Even though the main explanation is consistent and ties the whole movie together there are still a few parts of the movie that are not explained and have to rely on theory. Here are some of those questions with possible explanations and some common mistakes people make.
What Creates The Tangent Universe
Why exactly does a Tangent Universe (TU) occur? Are they a natural phenomenon or are they artificially created. There is one theory that scientists in the future build a machine that somehow causes a rip in time back in the past. Another theory is it could have been caused by Alien involvement.
Quite a common thought is Frank saving Donnie in the beginning is the cause of the TU. Donnie was meant to die and by surviving he altered things which caused the corruption. This is not true though, we are already within the TU when Frank wakes Donnie up. Frank's special powers only work within the TU so he would only be able to wake Donnie after the TU had started.
The same goes for the Artifact not being the cause of the corruption. The jet engine appears several minutes after the TU had started. The Philosophy of Time Travel states that the Artifact is the first sign of evidence that a TU has occurred.
The First Jet Engine
One major question is where does the jet engine in the beginning of the movie come from originally? If it came from the future where exactly and what day did it come from?
A common answer to this question is it's the same engine Donnie sends through the portal from the plane his mother and sister were on. The engine travels through time and lands on Donnie's house. It's exactly the same event as the end of the film only the first time round Donnie survives.
This is extremely unlikely though as the portals are just a gateway between the two Universes. The first engine lands in the Tangent Universe (TU) so if it came through a portal it would have to come from the Primary Universe (PU). The engine Donnie rips of the plane at the end is from the TU and travels through a portal into the PU so there is no way it can be the same event repeating.
If it did come from a future point in the PU once the corruption is fixed by Donnie that future event won't happen now so we will never find out exactly how it occurred.
Another theory is the Tangent Universe is a copy of the Primary Universe but as it's being formed there is a glitch or copying error. This error produces a duplicate engine that is then dumped into Donnie's bedroom. This anomaly makes the TU even more unstable and it must be sent into the PU.
Roberta Sparrow: The Philosophy Of Time Travel
Roberta Sparrow writes the book "The Philosophy Of Time Travel" which helps guide Donnie but how exactly did she know all this information? There are a few plausible explanations for this. It seems like she had a similar experience herself so either she was a Living Receiver or one of the Manipulated Dead in a previous Tangent Universe.
Both options would in theory give her all the information required. If she was a Living Receiver she would obviously have known what to do and the Manipulated Dead have a large understanding of what is happening within a Tangent Universe. It's possible she may have somehow retained some of the information from her experience once the Primary Universe started up again.
Does Donnie Have To Die
This subject is one of the most debated parts of the movie. A lot of people make the mistake of thinking Donnie waking up and cheating death in the beginning is what caused the Tangent Universe (TU) to occur. The assumption is then once the Primary Universe is restored Donnie stays in bed otherwise he risks causing another TU to start and the whole cycle will repeat. This theory is not correct though, Donnie and Frank have nothing to do with the creation of the TU.
We hear about other Living Receivers in The Philosophy of Time Travel who were killed by the Artifact they returned. If we include Donnie then it seems the Living Receiver always dies once the Primary Universe is restored. The question is what would happen if Donnie got out of bed again and survived? The moment we see Donnie laughing in bed at the end the Primary Universe is already restored. If Donnie got out of bed and dodged the second engine after that then in theory nothing would change as the corruption is already fixed.
Another important point is whether Donnie chooses to die. The Donnie we see in bed at the end is not the same Donnie from the last 28 days. How much knowledge he has of what happened in the TU is very questionable and it’s quite unlikely he knows he is about to die.
The question of destiny plays quite a big part here, Donnie was meant to die but Frank saved him. It’s possible he was chosen as the Living Receiver because his life is now expendable; he is going to die anyway. Once back in the real world it's Donnie's destiny to die.
