There are two fundamental ways of handling multiple dimension theory.

One, which we generally have called parallel dimensions, maintains that there is already an infinite number of universes which parallel each other.  In some iterations, each of them differs from all the others, frequently in extremely minor ways.  It could be that in this particular universe the only difference is that Bo Kim Sun, a peasant in Hong Kong, broke a fingernail last week and is still healing.  Usually such parallel reality stories assume that the parallel reality is different in a major way.  As Holly, the computer aboard Red Dwarf, once put it:

Maybe in this universe, Hitler won the second world war; or maybe it's something really strange, like Ringo was a really good drummer.

However, for time travel stories, it is essential that all parallel universes are exactly identical until a time traveler interferes, creating changes in one of them.  This is a major problem of the theory, as we have elsewhere noted:  If you change a parallel universe, it is longer identical to yours, but presumably in any parallel universe in which you did not make the change your parallel counterpart will travel to another universe and change it, and suddenly half of all universes are different from the other half.  If we take this story as a parallel universe story of this sort, that problem faces us repeatedly.

The other fundamental way of handling multiple dimensions can be distinguished as divergent dimensions.  This version maintains that there is initially only one universe, but when someone travels to a moment in the past it creates a divergent timeline, in essence a new universe which branches from the original one at the point of arrival and develops as its own world thereafter.  This has other problems, notably the issue of the conservation of mass and energy (how did we manage to create another universe ex nihilo) and the issue of what happens if the same traveler makes the same trip (does he merge with himself, or are there two of him), again discussed elsewhere.

These both also suffer from the problem that multiple dimension theory is not really time travel, but creates an illusion of time travel.  The traveler has left his home and will never return, and finds that in the new world a different version of him already exists.  He thus does not have a place in the new universe, but is missing from the old one.

The film takes some of these problems into account, but does not fully pursue them.

Our time travel begins paradoxically.  The main character, Aidan, is headed home to his apartment when he is confronted by someone who tells him to stay away from the East Gate Motel.  The entirely predictable result of this is, of course, that he goes to the East Gate Motel, trying to figure out why someone would warn him away from it; but the confrontation is more complicated than that.  The problem is that the person who warns him appears in every way to be himself.

There is a degree to which this makes perfect sense.  His visit to the motel is going to reconnect him with Lauren, the ex-girlfriend, and he is going to give her a ride home but on the way get into a major automotive accident in which he is rendered unconscious and she is killed.  In the aftermath her family is going to push to press charges against him, thinking that somehow he caused the accident intentionally, possibly as the murder-suicide plan of a depressed ex, and the police warn him that he will be arrested if he leaves the hospital.  When he subsequently discovers that he can travel back in time, it is obvious that he would want to prevent the accident, and the obvious way is to warn himself away from the motel.

The problem is, he never does.

The time travel takes him back half a day, and we see him do it scores of times.  Yet on none of those trips does he go tell himself not to visit the East Gate Motel.  There is a sense in which that makes sense--after all, he knows that he would not have visited the East Gate Motel had it not been that he told himself not to do so, so that's a mistake he is not going to make.  From a replacement theory perspective, if he prompts himself he undoes the prompting, and so never prompts himself.  We have a twelve-hour infinity loop, and that story ends.

That, though, introduces the other side of the same problem.  Had he not told himself not to go there, he would not have gone there.  Everything happens because some version of him arrived and told him not to go to that motel.

At one point, the film tries to sidestep this problem via Aidan's observation that he is not in the original universe because before he knew time travel was possible a time traveling version of himself visited him.  This does not solve the problem, though.  If all universes are identical initially and Aidan in this universe would not have gone to the East Gate Motel had another version of himself not arrived to tell him to (or not to) do so, then that would hold in every identical universe, and no version of Aidan would ever have gone to the East Gate Motel.  If, however, there is a universe in which this got started by some version of Aidan going to that motel without being prompted by the arrival of a dimension traveler, then the parallel universes are not identical, and given that a very small difference like that can have occurred at a point that is critical to finding the dimensional portal, it must be that the supposedly parallel universes have by now fractured into a nearly infinite number of variant versions.  Parallel dimension theory makes it impossible for there to have been an original cause in one universe that does not apply in every other, and so the predestination paradox that starts the entire sequence fails.  Right at the beginning, the story cannot begin.

Aidan goes to the motel and encounters Lauren, whom he has not seen in long enough that he did not know she worked there.  He apparently walked out on her some months ago, in a bitter breakup, but she is willing to let him buy her dinner and catch up a bit, wants to know how his grandmother is, and then agrees to let him drive her home.  That, as we noted, sets up the accident.

In another misplaced trope, the first time we see Aidan and Lauren talking in the diner we hear a dish crash.  The second visit to the diner has a time traveling Aidan spying on himself, and he bumps into the waiter causing the plate to drop that we heard crash.  That's a fixed time trope.  This is not a fixed time story, but a multiple dimension story.  The first time Aidan has this conversation with Lauren, he is not being watched by himself, and there is no crashed dish.  There would be another world in which that happened, but it would be a different Aidan talking to a different Lauren--and we know that there is a different Aidan in a different world, because in the end they choose a different action.

