5 Time Travel Paradoxes That Will Induce Headaches

5 Time Travel Paradoxes That Will Induce Headaches

You want to travel in time? You better know your paradoxes first.

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So Novikov Principle = "Fixed Points" from Doctor Who. Gotcha.

Actually, I'm a strong believer in the multiverse theory (heck, it's the basis of my fanfiction), which is why I never bother with time paradoxes.

CAPTCHA: respect me

I wouldn't go THAT far, Captcha...

Well, the other theory is of course that by time travelling you step outside of time and thus can make whatever changes you want without actually causing a paradox. Basically the universe knows you existed, and caused an event that prevented your own existence or time travel, and thus you do exist, even if the timeline no longer accounts for your existence.

This is common in a lot of science fiction, and things like the X-men used it heavily in explaining how say Bishop could travel back in time, change the past to prevent a nightmare future, and not cause a paradox as a result. The same science that sent him back in time ensured that he was effectively outside of time, and thus it doesn't even matter if he prevents his own existence.... the universe STILL knows what happened. Of course Marvel has also defined itself temporally a lot of different ways over the years and seems to largely fall back on the "Multiverse" theory which is why guys like Doctor Doom, Kang The Conqueror (actually a future descendant of Doom if I remember) and others haven't pretty much wrecked creation.

The cool thing about the Novikov self-consistency principle is that you can use it to do very difficult computations very easily. Simply set up your problem, then receive an answer from the future. If it's correct, send it back in time unaltered. If it's not the right answer, alter it, then send it back in time. So long as the alteration occurs in such a way that the entire space of answers could potentially be explored, then the only self-consistent loop is one in which the right answer is found and sent back unchanged. For instance, this can be used to factor prime numbers very quickly, which would undermine the basis of some of our most complicated encryption methods.

http://en.wikipedia.org/wiki/Novikov_self-consistency_principle#Time_loop_logic

Not only do I not have a headache, I love this kind of stuff. The only time traveling story/concept that gave me a headache was when I tried to work my way through the flowchart for the movie Primer. Seriously, urgh.....but at least they took into account their own world physics, and applied reasonable limitations. However, their paradoxse were avoided via human means (being careful not to run over their selves of yesterday with a car, for eg). I do not remember if they ever addressed what paradoxes could theoretically cause. Maybe they did; my brain erased most of that movie from its memory in an attempt at self-preservation.

There's the Donny Darko solution too (is that based on a real physicist's work? And what was that person smoking if it was?) which is a bit of a combo of the two solutions mentioned in the article. There's no widespread multiverse, but a time-travel paradox such as grandpacide results in a temporal blip of a divergent timeline, which naturally resorbs itself à la Novikov Principle. The way it does so, and the human agency required, doesn't make much sense at a physics level though. Physics at this level do not depend on moody teenagers deciding to step under falling jet engines in order to right the order of things. Or else the power unit of CERN must be very strange indeed...

I find the multiverse a bit of a cop-out as well, there's no theoretical math to support it that I know of. Plus it lends itself to multiverse type stories which annoy me, like the Earth 2 DC shennanigans; that's a multiverse that's way too centered on human agency and decisions for my taste. If you travel to another multiverse, you won't find yourself having breakfast with the version of yourself who became a rock star. A new multiverse branch should be created when an atom decays NOW instead of waiting a microsecond longer, or when a subatomic particle changes state, or any other change in the universe. So unless you have a way to 'aim' at the rock-star-version universe, you'll be visiting umpteen trillions of exactly replicated versions of your universe bar the position of a bunch of atoms here and there. Then there's the umpteen trillions of universes where earth never formed in its present cosmological position, and nobody seems to ever visit those (note to self: if I build a wormhole-science-based transdimensional time machine one day, I will equip it with a space suit, just in case).

