The Octacube is a large, stainless steel sculpture displayed in the mathematics department of Pennsylvania State University in State College, PA. The sculpture represents a mathematical object called the 24-cell or "octacube". Because a real 24-cell is four-dimensional, the artwork is actually a projection into the three-dimensional world.
Octacube has very high intrinsic symmetry, which matches features in chemistry (molecular symmetry) and physics (quantum field theory).
The sculpture was designed by Adrian Ocneanu , a mathematics professor at Pennsylvania State University. The university's machine shop spent over a year completing the intricate metal-work. Octacube was funded by an alumna in memory of her husband, Kermit Anderson, who died in the September 11 attacks.
The Octacube's metal skeleton measures about 6 feet (1.8 meters) in all three dimensions. It is a complex arrangement of unpainted, tri-cornered flanges. The base is a 3-foot (0.91-meter) high granite block, with some engraving. [1]
The artwork was designed by Adrian Ocneanu, a Penn State mathematics professor. He supplied the specifications for the sculpture's 96 triangular pieces of stainless steel and for their assembly. Fabrication was done by Penn State's machine shop, led by Jerry Anderson. The work took over a year, involving bending and welding as well as cutting. Discussing the construction, Ocneanu said: [1]
It's very hard to make 12 steel sheets meet perfectly—and conformally—at each of the 23 vertices, with no trace of welding left. The people who built it are really world-class experts and perfectionists—artists in steel.
Because of the reflective metal at different angles, the appearance is pleasantly strange. In some cases, the mirror-like surfaces create an illusion of transparency by showing reflections from unexpected sides of the structure. The sculpture's mathematician creator commented: [1]
When I saw the actual sculpture, I had quite a shock. I never imagined the play of light on the surfaces. There are subtle optical effects that you can feel but can't quite put your finger on.
The Platonic solids are three-dimensional shapes with special, high, symmetry. They are the next step up in dimension from the two-dimensional regular polygons (squares, equilateral triangles, etc.). The five Platonic solids are the tetrahedron (4 faces), cube (6 faces), octahedron (8 faces), dodecahedron (12 faces), and icosahedron (20 faces). They have been known since the time of the Ancient Greeks and valued for their aesthetic appeal and philosophical, even mystical, import. (See also the Timaeus , a dialogue of Plato.)
The Platonic solids | ||||
Tetrahedron | Cube | Octahedron | Dodecahedron | Icosahedron |
In higher dimensions, the counterparts of the Platonic solids are the regular polytopes. These shapes were first described in the mid-19th century by a Swiss mathematician, Ludwig Schläfli. In four dimensions, there are six of them: the pentachoron (5-cell), tesseract (8-cell), hexadecachoron (16-cell), octacube (24-cell), hecatonicosachoron (120-cell), and the hexacosichoron (600-cell).
The 24-cell consists of 24 octahedrons, joined in 4-dimensional space. The 24-cell's vertex figure (the 3-D shape formed when a 4-D corner is cut off) is a cube. Despite its suggestive name, the octacube is not the 4-D analog of either the octahedron or the cube. In fact, it is the only one of the six 4-D regular polytopes that lacks a corresponding Platonic solid. [note 1]
Attempts to picture the 24-cell | ||
Schlegel diagram | 4-dimensional rotation |
Ocneanu explains the conceptual challenge in working in the fourth dimension: [1] "Although mathematicians can work with a fourth dimension abstractly by adding a fourth coordinate to the three that we use to describe a point in space, a fourth spatial dimension is difficult to visualize."
Although it is impossible to see or make 4-dimensional objects, it is possible to map them into lower dimensions to get some impressions of them. An analogy for converting the 4-D 24-cell into its 3-D sculpture is cartographic projection, where the surface of the 3-D Earth (or a globe) is reduced to a flat 2-D plane (a portable map). This is done either with light 'casting a shadow' from the globe onto the map or with some mathematical transformation. Many different types of map projection exist: the familiar rectangular Mercator (used for navigation), the circular gnomonic (first projection invented), and several others. All of them have limitations in that they show some features in a distorted manner—'you can't flatten an orange peel without damaging it'—but they are useful visual aids and convenient references.
