In response to a question on another forum devoted to Champions Online, a discussion of how time-travel works in Champions came up, and I thought it might generate some ideas for folks to reprint that info here. I'd just like to stress that some of the assumptions I make below are only extrapolated from the available examples, and can't be considered definitive statements from the creators of those examples. Also, as I always say, this is a comic-book world. The needs of a given story, or what would be "fun" to play out, often supersede adherence to precedent.
I'll just throw out an opening salvo in this discussion, with a brief outline of the nature of Time from Book Of The Empress
pp. 23-24, dealing with Istvatha V'han
, perhaps the most accomplished time-traveler in the Multiverse: "According to her perceptions, as influenced by the research conducted by her scientists, there’s a single overall Stream Of Time that applies throughout the Multiverse... but each dimension’s “branch” of the overall Stream “runs” at its own speed. In some dimensions (such as two or more alternate Earths), time flows along at nearly the same rate, with the same events happening at more or less the same time. But in other planes time moves faster, or slower, or “curves” in unusual ways...
However, again according to her perceptions, every branch of the Stream Of Time has chronal nodes
— dates/events/incidents of such importance that their outcome can affect the future flow of time by splitting off a new “branch” of the Stream (and thus creating a new dimension in the process). The typical events in the life of a typical person don’t create or involve chronal nodes; they can be changed by time travelers without affecting the overall flow of time in any meaningful way. But events of great significance, or the actions of extremely important persons, are/create chronal nodes. Interfering with a chronal node thus can “change history” going forward from that point.
Some chronal nodes are very specific and discrete — such as whether a certain person does or does not cross a certain street at a certain time. But others are very “broad,” such as whether a particular war is fought and who wins it. (Some scientists consider the latter merely a large collection of specific chronal nodes, rather than a single large node; research is ongoing.)"
What I believe is implied by those statements is that it's possible for someone whose life and the events in it don't form a "chronal node" to go back in time and change those events for him/herself without causing a new branch of the Time Stream to form. Hence for everyone in that branch those changes would become the "new reality" which has always been that way. However, if a node is meddled with, rather than changing that branch, a new one is formed creating another "alternate" universe.
One example of the former case may be Istvatha V'han herself. In meddling with the past of her own home dimension, V'ha-1, for her benefit, V'han discovered she had inadvertently erased her own family from having ever existed, even though she continued to exist and V'ha-1 was mostly unchanged otherwise.
As to the second case, interfering with chronal nodes seems to be the M.O. of another time-traveling conqueror, Korrex
, a Human and ruler of Earth of the 51st Century (who is fully described in Golden Age Champions
). Korrex travels to a past era of Terrestrial history, conquering it and creating a new alternate Earth dimension. Korrex sets one of his followers to govern that new Earth, then moves on to another era.
OTOH not all dimensions have alternates like Earth or V'ha. Istvatha's scientists call those which do "keystone dimensions," but the majority of dimensions are unique. So changes to time in those may actually alter those singular dimensions without creating alternates. The fate of the dimension containing the planet Koratho may be illustrative of that. The Korathons were all immensely physically superhuman. When V'han's armies attempted to conquer their dimension, the Korathons crushed them. Istvatha was concerned that now they knew about other dimensions, the Korathons would eventually invade her own empire; so she traveled back to before Koratho coalesced into a planet, and prevented it from doing so. There's no indication that any alternate version of Koratho exists.