actually looper made no sense at all to me... the scars 'appearing' when the time traveller would remember all that... and just by being captured could be prevented from jumping back and escaping....
Those are all references to the causality paradox(es) due to time travel. The time traveller has already experienced reality one way, and in travelling back is changing (attempting to change) how that "reality" plays out, so their memories are necessarily false; what they remember is exactly what they are trying to avoid. In looper I think they mention headaches at one point as a cover for memory rewriting itself (because causality) the same as a scar they never had when they jumped back, suddenly appearing when their "current" self gains the injury that they never received in their version of history.
When considering causality violations due to time travel, the 2 ends of the scale are a pliable reality that allows time travellers to affect it (meaning causality necessarily gets broken as hell and you have magic appearing scars and disappearing limbs, and people disappearing up their freshly murdered grandfather's vas deferens), or that reality is fixed such that nothing time travellers can do can change anything (meaning that Fate is predestined and immutable), because it has already happened because they already came back and changed it before they decided to come back and change it. Which makes time travel irrelevant to the plot, because anyone travelling in time is basically running on autopilot and can only do what they are fated to have already done when they did it the first time.
That second option also pisses all over free will and suggests that the entire history of the universe is pre-scripted, so I don't really like that one. It also doesn't work well with quantum electrodynamics, you'd have to be a total bastard to script a fixed and immutable universe where even basic particles act like they just don't give a fuck about rules.
I'm also not a big fan of the Trousers of Time, but it has a little more credence than the Immutable Fate depiction, at least IMO.