Talk:Predestination paradox

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Grandfather paradox[edit]

The first paradox I learnt about when viewing the article is the grandfather paradox. Surely the first paradox to be explained should be the predestination paradox? -- (talk) 14:47, 19 January 2008 (UTC)

Don't think so. If you read an article about the son of a famous singer, the article will first explain who the famous singer is, and then go into detail about the son. The Grandfather paradox is just more well-known, so it's a good place to start the subject.--Mithcoriel (talk) 13:41, 13 December 2008 (UTC)

about the heart attack paradox[edit]

If a man discover that he will die (in the future!!!) from heart attack and then (in the present!!) travel to the past and say to himself to get fit, and then he overexerts himself, killing herself of a heart attack, how he will travel to the past now?? (since he is doing exercises, because he think the if he do the exercises he will not die from heart attack) And if he not traveled in time, how did he suffered a heart attack?? [since he discovered that he will suffer a heart attack on the future (after the traveling back in time)]

The way I understood it: Let's say his friend, after seeing him die of a heart attack, travels to the past and tells him: "Watch out, you'll die of a heart attack!" He exercises to prevent this, dies of a heart attack, and then his friend travels back in time to warn him. The text doesn't clearly state it went like this, but I'm guessing it must have been something along those lines. --Mithcoriel (talk) 12:35, 13 December 2008 (UTC)

That's why it's a paradox. If you try to make all the cause/effect scenarios fit together, they don't. LarryJeff (talk) 17:50, 30 June 2010 (UTC)

It's not a paradox![edit]

It may appear as such, but the "Predestination paradox" is not , in physics, really a paradox at all. Philosophically, it contradicts the idea of free will, but even this may be apparent, in as much as it is simply a case of free will not allow you to break the laws of the universe (for example, if I step off a cliff, I'd rather not fall, but no matter how much I will myself to stay in the air, the basic laws of physics state that I have to fall) 14:56, 21 May 2006 (UTC)

The paradox comes from the fact that in a causal loop, the events are both causes and effects of each other. Causality — that a cause precedes an effect — is thus seemingly violated. It might be useful to remember that paradoxes which have solutions can still be called paradoxes (Zeno's paradox, for example). --khaosworks (talkcontribs) 15:05, 21 May 2006 (UTC)
The 'paradox' comes from the question of 'how did this come to be in the first place'. In any example, if you go straight to the origin of the event you realize there is always going to be an inconsistency. For example, the heart attack instance is nonsense because the man clearly had a heart attack because he was overweight - if he went back and made himself into a fitness fanatic, even if he still had the heart attack, it would have been purely by conincidence and the whole past would have been changed. This clearly doesn't create a closed loop, so it is considered a paradox.
Regarding free will, the very idea that you would need to travel back in time is clearly an indication that the subject in question doesn't believe in non-deterministic free will - unless you think the universe is entirely causal, what reason would you have to believe time would repeat itself exactly, given identical starting states? Richard001
I have to agree here. The issue behind traveling back in time is that you would change something that needed to happen. But if you change the thing that needed to happen, then it didn't really need to happen. Classic paradox, and something that the universe (if it is at all sane) would realize and nullify by making NO event totally needed to happen, not even the beginning of the universe itself. I've always thought that there is a possibility that time is not immutable, but is changed on a daily basis by choices that people make. I also think that some people, simply live outside of the restrictions of time (able to travel back and forth at will), and have the ability to change the entire universe with one of their choices. There is the possibility of a Paradox in the creation of the universe itself, where the universe is created by the ending of itself, with few events changed.Christopher1000 06:34, 12 January 2007 (UTC)

In a multiverse (like the reality of quantum mechanics) this is actualy not a paradox. Protons can only exist because they are in balance with their own virtual presence, in other words without their virtual counterpart they could not exist. That results in about 90% of their mass that indeed doesnt exist, dough virtualy it does (but not here). The problem and solution is that quantum world doesnt respect our known world, things can be at the same places, or be linked on an informational level, over great distance. Quantum world can be interpretended as a many to many universes solution (at a micro scale, but also bigger scales). Its just that we cant observe an alternate world, in which our reality doesnt match. we only can observe the micro scale where we indeed see it does overlap. As to the quantum world there are no problem to flip between realities/virtualities (what happened inside protons), and so if there are many realities (where the othere 90% of the mass of a proton sits) then there is a many world reality and in such world this paradox could simply happen, a particle slipping to another reality create havoc there.. and that reality ends (well ends its just out of our evenhorizon, another reality.

I realize this attribution looks to weird, but read about the double split experiment that might be a good starter point to learn about quantum mechanics. As in a multiverse it isnt a problem. —Preceding unsigned comment added by (talk) 00:18, 8 January 2009 (UTC)

I have to agree that this is not a paradox. A paradox is when your assumptions seem reasonable but they lead to a logical contradiction. For example, the twin paradox purports to show that assuming special relativity leads to each twin being older than the other. Paradoxes can be resolved by showing that the assumptions are not correctly stated. In the twin paradox, the resolution is that one twin changed reference frames and the other didn't, and this breaks the symmetry and shows that both twins agree that only one is older.

But there is no paradox in the "predestination" case, because there is no logical contradiction.

