The 'Primeline'
A Comprehensive Guide to Primer (2004)
Here is my guide to Primer (2004) – possibly the most comprehensive one out there.
The events of the movie are divided into scenes as I saw fit for better organization and quick reference.
There are literal descriptions of what occurs on-screen, while theories and implications will be in italics.
This should leave no open questions.
I recommend watching with subtitles.
I present to you:
The Primeline
[1] – Intro
The lead-in begins with a phone call telling the recipient to stay quiet and simply listen as he lays out the following events, briefly describing a group of friends working on some sort of project.
[2] – Group discussion
It’s Christmas time. Four friends, Aaron, Abe, Philip, and Robert are meeting at Aaron’s place, discussing their side business. They experiment with electronic parts in their spare time, albeit with no major success. They’re currently selling JTAG cards (some kind of interface used to test electronic devices, from my understanding) but, to their dismay, only to “basement hackers” instead of major companies.
A man named Platts is mentioned who seemingly screwed over the group somehow, being a source of discontent.
Even though it is never specified in the movie, most sources assume that Platts stole patents from them to profit from their ideas. It can be said that he is a powerful, wealthy businessman, possibly a former partner or employer.
It is implied they have a system where everyone takes turns suggesting a project which they will jointly work on. It is now Robert’s turn.
We see Robert and Philip leave with leftovers from Aaron’s wife Kara.
[3] – Abe and Aaron talking
Aaron and Abe now conspire to start their own project without the others’ involvement, taking Robert’s idea for their own purposes. “They do theirs, we do ours.”
Here it is also revealed that Aaron has a toddler-aged daughter.
[4] – Constructing the machine
They begin construction on the project. The machine needs to be cooled with helium, but due to a lack of funding they devise a way to run it at room temperature. They are shown using parts from some home appliances, followed by a montage of attempts to gather makeshift parts for the machine at a low cost.
Initially, all four build together, but Aaron and Abe take note of everything used to make their own improvements.
[5] – Abe and Aaron experimenting
Aaron and Abe are experimenting with the machine. Aaron holds his hand over it, and feels something he doesn’t specify: “I don’t know if I’m making it up...”
Abe then empties some punched holes over the machine. They are floating, and it becomes clear that gravity in the machine’s influence is reduced.
They black out the windows; “can’t leave a gap in the field”. It’s impossible to make a window to see inside, so they use Aaron’s camcorder.
They put a Weeble (a wobbly toy) inside to see if its mass will be reduced, then fill the machine with argon. The mass indeed lowers. (So, the intended purpose of the machine was to lower an object’s mass by somehow reducing the force of gravity inside).
After flicking a switch, the machine starts to unexpectedly shake and is turned off.
[6] – Aaron wakes Abe
Abe wakes up to Aaron calling him, apparently having something important to show him.
Despite popular belief, the harsh cut leading into this scene doesn’t mean anything. Many initially theorized that this is Abe passing out or jumping through time due to the machine’s influence, but he is simply tired and confused when he wakes up the next day. It has been clarified in the director’s commentary that this was merely a strange editing choice.
The two meet up. Aaron berates Abe for letting his brother stay at his place. He then suggests getting a steak. This confuses Abe, until Aaron admits he was able to stabilize the machine, which would be cause for celebration.
[7] – Testing the machine
Aaron presents the machine, having made some improvements of his own. (“It looks like a dog digested it”). His solution is to power it up gradually, building an electromagnetic field until it plateaus.
The machine is now running, and is able to reduce the mass of the Weeble inside by roughly 10%.
They also realize the device operates with more power than they’re feeding it, and continues to run for minutes after disconnecting the batteries, making it obvious that it must have some strange properties beyond its intended use. (“What does that?”)
[8] – Abe and Aaron scheming
The two are now aware they have something very interesting and potentially profitable on their hands, and discuss cutting Robert and Philip out of the deal by pretending the garage is being sprayed for bugs.
They agree it is necessary to fully understand the device before going public to avoid being taken advantage of, like it might have happened once with Platts.
At a gathering, they meet a man named Thomas Granger who is their “last best hope of funding”, and Abe starts dating his daughter Rachel.