I like the time travel mechanism of Willis's Doomsday Book. Time is resilient and will not succumb to a butterfly effect because you went back to the age of the dinosaurs and sneezed once. Many changes are naturally resorbed, possibly via a Donny Darko split timeline blip that goes unnoticed and does not require moody teenagers and jet engines. However if the time machine coordinates try to drop you somewhere where you WILL cause an unresolvable disturbance in time, the machine simply does not work; the math/physics required simply will not compute and trigger the transfer. Whatever physical mechanism they use to break through the space-time barrier will not work if you are in any way, shape or form likely to be able to kill Hitler. Or step on the egg of the bird that will develop the final mutation of bird flue that will wipe out half the earth's population. Or something. Chaos theory suggests you could NEVER send anyone back with this machine UNLESS you theorize a Donny Darko blip to go along with it and I am now going to stop geeking about all this or I will do nothing constructive for the rest of the afternoon.

I love some of this stuff, Doctor Who LOVES to have fun with it:
image

Even OUTSIDE of the TV:
image

Time travel...it gets a bit.
Weird.

That's easy stuff. Try this one (from Lawrence Miles):
You find a spoon on the ground, pick it up, go back in time, and then place it on the ground... you then find a spoon on the ground, pick it up, go back in time, and then place it on the ground...

Never mind how the spoon got there, think about simpler physics. When you pick the spoon it, and carry it around, it loses some (tiny!) amount of mass due to friction and such, so when you put the spoon on the ground at the earlier point in time, it is smaller than when you pick it up later... wha?

I prefer the Timey Whimey Principle.

I don't understand how the last one is a paradox, you receive a prophecy and it comes true, which then leads the coworker to send you the prophecy, self consistent loop. As to how the loop started? Probably the end result of a whole bunch of prior cycles that kept changing until they fell into a self consistent one.

An episode of the Twilight Zone explored a bit of Novikov when demonstrating the Hitler paradox. Apparently, infant Adolf Hitler was killed by a time traveller (the protagonist), which distraught his parents so much that his mother adopted a child and named him Adolf, much to the dismay of the father, who loved his son so much, he hated the impostor and blamed his (Jewish) wife, causing him to brutally abuse the child, which gave rise to Hitler's infamous, unrelenting hatred... and the rest is (literally) history.

Put simply:
It happened because it happened,
It will happen because it happened, and
It won't happen because it didn't happen.

Temporal Science is fun.

I am of the belief that if you could travel through time, it would be IMPOSSIBLE to change ANYTHING!

There would always be a reason for travelling back in time and once you fulfil that reason there is no purpose for using the time machine to begin with; therefore you wouldn't travel back in time because there is no reason to.

Although you might be able to travel into the future and back to the present (the present being directly after you travelled into the future, not before). As for changing events or anything at all, we will never know. There is always a paradox when it comes to time travel. Still makes it fun to explore all possibilities though!

I feel that the article misrepresents the Novikov Self-Consistency Principle. When it says that "you cannot create paradoxes", it doesn't mean that the universe would magically alter itself to prevent you from killing your own grandfather but that our universe disallows time-travel so that you never get the chance on the first place. Of course it doesn't necessarily apply the same way to fictional universes, but at least in our universe, time-travel as depicted by popular media is straight up impossible.

As for solution to such paradoxes, there is always the stable time loop. Of course normally time loops are just as prone to paradoxes as any other form of time-travel, however it is mostly because authors usually only show you the loop itself but not how it started. To give an example, in Final Fantasy VIII, the Big Bad Sorceress Ultimecia is being hunted by the SeeD organization, so she tries to save herself by going back in time and merging the timestream so that she could destroy the SeeD organization before it even tried to hunt her down, which lets the heroes travel to her in the future and defeat her while also prompting the creation of the SeeD organization in the first place.

Sounds like a paradox, right? She goes back in time to stop the SeeDs hunting her and inadvertently creates the very organization, which than hunts her and prompts her to go back in time, rinse and repeat.

