It might be questioned whether Blackadder Back & Forth qualifies for consideration as a time travel movie.  That it is intended as a farce is not particularly relevant--the same might be said of Army of Darkness, Bill & Ted's Excellent Adventure and their subsequent Bogus Journey, Bender's Big Score, Hot Tub Time Machine, and Frequently Asked Questions About Time Travel, along with several other movies which were not so intended.  The issue here, though, is whether this is a time travel movie.  It is less than sixty minutes in total length, and bills itself as being the fifth "season" of the Blackadder television series, but is the only episode in that season.  On the other hand, however, it appears to have been shot on film for the big screen, and to have had a limited theatrical release in the United Kingdom before going to television.

It is also in other ways distinct from an episode of a television series.  Blackadder does not exactly follow the same characters through the entire run; rather, it creates a line of characters who are supposed to be British nobility, descendants of each other through the centuries.  There is always an Edmond Blackadder, played by comic great Rowan Atkinson, whose turns in this series and The Thin Blue Line gave him fans among Britcom watchers long before he gained fame more generally as Mr. Bean and Johnny English (and as the voice of Zazu in The Lion King).  He is supported by someone named Baldrick, a completely filthy incompetent servant provided by Tony Robinson, and by a cast of others whose identities change but who are usually provided by Hugh Laurie (in the mold of his wifty character rolls such as Bertie Wooster for which he was best known prior to becoming Gregory House), Tim McInnery, David Fry, Miranda Richardson, and a host of supporting characters.  Indeed, when Baldrick says that throughout history there has always been a Lord Blackadder and there has always been a Baldrick, the fictional history of the four previous series and occasional specials tends to support this.  (In the true irreverent form of Blackadder tradition, the short list of the cast also includes appearances by "Tyrannosaurus Rex" as "Dinosaur" and "Hordes of Scots" as "Scottish Hordes".)  This Edmond Blackadder and this Baldrick have never appeared in any previous episode of the series of series, and excepting one scene the characters from those previous Blackadder stories are not part of this story, save as ancestors of the main characters.  It is in that sense a stand-alone product; a viewer new to the characters would not miss much for not having seen the previous adventures.

That also mattered.  There was, after all, Blackadder's Christmas Carol, in which one of the famed Dickensian ghosts stops by the shop of a Blackadder descendant and regales him with tales of his unscrupulous ancestors, presented as scenes from earlier runs of the show, and a time travel movie that involved taking a the character into moments in the series would be too integrated with the series to be manageable.  However, there are no scenes here from those stories, and only the one scene in which characters from Black-Adder II are recreated by their original portrayers in an entirely new scene involving the new character, mistaken for his ancestor.

Some of the humor is crass, gross, or mildly vulgar, and there is a moment of brief faux nudity, all of which is within the bounds of British television standards.

And, as has often been the case with time travel movies made for laughs, in poking fun the story uncovers a number of interesting time travel problems.  We thus will begin examining the story.

On the eve of the year 2000, Edmond Blackadder is entertaining his friends in his family castle, and announces that he has built a time machine.  He gets them each to agree to a bet, whether he can or cannot bring to the future certain objects from history, of their choosing.  They name a Roman helmet, Wellington's Wellingtons from Waterloo, and a pair of two hundred year old dirty underpants.  Blackadder is always a scoundrel, and has devised an elaborate cheat.  He had Baldrick precisely follow plans for a time machine in one of Leonardo Da Vinci's notebooks, but has no expectation that this will work.  Instead, there is a trap door in the bottom, and he intends to enter the box that is the machine, have Baldrick bring him objects fitting the descriptions, and then emerge a moment later claiming to have been gone for a long time but to have returned to the same moment, and claim his winnings.  Unfortunately for him, Da Vinci's time machine actually works; also unfortunately, Baldrick never marked the controls with their original starting position, so they cannot simply return to the right time.  However, as often happens for the Edmond Blackadders of history, the comedy of errors works very much in his favor, as he wanders through time disrupting history completely and returns to claim his winnings.

It is an incidental pet peeve that they say it is the eve of a new century and a new millennium.  The year 2000 was actually the last year of the twentieth century and the second millennium; the first year of the new ones was 2001.  But it was a common misconception of the time.  However, it gives us a secure starting date.

