# Projection of a Torus

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## Revision as of 15:05, 10 July 2009

Projection of a 4-Dimensional Torus
Field: Algebra
Image Created By: Thomas F. Banchoff
Website: The Mathematics of In- and Outside the Torus

Projection of a 4-Dimensional Torus

A torus in four dimensions projected into three-dimensional space.

# Basic Description

It is impossible to visualize an object in four-dimensions, since we have only ever lived in three-dimensional space. However, there are ways to capture features of the four-dimensional object in three-dimensional space.

A useful analogy is a world map. We can capture the essence of the three-dimensional globe on a two-dimensional map, but only by using a projection, which translates a three-dimensional object onto a two-dimensional surface at the expense of distorting the object in some way.

A similar process is carried out to create this page's main image. An object in four-dimensional space, described further below, is projected into three-dimensions using two different projections.

# A More Mathematical Explanation

The four-dimensional torus is defined parametrically by UNIQ191ae341169df40 [...]

The four-dimensional torus is defined parametrically by $(x_1,\,x_2,\,x_3,\,x_4)=(cos(u),\,sin(u),\,cos(v),\,sin(v))$. The first two coordinates of the parametrization give a circle in u-space, and the second two coordinates give a circle in v-space. The torus is thus the Cartesian Product of two circles.

A stereographic projection is used to map this object, which lives in four-dimensional space, into three-dimensional space, using a projection point of $(0,0,0,\sqrt{2})$ for the first object in this page's main image. This projection is centered above the object, projecting the symmetric torus into three-dimensional space. For the second object, the projection point is shifted to be closer to one part of the four-dimensional object than the other, creating an uneven object in three dimensions. This projection's unevenness is similar to the shadow of a symmetric object becoming asymmetric because of the light source's positioning.

# About the Creator of this Image

Thomas F. Banchoff is a geometer, and a professor at Brown University since 1967.