One dimension actually refers to a line, which is understood as the left and right direction. It can also be understood as a point moving into the line, which refers to an object without area and volume. Objects in one-dimensional space have only length, but no width and height. For example, if we want to close a one-dimensional object (actually a line segment), we just need to add a point at each end of it. Two-dimensional is up, down, left and right, without front and back. The content on a piece of paper is two-dimensional. That is, an object with only area and no thickness. Three-dimensional refers to the spatial system formed by adding a directional quantity to the maintenance of plane two. The so-called three dimensions, according to the popular theory, are only three mutually perpendicular directions artificially specified. With this three-dimensional coordinate, it seems that the position of any point in the whole world can be determined. It turns out that the three-dimensional position is determined. Stereo is not only the three axes of the coordinate axis, that is, the X axis, the Y axis and the Z axis, where X represents the left and right space, Y represents the upper and lower space, and Z represents the front and rear space, thus forming a three-dimensional sense of human vision. Three-dimensional animation is a three-dimensional animation made by three-dimensional production software, which has realized the trend of further development. The so-called three-dimensional space refers to the space in which we live, which can be understood as having front, back, top, bottom, left and right. If you think of time as a physical existence, it will be a four-dimensional space, but you can go back to the past at will, which is not difficult to understand, but you should understand that "just now" and "now" are different substances, but in the physics of "just now" and "past", you can't go back to the four-dimensional space. The fourth dimension. Four-dimensional space. Which is time. Some people think that time is also a kind of space, and under certain conditions or circumstances, time can be reversed and crossed. Four-dimensional means that you can move from one place to another instantly in three-dimensional space, without being bound by time, and you can slow down or speed up the pace of time. I derived it from a data that looks at three dimensions from two dimensions: for four-dimensional space, most people may just think that it is on the axis of length, width and height, plus a time axis, but most people still know little about it. However, this statement was suddenly broken. Why? We can consider it from two dimensions. A two-dimensional creature (if any) thinks that the so-called three-dimensional space is absolutely different from our three-dimensional space-they will regard time as the third dimension because they can't feel the existence of this dimension. Similarly, we have now entered this misunderstanding and counted time as the third dimension. Maybe the four-dimensional creatures are sighing for us when they see us preaching this idea. So time is one-dimensional? In my opinion, time should be one-dimensional, that is, adding a dimension to the dimension of multi-dimensional creatures to form a new N+ 1 dimensional space, which is higher than the three-dimensional space, will also help us solve some problems and deepen our understanding. The concept of four-dimensional space four-dimensional space is a concept of time and space. Simply put, any four-dimensional space can be called "four-dimensional space". But the "four-dimensional space" mentioned in daily life mostly refers to the concept of "four-dimensional space-time" mentioned by Einstein in his general relativity and special relativity. According to Einstein's concept, our universe is made up of time and space. The relationship between time and space is to add a time axis to the three axes of length, width and height of ordinary three-dimensional space, and this time axis is an imaginary axis. According to Einstein's theory of relativity, the three-dimensional space we face in our life plus time constitutes the so-called four-dimensional space. Because the time we feel on the earth is very slow, we won't obviously feel the existence of four-dimensional space, but once we board the spacecraft or reach the universe, when our reference system starts to get faster or close to the speed of light, we can find the change of time by comparison. If you sail in a spaceship with a speed close to the speed of light, your life will be much longer than that of the people on earth. There is a potential field here, and the energy of matter will change with the change of speed. So the change and contrast of time is based on the speed of matter. This is why time is one of the elements of four-dimensional space. In the special theory of relativity, time and space constitute an inseparable whole-four-dimensional spacetime, and energy and momentum also constitute an inseparable whole-four-dimensional momentum. This shows that there may be a deep connection between some seemingly unrelated quantities in nature. When we talk about general relativity in the future, we will also see that there is also a profound relationship between the four vectors of space-time and energy momentum.