In the same manner that the exterior of the Earth is a 2-D skin (bent into the third dimension), the exterior of a 4-dimensional shape is a 3-D space (but folded through hyperspace, the fourth dimension). However, just as the surface of Earth's globe cannot be mapped onto a plane without some distortions, neither can the exterior 3-D shape of the 24-cell 4-D hyper-shape. In the image on the right a 24-cell is shown projected into space as a 3-D object (and then the image is a 2-D rendering of it, with perspective to aid the eye). Some of the distortions:
To map the 24-cell, Ocneanu uses a related projection which he calls windowed radial stereographic projection. As with the stereographic projection, there are curved lines shown in 3-D space. Instead of using semitransparent surfaces, "windows" are cut into the faces of the cells so that interior cells can be seen. Also, only 23 vertices are physically present. The 24th vertex "occurs at infinity" because of the projection; what one sees is the 8 legs and arms of the sculpture diverging outwards from the center of the 3-D sculpture. [1]
The Octacube sculpture has very high symmetry. The stainless steel structure has the same amount of symmetry as a cube or an octahedron. The artwork can be visualized as related to a cube: the arms and legs of the structure extend to the corners. Imagining an octahedron is more difficult; it involves thinking of the faces of the visualized cube forming the corners of an octahedron. The cube and octahedron have the same amount and type of symmetry: octahedral symmetry, called Oh (order 48) in mathematical notation. Some, but not all, of the symmetry elements are
Using the mid room points, the sculpture represents the root systems of type D4, B4=C4 and F4, that is all 4d ones other than A4. It can visualize the projection of D4 to B3 and D4 to G2.
Many molecules have the same symmetry as the Octacube sculpture. The organic molecule, cubane (C8H8) is one example. The arms and legs of the sculpture are similar to the outward projecting hydrogen atoms. Sulfur hexafluoride (or any molecule with exact octahedral molecular geometry) also shares the same symmetry although the resemblance is not as similar.
Cubane | Sulfur hexafluoride |
The Octacube also shows parallels to concepts in theoretical physics. Creator Ocneanu researches mathematical aspects of quantum field theory (QFT). The subject has been described by a Fields medal winner, Ed Witten, as the most difficult area in physics. [2] Part of Ocneanu's work is to build theoretical, and even physical, models of the symmetry features in QFT. Ocneanu cites the relationship of the inner and outer halves of the structure as analogous to the relationship of spin 1/2 particles (e.g. electrons) and spin 1 particles (e.g. photons). [1]
Octacube was commissioned and funded by Jill Anderson, a 1965 PSU math grad, in memory of her husband, Kermit, another 1965 math grad, who was killed in the 9-11 terrorist attacks. [1] Summarizing the memorial, Anderson said: [1]
I hope that the sculpture will encourage students, faculty, administrators, alumnae, and friends to ponder and appreciate the wonderful world of mathematics. I also hope that all who view the sculpture will begin to grasp the sobering fact that everyone is vulnerable to something terrible happening to them and that we all must learn to live one day at a time, making the very best of what has been given to us. It would be great if everyone who views the Octacube walks away with the feeling that being kind to others is a good way to live.
Anderson also funded a math scholarship in Kermit's name, at the same time the sculpture project went forward. [1]
A more complete explanation of the sculpture, including how it came to be made, how its construction was funded and its role in mathematics and physics, has been made available by Penn State. [1] In addition, Ocneanu has provided his own commentary. [3]
Artists:
Math:
A cuboctahedron is a polyhedron with 8 triangular faces and 6 square faces. A cuboctahedron has 12 identical vertices, with 2 triangles and 2 squares meeting at each, and 24 identical edges, each separating a triangle from a square. As such, it is a quasiregular polyhedron, i.e. an Archimedean solid that is not only vertex-transitive but also edge-transitive. It is radially equilateral.
In geometry, a cube is a three-dimensional solid object bounded by six square faces, facets, or sides, with three meeting at each vertex. Viewed from a corner, it is a hexagon and its net is usually depicted as a cross.
In geometry, a regular icosahedron is a convex polyhedron with 20 faces, 30 edges and 12 vertices. It is one of the five Platonic solids, and the one with the most faces.
In geometry, an octahedron is a polyhedron with eight faces. The term is most commonly used to refer to the regular octahedron, a Platonic solid composed of eight equilateral triangles, four of which meet at each vertex.
In geometry, a Platonic solid is a convex, regular polyhedron in three-dimensional Euclidean space. Being a regular polyhedron means that the faces are congruent regular polygons, and the same number of faces meet at each vertex. There are only five such polyhedra:
In geometry, a 4-polytope is a four-dimensional polytope. It is a connected and closed figure, composed of lower-dimensional polytopal elements: vertices, edges, faces (polygons), and cells (polyhedra). Each face is shared by exactly two cells. The 4-polytopes were discovered by the Swiss mathematician Ludwig Schläfli before 1853.