There is an incongruity here.  Aidan apparently rides his bicycle to school, locking it to the fence outside the school property.  (I guess Australian colleges don't have bicycle racks?  Or is the bicycle more likely to be stolen from the rack on campus where there is security than it is from outside the fence along a public road?).  He then visits his gran, and from there we see him walk to the motel.  He surveys it, goes inside, then takes Lauren to the diner, and when they leave they return to the motel, get in his car, and he drives her away.  First, if he has a car, why does he bike to school?  There might be a reasonable answer to that, but not to this:  if he walked to the motel and has not been there in long enough that he doesn't know his ex-girlfriend has been working there for a while, why is his car in the parking lot?  Or did he actually offer to drive her home to her house in her car?  Do they do that in Australia?

The accident is a mystery; the police do not know why the driver lost control of the car and hit a pole.  When we first see the accident, we are looking at the passengers from the dash; the second time we see them it is through the front window.  Lauren is just about to say something important (we never learn what) to Aidan when she interrupts herself to yell a warning, "Look out!", and he swerves and that's all she wrote until he awakens in the hospital trying to find out what happened to her.

It then gets complicated, as they pull another trope from fixed time theory.  When he has traveled to the past and realizes that he just saw Lauren get into his car, he races, on foot, across town.  I don't know whether he is just an incredibly fast runner or whether Australian towns have particularly convoluted road routes for cars, but several times he manages to outrun people in vehicles.  This time he winds up in the road waving his arms for them to stop.  As he does so, they see him, swerve to avoid hitting him, and crash.  In other words, he causes the accident he was trying to prevent.

That's not impossible, if we assume that the accident had some other cause and he disrupted that original cause.  He apparently did not remember being the cause of the accident, presumably because immediately upon awakening he could not remember the events of the accident well; but that does not explain how he got to be the cause of the accident.

It is further complicated as he travels back yet again, and at the last moment realizes that he is about to cause the accident he is trying to prevent, and races across town on foot yet again (at times it is reminiscent of Run, Lola, Run, but if the point of that film was to have a lot of footage of a buxom girl running, that point is lost when she's replaced by a somewhat geeky guy).  He reaches the accident scene in time to see himself waving to stop the car, and immediately tackles his self, pushing him off the road and punching him to render him unconscious.

The problem is that the accident happens anyway--a trope from movies like The Time Machine, where they pretend you can't change the past but are changing it even while they debate the matter.  It seems as if the car accident happens whether or not Aidan is standing in the road waving his arms to cause it.  We don't know why it happens; it seems fated to do so--but that makes no sense.  If Aidan caused the accident by trying to prevent it, then it did not happen until he tried to prevent it, but he could not have known to prevent it had he not caused it.  If Aidan did not cause the accident, then it is not unreasonable to imagine that he could prevent it by flagging down the car before it happens.

There is another bit of nonsense in these scenes:  after punching his other self in the jaw, Aidan rubs his jaw.  That seems like the sort of problem that destroyed Looper, in which injuries inflicted on the younger version of a person immediately appeared as scars on the elder.  They don't make an issue of it, but Looper is an effort at a replacement theory story (only one history of the universe, but it is mutable) and it made little sense there.  It makes even less sense in a multiple dimension theory story--the version of Aidan that Aidan hit is not the past version of the Aidan who hit him, but a parallel self from another dimension.  The Aidan doing the punching was never punched--if he was, he would not know that his waving his hands would cause the accident, because his memory of that event would be that he was knocked out of the road when he was trying to prevent it.

The IMDB credits for this film list a character as "Patient X", and there is one character, Aidan's hospital roommate, who seems to qualify for this designation.  The layout of the hospital room seems incongruous and inefficient, but was probably done that way to make camera angles comfortable during their conversation there.

That conversation gives us another predestination paradox:  it smacks of fixed time.  The patient, who seems crazy and has both wrists bandaged, knows that Aidan has traveled to the past because he, the patient, already saw Aidan arrive earlier in the day.  Yet this Aidan has never found the hole in the bathroom floor and so never traveled to the past.  Therefore he never arrived in the past.

Of course, we're working on the theory that there are an infinite number of parallel universes out there, so it would make sense that some other version of Aidan from some other universe came out of the hole earlier in the day.  The problem, though, is figuring out how, if all the universes are the same, any version of Aidan ever found the hole in the floor.  As we saw already, he has no reason to go to the motel if he does not arrive to tell himself not to go, and he will not arrive to tell himself not to go unless he went, so that will never happen.  Further, the only reason he checks the floor in the bathroom of room 41 is that Patient X tells him there's a hole there and that he has to enter it, and the only way Patient X can know this is if he has seen Aidan either enter or exit the hole.  Note that when Aidan goes to get a room at the motel, he is given room 11, not room 41; he has to break into room 41 to investigate the bathroom.  Indeed, the only reason he checks into the motel at all is that Patient X has told him he must go down the rabbit hole.

