Alternate timeline An alternate timeline was a reality that diverged from the " true " timeline due to the actions of time travel lers or other temporal phenomena . They were different from parallel universe s in that they did not separate cleanly at the point of creation resulting in the new timeline destroying the old one . ( PROSE : " Imperial Moon " ) The phenomenon may also have been described as an " interstitial spillage of time . " ( AUDIO : " Project : Lazarus " ) Physics . Alternate timelines could be visited accidentally by jumping a time track ( TV : " The Space Museum " , AUDIO : " The Mutant Phase " ) or contacting other anomalies ( AUDIO : " Colditz " ) in the Time Vortex . Deliberate travel to these timelines was possible if the traveller possessed something , such as the sigil ring , that allowed them to change time stream s . ( PROSE : " Goth Opera " ) They may have diverged from points in history when there was temporal fluctuation . The power required to adjust the timeflow and overcome temporal inertia on such a scale couldn ' t fit on a single planet , but beings with enough power were capable of doing so , such as Sutekh , the Guardians of Time , Rassilon , and the Chronovore s . Even the Doctor or the Master could have the know - how or inclination to create them . Because the universe only had a finite amount of mass and energy to exist as " one " universe , the creation of an alternate timeline adversely affected the real timeline , causing chaos throughout the universe ; releasing enough energy could destroy the timeline and set history back on its correct course . ( PROSE : " Blood Heat " ) Though a timeline could be negated , memories of it could still be retained . ( TV : " The Big Bang " , " The Impossible Astronaut " ) Sometimes these memories were subconscious and only surfaced in dreams . ( AUDIO : " The Time of the Daleks " , " Jubilee " ) Multiple timelines could co - exist in one continuum ; because of this , an individual with multiple futures could come in contact without any Blinovitch Limitation Effect s . ( AUDIO : " Peri and the Piscon Paradox " ) Occasionally , time was actually changed so that what was originally the future became an alternate timeline . These were not meant to replace the true timeline but were the result of changes to the real timeline including , apparently , WOTAN conquering Earth ( PROSE : " The Time Travellers " ) and the Doctor dying on Grace Alone ( AUDIO : " The First Wave " ) and later Trenzalore . ( TV : " The Name of the Doctor " , " The Time of the Doctor " ) This may have related to causality , with knowledge coming before an event rather than an event becoming knowledge . The Doctor encountered WOTAN after it ' d conquered Earth in 1966 , changing history when he later arrived in 1966 ; the opposite would be the Doctor arriving in an 1804 where the French Revolution was still happening , as he already knew this was incorrect . ( PROSE : " The Man in the Velvet Mask " ) Two Earth Reptile temporal scientists theorised that after changes were made to history , it took twenty minutes for the new timeline to become established . ( PROSE : " The Crystal Bucephalus " ) Metaphysics . From a metaphysical viewpoint , alternate timelines constantly winked in and out of existence with every decision made , ( AUDIO : " The Wrong Doctors " ) always being extinguished as fewer and fewer choices became open . This was particularly affected by time travellers who changed the future whenever they arrived in a new time . This was the cosmic pain of the universe and in this manner Gabriel and Tanith were personifications of the timelines that never existed . ( PROSE : " Falls the Shadow " ) The existence / creation of alternate timelines and parallel universes was held in check by the existence of the Time Vortex , which was sustained by the existence of the Time Lord s who created it . ( PROSE : " The Domino Effect " ) Terminology . The phrase " alternate / alternative timeline / universe / reality " was sometimes used interchangeably with " parallel universe " ; however , alternate timelines usually changed after a single moment in time , whereas parallel universes usually had more than one difference from the " normal " universe . Species from alternate timelines . Some species existed entirely as a result of diverges in time , including :