However, this is only the loop. It doesn't tell us about how it actually began. Say, what if there was an "original" timeline where SeeD doesn't exist and Ultimecia is still a tyrant. Now then, what if she tried using the whole "time compression" thing not as a means to defeat SeeD but just as a way to become immortal or something, but it led to the heroes (or even just Squall, since he is the only character whose appearance/gestures actually influence the formation of SeeD) arriving on her doorstep and defeating her. By doing that they create the first loop, whereas the original timeline is erased and now we have the usual timeline with the formation of SeeD and everything.

I know what you are thinking: Isn't that just too convenient? Well, it's convenient the same way as a square peg only fitting into a square hole is "convenient". As I said above, according to the Novikov Self-Consistency Principle, the only way a time-loop could form is if it doesn't create any paradoxes, so of course it all needs to conveniently fit together, otherwise it wouldn't occur. In a way it's a probability-fallacy our brain is not equipped to deal with.

I like the 'feedback' idea from 'Into the universe with Stephen Hawking'. The idea is that a time machine opens up to the past for a fraction of a second at t=0. A single joule of energy passes back one second in the past. Originally the universe had x energy at t=0 but suddenly it has x plus one joule. The machine opens at t=0 with x+1 energy and sends a joule back....

Original t-1=x, t-0=x, energy sent back so t+1=x-1

Next time* you turn on the machine t-1=x+1, t-0=x+1, energy sent back so t+1=x

Next time* you turn on the machine t-1=x+2, t-0=x+2, energy sent back so t+1=x+1

Remember; that first unit of energy is not created or destroyed, it is sent back in time.

*For you it's the first time

First, why the fuck is the "For Science!" article on the "Comics and Cosplay" channel? This only shows that this whole channel thing is a colossal waste of resources, if you can't figure out that there's a channel specifically for "Science and Tech".

Anyway, OT: As I see it, there's two possibilities.

Either a) there's one universe and one timeline, and any thing you do in the past is done because you had to have done to get you to the point where the place where you felt the need to time travel in the first place. ie. The actions of the Terminators in said movies were ultimately futile, because if they had killed off John Conner, then there wouldn't have been a John Conner for them to have sent the Terminators in the past, so there wouldn't have been anything to kill John Conner. Thus, the fact that there was a John Conner in their present meant any time traveling to kill him off was doomed to fail.

Or, b) there are multiple universes, and rather than time traveling to your own past, you're visiting the past of a different universe. Any change you inflict on "the past" won't affect the present of your universe, assuming you can ever find your way back to your own universe's present.

ritchards:
That's easy stuff. Try this one (from Lawrence Miles):
You find a spoon on the ground, pick it up, go back in time, and then place it on the ground... you then find a spoon on the ground, pick it up, go back in time, and then place it on the ground...

Never mind how the spoon got there, think about simpler physics. When you pick the spoon it, and carry it around, it loses some (tiny!) amount of mass due to friction and such, so when you put the spoon on the ground at the earlier point in time, it is smaller than when you pick it up later... wha?

That one's easy - there is no spoon.

As for the rest, there's one important point they all have in common - they all assume time travel is actually possible. The simplest solution to all time travel paradoxes is that time travel just isn't possible. While so far we haven't found anything in physics that definitively rules it out, we also haven't found any way it could actually occur in way that would allow such paradoxes. They also tend to require the use of exotic matter with negative mass, which as far as we know doesn't actually exist.

pfft multiverse *rolls eyes* , that's more a religious concept than a scientific theory. ie people believe it because its comforting not because there's any evidence to suggest its true.

the whole fixed point thing is just silly to. as it wildly discriminates the importance of an event based on our perception of its importance.

and paradox's obviously cant exist so the only thing that looks right is we have absolutely no fluffing idea how time works but its pretty sure the current assupmtions are not going to float.

my wild stab int he dark ... times relative and doesnt care, i think our basic assumption of travel is wrong we think of time travel much as we think of walking down the street, i was here then i made this car and it dropped me off 5 years ago.
i think its all pre set, not destiny just predictable. so my view of traveling back in time is you do just that. say you go back 10 years. you are now you 10 years ago with no future knowledge you just rewound the tape so to speak.

