How many dimensions does the world have, and what is the earth?

Three-dimensional space.

Three-dimensional space, in daily life, can refer to the space composed of three dimensions: length, width and height. Moreover, the term "three-dimensional space" used in daily life often refers to three-dimensional Euclidean space. A space where the location of a point is determined by three coordinates.

The objectively existing real space is three-dimensional space, with three measures: length, width, and height. The concept of multi-dimensional space introduced in mathematics, physics and other disciplines is a scientific abstraction made on the basis of three-dimensional space. It is also called three-dimensional space.

Four-dimensional space is different from three-dimensional space, which refers to standard Euclidean space, which can be extended to n-dimensional; Four-dimensional space-time refers to a misunderstanding of Minkowski's concept of space. As three-dimensional objects, human beings can understand four-dimensional space-time (three spatial dimensions and one temporal dimension), but they cannot recognize and exist in four-dimensional space, because human beings belong to the third spatial dimension.

Time is usually the fourth dimension, that is, the time dimension under the fourth dimension of space-time. The fourth dimension of four-dimensional space refers to the dimension of space with the same properties as x, y, and z. However, four-dimensional space-time is not a standard Euclidean space, and the essence of time is to describe the speed of motion.

Spatial division

According to Einstein's four-dimensional spatial division, the point is zero-dimensional; The line between two points is one-dimensional; The surface made up of countless lines is two-dimensional; Add height to the two-dimensional basis, and it is three-dimensional; Three-dimensional plus time is four-dimensional. On top of this, Einstein and other scientists have speculated that there is a higher dimension in the universe.

This kind of speculation is more vividly described in many science fiction **, such as "The Three-Body Problem" by Chinese science fiction author Liu Cixin, which once described a unique attack method of high-dimensional lifeforms.

Its principle is to throw a kind of ** called "two-way foil" into the space where the target civilization is located, so that the attacked civilization can quickly fall from the high-dimensional space to the low-dimensional space. Although it is only a conjecture and artistic creation of science fiction experts, it also gives us a deeper understanding of the concept of multi-dimensional space.

Three-dimensional space, which can be referred to in daily life, is a space composed of three dimensions: length, width and height, and is a space that people can feel. The three axes of length, width, and height in three-dimensional space are to explain the distance relationship between objects in three-dimensional space relative to the origin o.

Space and time are the forms of existence of matter in motion. Space is the extensibility of the existence of matter, and time is the continuity and sequence of the process of movement of matter. Like matter, space and time exist objectively and are eternal and independent of human consciousness.

Space and time are inseparable from the matter in motion, and there is no space-time that is separated from the movement of matter, and there is no matter that does not move in space-time.

The space we live in is a three-dimensional space, but we are also controlled by time, which can also be called a four-dimensional space.

This is actually just a concept, and different concepts have different understandings. Although we live in a three-dimensional space, all we can see is a two-dimensional plane, two eyes cross from different directions, and two planes observed at different distances overlap to produce three-dimensional vision that can judge the distance, because the human eye can only see three-dimensional, so it is difficult to explain more than three-dimensional.

Just as a person with normal intelligence who is born without one eye and one ear (so that there is no binocular effect and binaural effect), it is difficult for him to understand distance and direction, and he is likely to think that the world is two-dimensional. To put it simply: 0 dimensions are points, without length, width, or height.

One dimension is a line made up of countless points, only length, no width or height.

A two-dimensional is a surface made up of countless lines, with length, width, and height. A three-dimensional body is a body composed of countless faces, with length, width and height. Dimension can be understood as direction. To put it simply: n-dimension is the space formed by two perpendicular pairs of n straight lines.

Humans can only understand 3 dimensions, so the later dimensions can be constructed by mathematical theories, but it is difficult to understand them carefully. In quantum mechanics, we first assume that there are beings who live in two-dimensional planes, whose worlds are only long and wide, and who cannot understand the third dimension, the "high" dimension.

Take a three-dimensional look at this multi-dimensional universe.

One. As the simplest form of motion in the universe, it should be a linear motion, and we regard the movement of a point in 1-dimensional space as a straight line.

Two. A point in 2-dimensional space can move in two vertical directions at the same time at most, like a "circle".

Three. We are more familiar with the three-dimensional space, which is the three-dimensional space, which allows a point to move in three perpendicular directions at the same time, and the operation is like a combination of one-dimensional and two-dimensional space-time movement, that is, the spiral linear movement.

Four. The four-dimensional space is unimaginable for human beings in three-dimensional space, and the four-dimensional direction is at right angles to the front and back, left and right, up and down, etc., I can't show you what direction it is, but this direction does exist, because it can be expressed by the movement of the point in the four-dimensional space. It's amazing!

A three-dimensional spiral linear motion is like a vertical motion in its straight direction (plus one dimension), isn't this a four-dimensional space with (four perpendicular directions)?

There is no time in the real three-dimensional space, that is to say, everything in the real three-dimensional space is static, just like the three-dimensional model in the computer, if you don't set the various change parameters yourself, it will never change. In this way, after adding the dimension of time, the three-dimensional space will produce countless changes with the change of time, with time, chemical changes occur, new substances are created, life appears, and civilization is created, all of which are bred by time, so this can also explain the reason why the four-dimensional space has more mass for the content of the three-dimensional space.

This also explains why time is a dimension: with Timeline, three-dimensional objects are constantly changing under the influence of the timeline, rather than being eternally static.

As for the problem of using a pen to draw points, because your pen, your pen includes yourself in a four-dimensional space, and the pen is a three-dimensional object, so it is not a real one-dimensional (and one-dimensional is not a point, but a line, but your line is also three-dimensional), including the paper you said, these things are three-dimensional, in the strict sense no one says that it is two-dimensional, the paper is just a three-dimensional object with a slightly smaller unit, and you can't find a real low-latitude object in high-latitude space ( Including in four-dimensional space, any three-dimensional object must be affected by time, not the eternal immutability of three-dimensional space).

The real three-dimensional space, two-dimensional space and one-dimensional space are all things that can be proved to exist, but we can't reach them, because only low-latitude objects can enter high-latitudes, high-latitudes can't enter low-latitudes, and can only have projections at low-latitudes, for example, people as three-dimensional objects can cast a plane shadow on the ground, and in fact, the shadow is that we enter the two-dimensional space, because, the thickness of the shadow? Have you considered this? Shadows may be truly two-dimensional!