[9] – Abe has news for Aaron
Abe approaches Aaron on a park bench. Aaron claims to be listening to March Madness, a college basketball tournament. (It is now March).
Here we also find out that they work for a company called Cortex Semi, likely producing semiconductors (an electrical component).
Abe convinces Aaron to skip work to take him to a laboratory. He reveals that the Weeble after its exposure to the machine shows protein buildup of a fungus. Nobody there takes them seriously, as the quantity of what they say is few days’ fungus growth would only be possible after years. They realize their device is essentially a time machine.
[10] – Abe explains time travel
“We thought we were decaying gravity, blocking that information. i think we’re blocking more than that.” (It seems the functionality of the machine is based on ‘blocking information’ such as the natural flow of time and gravity to create a field with different properties within).
The basic concept of time travel employed by the movie is now explained. It functions as a ping pong effect. There is an A end and a B end, A being 12:00 and B 12:01 for the Weeble.
Inserted at A, the Weeble first travels forward in time like normal, to B.
But, instead of stopping there, time curves around to A again and continues bouncing between A and B for about 1300 times before the Weeble is removed, therefore having passed a much greater period of time by constantly traveling forward and backward than perceived from the outside, where we only see its eventual exit at point B, one minute later.
The exact number is based on some probability but is always around 1300. Every time the B end is reached, there is a small chance the Weeble stops, and, “for some reason”, only at around 1300 trips the chance is high enough. (So, the Weeble experiences 1300 minutes per real-time minute, hence the abnormal fungus growth).
The time channel inside the machine only stops when it is opened (similar to Schrödinger’s cat), which can only be done at point B, the future, so the Weeble always exits at point B.
If the Weeble is put in at point A, the number of minutes passed has to be odd, because it takes an odd number of trips to be able to exit at point B.
When they put it in at point B while the machine powers down and remove it at the same point, the number of minutes is even as it made an even number of trips.
Aaron leaves his stopwatch in the machine at point A; when he takes it out at point B it shows 1347 minutes. They power it down and insert the watch again, it now shows 1344 minutes.
“We’re blocking whatever makes it move forward (...). Inside the box, it’s like a street, and both ends are cul-de-sacs.”
They realize that, if an intelligent being were inside the box, they could open the machine themselves from the inside, measuring the time it takes to arrive at either point, thus being able to enter at point B and exit at point A, traveling back in time. (“If it were smart, it could enter at the B end and exit at the A before it flips back.”).
[11] – Seeing Abe’s double
They theorize about replicating the machine on a bigger scale, using multiple small plates instead of big ones to create the electromagnetic field.
They would need an undisturbed, climate-controlled space – the camera pans over to a self-storage facility.
Abe warns Aaron that he’s about to show him something serious. He looks through binoculars, and sees a duplicate Abe enter the facility from afar.
[12] – Abe reveals the box
It turns out that Abe had already had the same ideas, being one step ahead and actually constructing the human-sized time machine. This had created a double of him, his past self, which is now about to enter the machine himself to ‘merge’ with present-time Abe who had traveled back in time, effectively restarting his day.
They arrive at the storage unit, waiting 6 minutes to make sure Abe’s double is gone by then. He reveals the coffin-sized box.
Aaron asks what Abe did on his first loop of the day, while he (the version of him that traveled back in time) was restarting the day. He says he isolated himself in a hotel in Russellfield to avoid coming in contact with anything that could disrupt the timeline.
Aaron’s first idea is of course to win the lottery, but “it’s not until Saturday” (it is now Monday), so they decide to make lucrative stock trades by foreseeing the market trends.
[13] – Abe and Aaron’s first trip
The next day (Tuesday), Aaron wants to replicate what Abe did. The process goes as follows:
He calls in sick at work. He drops off Lauren (his daughter) at school and drives to the storage facility.
He parks his car out of sight, so that they can use his car for later, since Abe’s car can’t be used after traveling back in time (his original version would already be using it to hide at the hotel).
They go to the storage room and flood the boxes with argon. (By now, a second one has been built). They set a timer for the boxes to power up in 15 minutes. The boxes power up at 8:45. They leave and go to hide at the hotel.
