Time travel movies can quickly become complex; amid all the timelines, future and past selves, and toing and froing, some sci-fi movies even break their own rules. The concept of time travel has a long cinematic history and any film that employs the high-concept plot device must negotiate the hypothetical physics and establish its own time travel lore. Choosing between single and multiple timelines and whether time travelers can change the past or not is no mean feat, not to mention maintaining theoretical consistency and heeding to established rules across an entire movie and sometimes even sequels.
Fans’ love for these films transcends what could be seen as splitting hairs, getting bogged down in plot holes. Indeed, even the most lauded time travel sci-fi movies are guilty of breaking their own rules, yet the captivating stories and characters can eclipse any disobedience. However, though the very concept of time travel is implausible, some sci-fi films fare better than others at convincing their audience of their realism by avoiding flouting their rules, rendering them meaningless. These eight sci-fi movies have broken their own time travel rules, prioritizing their plot and impactful scenes over time travel mechanics and rule observation.
10 Back to the Future Part II
Perhaps the most famous time travel franchise of all time Back to the Future is beloved despite oft-observed plot holes such as George McFly and Lorraine Baines failing to recognize “Calvin Klein” in their son, Marty McFly. However, it is Back to the Future Part II that most egregiously breaks its own time travel rules. In the franchise’s established lore anything done in the past, no matter how seemingly inconsequential, can change the future, meaning that the future returned to would be a different timeline.
Unlike Back to the Future’s happy ending where Marty’s morality throughout pays off as he returns to an improved 1985 where his father can stand up for himself and is superior to Biff Tannen, Back to the Future Part II tries to have its cake and eat it. In 2015, old Biff picks up the Sports Almanac discarded by Marty and steals the Delorean to go back to 1955 and give the Almanac to his former self to make a fortune on. When he returns to 2015, he returns from the same timeline from whence he came. By the franchise’s own rules, this would be impossible.
The timeline that Biff came from should no longer have existed, wiped out by his benevolent actions toward his former self. Rather, he should have returned to the alternate dystopian 2015, the past of which is shown later in Back to the Future Part II in which a Donald Trump-like Biff lives rich from his gambling winnings in the clock tower, married to Lorraine. The fact that he returned to the 2015 where Marty and Doc Brown reside unnoticed, returns the Delorean and caters to the film’s plot, not its time travel rules.
9 About Time
.JPG?q=50&fit=crop&w=1500&dpr=1.5)
Richard Curtis’s time travel Rom-Com About Time follows protagonist Tim Lake as on his 21st birthday he inherits the ability to travel back in time. Tim’s father, James, delineates the rules and history of their familial time travel, namely, only the men of the family can time travel, they are limited to going backward in time, and they must be alive in the time they go back to. James warns Tim that previous relatives have run into dead ends using it for wealth and fame, so Tim decides to wield time travel to develop his love life.
About Time is more preoccupied with the romantic byproducts of time travel rather than its mechanics, choosing to prioritize narrative over consistency. The film subverts its rules when Tim, after learning that his sister, Kit Kat’s, disastrous relationship with Jimmy Kincade lands her in hospital, decides to use his power to intervene and take her, a woman, back in time to when she first met him where they see his true colors. How Kit Kat can circumvent the gender restrictions to accompany Tim and experience the past isn’t established in the film’s lore.
Tim and Kit Kat then travel back to the present which breaks another rule as, despite merely going back to their time of origin, they are technically traveling forward through time. Further, upon returning, Tim is horrified to learn that his daughter Posy has changed into a little boy as the film manifests a new rule to completely ignore: traveling back before one’s child’s birth alters the timeline and replaces them with another. Later in the film, however, Tim and James go back to Tim’s childhood and no such child substitution occurs.
8 Men in Black 3
Men in Black 3 similarly establishes a timeline and mythology, only to bend its own time travel rules to aid plot development, especially during the third act fight at Cape Canaveral as the Apollo 11 rocket counts down to launch. Throughout the film, the rule is established that when traveling back in time, the traveler is duplicated and can run into their former self. Having both traveled back in time by falling from the Empire State Building and using the time-jump device Agent J and Men in Black’s creepiest alien villain Boris come across themselves as they were in 1969.
When J must overcome Boris and survive the spikes that shoot from his hand he makes a point to remember where Boris aims, takes them in his chest, and jumps off of the launch tower taking Boris with him before using the time-jump device to go back one minute. Instead of there being two Js atop the tower (the one that’s just traveled back in time and the one from one minute ago), J inhabits his past self. This completely defies the time travel rules the movie sets up, as the scene opts to switch the time travel paradigm to advance the plot.
To add insult to injury, J’s chest is no longer full of spikes, rather, he resets back to his old unscathed self from a minute before. This detail breaks another of Men in Black 3’s rules because it erases the time elapsed between when J went back to and when he activated the time-jump device. Following the logic of this scene, J and Boris’s lives after 1969, including previous Men in Black movies, should’ve been erased, moreover, they should’ve traveled back to occupy their former selves, Boris as his 1960s bandana-wearing biker and J as a three-year-old child, making for a very different film.
7 The Butterfly Effect
The Butterfly Effect’s time travel rule break is so heinous that it still bothers fans. Protagonist Evan Treborn experiences amnesia during the most important moments of his life which are later revealed as periods that he travels back in time to. In-keeping with the film’s title, every time Evan goes back in time, any change no matter how infinitesimal produces another timeline.
