The direction of time is not necessarily one-way. When system B is taken as the time parameter of system A, if system B changes from state 2 to state 1, it means that time flows backwards. Such a graph is easy to draw. But when we analyze functional relationships, we don't like this kind of graph, we like single-valued functions. So we need to set a fixed time direction. If we think that the sun rises in the east and sets in the west every day, we can go back to the past and cannot calibrate the direction of time, then we can use the change of seasons as a reference to mark the direction of time. If we feel that the change of seasons is not enough to determine the direction of time, we can use slower changes as the coordinate system, such as human growth and aging. If that was not enough, some long-period systems could be artificially programmed, and various calendars were produced. Therefore, time reversal is not impossible, but is not conducive to human understanding of the world.

The movement of clock is the structural change. The time we usually say generally refers to the relationship between the structural change in a small period of a certain substance and the structural change of the clock. Each point on the time coordinate is a position of the clock hands, so the time we say often refers to the position of the clock hands. Before money came into being, people bartered, and later people used some special commodities as general equivalents, so there was money. A clock is also a "general equivalent". Initially, time is the relationship between any two structural changes, and later people use some special structural changes to express time, such as hourglasses, sundials, etc., and finally use clocks to express time, that is to choose a general equivalent which is most convenient and useful in the various structural changes of time. Therefore, the structural change of the clock is the frame of reference for all other structural changes.

(3)Time is not Reversible

Each of us measures the world by our own frame of reference. Clocks and all other equivalents are substitute standards, not the basic standard of time; each self of person is the basic standard of time. Our body changes and our consciousness changes can not go back. The clock can go back. You just need to modify the clock a little, it can go back, because a clock is a simple system. Changes in a certain part of the human body can often go back, such as recovery from injury, fever can be reduced, some of our ideas can go back. However, the human body and the whole consciousness are complex systems, and it is impossible to regress at the same time. This determines that time can not regress.