Four-dimensional, four-dimensional and four-dimensional space in physics, that is, the time concept of "four-dimensional space"; Guan Zhong's "four dimensions" theory of China ancient literature has a far-reaching influence on later generations. At the same time, in the ancient geomantic omen of China, gossip was divided into four dimensions and four corners; The pen name "Siwei" of Jing M.Guo, a post-80s writer.
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In physics and mathematics, a sequence of n(n can be non-integer) numbers can be understood in four dimensions.
Is a position in n-dimensional space. When n=4, the set of all these positions is called four-dimensional space. This kind of space is different from the three-dimensional space we are familiar with and live in because it has an extra dimension. This extra dimension can be understood as both time and the fourth dimension of space, which is the fourth dimension of space. Some people think that time is also a kind of space, and under certain conditions or circumstances, time can be reversed and crossed. The four dimensions in physics refer to length, quantity, temperature and time, which was summed up by Newton. Length includes: length, width, height, volume, etc. Quantity includes: quality, quantity, frequency, etc. Temperature includes: heat, electric energy, resistivity, etc. Time was supplemented by Einstein on the basis of Newton, including specific heat capacity, speed, power and so on.
Four-dimensional space concept
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.
Edit the concept of dimensions in this paragraph.
By removing all redundant vectors from any vector set that can stretch out the geometric figure X, you can pass through the base of a set X. The selected initial vector set is different, and the base that can stretch out X may be different. However, it can be proved that all these bases contain the same number of vectors. This quantity is called the dimension of x, in other words, if x needs at least n vectors to be stretched out, then x is n-dimensional. Intuitively, the dimension of a graph can be considered as the number of all the different directions that a person needs to move in order to reach all the points in the graph. For example, a point is a zero-dimensional graph. We don't need any vector to stretch it, because if we start from this point, we have reached all its positions. A straight line is a one-dimensional figure. Starting from a certain point on a straight line, we need a vector pointing in the direction of this straight line to reach other points on the straight line. Just one vector is enough, because we can reach any other point on the straight line through different degrees of expansion and contraction. The plane is a two-dimensional figure. Given the starting point on a plane, we need at least two nonparallel vectors to stretch the plane. If there is only one vector, we can only reach all points on a straight line; So we need another vector that is not parallel to it to go back and forth to the "two sides" of this straight line, so as to reach other points on the plane. As long as two directions are enough, because we can walk different distances along (or against) the front vector and then walk different distances on both sides to reach any point on the plane. A plane can also be understood as the "accumulation" of many parallel lines; If you want to move from one point to another on a two-dimensional plane, you need to move along straight lines and parallel lines first, and then move in the other direction through these parallel lines. In our eyes, space is three-dimensional. To reach a certain point in space, you must not only move back and forth, but also move up and down. In other words, a third vector is needed to reach all points in space. Similarly, space can also be understood as the accumulation of many parallel planes: to move from one point to another in space, we can go back and forth in one direction, then go to both sides and finally go up and down. Four-dimensional space is a space that needs four different directions to reach all points. This kind of space can be considered as the accumulation of many parallel three-dimensional spaces. To understand this concept, imagine the process of stacking paper side by side. If people don't stack them one by one, these papers won't extend into three-dimensional space. Similarly, if you want to enter the four-dimensional space, you must move in a new direction, which must be outside the three-dimensional space. To reach every point in the four-dimensional space, a person not only needs to move up and down, but also needs to move in a pair of new directions, that is, Anna/Kata mentioned above, or Wayne/Vio and so on.
Edit this paragraph dimension analogy
The expansion diagram of hypercube. To understand the essence of four-dimensional space, we can use a method called "dimensional analogy". Dimension analogy refers to inferring the relationship between n dimension and n+ 1 dimension by studying the relationship between n dimension and n dimension. In his book Flatland, Edwin Abbott tells the story of a square living in a two-dimensional world as flat as a piece of paper by dimensional analogy. In the eyes of this square, people living in the three-dimensional world have almost magical power, because they can take things out of the three-dimensional space (by going in and out of the three-dimensional space) without breaking the (two-dimensional) safe, see everything that seems to be blocked behind the wall in the two-dimensional world, and even stand a few inches away from the two-dimensional world to remain "invisible". Using dimensional analogy, people can infer that people in four-dimensional space should also have magical abilities similar to our three-dimensional perspective. Rudy Lacker showed this in his novel Space World. The hero of the novel meets a four-dimensional man with magical ability.
Edit the relevant understanding of this paragraph.
The length, width, height and time of four-dimensional space can be understood in this way. First, one dimension is a line. Time can also be seen as a timeline. You infinitely reduce a three-dimensional coordinate world with length, width and height to a point, and then let it (this point, the three-dimensional world) move along the time axis (that is, time passes), which is called four dimensions. Of course, if time is complicated, as science fiction says, there are n kinds of past or n kinds of future, that is, our three-dimensional points move on a plane or a higher level. Then it is possible that the space of our world is four-dimensional or more. . There is no proof. There is also a saying that four-dimensional space is understood as a distorted three-dimensional space. If a piece of paper is compared to two dimensions, its infinite superposition is three dimensions, then bending the paper can also produce three-dimensional effects. Based on this, is the distortion of three-dimensional space four-dimensional? Of course, its twisting direction cannot be limited to its own length, width and height. According to the general understanding, time is recognized as the fourth element. If time can be distorted in four-dimensional space, the time travel described in countless novels and movies will become a reality. However, a few people question that if there are creatures in two-dimensional space, their life development process should also have time. According to the theory that time is the fourth dimension, two-dimensional creatures may think that three-dimensional space is composed of length, width and time, but it is not.