Time travel has been a sci-fi archetype for many moons now. Novels, movies, books, and video games have been devoted to this intriguing fantasy.

But, sometimes, it just doesn't make any sense.

First of all, I'd like to give an example of when time travel (in this write-up, time travel means travel back into the past, not into the future) makes sense. The original Back to the Future movie is the best example. Michael J. McFly takes Doc's contraption back into the fifties, he obstructs the potential relationship between his mother and his father, and he needs to hook them up before he fades away. Now, this makes sense. Go back in time, screw things up which could injure the future, patch things up back together, and go back to the future (to a nicer house and car, in this case).

Of course, it does get a little ridiculous at times. ("My brother's head is gone!" I mean, wouldn't the three siblings fade at the same time? Actually, wouldn't the photo itself fade, since it was a photo of the McFly kids, and it wouldn't have been taken if they didn't exist.) But the basic premise of the plot holds, scientific limitations notwithstanding.*

But often it just doesn't work that way. Bill and Ted's Excellent Adventure is another Generation X classic. But the basic premise of the movie fails.

If the future is already a utopian society based on Wyld Stallyns, why does Rufus need to go back in time to ensure this?

If Bill and Ted were together for the rest of their lives and made some totally peace-making music, why did George Carlin go back in time to ensure this? That's like going back in time to ensure Abraham Lincoln gets elected president.

It happened in the past. You don't need to go back in time to ensure it.

The same goes for Sherman and Mr. Peabody of Peabody's Improbable History fame. Mr. Peabody and his boy, Sherman, would go back in time with the aid of the Wayback Machine, and there'd always be a problem. Some historical figure would have a fear of heights, or water, or there'd be too many Indians, or something. And Mr. Peabody would always rectify this problem.

But if the present is already as is, you don't need to go back in time to ensure it.

There's a new series on Cartoon Network called Time Squad. I admit I haven't seen it. But, from the commercials, it's fairly safe to assume it's a more modern take on Peabody's Improbable History. Eli Whitney invents a flesh-eating robot, Abe Lincoln is a prankster, uh-oh, call the Time Squad; they need to fix these things, post-haste! But, as said above, Lincoln sure as hell did become the 16th President of the United States. (There, now my w/u isn't entirely devoid of factual content.)

It happened. You don't need to go back in time to ensure it. (Have I said that already?)

Aside from these "let's fix the unbroken" cases, there are also the "that's far too convenient" cases. Perhaps the best example of this is Dragonball Z. Trunks goes back in time three years before he is born, tells Goku some androids are coming, and leaves. Eventually the rest of the Z Fighters learn that the androids are arriving, including Trunks's father, Vegita. Now, in Trunks's time, Vegita was unaware that there were any androids on the way, fell in love with Trunks's mother, Bulma, and knocked her up. But in this time, Vegita is prescient of the androids' arrival. His life revolves around the preparation for the battle, and yet he still manages to fall in love with Bulma, despite the fact that something like that would need to occur under very special conditions. And he had sex with her at the exact same time to the nanosecond that he did in the other time despite this drastic difference in lifestyle, because the present Trunks is the same as the future Trunks. But even worse than that ridiculous convenience is this: Trunks knew going back in time would endanger his birth. So why the hell didn't he go back after he was born, but for dramatic purposes! It certainly would have made a lot more sense if he did.

In conclusion, Time travel is a wonderful tool at a sci-fi creator's disposal to create a scintillating work that can inspire, challenge, and awe.

But PLEASE, people, just let it make some goddamned sense!

I agree that many time travel stories do not make sense, but In all fairness to authors there are some good ones. The best ones I have seen are by Larry Niven and one by Robert Robert Heinlein.
Larry Niven has a series of short stories and one novel based on the premise that in the future the world is in a state of great poverty under a world dictatorship, in which all life except humans and their food yeast is extinct. To cater to the whims of the current Secjen (Secretary General), a time travel branch is formed to go back in time and bring ancient animals to the future. The stories make sense chronologically and handle the issue of a paradox well. Niven's stories are collected in the paperback Rainbow Mars. Niven also mentions time travel in some of his other work, through different creative methods. In the Mote in Gods Eye (I think) it is noted that a Motie had once attempted to build a time machine, but failed. I am sure others will be able to provide more Niven examples, I have not read his work in some time.
Robert Robert Heinlein's contribution is an old short story whose exact title escapes me, but i think it was "All You Zombies-". Even though the entire story is a paradox, it is one which stretches your brain and is logical once you understand it.
Another author who creatively uses time travel in a way is Orson Scott Card, who explores the effects of relativity on people and the culture shock that would follow a journey at near light speeds. In his books Enders Game, Speaker for the Dead, Xenocide, and Children of the Mind, several charecters are forced to deal with what amounts to traveling forward in time due to trips at near light speed.

