Several readers extolled the Disney/Pixar animated time travel movie Meet the Robinsons about an inventive orphan who meets a time traveling family and then discovers--well, already the spoilers start spoiling to be released.  Suffice it that it is difficult to imagine how the story could be more disastrous temporally speaking, but it is an enjoyable and fun story worth watching on its other merits.

It begins with twelve year old genius inventor Lewis, left by his mother on the steps of the orphanage as a newborn, who is thinking he will never be adopted, and his roommate Mike Yagoobian, or "Goob", who is an ordinary kid who plays baseball.  Lewis decides to build a Memory Scanner, to find the memory of his birth mother's face so he can search for her and be reunited; but his first test will be at the science fair.

Meanwhile, in the future by about one generation, teenager Wilbur Robinson leaves the garage door unlocked, and someone he calls Bowler Hat Guy (whom we will call Bowler for convenience) steals one of only two working time machines, and travels to the science fair to sabotage Lewis.  His hat, whom he calls Doris, is independently mobile and artificially intelligent, and is in fact the brains of the team, Bowler himself being comically stupid.  He intends to steal the Memory Scanner and sell it to Inventco, in order to ruin Lewis' life.  Wilbur takes the other time machine and pursues Bowler to the past, trying to prevent this, but Lewis does not believe Wilbur is from the future so Wilbur takes him there on his promise to fix the Memory Scanner if he does.  Lewis then decides he doesn't need his Memory Scanner because he can use the time machine to go see his mother on the day he was delivered to the orphanage.  In the ensuing squabble the machine crashes, stranding Lewis in the future; Wilbur says his dad is going to kill him, unless Lewis, the genius inventor, can fix the time machine.  Lewis begins working on it--after taking a wrong step and being introduced to everyone in the Robinson family, except Wilbur's father, as a new kid in school.

In the past, Bowler cannot figure out how to activate the Memory Scanner, so he can't sell it; he goes to kidnap Lewis, and instead finds Goob.  Goob is upset because, thanks to Lewis keeping him awake all night, he fell asleep on the baseball field, missed an easy catch, lost the game, and got pounded by his team.  Bowler counsels him to let his hatred fester.  Doris then deduces that Lewis fled through time, so they return to the future to kidnap him and learn how to operate the machine.

This is a comedy of errors, but is relavant only when Bowler kidnaps a tyrannosaur from the past and mind controls it in another comically failed effort to catch Lewis.  The Robinson family offers to adopt Lewis, but then his hat falls off and they see his hair, and from this recognize him, knowing that he came from the past, and saying he must return to the past.  Doris then has Bowler offer a deal, to take Lewis to meet his mother in exchange for instruction on operating the Memory Scanner.  Lewis complies, but Doris double-crosses him, leaving him stranded in the future as the villains return to the past to sell the machine.

The future begins changing around him; it is evident that Doris has conquered the world.  Lewis frantically manages to finish repairs on the other time machine, races to the past, prevents the changes, then drags Bowler forward to see the future Doris would have created, as it changes around them to the future Lewis has restored.  Lewis returns to his own time by way of a quick stop on the day he was left at the orphanage, and we have a happy ending with several loose ends secured.

There are a few critical facts omitted from this which are worse spoilers than all that was said, and which are fatal to the time travel adventures here; we cover those next.

We gave a brief overview of the story, but said we would next hit the really big spoilers.  These all relate to the relationships between people in the future and people in the past.  For example, there is a girl at the science fair doing something with frogs, and in the future she is Wilbur's mother, Francis.  One of the judges, Dr. Krunklehorn, is Wilbur's grandmother on his father's side.  These relationships are significant but not critical; three others matter much more seriously.

The one we have called Bowler, who is trying to ruin Lewis' life, is the grown up version of Lewis' roommate Goob.  He has never forgiven Lewis for keeping him awake all night before that game and so causing him to miss the catch because he was, literally, asleep on his feet.  That bitterness has been evident in every adoption interview he had thereafter, and he was thus never adopted.  It thus is very significant that Bowler has a conversation with Goob, because that conversation causes Goob to make the choices that form him into Bowler.  Obviously we have a problem there.