The timer is necessary so they are not nearby when the boxes start, as this is the point where their doubles would exit after traveling back in time. (“I don’t want to be standing around when they do...”).
By 8:49, the boxes are “completely warmed up” (as seen with the smaller machine, the field powers up gradually, taking up to a few minutes for the bigger boxes).
The box can only go back in time to the exact point it was turned on. This is why the time travel in Primer is often described as the most realistic; it would only be possible to utilize a time machine as far back as it had actually started to function.
Abe and Aaron isolate themselves in the hotel room, cutting off all exposure to the outside world (they close the windows, unplug all devices, etc.) to not influence the timeline in any way, as their doubles are now out there living the same day.
Aaron notes “the boxes are one-time use only”, meaning that you cannot use the same box to travel through the same day, because your past self would already be occupying it.
Fun-Fact: They use ‘evacipate’ in Scrabble, a word that doesn’t actually exist. This is a neologism coined by the movie. The fandom has come to give it the meaning “to undo the past”.
At 2:30 PM, they each get an oxygen tank and mask from a medical supply store. (This is necessary for when they later enter the boxes, as they are filled with argon and no breathable air).
Then they check which stocks would be lucrative to trade on that day.
At 3:15, they return to the storage room and cut power to the boxes. They gradually power down to “a comfortable level” at 3:19. While they’re powering down but haven’t fully turned off, there is a few-minutes-long window where it is safe to enter. Aaron asks if it would hurt, Abe says it would be nothing more than a small static shock.
At this point, a document is shown, titled: “Rules to follow to evade causality paradoxes or generally screwing your life up!”
1. Do not disturb the box after you exit it. You or your double is in it.
2. When re-experiencing time, stay away from your double until he/she has started his/her journey backwards.
3. Worry about yourself first. Now is the only moment that has to make sense.
4. Don’t be too curious about your surroundings.
“I can imagine no way in which this thing would be considered anywhere remotely close to safe.”
They enter the boxes and have to remain inside for six hours, the six hours it takes to rewind time until back to 8:50 in the morning.
They also take dramamine, a motion sickness medicine, to withstand potential effects of the unusual timeflow.
They wait until the time window where the boxes are slowly powering down and it is safe to exit, using the exact timer on their stopwatches. (In reality, this is when the boxes were powering up after being remotely activated at the start of the day. Since they are traveling back in time, they are powering down from their perspective.)
Aaron becomes impatient and gets out a few minutes too early (from Abe’s perspective, a few minutes too late, as he is already back outside where time flows forward).
Aaron complains about the physical effects of the time travel, “that’s not a static shock, Abe!”, which were caused by his exiting slightly prematurely, showing how dangerous the boxes are if not used with precision.
They have now essentially become their doubles that climbed out of the boxes this morning, ‘fusing’ the timelines by entering the box to travel back to that exact moment so that only one version of them remains, able to restart the day.
They leave the boxes on, as they had found them running and powered them down to enter them in their original loop of the day.
Abe explains that at this point, their doubles are on the way to the hotel room in his car, hence having to use Aaron’s car to go home.
[14] – After restarting Tuesday
They buy a specific stock that will nearly double later that day. Aaron wants to know what it is that company does, but Abe doesn’t care. “All that matters is the price goes up.”
I think this is a crucial scene critiquing the concept of exploiting time travel for financial gain. it’s the first thing anyone would do, and yet, it feels strange to immediately take advantage of something they haven’t even fully understood.
They also say that “the volume is so high that the number of shares we trade won’t affect the price”, making sure their actions won’t impact their future selves’ predictions to avoid a causality paradox.
In the evening, they watch their doubles enter the storage facility through the binoculars.
[15] – Lottery hypothetical
They are now drinking and spending a lighthearted evening in Aaron’s home. He asks Kara what she would do if they won the lottery, but she can’t come up with a reasonable answer as she thinks it’s silly. (Here he is probably hinting at that they are indeed planning to win the lottery on Saturday.)
