Time travel is a recurring theme in movies; there are hundreds of films which include some element of tinkering with time, from major franchises like Star Trek to unknown gems like Happy Accidents.  Still, periodically a movie comes from nowhere and does something with time that has all the time travel fans talking.  Recently Primer was such a film, one that has become a cult favorite in that peculiar cult of people who think about time travel stories.  It is an intriguing and in some ways baffling film that forces the viewer to think.

The storyline follows a couple of research engineers who while experimenting in superconductors stumble into some anomalies that lead to the development of a time machine.  It is very limited--it anchors one end of a loop at the moment it is activated, and one person can enter it and travel back to that moment if he stays inside it for as long as the machine has been active.  That is, if you activate the machine at one o'clock and then at two you get in, an hour later (by your time) the machine will deactivate and you will get out at one o'clock.  This limits what can be done with it, but they quickly focus on what they can do, such as using closing bell stock reports in the evening to guide stock purchases of the prior morning.

The film asks many of the right questions, but it tends to give wrong answers.  Its theory of time is a bit inconsistent; there is insufficient information to establish exactly what concepts the writers were using to determine the outcomes of actions, and some of the events are inexplicable under any theory.

A detailed analysis of a film like this could run thousands of words.  Its complexity is comparable to films like 12 Monkeys or Millenium.  That level of analysis is for the hard core fans who want to trace out all the events in detail.  Here we will look at a few of the problems the film creates and some of the interesting points it raises along the way.

Our two garage inventors are Abe and Aaron; Abe is the one who determines that they have stumbled into time travel, and he makes the first trip to the past, setting the pattern for most of the trips to follow--but setting it incorrectly.  He is quite reasonably concerned that he might alter history, so he decides to avoid this by spending the entire day sequestered in a hotel, so that he cannot affect anything.  The problem is that he does this on the wrong day.  His reasons for doing it this way are obvious:  he wants to test it, to see if he really does return to the morning of the day he left, and he wants to be able to explain it all to Aaron and let Aaron see his alternate self heading toward the time machine at the end of the day.  The problem is that instead of preserving history he quite specifically alters it.  It would make sense for the time traveler to do whatever he wished his first time through the day, then travel to the past and sequester himself so as to have as little impact on the repeated playing of the day as possible.  However, we know that in the original day Aaron is at work all day while Abe is sequestered, and in the replay Abe asks Aaron to skip work so he can show him something "very important".  Thus whatever Aaron did in the original version of the day has been erased, replaced by Aaron traveling around with Abe.

As noted, it is obvious why Abe did it this way the first time; the problem is that thereafter he tries to do it that way every time, which means that in every case he is always changing history instead of never changing it.  That problem comes into focus the day Aaron gets a phone call that should not have been answered.

The problem of that approach is brought into stark relief when Aaron gets a call on his cell phone.

Abe, who discovered that the machine the two of them had built would enable them to travel back in time, had used his first trip to buy a stock he knew would be a strong advancer during the day, and to explain the discovery to Aaron.  On the second day, they both did what Abe did on the first day:  drive out to Russelfield and take a hotel room for the day, so that they would be completely out of touch with the world until late afternoon, when they could determine what were the best investments for the day before traveling back to the morning to make their purchase, then spend the day doing what they want.  (It appears that they are not in the Eastern time zone, as they can get stock market closing prices early.)  The problem with this approach, discussed last time, hits them this time, because while they are in the hotel in Russelfield, Aaron's wife calls him.  Completely uncertain what to do but having to make a decision quickly, he answers his phone and makes up an excuse for why he cannot join her for lunch.

That's not a big deal, really.  The problem is that when the duo returns to the morning and are spending the day downtown instead of sequestered in the hotel, right on schedule Aaron's wife calls him, and his cell phone rings.  He apologizes that he did not turn it off, and they again discuss the problem.  They conclude that if his cell phone is ringing here downtown, it is not also ringing in Russelfield.  That means that his other self, out at the hotel, cannot answer it.  Worried too late about changing history, Aaron does not answer his wife's call, which therefore goes unanswered.

