To begin, I want to commend author John Varley, who has converted a short story into a full-length motion picture which is intelligent and entertaining.  That in itself is no small undertaking.  Furthermore, the film asks the right questions, and usually worries about the right issues.  Although the film has some major flaws in it, I suspect most these are the handiwork of those through whose hands the project passed after leaving his.  So we will credit him with an excellent concept for a movie, and blame those who made the film for the problems in it.

For those who need their memories refreshed (and those who missed this one), the story begins with the mid-air collision of two airplanes in 1989.  It then follows the events in the life of National Transportation Safety Board (NTSB) investigator Bill Smith, as he becomes involved in both the investigation of the crash and a relationship with a stewardess named Louise Baltimore, who doesn't seem quite normal and who abruptly disappears.  Then he finds something in the wreckage which injures him, leaving him stunned, and he sees Louise arrive from nowhere to take it from him; but she doesn't seem to know him.

From there, we follow Louise.  She is a traveler from the future.  She and her team had recently boarded the plane which crashed, removed all of the passengers, replaced them with bodies, and let it crash.  One of them dropped the device, and they were coming to retrieve it when they encountered him.  From there, they board a doomed plane in 1963, and perform a similar operation, although this time with serious complications.  Then, in order to prevent Bill Smith from being present when the team comes for the dropped stunner, she goes back to 1989, to the time between the crash and the discovery of the stunner, and attempts to prevent him from going to work by engaging him in a relationship.  We see these events played out again, expanded by her perspective and some additional material.  She fails to stop him, which sets up the possibility of an anomaly which is referred to in the film as a "paradox".  In attempting to prevent this, she causes it, and the future is destroyed.

We will pursue the time line in a different sequence, treating it in the order in which events are altered, taking each time trip in turn.

It must be said that although only five trips to the past are documented in the story, it is intrinsic to the concept that Louise and her crew have done this many times, pulling thousands of people from the past just before their deaths.  It is suggested that in each case nothing was changed, that no paradox occurred.  This assertion requires some scrutiny, however.

The idea that you can go into the past and not change anything at all is indefensible.  Let us consider for a moment a few of the vast collection of things which are changed on each of the unreported missions.

First, as soon as the team from the future lands on the aircraft, the weight changes slightly, and the flight path is therefore altered.  The degree of change may be unnoticed by the pilots; but a fraction of a degree of angle in any direction could prevent a mid-air collision a minute later, or shift a crash site by several miles.  Then our team enters the scene, inhaling the oxygen of our day, and exhaling carbon dioxide brought back from the future--a net increase in elemental carbon in our time, balanced in the future by a net decrease.  The sweat from their bodies is picked up in the atmosphere, increasing the humidity, transporting water from the future to the present.  The team begins to move around, and--since every action creates ripples of reaction in the world--they create vibrations and movements which are different from those created by the original crew.  Then they off-load a couple hundred bodies and replace them with bodies which will not be distinguished by our examination.  But a body which is identical in appearance is not the same body.  The object of our team is to prevent men from knowing that the world has been changed.  They fully intend to change the world.  It is unlikely that any or all of the two hundred bodies removed from the plane has exactly the same mass, to the molecule, as those which replace them.  Even if it were so, the ratio of elements within those bodies will be very different.  Perhaps there will be more bone and less fat--an increase in calcium at the expense of hydrocarbons.  We are changing the chemical balance of the universe.  And, even if we assume anything so absurd as that our futurists have managed to transport the exact molecular weight of each chemical, it is still not the same matter.  At the moment at which the switch is made, countless molecules, unimaginable numbers of sub-atomic particles, are removed from the world for a thousand years, and replaced with other sub-atomic particles.  But these particles, these atoms, already exist somewhere in the universe.  We now have a temporal duplicate of each particle:  because it has been moved in time, it exists in two places at once.  Now, I have no problem with temporal duplicates; they do not in themselves cause major anomalies.  But they do mean that the universe has changed.  To suggest that the universe has not changed merely because humans existing at the time don't know it has is extremely parochial and anthropocentric, not to mention foolish.