Aaron says if he won the lottery, he would punch Joseph Platts in the face. He alludes to wanting to do this and then using the time machine to erase it. However, they know this wouldn’t be wise to do as they believe disturbing the original timeline would have disastrous consequences.
“But the idea had been spoken. And the words wouldn’t go back once they had been uttered aloud.”
Aaron’s wife here mentions hearing birds or rats in the attic. This will be important later.
[16] – Abe and Aaron’s second trip
On Wednesday, they time-travel again the same way they previously had. They continue arguing about the possibility of punching Platts and undoing it. Aaron says he doesn’t believe in paradoxes, and that the thought of a pre-defined fate terrifies him, “...that this is the second, or third time through”. This will also gain significance once we begin to understand later events.
They talk about the issue of Aaron hiding the time travel from his wife, to which he says he’ll let her understand eventually once he can surprise her with all the profit they made from it. They also bring up Robert and Philip, and continue wanting to exclude them but instead suggest appeasing them by turning over their patents and potentially properties. (Profit seems to mean everything to them now, to the point of hiding their invention from everyone they previously trusted.)
Aaron here also says they should build a box “the size of a room”, which could potentially be of importance to interpret a later scene.
They travel back to the beginning of the day again. After exiting the machine, Aaron notices he’s bleeding from his ear, again hinting at the unpredictable effects of time travel on their bodies.
[17] – Aaron’s ‘Hero’-moment
They open the garage to Philip and Robert again. They thank Abe “for the present”, implying that they already received some form of compensation.
Robert refers to Aaron as ‘Hero’, which confuses Abe. They then tell him what took place on Monday night. At Robert’s birthday party, Rachel’s (the girl Abe is dating) ex-boyfriend walked in with a shotgun. Apparently, Aaron had disarmed the man before anything happened, earning him the ‘Hero’-title.
He is then berated by Abe for this, as he put himself in serious danger.
Now, it seems uncharacteristic for Aaron to do this and especially not tell Abe about it. This will all make sense later.
Also, in this scene they seem to be looking for Aaron’s family cat Filby, which he however doesn’t seem too fond of.
[18] – Abe and Aaron’s third trip
On Thursday, they do the same time travel routine again. But this time, Aaron forgot to leave his phone, causing it to ring at the hotel. (It’s just his wife, asking about dinner.) Abe tells him not to bring it back in time with him to avoid causing a paradox.
After restarting the day, they watch a sports game at Abe’s place, already knowing the outcome.
They later discover Aaron accidentally traveled back in time with his phone (or deliberately? He doesn’t believe in paradoxes, after all). It rings again at the same time, but in the new timeline. They theorize that if the phone had duplicated, only the closest phone would ring, meaning the one their doubles have at the hotel that moment cannot be ringing.
They “broke symmetry”, but nothing bad seems to be happening. This proves that they would be able to change the past. (They now altered an event that already happened – Aaron took the phone call in the new timeline instead of back at the hotel.)
[19] – The ‘Platts Plan’
Abe is woken up by some kids setting off car alarms. He then goes to Aaron’s place and wakes him up. Aaron here talks about “36-hour days”, since the time travel means they additionally have to be awake during the time they re-live the day, putting a strain on their bodies.
Abe puts forward a plan for punching Platts in the face after all, as they now know they can retroactively alter the past. This would entail going to Platts’ home, then entering the boxes to go back to 5 PM, before they went to sleep. Abe reveals he had been turning on the boxes at 5 PM, so they’d be able to travel back to that point. After going back in time, they could then scare off the kids so they wouldn’t set off the car alarms, allowing the two to sleep through the night in the new timeline, altering the course of events so that they would never wake up and go to punch Platts in the first place, and then execute their routine as usual the next day.
This plan seems confusing and equally reckless. It means that there would be a point where three sets of Aaron and Abe exist simultaneously: Their current selves (1) who punch Platts in the face, their doubles who will sleep through the night and then do their usual routine (2), during which, as we know, they will create yet another double (3), the one that will re-live the day while the pair (2) hides at the hotel. It is not entirely clear how/whether this would avoid the creation of permanent doubles. Abe might be assuming that double (3) would never be created in the first place, as they would be on a completely different timeline that the two have never personally experienced. This would also mean (2) would disappear, as they would join this non-existent timeline, leaving only their current selves (1) behind, thus ‘fixing’ the timeline.