To sketch events briefly, the duo leaps back to the Jurassic era, where they use their fake trophies to fend off a tyrannosaurus.  The second stop is the court of Elizabeth I (who reigned 1558 through 1603, but is young here), then forward to a future in which spacefighters are shooting at each other, back to Robin Hood (a fictional character, but the events of his story are fixed to the period of 1195 to 1200 when Richard I was a prisoner), then to the Battle of Waterloo (Sunday 18 June 1815), then to the withdrawal of Roman troops from Rome by Emperor Hadrian (who became Emperor August 117 and had Hadrian's Wall built beginning in 122; however, he never withdrew troops from Britain, who remained there until the late fourth or early fifth century), and then home.  He finds that he has altered history in ways he finds unacceptable, and so launches a second mission in which he attempts to repair the damage.  We see brief visits to the same moments already visited at Waterloo, Sherwood, and Elizabethan England, and then he returns to find everything restored to normal.  Melchett then comments that an unscrupulous individual with such power might make serious changes to history, and Blackadder excuses himself once more for one more trip.  We do not know where he goes or what he does, but we do know the outcome, as he once more changes history.

With all the changes to history, we can safely say that this is not a fixed time theory story.  Thus as we watch the changes and the travels we will attempt to determine whether this movie works under any theory of time.

Someone once wrote (published somewhere in Omni Magazine) the "longest story ever told", a one page joke which began by telling of a man who lived and died, then of the sun dying and the end of life on earth, then of the universe reaching its extreme expansion and contracting back into a singularity, then of a second big bang and the development of the universe returning to the recreation of earth and the rebirth of this same man.  It was a cute gag.  Blackadder Back & Forth does not top that, but it does provide the longest temporal anomaly in the shortest movie, with a running time under an hour and a trip to the Jurassic era, forcing all of history to repeat from an early dinosaur era.

It may be a tip of the hat to A Sound of Thunder.  In the original story the hunters kill a jurassic Tyrannosaurus Rex.  The movie updated that to a more recent cretacious allosaurus, though, so that anomaly is not quite as long.

Potentially more serious, after Baldrick slays the attacking monster, Blackadder opines that it now is apparent that the dinosaurs were killed by Baldric's dirty underwear.  It will become apparent that this is not a fixed time theory story--history is changed several times in several ways.  Thus if this trip is responsible for the end of the dinosaurs, or even for the end of the jurassic era, then that end did not come (or did not come as soon) in the original history, and the time travelers never came into existence and never traveled to the past to bring that end.  It would be a predestination paradox, leaving us to search for the original cause of events.

Fortunately, though, Blackadder's statement can be reduced to dicta, the expression of an opinion having no binding force.  It is unlikely that the single pair of underwear would have killed more than a few dinosaurs, even granting that it carried infectious microorganisms unknown in that age.  Whatever originally destroyed the dinosaurs is still the cause of their destruction.  However, A Sound of Thunder also reminds us, through the precautions followed there, that even the premature death of a single creature so seemingly insignificant as a butterfly could so alter the gene pool as to change the future drastically.  This tyrannosaur might not only have produced offspring, it is highly probable that it would have prevented quite a number of other creatures from doing so before it died.

It is not impossible, though, that this poor creature was about to reach the end of its life anyway, that it would not have caught another meal or conceived another descendant, and thus that the impact of its death now was minimal.  That would enable us to escape the otherwise inevitable infinity loop which would have occurred had the shift in the population altered history enough to undo or significantly recast humanity.  So by the dumb luck that seems to follow Blackadder through most of his adventures, the universe survives the launch of this first anomaly.

As Edmond and Baldrick travel forward from the jurassic era, they stop in Elizabethan England.  It is perhaps peculiar that Elizabeth and her court happen to be in what would later be the dining room of Blackadder's castle, but we know that Blackadder has familial ties to royalty and thus not impossible that some minor former royal residence became part of his inheritance at some point.  We will excuse the fact that no one questions his use of "Elizabeth the First" (no monarch is called the first until there is a second) as plot exposition informing the viewer of the situation.

It is a cute throwaway that Blackadder's life is saved by Lifesavers™.  It is here, though, that we hit a potential snag.  Blackadder has been mistaken for his own ancestor, and threatened that he will be executed should he fail to provide more mints.  He of course escapes this threat by leaving history behind--but leaving his own ancestor to explain why he cannot produce more of the minty delights of which he knows nothing, or be executed.  If he has not yet fathered whatever child will continue the line, there is a substantial likelihood that Edmond has killed his own ancestor, and so cannot exist, and so cannot prevent his own existence.  Fortunately, Elizabeth as portrayed is flighty, ordering executions as a ploy to obtain what she wants but never executing the sentences (or anyone else).  The change to history might be minor.

