Time travel is always a complicated proposition. It’s easy to imagine the chaos that would result if someone was able to just flit back into the past and change things, or soar into the future and return with stock tips or laser weapons. That’s why most time travel stories focus on the challenges—should you kill Hitler? What happens if you fall in love with your own grandmother by accident? What’s the rule on repeating a first date 600 times in order to get it right?
In the ten stories below, all the complications are overcome, and time travel not only works, it actually saves the world. (Warning: spoilers throughout!)
The Doctor has been freewheeling through time since he stole a TARDIS more than 2,000 (subjective) years ago, and he’s saved the earth plenty of times since. Exhibit A: the Season Five finale, “The Big Bang,” wherein the Doctor moves back and forth across thousands of years and literally erases himself from reality in a bid to save the entire universe from destruction (don’t worry, he comes back via the power of Amy Pond).
Magic Tree House, by Mary Pope Osborne
This magical series has seen its young protagonists Jack and Annie travel from their humble home in Pennsylvania across millions of years, meeting dinosaurs, medieval knights, Egyptian mummies, and soldiers invading Normandy on D-Day, to name a few. What makes this series so special is that it respects children and their capabilities, telling stories of time travel that saves the day over and over again without condescending or doubting for one moment that kids are able to understand complex and occasionally disturbing history lessons—and remaining certain they would rise to the occasion if they were to stumble upon their own magic tree house.
Outlander, by Diana Gabaldon
There’s no clear threat to the world at large in Gabaldon’s fantastic, romantic, adventurous series, but the magic of a time travel story is that you can’t actually say that definitively. After all, Claire and Jamie are embroiled directly in major historical events on several occasions in their adventures. Who’s to say it wasn’t Claire’s presence (or the presence of any number of others who have traveled from the future) who ensured the world’s survival via some unforeseen consequence? That’s a little something called the Power of Love, friends.
Time Salvager, by Wesley Chu
Where most time travel stories insist the ability to move through time must be a secret, in Chu’s exciting novel, time travel is the key to humanity’s survival after a disaster drives people off Earth and onto other planets and moons. Traveling to the past to recover necessary resources without altering history too severely, Chronman James Griffin-Mars is stressed to the breaking point, and haunted by the people he has abandoned to the past to die. When he breaks the most fundamental rule of his job by bringing a woman with him into the future, the unintended consequences of his action spur an epic chain of events that ultimately might save the human race.
With every new entry in the Terminator film series, the timeline gets more jumbled and convoluted, but one constant remains: people keep traveling back in time to stop Skynet from gaining sentience and trying to destroy humanity…and the robots keep sending back increasingly spiffy Terminators to ensure it does. Since Skynet hasn’t yet launched a genocidal war against us, we have to assume the apparently endless loop of time travel is working so far.
No one actually understands this film completely, but the fundamental takeaway is that Donnie Darko, by (spoiler alert!) choosing to close his personal time loop and die, saves the world from complete destruction owing to temporal paradox. And you thought your high school years were confusing and difficult.
This underrated film’s internal logic doesn’t necessarily hold up to scrutiny, but up until the final surprise ending it rolls along as one of the best-conceived time travel stories in recent memory, centering on the ultimate personal sacrifice of its protagonist, who realizes at the crucial moment that the only way to prevent his horrifying future is to sacrifice it entirely, thus saving the world from a bloodthirsty madman.
All You Need is Kill, by Hiroshi Sakurasaka
The novel on which the film Edge of Tomorrow is based is one of the best science fiction novels of recent years, telling the story of a futuristic soldier who dies on the battlefield fighting an alien invader—and awakes at the beginning of a stable time loop, doomed to repeat the battle over and over. As in video games, the time loop allows him to hone his skills, learn to avoid deadly mistakes, and slowly figure out how to defeat the alien Mimics who have killed him over and over again. An inventive, modern take on time travel that saves humanity, this is an exciting story that’s equal parts military sci-fi, time travel story, and mystery.
Lest Darkness Fall, by L. Sprague De Camp
One of the most influential stories in science fiction history, Lest Darkness Fall is a more subtle example of time travel saving the world. Archaeologist Martin Padway is swept into the 6th century, right before the Eastern Roman empire invades Ostrogothic Italy, unintentionally ushering in the “dark ages.” Using the technological and strategic knowledge of the 20th century, Padway rewrites history, saving Italy and Europe from the ravages of war and saving the world from the Dark Ages altogether—with incredible potential impact on the future.
11/22/63, by Stephen King
Another subversion, as King’s story of a time portal to 1958 and one man’s quest to stop the Kennedy assassination ultimately sees him having to save the world from the timey-wimey damage of his own actions in the past. After stopping the assassination, Jake Epping returns to his own time to discover the law of unintended consequences has left the world he knew in ruins—and he must use time travel to save the world by undoing all of his work.