Thus Coventry's words become hollow:  "[Y]ou know...[very] well we can't change the past.  It catches up with us.  We change."  It is true that changing the past changes those alive after it.  But it is just as clear that Coventry, Louise, and the rest are involved in a systematic effort to do exactly what he says cannot be done:  change the past.  The molecules which are being removed from the past are very likely to have been found in people alive in the future--even in Coventry and Louise.  They are changing.  At the same time, to our perspective on the universe, the specific molecules which form our bodies are not so important as the events which form our history.  Thus when Coventry says, "His life affects thousands of other lives in an endless chain; and if you break it..." (completed by one of the team members as, "...you get a thousand years of bad luck, and none of us is here anymore"), he puts his finger on that distinction.  It is alright to change the past, as long as the changes you make do not make the present so different that you would not go back to make the changes.

However, the idea that a device could be used to detect changes in history is somewhat dubious.  The database of such a device would be altered the instant history itself is altered, and so it could not detect change itself.  It could only detect the divergence of an altered time line; and this always happens, and always happens totally and absolutely, whenever anyone returns to a point in the past.  Whether time has been altered so drastically as to create something other than a benign N-jump is much more a question of the details of history, not a question of a change in time itself.  The red spot should always appear on the board when Louise goes back; every change in history is a potential paradox, the severity of which is determined by the historic facts, the question of whether the past is dependent upon a future which is dependent upon that past.  An infinity loop occurs when an event prevents itself, or sometimes when an event is a necessary cause of itself.  A sawtooth snap occurs when the nature of an event or collection of events is altered by a change in its own nature.  An N-jump occurs whenever time is altered, but the nature of the change in the past will not change the nature of the change in the past.

Thus we can appreciate that the changes which were made by previous missions were such that the effect on the future was minimal.  All of our time trips prior to the opening of the film have produced relatively inoffensive N-Jumps:  all of history has been changed in ways which will be unnoticed by anyone at all, and which will not in any way prevent the fact that it will be changed in those exact ways.  All has gone well until the 1989 crash.  This time there are several errors.

The most critical error in the 1989 crash is that one of the team dropped a stunner on the plane.  It is not clear whether she was attempting to escape the plane before being seen, or if it was just carelessness.  However, the dropped stunner becomes a problem, and sets up the problems in the future.  But there are two other errors which are important.  One is that there are digital watches on some of the bodies, running backwards.  This I do not understand.  We are supposed to think that the digital watches are running backwards because they were exposed to the time field.  However, we don't imagine that the team removed watches from the wrists of passengers and put them on the corpses.  Like everything else on this plane, the copies come from the future.  And if passing through the portal would cause the watch to malfunction, those in the future would either design the watch so that the malfunction would make it appear correct, or make all of the watches non-functional.   Those watches are a nice touch, an interesting plot device, but an unlikely discovery.

The other problem is the bodies.  The plane has lost an engine, and part of a wing.  The damage cannot be seen from the cockpit, so the engineer leaves his seat to move back into the passenger compartment to visually inspect the damage.  He then sees the dead--all of the passengers have been removed and replaced with charred bodies.  Racing back to the cockpit, he announces this, and it is picked up by the cockpit recorder.  This becomes an important point in the mind of crash investigator Bill Smith.  The physical evidence says the bodies burned on impact, but the voice recording disagrees.

The bodies reflect another problem to me--the problem previously mentioned about making changes in the past.  Our futurists are not thinking clearly.  They have loaded charred bodies onto the plane.  That means they have already burned out some of the matter in the future which they should have returned to the present.  It also means that these bodies are going to be overly burned--they will be burned again when the plane crashes and the jet fuel ignites in the cabin.  And we are forced to wonder whether they were properly burned the first time--will there be residue of twentieth-century aviation fuel in the burns, or will there be some other chemical?  They are hoping we won't notice; but they have changed the past significantly none the less.