In addition, "predestination" has nothing to do with this so-called paradox. Predestination is about whether you can or cannot choose what you will do. Just because you do choose something, the outcome of which is known in advance, does not mean that you could not have chosen otherwise. For example, I drop a stone. At the moment of dropping it I know that it will hit the ground, but to say that it is "predestined" to hit the ground means that I had no choice in whether to drop it. Likewise, if I know that in the future I will perform some action it does not mean that I do not have the freedom to choose whether I perform it. It's the difference between "did happen" and "cannot have have happened any other way". Time travel discussions are often confused by this distinction.Shrikeangel (talk) 01:30, 27 January 2009 (UTC)

Nonetheless, it's referred to as "predestination paradox" in the literature. If you wish, it's like "black hole" which is used to describe something that's not really a hole -- nonetheless, the terminology has caught on in the literature and popular culture. DonQuixote (talk) 02:07, 27 January 2009 (UTC)
No, it's referred to incorrectly as a "paradox" in the literature, which is why actual physicists go out of their way to correct the error. It's really frustrating the way you're trying to rationalize inaccuracy. (talk)

You're referring specifically to a physical paradox, hence the physics reference. Saying that this is a philosophical paradox doesn't imply that it is a physical one, and so you're both correct, albeit using semantics that aren't precise enough to convey it. — Preceding unsigned comment added by (talk) 20:45, 19 February 2015 (UTC)

'there is no paradox in the "predestination" case, because there is no logical contradiction': If you kindly read the article about paradox, you'll note that "logical contradiction" is not always required, "defies intuition" is another way of acquiring paradoxness. Aside from that, if it is called a paradox by the literature, then that's what we state. If other WP:RS disagree, we report that, too. Our own opinions and judgments are unimportant. Paradoctor (talk) 20:10, 14 March 2010 (UTC)

Time-machine schematics paradox[edit]

I've heard the following paradox somewhere, but I don't know the name of it or who invented it.

A man designs a time machine from some schematics that were given to him. After testing the machine, the man travels back in time to give the schematics to himself on his 30th birthday. The man appears in front of his self and explains to him that he shouldn't worry about designing the time machine, as he has done it in the future and will give the schematics to his own self. The man's self receives the schematics and start building the time machine. Time passes until he finally completes it, test it, and remembers that he has to travel back in time on his 30th birthday to give the schematics to himself. He does and a time loop is created. The paradox is: who, where and when did the schematics were created?

So, in which category should this paradox be included?

--Maio 07:06, Jan 19, 2004 (UTC)

It's a staple of science fiction as well - see By His Bootstraps by Robert A. Heinlein for an example. Other examples include a time traveller going back in time and giving William Shakespeare a set of his complete works. It's a variation on the predestination paradox, but more properly should be termed an ontological paradox, since it deals with the origins of things. I've added it to the main entry with that clarification. --khaosworks 07:38, 30 Jun 2004 (UTC)
There's another story by Asimov, completely around this theme. It involves going through a time loop to ensure time travel remains in action, and ends by a man who chooses to not follow the loop, and at that very moment the time-travelling structure dissapears. Someone who has an idea about what novel it is?
Found it: The End of Eternity
This problem in mentioned in 8-Bit Theatre [1], when the characters find themselves in an alternate reality where time is slowed down, so that any action commited in the universe creates a series physical afterimages that follow directly before the last version. Thus, the set of characters the story is focused on can see not only what they have just done above them, but what they are about to do below them. When one of the characters discovers a way to get out, another asks, "Where did you come up with such a great idea?" "I saw the Future You doing it down there," says the first character. "I'm doing it in the future because you told me about it in the past..." says the second. "But only because you saw me doing it in the future. Where did the plan come from? Information cannot erupt into being from nothingness. It's a paradox!" The next future version of the second character then replies, "I try not to think about it."
Sorry if this seems like a waste of space, but I just thought I'd add on... --VolatileChemical 01:36, 26 August 2005 (UTC)
In the movie Somewhere in Time, an elderly Elise McKenna gives Richard Collier a pocketwatch in 1972. Later, Collier travels back in time to 1912, and meets a young Elise McKenna. He gives her the pocketwatch that she will later give back to him. There is no explanation as how the watch came to be.
Laserion 01:46, 23 September 2005 (UTC)
This also suffers from the same problem as the eyeglasses in Star Trek IV. I'm adding it as a comparison to that. --khaosworks (talkcontribs) 02:01, 23 September 2005 (UTC)

This isn't time machine related but time traveling.

In an episode of Andromeda, the ship is somehow sent back into time where they encounter an enemy fleet. I haven't watched the show for ages so I forget the name of the race. But they find thousands of enemy ships, but historical records indicate there were only a few dozen ships that were destroyed by a human fleet. The captain decides to interfere and uses some bomb which devastates nearly the entire enemy fleet. The guy with the spikes in his hand speaks to the captain in a seperate room. He tells him about a certain folklore story. There were thousands of ships and victory was guarenteed. But then an angel of death appeared and destroyed most of the fleet. He says something similar to this effect "I have met that angel of death".

Voyager reference[edit]

Unless I'm not very much mistaken the 999 years Braxton referenced was about the "Future's End" double episode and had not happened before the events of the episode "EPIC". As such I removed the last sentence of that paragraph. -_- 13:18, 32 Jul 2096 (not UTC)

Wrath of Khan scenario[edit]

I wonder if the Star Trek II: The Wrath of Khan scenario ("...the antique eyeglasses Captain Kirk receives from Doctor McCoy in Star Trek II: The Wrath of Khan, which Kirk leaves in the 20th Century in Star Trek IV: The Voyage Home so it can be eventually bought by McCoy") might be complicated by the fact that the glasses are intact when McCoy gives them to Kirk in the 23rd century, but one of the lenses is cracked when Kirk later pawns them in the 20th century. Assuming they're the same glasses, then they must be repaired sometime before McCoy buys them for Kirk, and with each repetition of this loop they age by another 300 years. Most of the other examples given involve the origins of information or genetic code (i.e. people), both of which can be reproduced easily. --Arteitle 05:45, Nov 6, 2004 (UTC)

To be frank, there is no reason to believe that the glasses will be the ones that McCoy buys in future aside from Kirk's remark. It's one of those things that should not be examined too closely lest it falls apart. -khaosworks 07:59, 6 Nov 2004 (UTC)

Back to the Future[edit]

I fail not to see how Back to the Future falls in this category, since the 1985 Marty returns to is definately not the 1985 he left. -_- ckape (talk) 07:22, 2005 Jan 19 (UTC)