Thanks to eponymous for the title to the Heinlein story

Many of the descriptions above assume that (1) there is only one time travel paradigm in science fiction, (2) it can be described using the current physical model of the universe, and (3) the current physical model of the universe is correct. These are huge assumptions.

"Back To The Future". Things that are altered by the time traveller fade away rather than vanishing instantly. Those who haven't experienced temporal shift do not realize anything has happened. Those who do have full memories of the universe as it was before things changed. Why is this?

Well, what does the flux capacitor do? "It makes time travel possible." How? In what way? These things are never explained, but I would guess that a thorough explanation of the inner workings of the device would shed some light on the subject. Perhaps a temporal wake is created by chronometric particles, a la "Star Trek: First Contact". Perhaps changes to the timeline do not propagate instantly, but rather ripple down the timestream. In some cases they cause physical damage ("Millennium"'s time quakes). In Marty and Doc's world, obviously not.

"Bill & Ted's Excellent Adventure" presents a different paradigm. Events of the past are NOT changed in this film. There is no dramatic altering of events in the film, no paradoxical destruction of cause-and-effect dynamics. To Bill & Ted, Lincoln, Socrates, and Joan Of Arc exist in the past. To Rufus, Bill & Ted exist in the past. To another observer, Rufus appears in the past. What does this mean?

It means that to an outside observer, all events are happening simultaneously. Think of the actual film stock that the movie is printed on. Each frame, from start to finish, already exists and can't be altered. Bill & Ted come to understand that, and as a result can spontaneously generate things out of thin air. They are committed later to go back and supply everything they've conjured, and indeed they must. They can't decide later that they don't want to. All events are predestined in this universe, but no one inside the universe can be sure of this. Only the outside observer can see what laws rule over Bill & Ted.

In "Time Tunnel", the protagonists jumped around through time, arriving for key moments in history, such as the assassination of Abraham Lincoln or the bombing of Pearl Harbor. No matter what they did to try to alter the course of history, they failed. Did the laws of the universe prevent them from changing history, or were they just really bad at it? One would assume the latter, or folks would rapidly lose interest in the show. But it's the author who determines the physical laws of the universe they're creating.

The "12 Monkeys" world precludes changes from being made -- Cole is sent back in an information gathering capacity. In desperation the board from the future decides to change the past. Cole fails to change things, instead fulfilling the predestined time cycle as a frightened young Cole looks on in the airport terminal.

The real key is to either obey your own rules, or have a damned good reason for breaking them when you don't. If you don't have a good explanation for how things work, just toss out a McGuffin. Fiction is all about the suspension of belief anyway...

I'm not sure if you're employing irony, though it's subtle if you are. I'm not sure if I'm misinterpreting your writeup completely (I sure hope not!) And I'm not sure if I'm just plain wrong... but to me the opposite is true.

What doesn't make sense to me is the 'fading' aspect in Back To The Future. I think this implies a pantheistic universe that knows when you're about to screw-up the time line. Not that there's anything wrong with an intelligent universe but I think it should be explained. If the only tool you're utilizing in your fiction is 'time-travel', that is everything that takes place takes place in a normal universe exactly like ours but with the addition of time-travel, then 'fading' seems a bit superfluous.

In 'Bill and Ted's Excellent Adventure' it doesn't matter that the future is a fact of the matter already. It still makes sense that retrocausality is necessary to achieve that future. For example: Someone greets you from the future with schematics for a time-machine, you build the time machine and then realize that you're the person who gave yourself the schematics originally. What do you do? You go back in time to give yourself the schematics. It doesn't matter that you already have the time machine, what matters is you know the causality behind you having the time machine.

You might say 'What if I don't go back in time and give myself the schematics?'. Sorry, bud, the event already occurred. In fact, in a four-dimensional universe every event that ever occurred and will occur is a fact of the matter already.

Two types of Time-Travel make sense, at least to me: Time-Travel with multiple universes (as explored in the Back to The Future Sequels) or Time Travel with fatalism (IE. Everything, past, present and future is a fact of that matter at all given times. The kind of universe where Laplace's demon would feel at home.)

As for Dragonball Z. Well, I stopped watching that after I realized there was nothing at stake for the protagonists. No matter how many times they died the other characters would always find a way to bring them back to life. When you have nigh invincible superheroes they should either have a weakness that every villain has access to (Superman) or personality disorders that cause them to be somewhat antagonistic (Dr.Manhattan).


I appreciate the points put forward by Orange_Julius about there being 'different concepts of time travel' but I think there are only two (the two I've mentioned) concepts of Time Travel that work paradox free. I'd be happy to be proven wrong, though.

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