Therumancer:
Well, the other theory is of course that by time travelling you step outside of time and thus can make whatever changes you want without actually causing a paradox. Basically the universe knows you existed, and caused an event that prevented your own existence or time travel, and thus you do exist, even if the timeline no longer accounts for your existence.

This is common in a lot of science fiction, and things like the X-men used it heavily in explaining how say Bishop could travel back in time, change the past to prevent a nightmare future, and not cause a paradox as a result. The same science that sent him back in time ensured that he was effectively outside of time, and thus it doesn't even matter if he prevents his own existence.... the universe STILL knows what happened. Of course Marvel has also defined itself temporally a lot of different ways over the years and seems to largely fall back on the "Multiverse" theory which is why guys like Doctor Doom, Kang The Conqueror (actually a future descendant of Doom if I remember) and others haven't pretty much wrecked creation.

Marvel Comics still uses multiverse theory, they just flip the definition from the standard one that the article uses (popularized by Ray Bradbury, IIRC). Basically, in Marvel terms, the original timeline becomes a "parallel universe", and the new timeline is now the mainstream universe. This makes a lot more sense in a story where time travel is possible and effective, yet paradoxes are not created.

The X-Men are, as usual, the best example. Rachel, Bishop and Nimrod are all from the "Days of Future Past" universe, which continued to exist after Kitty went back in time and prevented it from happening in the main timeline. Nimrod is a Predestination Paradox (the tech from past-Nimrod is used to design future-Nimrod), while Bishop is a Grandfather Paradox (the reason he went back in time is no longer valid thanks to his own actions) and Rachel is not really a paradox at all. (She time traveled specifically to escape her own timeline, and now affects only the main timeline.)

I like to think that, as a time traveler, you are exempt from the laws of causality. You no longer travel from A to B to C, but by jumping to random points you would be the Effect preceding the Cause. Thus you are able to go back and kill your own grandfather and still be able to exist, all without having to resort to the multiverse theory.

The Novikov self-consistency principle is problematic. He couldn't rule out time travel all together and he didn't want to abandon a basic assumptions about the nature of the universe so he figured what was needed to make these things fit together. What he came up with is basically a literal force of logic - a force that exerts itself in order to maintain logic. This seems highly suspect. I think it is much more likely that one or several of our basic assumptions about the nature of time and the universe is incorrect.

GabeZhul:
I feel that the article misrepresents the Novikov Self-Consistency Principle. When it says that "you cannot create paradoxes", it doesn't mean that the universe would magically alter itself to prevent you from killing your own grandfather but that our universe disallows time-travel so that you never get the chance on the first place. Of course it doesn't necessarily apply the same way to fictional universes, but at least in our universe, time-travel as depicted by popular media is straight up impossible.

The Novikov Self-Consistency Principle was created to explain the predicted existence of closed timelike curves. It does not flatly disallow the existence of time travel, it attempts to explain how a universe in which closed timelike curves exist could be logically consistent.

It is a purposed solution to time travel paradox, not a flat out denial that time travel is possible.

Robyrt:

Therumancer:
Well, the other theory is of course that by time travelling you step outside of time and thus can make whatever changes you want without actually causing a paradox. Basically the universe knows you existed, and caused an event that prevented your own existence or time travel, and thus you do exist, even if the timeline no longer accounts for your existence.

This is common in a lot of science fiction, and things like the X-men used it heavily in explaining how say Bishop could travel back in time, change the past to prevent a nightmare future, and not cause a paradox as a result. The same science that sent him back in time ensured that he was effectively outside of time, and thus it doesn't even matter if he prevents his own existence.... the universe STILL knows what happened. Of course Marvel has also defined itself temporally a lot of different ways over the years and seems to largely fall back on the "Multiverse" theory which is why guys like Doctor Doom, Kang The Conqueror (actually a future descendant of Doom if I remember) and others haven't pretty much wrecked creation.