The problem is that Aaron has just changed himself.  There is a version of Aaron in the hotel in Russelfield who has not spoken to his wife today because his cell phone never rang, and there is this version of him who has spoken to her from the hotel but ignored her call when he was downtown.  Presumably the version of Aaron who is staying at the hotel will tonight travel back to this morning, and it will be he who is downtown when his cell phone rings.  He, though, does not have the memory of having answered the call at the hotel, nor of making up that excuse; it is likely, then, that he will answer the call, and will invent an excuse for not meeting his wife for lunch, which may or may not be the same excuse, or might decide that meeting her for lunch is a good idea.

The problem exists at the other end as well.  When Aaron gets home tonight, will his wife ask him about the work that kept him from joining her for lunch, or will she ask why he didn't answer her call, or will she talk about whatever came from him answering the call downtown?  In at least three different versions of the day, at least three different things happened to her at that moment, so she has three distinct memories; yet she can only have one memory of that moment.

The logical solution (a solution alluded to by the narrator later in the film in relation to a different problem) is that whatever happens in the last version of history is what she remembers; it is also, then, what Aaron remembers.  The Aaron we have followed cannot be the Aaron who goes home that night--he has to be the Aaron whose cell phone did not ring at the hotel but did ring downtown.  Because he was not worried about changing history on his second pass but only on his first, he will assume that his predecessor answered the phone and will do the same without giving it a thought.

Fortunately, there is every reason to think that any future version of Aaron will do the same:  the phone will ring downtown, not at the hotel, and he will answer it when it rings.  Time thus stabilizes into that version of history, and those versions of Aaron and his wife are the ones who make it to the next day.  We have what the replacement theory calls a sawtooth snap with an N-jump termination--that is, we will repeat history a couple times but ultimately get something internally self consistent, and so the future will be built on that version of history.

Next we'll take a look at the peculiar incident of the shotgun at the party.

The filmmakers make the film challenging in part by sleight-of-hand, introducing a narrator who suggests he is telling the entire story in order, lulling us into believing this is what we are seeing; then he omits parts and restores some later.  The first piece out of sequence concerns a party the night after that first trip Abe makes.  Abe explained things so well that Aaron figured out much more.  Exactly when Aaron knew what is never clear; but on that night Aaron used the machine without Abe's knowledge.

Abe's girlfriend Rachel was at a party.  Her former boyfriend came and waved a shotgun around.  No one was hurt, but Rachel was badly shaken.  Aaron hears about it.  Knowing there is a time machine running that will take him back to before the party, he goes to the party and becomes a hero.  The next day people are talking about how Aaron saved the day.

Eventually Abe discovers how Aaron played the hero for Rachel, and wants to change history so that he can be the hero.  Thus they travel back to attend the party, and Abe saves the girl.

There are two points very troublesome about this.

First, it is fairly clear that Aaron travels to that party once from the same night that it happens and again from a day or so later.  He mentions in the telling (we now know he is the narrator) that he knows what happened the night he was not there, and on the night he was the hero, but that only the last time through, when Abe was the hero, "counts".  There must thus be two versions of Aaron at that party, and the arrival of the second Aaron, with Abe in tow, is going to change history for the original Aaron, who now is going to hear about how Abe intervened.  He has no way to know that this was Abe from the future, or that he came because Aaron had done this once.  History has become terribly unstable; there is no reason for Aaron to travel back to play the hero once Abe has done so, but Abe does so because he learned that Aaron already did.

This is not insoluble, though.  In the original history the ex threatens everyone at the party, and Aaron hears about it.  He travels back and plays the hero, revising history; he later hears what he did at the party, and knows that he must have traveled from the future to do that, so will do so again.  History stabilizes.  Abe hears how Aaron saved the party, and decides to take Aaron's place.  He arrives in the past, and plays the hero, displacing Aaron.  Later that night Aaron will hear about Abe being the hero at the party.  Now he has no reason to make that trip, and he won't.  Thus we have a version of history where neither was at the party, then one with Aaron being the hero, then one with Aaron being there intending to be the hero but Abe replacing him (and Aaron is also there again with Abe, so there are two of him there), then one in which that first Aaron does not come at all.  However, Abe will eventually hear how he was the hero, and he will realize that he has to make that trip to save the day.  History is stable.

