However, the film is not without its flaws.  And since I undertook this task knowing that it was about quibbling over nonsense, arguing about the realities of fantasy, I shall endeavor to quibble.  There are a few problems with the story as presented, at least from a time traveler's perspective.  As to the other aspects--the consistency with the Star Trek history, the strength and integrity of the characters and the world, the tension between the heroes and the villains, the protagonists and the antagonists, the desired outcome and the obstacles, it is a fine film, a worthy entry in the Star Trek series which should be remembered as one of the better pictures in the years to come.

The Borg are back.  They have targeted the Federation, and identified earth as the prime target.  Captain Jean-Luc Picard, now in command of the Enterprise 1701E (the sixth ship to bear that name and number, and the fifth to appear in the Star Trek movies), is ordered to patrol the neutral zone to assure that the Romulans don't take advantage of the situation to claim any territory.  At first you might expect me to applaud this thinking.  I've already said that following the great Borg attack of the series, the Romulans and Cardassians would most likely have moved into Federation space, cutting up pieces of it for their own empires.  However, this is not the time.  The Romulans are not going to create problems for themselves.  They will consolidate their situation, fortify their borders, and watch.  If the Federation falls to the Borg, they are in for a tough fight, and do not need to be recovering from even the minor scrapes of a quick conquest.  If the Federation defeat the Borg, that is the time to strike, and not a moment sooner.  (This might be a plot for a new movie--and it could bring in an appearance by Ambassador Spock, last seen assisting the Romulan underground, a plus for attracting hardcore original Star Trek fans.)  Picard and the new top-of-the-line starship are needed at that battle, and should be there, whatever reservations command might have concerning his reaction to facing an enemy which once captured and brutalized him.

The fleet is losing, and Picard knows it.  Violating his orders with full support of his crew (and who cares about the Romulans if the Borg win?), he charges at maximum warp (doesn't that violate some kind of environmental regulations for the protection of the fabric of sub-space?) and takes command of the fleet in the absence of the admiral (he should have been promoted to commodore as I suggested in Generations; it would make this more believable), and orders a very specifically targeted attack on Borg systems previously ignored.  He destroys the Borg Cube; but we are abruptly introduced to the Borg Sphere, something like an escape pod, but larger than a starship.  Picard orders a pursuit course, and in a moment our time travel adventure begins:  the Borg create a temporal gate of some type, and head for the past.  The Enterprise, caught in the wake, notices that the earth has changed in appearance, and scans to find it now a well-established Borg colony planet.  Realizing that the Borg have changed history, they follow the sphere through time to correct the changes and restore the Federation.

That moment--the moment at which they see an earth colonized by the Borg--is a problem.  That moment cannot exist on any set of assumptions you choose to take.  There is no history which will result in an earth fully colonized by Borg at that moment.  The logic of this is inescapable, once the alternative possibilities are clearly understood.

There are only two possible basic assumptions concerning the time travel events at the beginning of the movie.  Either the Enterprise and the Borg went back in time in the same temporal event, or they went back in two separate consecutive temporal events.  If there are two separate consecutive events, it doesn't matter whether the second, in which the Enterprise returns, is a consequence of the first, or even if it is a necessary consequence of the first (if because the Borg went back the Enterprise could not have avoided going back had they wished to do so); two separate events require the a separation of either time or space (or both), and since it is clear that the two events happen at the same point in space, they must be separated by time.  Indeed, if there are two separate events, the scan is revealing to us that the consequences of the first event have come to pass, and that the Enterprise must go back in time to undo them.  In contrast, if there is only one temporal event, the scan must be revealing the alterations to history caused by that one event in which both ships returned--a possibility we should examine in a moment.

It is clear that we are to accept the notion that the two ships went back in separate events; that the scan is revealing to us the consequences of the sphere returning into the past without the Enterprise behind it.  In a flash, we see a history develop:  arriving at some point in the past, the Borg quickly and easily overrun and conquer earth, destroying the Federation utterly.  All of humanity, all of the Federation, all of Star Fleet--everything we have come to know about the Star Trek universe--is obliterated in a single blow.  We know that it took place in 2063; we know that it is about 300 years later that the Enterprise has destroyed the cube, forcing the sphere to flee to the past.  But now the Federation and Star Fleet no longer exist.  The obvious consequence of this is that the Enterprise and its crew also cease ever to have existed; but the movie is ready with an answer to this one:  somehow (unknown to those experiencing it) being in the temporal wake, caught up within the confines of the time trip itself, the Enterprise is protected against this change.  It is a lame explanation--if history has changed, the Enterprise cannot have reached this point, and cannot be here.  However, I will not argue with the mechanics of time travel when they are not explained; besides, I don't have to.  The Borg have gone back in time to colonize earth before the Federation becomes a problem; the trip is a reaction to the circumstances of 2360 (an approximate date), with the intention to change those circumstances.  If the Borg fail (a remote possibility, but it is imaginable that the sphere is already damaged and will explode in the past before its crew can escape), then the history we are seeing in the scan never existed.  However, if they succeed--the implication of the scan--then the Federation never comes into existence, Star Fleet is never created, Jean-Luc Picard is never Locutus of Borg, the Enterprise cannot destroy the cube, the sphere will not go back to 2063, and history does not change.  But if history does not change, then it does change; and if it does change, it does not--that is, an infinity loop has been created, each alternate history dependent upon the events of the other.