I dare to suppose that this trip has caused an N-Jump.  The damage done to time is more serious, perhaps; yet we know that it was not fatal to the future, because nothing has happened which will necessarily prevent the events of the future, and the fact that the future occurs gives us reason to presume that nothing has been prevented.  Think about this for a moment:  the team from the future has lost a device.  Yet they still exist in the future, still have their time machine, still have made the trip on which the device was lost.  The team in the future falls into the mistake of thinking that if they make a mistake in the past, they can fix it before it destroys the future.  This is fuzzy logic, and will not hold.  By now, I would expect you could see why; however, Coventry and Sherman (the controller of the time machine and the personal robot) did not understand this at this point, so allow me to clarify it for their sakes.

At a particular instant in the thirtieth century, Louise Baltimore entered a time machine and went to a particular date in 1989.  Like Marty McFly visiting his parents, as long as she remains in 1989 her actions will alter the future.  Once she returns to 2989, those alterations have been effected:  whatever her history and the consequences from it, all has fallen into place.  No history of the world exists save the one in which her team went back to 1989 and lost the stunner.  If that stunner would eventually change her history in a vital way, by 2989 that change has already happened.  She cannot prevent that change from affecting her time; she can only attempt to reverse the changes by going back again to create a new altered history.  She cannot stop what from the 1989 perspective is going to happen, because once she reaches 2989, it has already happened.

However, the wisdom of the council does not comprehend this, and determines that it is necessary for Louise and her team to return to 1989 to recover the lost stunner.  Let me give a word of advice to time travelers.  If you lose something in the past, forget it, it's lost.  After all, if you have the ability to return to the past to recover the device, then you have not destroyed the timeline completely; there's no point worrying about what changes might have occurred, because they have occurred.  You cannot know how your present is different from what it might have been before you left it.  What you do know is that if you go back for it, you will change the time line again, and this time you might do something which will destroy time completely.  In our case, Bill Smith does find the stunner, and succeeds in stunning himself.  I would bet that in this time line (in which he has not previously met Louise, as that trip has not been made) he finds it interesting, but after showing it to a few people, attaches no importance to it, and tosses it in a drawer somewhere to look at another time, where it is forgotten.

As foolish as it is, Louise and her team go back for the stunner.  They find Smith, whom they do not recognize, lying on the floor; they get the stunner, but not the initiator, which he removed and still has in his hand.  Again the film demonstrates its ability to recognize the right questions:  Louise is upset because Smith saw her.  The memory of her appearance is itself a change she has made in the past.  In the original timeline, and in the timeline created by the boarding of the 1989 plane, no one had any memory of her.  But now she has left a thought impression of herself in the past.  It will affect the lives of those who saw her, at least in some way.  How it will affect them depends on what they believe about what they saw, and what they do because of it.  As to Smith, he has no idea who these women are or how or why they got to him.  All he knows is that he found some gadget he didn't understand, and was stunned by it in an unfamiliar manner, and that three strange women stepped through some kind of seemingly magical portal to take the gadget from him, leaving the same way.  He has a piece of it still, so he knows it is not a hallucination.  He may develop some of the paranoia we see in a later altered timeline, although not to the same degree.  Likely he will turn in a crash report which doesn't mention these details, and wonder about it for the rest of his life.  As it stands now, he probably won't even mention it to Dr. Mayer (we're getting to him in a moment).

Two plot devices are introduced at this point.  I am uncomfortable with both of them, but they are worth considering.  The movie introduces the timequake and temporal censorship.

The timequake, as a plot device, is an attempt to convey the dangers of changing history in a dramatic way to a mass audience in a theatrical experience.  We will forgive it on that basis; it's actually a rather compelling effect.  But there are several levels at which it does not withstand scrutiny.  First, perhaps I am mistaken, but whether you change history a tiny bit or a great deal, you have created an entirely new history.  It may appear the same in many ways, but it will be different.  For example, we have replaced the matter constituting the bodies of the living with the matter constituting the bodies of the dead.  These bodies, whether the originals or the replacements, would have been disposed of in ways which return their matter to the environment--whether by decay or by burning, the molecules are released.  Some of those molecules will find their way into the bodies of other people over the centuries.  Even if those same people perform the same actions, it now will not be the same molecules performing those actions, as the original molecules have been removed and replaced by others, temporal duplicates of molecules which exist elsewhere in the universe.  Thus at one level--the level which is important for the physical consequences of a change in history--every change is total, creating a totally unique time line, and therefore creating a full-scale timequake.  It is not the shaking of the world which is the outcome of a change in history.  It is the changing of events and of people which matters; it is the growing danger that because of something in the future, something will happen or not happen in the past which undoes the thing in the future that causes the change in the past.  Once that happens, an infinity loop is created, and time exists no more, save in its own perpetual repeat.