A much bigger problem arises because the inventive Lewis is Wilbur's father, inventor not only of the Memory Scanner but of a wealth of other products including the time machine.  When Wilbur takes Lewis to the future--well, that's several problems.

Finally, among Lewis' future inventions is a bowler hat with some artificial intelligence that was intended to help people get dressed, but which wanted a larger role in life, was taken out of service, and escaped to become Doris.

Time travel fans, and particularly those who follow this series, undoubtedly already recognize multiple problems here, and may be mentally scrambling to find solutions.  The filmmakers have done an excellent job of blocking all the obvious ones and several of the illogical ones as well.  We will address the story from the beginning, and create the timelines as they are formed, beginning with an effort to reconstruct the original history.

We know that there will be no time machine unless Lewis (who will change his name to Cornelius) invents it, and thus we know that he must become a successful inventor.  Further, Doris sabotages the Memory Scanner at the science fair, and then steals it expecting it to work once she fixes the part she broke (very risky, since operating it while it was sabotaged appears to have broken other parts).  Thus it seems most likely that the Memory Scanner works at the science fair in the original history.  Lewis wins, and is adopted by the judge and her husband, to become Cornelius Robinson.

While Lewis is winning the science fair, though, Goob is loosing the baseball game and being assaulted by his teammates.  He returns home, and now we step outside of certainty.  In the timeline we see, Goob is upset about losing but determined to get past it; Bowler persuades him to cultivate his bitterness instead.  Bowler is not here in the original, and that suggests that Goob will deal with the loss and move forward in life--and so never become Bowler.  Yet the problems start because Bowler steals the time machine, and so Goob must become Bowler.  What will bring us to that?

There is another difference in the history we see, though, as compared to original:  in the presented history, Lewis lost at the science fair and left with Wilbur to see the future, but in the original history he won and returned to the orphanage victorious.  Further, it is clear that following this victory he is adopted, the roommate whom Goob thought could never be adopted, certainly not before he himself was.  Goob's bitterness must arise from the fact that not only did everything go wrong for him, everything went wonderfully right for the kid whose fault it is, and indeed it all goes right for Lewis because Lewis chose to keep Goob awake all night while working on his project.  So Lewis kept Goob awake, and then while Goob was losing the baseball game and taking a beating for having done so, Lewis was winning the science fair because of his night of work, and to add insult to (quite literal) injury, Lewis gets adopted leaving Goob alone in the room at the orphanage.  Goob forgets about getting over his bitterness and lets it fester.

Lewis, meanwhile, becomes rich and famous, and marries Fran--but here we hit a snag.  For Bowler to come to the past he must steal the time machine; for him to do that, Wilbur must leave the garage unlocked.  That means Wilbur must be born, and thus that Lewis must marry Fran.  But Lewis has not yet met Fran--she is another contestant at the science fair, and he is entirely preoccupied with making his Memory Scanner work, and (once it succeeds) with seeing the face of his birth mother.  Then before the day has ended he is whisked away to a new life as a member of the Robinson family.  Yet if he does not meet Fran, only part of the future will come to pass, and Wilbur will not be there.  It is a complex issue that requires our attention.

Meanwhile, we also have the problem that he built the memory scanner so he could see the face of his birth mother--and it worked.  That was the first step in a plan to find her, so he could be reunited with her.  That is also an issue to be considered before we can get to the future.

It looks simple enough:  Lewis and Fran are destined for each other, and they meet as twelve year olds at the science fair, and stay together, ultimately marrying and raising Wilbur; Lewis knows that Fran is the love of his future, because he went to the future and met Wilbur's mother and her singing frogs, the musical marvels Fran is already training.

It is not simple.

If all goes well at the science fair, and Lewis does not travel to the future, he probably never meets Fran; she's just another contestant in the fair with a wild idea about teaching frogs to sing.  Lewis wins, and in a whirlwind rush he is then interviewed by the Robinsons, who adopt him, and he probably never sees Fran again.  The probability that they would meet later is minimal--her studies are all in animal behavior, the biological and social sciences, and his are all in engineering, physics, mechanics, and electronics.

