Rian Johnson, director of Looper (2012), mentions in the "Directors Commentary" that not only is Primer the best time travel movie ever made but that when he sent the script for Looper to his friend Shane Carruth, Carruth told him all his time travel was wrong.
One scene that did not make the final cut showed that Abe was diabetic. The shot, which showed him taking time out of a conversation because he needed to give himself an insulin injection, was intended to establish that the circumstances of Abe's life have taught him to be careful and methodical.
Shane Carruth took up the job of writing, producing, directing, editing and scoring the movie with no prior experience in any of these fields. It took him three years to complete the movie, writing the screenplay over the period of a year and working on an independent movie as a microphone operator to get the hang of filming techniques. Shooting the movie took only a month, but the film spent nearly two years in postproduction due to editing problems. During that period, Carruth claims to have quit the movie 3 or 4 times.
In order to cut costs, Shane Carruth did mostly single takes of shots, and filmed on 16mm stock. This was then transferred to mini-digital video film which he could edit on his PC. This caused some unforeseen problems: the editing software couldn't handle the sound properly, and two months of editing were needed just to synchronize the audio to the video. The biggest problem, however, was the relative lack of footage, which made made it difficult to work around continuity errors and technical problems because there often wasn't an alternate take that could be used.
Over a hundred people auditioned for the parts of Abe and Aaron. David Sullivan was cast as Abe without professional acting experience, and director Shane Carruth cast himself as Aaron when he couldn't find the right person for the role.
In the scene in which Abe-2 knocks out Abe-1 with nitrous oxide, the container he is holding is actually a rice cooker. Also, we see sleeping Abe's profile, but not standing Abe, because the latter was Shane Carruth standing in for David Sullivan.