4D, meaning the 4 common dimensions, is an important idea in physics referring to three-dimensional space (3D), which adds the dimension of time to the spatial dimensions of length, width, and depth. In geometry, the fourth dimension is related to the other three dimensions by imagining another direction through space; just as the dimension of depth can be added to a square to create a cube, the fourth dimension can be added to a cube to create a tesseract.
In mathematics, four-dimension space is an abstract concept which has been studied by mathematics and philosophers for many years. Mathematicians who studied four-dimension space in the 19th century include Möbius, Schläfi, Bernhard Riemann, and Charles Howard Hinton.
In the 20th century, the idea of spacetime was developed by Albert Einstein, connecting space and time together. The difference is that spacetime is not a Euclidean space, but instead is called "Minkowski spacetime".
- RAq2w, Paradoxy vedomi. Praha: PedF UK 1994, str. 78n