The film conveniently abandons this rule when, after Evan is incarcerated for murder, he convinces a fellow prisoner of his time traveling abilities. Evan travels back to his childhood, brutally injures his hands, and returns to the present with scars that appeared as if by magic. There is certainly no butterfly effect here as, breaking the film’s logic completely, Evan’s actions don’t create a new timeline and no consequences result from his extreme meddling with the past.
6 Last Night in Soho
Last Night in Soho follows Ellie Turner who moves to London to attend fashion school and soon begins to time travel in her sleep into the body of an aspiring singer from the 1960s, Sandie Collins. The film fails to establish a rule one way or another, darting back and forth between time travel paradigms. Director, Edgar Wright, substitutes different rules when it suits the plot.
In the first time travel sequence, Ellie inhabits Sandie fully, even waking up with physical marks contracted by the singer decades before, such as a hickey, suggesting a direct link between the two women. Curiously, sometimes in the same scene, Ellie is presented instead as an audience to Sandie’s past. Swapping between first and third person, Wright neglects to confirm a time travel mechanism.
Last Night in Soho’s plot hole and time travel ambiguity could be Wright using his creative license. The film presents Ellie’s time travel in disparate ways to preserve a nighttime dream aesthetic. However, having no explanation, or concrete time travel lore established means that Last Night in Soho continually breaks its own flimsy rules.
5 Looper
4 
Looper is a sci-fi, time-traveling gangster movie in which a mob from the near future sends back in time people they want to be killed where a looper, like the film’s protagonist, Joe, kills them. Once the mob has finished with a looper they send them back to be killed by their younger self. It is this twist that ensures Looper falls victim to the Grandfather paradox, which posits if one were to go back in time to kill their Grandfather, they couldn’t then be born to then go back and kill their Grandfather.
The film sets the rule that any physical injuries that happen to a character’s younger self will be evident in their older body. When Young Seth is kidnapped by the mob for not killing his older self they cut an address into his arm, and it appears on Old Seth’s arm. The mobsters then start removing Young Seth’s body parts and Old Seth all of a sudden loses his fingers, nose, and limbs. While the scene makes for impactful viewing, Old Seth should remember having lost these limbs as a young man rather than looking in horror at his limbs vanishing before his eyes.
In Looper’s overly neat ending, to prevent Old Joe from killing Sara, thereby creating the villain of the film, Rainmaker, Young Joe kills himself to erase Old Joe. According to the film’s logic, however, the entire movie never happened because if Old Joe is erased from existence so is the motivation for Young Joe to kill himself. This paradox could have been resolved by the existence of alternate timelines, branching off when changes occur in the past but the film’s focus on the connection between old and young backs it into a single-timeline corner.
3 Hot Tub Time Machine
2 
Hot Tub Time Machine follows the dynamic time travel theory: travelers can alter the timeline and change their past, present, and future. Therefore, the film establishes through a hot tub repair person that the characters must be careful with changing time. However, the finale’s twist sees Lou Dorchen stay behind in 1986 to fundamentally change time and make billions by founding “Lougle” before Google can be invented.
The trip that the characters take to Kodiak Valley ski resort is motivated by Lou’s, who experienced the best days of his life on the mountain, potential suicide attempt. Through Lou pouring the Russian energy drink Chernobly on the hot tub, they go back in time to his glorious youth; it is no surprise Lou chooses to stay behind. In this new altered timeline, however, Lou is overjoyed at his life cultivated in the decades between 1986 and 2010.
Running into time travel foe, the Grandfather Paradox, Hot Tub Time Machine doesn’t close its loop. Without motivation for the trip, in the new timeline, Lou never goes up to Kodiak Valley and goes back in time to stay there and alter history. The whole flim collapses unless Lou and the group make the exact same trip again, however, these characters are new versions altered by Lou making this impossible. Changing time, the film breaks its own time travel rule to become a paradox.
1 Avengers: Endgame
Time travel in Avengers: Endgame faces no risk of the Grandfather paradox because you can’t change the past since it has already happened. Nonetheless, the film seems to establish this rule to preserve the events of previous movies but break it when it becomes inconvenient. The film’s time travel follows Novikov’s self-consistency principle which states that it is impossible to create time paradoxes; the time traveler can only do in the past what does not change history, elucidated in the film by Bruce Banner.
“If you travel back into your own past, that destination becomes your future, and your former present becomes the past, which can’t now be changed by your new future.”
Avengers: Endgame’s finale reveals that instead of Captain America promptly returning to the Sacred Timeline after replacing the infinity stones and Mjolnir to their respective timelines he stays in the past to grow old with Peggy Carter and shows up as an old man to pass on his shield. This breaks the film’s rules, changing history and the present, leaving the time loop open. By the film’s logic Steve Rogers has done the impossible and changed his future, something Avengers: Endgame doesn’t justify nor explain.
Subsequently, the Russo brothers have explained Captain America’s Avengers: Endgame time travel ending and how it doesn’t break the film’s rules. They use the logic of a branched reality, something that the Ancient One alludes to in the movie, which would have Cap moving between timelines, living out his life with Peggy, and somehow making it back for the end of Endgame. However, as the MCU clearly has ridiculously complex time travel rules and an elaborate workaround to Novikov’s principle is required which the actual film is less than clear about, Avengers: Endgame is just as guilty as the other movies on this list.