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This is discussion archived from a time before the current discussion method was installed.

Temporal Paradox classification launched as Temporal Paradox: From YKTTW

Medinoc: Well, here we go! I've archived the old page and rearranged it.

Yongary: Removed
  • My Mother The Car has the main character's mom reincarnated into a 1928 Pierce Arrow.

since it's not actually an example of a time paradox, just a (really stupid) plot device.

NOTE: These are the dissussions that were on the old version of these page
Red Shoe: Sorry about treading on your toes there, LT. I'm going to wait a few minutes to make sure I don't do it again, then fix it.

Looney Toons: No problem. I didn't know anything of the sort had happened, until I saw this note.

Ununnilium: I dunno, they seemed more like killer flying time dragons.

Red Shoe: While I accept that they are actually not much like monkeys, the phrase "flying killer time monkeys" has gained some popularity on rec.arts.drwho, and as I really like the phrase, I try to do whatever I can to spread it.

Ununnilium: Ah, objection withdrawn. Flying monkeys deserve more PR.

Ununnilium: How is bootstrapping not a paradox?

Robert: It's not self-contradictory. Killing your own grandfather makes your existence a logical impossibility (If you exist, your grandfather died childless. If your grandfather died childless you cannot exist.) Being your own grandfather merely defies common sense, which is not exactly a reliable guide to the possible anyway. It is not a logical impossibility, so not a full blown paradox.

Chrome Newfie: True - you can become your own grandfather if, as the old joke and song goes, you have a son, he marries a woman, and you marry the woman's daughter.

However, some time travel theories would say that killing your grandfather (before your father was conceived, important caveat) makes your existence a causal impossibility, not a logical one. If you return back to your "own" time, you are identical to an assembly of particles which just happens to look like you and think you should have a father and existence. You may take your headache meds now....

Ununnilium: Isn't something without a first cause a logical paradox, though?

Robert: Much debated. Either there is an uncaused cause, traditionally God, or an infinite recess of causes. Both alternatives have been called logical absurdities, by different eminent philosophers. Modern physics takes the view that both are possible - radioactive decay is an event with no cause, and various infinitely old universes would have an infinite recess of causes.

Either way, it's a lesser problem than the outright logical contradiction entailed by the grandfather paradox. We can talk coherently about causal loops, but if you can prevent yourself being born (for real, not some kind of trick) then logic is dead and reason pointless.

(random passer-by): There's an old Larry Niven short story about this idea taken to its logical extreme. I can't recall the name of the story, but the central idea was that if time travel is possible, then time travel will never be discovered. It works like this: let's say that tomorrow, someone builds a time machine and announces it to the world. Sooner or later some crazy person will buy or steal a time machine, and travel back in time to kill the inventor. And if at a later point another inventor builds a time machine, he will suffer the same fate. And on and on, for all sentient species in the universe that discover time travel, forever and ever until the end of time. Any inventor of a time machine will be set upon by a time-traveling madman and killed before he can build it.

Seanette: Uh, Chrome, would it matter to kill the grandfather before your father is conceived if it's your maternal grandfather? ;-)
Looney Toons: I liked the "No, really" at the end of the Doctor Who example, so I put it back.

Kizor: You're the super-duper editor, so please yourself. I took it out because I found it funnier deadpan.

Looney Toons: I'm what?

Kizor: I don't know, I'd never use that expression.


Susan Davis: Split off Stable Time Loop as its own trope, and moved the time loop examples there.

Eternity: The nature of the "temporal paradox" is wholly dependent on the way you want to travel backwards in time. As there are no known ways to do this, the entire subject is rather ambiguous. However, if you do travel back in time, you may not assume that the future you left still exists at all, which is the entire basis for a temporal paradox. You, the time traveller, now exist outside of the timeline that spawned you. As such, the time you ended up is now "the present" for all intents and purposes. Any grandfather-killing and screwing with the timeline you do reflects on what is happening "now". Just because you have destroyed your own chance to be born does not mean that you no longer exist. You are now a separate entity, much like any other human being now around you. Any travelling into the future you do now-such as by waiting, which is how we all travel into the future-will not reflect the future you know but the future as it will progress with your meddling. When you time travel, you destroy everything you know and love while you yourself are immune to the effects. Good work. My point is that time travel should not work as a jump mechanism: "jumping" from one time to another and then "jumping" "back". Indeed, there is no back to the future. The future always lies in front of you. And as for the future you left behind? Well that's gone now.

magic9mushroom: The "Ontological Paradox" category is not a paradox at all, it merely makes people's heads hurt. It all falls under Stable Time Loop.
tibieryo: How is this a Self-Demonstrating Article exactly? I found it all rather straightforward... then again, I got a huge Swiss Moment over that syntax one.... What am I missing?


VVK:

Removed (from under "The Object Loop"):
  • This reasoning is itself fallacious. The ravages of time aren't certain, just overwhelmingly probable, but time travel can play havoc with probability. Once paradoxes are ruled out, whatever remains, however improbable, must be the true outcome, as Sherlock Holmes almost said. Thus, the watch can defy expectations by doing the astronomically improbable, and not age. However, authors generally stick to common sense rules, and treat this as a paradox.

This reasoning is more fallacious. The universe does not right itself to avoid paradoxes; paradoxes, or more specifically speaking contradictions, should never arise because they are impossible to begin with, not because an extra causality intervenes to make sure they are not created. The author of the above argument seems to think it's an example of the first notion, but it's really the second. There is no reason why it should be impossible to send a watch back in time so that it would physically age in between the time travels, and the universe will not specifically interfere to make it so. You could say it's impossible because it will create a paradox, but no. There has to be something about the event itself that's contradictory for it to be impossible. On the other hand, the explanation that with infinite loops with slight differences one will eventually occur that ends the loop involves a solution that will arise naturally without the events being altered by some quasi-logical rules.

Robert: I'm not suggesting that the universe rights itself to avoid paradoxes, quite the opposite. Because paradoxes are impossible, a watch ageing during a stable time loop is flatly impossible, being a paradox. Quantumly, we do a Feynman-style sum over histories, and find that the paradoxical ones have zero probability. The calculations have been done, for toy problems with hard spheres popping in and out of wormholes. Note that talking about the different historyies happening one after the other is classical logic, and the world isn't classical.

It may help if you consider that a stable time loop imposes a different boundary condition on the stuff inside, and boundary conditions matter. The second law rests on the boundary conditions at the beginning and end of time, loosely speaking, but inside the stable time loop, those boundaries are irrelevant since it touches neither of them.

I'll see if I can come up with a clearer explanation.

VVK: Also from under that:
  • Possible solution to the concerns of both the "Immortal watch" critique and the "Vanish from the timeline" critique: "My grandfather's axe", aka the Ship of Theseus. Short version: "This is my grandfather's axe. My father inherited it from his father, but the handle was a bit worn, so he replaced it. I inherited it from my father, but the blade was a bit rusty, so I replaced that." An object travelling through time does not need to be composed entirely of the original parts, and while the "watch" itself may be immortal, the replacement parts composing it have a finite age at the time they're added to the watch; the nice thing about this is it leaves no loose ends - thanks to time travel, when a replacement part gets worn out, it can be replaced by a young version of itself, because the watch has traveled back to a point in time prior to when the part was used to repair it.

This describes a special case; the paradox still "exists" because there's no reason why the agents involved would be compelled in all cases to follow this procedure. And even if they did, there could still be infinitely many slightly different variations of the events until one of them involved the loop stopping for some reason or other. So this doesn't really solve anything, interesting as it is.