But there is the other problem here:  Aaron casually suggests that they repeated the trip several times to get it right.  That means they first (after Aaron's solo trip) traveled back a couple days, then didn't like the way it went so they traveled back a few hours to do it again, and again, and again--and the number of duplicate versions of Abe and Aaron at that party increases each time they try to "get it right", because every previous version of themselves must also be there.  But they will be in each others' way unless they take steps to prevent previous versions of themselves from acting; and if they do that, they tamper with their own pasts and prevent themselves from learning from mistakes they are now prevented from making.

Such a scenario does not work right under any familiar theory of time travel.  We could wonder what Aaron and Abe were thinking, but the real question is, what were the writers thinking?

At some point Aaron decided to make recordings of everything that happened on the day Abe showed him the time travel secrets, probably on this solo trip.  That is our next time problem.

At some point, probably on that same solo trip that took him to the party, Aaron records every conversation he has that day, which he uses to play himself in repeating the day.  He tells us that having the recordings in his ear gave him a two-second lead on the world, enabling him to control how things would happen.

This means that whether or not he attends the party, he still makes the trip, because he has determined to make the recordings.  Since this provides a second motive for the trip, he will make it.

What he does not tell us is that the version of that day which we watch the first time is not the original version.  Aaron has not only already lived through the day, he has already recorded it, and is playing his part from the recordings.  That makes this the third time through--once to recognize the importance of the day, again to make the recordings, and again to use them.

There are three clues that confirm this is what is happening.

• First, everyone can see the earphone in Aaron's ear.  He claims to be listening to "March Madness", the college basketball tournament, but he does not know what is happening in the game and steers people away from that topic.
• Second, when he is in the office he is asked if he knows where someone is, and he says no and asks why; then he says yes he does know, and will relay the message.  He delivers the message on the basketball court outside.  The best explanation for this is that his recorded script says he does not know, which he recites on cue, but then he remembers that he will see the man later.
• Third, also in that office he is asked where he is going, and he gives the setup for an unfunny joke which identifies the man he is going to see.  Later when that man gives the setup Aaron does not know the answer.  This follows if in the office he diverges from the script to deliver the line, then later is following the script in pretending he has never heard it.

Aaron acts as if this were the most logical course of action available:  you can travel to the past, prevent your previous self from taking certain actions, and save history by doing those actions yourself.  Yet what Aaron misses is that he has failed to save the history that matters most:  his own history.  If the Aaron that he was does not make the trip that he made, he cannot be where he is.

It might be suggested that Aaron can save the future if he remembers to make the same trip himself at the right moment.  Another author used such a solution once.  The problem is, Aaron gets older, if only by a day, every time he makes this trip; and if he has to make the trip himself to preserve the past, he will age to dust before he can escape the loop.  Besides, if he must always make that trip, he cannot have any existence after that trip.

Aaron's actions make sense if we assume divergent dimension theory, that whenever someone travels to the past he creates a new universe.  Problems with that theory are discussed elsewhere, but if Aaron were actually killing his duplicate and taking his place, he would avoid at least some of these.  This, though, does not appear to be what Aaron is doing; he has temporarily disabled his alternate, not ended his existence.  If that is correct, there are now two of him in this world, and their lives will diverge significantly from here.  This Aaron will ultimately leave for another universe, and his counterpart will remain here, unaware that his partner discovered time travel in his own garage.  Given the number of trips time travelers are making in this story, the histories of the many worlds that would thus be created are much too complex to examine, as Aarons and Abes meet each other coming from different histories.

However, divergent dimension theory does not explain other facets of the story still to come, including the next event in our reconstructed chronology, when Aaron decides to punch someone in the nose and then cause it never to have happened.  That we will examine next.

The problems have become progressively more complicated; now we come to an event that has the marks of disaster.

It starts with a passing comment:  Aaron says if he could do anything, he would punch a man named Joseph Platts, a venture capitalist who for a long time pumped them for information about their projects without investing in their operation.  Aaron would only do it, though, if he knew he could make it so that it never happened.  As the narrator says, "the words wouldn't go back after they had been uttered aloud."  They wonder what would happen.

