The Time Traveller's Dilemma

So you've decided to Set Right What Once Went Wrong. Temporal Paradox is not a problem; once you make this change, the dark future (your old present? Whatever) will utterly change.

There's a very dark possibility of The Sadistic Choice here. What if there's no such thing as In Spite of a Nail? What if the holocaust you're trying to prevent resulted in someone being born who will no longer exist if the situation of his parents getting together changes? What if there's millions of people who will be changed or erased against their will? What if this timeline had someone do a Heel Face Turn who won't in the original timeline?

This is a heavy responsibility.

Many writers don't like dealing with this, so they'll often write that the better future is better in every way imaginable with no exceptions; and nobody left out. Or that The Multiverse means that world, those people and its choices somehow still exist... somewhere. But not everyone does, and it's a disturbing train of thought.

Related to All the Myriad Ways.

Anime and Manga

 * Kyon of The Melancholy Of Suzumiya Haruhi once changed the world back to his old one via Time Travel. He still has nightmares of the implications of what he did, mostly because.

Comic Books

 * In the "Age of Apocalypse" arc of Marvel Comics; set in a changed present where Charles Xavier was killed in the past; Magneto and Rogue have a son. The Time Traveler Bishop wants to change things back. Magneto supports Bishop in this, but reminds him that if they succeed; his son will be gone forever.
 * Presumably this also bothered some writers; who later wrote that this world continued to exist as an Alternate Universe. (Btw, Jean Grey stopped the nukes in the end.)
 * The DCU explored part of this with alternate timelines where good versions of Doomsday and Vandal Savage change things back; ironically back to where they are villains.
 * The end of Neil Gaiman's Marvel 1602 sets right the circumstances that caused the temporal divergence that brought about the 'Age of Marvels' in the Elizabethan era. Thus, the timeline is overwritten, and history proceeds as necessary. The Watchers, however, step in and save the 1602 world as a pocket universe, kept in a glass globe by this version of Uatu.
 * Pointed out in Astro City. Samaritan changes the future into a utopia, but his family was never born, and his old house is replaced with a future Taco Bell.
 * It's revealed in "The Eagle and the Mountain" that this is actually one of Samaritan's powers. No matter what happens in history, he will still exist.
 * The DCU's second Chronos spent some time trying to change history so his mother wouldn't die in a car accident. He eventually realised that the only way to ensure this was to never be born. He still exists as a time traveller, but his history up to the point he found Chronopolis has gone.
 * In the JLA/Avengers story arc, at one point the histories of the DC and Marvel universes were altered by the retroactive effects of a history of the two universes interacting through their respective heroes. When they realized it needed to be fixed, they first asked to see what they were saving. Barry Allen and Superman saw their deaths, Hal Jordan saw that he would become the power-mad Parallax, Hank and Janet Pym saw Hank striking Janet, etc and they realized they were deciding the fates of potentially billions of people. The heroes decided to go forward in spite of what would happen to them.
 * The cost of salvaging anything at all of the original multiverse in Crisis on Infinite Earths was to produce a new single universe and erase the original multiverse entirely from history. So, from a very real standpoint, nobody survived the original Crisis (except Superboy Prime and co., and maybe Power Girl and Psycho Pirate), and all the current heroes are temporal copies of the originals.
 * The Young Avengers team was started by the time-traveling villain Kang the Conqueror, who got a look at what he was going to grow into and ran away to our time to try and avoid growing into him. Which he did apparently succeed in, but unfortunately no Kang meant that none of the many fights he'd had with The Avengers over the years and in some way that lead to almost all of them being killed, the small amount of the alternate world we see looking pretty dystopian, and the members of his team who were children of Avengers members (except for the daughter of the one whose death might actually have been prevented in the new timeline) fading out of existence. He realized that he had to go. Although we've found out since that he's still time-traveling trying to find a way to avoid becoming a villain, he's just looking for a way that won't wreck things for everyone.

Fan Fiction

 * Averted in The Three Whooves, where.

Film
"Major General Hank Landry: My goodness, people, the arrogance of what you're asking us to help you do is mind-boggling!"
 * Subverted in Stargate: Continuum when the government in the new timeline refuse to help the team try to Set Right What Once Went Wrong.


