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The centrepiece of McAllister building, which houses the math department at Penn State, is the Octacube, designed by Adrian Ocneanu.

alt text

There's a bit of a description of the mathematics behind the Octacube on the Penn State website, but unfortunately, that's the most material that I can find online. There are all kinds of animations set up to display on a computer terminal in McAllister building, but they don't seem to be available online anymore.

Very briefly, the mathematics of the sculpture is as follows: consider the four-dimensional regular convex polytope whose vertex set is the union of the vertex sets for the four-dimensional cube {(±1,±1,±1,±1)} and the four-dimensional octahedron {(±2,0,0,0), (0,±2,0,0), (0,0,±2,0), (0,0,0,±2)}. Consider the 1-skeleton of this polytope (vertices and edges), and project radially to S3 ⊂ ℝ4. Project the resulting "inflated polytope" stereographically to ℝ3, and "fatten" the edges so that a cross-section of an edge is no longer just a point, but a Y-shape (see the corners of the sculpture). What you get is the sculpture shown.
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The centrepiece of McAllister building, which houses the math department at Penn State, is the Octacube, designed by Adrian Ocneanu.

alt text

There's a bit of a description of the mathematics behind the Octacube on the Penn State website, but unfortunately, that's the most material that I can find online. There are all kinds of animations set up to display on a computer terminal in McAllister building, but they don't seem to be available online anymore.

Very briefly, the mathematics of the sculpture is as follows: consider the four-dimensional regular convex polytope whose vertex set is the union of the vertex sets for the four-dimensional cube {(±1,±1,±1,±1)} and the four-dimensional octahedron {(±2,0,0,0), (0,±2,0,0), (0,0,±2,0), (0,0,0,±2)}. Consider the 1-skeleton of this polytope (vertices and edges), and project radially to S3 ⊂ ℝ4. Project the resulting "inflated polytope" stereographically to ℝ3, and "fatten" the edges so that a cross-section of an edge is no longer just a point, but a Y-shape (see the corners of the sculpture). What you get is the sculpture shown.
show/hide this revision's text 2 Corrected a typo in the list of vertices

The centrepiece of McAllister building, which houses the math department at Penn State, is the Octacube, designed by Adrian Ocneanu.

alt text

There's a bit of a description of the mathematics behind the Octacube on the Penn State website, but unfortunately, that's the most material that I can find online. There are all kinds of animations set up to display on a computer terminal in McAllister building, but they don't seem to be available online anymore.

Very briefly, the mathematics of the sculpture is as follows: consider the four-dimensional regular convex polytope whose vertex set is the union of the vertex sets for the four-dimensional cube {(±1,±1,±1,±1)} and the four-dimensional octahedron {(±2,0,0,0), (0,±2,0,0), (0,0,±,0), ±2,0), (0,0,0,±2)}. Consider the 1-skeleton of this polytope (vertices and edges), and project radially to S4. Project the resulting "inflated polytope" stereographically to ℝ3, and "fatten" the edges so that a cross-section of an edge is no longer just a point, but a Y-shape (see the corners of the sculpture). What you get is the sculpture shown.
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