The more significant change arises from the immediately subsequent encounter with William Shakespeare.  It is a history error that he is carrying the script of MacBeth:  Elizabeth died of old age in 1603, and MacBeth is thought to have been written between 1603 and 1607, and thus certainly not while a young Elizabeth reigned.  (It is also unlikely that an actor/playwright would have been wandering unescorted in the palace or anywhere else the Queen was in residence, but the jokes required it.)  The problem, though, is not so much that they met as that they interacted, in two significant ways.

Blackadder hands Shakespeare a cheap ballpoint pen, asking for his autograph.  Quills were the popular writing implement of the time, and the playwright marvels at the object in his hand.  Edmond then forgets the pen and addresses his anger at having had to study Shakespearean literature in school, giving the famed genius a verbal and physical thrashing before storming away.  In consequence, William abandons his literary career and instead reverse-engineers the pen, becoming its entirely-too-early inventor.  It would have been a remarkable achievement.  Even with some substitute for plastics, techniques in metallurgy, quick-drying inks, and mass production are all far in the future such that any such success would revolutionize technology on many levels and so drastically alter the future.  Although the introduction of technology from the future is not always fatal to that future (witness transparent aluminum and transwarp teleportation in Star Trek), so significant an alteration so far before its time cannot help but have unpredictable effects in so many fields.  The repercussions thereof create a near certainty that the world as we know it never existed.

That creates a serious problem for our time travelers, which will become evident as they return to their time machine.

For his next trick, Edmond Blackadder leaps to some point in the future.  He does not know when, but the spacefighters shooting at each other look remarkably like those used in Buck Rogers in the 25th Century, so we will suppose it to be four to five hundred years in our future.  What matters to us, though, is that he has leapt past his original point of departure, and therefore before there can be a future in which he can arrive, there must be a stable past, and we must resolve any anomalies into an N-jump.  There is only one anomaly, but it is a bit complicated, and we need to know whether Blackadder has altered history in any way that will change his own travels.

Most of what he did is at least potentially benign.  He killed a dinosaur, which as noted might have serious consequences but then might not.  He visited the court of Elizabeth the First, and put the life of his own ancestor in jeopardy, but it might amount to nothing of consequence.  Nothing he did would necessarily change dinner with his friends in the castle, his announcement of his intended trip, their choice of proofs, or the moment of his unintended departure.

There is, however, the Shakespeare problem.

In the history Blackadder knows, William Shakespeare was a famed playwright whose works were the bane of students throughout the English-speaking world.  In the history he creates, he makes this clear to the poet, and so discourages his career, while at the same time handing him a ball-point pen which the man back-engineers to become inventor of the device.  That Melchett recognizes the name is not that important ("the inventor of the ballpoint pen").  Blackadder would not have known either Shakespeare's identity or his connection to plays.  He probably would not have stopped the man for his autograph, and certainly would not have thrashed him for work which, in that history, he never did.

That means, of course, that Shakespeare will neither be deterred from his writing career nor inspired toward invention, and so in the next history he will be the playwright; which means that Blackadder will know him and divert him to becoming the inventor.  We have an infinity loop, in which two histories alternate, each of them causing the other.

Since history now cannot stabilize, neither can it continue, and there is no future for Blackadder to visit.  Our story must end here, as time itself ceases to advance and Blackadder and Baldrick vanish along with everyone else as they attempt to travel to a future which cannot exist.

We knew up front that it was all silliness and bound to collapse into disaster.  It has done so.  The writers, though, either did not realize that or did not care, and so the movie continues, and so does our analysis, determining what would happen had that not derailed us.  Next we visit Sherwood Forest.

In Blackadder and Baldrick's big adventure they next are captured by Robin Hood and his Merry Men.  The fast-talking Edmond saves them by persuading the men to turn against Robin, in the process impressing Maid Marion enough to wander with her off camera and reminisce about her later.

This may be one of the most difficult anomalies to analyze we have yet considered.

We know what happens to the history of Blackadder's world:  Robin Hood was killed by his own men and never achieved the fame that makes his name legendary.  Blackadder's friends at the end of the millennium have never heard of him.