I agree that it's a "pure" predestination paradox, cuz Marty's time trip is predestined to happen, but that he creates a grandfather paradox which he then has to correct by not substituting a predestination paradox for it, thereby ensuring his own history, the end result is the same. I've rewritten the paragraph slightly not to account for this. -khaosworks 15:23, 19 Jan 2005 (UTC)

I agree (<--- NOT), Back to the Future implies the opposite to what u said. This paradox require the space Traveler not to be the original one to inspire the paradox. But in the beginning of the movie they are in an altered time line in which Marty traveled back to 1789 (as seen by the unbroken ledge), and Goldie Wilson did run with Marty's suggestion, and Johnny B Good was written with Marty's help. there is no relation with this paradox and BTTF. <-- lie 23:46, 29 November 2005 (UTC)

Predestination Paradox vs. Self-fulfilling Prophecy[edit]

In some respects, predestination paradox and self-fulfilling prophecy can just be a case of to-MAY-to and to-MAH-to. From the perspective of a paradox, receiving information about an event from the future that causes a series of events that culminate in the said event if and only if the information was sent back in time in the first place is a predestination paradox. DonQuixote 17:51, 1 Jun 2005 (UTC)

By this definition, I don't think the scenorio from Revenge of the Sith counts as a predestination paradox. I recall Yoda said in The Empire Strikes Back that visions of the future seen through the Force are possible futures, rather than definite futures.
Possible or otherwise, the fact is that information is sent from the future that ultimately creates that future. I don't see a problem with this; it's the classic Oedipus tragedy. --khaosworks July 3, 2005 02:31 (UTC)
Okay, so if you were one who believed in divination (such as prophecy, as in the fictional example above), and one were to receive a tarot reading that caused one to take a course of action that lead to the event described in the tarot reading coming to pass, then wouldn't this also have to be a predestination paradox? You might state that it wouldn't be, because divination doesn't actually work in the real world, but then that leads to some pretty arbitrary line-drawing if one considers other implications would have to logically follow such a decision (the decision not to include self-fulfilling tarot readings). Where do we draw the line? If we decide to draw a line, is there any NPOVly non-arbitrary place to put it? --Corvun 01:25, 24 September 2005 (UTC)
I'm not sure I follow your argument. The line here is that all our examples are fictional. Divination may or may not be real, as you say. Could you provide an actual example of such a reading that isn't original research? --khaosworks (talkcontribs) 01:36, 24 September 2005 (UTC)
No, I wouldn't be able to provide and example of any tarot reading that isn't original research. Those things are rather personal and tend to have only anecdotal evidence associated with them. That there is anecdotal evidence to suggest that tarot readings do occasionally self-fulfil isn't controversial (though whether the anecdotal evidence is correct certainly would be) or obscure, I wouldn't know where to begin looking for an example from a non-anecdotal source. My question was, where do we draw the line between what is actually a predestination paradox and what is not? I used tarot for an example because they too deal with "possible futures", however, depending upon one's perspective, there is only one "possible future", the one that actually happens, with all other "possible futures" being nothing more than hypothetical, extrapolated for the purposes of warning; even if one believes in tarot and receives a self-fulfilling reading, how does one know that a predestination paradox has occured, rather than just a series of events that happened to bring about a previously hypothesized future? Following this question, how would we apply said determination to fiction, and where would that line then need to be drawn? Forgive me, but when I find myself fascinated by a subject I try to dissect it from every weird angle I can think of. --Corvun 02:00, 24 September 2005 (UTC)
No need to apologize, really. :) The reason for my asking for clarification is because I thought the line was clear. In my view, the definition is stated in the various examples herein. Generally, a causal loop is formed when information (in the form of mere information, or a person possessing that information) acts on the past to produce the "future" that the information comes from. This is what is a predestination paradox, and by implication, an ontological one as well.
If a line is to be drawn, I suppose you could draw a line between the supernatural aspect of a self-fulfilling prophecy, or, alternatively say that were it is mere information, then it is a self-fulfilling prophecy, but where there is an actual traveller from the future acting to produce his future, inadvertently or otherwise, then it becomes a predestination paradox. It's not a distinction I am entirely happy with, but I can see the merit in that. --khaosworks (talkcontribs) 02:18, 24 September 2005 (UTC)
Responding to ...if... one were to receive a tarot reading that caused one to take a course of action that lead to the event described in the tarot reading coming to pass, then wouldn't this also have to be a predestination paradox? This could only count as one if the events actually caused the original tarot prediction to be made. If tarot cards are not in fact affected by future events, it would be only a self-fulfilling prophecy. Think of it this way... a self-fulfilling prophecy works one way only, forwards; it is a prediction that causes a chain of events which make it come true. Predestination paradoxes are continuous cycles, playing out forwards and then changing the past to start themselves over again. I think this could be done through any means, whether information or action. -AndromedaRoach 04:07, 1 July 2006 (UTC)

The following isn't really a paradox since the future event doesn't cause itself. It's just something that happens of its own accord.

"In Douglas Adams' Life, The Universe and Everything, Arthur Dent gets told by Agrajag that there will be an attempt on his life at a place named "Stavromula Beta". Arthur, who has never even heard of the place (and assumes it's a planet), realises that he must go there sometime in his future and therefore is free from worrying about his possible death before he arrives there. He therefore considers himself to be free from death unless he travels to the planet of Stavromula Beta. At the end of Mostly Harmless, Arthur survives an attempt on his life in an Earth dance club called "Beta" owned by "Stavro Mueller". The predestined event having occurred, there is nothing to stop the Vogons from making Earth (and all possible Earths) cease to exist, taking Arthur with it."

DonQuixote 05:40, 25 September 2005 (UTC)


This hardly qualifies as a predestination paradox, because it is constantly made clear that the past can be changed, therefore the movies are set in a mutable, not fixed timeline. Therefore, the timeline in which Skynet is built by Cyberdyne using parts of the first Terminator follows a timeline in which Skynet is built by some other company, later, and Judgment Day therefore occurs later than 1997. This company presumably builds Skynet in the timeline shown in T3, when Cyberdyne is destroyed.