Temporal censorship is an entirely different matter.  We should have guessed that our futurists had a means of viewing the past without entering it.  They create a couple of ground rules--first, that they cannot return to the same point in time twice.  I cannot think of a reason in physics why this would be:  if you can have a temporal duplicate of the matter comprising your body once, why could you not have a dozen, a hundred, temporal duplicates of that matter?  And if you assume a spirit-based sentience (rather than a fully materialistic one, which affords no reason at all to question why a personality could not exist in two places at the same time), why could a spirit capable of being moved non-sequentially in time not also exist in two places at once if temporally duplicated?  However, it is a good ground rule not to return to meet yourself, because you will then remember the meeting, and that memory will change the experience, changing the memory, changing the experience, creating a sawtooth snap, a rather unstable anomaly which once begun is difficult to predict.

The other ground rule is the suggestion that the temporal viewer cannot see the events of any time to which the team has traveled or will travel.  At first, I was tempted to write this off as a foolish but necessary plot device--it would make the story very awkward if the time travel team could see what they had not yet done in the past.  But there is no intrinsic reason why they should not be able to see what they have already done in the past, even if they have not yet done it in the future.  The effects of their actions have left traces in history.  There could even be newspaper accounts and photographs related to the crash.  With enough research, the team could discover themselves in history.  The reason for not allowing them to use the machine to see themselves would appear to be plot-related.  Consider:  is it only to times to which they have traveled or will travel that they can't see, or to times which will ever be the target of any time travel by anyone anywhere in the universe?  If the latter, then there will be huge periods of time completely inaccessible due to the proliferation of the use of time machines in the future of those societies which manage to create them (in whatever galaxy); but if the former, then all we have to do to see those portions of the time line is to have Louise leave the room.

But perhaps the film has oversimplified the concept.  Let us suggest instead that it is not that the viewer cannot see any time to which anyone has traveled or will travel.  Instead, let us observe that the instant the altered timeline occurs is the same instant the time traveler steps into the past, but that the spatial location of the arrival is immediately the focus of all of the changes which will occur.  At those time-space coordinates, two universes exist, two timelines, close enough that they could interfere with each other.  On this assumption, it should be possible to view that moment, as long as you did not attempt to view that place.  So I will allow a localized temporal censorship to be more than a plot device, an actual possible description of the effects of attempting to use certain types of temporal viewers to observe moments in time in which anomalies are focused.  Now, back to the story.

The next anomaly is created when the team goes to a 1963 crash.  Were I Coventry, I would not have allowed this trip, not because I could have forseen any of the problems which occurred, but because there were too many risks involved.  Let us consider the ramifications of this trip.  We know that a plane crashed in 1963; we know everyone on board sufficiently to create replacement bodies.  But we also know that there was one--only one--survivor of the crash, about whom we know so little that we aren't even aware that he will grow up to be NTSB crash investigator Bill Smith.  Furthermore, we don't know what caused the crash.  Therefore we are faced with the challenge of removing everyone from the plane before it crashes without the boy noticing, and then duplicating the crash with such precision that the boy still survives--without knowing anything about what the boy did which caused him to be the sole survivor!  Did he sleep through it (which is what he will do this time, thanks to their stunner), or run screaming through the aisle?  Did the passenger in the next seat throw himself on top of the child to protect him?  There are too many unanswered questions to pull this off, unless we plan to stun the boy and dump him on the grass fifty yards from the crash site, giving the FAA another mystery to resolve.

