 Rather, it is a physical effect that occurs when two versions of the same person from different time periods make physical contact.This results in an energy discharge, shorting out the "time differential" between them.The "Mawdryn Undead" storyline establishes that the younger version of the character involved in the discharge, Brigadier Lethbridge-Stewart, is traumatized by the event and, for the next several years, loses his memory of the Doctor.