The assumption that the movies take place in altered timelines, and the original timeline is never shown, not only follows the plot more accurately (allowing the past to change), but also resolves most, if not all, predestination paradoxes. For example, John Connor was Kyle Reese's son in the T1 timeline and all the subsequent timelines, but he was born from a different father in the original timeline where Reese had yet to be sent into the past.

The message is said to be memorized, so John must forcefully learn it and make sure it reaches the future unchanged. I believe this is done to make sure the message is delivered the same way as it was in the original timeline. To clarify: in the original timeline, John creates the message (here we have its necessary original source) and passes it to Reese, who alters the past by his very presence (let alone replacing John's original father with himself), and if John does not memorize the message the way it was, the message he creates himself may be different from the one he created in the original timeline, which would result in a different Reese arriving into the past (as long as Reese remembers a different message), a different past, a different future etc. - an incredibly dangerous loop that will most probably terminate with a variation of the grandfather paradox. However, as John remembers the original message, he may pass it to Reese unchanged.

That's it. Ideas shamelessly taken from . I post it here because I can imagine no way to weave it into the article - explanation of the basic principles would be worthy of a separate article itself, which would be immediately deleted as original research. - Sikon 09:51, 26 July 2005 (UTC)


I don't think John Conner ever had a father who wasn't Kyle. In the original timeline, I'd suspect that there was *no* John Conner and that the humans were on the verge of defeat (as opposed to having just won) when they sent Kyle back through time. Though this time, not to protect Sarah Conner, but to warn humanity of the coming storm. Obviously, they all think he's crazy, but for some reason he meets and befriends Sarah, who believes him, which eventually leads to John.

Which in turn leads to there being an exceptionally skilled general with foreknowledge of the rise of the machines. After all, we are lead to believe that the only reason John Conner becomes the "great military leader" is because his mother is preparing him for it. In a universe in which John's father is not Kyle, in which there was no time traveller, there is no reason for this preparation.

That said, before the arrival of the sequels (and until the ending of T2), Terminator 1 was a *perfect* example of the predestination paradox.

Personally I prefered it that way. (Ulicus 04:08, 9 January 2006 (UTC))

I agree with the Sikon. That explanation would solve the pardoxes. But how stupid must Skynet have felt, when it realized that the effort of sending back the terminator was in vain..since this wouldn't alter its timeline and therefore make the machines win the war :o)

Night Watch[edit]

I don't think Night Watch is a predestination paradox. Lu-Tze clearly states that the Vimes who goes back in time was trained by the real John Keel. Things happen much as he remembered them (although not exactly), but that's because he's trying not to change things too much. In other words, it's a "branching universe" type of time travel, but the protaganist is being careful that a future similar to the one he left will result.Daibhid C 21:16, 10 April 2006 (UTC)

That's correct. The real John Keel, we are told, was killed by the other time traveller. Vimes simply follows through with what Keel had done. 19 April 2006

Huh. DNA.[edit]

If you went back and impregnated your great-great-grandmother, your DNA in the present would slowly become more like yourself than yourself. This would be akin to Russell's Paradox. How can your DNA be more like itself than itself.? This would casue the universe to explode, even if you killed you real great great grandfather. Wait, uh, where is the paradox in that? Anyways, tell me what you think. --HomfrogHomfrogTell me a story!ContribulationsHomfrog 20:59, 8 May 2006 (UTC)

