perhaps I'll sound like a madman, but
an interesting aspect of dark (2017) is that while its depiction of time travel is fairly realistic, still obviously moving in the realm of pure theory, it has no significant plotholes. however, it still ends in the inevitable impossible conclusion a time traveling show could ever end with, the grandfather paradox.
yet nobody ever mentions it.
one thing I really appreciate about this show is that it's not trying to spoon-feed you theory tell-not-show, toddler explanation stranger things style, it hints, sometimes. a few characters across the timeline talk about scientific and theoretical shenanigans important to the plot, but never this paradox.
at first I thought it was because it's such obvious time traveling handbook knowledge, they never bothered.
as the origin of h. g. tannhaus's book is revealed, he talks about the bootstrap paradox (but we as the viewer have already witnessed it multiple times before).
but those two are different - the bootstrap paradox is realistic, it supports the loop repeating again and again, no beginning, no end, future influences past just as past influences future etc etc. the grandfather paradox is a paradox because it can't happen. [proof of this is constant: jonas cannot end his life, nor can anyone else try, the time will always protect him.] yet, it happens.
you cannot travel to the past and kill your ancestor and prevent them from procreating, because if they never contributed to your birth, you wouldn't have been able to travel to the past to kill them in the first place.
jonas and alt!martha cannot just travel to an alternate reality and prevent an event from happening that originally triggered the creation of their realities, because if they never existed, who just traveled to this reality to prevent marek, sonja and charlotte's accident?
the entire complicated plot to this series is purely schrödingerian and happening in an overthinking theorist's mind. what if this random scientist's family died and he accidentally created two more realities for them to be reincarnated in? and what if their souls fought so hard to erase the chaos and pain this invoked that they broke out and prevented themselves from dying?
fate had an accident in mind, but maybe they just never died in the first place, thanks to an unseen force, and that's up to your interpretation. I personally envision them being tied by an invisible red string and simply adamantly refusing to be separated, because the knot they tied on it is stronger than fate.
