Time travel has one important rule: it must be internally consistent.
As far as we know, time travel isn’t real, which means that movies, TV shows, books, comics, and other attempts at world-building that deal with time travel are fiction, and the goal is to make time travel work within that fiction. Maybe it’s branching timelines in a multiverse, like the MCU, or maybe going back in time risks changing history and erasing you from existence, like Back to the Future.
The exact nature of the rules doesn’t really matter, as long as they’re consistent. If going back in time sends a copy of you back to the past along with your original past self, then it should always work that way. It would be confusing if the way time travel worked in your fictional world suddenly changed, and now you had to replace your old self to go back to the past. That would be silly, right?
Unfortunately, 2012’s Men in Black 3, an otherwise pretty solid entry in the Men in Black series, does exactly the same thing. Let’s take a closer look at why the time travel rules in Men in Black 3 are internally inconsistent.
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Men in Black 3’s vague “rules” of time travel
In Men in Black 3, Agent J (Will Smith) travels back in time after the evil alien Boris the Animal travels back in time to assassinate Agent K (Tommy Lee Jones). Without K, a vital shield protecting Earth from evil aliens will not be built, and J must stop the assassination. J meets a young K (Josh Brolin) in the late 60s, and after convincing his partner that he is from the future, they work together to thwart Boris the Animal and the young K’s plot to bring him back to the 1960s.
There are two Boris the Animals running around in the 60s, one from the present and one from the past. Later in the film, it’s revealed that there are two J’s running around as well, and the boy J met was a young “James”. So going back in time in Men in Black 3 means a character is sent back in time to coexist with their past selves who may have existed in that time. Sounds simple, right?
However, when J is battling Boris on the Apollo 11 launch tower, he uses time travel in a different way to defeat the pesky alien. J lunges at Boris and, having memorized the pattern in which the bad guy fires his spikes, knocks him off the tower. The fall activates J’s time travel device, rewinding everything and finding himself at the top of the tower. Now knowing where Boris will fire, J dodges the oncoming spikes and knocks Boris off the cliff to his death.
But time travel doesn’t work that way!!! The stipulation in Men in Black 3 was that when J went back in time, there would be two J’s standing on that shelf, his current self and his very recent past self, side by side. He shouldn’t “replace” his older self. If that were the case, Boris the Animal would have replaced his 1960s self and J would have been replaced by a little kid version of himself already. That would probably have been horrifying.
Men in Black 3 is currently streaming on Peacock alongside Men in Black and Men in Black 2.