We know that the Memory Scanner must have worked, because otherwise it would be meaningless for Doris to sabotage it.  We also know that if it worked, Lewis will have seen the face of his mother from twelve years before, and that his attention is already divided between the face of his mysterious birth mother and the new chance to be part of a family, adopted by one of the judges and her husband.  He is not going to notice Fran.

All of this means that there must have been some other way for Lewis to meet Fran at a later time, and for the two of them to become interested in each other and reach the point that they marry, from an entirely different path.  Then when Lewis sees that in the future they are married, he discovers that he met her earlier at that science fair, and knowing that she is the girl he is going to marry he pursues a relationship with her sooner.

Which begs the question, will that work?  That is, it is not impossible for a couple to get together in middle school or junior high, at twelve or thirteen years old, and stay together for years, marry each other, and remain together until one of them dies (my brother-in-law and his wife did just that).  Nor is it impossible for two kids to meet each other, then meet each other again years later and connect, or even to know each other as acquaintances when young only only discover each other as lovers when they are older.  The question is whether the kind of people who would fall in love at twelve and stay together through adulthood are the same kind of people who would have casual relationships through high school and then discover their partner later.  Dating is very complex--people date as a process of learning with what kind of person they really would want to spend their lives, and frequently change quite a bit through the process.  The Fran and Lewis who meet in middle school would not be the same couple as the Fran and Lewis who find each other in college.  It changes who they are.  As Back to the Future (part I) taught us, if you change the way a relationship begins, you change its character entirely.

It may also change who their family is--Wilbur would be born in one scenario, but not in the other, or at least, not the same Wilbur, and possibly Wilhemina.

We thus have hit a potential snag:  how do we get Lewis and Fran together when Lewis does not know she is the girl in his future, and have it be the same relationship when he does know that?  It is going to be different.  It might even be fatal to time, as enough would change to alter events.

The only consolation, really, is that the film is about to do some much worse things with time.

A significant part of the action in this movie is motivated by Lewis' desire to find the mother who left him at the orphanage.  That is why he invents the Memory Scanner which he enters in the science fair.  We have established that without Bowler sabotaging the device, it will work the first time, and seeing the face of his mother in the scanner will distract him.

The question is what he does next.  Lewis did this because having counted the number of potential adoption interviews he believes he will never be adopted by anyone other than his birth mother.  Now he has the face of his mother, and he has that single-minded determination that caused him to keep Goob awake all night and which had him rushing to the science fair and telling the head of the orphanage that he wasn't interested in meeting another family.  Yet at this moment something must cause him to change his mind, just as he has accomplished an unimaginably major step in his plan.  Lewis is scheduled to meet the Robinsons, not in the future but right now, and if he does not do so he does not become Cornelius Robinson.

This raises many other problems.  He still invented the Memory Scanner, and is likely to become the same famous inventor.  He might still marry Fran (although now we have a third entirely different route to the same wedding), and he might have a son named Wilbur--but not Wilbur Robinson, son of Cornelius and Fran Robinson.  Also, they would live somewhere else--the Robinson home in the future is an expanded version of the one to which Lewis moves upon being adopted.  The future must be changed in the detail, if he fails to make this connection.

It is further complicated by the fact that Lewis rushes into this adoption because he recognizes Mr. Robinson as Wilbur's grandfather, and thus realizes that these are the people who in fact adopted him in the future he saw; if he did not travel to the future, he would not have recognized either them or the home they buy.

The best answer is not entirely adequate.  We must suppose that Lewis saw his mother's face, and then realized that he did not know the next step--how does he find her, given only her picture from a dozen years before?  He thus is persuaded that while he is considering that, he talk with this family who is interested in adopting him.  They are of a scientific and inventive mind, and would very much love having a genius son like Lewis.  Since the motivation for seeing his mother's face was the hope that she would adopt him and they would become a family, he now has a more certain possibility of a family against a twice weak hope--that he could find her from her picture, and that she would be eager and able to adopt him now.  So he accepts the Robinsons, and they accept him, and we have to run through history more than once to get the kind of Robinson family that arises when Lewis already knows the future.