They decide to go through with the plan, but a car follows them on the way. It’s Thomas Granger, their sponsor. Aaron notices his beard having grown while he remembers him being clean-shaven, alluding to this being a future version of Granger. They call him, and the man answering is at home, and not who is following them. This means Granger must have created a permanent double of himself by traveling back in time.
They chase him, and Granger collapses. They deduce he must have exited from the 5 PM box. They could shut them off and find out if he is using any of the boxes right now, but decide not to as this could produce unpredictable effects.
Here it is revealed that Granger inexplicably passes out when near Abe, alluding to him having something to do with the reason Granger time-traveled in the first place. There must have been some major event in the future, causing Abe to tell Granger about the time machine despite having sworn not to.
Shane Carruth (director and Aaron’s actor) has since clarified that Granger is “suffering from recursion”. (He also stated that the reason Granger decided to time-travel is the “one big question” of the film, so it is a deliberate loose end). I will paste a direct quote of his here as I think it best explains the matter:
“What I think happened is that Abe told Granger about the machine. This man who’s been told by Abe about the machine uses the machine to come back and somehow has an interaction with Abe so that now Abe probably won’t tell him about the machine and yet he still finds himself there. Without coming out and saying it, the film is built on the idea that these paradoxes are a way to understand things. The universe is not going to explode or break down if you create a paradox. Whatever’s going to break is probably going to be you.”
So, while paradoxes are technically possible, the effects on the human body would be severe.
[20] – Abe uses the ‘Failsafe’
The narrator voice from the phone call returns: “The permutations were endless.”
Granger remains in a vegetative state. They hide him at Abe’s place, and have to admit that they will never be able to grasp the full effects of their technology as they cannot foresee the future.
Now is when things get really confusing.
The narrator explains the items that Abe is shown carrying to the storage facility: 2 mg of oral triazolam (an insomnia medication in a dangerously high dose) taken every seven hours to induce a continuous rest state, enough oxygen and water for four days, and nitrous oxide (laughing gas, used as an anesthetic).
It is now revealed that Abe had secretly built a failsafe box in a different storage unit that had been running since Monday morning – before he ever started the box in the other unit and told Aaron about it.
Abe after traveling back to Monday, who we will refer to as Abe (2) from here on, enters his own house where Abe (1) from the past is still sleeping peacefully. He uses the nitrous oxide to sedate Abe (1) and takes his place.
There is now a permanent double of himself, since he fundamentally changed the timeline already by preventing Abe (1) from traveling through time.
Now, this is where I got confused, and maybe you will, too. How are they able to create permanent doubles by preventing themselves from entering the box? Shouldn’t the existence of the double already predetermine their entering the box later? It turns out, the system of time travel Primer employs deliberately circumvents this by making paradoxes possible. It is feasible to travel back in time and then prevent yourself from traveling back in time. To understand this better, imagine you had actually traveled back in time and created your double already. Then, as your double, you alter the past to prevent your original self from traveling back in time and merging with your timeline – thus they are creating an alternate timeline in which both of you exist simultaneously. So, you had already made the trip to create the double, only that it was retroactively erased – yet before it even happened. Therefore, what should logically be a paradox only leads to a clone of yourself existing in the same world. After all, Aaron himself says he doesn’t believe in paradoxes – “it has to work itself out somehow.” [16]
This is why the two are first so careful not to interact with the world at all as they stay in the hotel – they fear that any interference with the timeline might cause them to somehow be prevented from entering the box.
[21] – Second park bench scene
Now, a scene we saw earlier replays, the one where Abe met Aaron at the park bench to tell him about the box for the first time. Aaron repeats the same lines in an almost rehearsed way (we will see why), but Abe starts feeling sick and passes out, as he had been subsisting on only water and drugs for the four days in the box. Remember, when we first saw this scene, Aaron said he was listening to March Madness, but it is now revealed that he is actually listening to a recording of the conversation they originally had.