In geometry, the rhombicuboctahedron, or small rhombicuboctahedron, is a polyhedron with eight triangular, six square, and twelve rectangular faces. There are 24 identical vertices, with one triangle, one square, and two rectangles meeting at each one. If all the rectangles are themselves square, it is an Archimedean solid. The polyhedron has octahedral symmetry, like the cube and octahedron. Its dual is called the deltoidal icositetrahedron or trapezoidal icositetrahedron, although its faces are not really true trapezoids.
In geometry, a tesseract is the four-dimensional analogue of the cube; the tesseract is to the cube as the cube is to the square. Just as the surface of the cube consists of six square faces, the hypersurface of the tesseract consists of eight cubical cells. The tesseract is one of the six convex regular 4-polytopes.
In geometry, the truncated octahedron is the Archimedean solid that arises from a regular octahedron by removing six pyramids, one at each of the octahedron's vertices. The truncated octahedron has 14 faces, 36 edges, and 24 vertices. Since each of its faces has point symmetry the truncated octahedron is a 6-zonohedron. It is also the Goldberg polyhedron GIV(1,1), containing square and hexagonal faces. Like the cube, it can tessellate 3-dimensional space, as a permutohedron.
In geometry, the 24-cell is the convex regular 4-polytope (four-dimensional analogue of a Platonic solid) with Schläfli symbol {3,4,3}. It is also called C24, or the icositetrachoron, octaplex (short for "octahedral complex"), icosatetrahedroid, octacube, hyper-diamond or polyoctahedron, being constructed of octahedral cells.
A regular polyhedron is a polyhedron whose symmetry group acts transitively on its flags. A regular polyhedron is highly symmetrical, being all of edge-transitive, vertex-transitive and face-transitive. In classical contexts, many different equivalent definitions are used; a common one is that the faces are congruent regular polygons which are assembled in the same way around each vertex.
In mathematics, a regular polytope is a polytope whose symmetry group acts transitively on its flags, thus giving it the highest degree of symmetry. All its elements or j-faces — cells, faces and so on — are also transitive on the symmetries of the polytope, and are regular polytopes of dimension ≤ n.
In geometry, the rhombic dodecahedron is a convex polyhedron with 12 congruent rhombic faces. It has 24 edges, and 14 vertices of 2 types. It is a Catalan solid, and the dual polyhedron of the cuboctahedron.
In geometry, a cross-polytope, hyperoctahedron, orthoplex, or cocube is a regular, convex polytope that exists in n-dimensional Euclidean space. A 2-dimensional cross-polytope is a square, a 3-dimensional cross-polytope is a regular octahedron, and a 4-dimensional cross-polytope is a 16-cell. Its facets are simplexes of the previous dimension, while the cross-polytope's vertex figure is another cross-polytope from the previous dimension.
In geometry, the 16-cell is the regular convex 4-polytope (four-dimensional analogue of a Platonic solid) with Schläfli symbol {3,3,4}. It is one of the six regular convex 4-polytopes first described by the Swiss mathematician Ludwig Schläfli in the mid-19th century. It is also called C16, hexadecachoron, or hexdecahedroid [sic?].
Four-dimensional space (4D) is the mathematical extension of the concept of three-dimensional space (3D). Three-dimensional space is the simplest possible abstraction of the observation that one needs only three numbers, called dimensions, to describe the sizes or locations of objects in the everyday world. For example, the volume of a rectangular box is found by measuring and multiplying its length, width, and height. This concept of ordinary space is called Euclidean space because it corresponds to Euclid's geometry, which was originally abstracted from the spatial experiences of everyday life.
In four-dimensional geometry, a runcinated tesseract is a convex uniform 4-polytope, being a runcination of the regular tesseract.
In four-dimensional geometry, a cantellated tesseract is a convex uniform 4-polytope, being a cantellation of the regular tesseract.
In geometry, a truncated tesseract is a uniform 4-polytope formed as the truncation of the regular tesseract.
A regular dodecahedron or pentagonal dodecahedron is a dodecahedron that is regular, which is composed of 12 regular pentagonal faces, three meeting at each vertex. It is one of the five Platonic solids. It has 12 faces, 20 vertices, 30 edges, and 160 diagonals. It is represented by the Schläfli symbol {5,3}.
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