That brings up more issues, and major ones; but we shall approach them sequentially.

Lewis' roommate Goob, not as well known as Mike Yagoobian, grows up to become the person we have been calling Bowler, the human villain of the story.  (Bowler is so intellectually ineffectual that we might wonder how an ordinary kid like Goob became so stupid, but that's a small point.)  We have already recognized the problem that Bowler encourages Goob to be bitter, but we found an alternate way for that bitterness to root.  At this point we are attempting to determine what happens when Bowler, directed by Doris the hat, steals the time machine from the Robinson garage and travels to the past to ruin Lewis' life.  Here we have trouble, already.

In the long term, if Bowler succeeds in destroying Lewis' life, Lewis never becomes the inventor, and never creates Doris or the time machine.  Without Doris, Bowler has no hope of plotting Lewis' demise, and without the time machine he cannot return to the past.  This undoes everything he did in the past, restoring the original history in which Lewis succeeds, and giving us an infinity loop.  Further, in the short term, Goob now does not have to face Lewis' success, and so will work through his bitterness and not become Bowler in the future, and so not want revenge.

Fortunately, there is reason to believe this will not happen.  Neither Bowler nor Doris knows how to operate the machine, and thus they cannot demonstrate it and so cannot sell it; they must kidnap Lewis and force him to tell them how it works.  This, though, tells Lewis that it in fact does work.  He might be able to rescue his machine and restore his original life; even if he does not, it confirms to him that he is an inventor and can invent useful and valuable devices, putting him on a path in life that is at least similar to the one he lost.  Hopefully he will be adopted by the Robinsons, and will become known as the inventor of everything except the Memory Scanner.

There is some danger that he will recognize Doris and so avoid inventing her; but at this point he does not know that she is his invention and if he does not discover this he should include that idea in his work.

Meanwhile, in the history we see Bowler encounters Goob while searching for Lewis, and might do so again, giving him the same advice and so becoming who he becomes.  There is some question about Lewis connecting with Fran, but it again is not impossible, and there is time for that to happen.

Thus, with some modifications, we get a history in which Bowler and Doris steal the machine, but do not prevent Lewis from becoming the famous inventor Cornelius Robinson, marrying Fran, having Wilbur, and inventing Doris and the time machine.  History can resolve to that version, and so continue to the next event.

It is obvious that if Bowler destroys time then Wilbur cannot follow him.  At the same time, if Bowler does not destroy time, then Wilbur knows that whatever Bowler did with the time machine has resulted in the world in which he lives, and he cannot know how it would otherwise have been.  He has no motivation to "fix history".

Fortunately, that is not actually his motivation for pursuing Bowler.  His immediate problem is that he left the garage door unlocked and someone in a bowler hat stole his dad's time machine, and he is trying to recover it before his dad discovers this and punishes him for it.  Thus he will pursue Bowler, not because he hopes to fix history, but because he hopes to recover the machine.

How he tracks Bowler is a separate problem, but there are at least two ways it might be done.  One is if time machines have equipment to trace disturbances in time caused by other time machines.  It appears that Doris is able at least to detect such disturbances, and thus it seems likely that this feature would be included in early time machines.  It becomes useless eventually, of course, because the more time machines move through history the more disturbances pass through the present--and indeed Bowler's trip might be entirely in the past by the time Wilbur pursues him.  The alternative is that Wilbur heard Bowler exclaim that he was going to travel back and destroy Cornelius' life by taking that Memory Scanner from him, which would give Lewis a time and place to check.

Either of these solutions is made more plausible with one minor adjustment to our reconstruction.  We know that Bowler stole the time machine, and that Wilbur pursued him.  Yet it is unlikely that even Doris knew how to operate the machine the moment it was in their possession, and so they probably flew it out of the garage and took some time interpreting the controls.  Since Wilbur saw them leave, he immediately gave chase.  He might then have left the future before Bowler did.  If he heard Bowler raving about his next stop, he easily might have engaged the time travel circuits and rushed back to our time to intercept him.  This, though, leads to one of two odd anomalies.

