Four-dimensional space, also called Euclidean four-dimensional space, is a standard Euclidean space. It is a mathematical concept, which can be extended to N dimension. The fourth dimension of four-dimensional space refers to the spatial dimension with the same properties as X, Y and Z.

In physics and mathematics, a sequence of n numbers can be understood as a position in an n-dimensional space. When n=4, the set of all these positions is called four-dimensional space. Four-dimensional space is different from the three-dimensional space of human life because there is one more dimension.

Through the evolution of one-dimensional, two-dimensional and three-dimensional space, people have put forward some conjectures about four-dimensional space. Although these conjectures can't be proved to be correct yet, many scientific theories begin with conjectures.

Nowadays, scientific theories are generally based on summarizing the laws of phenomena, but there is not enough accurate and clear understanding of the phenomena in four-dimensional space, or we did not think that this phenomenon was caused by four-dimensional space after seeing it.

Of course, the topological space of points, lines and surfaces can also be defined as the fourth dimension, the fifth dimension, the sixth dimension or even the nth dimension. This is easy to realize in mathematical formula reasoning, but it is difficult to correspond and imagine in reality.

However, when people refer to "four-dimensional space", they are often confused with "four-dimensional space-time" mentioned by Einstein in his theory of relativity (called "Minkowski space").

Introduction to four-dimensional space-time and thinking space;

The four-dimensional space-time mentioned by Einstein in his general relativity and special relativity (called Minkowski space) is mainly manifested as "the universe is a four-dimensional space-time composed of three-dimensional space and one-dimensional time", and the "fourth dimension" referred to is completely different from other three-dimensional properties.

The fourth dimension in the concept of "four-dimensional space" refers to the same spatial dimension as other three-dimensional attributes.

These two concepts are completely different, but long-term misuse makes the public often confuse these two concepts. When people talk about "four-dimensional space", they often refer to the concept of four-dimensional space-time, which leads to the confusion that "the fourth dimension of four-dimensional space is time".

This common misuse is due to the popularity of popular science and literary works related to relativity. For those who don't know the theory of relativity, it is very easy to misunderstand it.