On top of that, even if everything went right, nuances may be extremely important, and extremely important to the particulars of the time line between 1963 and 2990.  Remember, every crash in the United States is meticulously investigated.  Everything that is learned from each investigation is used to improve safety throughout the airline industry, so that future crashes may be prevented.  But the team, from its time line, has already boarded planes crashing after 1963.  Something they do now, on this 1963 crash, could change the information gained from the crash by the investigators.  If something is learned that was not learned in the original timeline, or if something learned in the original timeline is not learned this time, it could have a major impact on which planes will crash in the future.  Coventry and the council pretend that they are so very careful; but I would never send a team back to a crash which is earlier than another crash I've already visited.  It creates too many risks.

In the actual case, things could not have gone too much worse.  The plane crash was apparently caused by a terrorist firing a gun; our team does not know when he fired it or where he was at the time.  One of the team takes a bullet; another fires the stunner in full view of the survivor (whose age I estimate at about 14, old enough to know a ray gun when he sees one).  The boy is left on the plane, stunned and strapped in, as the others are off-loaded in a haphazard way.  A stunner is dropped, and the survivor sees it, but it goes down with the plane.  Coventry orders an explosive placed on the windscreen to simulate the effect of the bullet.  (This can't possibly work.  In order for that boy to survive, the crash must be identical.  The plane must be in the right place moving in the right direction at the right velocity, the explosive must go off at the right instant, the cockpit crew must do whatever they did, even if it was only tilting the plane as they are yanked from the controls and blown out the windscreen.  Only then will the plane hit the ground in the same spot at the same angle; and only then will the boy be guaranteed survival, and the FAA/NTSB investigation draw the same conclusions.)

This creates another question about the original time line.  We have seen a Dr. Arnold Mayer who is always asking questions, seeking the inexplicable in crashes.  The Nobel laureate lectures on the possibilities of time travel, and we can hear suspicion in his voice.  But in the altered timeline, he has the stunner.  Dropped in 1963, it came to him in 1964, minus an initiator.  His interest in time travel may stem from this device.  We are forced to wonder whether Dr. Mayer took any interest in airplane crashes in the original time line.  In any event, his interest and his questions reflect his knowledge that he has something which cannot possibly exist unless it comes from either the future or another world.

The council has a very different concern.  They perceive that Bill Smith has an initiator and knows what it does, and Arnold Mayer has a stunner; they conclude that if Dr. Mayer gets what Bill has, he could come to understand the stunner before it is invented, and create a paradox.  They wish to prevent this.  However, this only reveals how poorly the council understands the nature of temporal anomalies.  Their logic is fuzzy on several points.

First, if the disaster they wish to avert is going to happen, they are too late.  By 2989, all of the consequences of that dropped stunner will be part of history.  If it would destroy or damage the time line greatly, it has done so.  When Louise says," I can still stop the paradox, if I leave right now", what's the logic of that sentence?  If the disaster actually happened, they would not be able to discuss what to do about it; if the disaster has not happened, it matters little whether she goes immediately or next year!  So they should just leave well enough alone.

Second, their idea of a plan is to send Louise back to prevent Smith from being in the hanger at all.  One of the first rules about time travel that I constantly emphasize is that you should never go back into the past with the specific intent to change the past.  If the universe is lucky, you will botch so badly that you disappear from the timestream entirely.  Otherwise, there are only three possible outcomes.  You could fail completely, but leave the history intact enough that you will be foolish enough to attempt to make the change at the same point in time in the altered history.  This is the best possible outcome, and the one which happens in this story.  You could fail and in the process make it impossible for you to make the attempt; for example, if you were to accidentally kill someone whose work would ultimately make time travel possible, you would have erased your ability to return to the past, and thus undid the change, restoring the possibility, and the change, and so looping infinitely.  Or you could succeed--very likely the worst possible outcome.  Imagine for a moment that you decide in 1998 to prevent the Holocaust and derail World War II by killing Adolph Hitler while he was still a young lad.  So you go back to the years before he was known, and kill him, and return to 1998.  But now history is different.  Time has moved from the 1940's to the 1990's without Hitler.  Perhaps there was a war; there may even have been a holocaust.  Or perhaps this was all averted.  But the name Hitler has no meaning to anyone.  It has no meaning even to the you that has lived in this timeline and gained the ability to travel back in time.  So you have no reason to seek the boy or to kill him, and you won't.  But since you won't do this, he will come to power, which will restore your reason.  Time again is caught in an infinity loop, unable to advance beyond the moment at which you did or did not go back to kill Hitler.