On the other hand, there is little evidence that Robin Hood ever actually existed, or that any of the stories told of him were true.  There probably was a "Robbing Hood" in Sherwood Forest, but it would be centuries later that a love song elsewhere in England about a soldier named Robyn and his distant girl Marian became confused with this Robbin' and so re-spelled his name and provided the girl.  Giving to the poor, fooling the shire reeve with fake deer, fighting Little John on a log over a stream, the persons of Will Scarlet and Friar Tuck are all parts of stories from authors both anonymous and known (they appear in Sir Walter Scott's Ivanhoe).  He ranks with Camelot among the richest pieces of English folklore.  What exists is not the man himself but the stories told and retold which created him.  How, then, do we evaluate the undoing of the existence of a man who perhaps never existed in the first place?

Taking the story on its face, though, we must accept that in this world, Robin Hood was famous because he existed and was much of what was reported, and that removing him from history means that the Errol Flynn and Kevin Costner movies were never made and we read and heard none of those stories about him.  Perhaps we have some other legendary altruistic example of civil disobedience; if not, our culture is the poorer for it.

What other impact this has depends on what other tales are true.  Although it seems implausible that a highway robber in a rural shire noted for his altruism could also raise the million pounds of silver to ransom King Richard from the Germans (it was actually raised and paid by the rising British middle class), a connection between Robin and Richard is reported fairly early in the stories, as if the beloved monarch needed the assistance of a peasant rabble to reclaim his throne from his despised younger brother.  Richard, though, never married nor had children, so in a few years John will be king anyway--the only king so bad that the royals have never re-used the name, but the one who under threat signed Magna Carta launching the beginnings of the concepts of the rights of man in the western world.  None of that should change.

What is more difficult is assessing how our culture would be different without this glorification of the good villain, this exemplary criminal famed and honored not despite but because of his lawbreaking.  Does it undermine the history of civil disobedience so important to such as the civil rights movement?  Probably not.  The American Revolution was founded on the same concepts that led to the Magna Carta; Greek philosophers wrote of civil disobedience.  Eventually we imported tales of ninja, making them the defenders of the commoners against the oppressive government (whatever they were in Japanese culture).  Even without Robin Hood, we would have discovered the trope of the hero in the black hat, the good villain.  All that we would lose would be the name, and some of the color.

The loss of the name, though, creates a separate problem.

We see Blackadder depart from his friends, and assume that they know who Robin Hood is, just as we do.  When he returns, they no longer know.  It is not, however, as if they have forgotten.  They did not know five minutes before.  Neither did the Blackadder who left a moment ago.  That means when he was captured in the forest, he had no better idea who captured him than his future friends; he knew nothing of robbing from the rich and giving to the poor.  He has undone his own knowledge.  Without that knowledge, he cannot seduce the men of Sherwood into betraying their leader.  He will die in Sherwood--and Robin will go on to become famous and so his story will be known and Blackadder will be able to use it against him.  We again have an infinity loop, as time is trapped between two alternate versions.  History grinds to an abrupt halt.

Edmond is not yet finished destroying time, though; he has yet to come to his Waterloo.

For his next stop, Blackadder hits Wellington--quite literally, landing the time machine atop him very like Dorothy's house atop the witch.  Then, again recalling the trope from the famed fantasy film, he removes Wellington's Wellingtons from feet jutting from beneath the TARDIS-like box.  Without Wellington's brilliant plan, Britain and the outnumbered united armies of Europe lose to Napoleon, who then completes his conquest of England.

It would be absolutely no disrespect to Wellington's importance to say that his death at that moment probably would not have cost England the battle.  The Duke's genius was in choosing the battleground and arranging his fortifications, all done well in advance of Napoleon's arrival.  Simply by holding their positions until reinforced by the approaching Prussians, the British (and Belgian and Netherlands) armies won the day.  Most of the important decisions thereafter were made by officers in the field, and those which were made by Wellington himself probably would have been the same if made by others.

That is not to say that his death would not have mattered.  Arthur Wellesley, 1st Duke of Wellington, would later be Prime Minister, and would remain Commander-in-Chief of the British Army until his death almost four decades later.  His personal impact on British law and policy was significant--after all, even Baldrick observes that you can have an impact on changing the world if you're Prime Minister.  It just is not obviously the case that the French would have won Waterloo had Wellington been killed.

Nor is it obvious that a French victory at Waterloo would have meant a French conquest of Britain.  Napoleon was desperate--seven European nations had agreed that he had to be removed from power, and his pre-emptive strike against Belgium was an effort to prevent them from bringing all their forces against him simultaneously.  He needed to consolidate, not expand, and the only justification for his offensive effort was that it would make the subsequent defense much easier.  He might have annexed Belgium, but he was a long way from threatening the other major powers of Europe at that point, given that they had allied against him.