[22] – Aaron reveals his secret
This is where the main twist of the movie starts to unravel – Aaron has a recording of a conversation that he must have made in a previous timeline, meaning the timeline we were following the entire movie is not the original timeline, and this is not the original Aaron (1).
Because Abe (2) doesn’t know his lines, it is clear to Aaron that this cannot be the original Abe.
Aaron then explains everything to Abe. He reveals that he knew about the storage manifest, on which two rooms are rented under Abe’s full name Abram Terger (Terger is backwards for regret). This is how Aaron found out about the failsafe.
It is explained that the boxes are, in fact, “not one-time use only”, as you can fold one up, take it with you into another box, travel back through time, and then set up the box you brought to travel back to the same point in time again, which could in theory be repeated endlessly.
When Aaron begins his narration, there is also a scene showing Abe now bleeding from his ear due to his prolonged exposure to the machine.
Through the following scenes, we can now deduce Aaron’s actions so far:
The very first Aaron (1) from the original, unaltered timeline discovers Abe (1) set up a failsafe box.
Aaron (1) discovers the boxes are recyclable. He builds his own failsafe box, folds it up, and takes it with him to travel back to Monday morning using Abe’s failsafe box. (It is unknown when he got in the box, but probably somewhen toward the end of the week once he realized that Abe might try to prevent them from ever using time travel. Not that it matters, because all previous timelines are irreversibly altered now.)
After exiting Abe’s failsafe box, he presumably resets it, to close the timeline inside so that Abe will be able to use it eventually.
This means that Aaron will always be one step ahead of Abe, because he exited the failsafe box before him and Abe can now never go back further than Aaron.
Aaron (2) has now permanently been created. This is the person in the black hoodie. Aaron (2) obviously already knows what Aaron (1) had for breakfast, so he poisons his cereal, and locks Aaron (1) in the attic to take his place.
Throughout the entire movie, this Aaron (1) is trapped in the attic, hence the noises his wife points out in scene [15].
(We will never see the original, unaltered timeline, as every Aaron we see in the movie is a future, time-traveler version of Aaron who has already altered reality.)
This is also hinted at when Aaron said in scene [16] how scary it would be “...that this is the second, or third time through”.
The narrator then says “And that’s where I would’ve entered the story...”, clarifying that Aaron (2) is the voice from the phone call we were hearing in the beginning and throughout.
He also says “...or exited, depending on your point of view.” This refers to what is revealed next – Aaron (2) isn’t the Aaron we were seeing throughout the movie either. Instead, Aaron “came back the second time”. So, Aaron (2) at some point decided to alter the timeline again, traveling back in time with his own failsafe box, remember, the one he folded up and took back with him the first time to have an additional failsafe on Monday. By using this box and altering the timeline again, he permanently creates Aaron (3), and this is the version of Aaron we were following up to this point.
Aaron (2), against Aaron (3)’s expectation, refuses to let him take his place and briefly subdues Aaron (3). This is because Aaron (3) has now been using the time machine the longest and was in it twice for four days at a time, weakening him considerably.
This might also be why Aaron (3)’s ear is bleeding in an earlier scene [16], while Abe’s doesn’t – he has been exposed to the effects of time travel for much longer.
It seems like the two Aarons then reach some form of agreement, and Aaron (2) lets Aaron (3) take his place. This is technically where the movie starts.
Now, of course, Aaron (2) doesn’t actually enter the box at the end of the week, because Aaron (3) retroactively altered this timeline. (See the explanation on Primer’s paradoxical time travel logic at the end of [20].)
Aaron (2) leaves the country for now.
This is why Aaron (3) has all conversations recorded in his earpiece with a three-second delay – in the previous loop, he had recorded them as Aaron (2). Of course, this timeline is now altered through Aaron (2) leaving, so he doesn’t have to do this again; he already did it, but the past changed in hindsight.
So, by mimicking the previous conversations, Aaron (3) was able to keep the world around him mostly unchanged.
[23] – Basketball court scene
It turns out, Aaron has been resetting the week to try and stop the incident of Rachael’s ex-boyfriend brandishing a shotgun at Robert’s birthday party.