That is the danger Louise faces.  As soon as she goes back in time, she creates an alternate timeline.  But it is this altered history which we have watched.  We should consider what the original time line was like.  There is already an N-jump created at 1963; Dr. Mayer has the stunner in the altered timeline from that event.  We have also branched off to a new timeline with the boarding of the 1989 crash and the loss of the stunner there.  Bill Smith is investigating the crash, and something bothers him--the cockpit recording perhaps, or the watches, or Dr. Mayer's questions concerning what unusual facts had been uncovered.  He stays with the scrap after closing, finds the stunner, pulls the initiator from it, and is stunned.  Three strange women appear from nowhere, take the stunner (but not the initiator), tell him things will be alright, and vanish just as quickly.  He recovers.  He is confused, perhaps disoriented.  But he no longer has the stunner.

I have wondered why Bill Smith does not show the initiator to his NTSB superiors.  He knows it doesn't belong in that wreckage.  He probably knows it has nothing to do with 20th century earth technology.  But in the unseen timeline, he either did think to give the device to the NTSB, where it was lost in government red tape, or decided that the device had nothing to do with the crash, and filed a report which left out the details which might cause his boss to think him crazy.  Perhaps to satisfy his own curiosity he did visit Dr. Mayer; or perhaps he did not.  His motivation in the matter is very different:  Louise was nobody to him then.  He didn't even know her name.  And, since it is not necessary that the future would be destroyed at this point and we see that the future was not destroyed, we are justified in concluding that the consequences of Bill Smith having the initiator are minor.

But the council doesn't see it that way.  They decide that Louise must prevent Smith from finding the stunner, and send her back to prevent him from being in the hanger at all.  In sheer foolishness, they declare that the fact that that time is hidden by temporal censorship is proof that she will make the trip.  (If she has already made the trip she will make, then she must have failed, no?  Had she succeeded, then Smith would not have been in the hanger!)  She makes a point of meeting him, seducing him, and trying to prevent him from going to work.  She fails.  But she does succeed in getting him emotionally involved with her; and she succeeds in disrupting his perception of the universe.  She has begged him to stay, and he has walked out.  Believing that she has failed, she calls for the gate to the future, and exits in seconds.  He returns to the room to say something else, and she's gone, vanished into thin air.

This time they have done some damage.  Smith is now fixed on finding out what happened to the girl, even more than the gun or the plane.  He has no idea who she is, where she came from, or what's going on.  But he is intent on finding her, and it's affecting his work.  Again, I wonder why he does not show the initiator to his superiors--it is the one piece of real evidence he has that something is happening here outside the ordinary.  But it becomes apparent to everyone that he intends to solve this, and to find the girl.  He is going to go see Dr. Mayer.

And again the time travelers demonstrate their ignorance.  Louise says she must go back and prevent Dr. Mayer from discovering the true nature and purpose of the device, even if she has to reveal who she is.  Now, why she can't meet Smith on his way to Mayer, and take the device from him then, I have no clue.  Instead she shows up while the two are talking about her.  But a more basic question is, why does she have to interfere at all?  Face it, we are in the same situation all over again.  If the meeting between Dr. Mayer and Bill Smith will be a disaster, the disaster has happened.  If Louise is capable of interfering, then her timeline has not been destroyed by her actions.  She does not need to change time to save her world; the damage is done, and her world has survived.

But she does go back.  She comes into the room where Dr. Mayer has just explained to Smith that she must be a time traveler; and this time she doesn't get away with it.  Dr. Mayer, who was to have lived another six years and make at least one more significant contribution to science, is killed when he puts the initiator onto the stunner.  History is changed.

