Temporal feedback loop

According to the "Ruth" Doctor, a temporal feedback loop could be caused if her TARDIS were to get too close to the Thirteenth Doctor's TARDIS. (TV: Fugitive of the Judoon) High Tutor Albrecht, an instructor at the Time Lord Academy, regenerated as a result of an experiment by Theta Sigma involving a perigosto stick and a temporal feedback loop. (PROSE: The Time Lord Letters)