If we assume that Wilbur heard Bowler declare his destination, and Wilbur managed to leave first, Wilbur arrives first, sequentially (whether he arrives earlier or later than Bowler is a separate issue), and finds that Bowler never arrived.  This is because once Wilbur leaves for the past, all of history must be rewritten to the moment of his departure before it can continue, and thus before Bowler can also leave.  Probably Wilbur will spend a few days in the past trying to track Bowler, then return to his own time.  This in essence unlocks history so it can progress, and Bowler leaves for the past.  This changes Wilbur's experience in the past, because now Bowler arrives and Wilbur attempts to recover the time machine, and more pointedly thwart Doris' now unfolding plan.

If, though, we assume that Wilbur is tracking Bowler's time trail, we have the oddity that Bowler must leave first sequentially, but Wilbur must leave first temporally.  That is, if Bowler leaves at ten o'clock, then his trail runs from ten to nine to eight and back into the past, and by eleven there is nothing to follow, thus for Wilbur to find Bowler's trail he must find it before ten.  Yet it does not yet exist at nine until Bowler leaves from ten; but Bowler does not stop at nine, but travels back about twenty-five years.  Thus Bowler leaves at ten and arrives in the past, and history rewrites itself up to nine o'clock, at which time Wilbur is looking for Bowler's temporal trail, finds it traveling backwards from ten and follows it into the past.  Wilbur's anomaly must then resolve in order for Bowler's to do so.

If this were all of it, it would resolve fairly simply.  However, Wilbur does something that proves fatal to the story from a time travel perspective.  We can excuse him for this because it was a snap decision under duress, but at this point there is no saving the movie.

Wilbur is desperate to recover the time machine Bowler stole, and to restore the history he sees unraveling around him, and decides that Lewis can help him.  Lewis is reluctant and incredulous--the flying car does not persuade him that Wilbur is from the future--so Wilbur removes Lewis from the past, and brings him to the future.

In Back to the Future part 2, Doc takes Marty from 1985 to 2015, to help Marty's son.  As we observed, once Doc takes Marty and Jennifer to the future, they do not exist in the past, never marry, and never have that son; but then when a confused Doc restores them to their own time he restores them to history, and all of that can come back into existence for the next versions of themselves, and we can arrive at the history we see.  Similarly, before Wilbur can arrive in the future all those years have to pass as he speeds beyond them, and they have to pass without Lewis.  That means Lewis is not there to sell his Memory Scanner or to do any of the other things he did in the original history.  A few of the major ones are that he will never invent Doris, he will never marry Fran and father Wilbur, and he will never invent the time machine.  That means there is no time machine in the garage, no Wilbur to leave it open, and no Doris to mastermind the scheme to destroy Cornelius Robinson.

With Marty, none of the critical factors were dependent on what he had not yet done--Doc was born first, and Doc invented the time machine with little if any input from Marty.  Thus whatever else went wrong, Doc and the time machine still existed.  Lewis does not have that advantage:  the time machine only exists if he invents it, and its operator only exists if he marries Fran.  If he travels to the future, he makes it impossible for himself to do so, because Wilbur will never exist to bring the time machine to him, which also will never exist without his inventive successes.  Indeed, Bowler and Doris cannot be in the past, the latter because Lewis will never have invented her, the former because there is no time machine for him to steal and no successful Lewis for him to envy.

Having undone all of this, Wilbur ultimately undoes his own trip to the past and correspondingly undoes Lewis' trip to the future.  That leaves Lewis in the past, and allows him to sell his first invention and continue from there to become Cornelius Robinson, marry Fran, invent Doris, sire Wilbur, invent the time machine, be envied by Bowler, and so ultimately be taken to the future.  However, once again as soon as he leaves the past he makes his own trip to the future impossible--and since Wilbur is taking Lewis to a time after Wilbur left the future and now cannot have left the future, they again will never arrive.  That time does not exist.  We have an infinity loop, each history causing the other.

When the robot said that there was a 99.999999% chance that Wilbur would not exist, he was overly optimistic.

The movie is not yet finished even though it has managed to finish time.