Please note that this must not have happened in the previous timeline.  Dr. Mayer had to have survived.  Therefore either Smith did not give him the initiator, or Mayer was a lot more careful about what he did with the two pieces.  It is Louise's presence which inspires Mayer to carelessness, to taking rash action before she grabs his precious stunner and runs.  It is this last trip which causes the disaster.

How that disaster is caused is not fully explored.  There are several possibilities, of which I will only note a few.

Mayer was a physicist; it is possible that the work on the time machine is built on his theories.  Although in the realm of science it is generally the case that ideas are due, and will be discovered by someone else soon enough, the most significant ideas, such as Newtonian Mechanics and Einsteinian Relativity, may lie undiscovered for a generation if missed by the genius whose name they bear.  Mayer has been curious about time, and lecturing on it.  He is a Nobel laureate in physics and a professor, so he undoubtedly serves as a counsellor for Ph.D. candidates, any one of whom could have been radically influenced under his guidance to discover an essential aspect of time for which he would not have looked without the doctor's comments.  Thus it might be that the time machine itself would not have been created in time for these trips to have been made, and therefore the trips could not have been made, and Mayer's life would not have ended.

Of course, Mayer was a prominent teacher, the kind of man who attracts students to a school who hope to have the opportunity to learn from him.  This creates another area for potential change.  If as few as two people meet here and marry each other who would not have done so without Mayer--if they would not have been in the same class, or even in the same school, because the school or the class would not have had the draw of a Nobel prize winning scholar--there would be a ripple effect.  It is likely that these two people would have married two other people.  Those two other people now would not have married their original intendeds, and so two other people will have married two other people.  The ripple effect of this is apparent and, although it will not spread to the entire population of the world, its impact is multiplied by the birth of a portion of the next generation whose identities are entirely different, and whose interaction with the gene pool will again create new people.  By the year 2989, it is likely that no one who would have been alive was ever born, but that others were born in their stead.

Finally, Mayer was a noted ecologist.  For better or worse, his six remaining years could have had some impact on the state of the earth.  The survival of humanity is at stake here, and if his actions saved even one generation, it could be the generation of Louise and Coventry, the generation that builds the time machine and travels back to us.

Thus we see that there are at least three distinct ways in which the death of Mayer could create an infinity loop, ending the progression of time itself.  Although it is not a necessary consequence, it is the definition of the type of paradox which those in the future hope to avoid; and since the paradox has happened, something like one of those things must have resulted from Mayer's death.

Louise panics and, adding insult to injury, she grabs Bill Smith and takes him to the future with her.  The audacity of this is astounding.  After all, Smith's life is in the past.  Whatever changes are made in the future, the year 2989 is far enough away that he will never reach the point at which time ends.  Louise Baltimore is taking him to the point in time which may no longer exist, and increasing the probability that it will be destroyed by removing someone from the past who still might have some impact on the future.

And after all this, the narrow-sighted Coventry blames Smith for destroying the timeline.

Council leader Stockholm sums up the nature of the disaster quite succinctly, but then ignores her own analysis by suggesting an impossible ending to the story:  "Our world is at an end.  All evidence of our existence will be washed away.  We must attempt to send those we have saved into a distant future that may lie beyond the gate.  Coventry:  reverse the gate."

The disaster must be as Stockholm says:  she and all her people, Coventry and Louise and the time machine, have all ceased ever to have existed.  But if that is the case, then all of their work has been undone, and no one has been saved.  This is the infinity loop:  two alternating histories, each caused by the other, dependent upon the other, each repeating in perpetuity as the events which support it vanish and are replaced by the events which support the alternate timeline.  Time does not pass beyond the moment the last time traveler went back and created the problem.  So there is no one to save, and no one to save them.  Beyond that, there is no future beyond this time, no better time to which they can be sent (unless there could possibly be some type of convergence of history, some point at which all things would be the same regardless of what the history of the world in this millennium might have been--but how could time advance through the intervening years to reach such a point?).

No, Sherman's closing words of wisdom are wrong.  This is not the end of the beginning; nor is it the beginning of the end.  It is, in fact, the end--a cul-de-sac in time, but the end nonetheless.