Yet there remains a problem concerning Wellington's Wellingtons.  High rubber boots of that style took his name some time later, because of his fame and success.  He undoubtedly wore them; but had he been killed at Waterloo, no one would have called those boots "Wellingtons".  Then, given that part of the reason for asking for them is the idea that these would be the most famous such boots, the reason for selecting these as one of the items Blackadder is to retrieve vanishes.  They ought to receive the same reaction as Robin Hood's hat and Shakespeare's signature, and further there ought to be some other object which would have been requested instead--Napoleon's hat would have been a more likely prize selection on the assumption that he ultimately conquered England.  It would mean that Blackadder brought back some trinkets, but not the object for which he had been sent.

We thus have an infinity loop--yes, yet another one.  But then, we knew up front that this intentional time travel farce was unlikely to give us a functional story, so we will overlook this problem and follow him back a few centuries to Hadrian's Wall.

We have an anomaly within an anomaly, as Blackadder, not having yet returned to the end of the twentieth century, leaps back from the early nineteenth century to the Roman occupation of Britain.  To clarify briefly, having first traveled back to the late twelfth century to visit Robin Hood and then leapt forward to the early nineteenth to kill Wellington, he has created a history of events in which the changes he made in the twelfth century must play through to reach the nineteenth.  Now he leaps back further, to perhaps the second century (the date is unclear, as Emperor Hadrian began the wall in 122 A.D., but the reference to the emperor who married his horse is to Caligula, almost a century earlier).  Thus the changes he makes in the second century must resolve to a stable history by the nineteenth before time can continue attempting to resolve to the dawn of the twenty-first (and, of course, on to the twenty-fifth and its space battle).

Fortunately, in one sense the changes he makes here are relatively minor.  That is not to say that they could not have a serious impact on the future, but only that they do not necessarily have to do so.  He steals a Roman helmet (one of the items for his bet) and incidentally deprives several Scottish barbarians of their weapons (stuck through the door and walls of his time machine), and these incidents could change who lives and who dies in the battle--a serious matter which as discussed in connection with Timeline can change who is born or not born in the future.  But then, I doubt whether either the Blackadders or the Baldricks of the future have much Scottish blood, so as long as their Roman ancestors survive (the comment is made that the machine is finding their DNA, to explain why the Roman soldiers and officers look so much like Blackadder and his friends) and provide the proper descendants, our travelers could be born on schedule.

Otherwise, this visit to Hadrian's Wall is remarkable because it is the last place the duo visit before returning to their own time--or not their own time, as they discover the impact their journeys have had on their own people.

We have followed Edmond Blackadder and his sidekick Baldrick as they make their bet on the eve of the millennium and then stumble back to the Jurassic era where they kill a dinosaur (but not, we think, all dinosaurs), then forward to Elizabethan England to endanger the life of his ancestor and derail the literary career of Shakespeare, then into a distant future, back to the age of Richard the Lionhearted and Robin Hood, forward to Waterloo, and back over a millennium to Hadrian's Wall.  Now, thanks to a slight modification of one of Baldrick's cunning plans, they have returned to the very minute of their original departure, to find his three friends waiting.  He disembarks and pours the contents of his treasure bag on the table.

The first problem we should note is that the stinking underpants are there.  Baldrick removed those from his own body and put them in the bag before they left, but when they faced the dinosaur they tossed all their fake prizes out the door and left them, including the pants, in the Jurassic age.  They since acquired the real boots and a real Roman helmet, but they never replaced the pants.  However, they make no reference to the pants, so we can overlook them and suppose they are not there.

They then discover how they have altered history, and they are not happy about it.

The first shock is that no one knows who Robin Hood is.  As we noted, this creates an infinity loop for us, because it means that the Blackadder and Baldrick who left a moment ago do not know this either, and will not know who he is when they meet him, and so will not be able to use their knowledge of him to escape.

The second shock is that Shakespeare is remembered as the inventor of the ballpoint pen (the object Blackadder left in the past).  It seems that despite his anger at all the schoolwork the Bard's plays inspired, Edmond still thinks him important, or is at least disappointed that his associates are unimpressed by the autographed Macbeth title page.  This, again, will create an infinity loop, for similar reasons, the duplicate Edmond having no knowledge of the plays that now were never written.

