Primer understands something most time-travel narratives do not: the mechanism cannot be theoretical.

The film's central device—two boxes, copper coils, repeated iterations, the compulsive building of redundant systems—treats time travel as a plumbing problem, not a thought experiment, and this is not a flaw in imagination but an argument about how reality actually works.

The four engineers in Primer don't discover time travel through a unified equation or a software insight. They stumble into it through brute empirical repetition—running the same box configuration, measuring outputs, building atop what works—so that the scene where Abe and Aaron construct their second box in the storage locker becomes the film's epistemology made visual: not elegant, not theoretical, just systems nested inside systems.

String theory promised to unify everything, but loop quantum gravity didn't, and the 2010s physics turned away from grand synthesis and toward discrete, testable systems—quantum error correction, actual measurement protocols, engineering-grade reproducibility—because this is Primer's world winning. What the film got wrong is revealing: it assumes isolation works, because the boxes require secrecy, hidden redundancy, compartmentalized knowledge. Physics actually went the opposite direction—open collaboration, shared data, reproducible failure.

The mechanism was right. The mythology of the lone engineer was not.