Following what was for all intents and purposes the removal of the Time Lords, the Doctor believed himself to be the last of his race. The removal of the Time Lords also had a profound impact on time travel. In the 2006 episode "Rise of the Cybermen" when the Tenth Doctor, Rose Tyler and Mickey Smith are trapped in an alternative reality, the Doctor explains that, when the Time Lords were around, travel between parallel universes was less difficult but, with their demise, the paths between worlds are now closed. The Time Lords could also prevent or repair paradoxes such as the one created by Rose in an attempt to save her father's life in a traffic accident. After the Time Lords' disappearance, such a paradox summons the Reapers, who descended to "sterilise the wound" in time by devouring everything in sight, and are only stopped by Pete Tyler killing himself.