(What we are seeing currently is the loop caused by Abe (2)’s resetting of the week, effectively erasing Aaron’s memory of everything prior to this and creating a new timeline in which Aaron (3) encounters Abe (2) and has to involve him in the plan.)
Aaron (3) makes sure the (unnamed) ex-boyfriend is invited in this timeline by asking his cousin Will to bring him.
A funny bit happens here: Aaron’s recording says that Will is supposed to say “Nice shot, Aaron!”, but in this timeline, Aaron misses the shot, leading to the dialogue changing slightly as Will berates him for missing instead.
[24] – The ‘Party Plan’
Aaron aims to apprehend the ex-boyfriend and get him arrested. This is to provide a permanent solution, as he says that simply preventing him from attending will only be “good for tonight”, but, as the ex-boyfriend already seems to be an unstable individual, might mean he could do worse at a later point. So, he wants to ensure he is caught at the party with the shotgun to make his arrest feasible.
They are now planning to reverse-engineer a perfect situation to produce this result.
Aaron (3) says “he never fires”. Not in the presumably original timeline, where Abe didn’t even attend the party but Aaron (1) did, not on the second loop where Aaron (2) apparently tried to rush him, and he won’t that night, either.
This is what the scene [17] where Robert refers to Aaron as ‘Hero’ is talking about – Aaron (3) didn’t tell Abe (1) about this reckless plan because Abe couldn’t know Aaron (3) is a mere clone with not much to lose. While Aaron (3) seems to already have disarmed the gunman successfully in his loop, this event now is yet to happen, due to Abe (2)’s altering of the timeline. This is why Aaron (3) says here: “And from what Robert tells you, he didn’t tonight.”
Just to clarify, since this initially caused me a great deal of confusion: Everything we see happening in the movie until Abe uses the failsafe is Aaron (3)’s timeline, however, this timeline becomes altered when Abe (2) enters it. Thus, Aaron (3) now has no recollection of everything we saw, because Abe (2) has effectively reset the week for everyone but himself. Aaron (3) still knows what approximately happened because he recorded everything as Aaron (2) and tried to keep things the same, except for what he intended to change at the party by apprehending the ex-boyfriend. He basically already succeeded, but they have to do it again because of Abe (2)’s restarting of the week.
There is also the scene [17] outside which makes more sense now; Abe (1) berates Aaron (3) for risking his life, but Aaron (3) already knew his original version Aaron (1) was trapped in the attic, and Aaron (3) has nothing to lose since he has no right to Aaron (1)’s family anyway.
This is not clarified, and pure speculation on my part – we never see what happened in the original timeline, but it might have been something much worse, leading Aaron to go to these lengths to prevent it. Even though it seems insignificant in the grand scheme of things, the party incident is a central event of the movie. It details their desperate attempts to change the past, going against all laws of reason and science, permanently corrupting the timeline. This to me is indicative of something darker having happened originally, severe enough for them to fix it by any means. Maybe Aaron (3) also assumed that Granger’s returning had something to do with the ex-boyfriends future actions if he is not apprehended. It might be that Aaron (3) originally thought that the problem was finally solved in his loop, but then Granger appeared, indicating that he was trying to solve an emergency dire enough for him to be told about the box. (Potentially Rachel’s death – this would explain why Granger as her father would become involved.)
Aaron (3) now might not remember that they encountered Granger in this timeline before Abe (2) restarted the week, but Abe (2)’s existence should tell him that things still didn’t go right, thus devising the ultimate perfect plan to disarm the ex-boyfriend and get him arrested.
It is also unknown if Granger showed up in the original or second loop, but I assume he must have, giving Aaron (2) a reason to travel back in time again. The Aaron (2) from Aaron (3)’s perspective doesn’t remember this, because he was sent away on Aaron (3)’s loop, erasing his memory of a week that was yet to happen, much like Abe (2) has now done for Aaron (3).
Amidst this conversation, Abe asks an intriguing detail: “What’s wrong with our hands?” As we could already see in scene [23] at the basketball court, their handwriting looks rather crude. Aaron compares it to writing with his left hand.