Marvel Comics still uses multiverse theory, they just flip the definition from the standard one that the article uses (popularized by Ray Bradbury, IIRC). Basically, in Marvel terms, the original timeline becomes a "parallel universe", and the new timeline is now the mainstream universe. This makes a lot more sense in a story where time travel is possible and effective, yet paradoxes are not created.

The X-Men are, as usual, the best example. Rachel, Bishop and Nimrod are all from the "Days of Future Past" universe, which continued to exist after Kitty went back in time and prevented it from happening in the main timeline. Nimrod is a Predestination Paradox (the tech from past-Nimrod is used to design future-Nimrod), while Bishop is a Grandfather Paradox (the reason he went back in time is no longer valid thanks to his own actions) and Rachel is not really a paradox at all. (She time traveled specifically to escape her own timeline, and now affects only the main timeline.)

It could be argued that Marvel uses the Multiverse theory now, it hasn't always done so. Largely because Marvel has an increasingly vested interest in keeping as many versions of it's various IPs out there as possible. I thought I mentioned that originally. There is a difference between how Bishop was originally conceived, defined, and handled, compared to where they went with it later. Especially when you look back at some of the comments made when guys like Kang have showed up from the future (he's not a moron, and the point is he's not splitting the timeline which is what made him so terrifying, but they use him increasingly less), not to mention very old Story Arcs where Spider Man hitched a ride on Doctor Doom's time machine. After all when Spidey returns to the present the last time and there is no more time travelling going on, he doesn't suddenly run into a second Spider Man. Granted there are a number of conceptually unlikely ways of dealing with that (like say every Spider Man sidestepping into another reality at that time so none of them ever meet each other) but that wasn't in the spirit of the story from what I remember. Ditto for the whole Bishop thing, where the whole point would have been rendered irrelevant if travelling back in time would have accomplished nothing (which is something Forge of all people likely would have known).

But yes, other odd Paradoxs do show up, and stories about Cable fighting Apocolypse, heavily exploit that possibility. Way back during "Contest Of Champions 2" they even had a weird match up between Cable and The Scarlet Witch which was never resolved. The Scarlet Witch fundamentally changes probabilities, while Cable travels/bodyslides through time and space to use foreknowledge to counter problems he's encountered in the past (well in his most over the top portrayals). The "match" as far as it went involved Wanda hexing, and Cable entering flux (shadows of multiple versions of him there as he ran through possibilities of beating her) as they started countering each other continually before it was interrupted. While I suppose one could argue billions of alternate realities were created right there (billions is nothing when your dealing with the infinite) I'm not buying that within the spirit of the entire thing, even when one argues the Cable is fighting Apocolypse across multiple realities at any given time.

What bothers me and it is almost never discussed is that the atoms (whether in a time traveller's body or object) are already in use in either the future or the past by another object. We cannot create mass/energy

Yes, this could be explained by the parallel universe theory: one would arrive at a universe where exactly the number of atoms in your body would be there already... in your body.

So, if I were to travel to 100 years to the past, the atoms that make up my body, clothes, etc would be already in use by a potato, a train, some Ukrainian woman's scarf and 6 of my atoms would be part of Einstein's body (probably his balls)... apparently, we all need to have someone famous' atoms in our body today. The point is that I could not be there.

Same thing if I travel 100 years in the future. Most of the atoms that compose me today would be scattered and in use someplace else. My mass cannot occupy that space... even if I am scattered in trillions of little bits all over the world (although most likely in a pile of dirt or ash).

Imagine we made the sun travel 1 second into the past, now we got 2 suns. We could essentially duplicated anything like in diablo 1 by making it travel back in time. It fucks thermal dynamics in the face and then some. The problem with pseudoscience like time travel is that it fucked up all the proven science.

