So we all know that the loopers eventually get sent back 30 years in order to be killed by his younger self. If the looper fails to kill his older self and is not found out (say, by collaborating with his older self), what would happen 30 years later? Is this going to cause some sort of weird loop?
Given the 'retroactive effect' theory of time travel that Looper seems to use (that is, an older self who has time traveled back in time will experience changes occurring to their younger selves concurrently with those changes happening in the time they have reached, and will possess a mixture of memories/effects from their own timeline and ones from the modified timeline). This means that if the person does not travel back, events happen one way. If they do travel back, then any differences in the timeline must be connected to the time-traveler. The time-traveled older self's mere existence starts the butterfly effect you see in many time travel theories (note A Sound of Thunder, or similar works). This form of keeping continuity consistent has problems like any time travel theory, but we'll go with it.
If the older self is collaborating to survive with their younger self, and neither are found out in this, one of two possibilities present themselves:
- The timeline the older self came from was one where they killed their older self. Like Joe, this old looper prevents their younger self from repeating the performance, and both go free. When the whole thirty years come along, and the young looper goes back, they won't have killed their old self. They could easily die, having lived a different life (which may produce a closed loop of two timelines, figure-eighting into each other), but don't have to (especially if their previous older self did something particular to survive the trip back, and the formerly younger self emulates it when it is their time).
- The timeline the older self came from was one where they avoided killing their older self. This is a nicer closed loop, as only only one timeline is necessary. Having not killed their older self, and not having been found out, they get sent back, and don't die until they reach old age.
Both of these assume the looper stays in the program after letting their older self go scot free. If they don't, or if the circumstances of going back change each time, each travel back may produce a different timeline, and as each new timeline contains a new travel back, you'll find anywhere from just the one to an infinite number of possible timelines occurring in sequence.
So yes. It could just be a simple "went back, survived, got old", or it could create some crazy loops.
Even though they strongly hint of a singular timeline (mutilation of younger self affects older self, memories of older self are future events of younger self), the fact that:
Joseph kills himself in order to stop his future self
...is a direct conflict of the the singular timeline concept and that entails that the "older self" is really an older version of oneself in another separate timeline.
So what does that imply? If the younger self had worked together with the older self, there would not necessarily be any preconditioned future. Anything that repeats itself is entirely coincidental combined with the fact that many things remain the same between timelines and therefore might happen in the same way regardless. However in theory, they could stop the Rainmaker when he was young and nothing would happen since it would only stop time travel from occurring in the present timeline. There only seems to be a strange link between the older self and the younger self that would contradict this theory, but you could explain that away by saying that there are ties between versions of oneself from different universes regardless of the fact that the older self's timeline is a separate one.
If its a singular timeline, older-self is sent back in time and younger-self is waiting there to shoot and when the older-self appears he(younger one) doesn't shoot him.
Confusion starts here, 1) if they don't see each other and walk in different direction, we can expect the young one to go through all walks of life as the older one did and after 30 years sent back in time and not get shot and continue his life and die old in the past.
2) if they see each other and if the older tells about his life experience, there is a lot of chance, the younger one may decide not to do the same thing what older did, then older self will cease to exist and disappear, all the experience and time spent with the older one, will be just a fragment of memory that has disappered suddenly but there might be a feeling of missing something but not knowing what it is? Sort of (Presque vu) its in the tip of the memory, which cannot be described.
Time travel in Looper don't really follow a particular rule. The rise of the Rainmaker and his hatred of Loopers is implied in the final scene to stem from the older looper killing his mother, yet the only reason this older looper could find his address is from his panicked (partner? fellow looper?) who send him the information to hunt down the Rainmaker, which won't be necessary if the Rainmaker hasn't begin his reign of terror. Also, remember the first old looper that tried to escape while his younger-self is being mutilated to the point that he can't walk. He won't be able to escape in the first place under that condition.
EDIT : I think that mutilation scene could give a hint. Either the older looper disappear at that moment (since the younger looper don't walk into any time machine) or the younger looper got into a situation where he's forced to return to the past.