A popular fan theory says that this is due to their hands’ exposure to the machine in scene [5], where Aaron alludes to some sort of sensation when reaching inside. I think this is largely implausible as the machine wasn’t even complete at that point. It is more likely that this is yet another degenerative effect of time travel which is intentionally left unexplained. It could also be theorized that they are constantly creating mirror images of themselves – hence the connection to left-hand-writing.
Aaron (2) continues narrating, clarifying a central aspect on the mechanics of time travel – “The last revision is what counts.” His actions in his loop are irrelevant to the viewer, as everyone else’s memories will be reset when someone travels back in time. He wonders how many attempts it would take Aaron (3) with Abe (2) to reverse-engineer the perfect moment, as he has now way of knowing, but it seems like they succeeded on the first try.
They go to the party, open the ex-boyfriend’s car after stealing the keys and unload the shotgun, just to be safe. Then Aaron is finally able to apprehend him in a perfectly planned scenario and presumably get him arrested.
[25] – Airport scene
Aaron (3) and Abe (2) wind up at the airport. (It is now Tuesday again, by the way. The movie never leaves the single week in which all events take place.) Aaron (3) wants to leave the country and live comfortably by continuing to make money through time travel. He suggests they steal Aaron (1)’s and Abe (1)’s passports and go to Star City, an astronaut training facility near Moscow. Abe (2) however wants to stay.
The scene is interjected by Aaron (1) and Abe (1) both breaking out after being locked away by their doubles.
Aaron (3) says “yours already knows what they’ve built”, which refers to how Abe (1) had already figured out how the time machine works and is about to construct the bigger box. Abe (2) will never be able to go back in time far enough to prevent himself from discovering time travel, but his goal now is to make Abe (1) give up on ever using it by sabotaging the boxes.
Aaron (3) and Abe (2)’s argument escalates when Aaron even accuses Abe of jealousy toward his family, and they end up parting ways. Aaron (3) remains at the airport, probably following through with his plan of leaving the country forever.
[26] – Final scene in the warehouse
The final scene shows Aaron (2) in a warehouse, directing French workers to build something.
This is most commonly assumed to be a gigantic version of the time machine, as Aaron in scene [16] mentioned wanting to expand it. However, to me, it seems way more plausible that he is building a multitude of smaller time machines that could be activated over time to enable him to travel to any specific day. He says “Every half meter. Everywhere.”, as if directing them to place an array of structures. Also, this would be a far more useful project than whatever could be done with just one big time machine.
Closing notes
Let’s talk about the phone call. It clearly is Aaron (2) speaking, and the recipient is Abe (1). This had previously been up to speculation, but was since confirmed by the director.
Aaron (2) is calling Abe (1) at some point that week to ensure Abe (1) will continue constructing the time machine. While Abe (2) wanted to sabotage this, Aaron has always been one step ahead. In calling Abe (1), he secures his own existence, as there is no saying what would happen to the Aaron-doubles if time travel was never invented in the first place. Since Aaron (2) now seems to have bigger plans for the machine, he needs to make sure Abe (1) knows his clone might try to prevent him from time-traveling. As long as Abe (1) knows that time travel is possible and that he has succeeded in it once before, he has no reason to give up on it.
“Now I have repaid any debt I may have owed you. You know all that I know.”, meaning Aaron (2) is indebted to Abe for enabling his existence and now repays this by telling him all about their invention.
The ‘Primer’ the movie title refers to is this call. A primer in biology is the initiator for splitting a DNA sequence, essentially duplicating itself.
Far beyond the intricate time travel mechanics, the movie is at its core about the destructive effects of greed. Abe and Aaron deliberately hide the time machine from their friends, using it for their own profit. Just like Platts had once done to them, they now took Robert’s idea, expanded on it, and kept the results to themselves. Ultimately, Abe too finds himself betrayed, as Aaron had continuously been ahead of him to prevent his interference with their creation of the machine. Aaron now goes on to replicate their invention, disregarding the chaos he caused in the timeline to further exploit the technology.
Ultimately, nobody likes sharing – especially when it is the power to change time.