Failing to find Lewis in the past, and finding traces of another time machine, Bowler and Doris return to the future hoping to find Lewis and persuade him to show them how to operate the Memory Scanner.  This is a bit problematic, because we do not know when, if ever, Bowler would have left the past had Wilbur not taken Lewis to the future.  On the other hand, most of what Bowler has done since Wilbur arrived has involved reacting to Wilbur's presence, and so this is simply another change made by Wilbur, whose impact as we have already seen was disastrous.

Once back in the future, Bowler attempts several less than entirely clever ideas to attempt to capture Lewis.  The one that matters from a time travel perspective is that he leaps back into prehistory and captures a tyrannosaurus, which he controls with the mind control technology Doris uses.  This makes for both suspenseful and comic moments, but raises the issue of the missing dinosaur.  That is, in A Sound of Thunder, great effort was made to ensure that the hunters in the past killed a dinosaur which would have died within minutes anyway, and the trampling of a single butterfly changed the world completely.  The impact of removing one tyrannosaurus (a ravenous predator at the top of the food chain) on which individual creatures survive to pass their genes to succeeding generations is difficult to assess, but will certainly matter more than killing one butterfly whose life expectancy was not more than a few minutes as it was.  This was a dangerous and serious potential change to history.  It is perhaps only the irreverence of the story that obscures the problem; but of course it might have been that that particular dinosaur no longer mattered.  It thus falls into the category of potentially disastrous changes to history which fortuitously happened not to matter.

It is significant that while Lewis is in the future he learns the slogan used by his future company, "Keep Moving Forward"; it is more significant that the Robinson family teaches him the important lesson of learning from failure, which by then has become the basis for his success.  He would not have learned that as soon, perhaps; but then, he would have succeeded with the Memory Scanner absent Bowler's interference, and so would have been bolstered by his first success and probably learned the lesson in time.

There are worse disasters ahead, though, as the film is really only starting to foul time.

Bowler tricks Lewis into explaining the operation of the Memory Scanner by falsely promising to take him to see his birth mother; he then rushes to the past, sells the device to Inventco, and then starts creating more "helping hats", artificially intelligent bowler hats like Doris.  These then proceed to conquer the world, turning humans into their slaves.

Lewis is trapped in the future, and at his end people around him are either ceasing to exist or becoming bowler zombies.  His one hope is to fix the other time machine (while under attack) and escape to the past, where he might be able to correct the disaster.

This idea of the future changing slowly, as if in waves of temporal change, is somewhat popular, but entirely illogical.  We addressed such a concept in connection with A Sound of Thunder, but here the changes seem more random and thus even less rational.  The only logical way for time to change, from the experience of those within it, is instantly, abruptly.  (That the changes must happen sequentially does not alter the experience that they occur instantly, as illustrated by the example of a spreadsheet.)

On the other hand, at this point the entire story becomes an impossibly complicated infinity loop.  Bowler and Doris have traveled from the future, and have altered the past including removing Lewis from it so that he will never invent anything other than the Memory Scanner which they stole from him.  Lewis thus does not invent Doris, so she ceases ever to have existed.  Lewis then fails to invent the time machine, so neither Doris (now non-existent) nor Bowler can travel to the past.  Since they cannot travel to the past, they cannot sabotage or steal the Memory Scanner, and thus the original history is restored in which Lewis becomes the famous successful inventor Cornelius Robinson, inventing the helping hat Doris and the time machine, and becoming father to the son Wilbur who leaves the garage unlocked allowing Bowler and Doris to steal the machine and restart everything.

This notion of time changing in waves is repeated later in the movie, similarly irrationally.  After Lewis has saved history by stopping Doris (another problem still ahead) he grabs Bowler and drags him into the future, racing against time in a very literal sense, getting ahead of the change so that Bowler can see the world his actions created, and watch it restored to the world he had destroyed.  Thus rather ridiculously they are able to travel to the future that has been prevented, that will never come to be, because in one sense it is the future that has been undone, and they are able to travel faster than the events can undo themselves.  Yet whether the change happens instantly or at the speed of time or at some other speed, the only logical result of traveling forward from any point in time is to arrive in the future that derives from that moment in history, and not in some history that might have been had things been otherwise at the moment of departure.

