The time we perceive in everyday life is a normal concept but there is still no real answer to what is time? It is difficult for us to imagine that our minds and perceptions are placed in a universe with a huge amount of matter and extremely bustling events. This research designs a fictitious but feasible λ closed universe model. In this universe everything seems very simple, there exists only one mathematical entity called the entity σ and there is absolutely nothing else besides this entity. All events occurring in the universe λ are caused by the behavior of entity σ. The signal diagram is a time axis to measure time in λ. When the entity σ exists at a time on the time axis, it is clear that the previous times are all past times of σ in λ and the time domain. This time is called the time domain P. So let's assume entity σ can enter the time domain P on the signal diagram and then analyze how the state of λ will change. According to the butterfly effect, every small impact also creates big changes. The impacts of the entity σ in the time domain P, whether large or small, also create events that are different from the events that happened in λ, even the fact that σ exists in the time domain P is an impact. Because those event changes have created a different universe than the original universe, applying the multiverse theory, it can be said that σ entering the time domain P means σ entering a parallel universe. But it is still not possible for σ to enter a parallel universe, but research has come up with a method called the λ synchronous method. Because of the special properties of the closed universe system λ and the entity σ, it is entirely possible to create another closed universe system exactly like the original system, then all the events in the original system λ are recreated in the new system λ and adjusted so that events in the new λ begin to occur a period of time later. At this time, let the entity σ jump to the new λ system and one thing has completely happened: the entity σ has entered its own past. When using this method to let σ enter the time domain P, we can see that the time in the original λ system and the new λ system are events that occur in λ itself, when no events occur, or we can say when the entity σ is at rest, time is also considered to be standing still. Only when σ moves to create events can we feel the existence of what we call "time". So when we gather all our minds and perceptions into such a simple closed system, we can envision two answers to two problems. Firstly, traveling to the past is just going into another parallel universe and wanting to go into another parallel universe is completely feasible but on an extremely small scale and simple until the present times. Second, time can simply be the movements that make up events. If we consider the entity σ as a bit of information, then the λ synchronous method of bringing σ into the time domain P can also be used to store and communicate information in a new way. One can imagine how exciting it would be to be able to project bits of information into one's own past and influence to change information that happened before.