What would happen depends on your theory of time.  Under replacment theory, preventing yourself from doing what you did almost always creates an infinity loop, because you probably also prevent yourself from preventing it, so two alternate histories are causing each other perpetually.  Under fixed time theory, the entire question is nonsense, because you cannot change the past and therefore if you succeeded in delivering the punch you must have failed to prevent yourself from doing so.  Parallel dimension theory fares only slightly better, as the time travelers vanish from their own world but their counterparts do not vanish from the world they have entered (as illustrated in The Two Brothers:  Why Parallel Dimension Theory Is Not Time Travel).  In any case, it is a bad plan; but it became their plan.

The plan reached fruition one night when kids in Abe's neighborhood set off a car alarm, rousting him from sleep.  He gets this idea, to awaken Aaron, find Platts and deliver their message, and then travel back to earlier that evening to wait in Abe's neighborhood to prevent those kids from executing their mischief.  He figures in that case the car alarm will never awaken him, he will never awaken Aaron, they will never punch Platts in the nose, and the history they created will be undone.

The problem is, if they undo that history, they also undo their own trip to the past with the result that they will not be there to prevent the car alarm.  The Abe who is awakened then will not know any of what happened, and will think that his idea of finding Platts and then preventing the car alarm from sounding is new, so he will awaken Aaron and they will do it.

In the movie they never get that far.  They are interrupted by the appearance of someone who cannot be there, and the only explanation they have is that he discovered their time machine and traveled to the past to spy on them.  That is a problem for next time; this time, it means that our current problem is not answered by the film, and we have to consider the possibilities.

The worst outcome would be that they succeed, that they find Platts and hit him and make the trip to the past, then prevent the car alarms from awakening Abe.  As noted, this leads to an infinity loop, history permanently unstable.  That would for practical purposes be the end of the story, and nothing else that we see in the film could ever happen.  The interruption that comes from the future to prevent them from succeeding never comes.  However, even without that interruption they might fail, and in this case that would be good.

It might be that they spend hours trying to find Platts, but never find him; remember, they must enter those time machines before their counterparts shut them down and restart them in the morning.  Perhaps he is not home.  However it was, it could be that they never delivered the intended punch.  Not having punched anyone, there was no reason for them to make the trip to the past to undo what they had never done.  Of course, failure of the mission does not mean they would not attempt to prevent the car alarms from sounding; it just makes it less likely.

They might succeed in the first part but fail in the second--that is, punch Platts in the nose, but not manage to prevent the car alarms from awakening Abe.  That would be unfortunate for Aaron, who now would undoubtedly face assault charges (and whose new-found wealth would be discovered in the process, leading to all kinds of complications).  However, it may be the best outcome for history, and it does help explain what happened next.

That, though, is next:  the inexplicable traveler.

Abe and Aaron were on their way to find Joseph Platts and punch him in the nose when they were interrupted by the appearance of someone who could not be there, and abandoned their plan.

As mentioned, Aaron and Abe are on their way to assault Joseph Platts, intending then to use their time machine to undo what they did.  Enter Thomas Granger.  Granger has been seen before.  He is father of Rachel, the girlfriend who was threatened by the shotgun at the party.  He is also a venture capitalist, and the best hope they have for funding at this time.  Our time travelers spot him on the street as they leave Aaron's home, and realize first that he appears to be following them and second that he has three days' growth of beard, although he had been clean shaven that morning.  They call his home and get him on the phone, confirming what they fear:  the man who is following them has traveled from the future.  Somehow he discovered their well-kept secret of time travel, and used either their machine or another.

They never find out what happened.  They chase him, he runs, and he slips, hits his head, and is last seen lying comatose in Abe's apartment as they struggle to sort out the puzzle for which they now have insufficient pieces.

Aaron and Abe spend hours wrestling with the question of what happened, and never reach an explanation.  Such an explanation could take months to unravel, and they do not have months; they barely have minutes.  However, there is an explanation that fits all the known facts, and although it requires extrapolation, something much like this must have happened.

