Four and a half years ago, IchabodE asked a very famous question about what would happen if everybody experienced a single-day loop like the one in Groundhog Day.
Recently I saw the question again (I believe somebody did an edit of some sort), and thought: "What if everybody had a groundhog-day loop going from the beginning of their life until the end?" Since I spend a lot of time here in WB.SE, I decided to ask it here.
I want my time loop to have each person live their life, from birth to death, over and over again. However, people's lives overlap, with one person's actions effective everybody else's via the butterfly effect. Given the following conditions, is it possible to create looping time for individuals that doesn't require everybody else to be a parallel-universe doppleganger?
EDIT: To clarify, I am trying to fix the causality issues with as little meddling by "Q" as possible.
Everybody experiences a loop.
The "a" qualifier in Condition #1 is very important; everybody has their own loop.
The "start" and "end" of a person's loop corresponds with their birth and death.
People remember past loops as if it were all linear time.
Due to biological limitations on long-term memory formation, they can't remember the first two to three years of any particular loop.
The effects of Alzheimers, Dementia, TBIs &cetera do not carry over to the next iteration; memories lost as a result of these conditions are restored at the beginning of the next loop. However, memories that are not formed at all as a result of these conditions will remain lost.
The source of the looping phenomenon is unimportant; for all intents and purposes, act on the assumption that Q is using his powers to conduct a sociology experiment on us puny humans.
Anybody who is born after the phenomenon starts will have their own loop, compliant to these Conditions. This means that, in mathematical terms, the domain of this phenomenon is effectively +∞. However, you need only consider the first 5-10 generations in your answers.
The actions of parents during any particular iteration will effect their child(s)' corresponding iteration.
As a result of #9, any loop where a person's parents' actions keep him from being born will be skipped.
Although memories are maintained, you can't bring anything with you into the past.
All paradoxes (excepting the one that ultimately ends the phenomenon) are taken care of by "Q".
Although most paradoxes are handled, there are some which are not. When done, they break the person who creates them out of their loop, allowing them to permanently die at the end of their current iteration. While it's possible for almost anybody to create one, they are complex enough that characters generally can't create one accidentally.
In order to avoid some annoying causality issues, once somebody leaves the loop the last "version" of them remains present as an "NPC" of sorts. Essentially, from the point of view of the people still in the loop they become like one of the townspeople in Groundhog Day.
: "they" could cause confusion here, so I'm just assuming the male gender for simplicity.