 The Doctor states that the Time Lords were sworn never to interfere, only to watch.It has been suggested that, since perfecting the science of time travel, they have withdrawn, bound by the moral complexity of interfering in the natural flow of history; in "Earthshock",<ref></ref> the Cyberleader, when notified of the arrival of a TARDIS, is surprised at the presence of a Time Lord, stating "they are forbidden to interfere".In "The Two Doctors", it is suggested that Time Lords are responsible for maintaining a general balance of power between the races of the Universe.