Thus there can be no universe in which Patient X tells Aidan where to find the portal unless in some universe Aidan finds the portal, and no way for Aidan to find the portal unless Patient X tells him.  We have another impossibility.  An infinite number of identical universes does not solve this for us.

This situation becomes more confused.  Aidan finds the portal as Patient X told him, and uses it, emerging earlier in the day to find Patient X jumping on the bed holding a knife.  Aidan leaves and then returns.  He finds that Patient X has cut his wrists with the knife, and he calls emergency services for an ambulance before again vanishing into the hole in the bathroom.  This causes Patient X to be hospitalized as Aidan's roommate.  In order for Patient X to be in the hospital, he must cut himself in the hotel room, and Aidan must find him in time to call the ambulance.  If Aidan did not make the trip to the past, Patient X never reaches the hospital and so never tells Aidan to travel to the past.  Our impossibility is complicated.

Patient X gives us more problems over time.  His particular form of insanity seems to include that he correctly surmises facts about the future.  Most notably, we have the sequence that Aidan saw him in the hospital with his wrists bandaged, then saw him jumping on the bed with the knife, then found him with his wrists slashed and called an ambulance, then later again encountered him jumping on the bed with the knife.  This time he tries to warn him, and Patient X goes into a strange line about whether this is the first time they met here or the second, and says (reminiscent of the error in The Time Machine, in which the Morlock claims Hartdeggen can't save Emma because it would create a paradox so he is prevented from doing so) that Aidan can't prevent him from cutting himself because were he to do so he would never meet in the hospital and would never be here.  That, though, is not multiple dimension theory--the entire point of multiple dimension theory is that the other version of you in this world is not your past self but someone else, and that means the Patient X jumping on the bed the second time is not the same Patient X as either the one he met in the hospital or the one who cut his wrists.  They are in different universes.

Aidan shares an apartment with Nick and Jess.  We first meet them when he returns from meeting his temporal duplicate, and he attempts to explain to them what happened.  They are waiting by his bedside when he awakens following the accident.  Then they appear in one other scene, conversing with him while he is trying to persuade them that he is a temporal duplicate.

At this point it is getting difficult to know what is happening without a scorecard, and they have not provided one.  We are not certain whether this is the Aidan who warned Aidan, or whether this is the Aidan who was warned now having made another trip to the past.  What is more interesting, though, is that Aidan appears to have taken a lesson from Primer, observing one of their mistakes and using it to his advantage.  He deactivates his cellular phone, places it on the table, and tells Nick to call him.  Nick does, and reaches Aidan--the Aidan for whom this is the original universe--visiting his gran.  Because the phone Nick can see is deactivated, the system finds the other identical phone.  Of course, Nick thinks it a trick, but can't determine how it could be done.

There is a simple way it could be done.  Aidan needs to find someone who can sound like him and pass for him, and give him his phone, then get an identical phone to put on the table.  Nick probably would not be able to tell that this was not Aidan's phone, so the difficult part really is whether someone else can pass for Aidan that way.  But Nick doesn't think of that, and Aidan isn't actually doing that, so it's kind of moot.

More than anything else, though, this encounter demonstrates to us that the multiple universes are becoming extremely varied, all from the travels of the multiple versions of a single traveler--and that raises another question for us.

It is not always simple to distinguish varying versions of multiple dimension theory simply from observation, but there are some clues here that may help.

When Aidan is being questioned by the police, he makes the statement, I'm not the only one out there.

Every time any version of Aidan travels to the past, he leaves that universe--that version of him is gone.  There is some other universe in which he has arrived.  He duplicates himself for as long as he is in that universe--forever, effectively, unless he again departs.

If the concept is one of divergent dimensions, there is initially only one universe, which we will call U1.  There is likewise only one Aidan, A1.  When he travels to the past, his impact is to "change the past" such that at the moment of his arrival a new universe, U2, is created, in which there is another Aidan, A2, whose life to this moment is the same as that of the other Aidan to this moment.  That entire universe is identical to U1 except to the degree that it is altered by the presence and actions of Aidan within it.

Aidan can never leave U1 again, because he left it and will never return.  However, there are now two Aidans in U2, and either or both of them can leave.  If A1 leaves again, he creates U3; if A2 leaves instead, he creates U3.  However, U3, under divergent dimension theory, is peculiar, because it is a copy not of U1 but of U2--the universe that is different because A1 arrived.  If A2 leaves U2 and creates U3, then A3 is already there, and A1 arrives on schedule.  But if A1 leaves U2 and creates U3, then A3 is there and A1 arrives from U2 but also (because U3 is a perfect copy of U2) arrives on schedule from U1.  We thus have A1(a) (coming directly from U1) and A1(b) (coming originally from U1 by way of U2) in U3.

