Pedz wrote:Anyone?
It was probably referring to "closed timelike curves" and the resultant "Novikov self-consistency principle".
One way to investigate whether time travel is possible is by describing the time travel scenario mathematically, then seeing whether that maths is a valid solution to Einstein's equations.
Situations which solve Einstein's equations look like this: 1. you throw a ball at a wormhole which links to a few seconds in the past; 2. as the ball is in the air, the ball from the future comes out of the wormhole and just misses the ball you threw; 3. your ball enters the wormhole.
Those situations are called "self-consistent".
Situations which do not solve Einstein's equations look like this: 1. you throw a ball at the wormhole; 2. the ball comes from the future and knocks the ball away; 3. no ball enters the wormhole.
That would be a paradox, because now there's no ball going into the wormhole to come out and knock the ball you threw away.
tl;dr Einstein's equations imply you can't change the past even if you have access to a time-travel wormhole.