Primer (movie)
Thomas Granger is the father of Abe's girlfriend Rachel. Somehow he discovers that the time machines exist. He time travels, but because he does not do it correctly, he ends up in a coma.  Aaron thinks that, at some unknown time in the future, Granger entered the box (for unknown reasons). This changed the timeline in bad ways. Abe is frightened by this and decides that time travel is too dangerous to keep doing. He tries to stop his past self from using the machine any more, so he won't get any bad effects. He uses a "failsafe" machine, which he had already built secretly and kept running in a hidden location. He travels back farther in time than his first trip (four days) and before he had told Aaron about time travel. He thinks this will repair any problems.