Blinovitch Limitation Effect
The Blinovitch Limitation Effect was a natural function of the universe that described the effects of approaching and/or making physical or causal contact with a future or past version of yourself, an action that was also referenced as "crossing your own timeline". Several other concepts, such as temporal paradoxes, were related to the Blinovitch Limitation Effect, and it was sometimes unclear which specific observed reactions were due to this effect.
The effect was named after Aaron Blinovitch who, in 1928, formulated the Blinovitch theory in the reading room of the British Museum. (PROSE: The Ghosts of N-Space)
The Ninth Doctor said that prior to the time-locked destruction of the Time Lords in the Last Great Time War, his people could have prevented or mitigated the effects of a paradox. (TV: Father's Day) The Blinovitch Limitation Effect was modified by the Time Lords and their temporal technology on Gallifrey, although crossing one's own time stream required enormous amounts of energy and broke the First Law of Time. (TV: The Three Doctors)
The Doctor mentioned the effect when explaining why he or another cannot simply go back in time to take another try when a plan fails. (TV: Day of the Daleks) The Time Lords and other time-aware and time-active groups could, with technological assistance, suppress the effect. The Time Lords expended energy to suppress these effects in TV: The Three Doctors, the Eleventh Doctor used the sonic screwdriver to do so in PROSE: Touched by an Angel, and the Doctor's TARDIS did so herself when reconfigured into a multi-dimensional city in PROSE: Cat's Cradle: Time's Crucible.
When a person used time travel to attempt to change their own existing timeline, the deviation could create a time loop, which was a type of paradox. (TV: Day of the Daleks)
Blinovitch limitation field
If an item or person crossed their own timeline and the past and future versions came near each other or physically touched each other, energy would be released. The Fifth Doctor called this "shorting out the time differential." In some cases, this energy caused memories to be transferred from the past to the future person, who then suffered amnesia until both versions of the person have experienced the event. (TV: Mawdryn Undead) The energy released from contact between two versions of a person was usually enough to overload any surrounding technology. Just by being in the same room, the two versions created a Blinovitch Limitation field, a crackling blue energy resembling lightning. (PROSE: Touched by an Angel) The Doctor has been able to purposefully dampen the effect through the use of a sonic screwdriver. (PROSE: Touched by an Angel)
During the total event collapse created by the explosion of the TARDIS, the Eleventh Doctor's sonic screwdriver sparked when touched to a later version of itself. The Doctor took this discharge of temporal energy as a confirmation that it was the same screwdriver, although he didn't name the effect. (TV: The Big Bang)
It gets complicated
However, in a majority of occasions when two individuals were in close proximity or touching, there was no energy discharge or energy field. In some cases, Time Lord or other temporal technology was available to dampen the effect, but even so previous incarnations may have temporarily aged as a result of the time differential.
The Doctor physically interacted with different incarnations of himself or with another version the same incarnation without the proximity or interaction triggering a Limitation Field or energy discharge. (TV: The Three Doctors, The Five Doctors, The Two Doctors, Time Crash, and COMIC: The Collector) At one time, the Eleventh Doctor was in an alternate universe that was suffering total event collapse as a consequence of the explosion of the TARDIS. He touched and was touched by a future version of himself. (TV: The Big Bang)
Even some humans did not trigger the effect. Rose Tyler created a temporal paradox by saving her father, Pete Tyler, from death. The Ninth Doctor had allowed Rose to make a second attempt to comfort her father while he died, and they hid from their earlier selves. Rose rushed out passing within several feet of herself from an earlier time, and their earlier selves disappeared. Later, when Rose was standing near herself as a baby, and later still, when Pete thrust Rose, the baby (well bundled), to adult Rose, to hold. This did not produce an energy discharge, but produced enough of a temporal paradox to allow a reaper to enter the church in which they were sheltering. (TV: Father's Day)
Two versions of Kazran Sardick touched each other without triggering the effect. (TV: A Christmas Carol)
Similarly, different versions of Amy Pond (or the Amy Pond Ganger) touched on at several occasions. Older Amy put her hand on the head of younger Amy near the Pandorica, during total event collapse. (TV: The Big Bang) Amy also remembered an older version of herself replacing an ice cream cone she had dropped. She did not mention any unusual effects. (TV: Good Night) Two incarnations of adult Amy (or possibly her identical Ganger), approximately one minute apart from the other, touched each other flirtingly, within/outside the TARDIS (as the two concepts were the same at the moment), with no discharge. (TV: Time) While she was trapped in a facility where time was compressed by great temporal engines, an older version of Amy interacted with, but did not physically touch, a younger version of herself. (TV: The Girl Who Waited)