My personal favorite paradox is from the Robert Heinlan story 'All You Zombies' Spoilery summary, with the really big spoilers in a spoiler box

An agent for a time travel agency wants to recruit a man Known as 'the unmarried mother'(TUMM), and listens to his lifes tale - of how he was abandoned on the doorstop of an orphanage as a girl (bear with me), and as a teenager was seduced by an older man who got her pregnant and then abandoned her suddenly, with the birth revealing she had both sexual organs, and the pregnancy had ruined the female, so they set her up with the male organs. As a man he bonds with his new daughter, until the father (though described as being older than he would have been) kidnaps the baby and disappears.

The recruiter offers to help TUMM find the guy and take his revenge, taking him back in time...

Hagi:

I believe that is the Predestination Paradox :)

Rhykker:

Hagi:

I believe that is the Predestination Paradox :)

I was under the impression that the predestination paradox is a time traveller causing himself to go back in time.

As in a person as an infant getting saved by a mysterious man, causing him to live to an old age where time travel is invented. In order to find out who saved him he travels back in time, only to find an infant on the verge of death and him the only person who can save said infant.

Killing Hitler seconds before he commits suicide hardly constitutes causing your own journey, you'd have to cause Hitler to happen for that paradox to go.

See, this is why Looper is my favorite piece of time travel fiction. It just loudly proclaims that it doesn't want to deal with all the bullshit of time travel... so it doesn't, expediting the problem and getting to what everyone was there for in the first place.

I liked Stein's gate idea that time is "set to a channel" and you can 'flick the channel' but the timeline tries actively to avoid changes.

Hagi:

Rhykker:

Hagi:

I believe that is the Predestination Paradox :)

I was under the impression that the predestination paradox is a time traveller causing himself to go back in time.

As in a person as an infant getting saved by a mysterious man, causing him to live to an old age where time travel is invented. In order to find out who saved him he travels back in time, only to find an infant on the verge of death and him the only person who can save said infant.

Killing Hitler seconds before he commits suicide hardly constitutes causing your own journey, you'd have to cause Hitler to happen for that paradox to go.

The example you gave is an example of the predestination paradox, but the predestination paradox doesn't have to involve a time traveler causing himself to go back in time. Check out the example given in the article -- it doesn't involve anyone traveling through time at all :)

Rhykker:

Hagi:

Rhykker:

I believe that is the Predestination Paradox :)

I was under the impression that the predestination paradox is a time traveller causing himself to go back in time.

As in a person as an infant getting saved by a mysterious man, causing him to live to an old age where time travel is invented. In order to find out who saved him he travels back in time, only to find an infant on the verge of death and him the only person who can save said infant.

Killing Hitler seconds before he commits suicide hardly constitutes causing your own journey, you'd have to cause Hitler to happen for that paradox to go.

The example you gave is an example of the predestination paradox, but the predestination paradox doesn't have to involve a time traveler causing himself to go back in time. Check out the example given in the article -- it doesn't involve anyone traveling through time at all :)

You don't have to travel through time to cause time travel.

Your given example involves the coworker sending information back in time that causes an event that causes her to send information back in time. Thus she herself is causing her own action of time travel.

Killing Hitler, after he's already committed the atrocities doesn't match this pattern. Him committing said atrocities, the cause of the time travel, isn't impacted by the time travel. Regardless of whether or not the time travel actually occurred the cause for it remains.

The predestination paradox involves a cause for time travel that wouldn't have occurred without that time travel. In effect meaning the instance of time travelling is causing itself, thus it's called predestination.

Going back in time and killing Hitler in 1945 because of atrocities committed before that is not a paradox, predestination or otherwise. The cause for going back in time remains fully intact and unaltered even after the time travel.

Of course the other possibility is that the universe is predestined, everything that will happen has in effect already happened, and you can change nothing because your 'change' is what already happened. IE we know that noone ever goes back in time to kill Hitler, because he didn't get killed.

 

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