We might invoke Niven's Law to suggest that once Doris and Bowler reach the past they are protected from any changes they make to the future.  That is, if they change the past such that they do not exist, that does not alter the fact that they exist in the past, even though they never will depart from the future.  That is a rather extreme application of that already somewhat dubious rule, but even if we accept it, the future will still change instantly, not gradually, and Lewis will cease to exist abruptly with no warning or opportunity to prevent it.

Any notion that Meet the Robinsons might be resolved by fixed time, parallel dimension, or divergent dimension theories has been quashed by the suggestion of waves of change.  Although they are ridiculous and unworkable, they are clearly an effort to work with a form of replacement theory.  That comes into focus again as Lewis escapes the future and returns to the past to undo all that Bowler has done.

It should be evident that any effort to "fix" the future based on knowledge from the future is doomed--either it will fail to make the change, such that the future is not altered, or in succeeding to do so it will (barring the somewhat dubious application of Niven's Law) undo all knowledge and motivation necessary to make the change.  That we thus would have yet another infinity loop is not at all surprising in a movie whose basic plot seems to be built on two groups fighting over making the past conform to their own preferences.

What does shock is the moment Lewis confronts Doris.  She is winning; she is going to conquer the world.  Suddenly he shouts at her, "I am never going to invent you"--and with that, she vanishes.  Therein lies the rub.

It is already obvious that if Doris wins, Lewis will never invent her.  This we have observed several times by this point, and yet the fact that a Doris victory must have that outcome never mattered until this moment, when Lewis declares his intent.  Yet nothing else has been changed instantly like that--when Doris wins, her time machine, now never invented by Lewis, does not cease to exist, and Lewis is not instantly prevented from traveling to the past (nor indeed is Wilbur).

On the other hand, if indeed Lewis has decided he will never invent Doris, then she was not there a moment before, because she could not have existed if he will never invent her; and that means he cannot declare that he will not invent her, and she cannot vanish.  Indeed, if he never invents her, he will never know not to do so, and so he undoubtedly will, and again we have an infinity loop.  However, his declaration that he has decided never to invent her changes nothing, as ultimately he would not have invented her had she won, which means that she would not exist and not be able to win, which means he would have invented her.  She does vanish, but only in the sense that she is not created on schedule and so does not exist to make this trip at the end of this version of history (thus not appearing to create the next iteration).

It might be argued that she can make that trip herself, that is, that the version of Doris currently fighting to conquer the world can at the end of this iteration of history make the same trip she already made.  That creates a sawtooth snap, because each time Doris makes the trip she is older, changed, and like the watch in Somewhere in Time, eventually she crumbles to dust.

There are other ramifications to Lewis' decision.  It is part of the experience of the inventor that he learns from his inventions and uses what he learns in his future efforts.  We do not know what he will invent when, but we should be concerned that, for example, the robot might not be invented, or might not be the same, because Lewis will not have the knowledge gained from building Doris.

There is one more trip to the past to be considered.

In the end, Lewis gets both of his wishes.  Not only is he adopted, before that he has the opportunity to see his birth mother.  Wilbur takes him to that moment and parks on the street, so Lewis can watch the woman drop off the baby and flee the scene.

He chooses not to look at her, but spares a moment to look at his younger self.  By this we know that Lewis has reconciled himself to his life, to the knowledge that he will become part of a family eventually, and he does not have to look to the past to find a future.

This final trip to the past appears to be about as benign as an anomaly can be.  Lewis is not more than an observer; Wilbur is less than that.  Lewis risks being seen but is not seen, may have been heard but not clearly enough that anyone is certain, might have frightened his mother into leaving a moment sooner and called the orphanage matron to the door but did not otherwise disrupt events.

There is an unexpected nod to fixed time theory here:  in the opening scene, his mother heard the noise which he now makes, hinting that he was always there.  the weirdly changing histories and the abrupt disappearance of Doris both demonstrate that this is not a fixed time story, and we are left with the question of what really happened in the original history.  Yet the mother certainly left Lewis, knocked, and fled, so the difference is negligible.