The unacceptable shock, though, is that France conquered England.  Although this is implausible, it is perhaps not impossible that Napoleon would have defeated the rest of Europe and become the emperor, making England part of France.  This, and the prospect of feasting on a pudding with whole cloves of garlic, Blackadder finds unacceptable, and so he determines to correct matters by traveling to the past once more and repairing the changes he made.

The impossibility of this under replacement theory ought to be obvious.  His own knowledge of the original history must have been replaced when the history itself was undone--no Blackadder can be alive at this moment who remembers the history that never was, as he must be replaced by that Blackadder who lived through the altered history.  His ability to put it right quite aside, his ability to know it is wrong is a serious problem.

A more practical problem is the fact that the same companions are waiting in the same castle to pay the same bet, more or less.  Although we cannot imagine that they would have asked for Wellington's Wellingtons, they are satisfied that he traveled to the past and offer to pay the ten thousand, but francs rather than pounds.  We ought to be stunned that these people are here.  The nineteenth century fall of England to France so alters the twentieth century map of Europe as to completely rewrite both world wars, changing the identity of every living person in most of Europe.  Blackadder's world should be unrecognizably altered.  Certainly his friends would not be awaiting him in his basement.

However, he now embarks on the fool's errand of fixing what he has done.

Standing advice to time travelers:  do not attempt to fix history.  If you succeed you make things much worse.  After all, if the Blackadder who does not know who Robin Hood and William Shakespeare are, who did not come from the world in which Wellington won Waterloo, somehow learns that these are mistakes in history and successfully changes them, how will the Blackadder who then was born in the corrected world know that those events will not happen properly if he does not intervene?  Successfully intentionally changing the past results in an infinity loop except in very strictly controlled situations, and even then it's a crap shoot.

However, there is a more confusing problem in the quick repairs that Edmond Blackadder makes to those events he altered:  where is Edmond Blackadder in these events?  That is, we have an Edmond Blackadder who left at 11:30 and traveled to all these times, and then we have another who left at 11:35 and went to several of the same times and places.  He did not prevent his earlier self from making the trips; he simply also made them, and having done so ought to have encountered himself.

So at Waterloo, a second time machine would arrive and a second Blackadder emerge, perhaps at the same moment as the first; but this does not prevent the first time machine from landing on Wellington.  The best hope is that the second Blackadder arrives first and steers the Duke away from the landing site of the first, so that when the first arrives it does not kill the man.

So, too, with Robin Hood, which Edmond is caught, and what does the other do?  Where is the 11:30 Blackadder while the 11:35 Blackadder is sweet-talking Robin to win his friendship?

In the court of Elizabeth I, does he avoid the Queen and let his earlier self offer the mints?  Does Shakespeare have the experience of encountering two Edmond Blackadders (perhaps an inspiration for The Comedy of Errors), one of whom defends him from the other?

It becomes more complicated.  The 11:35 Blackadder returns with many of the same proofs as the 11:30 one.  But was he not already there?  If he was not, how did the 11:35 Blackadder know that he had to fix history?  But then, if he was, doesn't he have the title page from MacBeth, the Queen's crown, Robin's hat, and Wellington's boots?  Indeed, how did this second Blackadder get the boots off the Duke while he was alive and preparing to fight a difficult battle?  If his second trip followed his first, then some of those objects only one of him can have and some cannot be had by either.  If, though, his second trip replaced his first, then the second Blackadder cannot have those objects he did not also collect.  Neither solution works.

It is, of course, a joke, that having recognized the changes he has made to history (which he cannot have recognized) he fixes them by returning to those times and changing what he did (when in fact he ought to have found himself already there doing what he wishes to prevent).  As a time travel story, though, it is a disaster.

He then returns, somehow still possessing some of the items he now could not have acquired (the boots) along with some that he has now acquired twice (the MacBeth page), finds history suitably restored, collects his winnings, and chats nonchalantly about the dangers of changing history as if nothing were ever wrong.  Then the innocent Melchett speaks of what an unscrupulous person so equipped might do to history, and the unscrupulous Blackadder decides to make one more trip to the past.

Having had his attention called to what an uscrupulous person armed with a time machine might do, Edmond Blackadder devises his most cunning plan and does something only an unscrupulous person would do.  He alters history such that he is king, and his improbable sidekick Baldrick is Prime Minister.  As the icing on the cake, he makes Maid Marion of Sherwood his bride.

Can he do it?

