Throughout the course of the film, many abnormal events occur, and many supernatural forces are at play. The Tangent Universe is one such occurence, and the events of the film revolve around the creation of said Universe.
To summarize, Donnie Darko begins in what is called the "Primary Universe". This is by all means, the normal universe. However, shortly after the beginning of the film, Donnie and everything in existence is transported to the "Tangent Universe", a duplicate universe where abnormal and paranormal events transpire. This transfer is not shown when it happens, it simply occurs. The movie's setting transitions from the original universe to this other one without any clear indication of it. The only signs that the tangent universe has happened are the abnormal events that unfold afterwards, such as the appearance of Frank and the jet engine. At the end of the movie, we return to the original universe, when Donnie wakes up in his bed again on October 2nd.
Without researching the explanation for the film, it may be very difficult for one to understand what happens in it, and simply seem like a sequence of bizzare and abnormal happenings. The exact explanation for what happens throughout October of 1988 remains somewhat poorly understood, and may be difficult to decipher just by watching the film. However, Philosophy of Time Travel, the fictional book written by the character Roberta Sparrow, and the explanations deducted from it, provide substantial information as to what transpires.
A Tangent Universe is essentially a duplicate of everything in existence and the original universe, an alternate universe in other words.
The reason for the occurence of a Tangent Universe is still unknown, but the leading theory suggests that these phenomena are caused by "corruptions in time", or "glitches" in reality. Roberta Sparrow's book states something similar to this. However, the exact explanation or cause remains ambiguous.
When a Tangent Universe is created, the original universe, the one of which the Tangent Universe is a copy of, is said to be put on "hold". This means that time stops within the original universe from the moment the other one is created. Essentially, everything in the original universe is "paused", and time begins in the Tangent Universe. The next few weeks which would have happened within the original universe transpire within the new one. Tangent Universes cease to exist within only a few weeks. Once they do so, and if certain events explained below occur, the original universe will be "unpaused", and time will continue as normal within it from the moment that it was put on hold.
One of the important facts to remember is that once the Tangent Universe occurs, and the film begins taking place within it, the event is not clearly indicated. There is no clear transition shown, it simply occurs on October 2nd at the start of the movie, and the days following that take place within the alternate universe. The tangent universe ends when Donnie wakes up on October 2nd again at the end of the movie. None of the characters, except for Grandma Death, and to an extent, Donnie himself, are aware that this is happening. After the tangent universe ends, the only knowledge or memory they will have of this will come in the form of dreams, soon to be likely brushed off and forgotten.
To elaborate on their lifepsan and temporary nature, according to The Philosophy of Time Travel, and what many have deducted from it's content, Tangent Universes are highly "unstable", and can only exist for a few weeks before "collapsing", or ceasing to exist. Due to their unstable nature, and the occurence of Artifacts, phenomena in which a certain metallic object unexplainably appears within these universes and makes them even more unstable, when a Tangent Universe's lifespan ends, it risks creating a black hole capable of consuming everything in existence, including the original universe. This essentially implies that the formation of Tangent Universes poses a threat to everything, and jeopardizes all in existence.
As stated before, with the occurence of a Tangent Universe, also comes the appearance of an "artifact", a certain object that appears spontaneously into it. According to the common consensus, when a tangent universe is formed, it is a seemingly exact copy of the original one, with one of everything copied into it. The exact origin of the artifact is unknown, however, it is thought that during the copying process, an "error" occurs, causing an object which is being copied into the tangent universe to duplicate. This means that there will be two of that exact object existing within the Tangent Universe. The fact that there are two of the exact same objects within one universe, through unknown means, makes the Tangent Universe extremely unstable, meaning that once it's short lifespan ends and it ceases to exist, it can create the previously mentioned black hole capable of destroying everything. One theory for this is that the tangent universe is supposed to be an exact copy of the original one, and the fact that it has two of an object when there is only supposed to be one means it no longer fufills this, which somehow makes it unstable. The only known way of preventing the unstable collapse of a tangent universe and it's subsequent black hole, is by "returning" the artifact to the original universe, which doesn't have a short life span and for some reason can handle the anomaly of a duplicate object without causing a black hole.
Another mysterious phenomena that comes with the occurence of a Tangent universe is the selection of a Living Receiver. This is a poorly understood event in which a human, living within the Tangent Universe, is "selected" by an unknown force or higher power, presumably god or something of the like, to fufill a certain duty. So far, the only duty living receivers are chosen to fufill is that of saving everything in existence. Because of the fact that the original universe and possibly everything in existence is threatened by the occuring and collapsing of a Tangent Universe and an artifact within it, it can be reasoned that this is why a Living Receiver is chosen, though the full workings of this process and full explanation for the events occuring remain unknown. The only known way for a living receiver to save everything in existence is if he or she "returns" the artifact to the original universe before the collapse of the tangent universe occurs. So far, the only known way to do this is by creating a portal of sorts, a supernatural ability which living receivers are said to be often granted, and transporting the object to the original universe using said portal.
