The world we live in has three dimensions, which are length, width and height. Plus one-dimensional time is four-dimensional spacetime. In other words, we exist in three-dimensional space or four-dimensional spacetime. (Time cannot calculate dimensions, but it runs through all dimensions. In this regard, many people said: "After human beings enter the four-dimensional space (that is, the five-dimensional space), can they really travel back to the past through time and space like the protagonist in the movie?" You might think. The concept of dimension originated from mathematics. The 1 1 dimension of superstring theory is based on mathematics, and all dimensions of mathematics are based on standard Euclidean space. For a simple example, the dimension of mathematics is a straight line passing through a point, the two dimensions are two mutually perpendicular straight lines passing through a point, and the three dimensions are the space of mutually perpendicular XYZ plane rectangular coordinate system created in our mathematics. In this way, in mathematics, n dimension refers to n mutually perpendicular straight lines passing through any point.

Therefore, in the standard Euclidean space of mathematics, human beings cannot enter the four-dimensional space. This four-dimensional space is only a model to solve a specific mathematical problem, and the dimension of crossing the past and the future mentioned in the film is the scientific dimension. This dimension is based on Minkowski space, which is equivalent to the falling dimension of three bodies. The scientific level may be everyone's greatest concern. Because if you have a scientific level, you can travel through time and space to the past and the future. But so far, science does not admit that there is a four-dimensional space in the world, but it does not deny that it should not exist. At least not yet.

According to Einstein's theory of relativity, the three-dimensional space and time we face in our life constitute the so-called four-dimensional space. Because the time we feel on the earth is very slow, we can't clearly feel the existence of four-dimensional space, but once we board a spaceship or reach the universe, when our reference system accelerates or approaches the speed of light, we can find the time changes we can cope with. If you sail in a spaceship near the speed of light per hour, your life will be much longer than that of people on earth. There are some potential places where the energy of matter changes with 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.

Orthodox dimensional research methods are usually inseparable from the principle of human survival. For example, if space is two-dimensional, two-dimensional animals cannot digest normally. If the space is more than four dimensions, the world will be better. If we are animals in four-dimensional space, then Poincare's speculation about three-dimensional balls can't be a century problem. Unfortunately, the extra three-dimensional space will become more serious with the distance, so that electrons smaller than the nucleus are no longer stable to the planets in the solar system, and will soon fly to the distance or hit the center in a vortex way.