Note that if A1 has already left U2 and created U3, and then A2 leaves from U2, A2 does not land in U3 with A1, because the universe he creates, U4, is another identical copy of U2 from which he leaves, not a copy of U3.  That universe will contain A4, A2, and another duplicate, A1(c), who came directly from U1.  The number of Aidans keeps increasing, and they are not all in the same universe, but there are copies of copies:  Since A1 created the first divergent universe and there is no other Aidan to leave universe 1, every universe is a copy (of a copy of a copy of a copy...) of universe 2, incorporating the arrival of A1.  That arrival cannot be erased; it is part of every universe after the first.

Also, significantly, since every universe created by the departure of any version of Aidan is a duplicate of the universe from which he departed, once we see the arrival of any version of Aidan in any universe through which our Aidan travels, that version of Aidan must arrive in every subsequent universe to which he travels--his arrival is duplicated along with all the rest of the history of the departure universe.  That means that when Aidan leaves the first time we see him leave, inspired by the arrival of his doppelganger, every universe to which he travels, every universe he subsequently creates, must have the arrival of that same Aidan on that same mission.  However, that Aidan is conspicuously absent from the final version of history when someone else arrives to the same point in time and space and tells Aidan not that he should stay away from the motel but that he must go there.  Divergent dimension theory breaks down at this point, because the film fails to recognize the complete duplication of each version of history.

Some will take an alternate view, to the effect that there is an original baseline history and any time traveler creating a new history does so not from the universe he knows but from that baseline history.  There are many problems with that, but the most glaring would be that ultimately there can only be two Aidans in any history--the original one who never left, and the one whose arrival created this divergence.  There cannot then be "others" out there, only one other, and only one knows that there is more than one of him unless he has already contacted the other.  That is not consistent with what we see in this film, either, particularly as old Aidan (still ahead) exists in every universe we see, which would preclude the possibility of any younger version of Aidan arriving in that universe.

With parallel dimension theory, the number of universes is vast.  It might be infinite, but that's not particularly relevant.  What matters is that it is fixed--and so is the number of Aidans.  The other issues are the arrival points of the various Aidans, and the fact that all universes are identical except to the degree that they are diversified by the arrivals of time travelers.

To illustrate, A1 leaves U1 and arrives in U2.  Presumably (because as we noted it is necessary for some version of Aidan to travel to the past without prompting from some other version of Aidan who already did so) whatever happened in his universe caused him to find that hole in the bathroom floor of room 41 at the East Gate Motel.  That, though, means, given that every universe is identical, that either every Aidan in every universe is going to find that same hole at the same time in the same way, or the actions of A1 have been such in U2 that A2 does not find that hole.

(There is the possibility that the actions of A1 are such that A2 finds the hole at a different time because of different causes, but that is a distinct problem.)

If A1 changes nothing that prevents A2 from finding the hole the same way at the same time, then all the universes are still the same except probably U1 (from which A1 departed but to which no Aidan arrived).  However, if A1's arrival in U2 prevents A2 from departing, then no Aidan arrives in U3--which means that A3 will leave U3 and arrive in U4, preventing A4 from leaving for U5, allowing A5 to leave for U6.  The result is that our vast collection of universes has now been divided into two groups, in one group of which Aidan left and was gone thereafter, and in the other of which Aidan arrived and thereafter there were two of him.  The vast collection of universes is no longer coherent; there are two different kinds.

That, though, inherently assumes that there is a fixed relationship between these universes, that for any universe X the same traveler departing in the same way at the same time would find himself in universe X+1.  What if the relationships are random?

Let's just keep the example simple:  assume four universes.  In each universe, events have led to Aidan's departure.  Each of the four Aidans will go to a different universe from his universe of origin, which means one chance in three of any one of them landing in any particular universe other than his own.  If I'm doing the math right (and don't hold me to it--I tackled it four times before I found a method that I thought was getting me what I needed), The odds of each of them landing in a different universe are only about one in thirteen (12 cases in 156 possibles, once you exclude all those in which a traveler goes to his own universe), and thus only one chance in thirteen that we get one traveler arriving in each universe when one departs from each universe.  The most likely outcome at just over four in ten (64 cases) has two arriving in one universe and none in one of the other three; This is closely followed (56 cases, better than seven in twenty) by two in each of two universes, with none in the other two, and even the odds of three in the same universe and one in another are better than all even (24 cases, about three in twenty).

The disparities worsen as the number of universes increases.  Given the vast number of parallel universes assumed, that means that many universes would have dozens, possibly hundreds, of Aidans arriving from the same departure time, and other universes would have none at all, with most universes having a very few but not many having exactly one.

This is complicated by the fact that the mode of transport takes Aidan from and to exactly the same geographical coordinates--multiple Aidans would be emerging from the same hole at the same moment.  The bathroom in some worlds will be very crowded.

Based on this, it seems unlikely that we are looking at an original cosmos of many parallel universes, and more likely that this is a divergent dimension scenario in which the arrival of Aidan creates a new universe branching from the one from which he departed.  Yet it does not appear that divergent theory works either.

In Bill & Ted's Excellent Adventure, the intrepid duo several times use the future to change the past.  (They do this again in their Bogus Journey, but that's not a new idea anymore then.)  Of course, the Bill & Ted films do not work in multiple dimension theory--they only work in fixed time or replacement theory, because in multiple dimension theory you cannot change events in your own past, and therefore they could not have gone back and planted the keys where they could find them because those keys would not be in that universe.