Humans involved with the tangent universe, who comprise of the living receiver, those connected to he or she in any way, such as friends or family, and those living near where the artifact appears, are said to be all affected in ways somewhat explained below.
According to the Philosophy of Time Travel, and the events of the film, those who meet said criteria will all be part of the living receiver's destiny of saving the universe, wether living or dead.
People associated to the living receiver, such as friends, family, teachers, etc, who are alive, and who remain alive during the duration of the tangent universe, are referred to as the Manipulated Living. While seemingly completely oblivious to what is happening, they subconsciously aid in guiding the receiver on his or her mission of saving the universe. Again, the driving force that causes them to perform these actions is still unknown, but it essentially compels this group of people to unknowingly set in motion the events leading to the receiver accomplishing his task. They can be seen as chess pieces on a chess board, moving to the exact positions required to win. Technically, the manipulated living are also saving themselves from doom, as the living receiver failing his or her task would lead to their demise as well.
One of the most mysterious, eerie, and peculiar abnormal aspects of Tangent Universes is the occurence of the Manipulated Dead. Like the manipulated living, the manipulated dead are also those who were connected to the receiver, but died in the tangent universe. When someone connected to the receiver dies within this universe, they will become one of these beings. They are extremely powerful, and have numerous paranormal abilities, including time travel, teleportation, and to an extent, knowledge of the situation. Like most of the phenomena mentioned before, this occurence has no explanation, other than a higher being or force. The manipulated dead will directly guide the receiver to save the universe, via instructions and information. They appear to the reciever at various points in time, and directly communicate with them in order to push them towards doing what must be done.
As previously stated, Tangent universes are highly unstable, and can only sustain themselves for a matter of weeks before collapsing and ceasing to exist. There are two known possible ways for a Tangent Universe to collapse.
- If the living receiver fails to accomplish his or her task, and the artifact is not "returned" to the original universe before the collapse of the tangent one, the dying tangent universe will create a black hole, endangering the original universe and likely spelling doom for everything in existence.
- If the living receiver does what is required and the artifact is "returned". The tangent universe will safely collapse. The way this collapse occurs is not fully understood, but the film shows it as beginning with abnormal black clouds and odd structures forming in the sky, that which seemingly only the living receiver can see, followed by time stopping and the weeks that occured within it "rewinding" rapidly in reverse. The tangent universe will ultimately cease to exist, and the "paused" original universe will "unpause" from the point in time where it was stopped. Everything that happened in the tangent universe did not occur in this one, so it will continue as normal from there
Once the original universe is "unpaused", it will continue as usual. It is difficult to explain the matter of wether the weeks that happened in the tangent universe legitimately existed or not. It can be reasoned that the events simply occured in the tangent universe, which is a separate one from the original one. The fact that the living receiver completed his or her mission and prevented the black hole, however, seems to span across both universes, as their actions within one universe determined the fate of another. And those who were involved with the tangent universe, either as manipulated living or manipulated dead, will often experience what happened in the tangent universe in the form of dreams, but don't seem to fully remember or aknowledge that it occured. The living receiver themselves likely remembers or knows of their time in the tangent, the extent of their knowledge and understanding of this is unknown.
In Donnie's situation, a tangent universe began on the night of October 2nd, when it was somehow created, and the 28 days after that unraveled within it. Frank, a manipulated dead who was killed at the end of those 28 days, traveled back in time in that form and began guiding Donnie through his journey. The artifact in this case was a massive jet engine, which fell right into Donnie's room. Donnie was saved by Frank when the latter guided him out of his house before the jet engine fell into it, allowing him to live on and continue his mission. Frank continues guiding Donnie to undertake actions leading to him saving the universe, while those connected to Donnie subconsciously behave in the exact way needed to ensure that Donnie fufills his destiny. While Donnie is not aware of his purpose at first, and never seems to fully understand it, as the film progresses he seems to develop a decent knowledge of the situation and his mission. Donnie eventually rips the duplicate jet engine from an airplane, sending it through a portal into the original universe and allowing the Tangent to collapse. Donnie awakens in the original universe on October 2nd, seemingly remembering and knowing some of what has happened, despite the fact that it occured in another universe. He sits in his bed laughing, seemingly content with life and at peace with death, the jet engine which he sent through a portal into the current universe falls upon his room, killing him