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.

Theorem: For any complex system, as long as any part of the system cannot go back to the past state at the same time, then the system can not regress.

Regression is not equal to reversion, and non-regression is not equal to irreversibility. Reversion is a special concept in dissipative structure theory, which is related to the change of entropy, while regression is not necessarily related to the change of entropy. Both reversible and irreversible processes are non-regressive.

Now many people like to talk about going back in time and changing history. It may be possible to see the past, but it is completely impossible to change the history. Because to change the histroy means that not only you alone go back to the past, but all people and all things go back to the past at the same time, which is transforming the whole world.

In fact, all our observations are looking into the past, because the light reflected by any matter has a period of motion before it enters our eyes, but the motion of the light is so fast that the observation of nearby things can be regarded as simultaneous, and the observation of distant stars is obviously of the past. Looking at the past doesn't mean we can go back in time, because it takes time for the light we reflect to reach distant stars, so we can't interact with things from the past. If I can see what my great-grandfather is doing, then this observation is only one-way, he can't see me, he seeing me means he can see the future. So looking at the past doesn't mean going back in time.