That seems to be the mistake made here.

Aidan has been arrested, and made the comment to the police that he is not the only one of him out there.  Another version of him meanwhile is working to set him free.  He hides a hacksaw under a trash can near a lightpole outside the police station, and then calls in what is probably a bomb scare so that the police will have to evacuate their own building.  The Aidan in custody thus is removed from the building where they had been interrogating him and handcuffed to that light pole along with another prisoner while officers attempted to deal with the bomb scare.  Aidan knocks over the trashcan, and finds the hacksaw, maneuvers to pull it to himself, saws through the chain on his cuffs to escape the pole, and flees leaving the hacksaw behind.  Evading the police, he goes apparently to his own workshop (we have never previously seen it), finds an identical hacksaw, and saws the cuffs themselves to remove them completely.  He then takes the hacksaw with him back to earlier in the day, goes to the parking lot where he would later be cuffed, and hides the hacksaw under the trashcan.

Rewind a bit.  During his interrogation, Aidan has told the police that he found a way to travel through time; that was why there was more than one of him out there.  One of them asks why, if he can travel in time, he doesn't help himself escape.  When the alarm sounds, he says, "Thanks for the idea."  It thus appears that he looks for the hacksaw because while he was in custody he devised this plan to free himself.  It is, of course, a fixed time trope:  he cannot free himself if he is not freed, and he cannot be freed if he does not free himself.  We have a fairly obvious predestination paradox (yes, another one) but with another complication.

The only reason for Aidan to hide a hacksaw under the trashcan is that he knows he is going to be handcuffed to that specific pole.  That means he must have been handcuffed to that specific pole at some time when there was no hacksaw under the trashcan.  If so, though, he did not find the hacksaw and escape, and did not thereafter retrieve the hacksaw and take it to hide under the trashcan.

The only solution that works is that some version of Aidan knew that some version of Aidan was going to be chained to that pole, and that the trashcan would be tipped when the police were not watching.  That almost certainly has to be a version of Aidan that was chained to the pole.  He must later have escaped some other way, and then picked up the hacksaw and taken it back to hide under the trashcan, hoping that somehow it would wind up where his other self could get it.  Note, too, that he must have taken the hacksaw from some point in the future and carried it back to the past:  had he traveled to the past and then picked up the hacksaw to take to the park, when his doppelganger reached the workshop the hacksaw would already have been removed.  All of this is layers of complication; we cannot begin to guess how Aidan managed to escape the police without the hacksaw and then think to hide the hacksaw there in any version of events in which he did not start by finding the hacksaw under the trashcan.

It also does not work in multiple dimension theory--that is, when Aidan escapes, gets the saw, and takes it back in time, he is not leaving it for himself but for some other Aidan in some other universe.  It looks like we have not a loop, but it is again not a loop but a chain--Aidan 4 found the hacksaw left by Aidan 3, who found the hacksaw left by Aidan 2, who found the hacksaw left by Aidan 1, who did not find the hacksaw but had to escape some other way.  In fact, Aidan 1 was never chained to that pole, because there is no previous Aidan out there to make the bomb threat; and that means even if Aidan 1 thinks to make a bomb threat and hide a hacksaw, he does not know where the police will put Aidan 2 and so does not know where to put the hacksaw.

Aidan might eventually devise a plan to free himself, but it would take several passes through the situation to get the details right, and until he does he is going to have to escape some other way.

Aidan learns that he actually can change the world when he meets a well-dressed lawyer in that same diner, whom he recognizes as being his hospital roommate, "Patient X".  He asks a few awkward questions and discovers that there was a point in the man's life when he was about to go to war, and then something interrupted and he didn't go.  This, Aidan concludes, is the change.

At first it seems as if perhaps this is one of those "every possible universe exists" stories, and we have only now encountered a noticeable difference between this universe and all the others we have seen.  (After all, if "every possible universe exists" you must exist in hundreds that differ from each other solely by what I ate for dinner.)  However, not long thereafter we learn that the other Patient X is also in this universe, and he believes that he is responsible for his doppelganger's life because he did something that prevented the doppelganger from going to the war.  He says that the way to change someone's life is to remove him from the situation so he never faces that choice.

There is a flaw at this point, but it's probably an unavoidable one:  for X to be a successful lawyer, he will have had to have spent quite a few years in study and work to reach this point; that means that Patient X must have traveled back quite a few years to effect the change in Lawyer X' life, and since you cannot travel forward in time, Patient X must be quite a few years older than Lawyer X.  That's not easy to do convincingly in live actor movies, and they fail to make the effort (no makeup is used to age or youthen the actor in either role).

