Blinovitch Limitation Effect

The Blinovitch Limitation Effect was the effect or non-effect of crossing timelines.

The effect was named after Aaron Blinovitch who formulated the Blinovitch theory in a reading room in the British Museum in 1928 on Earth. (MA: The Ghosts of N-Space)

Theory A
The Limitation Effect limits how much a person can change his or her timeline; in fact, any changes which cause a deviation create a time loop. (DW: Day of the Daleks)

Theory B
The effect when crossing one's own timeline and interacting with a past self (or future self depending on perspective)  is energy released  by the shorting out of the time differential between the two iterations. The energy causes memories to be transferred from the past self to the future self. It also causes the person to suffer amnesia until he completes the interaction from the other side. (DW: Mawdryn Undead) This aspect of the effect, however, does not appear to come into effect when different incarnations of a single Time Lord, such as the Doctor, interact with each other (DW: The Three Doctors, The Five Doctors, et al.), or when different versions of the same incarnation interact. (DWM: The Collector, DW: The Big Bang)

The energy released from contact between two versions of a person is usually enough to overload any surrounding technology. Just by being in the same room, the two versions create a Blinovitch Limitation field, a crackling blue energy resembling lightning. (NSA: Touched by an Angel)

The Blinovitch Limitation Effect could sometimes be suppressed, permitting two versions of a being to touch with no ill effects. (DW: A Christmas Carol) One method of dampening the effect was through the use of a sonic screwdriver. (NSA: Touched by an Angel) When the TARDIS was reconfigured into a multi-dimensional city, the ship itself contained the energies that would have been released by the Blinovitch Limitation Effect. (NA: Cat's Cradle: Time's Crucible)

Theory C
The Limitation Effect stops a time traveller from messing around with his or her own personal timeline. The limitation effect is possibly a precursor to a paradox. (DW: Day of the Daleks)