The simplest of his three tasks is to kidnap Marion from the end of the twelfth century.  Here we have the genetic complication--the problem considered in connection with Timeline, that one change in who marries whom propagates to change entire populations in very few generations.  The problem here is that as far as we know, Marion is a fictional character and so part of nobody's ancestry; but Blackadder cannot recover a fictional character from the past, so she must have been real in his universe, and therefore a factor in the British genome.  Even had she married no one and borne no children, she would have been viewed an eligible bachelorette and so might have deterred some men from marrying other women, or of marrying as soon.  This probably undoes the identities of nearly every person in England.

Perhaps it is because this author is American, but when it is said that Baldrick is serving his fifth term as Prime Minister and Parliament has been dissolved, that seems internally contradictory.  Prime Ministers do not serve terms as Prime Ministers; they serve terms as locally-elected members of Parliament.  To analogize it for Americans, imagine that each congressional distict elects a member to the House of Representatives, and they among themselves, probably along party lines, select one of their own to be President.  He remains President as long as his party controls the House--as if the Speaker of the House were the President.  In England, technically the monarch selects who will be Prime Minister for as long as the King pleases; practically, the monarch chooses the one who has the support of the majority of Parliament (monarchs have tried doing it otherwise, quite unsuccessfully).  So Baldrick serves one term as Prime Minister, the one to which Blackadder appointed him, for however long he remains in office.  He could serve several terms as a Member of Parliament, as long as the locals re-elected him--as long as there were still Parliamentary elections, which ceased when Parliament was dissolved.

Since technically the monarch can always select his own Prime Minister, though, it might not matter whether Baldrick was ever elected to anything.  If Blackadder can make himself King, he can make Baldrick Minister.  He might offend a few people in the process, but it appears he was able to usurp all power in the realm to himself and eliminate those pesky democratically-elected politicians, so Baldrick's position is plausible given Edmond's.

The task of making himself "King Edmond" is considerably more difficult, but perhaps not impossible.  It is plausible because the Blackadders are in one of the royal lines (the first of the series made him the second son of the fictional fifteenth-century King Richard IV, and he might have been king; there are several episodes in the series which suggest ways in which Blackadder could have usurped the throne).  The problem here is one of balancing the path of succession against the changes to the gene pool.  For Blackadder's line to remain in contention, some people must die and others must abdicate, dubious elections must be clarified in his favor, even certain wars must fall the right way.  All of these events impact what nobles marry what nobles, and so reduce the probability that Edmond Blackadder will be born in the twentieth century at all.  Thus every step that increases his chance of legally taking the throne reduces the probability that he will be who he is.  It is a highly improbable outcome which might require more genius, more knowledge of the political movements through history and his own ancestry, than any one man could possess.

We have uncovered several impossibilities in the film; but what if it follows different rules of time?

We have written quite a bit finding how BlackAdder Back & Forth is impossible under replacement theory; it is self-evident that a story in which history changes cannot be resolved under fixed time.  That leaves us with various versions of parallel or divergent dimension theories.  Could such a story exist under these?

Let us suppose that each time Blackadder travels to the past he creates a new universe, but when he travels to the future he arrives in the universe he created.  Sketching his first set of trips, having made his bet he killed a dinosaur, which might not matter.  He comes forward into the court of Elizabeth I which is little altered by the death of the dinosaur, and interferes with the life of Shakespeare.  Now when he leaps forward into space in the future, it does not matter that he changed history; he knows nothing of what it would have been, or whether the absence of Shakespearean literature would have resulted in a different space program.

He then leaps back to Sherwood, eliminating the fame of Robin Hood.  We cannot say that he did not make a significant change to history here, nor that he did.  This being another backwards trip, it creates a new history, diverging from the previous one.

We face theory101.html#problem">the problem of whether this version of history diverges from the original one or from the one Blackadder has already created--that is, in this new history has he already arrived in the still-future Elizabethan court, or has he created a new history in which that has not happened?  The movie answers that for us:  Blackadder must have previously arrived at the later date, because his impact on Shakespeare is part of the history when he returns to the twentieth century.  Thus we conclude that subsequent earlier visits do not erase previous later ones.

He then moves forward to Waterloo where he kills Wellington, and the French win the war.  England falls to Napoleon, but this Blackadder never came from that England, so his knowledge is not an issue.  Here we have the other side of the same problem, and can see that since changing history in the early nineteenth century does not undo changes made in the earlier ages of Elizabeth or Richard (Sherwood), subsequent later visits do not erase previous earlier ones.