It does raise the question of motivation.  Patient X does not in any way himself benefit from having steered his doppelganger's life into becoming Lawyer X.  Similarly, Aidan can create a world in which Lauren is not killed in the crash and possibly his doppelganger manages to reunite with her, but the Lauren he knew is still dead and he lives in a world in which he has no place, can claim no identity, and will probably always be alone.  He is in effect the brother that never actually existed in this world, and although it might make him feel a bit better to believe that there is a universe in which Lauren lives, it is not his universe; he's a stranger there himself.  The film recognizes this during the philosophy discussion and Aidan's insigful observation is, "That sucks."

However, it tells him that there are ways to change events, and he decides he should do that.

There is an unexplained sequence of events that leave us wondering what Aidan was doing, or trying to do, but which also tells us something about that hole in the floor.

After failing to prevent the crash, one of the Aidans who has already come from the future removes Lauren's dead body from the vehicle and carries it to the motel.  It then appears that he put her body into the hole in the floor and followed her down.  We next see him emerge; we do not again see Lauren.  However, as he emerges, he reaches back into the hole as if he is trying to grab something--as perhaps you would do if you had a suitcase in such a situation, climbing through the hole yourself and then reaching back to grab the handle of the bag you left behind.  The problem is, the suitcase can't be there, or more accurately, his hand can't go wherever the suitcase is.

It is unclear exactly how, or when, the hole works.  We know that if he enters it entirely and exits entirely, he is twelve hours in the past.  Apparently, though, he can stick his hand into the hole without the hand traveling into the past, or if it does he can draw it back to the future if he has not followed it.  However, the suitcase, if it actually "is" anywhere, is in the corridor leading from twelve hours in the future to what is now a moment ago (just before he emerged), and if he reaches into the hole he cannot reach it.  Anything you drop in that hole that you do not recover before exiting it is gone forever.

It also raises another issue, one that we considered briefly in connection with Primer.  Aidan enters the hole at two in the afternoon and emerges at two in the morning.  He looks around, and at five after two in the morning he enters the hole--but he is already in that hole, traveling back from eleven hours fifty-five minutes in the future, and will not emerge until five minutes ago.  Does he encounter himself?

The answer in this case seems to be that he is never really "in" the hole, as in a static place like the various incarnations of Wells' time machine (H. G. Well's The Time Machine, Time After Time, The Time Machine).  He rather must leap from point to point, crossing time (and the dimensions) in an instant.  He is not really "in the hole" at all, but passing through a doorway from one point to another.

It is an interesting design that would probably work, from a metaphysical perspective, if it weren't buried in a film that has so many other problems.

It is at one point stated that every time Aidan passes into and out of the hole he travels back twelve hours.  For most of the movie, that's not such a big issue.  However, it becomes an issue as the film moves toward its climax.

We might estimate that it takes perhaps twenty to thirty seconds to climb into the hole and out again.  It is also exercise, something less strenuous than pullups perhaps but more strenuous than stair climbing.  If one trip takes him back twelve hours, it would take seven hundred thirty trips to travel back a full year. Assuming that he can, from his perspective, make three trips in a minute (twenty seconds apiece), that's minimally two hundred forty-three and a third minutes, or four hours plus two hundred seconds, of climbing into and out of the hole in the floor to travel back one year.

Aidan travels back to the time when his grandparents were newlyweds.  Conservatively that's forty years; it's probably closer to fifty and it could be sixty--at one point there is mention of a picture Lauren gave Gran for her eightieth birthday--but forty is sufficient to illustrate the problem.  That means that he went through the process twenty-nine thousand two hundred times, and it took minimally one hundred sixty-two hours at three trips per minute.

Obviously he did not do that in one stretch.  For one thing, he would be exhausted probably before he finished the first hour.  This would slow his progress, so that it would take longer.  He would have to eat, rest, sleep.  If he sleeps for eight hours, he loses two thirds of a trip, and that's that much more he has to do to get back that far.  We also see events along the way, as if he stopped for some sightseeing, and while he seems to be a fast runner in good shape, that's going to interrupt him for several hours.

It's also curious what he might have eaten.  He's not making money along the way, so he can't replace any he spends.  If he's using plastic, there will be a date before which it is not valid.  Even if he's carrying a lot of cash, it's probably date-stamped sometime within a few years, most of it within the decade, and before that time it's going to be perceived as counterfeit.  Unlike Richard Collier, Aidan did not prepare for his trip by obtaining antique currency.  Checking my own pockets in January 2016, the earliest date on my four bills is 2009, and among my nine coins I have a quarter from 2004, one from 1996, and a 1991 penny.  Odds are not good that he's carrying old money.  Nor can he, before a reasonable date, pass himself off as himself to beg help from friends or family along the way; he will appear too old.

This is not an impossible trip to the past, but it is a very difficult one, and one which Aidan probably would have had great trouble making.

It also leaves him stranded in the past.  The only way to move to the future is to live through the years--which he does, and we'll come back to that shortly.