We know that Abe and Aaron were planning to assault Platts and then attempt to undo that assault by traveling to the past and preventing the activation of the car alarms.  Had they succeeded in the second part of their plan, they would have undone not only their assault on Platts but their trick of preventing the alarms, and so would have created an infinity loop, two alternating histories with no future beyond them.  Had they succeeded, then, Thomas Granger could never have traveled from the future, because there would be no future.

Yet the question being asked is, what could possibly have induced either of them to give Thomas Granger the information about the time machine, such that he could make that trip?  There is an answer they overlook.  Their plan is to assault a very wealthy man and then use time travel to undo the assault.  If they succeed in assaulting him, though, they will almost certainly be arrested.  If they are arrested before they can reach their time machines, they will find themselves jailed awaiting a judge's descision on bail--and every minute that ticks makes it that much more difficult to survive in the box that will take them back to earlier that evening.  They need someone to make that trip and prevent them from committing their crime.

It does not matter whether they told Thomas Granger, or whether they told Rachel Granger who told her father, or whether they told Aaron's wife who told Rachel.  What matters is that somehow the job fell to Thomas Granger, who made the trip to prevent them from committing the crime.

He succeeded, not as he intended but certainly so.  That is bad news for history, because a time traveler changed the past based on information from that past, information now erased and unavailable to him.  Further, the intrepid pair cannot figure out what happened, and so they cannot create an adequate substitute for it--and certainly they cannot expect that Thomas Granger will volunteer to travel back several days to die of a head injury just to prevent his daughter's boyfriend from being convicted on a well-deserved assault charge.  We have an infinity loop.  It was not the way anyone thought the deed would be prevented, but the deed was prevented, and the film brings us to the end of time.

It is not, however, the end of the movie.  There are still a couple more problems that need to be addressed.

Since this is the final chapter, we should try to tie up a loose end:  Aaron's ear bleeds, and they never explain this.  It's not that difficult to explain, though.  We know that gravity inside the time machine drops slightly; atmospheric pressure is dependent in part on gravity, and so that would also drop.  Normally the body compensates for changes in atmospheric pressure, as the eustachian tubes connecting the middle ear to the pharynx in the throat equalize the pressure--but because the chamber is flooded with inert argon gas, Aaron is breathing from a pressurized oxygen tank through a mask.  This will at least reduce his ability to adapt to the exterior change in pressure, causing blood vessels in his ears to break.  That would explain that.

The movie ends, but it ends badly.

That Abe built a failsafe machine is not surprising, nor is the fact that Aaron discovered and used it and replaced it with another.  The idea of the failsafe is that if something goes seriously wrong, they can travel back to the day before Aaron's first trip and undo everything that was done.  The only part they cannot undo at this point is that Abe has conducted the experiments and started the failsafe machine.  However, Abe believes he can prevent himself from making that first successful trip, by sabotaging the time machine before it is used.  He will continue to sabotage the machines until Abe and Aaron abandon the effort and do something else.

Again different theories of time will predict different results with such an act.  Following the replacement theory, though, their plan is a recipe for disaster.

As it was with the wrong Aaron, Abe and Aaron somehow have the notion that they can temporarily disable their younger selves and preserve history by playing the parts; but it is precisely because their younger selves lived those lives that they are here now.  They are undoing their own past; without that past, they cannot reach this present.

That puts the end of the story into an infinity loop.  They traveled back four days, changed the history of the party, and then prevented themselves from making that trip.  When the fourth day arrives, they will not depart from the future; not departing from the future, they will not arrive in the past, and so will not prevent themselves from doing all that we saw in the movie.  It is a classic mistake, the sort that takes a very smart person to make.  It is also disastrous.

Thus as intriguing as Primer has been, in the end it brings the world to an end.  Our narrator must have called before the end of the fourth day, because after that no one will ever call anyone at all.

We will return in a second article to answer a few questions that have been raised by readers particularly about Primer, and then move to another film.  Feel free to address your questions to the author by e-mail or through the comments sections of the articles.  When we return to Primer, we will resume with a question from a reader concerning what he calls the disappearing Abe.