 * And played relatively straight anyway once everything starts going to pot (Baal dies, snakeheads attack, Earth in deep trouble). Apparently, Earth humans (as opposed to "alien" humans) living as slaves under the Goa'uld is not to be thought of - and we'd be better off never existing in the first place.
 * To be fair, the team from the original timeline always wanted to fix everything, they just never had a chance before then.
 * The ending of The Butterfly Effect invokes this trope:

Literature

 * Averted in Animorphs Megamorphs 3. Some things in the altered future may have been better, many things were worse, but in the end when Rachel asked Cassie if they fixed everything, all Cassie could say was that "they put it all back."
 * Although, seeing how the Yeerks were just a couple steps from taking over the Earth, the Nazis won World War II, "unfit" people were being eradicated, rebellious people were being "reeducated", "fit" people were forced to breed repeatedly, and the only videogame in existence was Pong, I doubt it could be much worse.
 * Yes, originally, that was true. But once the Ellimist and Crayak sent the kids back and they started trying to stop the Bad Future from happening, other, possibly good things started happening. D-day still occurred, for example, but Hitler was just a driver, and there was the distinct possibility that the Germans were the good guys. It was never made clear (which was completely intentional, of course).
 * In Megamorphs 2, this trope is in effect big time, though played...interestingly. To elaborate, the Animorphs go back to the end of the Cretaceous Era and soon discover not one but two sentient alien races who had colonized the Earth. They also soon discover that there is a giant freakin' comet flying through the sky, which Ax informs the group will just barely miss the Earth, based on its trajectory. The two alien races are at war with each other, but with the Animorphs' help, the "good" aliens drive off the "bad" ones. The "bad" ones respond by moving the comet off its path, aiming it towards the Earth in order to wipe out the entire "good" alien population. If you know anything about the age of the dinosaurs, you've probably guessed by now where this is going. The "good" aliens try a last ditch effort to blow the comet back into not hitting the planet and killing them all, but Tobias secretly has Ax rig the explosive to be a dud. Tobias insists that he did what had to be done, realizing that in order for humanity to rise, the Animorphs can't change history such that the "good" aliens (and the dinosaurs) survive, because they know from the lack of either in the present that they don't. Tobias also insists that he didn't consult the others because he didn't want them to live with the guilt of having condemned an entire sentient species to extinction. This still leaves Ax and Tobias with that guilt, and the question of whether dooming one innocent species to ensure their own existence was the right choice. This therefore is the unusual case of ensuring a Stable Time Loop being highly morally questionable.
 * Addressed in Orson Scott Card's novel Pastwatch, where the organization that just discovered time travel is quite aware that interfering with the past will erase the existence of everyone in the current timeline and insists on having the world vote on whether or not to Set Right What Once Went Wrong. As humanity is facing imminent extinction anyway at that point, the vote passes.
 * In the Peter David Star Trek Expanded Universe novel Imzadi, Admiral Riker wants to go back some thirty years to the time of late-season TNG to save Deanna's life, since he believes someone already altered time by traveling back to kill her; Data objects on these grounds. When it's done and everybody has time-traveled home, the Guardian of Forever--time-travel mechanism of choice today--points out that "All is as it was." When asked why it didn't bother to mention that yes, Riker was restoring the proper flow of history, it answers.
 * In The Time Ships, the Time Traveller's second trip into the future sends him to a completely different world from the one he remembers. He concludes that with every use of the time machine he is potentially committing murder on an unimaginable scale and vows to prevent himself from ever creating the machine. Later subverted when it turns out that the many worlds model is in effect.
 * Discussed and averted in Island in The Sea of Time and 1632, both novels involving the permanent transplantation of a modern town to the past. They came to the conclusion that it was a once-in-a-universe cosmic event, so they were astronomically unlikely to go back, therefore they didn't have to worry about changing the future because they'd already changed it by their very presence.
 * encounters this in The Void Trilogy.

