: Four-Dimensional Archimedean Polytopes, Proceedings of the Colloquium on Convexity at Copenhagen, page 38 und 39, 1965
  • Davis, Michael W. (1985), "A hyperbolic 4-manifold", Proceedings of the American Mathematical Society 93 (2): 325–328, doi:10.2307/2044771, ISSN 0002-9939, MR770546 
  • N.W. Johnson: The Theory of Uniform Polytopes and Honeycombs, Ph.D. Dissertation, University of Toronto, 1966
  • Four-dimensional Archimedean Polytopes (German), Marco Möller, 2004 PhD dissertation [2]

External links

H4 family polytopes by name, Coxeter-Dynkin diagram, and Schläfli symbol
120-cell rectified
120-cell
truncated
120-cell
cantellated
120-cell
runcinated
120-cell
bitruncated
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cantitruncated
120-cell
runcitruncated
120-cell
omnitruncated
120-cell
CDel node 1.pngCDel 5.pngCDel node.pngCDel 3.pngCDel node.pngCDel 3.pngCDel node.png CDel node.pngCDel 5.pngCDel node 1.pngCDel 3.pngCDel node.pngCDel 3.pngCDel node.png CDel node 1.pngCDel 5.pngCDel node 1.pngCDel 3.pngCDel node.pngCDel 3.pngCDel node.png CDel node 1.pngCDel 5.pngCDel node.pngCDel 3.pngCDel node 1.pngCDel 3.pngCDel node.png CDel node 1.pngCDel 5.pngCDel node.pngCDel 3.pngCDel node.pngCDel 3.pngCDel node 1.png CDel node.pngCDel 5.pngCDel node 1.pngCDel 3.pngCDel node 1.pngCDel 3.pngCDel node.png CDel node 1.pngCDel 5.pngCDel node 1.pngCDel 3.pngCDel node 1.pngCDel 3.pngCDel node.png CDel node 1.pngCDel 5.pngCDel node 1.pngCDel 3.pngCDel node.pngCDel 3.pngCDel node 1.png CDel node 1.pngCDel 5.pngCDel node 1.pngCDel 3.pngCDel node 1.pngCDel 3.pngCDel node 1.png
{5,3,3} t1{5,3,3} t0,1{5,3,3} t0,2{5,3,3} t0,3{5,3,3} t1,2{5,3,3} t0,1,2{5,3,3} t0,1,3{5,3,3} t0,1,2,3{5,3,3}
120-cell t0 H3.svg 120-cell t1 H3.svg 120-cell t01 H3.svg 120-cell t02 H3.png 120-cell t03 H3.png 120-cell t12 H3.png 120-cell t012 H3.png 120-cell t013 H3.png 120-cell t0123 H3.png
600-cell t0 H3.svg 600-cell t1 H3.svg 600-cell t01 H3.svg 600-cell t02 H3.svg 120-cell t03 H3.png 120-cell t023 H3.png
600-cell rectified
600-cell
truncated
600-cell
cantellated
600-cell
runcinated
600-cell
bitruncated
600-cell
cantitruncated
600-cell
runcitruncated
600-cell
omnitruncated
600-cell
CDel node.pngCDel 5.pngCDel node.pngCDel 3.pngCDel node.pngCDel 3.pngCDel node 1.png CDel node.pngCDel 5.pngCDel node.pngCDel 3.pngCDel node 1.pngCDel 3.pngCDel node.png CDel node.pngCDel 5.pngCDel node.pngCDel 3.pngCDel node 1.pngCDel 3.pngCDel node 1.png CDel node.pngCDel 5.pngCDel node 1.pngCDel 3.pngCDel node.pngCDel 3.pngCDel node 1.png CDel node 1.pngCDel 5.pngCDel node.pngCDel 3.pngCDel node.pngCDel 3.pngCDel node 1.png CDel node.pngCDel 5.pngCDel node 1.pngCDel 3.pngCDel node 1.pngCDel 3.pngCDel node.png CDel node.pngCDel 5.pngCDel node 1.pngCDel 3.pngCDel node 1.pngCDel 3.pngCDel node 1.png CDel node 1.pngCDel 5.pngCDel node.pngCDel 3.pngCDel node 1.pngCDel 3.pngCDel node 1.png CDel node 1.pngCDel 5.pngCDel node 1.pngCDel 3.pngCDel node 1.pngCDel 3.pngCDel node 1.png
{3,3,5} t1{3,3,5} t0,1{3,3,5} t0,2{3,3,5} t0,3{3,3,5} t1,2{3,3,5} t0,1,2{3,3,5} t0,1,3{3,3,5} t0,1,2,3{3,3,5}

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Look at other dictionaries:

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  • Omnitruncated 120-cell — In geometry, the omnitruncated 120 cell is a convex uniform polychoron composed of 2640 cells: 120 truncated icosidodecahedra, 600 truncated octahedra, 720 decagonal prisms, and 1200 pentagonal prisms.It also has 14400 vertices, 28800 edges, and… …   Wikipedia

  • Bitruncated 120-cell — In geometry, the bitruncated 120 cell is a uniform polychoron. Alternate names * Bitruncated 120 cell / Bitruncated 600 cell (Norman W. Johnson) ** Bitruncated hecatonicosachoron / Bitruncated hexacosichoron ** Bitruncated polydodecahedron /… …   Wikipedia

  • Rectified 120-cell — In geometry, the rectified 120 cell is a convex uniform polychoron composed of 600 regular tetrahedra and 120 icosidodecahedra cells. Alternative names: *Rectified 120 cell (Norman Johnson) *Rectified hecatonicosichoron *Rectified… …   Wikipedia

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  • Truncated 120-cell — In geometry, the truncated 120 cell is a uniform polychoron, constructed by a uniform truncation of the regular 120 cell polychoron. It is made of 120 truncated dodecahedral and 600 tetrahedral cells. It has 3120 faces: 2400 being triangles and… …   Wikipedia

  • Icosahedral 120-cell — In geometry, the icosahedral 120 cell is a star polychoron with Schläfli symbol {3,5,5/2}. It is one of 10 regular Schläfli Hess polychora.It is constructed by 5 icosahedra around each edge in a pentagrammic figure. The vertex figure is a great… …   Wikipedia

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