Leaping back to the Roman occupation, he steals a helmet and a few weapons (which mysteriously vanish).  This is the third and final universe he creates on this series of trips, and he now leaps forward to the moment of his departure.

Since this is a new universe (marked by his trip to Hadrian's Wall) but his interactions with Shakespeare, Sherwood, and Wellington are all part of its history, we conclude that when a time traveler creates a new universe it diverges from the history of the one from which he departed, including the arrivals of any time travelers, including himself, on previous trips.  That complicates the next part of the story.  Blackadder returns to those three locales attempting to fix what he has done by replacing himself; but there is no reason to believe that he would replace himself--he would instead find himself already there, arriving just before or just after he does, or possibly at the same moment.  If that were not so, then the changes he made in those three places would have been undone when he created the new universe at Hadrian's Wall.  That is, we have established that the arrival of a time traveler to any point in history will not erase the arrival of a time traveler on what we would call a previous trip either to any earlier or any later point in history.

Someone will object, though, that it is different if the same traveler arrives at the same time.  Then he replaces himself.

As to it being the "same" traveler, two things must be said.  First, in all our examples, it was in that sense the "same" traveler who arrived earlier or later, and that did not undo other trips.  Second, though, since this is a diverging universe, that traveler is a temporal doppelgannger.  It is inherent to this "solution" to time travel that the Blackadder who arrived at Waterloo the first time came from a different universe than the one who arrived the second time; if the second arrival killed the first, he would not be undoing his own past but the past of a different version of himself.  Further, he would not be identical to an earlier version of himself--even if it has been only five minutes, he has aged, cells have died and others generated, the molecular composition of his body has changed, his memories are different (they include the time since his visit), and he is in many ways a different person.  So the idea that he is identical to himself is untenable.

However, the issue of arriving "at the same time" is more complicated, and will have to be examined in more detail.

It was suggested that if Blackadder returns to the same exact moment he previously visited, he would replace himself.  It was already shown that he is not the same person, and therefore cannot be said to be the same person who previously visited; but there is also the problem inherent in the idea that arriving at the same moment would mean that his other self would not arrive.

Part of the problem lies in the definition of at the same time.  How accurate does that concurrence have to be?  Is it sufficient if he arrives to within the nearest hour?  That hardly seems to be "the same time".  What about the nearest minute? nearest second? nearest nanosecond?  When we say he arrives at the same time, do we really mean that there is not the slightest difference by any standard of measure between the two arrival times?

That in itself would be somewhat incredible, given the crude (in the sense of rough and inaccurate) nature of the controls (levers and dials with no markings for relative positions) and the crude (in two senses) means of navigation (what we might call the pearl diver memory technique).  The idea that Baldrick could get the controls set correctly to the nearest day boggles the mind; that he hit the same instant by any standard is entirely incredible.

However, if we overlook that, we still have the problem of why simultaneous arrival should be different.  We know that if they arrive years before their previous arrival they do not undo their previous arrival; we know that if they arrive years after their previous arrival they do not undo their previous arrival.  We can reasonably assume that this would be so if the interval were months, or weeks, or days, or hours.  We get down to minutes, and still have no problem imagining both time travel teams arriving, one after the other, possibly interacting with each other as temporal duplicates.  From minutes it is a small step to seconds, and from seconds to nanoseconds, picoseconds, perhaps down to yoctoseconds, we are forced to agree that as long as one party arrives incrementally before the other, each should arrive and be distinct time travelers.

What, then, would be the logic of suggesting that if somehow a time traveler arrived at the exact same instant as a previous version of himself, he would replace that previous version?  Two people can pass through a door together; two people can enter the same room from different doors at the same moment.

Perhaps it is because they would occupy the same space, and so would merge.  Why they should merge instead of colliding and knocking each other out of the way is unanswerable; but then, if we accept that they do merge, why should the older version of the time traveler, that is, the metaphysically second one to arrive, be the controlling mind?

If this is a divergent dimensions story, then everything we learn about how those divergent dimensions work in the first trip is contradicted by the second one.  It is internally inconsistent.

Without belaboring the issue, this is also so if we adopt a parallel dimension theory explanation.  Some of the problems would be slightly different, but ultimately we face the issue that the events of the first string of travels demand one set of time travel rules, and the events of the second string break those rules completely, so no time travel theory will work to explain all the trips.

Blackadder Back & Forth is a fun and humorous (if sometimes a bit crass) movie, but it is, as anticipated, a time travel fiasco.