Live Action TV

 * Played straight in Star Trek: Voyager "Timeless", in which Harry Kim is driven to Set Right What Once Went Wrong, a mistake on his part which killed the crew except for him and Chakotay who were in the Delta Flyer, but both Chakotay and his girlfriend know that this will cause them never to meet. Starfleet also saw it as dangerous and sent LaForge to stop them.
 * Voyager also had a story arc about an an alien Well-Intentioned Extremist who built a weapon that could erase things from history; his intent was to get rid of his species' enemies, but in so doing managed to get his wife killed, leaving him continuously trying to undo the damage by erasing more civilizations. Ironically, even after hundreds of years doing this he never realized what he really needed to erase was.
 * It's not that he didn't realize it, it's that he wouldn't consider that a solution. The entire point of the weapon was to wipe our his civilization's enemies. If he has his wife back but that core goal isn't satisfied, then he's still failed.
 * Admiral Janeway's plan in the finale is to send Voyager home NOW. Captain Janeway points out that she did get Voyager home after another sixteen years. The plot takes over before they get too philosophical, to the disappointment of many watching.
 * Mentioned and averted by way of Q in Star Trek: The Next Generation. Picard's artificial heart is damaged and he's about to die, so Q gives him the opportunity to change his past to prevent the injury that led to him getting the transplant. Picard worries that any action he'll take in the past could have disastrous consequences, but Q brushes him off with, "Nothing you do will cause the Federation to collapse or galaxies to explode. The only life at stake here is yours. In short, you're not that important."
 * Of course, while it doesn't have disastrous consequences for anyone else, the consequences to Picard's own life after not getting in the fight that caused the injury are so bad he immediately asks Q to change it back even if he does die. So averted on a galaxy-wide scale, but definitely present in his own life.
 * On Lost, several have tried to save the past...and all fail miserably and cause the event, since everything that has or will happen has already happened. Most notably, Daniel's attempts to not only results in, but probably caused the Incident, since , a event referenced in the very first episode with him in it.
 * Maybe. Something was going wrong at the Swan site before they stepped in.
 * And it seems as though he both succeeded and failed.
 * Neither.
 * More specifically,
 * Acknowledged and arguably justified in an episode of Buffy, involving not time travel but alternate realities. In the Season Three episode "The Wish", Cordelia wishes that Buffy had never come to Sunnydale, creating an alternate reality in which the town is overrun by vampires. Alt-Giles figures out how to reverse the effect, but at the last second, the demon responsible for it tries to stop him, asking why he thinks the alternate (original) universe is any better than the one he knows. Giles' response? "Because it has to be."
 * Done beautifully in the Doctor Who episode The Fires of Pompeii. The Doctor is saddled with the choice of not setting off Vesuvius, thereby saving Pompeii, or sending those people to their deaths in order to keep history intact
 * Turns up even earlier in Genesis of the Daleks. The Doctor is given an opportunity (an order, even) to prevent or seriously alter the creation of the Daleks. The only obvious downside is that at that point the Daleks hadn't done anything wrong (yet), and so he'd be committing genocide against a thus-far innocent race, who he knew would turn evil and try to wipe out entire species...
 * An episode of Star Trek: Deep Space Nine has the Defiant crash on a world populated by the crew's descendants (and a future Odo), thanks to a time loop. The characters decide they have no choice but to make sure these people live, and prepare to trap themselves in the past.  Kira doesn't take it well.
 * Stargate SG-1 does it in the episode "2010" with Carter's husband wondering if the other timeline will really be better and what happens to them if the plan succeeds. Carter then bluntly tells him that "they" won't exist or exist but in a different way and that the new timeline cannot be worse than the absolutely certain destruction of humanity in less than 200 years. As we know, despite the new enemies appearing later on, she was entirely right.

Video Games

 * While it's hard to tell (since the game is currently in alpha), the plot of Achron will probably explore this. It's already been referenced on the developer blog before.
 * It's implied in a letter from Lucca in Chrono Cross that the main characters of Chrono Trigger have to die as karmic punishment for changing the future.
 * This trope is the springboard for the entire plot of Crimson Echoes.
 * Aversion: Not Time Travel, but worth commenting on; an Ass Pull justification that Marche of Final Fantasy Tactics Advance gives regarding changing Ivalice back into "The Real World" is that surely the Magical Land Ivalice will continue to exist as Another Dimension after he destroys it.
 * And it does.
 * Entirely false. Word of God states that Marche's (real) world is at the end of the Ivalice timeline, preceeded by Final Fantasy XII, Final Fantasy Tactics, and Vagrant Story in that order. The fantasy Ivalice was created based on Ivalice's history.
 * It was still populated by a bunch of apparently self-aware beings who all vanished because Marche decided their lives weren't "real".
 * I'd like to see what Word of God you're referencing, because that explanation can't account for the ending of Final Fantasy Tactics A2, where the professor who's book Luso got sucked into Ivalice through is a grown up Mewt from Final Fantasy Tactics Advance.
 * Pokémon Mystery Dungeon: Explorers of Time/Darkness/Sky reveals in its final chapter that
 * One of the bonus chapters in Sky reveals that even though the Bad Future was prevented, it still exists in some other universe., but thinking about this further can lead to the conclusion that it might still be sticking around in other universes.

Web Comics

 * General Protection Fault had a massive story arc in which the future son of the two main characters went back in time to prevent his Bad Future from occurring, knowing full well (and accepting) the fact that doing so was likely wipe him from existence.
 * Briefly addressed in Schlock Mercenary. The cast didn't dwell on it much, probably because their universe was doomed anyway.
 * Though the metaphor used when he makes the jump softens the blow. It also helps that it had only been a few weeks.

Western Animation
"Martian Manhunter: You understand that if we do change the past, you - this version of you - will never have existed?
 * Averted in the Justice League episode "The Savage Time", where Alternate Batman doesn't like living in an authoritarian regime after the Allies lost World War Two.

Alternate Batman: Nothing would make me happier."


 * Also, when Alternate Batman mentions his parents were killed for opposing the government, he later seems hopeful that they'll have survived if the Justice League changes the past. Superman mentions very tactfully that this may not be the case(They don't).
 * Star Trek: The Animated Series episode "Yesteryear". We certainly hope Thelen the Andorian got a comparably good job in the rewritten timeline. At least he accepts his fate bravely and Spock wished him a long and prosperous life in whatever circumstances he would be placed in. (Like most Trek time travel, it's unclear whether or not he got to stick around in a divergent timeline.)