Quote:Ah, like classic trek where the matter antimatter Lazerus were forbidden to ever meet!
Weeeeellll... Kind of. But totally different. But if thinking about it that way helps... It's all good.
Bringing matter and antimatter together is just a bad idea. The two sets of particles will annihilate each other in a massive burst of energy. You can do it easily, but if you were standing too close to the event, you'd be having a very bad day.
Bringing two versions of the same person together from different points in the same timeline isn't just a bad idea, it's impossible. Probably.
In (Real) physics, we have the 'Pauli Exclusion Principle'. Basically, Wolfgang Pauli proved mathematically that certain kinds of particles - quarks, leptons and baryons, amongst others - can't exist in the same place with the same physical properties.
What that means for time travellers is, if the particles that make up the bodies (And clothes, and other objects) of the two versions are in the same quantum state, then there may be a physical property of the universe that prevents them ever meeting.
However, there's no guarantee that they would actually be in the same quantum state, so I'm on the fence with this one.
The Whoniverse has it's own version of the 'Pauli Exclusion Principle'. They call it the 'Blinovitch Limitation Effect'. First mentioned in Day of the Daleks, and seen in operation in Mawdryn Undead.