To show us that Aidan is traveling back a long time, they keep flashing the room (which he probably does not see every time, since there is little reason for him to leave the bathroom and return after every trip).  It makes sense that the room would change.  It would probably alternate between day and night, since he probably is there sometime after midnight and sometime after noon (the two times when the bathroom is unlikely to be occupied in a hotel room).  It also makes sense that at night the room is sometimes occupied and sometimes vacant, and by day it is rarely occupied but sometimes made up and sometimes in process of being cleaned and changed.  It is also certainly true that over the years the decor would change.  Sensibilities for what makes a nice hotel room in two thousand are probably significantly different from the same attitudes in nineteen seventy.  However, watching the rapid montage of the room is a bit confusing.  At first I thought they kept changing the decor, but on closer examination they have rather attempted to make it appear as if they changed it by sometimes inverting the bedspread--it has a brightly-colored quilt-like pattern on one side and a white lining on the other, but when the lining side is up you can see the bright quilt pattern on the edge.  It probably was not really intended to be reversible, but they reverse it.

And over the course of what we said has to be at least forty years they never change the curtains and always have that same bedspread.

Let us suppose that the hotel manager decides to put plaid curtains in room 41.  Since hotels spend a lot on decor, he is going to install durable curtains, and they are going to last a number of years.  Eventually, though, he is going to replace them, and when he does it is unlikely that they will be saved to be reused (although not impossible).  He does not change the curtains, or the bedspread, or the carpet, every day, or even every month--but he does change them sometimes.

If every universe is the same, the decor is the same in all of them at the same time, and it changes at the same time.  But they probably don't invert the bedspread.

It is obvious why the filmmakers did it.  They were attempting to create a flipbook feeling of running through thousands of trips, seeing the room a bit differently each time, changing the decor by flipping the spread.  Bravo--except that the room would not be different each time.  As with the mannequin in H. G. Wells' The Time Machine it would change a bit at a time and then stay that way, and we would see night and day flash against a decor that then abruptly changed to a new decor and stayed that way for a while as night and day flashed past it.  We would of course see occupied and unoccupied rooms, rooms being changed and rooms ready, but the decor would stay the same.  The filmmakers intended for us to see an identical room showing the passage of time; what they actually showed us was that all the universes are a little bit different, and if they can be different in little things like the bedspread they can also be different in big things like whether King John ever signed Magna Carta or Emperor Constantine ever made Christianity the recognized religion of the western world.  Either the worlds are identical, or they are entirely different.

This is the more complicated for our divergent dimension theorist, because each time Aidan emerges he is creating a new universe that diverges from the one he just left twelve hours earlier.  The bedspread is not going to change twice in twenty-four hours in a motel room.  The room in which he emerges is identical to what the room he left would have been twelve hours before he left it.  Rapid changes in decor are inconsistent with divergent dimensions; with parallel dimensions, they indicate variation, and thus not uniformity.  They goofed.

Or maybe the maid just doesn't know which side of the bedspread is the top so she puts it on upside down some days.

It is still strange that the motel room never changes over all those years, and indeed the motel itself seems not to have changed.  Of course, that could be a budget issue; we can't demand too much from independent films.

That raises another issue incidentally.

In order for Aidan to travel back to when his grandparents were newlyweds, he had to make over twenty-nine thousand trips back half a day.  He enters and exits that hole each time, and each time he is in a new universe--a universe which differs from all previous universes solely in the fact that he emerged from that hole at that moment.  Assuming a rapid turnaround, that is the only difference, and that difference will be included in the next universe, in which he again exits twelve hours earlier.  However, if this is divergent dimension theory, he must create one new universe with every twelve hour hop, and that means over twenty-nine thousand universes are created before he creates the one in which he saves his grandfather and stays in the past to become old Aidan (whom we will address again in a moment).

That, though, means that in these twenty-nine thousand universes (and in any other universes diverging from them, which will happen exponentially because every time he creates a new universe from an earlier point in time, every version of him that departed from the previous universe will depart from this new one and in turn create new universes) Aidan never reached that moment in the past, and so does not exist as old Aidan, the hotel manager.  Those universes are very different from the ones we see.  However, as he says to the philosophy discussion group, he is not the first version of himself to do this.  There are already perhaps billions of diverging universes all of which exist so that he can have reached the point in the past at which he saves his grandfather and becomes the hotel owner.

More than once, Aidan's Gran comments that she wishes his grandfather were there, and more than once she mentions that he drowned because of a golf ball.  When Aidan is talking with Lauren at the diner and she asks about his Gran, he jokes that you can't talk with her for more than a few minutes without her mentioning that golf ball.

When he is talking to his philosophy professor about traveling to the past, the professor suggests that if he ever does get to change the past, he should make sure he changes the important things.

Ultimately he travels back to when his grandparents were newlyweds, and wanders into the woods by a body of water where a young man, his grandfather, is about to hit a golfball into it.  He interrupts the process, and they become involved in conversation, and the golfball is pocketed, not hit.  It is hit the next day, but before Grandfather (Wyatt?) goes into the water to pursue it, he realizes that the gift Aidan gave him the day before is a golf ball, so he does not need to chase the one he just lost.

For what it's worth, I take it to be a river.  This is just one of those things you learn with wilderness skills:  lakes and ponds are perfectly level, but the surface of a river angles downhill.  In the scenes looking across the water, it appears to be slightly higher on the left edge of the screen than on the right, so I conclude either it is a river flowing from left to right, or the camera is sitting on uneven ground, and the actors are leaning to the left to compensate.