Donnie does not want to just simply get out of bed at the end. This scene has nothing to do with all of this "Tangental Universe" mumbo jumbo that the director decided to reveal on the DVD. Throughout the film Donnie struggled with the concept of death and the possibility of dying alone, a very real existential fear for a very intelligent adolescent. As Donnie progresses the plot he eventually learns that he does not in fact die alone, his therapist suggesting that Frank to Donnie was his own god and that with Donnie's death there would only be Donnie and Frank, no one else. This also alludes to Frank the hallucination not actually being the Frank that gets shot in the eye, rather that Frank the hallucination is really either Donnie's ego or a higher power taking physical form. After all, the separate universe CAN only be created by a Godly force, as described by the Philosophy of Time Travel. At this point in the movie, along with other allusions to higher power (think "The Last Temptation of Christ" being played alongside the "Evil Dead"), it is safe to assume that Donnie finally came to terms with existential distress at the end, hence why he was laughing joyfully in bed at the end.
how do we know all the stuff written here about what happens after???
I first saw this movie at 13 in 2003 and though I didn't understand all of it, I always thought the jet engine from the plane went through a black hole and that's what created the dysfunction in the time line.
An explanation for the jet engine and the creation on the tangent universe could be explained with two alternate primary universes. If we consider that the first primary universe is where the tangent universe is never created and events unfold in a natural order. The one event that we see being influenced in my explanation is Frank ordering Donnie to burn Cunningham's house which leads to Kitty forcing Rose to take the dance trip. This flaw can be explained with Kitty's unstable and obsessive personality. This would mean that the first primary universe creates the circumstances for a plane to be over the Darko household. And if we assume that the time portals are a naturally accusing phenomenon instead of it being created by an external entity, then the slight differences between the first primary universe and the tangent universe mean that the artifact travels into the tangent universe naturally would set in motion the film. To answer the creation of the tangent universe, though a time portal forming may be natural, travelling through the portal is unnatural and in the universe's self-correcting theory, the universe creates a collapsing tangent universe to compensate for the duplicate artifact. This them means that is is the self-correcting theory that creates the manipulated and the unstable structure of the tangent universe that allows the time travel and foresight that Frank has in the tangent universe. This theory removes the ideas of divine intivention. I believe that the idea of divine intervention was incorporated into the story less as a key factor in the story but more as a controversial and thought-provoking topic to raise questions about our own universe.
Since black holes are involved in the possible fate of the TU if Donnie is unsuccessful, I can't shake the feeling that the danger somehow has to do with mass. This new TU (with the artifact that came from the PU) now has extra mass. The PU now has less mass and while it's just a jet engine maybe it's just enough added mass to cause the black hole, where it would otherwise (without the artifact) cancel out. So by returning the artifact, Donnie is restoring the balance in mass between the two universes which also alows the main universe to survive when the tangent universe collapses into nothing.
Just had to add one more example
"If the Ensurance Trap is successful, the Living Receiver is left with no choice but to use his Fourth Dimensional Power to send the Artifact back in time into the Primary Universe before the Black hole collapses upon itself."
Awesome job to the site creator for explaining things so well. To those who refute the notion that the artifact is NOT from the PU, I site TPoTT..."The Living Receiver is chosen to guide the Artifact into position for its journey back to the Primary Universe." Notice the word BACK to the PU. There are other lines from TPoTT that use similar terms: return, back, etc. The movie clearly states the artifact is from the PU.
Could have Donnie taken the pills some how have changed the way things would conspired as in him being chosen to save a reality?
just a thought, something to add to this ambiguity. What if donnie was so afraid to die alone, roberta sparrow living long and alone, emulating his fear. Then maybe (if he even remembers anything of the tu when it goes back to the pu at the end) knowing these people that have died in the tu hes content with dieing knowing everyones alive.
My theory is that Donny darko is completely useless towards fixing the (TU) but it's the squirrel that fixes it, no not the bunny the squirrel. The squirrel is never mentioned but this squirrel is one day bestowed with the fact that he has to fix this universe