Simply put: zero dimension is a point, without length, width and height. One dimension is a line composed of countless points, with only length and no width and height. Two-dimensional is a surface composed of countless lines, with length and width and no height. Three-dimensional is a body composed of countless faces, with length, width and height.
Because the human eye can only see three dimensions, it is difficult to explain more than four dimensions. Just like a person with normal intelligence and only one eye and one ear (so there is no binocular effect, binaural effect), it is difficult for him to understand the distance, and he probably thinks that the world is two-dimensional.
To put it simply: N-dimension is a space vertically formed by two or more N- 1 dimensional objects.
Because humans can only understand three dimensions, the latter dimensions can be constructed by mathematical theory, but it is difficult to understand them carefully. In quantum mechanics, string theory, which is still under construction, holds that the world is 1 1 dimension. (ten dimensional space+one-dimensional time)
First of all, the wrong statement is that "four-dimensional space is defined as three-dimensional space+time axis", while "three-dimensional space+time dimension" is another statement. The former is not a four-dimensional space-time, and the four-dimensional space-time itself is a false concept. It's simple: "Time is just a concept that appears because of particle motion and the expansion of the universe. Why can it become the fourth dimension?" In addition, the concepts of space-time and four-dimensional space are different. Defining four-dimensional space as three-dimensional space+time axis is a misunderstanding of Minkowski's concept of space, and why is this misunderstanding so widespread? Quite simply, countless science fiction novels and even popular science books have deliberately and forcibly applied such a thing, which has caused a wide range of readers' influence. Among them, this involves a set of four-dimensional vector fields, namely:
The difference between four-dimensional vectors lies in the sign of their (Minkowski) inner product. It can be divided into time-like, space-like, space-like or light-like. however
A useful result about zero vectors: "If two zero vectors are orthogonal (that is, the inner product value is zero), they must be proportional (constant)."
The choice of time direction at the bottom of zero base and the above concept of time-like vector make many people mistakenly think that "space and time constitute another space", but in fact they only describe the synergy between time and space. This is the source of the previous statement. In fact, the time dimension is an alternative statement, not to say that the fourth dimension is time, which is different from the previous statement. The fourth dimension is continuous in the mainstream view. The famous mathematical model Klein bottle passes through the three-dimensional essential polyhedron, but the essence of four-dimensional space is still space. Why is this dimension defined as a time dimension? It is because a certain school thinks that the extended "time" is spatial that there is an alternative view. You can call it whatever you want. It is a unified and clear naming method based on the independent concepts of different schools. Some students are a little entangled in the statement of "time and space". Let me start by saying that there is another reason why there is no four-dimensional time and space, that is, the concept of time and space in modern physics is originally four-dimensional, so there will be no five-dimensional time and space, and there is no special description of time and space as four-dimensional. A school of modern physics believes that time and space are mutually variable, and their variables exist in each other. Under certain conditions, the vast area they correspond to is called time and space (the earliest people did equate time and space with the time axis, but now they are more avoiding this original definition). Time and space may be distorted or depressed by the influence of matter and energy, and the minimum units are Planck time and Planck length. This is the origin of this concept, but many people confuse time and space with four-dimensional space. They are related, but they cannot be confused.
Broadly speaking, a dimension is the number of "connected" abstract concepts of things, and the "connected" abstract concept refers to an abstract concept formed by connecting two abstract concepts, such as area. So four dimensions are composed of four related abstract concepts, the fourth abstract concept is real time, and the fourth related value is speed.