Hmmmmmm.....well, I think it would cause a paradox because if you went back in time and impregnated your great-great-grandmother, then your great grandparent would be more and more like you and due to the DNA of your original ancestors having part of the same DNA as your great-great-grandmother, they would be more like you also, and then eventually your parent, that parent's parent (your grandparent) and grandparent's parent would all look more similar to you, but because of the way it all works, it might be possible for all your parents, grandparents and great-grandparents to all have remarkably similar DNA to you. I think there's an extremely small chance for any gene to mutate, but after an infinity of iterations of working this all out, you might be really mutated for the worse and then unable to reproduce (because of death or maybe just sterility) and therefore not able to initiate the predestination paradox in the first place, making it into a grandfather paradox or something. Or maybe instead of mutation, your ancestors looking different might cause them to not get together in the first place, thus making you not ever being born. Not sure, probably a million different ways to cause a paradox. I don't think in fact it would make you look more like yourself, in fact, due to you having some of your great-great-grandmother's DNA, you would probably become more and more like your great-great grandmother (but not too similar, because you're great-great-grandmother isn't directly related by DNA to all your relatives).
The lesson here, Don't go back in time and impregnate your great-great-grandmother (or anyone else that you're related to for that matter). Seeya later, 12:20, 3 June 2006 (UTC)
Why not? It's widely regarded that the entire human race is related. Genetic chance itself has the potential of siblings being entirely dissimilar in terms of autosomal DNA, so it's no real worry. 11:18, 11 June 2007 (UTC)
You raise an interesting point but in a universe that follows the predestination paradox in the purest sense, I believe the idea is that the individual's DNA would never change from "iteration to iteration" (ie. it's one complete loop, rather than the loop going through multiple "iterations" with details differing between iterations). That of course is still peculiar: since we only inherit half of each of your parents' DNA, this means roughly that only 1/8 (1/2 x 1/2 x 1/2) of the DNA is preserved in the loop; the non-preserved parts must then be supplied by the "other parent" in each generation. Basically this would be as startling as a non-time-loop scenario where the great-grandmother and you, by sheer improbable luck, share the exact same DNA. 04:20, 16 June 2006 (UTC)
There is a way that a person could be his own grandfather, without having the DNA that is given to him become more and more pure each time. Your DNA comes 1/2 from your mother and father. You go back in time and impregnate your grandmother (whose DNA is totally different from yours), and your father's DNA is born. Your father then marries your mother (whose DNA is totally different from his), and your DNA is totally different from his. Therefore, when you go to the past and impregnate your grandmother, you do not create the 'pure' strain.Christopher1000 06:42, 12 January 2007 (UTC)
To expand on this, there IS a temporal paradox where something could be seriously messed up: you find out that every male through the past of your family was you yourself, i.e. you marry your great-grandmother, then your grandmother, then your mother, going further back in time to the beginning of time. Though even then, the DNA would change so much over time through the combination of chance and natural genetic abnormalities from illness and other factors, that it might not become and issue.Christopher1000 06:46, 12 January 2007 (UTC)
Concerning the DNA matter, you wouldn't look 'more' like yourself (that is by definition impossible - imagine a number that is closer to 1 than 1 itself!). Instead you would, as mentioned above, be replacing your great-grandfather's DNA with that of a mixture of your 8 great grandparents. You therefore would become more like your other 7 grandparents, and less like your 'original' grandfather. Of course, if you had an 'original' grandfather in the first place, it wouldn't really be a pre-destination paradox. There is of course the matter of completely changing the past - it would be perfectly possible that your great grandmother's new child might die at a young age, or be infertile. Even if it did have children itself, what are the odds of its parter being the same person as in the original timeline?
Hopefully that clears up the DNA problem Richard001 06:33, 12 September 2006 (UTC)
To the person above the person above me who said: "Even if it did have children itself, what are the odds of its parter being the same person as in the original timeline" Wait wait, you're making a fallacy here. That's the whole point! Right from the beginning, that man who died probably wasn't meant to be Fry's grandfather. He was his own grandfather right from the start. He therefore didn't really change the past, he caused it to happen.
I think the DNA-Paradox is simpler than it looks: Let's say A symbolizes a gene you have, and X is one you don't have. Here's what the family tree could look like: ("you" and your descendants are on the left, with the new partner on the right)
AAAAAAAA AXXXXXXX (Greatgrandparents, one of which is you)
AAAAAXXX AAXXXXXX (Grandparents, one of which is your child)
AAAAAAAX AAAAXXXX (Parents, one of which is your grandchild)
Explanation: Your grandfather/son has 5/8 your genes, 4/8 of which he inherited from you, and 1/8 of which he inherited from your great-grandmother/wife.
Your father has 7/8 of your genes, 5/8 of which he inherited from "your side of the family", and 2/8 from your grandmother.
You have 8/8 your genes, 4/8 of which at least you inherited from your father, and the other half, being almost identical in both, could have come from either.
Of course there can be variations here. Due to coincidense, your child might only inherit very few of your genes, and get more later, from other parents. And of course it's not common to have a father whose DNA upto 7/8 similar to your own, but picture it like a regular family with incest.
On another note: The book "The Man who Folded himself" has a much more logic solution for this. In it, the protagonist is not only his own father, but also his own mother, which would explain why his DNA is 100% that of his father, i.e. that of himself.--Mithcoriel (talk) 13:21, 13 December 2008 (UTC)

Timeline based[edit]

Could it possible that if a person were to go back in time, and changes the furute, a parreal timeline would occur in diffrent realms?

No, the reason is that if that were to happen, then the time must be something standing still, but in fact there's no past and no future, only the present is existing. Therefor none of these things can happen. Also if someone goes back in time and changes the future people back in the stoneages would be affected, especially if it was a loop that was created. A loop = erasing of the universe, as time is something unified that one cannot alter or change, a loop would cause time itself to loop, therefor it would seize to exist.. or something.

Black Sabbath's "Iron Man"[edit]

As is being discussed on the Iron Man page, the song has nothing to do with witnessing a future apocalypse.

Too many fiction references[edit]

This article seems to be turning into a library of pop-culture references. The section dedicated to the original concept is now only a tiny portion of this article. I feel there should be more about the subject itself (which still seems utterly illogical to me) and a lot less references - perhaps the references could be moved to a new article about time travel references in fiction (or something similar) and just a small list of the most notable, predestination paradox specific references included. Opinions? Richard001 08:10, 12 September 2006 (UTC)

I've seen this happen to lots of other articles on subjects like this, and usually what happens is that the enormous list gets split out into a "List of"-style article as you suggest. That way every editor with a personal favourite example still has a place to put it while allowing the main page to be kept clean with without major fuss or constant supervision. For example, see Dyson sphere and Dyson spheres in fiction. For this particular page, how about predestination paradoxes in fiction? (I like to avoid a literal "List of" title if I can help it, especially in a case like this where each entry has a few sentences to a paragraph of descriptive text to go along with it) Bryan 08:33, 12 September 2006 (UTC)
In that case, let's add the list from Ontological paradox to it as well, since it's similar and overlaps almost all the time. Wait, I'll mention it in the discussion section of the list article. --Mithcoriel (talk) 13:56, 13 December 2008 (UTC)

Delete this entry concerning the Doctor Who episode 'Parting of the ways', which does not include a paradox, as the character(in a paranormal state) simply puts little reminders through time about her future,- as a reminder to go back and help, not as a causal agent of anykind. If this is a paradox then all Doctor Who episodes are a paradox as why does the doctor not just go to his adventures prior to his "medling",- they usually state "first law of time" or "nature of the universe" as to him not doing this. Book M 11:17, 15 September 2006 (UTC)Book_M

Yes, but the first law of time is an artifical construct created to prevent Time Lords (who live outside of the normal boundaries of time) from changing their own pasts. Even so, there is one Time Lord who is KNOWN to have done this: The Great Rashelon (misspelled perhaps). He is known to have gone back in time and changed his past to make it so he wouldn't become immortal, but he messed up things, so he stopped himself from keeping himself from becoming immortal.Christopher1000 06:49, 12 January 2007 (UTC)

Various fictional predestination paradoxes that aren't...[edit]

Someone (or more than one) seems to be confused about the meaning of predestination paradoxes. Going back in time and changing the future is not a predestination paradox, unless you change the future in a way that makes it inevitable that you would have gone back in time. Some of the examples given are in fact the exact opposite, the extended version of the grandfather paradox, changing the future in such a way that it's impossible for you to have gone back in time.