He then returns forward to his own time, where the pieces fall into place--he recognizes his adoptive father, embraces his future family, and changes his name to Cornelius Robinson, as his invention is a success.  We wonder whether he really always wanted to change his name to Cornelius or whether he got the name from his future self, but he says he always liked the name so we can reasonably take his word for it.  There is only one new glitch at this point (we already addressed the others), and that concerns Goob.

Bowler, who is of course Goob in the future, told Lewis that all of his bitterness arose because of missing that catch.  Lewis rushes to the ball field and alerts Goob, so that Goob will be awake when the ball comes, and instead of being the disappointment everyone hates he becomes the hero everyone loves, changing his future.  This has problems throughout.  It means, first, that Goob will never become Bowler; if he does not become Bowler he will never tell Lewis--indeed, he will never know himself--that his life was ruined by missing that catch, which he always blamed on Lewis for keeping him awake all night so he was asleep on the ball field.  Since Goob can never tell Lewis what happened, Lewis cannot prevent it from happening.  Thus this final act of kindness that puts all things right becomes yet one more temporal disaster in the film, another infinity loop destroying time.

And so they all lived happily ever after until the moment it all unravels and returns to the present, and everything goes through it all again, and again, and again, until we have met the Robinsons more times than we can say, and yet never have met them at all.

There is an issue implied in the actions of the characters that is very misleading and so must be addressed; it pertains to the fact that the Robinson family insisted on sending Lewis back to the past the moment they knew who he was, but not before.

The first clue we get is when Wilbur insists that Lewis wear a hat--any hat, a goofy fruit hat at first, replaced by a baseball cap later--because if anyone were to see his hair they would know he was from the past, and Wilbur would be in trouble for using the time machine.  Lewis raises the obvious question--why would his hair tell people he is from the past?--but Wilbur avoids answering.  We might imagine that Lewis sports a dated hair style, but in fact it is not that his hair identifies him as someone from the past, but rather that it identifies him as someone specific from the past, namely Cornelius Robinson, inventor of much that makes the future what it is and father in the Robinson family.

It is at this point that the implication arises:  Lewis must return to the past because he matters; if he does not return to the past and become who he will be, the future dissolves and we have a temporal catastrophe.  (We have already discussed the problems arising when Wilbur takes Lewis to the future; the film merely fails to recognize that they must already have occurred.)  Yet the paired implication is that it is only because he matters to the future that Lewis must return to the past--that if he were always an insignificant orphan boy who never amounted to anything important, he could be removed from history without complication.

In fairness, the film does not actually say this; however, it is a mistake sometimes made.  In one original StarTrek episode, the Enterprise saves the life of a twentieth century pilot who is chasing it as a UFO, and upon checking their database they decide that his life is inconsequential and so it would be better to take him to the future than to let him return with his knowledge of the Enterprise.  They then change their mind when they discover that his as yet unborn son would be a key figure in the moon landings, so he has to be returned to father that child.

The problem with this kind of thinking is that it overlooks the butterfly effect, in the fact that humans interact with each other.  Lewis might never be adopted, but we know that he has an impact on Goob, and if he stays at the orphanage he will undoubtedly impact others.  If he never married Fran we would have the genetic problem, that she will probably marry someone else who in turn will not marry someone else who will marry someone else, and the ripple changes the identities of many of the children born in the next generation--even ignoring the fact that Wilbur would have been one of them.  To travel from the future and remove someone from the past changes the future in unpredictable ways, even if the individual involved is never mentioned in history books.

So yes it was important that Lewis be returned to the past because of who he was, but it was potentially disastrous even to remove him from the past "temporarily", that is, to remove him for thirty years and then replace him at a point in the past near his original time, even had he been thought to be no one of consequence.  Replacing him would not fix it, but would introduce an entirely new unpredictable set of changes, which again would be potentially disastrous.  No one is truly inconsequential to the progress of history; the impact we have on each other in life changes the future in unpredictable ways, even if we are not more than orphan beggars on city streets.