Apeirotope
An apeirotope or infinite polytope is a polytope which has infinitely many facets. There are two main geometric classes of apeirotope:[1]
- honeycombs in n dimensions, which completely fill an n-dimensional space.
- skew apeirotopes, comprising an n-dimensional manifold in a higher space
Honeycombs
In general, a honeycomb in n dimensions is an infinite example of a polytope in n + 1 dimensions.
Tilings of the plane and close-packed space-fillings of polyhedra are examples of honeycombs in two and three dimensions respectively.
A line divided into infinitely many finite segments is an example of an apeirogon.
Skew apeirotopes
Skew apeirogons
A skew apeirogon in two dimensions forms a zig-zag line in the plane. If the zig-zag is even and symmetrical, then the apeirogon is regular.
Skew apeirogons can be constructed in any number of dimensions. In three dimensions, a regular skew apeirogon traces out a helical spiral and may be either left- or right-handed.
Infinite skew polyhedra
There are three regular skew apeirohedra, which look rather like polyhedral sponges:
- 6 squares around each vertex, Coxeter symbol {4,6|4}
- 4 hexagons around each vertex, Coxeter symbol {6,4|4}
- 6 hexagons around each vertex, Coxeter symbol {6,6|3}
There are thirty regular apeirohedra in Euclidean space.[2] These include those listed above, as well as (in the plane) polytopes of type: {∞,3}, {∞,4}, {∞,6} and in 3-dimensional space, blends of these with either an apeirogon or a line segment, and the "pure" 3-dimensional apeirohedra (12 in number)
References
- ↑ Grünbaum, B.; "Regular Polyhedra—Old and New", Aeqationes mathematicae, Vol. 16 (1977), pp 1–20.
- ↑ McMullen & Schulte (2002, Section 7E)
- McMullen, Peter; Schulte, Egon (2002), Abstract Regular Polytopes, Encyclopedia of Mathematics and its Applications, 92, Cambridge: Cambridge University Press, doi:10.1017/CBO9780511546686, ISBN 0-521-81496-0, MR 1965665