  • There is a Simpsons segment titled Time and Punishment (episode 109, 1994) which parodies Ray Bradbury's 'A Sound of Thunder', another classic in the time travel genre.
    • This is not a predestination paradox; it's just changing the future.
  • In Futurama, the video game based on the series, revolves around several paradoxes revolving around Hubert Farnsworth selling Planet Express to Mom, including the trashing of the Planet Express Ship, the death of Leela, Fry and Bender, and Farnsworth's Mexican sombrero.
    • There's not enough information here to be sure, but from what I understand, the game actually features a grandfather paradox.
  • In the 3D animated television show Beast Wars (which is related to the Original G1 Transformers story line), the descendants of the original Transformers, Maximals (Autobots) & Predacons (Decepticons), travel back in time to prehistoric Earth, when their ancestors were still in stasis in the Ark. They almost cause the destruction of the Autobot leader Optimus Prime & therefore jeopardize their own existence. Even though they manage to save their ancestors & eventually return home to their own time, their actions in the past still alter their own future. It’s later revealed that their actions in the past were foretold by a powerful Oracle as well, which is also arguably a self-fulfilling prophecy (see below).
    • This would have been a grandfather paradox; since they avert it, there's no paradox at all.
  • In the Video Game TimeSplitters Future Perfect, the main character co-operates with his future and past-selfs multiple times.
    • Cooperating with your future and past selves doesn't make a predestination paradox. There might be one in the game; I don't know (forcing you to go along with what you saw your future self do when you become that future self and travel into the past might qualify), but I doubt it.

Many of the other examples are questionable at best, or better described otherwise (e.g., as ontological paradoxes), but I didn't take them out.

Also, while the first few examples are clearly notable (Futurama, Star Wars, Terminator, Planet of the Apes), does anyone other than a rabid fan think that Mucha Lucha, Time Warp Trio, or TimeSplitters really makes an good encyclopedic example? But again, I didn't take these out. -- 15:48, 10 June 2007 (UTC)

Donnie Darko[edit]

I just watched the movie and the wikipedia article kinda sent me into this article. Anyway. The idea that Donnie choose to stay in his room and die when the engine fell based on what he new from the former time line could be a beginning of a causality. That's why I figure put the reference here since it is quite confusing and would require a great deal of deliberation on interpretations of the plot. Sukima 07:24, 7 August 2007 (UTC)

La Jetee[edit]

Chris Marker's La_Jetée is probably an instance of the Predestination Paradox. The protagonist is chosen for his mission in part because of his clear and sharp memory of the incident from his childhood in which he saw a man killed in the airport. That man, of course, is his future self on the time-travel mission. —Preceding unsigned comment added by (talk) 20:21, 23 October 2007 (UTC)

Artemis Fowl: The Time Paradox[edit]

Should it go into Examples from fiction section? I'm not absolutely sure if it's plot consists of a predestination paradox or not... Goomba Smackdown!! (talk) 17:56, 15 April 2009 (UTC)

Is this really a Paradox?[edit]

The solution to this "paradox" seems quite simple. I'll use this as an example: Person R hears Song X, created by Musician Z. R then time travels to before Z made X and shows X to Z. Z then creates X, which inspires R to time travel back..... but I think that Z would have created X anyways because of events that would have happened regardless of R time traveling. (talk) 03:14, 13 July 2009 (UTC)

What? Dude, can you try rephrasing that, using real names and actual hypothetical scenarios? All these X's, R's, and Z's make it hard to follow your logic. (talk) 19:36, 17 October 2009 (UTC)

Hitler assassination[edit]

I deleted the paragraph about the Twilight Zone episode where Hitler was assassinated because it doesn't technically qualify as a predestination paradox. See, the paradox lies in the notion that cause and effect are one in the same, and how one action directly caused someone else to go back and try to stop it, but ultimately causes it. I don't see how a botched Hitler assassination would fall into this category. Feel free to explain it to me, but please remember Wikipedia's policy on Wikipedia:Edit warring while you do so. (talk) 19:36, 17 October 2009 (UTC)

Hitler was a person who did a lot of horrible things. This causes someone to travel back in time to assassinate him and stop all those awful things. The assassinated (and innocent) child gets replaced by another child who eventually grows up to be Hitler who does a lot of horrible things. This causes someone...etc. DonQuixote (talk) 03:19, 18 October 2009 (UTC)

Not Synonymous with Causality Loop[edit]

A predestination paradox does not require a causality loop. The paradox (such as it is) lies in the predestination aspect, not the causality loop, and predestination occurs any time effects precede causes in time. If my actions are already a part of history, I'm predestined to travel back in time as surely as if I were part of a causality loop. The wiki definition of predestination paradox is thus flawed and misleading.