If there are two trips through time, then that intervening moment in which the scan was made (whether it is a picosecond or a millennium) occurs after the first trip.  But if the first trip makes itself impossible or prevents itself from happening, then there is no time after the first trip.  The original time line advances to 2360 and ends when the Borg return to 2063; the replacement timeline advances to 2360 and ends when the Borg fail to return to 2063, restoring the original timeline.  That next picosecond does not exist; therefore it cannot be scanned--if there are indeed two separate time travel incidents.

Before we examine what would happen if there were only one time travel incident involving two ships, I would mention that although there is a similar problem with the (now impossible) second trip, it would not have proved fatal.  Let us suppose that Picard was able to scan earth while pursuing the sphere.  Does it particularly matter what he finds?  Picard is a man possessed, obsessed with the destruction of the Borg.  Whether he knows what they are doing or where they are going, he will follow them; and even without the scan, it will be apparent to everyone on board that if the enemy which has now twice decimated the fleet attacks in the past, earth will fall and become a Borg colony.  And no one would doubt that if the Vulcans don't chance to stumble on the humans on schedule, the Federation is in jeopardy.  Neither the Captain nor the crew need to be told that the Borg must be stopped before they destroy the time line; his trip to the past does not hinge on altering a time line already established (even a previously altered timeline is an established time line), but on a desire to stop his adversary wherever it may be found.

If both ships go back in the same temporal trip--if our travel through time is a single extended event during which the Borg and the Federation both enter the past--then it is obvious that the scan of earth will reveal the results of both ships being in the past.  If in this case the scan reveals that the Borg have conquered earth, then we know that the Enterprise has already failed, and will not succeed.  However, once again we are faced with an infinity loop, and it is doubtful to me whether in leaving from the end of one segment, one side of the loop, you would be able to see the end of the other segment, the alternative history.  Beyond that, if the Borg win in the past, they again lose the incentive to return to the past, and they fail to attack in the past.  Thus the same infinity loop is created when the Borg win, whether or not the Enterprise travels to the past.  But if, as the rest of the story tells us, the Borg lose, then the scan will reveal an earth populated by humans and part of the federation, although there may be minor changes to the world as a whole.  But if the Borg would have won except that the Enterprise learned something from the scan which will cause the Borg to lose, when the Borg lose that information is erased, and the Borg will win and another infinity loop is created.  So whether there is one time trip or two, and whether the Borg win or lose, that moment of that scan cannot exist, except if there is one trip, the Borg win in the first segment, and the Federation wins in the second segment, both relying on information from the end of the other segment, both creating an infinity loop--and Captain Picard's future is no longer waiting for him in the twenty-fourth century.

However, we will forgive the scan.  Although it is impossible on any save the worst and least likely outcome, it is an important plot device.  The crew knows the consequences of the Borg returning to the past (although they might not comprehend specifically the dangers of an infinity loop).  It is for the sake of the audience that the film treats what might happen as if it had happened--much as the mushroom cloud which is shown not happening over Europe when the Q-bomb does not explode in The Mouse That Roared.  It lets the slower thinkers in the audience keep up with the ideas in the movie.

The changes which the Borg make in the past are potentially critical.  They kill a number of mostly young and intelligent human beings; although this is a relatively small number in the total population, we observed in Star Trek IV:  The Voyage Home that the removal or continuation of a single person in the time line could alter the genetic pool so drastically that in 300 years no one will have been born who would otherwise have been.  This does not seem to have happened--with over a thousand crew and family members on the Enterprise E, a drastic change in the population of earth would have been noticed in the personnel roster (remember, Troi is half human, and Worf was raised by human parents who encouraged him to enter Star Fleet--even they are not immune to this effect).  Somehow it must be that the impact of the dead would have been minimal beyond what they did on the Phoenix project; it seems unlikely, but it is not impossible.  They have also not merely attempted to destroy the Phoenix project, they have also rewritten a chapter of its history.  Heroes of that original warp voyage are now dead, and new heroes are replacing them.  But these minor details of history are not inevitably destructive of the time line, only potentially so; and the movie may be excused for deciding that none of the changes were significant to the shape of 2360.

