Donnie Darko is a very mysterious and beautiful movie about time travel that has so much, very deep meaning. There are different variations of what I'm about to explain, but this is my interpretation of what the movie is about and it might be a little messy and all over the place but I need somewhere to let this all out. So in the beginning the film, Frank the bunny rabit leads Donnie out of his room (and off of his path in life and time), and tells him when the world will end which is in 28 days, 6 hours, 42 minutes, and 12 seconds. So now that when the jet engine falls into his room from the future/alternate reality, he doesn't die which goes against his path. Donnie keeps following the path that Frank gave to him as he is afraid to be alone, and is thankful that Frank saved him, but this turns out to be a mistake from the begging. Donnie is struggling between following Frank's path for him, or his own set path in life and time. Donnie, later in the film, almost runs into the old science teacher who used to be a nun in her early days, but is now an elderly and retired science teacher who wrote a book about time travel after she left the church and was seemingly in a loop of checking her mailbox constantly. This is symbolic to the movie, but anyway, Donnie walks up to her wondering if she was ok, but she whispers into his ear, "Every living thing, dies alone." This apparently means that she has lost faith and knows for a fact that God doesn't exist. In her book, she wrote about how time travelers can see their path in space and time, which would go against "gods path" for a time traveler as they would have a choice between which paths they would like to follow. Donnie finds out about this book later in the movie from his current science teacher. It's like most of the people in this movie, subconsciously knew that the world will be forever in an endless loop if Donnie doesn't go back in time to the past to let the jet engine kill himself. I believe this to be true as everyone gives him little hints here and there which you would realize if you watch the film very closely as I did. I feel that I should explain the time loop in more detail. The time loop is created when Donnie's mom and sister, (near the end of the film) are in a plane coming back from LA. I feel that I should clear something up before continuing. In the book about space and time that Donnie and his science teacher discuss in a seen, there is a page in the book, explaining that wormholes are man-made time woarps, and Donnie is seemingly a time traveler, who can manipulate time, and can see people's paths in space and time as portrayed in the film. The flight that his mom and sister are on hits this wormhole, which causes the plane to go missing, and the jet engine to fall back in time into Donnie's room in the past. This could create an infinite amount of alternate universes or just keep looping. I feel as though donnie is creating this wormhole, (as they are man made and he can control time) and this is why donnie goes back in time and kills himself to break this never ending loop. Now that that's out of the way, let's get back to the rest of the movie. Donnie meets a girl who becomes his girlfriend (this is important later in the film). Earlier in the film, his english teacher is teaching the class about a book about kids who flooded a house, found money in that house, and burned the house and money to the ground just like what donnie did in the movie besides the burning of the money. I feel that the money has symbolic meaning to the movie as it is ironic that they burned the money in the book and the film is ironic as Frank leads Donnie to the very gun that killed Frank in the first place which contributes to the loop. Frank is angry about the fact that Donnie killed him and this is why he pushes him off of his path to cause this loop. This is all ironic just like burning the money. After Donnie reads the time travel book, he writes back to the old woman who wrote it and she finally gets what she was looking for all of those years of checking her mailbox, a response from Donnie. At the very end you can hear what he wrote back to her after he goes back in time to end his life. Donnie decided to throw a party at his home after finding out that his oldest sister made it into her college and his parents were gone to LA for his younger sister's dance team which loops back in the movie as the plane falls into the time loop later in the film on their way back home. During this party, Frank, (who is in this reality a normal real person) goes out to get beer. Donnie and his girlfriend and friends decide to go to The symbolic Cellar Door which is at the old woman's home. By doing this, Donnie was following his path. While there, they are attacked by two school bullies who chased them outside. They were apparently trying to steal from the old woman. Suddenly, a car comes racing down the dirt path, slightly missing the old woman as she was checking her mailbox, and running over his girlfriend and chasing off the two bullies. Frank and his friend come out of the car to see what happened as they apparently didn't mean to kill the girl. Donnie then pulls out the gun that Frank lead him to, and shoots Frank in the eye, killing him. Donnie realizes that Frank is evil and is devastated knowing that if he had just died that day, she would be alive still. Time is almost up until the world seemingly ends and Donnie realizes that everyone dies alone as the old woman said. Donnie finally accepts his death but writes back to the woman before leaving. As the jet engine falls through the wormhole, Donnie turns back time to when he should have died and let's himself die. This resets everything and breaks the time loop. But he is not forgotten and his story is still with the hearts of the people he touched in his life. The time travel book tells that if something like this were to happen, everyone who the time traveler has touched in their lives, dreams of all of the events that took place in the alternate reality that no longer exists, or does exist in another universe. Donnie's fear had always been to be alone and forgotten, but he wasn't and that's part of the reason why he accepted his death. In the end it's like the old woman specifically made the book for Donnie as she is a time traveler too and knew what was going to happen. This entire thing is probably pretty scrambled, but you should watch the movie and then read this because it would make a lot more sense if you did. This movie is in my opinion one of the most beautiful and well written pieces of art out of any other. It has so much meaning to it. I hope you found this theory helpful.