Here's a simple example that illustrates the point. A man lives in a town with a broken clock. He later falls through a natural wormhole into the past. While there, he somehow breaks the clock inadvertently. Technically, this isn't a causality loop because the broken clock didn't cause him to travel back in time. But it is still a predestination paradox because his act was already a part of history, predestining him to travel back in time. (talk) 17:22, 14 February 2010 (UTC)

That's "predestination", but it's not a "predestination paradox" -- the key being "paradox". The "paradox" part is that A causes B which in turn causes A. DonQuixote (talk) 22:40, 14 February 2010 (UTC)
Predestination is the paradox (such as it is). People find it counter-intuitive that their time travel can already be a part of history before they actually time travel. (Don't we all have free will?) Their confusion results from what's called the "second time around fallacy." By contrast, there's nothing remotely paradoxical about A causing B causing A. Such circular causal loops occur regularly in linear time -- see, e.g., feedback loops. (talk) 18:59, 15 February 2010 (UTC)
Sorry, counter-intuitive does not a paradox make. The paradox is in what started the causality loop (was it A or B?). As for your feedback loops example, that's not a causal loop but rather an additive loop. Feed A into B to get C, then feed A+C into B to get D, then feed A+D into B to get E, etc. DonQuixote (talk) 20:37, 15 February 2010 (UTC)
As others have already correctly noted above, a predestination paradox is not a true paradox in the sense of being logically contradictory -- it's simply counter-intuitive. Nor have you identified any paradox in a causality loop -- circles have no beginnings or ends by definition. Finally, if feedback loops aren't causal loops, why are diagrams of them called "causal loop diagrams"? (talk) 20:48, 15 February 2010 (UTC)
Ok, I see the problem. You're confusing two different types of causal loops. As stated in this link [2] "Causal loop diagrams are maps of cause and effect relationships between individual system variables that, when linked, form closed loops." That is, A affects B which affects C which affects D which affects A, which leads to a feedback. This is different from a causal loop in predestination paradoxes where event A at time t1 causes event B at time t2 which in turn causes event A at t1, which leads to a paradox in that it can't be determined which event was the first event. [3][4] Note that the first loop has time progressing (lab frame time) while the second loop describes two events in spacetime. DonQuixote (talk) 01:33, 16 February 2010 (UTC)

Thanks for the clarification, DonQuixote, but you've simply restated what I originally said -- i.e., causal loops occur regularly in linear time. The point is that there's nothing intrinsically paradoxical about saying A causes B causes A. You can remove the time dimension from causal loop diagrams and they remain logically valid.

Again, a causality loop isn't a true paradox because there's no logical contradiction. A causing B causing A through time travel is simply counter-intuitive. I'm not sure where you're getting this erroneous notion that it's paradoxical not to know which event comes first. (Maybe you're confusing this with the chicken-and-egg problem?) The whole point of the block time/universe model is that all events exist simultaneously in spacetime. You're committing the "first time around" fallacy I mentioned earlier. There's no "first" event in my example of the broken clock, either.

Your own cited sources support my position. Although they mention causality loops, the explanation for why such loops paradoxical relates solely to the "predestination" aspect. Link 2 explains that predestination is required to keep the timeline self-consistent. Link 3 actually notes that this non-paradox applies to predestination in linear time, as well. Again, the "paradox," such as it is, relates solely to the tension between predestination and free will -- it has nothing necessarily to do with causality loops.

Ironically, the wiki definition itself has become a kind of self-fulfilling prophecy. The more people repeat the erroneous requirement of a causality loop, the more it becomes cemented as a requirement, even though it's superfluous. But you could erase that claim from the wiki and the rest of the definition would still apply. All causality loops may be predestination paradoxes, but not all predestination paradoxes are causality loops. (talk) 21:00, 16 February 2010 (UTC)

