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.

(4)Definition of Simultaneity and Sequence

According to the previous definition, time is the relationship between different states of the world as a whole resulting from changes in the structure and function of matter. Time relation includes simultaneous relation and sequential relation. Then what is simultaneous relation? If a person sees an object and at the same time sees another object, the two objects produce two senses in the person's consciousness, and the two senses appear in consciousness at the same time, so that the two senses will establish some of the same associations with other consciousness. What is meant by simultaneity is actually the commonality of this conscious association.