The changes made by the crew of the Enterprise are minor in comparison.  Of course, both ships and their crews will leave material behind and take material away--from sweat and waste heat to space ship pieces.  But there are three changes which are made by Enterprise which are independent of those made by the Borg.

Zefram Cochran's view of himself has been altered.  He has learned that history regards him a hero, a pioneer, the architect of a new world.  He is none of those things in his own mind.  Now he has seen pieces of the future--things he will do, things he will say, things which will be done in his honor.  At first it is overwhelming, even undesireable.  But as he shakes hands with the Vulcan visitor, it is a different Zefram Cochran who does so, with a different view of himself and his place in history.  Perhaps it will make some difference in the world of 2360.  After all, words said or written by Thomas Jefferson, Abraham Lincoln, and Benjamin Franklin have all changed some parts of the way we view the world today--and there are others before them whose names and words are forgotten to most of us, but whose ideas have become so much a part of our thought that had they been different, we would be different.  The effect on the world of the change in Zefram Cochran cannot be guessed; it should not be underestimated.

Lily has also changed.  The female first assistant to Zefram Cochran was part of a project.  But she has been on the Enterprise, has seen the warp drive star ship of the future--and has encountered both friendly and hostile aliens.  Her conception of the universe has changed completely.  Will she tell anyone what has happened to her?  Perhaps not; but her new view of reality will be infectious.  The world will change because Lily has been somewhere she could never have imagined.  Again, the effects of this are difficult to gauge.  Other members of Cochran's team will have also been changed at least a little by their encounters with the men from the future, and in unpredictable ways; but Lily is the one who will be most dramatically different.

The third point is best illustrated from another direction.  I would wager that in the population of the world at large, at least one in ten people would be able to identify the names Buzz Aldrin and Mike Collins.  (Of those who would be reading a paper of this sort, I would invert that number:  only one in ten would not know these two names.)  Neil Armstrong was the first man to step on the moon; but he was commander of a three-man mission, and history has not forgotten the names of his two companions.  However, the two companions of Zefram Cochran will now be remembered as William Thomas Riker and Geordi LaForge.  Perhaps the original team could not do it--Lily was, I think, intended for flight engineer, and she has just escaped from the Borg on the Enterprise and is not there yet; the other team member may have been killed in the attack.  But unless everyone involved agrees to the same lie (and someone will probably tell the truth eventually), those names are lost.  It is a small thing; but it is a change in the history books themselves, a detail that would have been recorded but is now lost.  This is, of course, why a sawtooth snap is created.  It is doubtful that Riker, LaForge, and the others could know so much about Zefram Cochran and the flight of the Phoenix, and not one of them know who sat in those other two seats.  Thus in the A-B segment, those names are probably known to history, and the crew that returns to the C-D segment knows them; but at the end of the C-D segment, those names are lost or replaced, and the crew that returns to 2063 does not know them--a minor change, but enough of a difference that it requires an E-F time segment to accomodate the difference.  In fact, the Zefram Cochran of history, the Zefram Cochran whom Zefram Cochran says doesn't exist, may himself be the result of seeing his own future; and this may induce a couple repeat snaps, while the information stabilizes.

While we are quibbling, I am a bit suspicious about how the Enterprise E will return to the future.  They don't actually get there in the film as shown, they merely say they will recreate the time passage by duplicating the output of the sphere, and follow the path in the other direction.  But first, since the Federation does not understand how time travel is accomplished they cannot be certain which of the many fields generated by the sphere was important, or even whether there was the generation of an energy field completely unknown to them and therefore undetected.  This seems the more likely, since the Borg have accomplished effortlessly what the Federation has yet to understand conceptually.  But even if the necessary energies could be precisely duplicated, that should logically result in Picard and company returning to 1863, and catching the age of the American Civil War--the event that they are copying was a trip back in time.  It is not even certain whether the same technique can be used to travel to the future; and yet the crew expects it to take them back to the future if they recreate exactly the same conditions that brought them to the past.  This is fuzzy engineering.  But of course, we don't know whether it worked.  The next film might be about the crew of the Enterprise E trying to scrounge parts and materials in the late nineteenth century as they work on a theory of how to get home to the Federation.  They might even enlist the assistance of Mr. Edison.  However, I, for one, would be content to have this be their last attempt to tinker with time.  As good as this was, the record preceeding it is spotty; and if it starts to come apart, they can no longer ask Mr. Scott to hold it together.