Threedimensional space is a geometric model of the physical universe in which we live. The three dimensions are commonly called length, width, and depth (or height), although any three mutually perpendicular directions can serve as the three dimensions.
In physics, our threedimensional space is viewed as embedded in 4dimensional spacetime, called Minkowski space (see special relativity). The idea behind spacetime is that time is hyperbolicorthogonal to each of the three spatial dimensions.
In mathematics, analytic geometry (also called Cartesian geometry) describes every point in threedimensional space by means of three coordinates. Three coordinate axes are given, each perpendicular to the other two at the origin, the point at which they cross. They are usually labeled x, y, and z. Relative to these axes, the position of any point in threedimensional space is given by an ordered triple of real numbers, each number giving the distance of that point from the origin measured along the given axis, which is equal to the distance of that point from the plane determined by the other two axes.
Other popular methods of describing the location of a point in threedimensional space include cylindrical coordinates and spherical coordinates, though there are an infinite number of possible methods. See Euclidean space.
Another mathematical way of viewing threedimensional space is found in linear algebra, where the idea of independence is crucial. Space has three dimensions because the length of a box is independent of its width or breadth. In the technical language of linear algebra, space is three dimensional because every point in space can be described by a linear combination of three independent vectors. In this view, spacetime is four dimensional because the location of a point in time is independent of its location in space.
Threedimensional space has a number of properties that distinguish it from spaces of other dimension numbers. For example, at least 3 dimensions are required to tie a knot in a piece of string ^{[1]}. Many of the laws of physics, such as the various inverse square laws, depend on dimension three ^{[2]}.
The understanding of threedimensional space in humans is thought to be learned during infancy using unconscious inference, and is closely related to handeye coordination. The visual ability to perceive the world in three dimensions is called depth perception.
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threedimensional (comparative more threedimensional, superlative most threedimensional)
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