Alternative Timeline

Any time line which is different from the currently valid time line, in particular a time line which does not exist any more because of a time travel or another method to alter history. An alternative time line is equivalent to the "normal" course of time, since only an external observer not affected by time line changes is able to perceive the difference. The concept is similar to a parallel universe, still, parallel timelines depend on each other which is inevitably connected with paradoxes.