Shortly after not only travel through time, but also between worlds was discovered in the 26th Century, it was surmised that certain events could be changed without damage to the timeline. Instead just creating a parallel reality. With some experimentation, this was proven. Time Can Be Changed
I don't know what was wrong with me the other day but whatever it was has passed. Sorry if I was short with any of you or said anything utterly depressing. I swear I'm not normally like that, just ask Grant and Fitz, they'll tell you.