Predestination paradoxes are defined by causality loops. Whether or not they should have been labeled as "paradoxes" is moot since the term itself has been adopted by popular culture. It's like trying to tell everyone that black holes aren't actually "holes" and should be called something else (like gravity well)--it won't get you anywhere in the end.
Anyway, you can reduce it to a "block-time" problem, but that doesn't tell you anything. You can also reduce an ontological paradox to a "block-time" problem, but that doesn't tell you anything either. Basically, yes, predestination paradoxes deal with "chicken-egg"-like concepts, but that's philosphers for you--just like ontological paradoxes philosophically ask "Where did the item in the loop originate?"
So...I guess you can go on a campaign to correct the term, but until you get everyone to do so, Wikipedia will most probably reflect the popular usage. DonQuixote (talk) 21:59, 16 February 2010 (UTC)
No, predestination paradoxes are INCORRECTLY defined by causality loops. Whether or not they SHOULD be labeled as such is precisely what we're arguing. Just because popular culture embraces an INCORRECT definition is no reason for wiki to repeat the error. That's just ridiculous and underscores the weakness of your claim.
Equally weak is your analogy to black holes. No one seriously objects to the use of the term "hole." By contrast, physicists will go out of their way to emphasize that there's nothing logically contradictory (i.e., "paradoxical") about predestination. Here's a blog entry by physicist Sean Carroll where he discusses predestination on the television show LOST.[5] Note how he stresses that "there are no paradoxes" and time travel on the show "makes logical sense." Similarly, the Novikov Consistency Principle was formulated to AVOID paradox.
Your block time response simply confirms your error. Block time is illuminating because such a perspective resolves the apparent paradox. That is, it shows how predestination in circular time is no different than predestination in linear time, A POINT YOUR OWN CITED ARTICLES MAKE. It's counter-intuitive, not a logical paradox. By contrast, a block time perspective doesn't resolve ontological paradoxes because the puzzle of self creation remains.
To clarify, an ontological paradox is a special case of predestination paradox. The former MAY involve logical contradiction (i.e., be a true paradox) because objects and information have NO origin and NO existence outside the time loop. I say "may" because I honestly haven't thought carefully about whether an ontological paradox is a true paradox. But there's clearly more at work than a generic predestination paradox, making your analogy flawed.
PS: I note that you began by claiming that "counter-intuitive does not a paradox make" but now take precisely the opposite position. (talk)
Er...yeah, I'm a physicist, and I don't "go out of my way" to emphasize...etc. Anyway, you've missed the point of the article that you cited.
"[T]he point of Lost is not to present a realistic depiction of time travel according to the laws of physics...Which is fine; it’s a TV show, not a science documentary...It’s much more important that time travel in Lost makes logical sense — it’s consistent and obeys rules, even if the rules are not those of the real world." (emphasis mine).
And please, don't quote out of context.
You: Predestination is the paradox (such as it is). People find it counter-intuitive that their time travel can already be a part of history before they actually time travel.
Me: Sorry, counter-intuitive does not a paradox make.
Anyway, as I've said, the term "predestination paradox" is defined by the condition "[space-time event] A causes [space-time event] B which in turn causes [space-time event] A", which is a loop in space-time. This is different from a feedback loop where "[object] A affects [object] B which affects [object] C which affects [object] D which affects [object] A, which leads to a feedback" -- that is, it's a helical structure in space-time.
Now, whether the term should be called a paradox to begin with is a matter of physicists/mathematicians vs philosophers. Anyway, no one seriously objects to this being called "predestination paradox" just like no phycisist seriously objects to a space-time singularity being called a "black hole", so the case is moot. Besides, there are lots of things called "paradoxes" which aren't paradoxes -- in fact, these things have solutions that resolve the supposed paradox, such as the ladder paradox and the twin paradox.
The bottom're arguing this with the wrong guy and in the wrong place. If you want to change what a "predestination pararox" is or what the topic in this article should be labeled as, write and publish a paper or something. And if you get it changed, this article will reflect that. DonQuixote (talk) 22:40, 14 March 2010 (UTC)
'lots of things called "paradoxes" which aren't paradoxes -- in fact, these things have solutions that resolve the supposed paradox': A paradox doesn't cease to exist just because the logical problem is solved. In fact, observational paradoxes pose no logical problem to begin with, it is clear that the theories contradicted by the observations must be false. Paradoctor (talk) 00:12, 15 March 2010 (UTC)
But unlike the ladder paradox and the twin paradox, "predestination paradox" doesn't appear to be a term that is used by scientists--check out the google books search here, which looking at the dates of the books involved suggests that the term may have been first used in a time travel context in "Star Trek". And in Star Trek it appears to be used specifically to refer to a case where a time traveler's actions in the past were responsible for the conditions that caused them to travel back in time in the first place, not for any type of causal loop involving time travel. It might be more useful or logical to use the term to refer to any type of causal loop, but in this case we may be using wikipedia to promote a particular interpretation of a neologism (see Wikipedia:NEO). Hypnosifl (talk) 08:02, 15 March 2010 (UTC)
WP:NEO doesn't apply, see [6] and [7], both academics. The real problem is WP:V, this article needs sources, as in "actually contains the term 'predestination paradox'". Paradoctor (talk) 09:32, 15 March 2010 (UTC)
Neither of those sources really defines what they mean by "predestination paradox" though...the first just mentions it briefly without even giving examples, the second gives some examples but you have to infer the meaning implicitly, it's not clear if they're talking about just any form of causal loop or a more specific kind where a person's knowledge of a future event influences their behavior in a way that helps cause that future event. It would help to find a non-Star-Trek source that uses the term and gives a clear definition of what they mean by it. Hypnosifl (talk) 03:02, 16 March 2010 (UTC)
That would be helpful, no doubt about it. But sometimes, unclear, even conflicting usage is all we have. In such cases, we have to report that the literature does not exhibit a consensus position. As I said, we need more sources. ;) Paradoctor (talk) 12:30, 16 March 2010 (UTC)

Change title of article to "Causal loop"?[edit]

"Predestination paradox" appears to be a term coined by Star Trek, try doing an advanced google book search where you put "predestination paradox" in the "with the exact phrase" box (no need to put quotes around it) and under the publication date, restrict the search to books published between 1900 and 2000. You can see that at least up until 2000, the only books that use the phrase in a time travel context (as opposed to some Christian sources that talk about a free will/predestination paradox) are books from the Star Trek franchise. And if you don't restrict the dates, I still only get 42 results, many Star Trek related and others which may have been influenced by Star Trek or by wikipedia articles that use "predestination paradox" as a synonym for causal loops. In contrast, doing a book search for "causal loop" and "time travel" (both phrases in quotes) turns up 65 results, many of which seem to be written by scientists, science journalists, or philosophers (I didn't see any results under "predestination paradox" that seem to have written by professionals of these types). Similarly, a search of "causal loop" and "time travel" on google scholar turns up 119 papers and articles, while a search for "predestination paradox" turns up only 23, and "predestination paradox" with "time travel" gives only 11 (most of which are discussing Star Trek or other works of fiction like Harry Potter and Superman). So it seems to me that "causal loop" is probably the more common term, especially among scientists and philosophers, so the wiki article should reflect that. Does anyone disagree? Hypnosifl (talk) 16:15, 26 August 2011 (UTC)

Redirecting "Causal loop" to this article is a bit like redirecting "Vehicle" to "Model A Ford". A Predestination paradox is a very specific type of causal loop - one involving time travel! A search on google scholar of "causal loop" alone (without time travel) turns up over 7,500 articles and papers, several of them very highly cited (e.g., Business dynamics - cited by 4972).
Renaming this article to "Causal loop" would therefore be inappropriate and confusing. I would suggest a "Causal loop (Disambiguation)" page. --Trevithj (talk) 21:30, 30 May 2012 (UTC)

Specifically I don't remember ever seeing the term prior to Star Trek DS9: Trials and Tribble-ations aired November 1996. Wi-kiry-lan (talk) 00:16, 8 August 2014 (UTC)

Misfits section wrong[edit]

Could a more proficient/known wikipedist with knowledge of the Misfits series (current) ending edit the Misfits section accordingly? Unless there was a serious retconning involved, the paradox described in the section went quite differently. — Preceding unsigned comment added by (talk) 21:00, 12 October 2012 (UTC)

Clear Examples[edit]

The first example (Oedipus), as suggested in one of the discussions above, is a good example of a "self-fulfilling prophecy," but closer to an edge case for a "predestination paradox." The plot would unfold as is if we include the Soothsayer being bribed to say what he does without any knowledge of the future. If we are providing examples, they should be a bit clearer: the "-All You Zombies-" examples should at least lead the list? --John (User:Jwy/talk) 16:57, 31 May 2015 (UTC)