The act of time travelling is the phenomenon that allows an individual to travel through time. It is a rare act that allows one to travel to either the past, or the future, typically with intention to alter one or the other. According to Whis, the flow of time is meant to proceed linearly. Even simple acts of going back in time can have drastic effects on the future; to the point that a planet which was not meant to be erased from the Universe could wind up destroyed. Only Gods themselves are allowed pass through time, and even in their case, it is not to be taken lightly.
When a human using the Time Machine that Bulma created passes through time, it causes a shift in the timeline, branching the former past on the road to a new future, rather than directly affecting the future the traveler came from. In the manga, this is a change to the point that the former past and former future can no longer be considered as just such, and are instead separate dimensions. This poses limitations on traveling to and from the future, and the bond between the two dimensions gradually weakens. Another way to create a branched timeline is to destroy an individual in the past, while their direct counterpart in the future wears a Time Ring. This enables the one in the future to survive, creating a split timeline once more.
If one uses the Time Ring, they are capable of a more controlled form of time travel. With this method, they can only travel to the future, and cannot travel to the past except to fix distortions caused by existing time travel, or to return to their own time. Time Rings are only able to be used by Kaiōshin, or those wearing a Potara of a Kaiōshin color.
It has been noted repeatedly that it is forbidden for humans to alter time. Both Gowasu and Whis have mentioned on occasion that mortals interfering with time is a grave offence. Within the scope of human law, time travel and control is also forbidden, as the Galactic Patrol places it within the confines of galactic law that time may not be manipulated in any form.
- According to Akira Toriyama, the non-serial movies preceding Movie 18 take place in alternate timelines from the manga, implying that other timelines exist naturally alongside the main timeline, without Trunks' time travel having interfered.
- The idea to make Time Travel taboo may have come from Dragon Ball Online, where Chronoa first mentioned this to Trunks. Fittingly, Chronoa can control time in a way that her time machines do not split the timeline.
- Time Travel and manipulation as a crime is parodied in Dragon Ball Fusions. If the player adjusts the time on their Nintendo 3DS, Jaco will warn them against committing the crime, and time based events no longer occur for two days.