The timelines of DBZ are quite an intricate topic. I've been interested in it for a long time and I've finally come up with a satisfying theory. The most interesting thing about this theory is that the existence of a second "main" timeline is confirmed. This is going to be a long read.
The events concerning Cell and Trunks require various timelines to explain. The first confusing fact is that Cell appeared to have stolen the time-machine from Trunks. However, in the episode 'Free the Future', Trunks defeats Cell easily. The two events are different, so there must be a third timeline, in which Trunks dies at the hands of Cell. In DBZ, it is also stated that Cell hijacked Trunks' time-machine because the Androids had been defeated by Trunks somehow. But Trunks returns to the future and not only kills the Androids, but Cell, too. This means that the Trunks from Cell's timeline had traveled to and returned from an entirely different past. In this past, Trunks never learns of Cell, nor does he develop the powers needed to bring Cell down. Instead, he finds some means to defeat the Androids in his own time. This makes it a very different timeline.
In this hidden timeline, all Z-warriors are likely to have survived, which in turn allows for a whole different Majin Buu saga. Furthermore, the Cell from this timeline was never found, so he will appear after the Majin Buu saga, perhaps with even more genetic material than the Cell we know (Majin Buu and Dabura, perhaps even Broly). Many of the TOEI movies could have happened in this timeline, because the events are very different.
To prove the above theory, there are several rules of DBZ-style timetravel, judging by the facts presented in the manga.
First of all, multiple timelines can coexist, but can't normally interact. The various timelines are best viewed as planes in a four-dimensional space (or just call them different dimensions). Changing the past means creating a new timeline while your future remains unchanged. Trunks explains this during the Cell saga.
Secondly, the time-machine has the uncanny ability to return to its original future. This means that continued interaction between the past and future is possible, as long as the time-machine is operational. The original future is preserved, if you will.
Thirdly, the time-machine always travels to the newest-created timeline. This is evidenced by the fact that Trunks' second trip is to the already changed future, even though the future where he came from was still the same.
Fourthly, when someone travels to a destrination that precedes a previous trip, he will create yet another timeline. This is what Cell did by arriving one year earlier than Trunks. Since this act altered the history of this Trunks, the future to which he would return was also changed - i.e. another future timeline was created.
We begin with the normal future timeline, the Dark Future. When Trunks travels to the past, he creates a new timeline according to rule #1. This is the 'Dark Past'. When Cell preceded Trunks' trips, he created the main timeline. Finally, when the Trunks from the main timeline returns to his future, he creates the final future, in which Cell and the Androids are killed.
I'd like to hear what you think about all this. I hope I haven't driven anyone insane with this
Greetings, Terra-jin.