We are then privileged to see that in this world, Grandfather is sitting by Gran's bed as she lies dying.  Aidan gave her her wish.  He doesn't know it, though.  He might one day know it, but at the moment he has no way of reaching the future except by growing old--which he apparently decides to do in this dimension, and tampers with a few other things along the way.  No one else knows it either, because in any universe in which Grandfather does not die, no one knows he would have.

The point is that he changed the world for the better for the person who most mattered to him.  So despite all the trouble time travel caused for him, it did ultimately do something good for him, even though he is the only one who will ever know.

There is another predestination paradox here.  In the future, after Aidan has confronted himself, he asks Gran whether there's any mental illness in the family, and concludes ultimately that it's not all in his head.  She tells him, "Isn't everything just in your head?"  Then when he's in the past, a similar conversation reverses their roles, and he says to her, "Isn't everything all just in your head?"  It appears that he got the quote from her which she got from him.  That's not a big deal in fixed time, because of course things don't really happen sequentially--they happen all at once, causation is an illusion, and we perceive them sequentially.  It's not a big deal in replacement theory, because it's simple enough to suppose that one or the other of them (probably Gran) heard the expression from someone else at some point in their lives and so introduced it to the loop from the other source.  However, in multiple dimension theory it is a trope out of place:  Aidan is not saying it to the younger version of the woman who said it to him, but to a woman who will never know him in the future, but will instead meet a different person living his life in this world.  It looks like a loop, but again it is not a loop but a chain, in which each person who repeats the statement is delivering it to someone else.  That's actually less interesting than a predestination paradox.  It suggests that the writers were borrowing tropes from other time travel stories without really understanding them.

In another trope taken from fixed time stories, we discover as we reach the end of the film that after he traveled to the past Aidan stayed in the past and ultimately became the manager (owner?) of the East Gate Motel.  He was the one who put Aidan in room 11 (not room 41); he gave Lauren the job.  He did not attempt to warn them about the accident.

As an incidental, he does not seem to be quite old enough.  Aidan visited his grandparents when they were newlyweds--maybe not newlyweds, but it seems they had not yet had their first child, and the appearance of their circumstance puts them in the world of people who married young and had children early.  What we know of them and what we know of Aidan suggests that when he meets them in the past he is about their age, possibly even older than they are.  If we give them the benefit of the doubt, we might argue that he is not more than ten years younger than they are, and it appears he becomes friends with them along the way putting him solidly in their generation.  Yet his grandmother seems much older than the hotel manager, probably twenty years (we know she is past eighty, he is probably still some years shy of seventy), and that does not fit the observations.  It is a small thing, though, and it may be that Gran is not as old as she looks, old Aidan is older, and there is more of an age difference between them than appears when they are in the past.

In this universe, though, he goes to tell his younger self that he needs to go to the East Gate Motel.  That is exactly opposite from the message his younger time traveling self gave to him.  Yet it has the same effect--absent the aspect of having seen someone who looks like himself, because the motel manager does not look much like him (at least, when we first meet the motel manager we are not in the least suspicious that it might be him).  That, though, gives us another problem, and it's a significant one.

Our first Aidan lives in a world in which his grandfather is gone.  He travels to the past to create a world in which his grandfather never drowned chasing a golf ball ruining grandmother's life, and succeeds, and then as he ages he becomes the manager of the motel in which the time travel hole in the floor is located.

However, our Aidan lives in a world in which that elderly Aidan is the manager of the motel, and the only way he can be there is if he previously traveled to the past, and the only reason he would have done that was to prevent his grandfather from chasing the golf ball--and we know that if he attempts to do that, he succeeds.  Therefore, any universe in which old Aidan is the manager of the hotel must be a universe in which young Aidan arrived in the past and saved his grandfather, a universe in which his grandfather is sitting beside his grandmother's bed and there is no story about a golf ball.  Further, since there is no story about a golf ball, there is no possibility that the Aidan of that world would travel back to save his grandfather.  The events are mutually exclusive; they cannot exist in the same universe.

Certainly they could if this were fixed time, and if it were replacement theory there might be a convoluted way of solving it (probably involving old Aidan regaling young Aidan with the story of his life and why young Aidan needs to travel to the past to save his grandfather--but that's not a likely scenario).  In multiple dimension theory, though, any universe in which old Aidan manages the hotel is a universe in which Grandfather is sitting at Gran's bedside and there never was a golf ball story; and any universe in which a lonely Gran wishes that grandfather were here and tells the golf ball story is a world in which Aidan never arrived in the past and never became old Aidan, manager of the East Gate Motel.  The world in which we started cannot exist.

So we end in an impossibility.

It seems to be one of those movies that attempts to do something no one can figure out, in the hope that in trying to figure it out fans will say it's difficult and deep.  It's not really either, just a temporal impossibility that creates a pastiche of incompatible tropes from other time travel movies.  It just does not work, ultimately.