Temporal Paradoxes in live-action TV.
- Babylon 5 had a very weird one. During the Minbari War, the aforementioned aliens stopped short of destroying humanity when they discovered that a character held Valen's (Alien Jesus) soul, explaining where the souls of the Minbari had been going in the past centuries. They believed that Valen re-incarnated into that character. However, in a later episode, it is discovered that this character travels back in time and assumes the role of Valen. So, it's not that Valen's soul went into that man, but that this man was the original Valen soul. One has to wonder if there isn't a 2nd receptacle for Valen's soul (or more; Minbari souls are more complicated than straight reincarnation, and the device they use to prove it reacts in the same way to blood descendants).
- This also falls into the ontological paradox category when you think about it for a bit. If the Minbari had chosen a different fighter from among the thousands at the Battle of the Line to capture, the triluminary would not have activated, and rather than sparing humanity they would have wiped them out. Which would mean that Sinclair would never have gone back in time, which would mean they never would have gotten the triluminary (or defeated the Shadows, probably), which would...yeah.
- Furthermore, if Valen, who founded modern Minbari society and taught them their globally-accepted philosophy, actually learned everything he knows about Minbari society and philosophy from modern Minbari themselves, that creates an Information Loop: he is teaching them things he only knows because they taught him first.
- This event also contains an Ontological Paradox in the form of the triluminaries that Sinclair brought back with him, which became some of the holiest Minbari relics. They were built in the Great Machine just before Sinclair left by Draal, himself a Minbari - so Draal was able to use his knowledge of the existing artifacts' abilities in order to create them in the first place.
- In The Big Bang Theory, in one episode, Sheldon, Leonard, Raj, and Wolowitz buy the original time machine prop. Events in the episode lead to Sheldon and Leonard trying to decide if Leonard could have gone back in time to stop himself from buying the time machine, leading Sheldon to say, basically, "No."
- One has to give credit to Doctor Who, in that a show with a time traveller as the main character delves into temporal paradoxes relatively infrequently; in most cases, the time travelling is just a way to set stories in different periods, the temporal version of Adventure Towns. It does have its fair share of 'em though (especially after Steven Moffat started writing for the new series):
- "The Time Meddler" has characters speculate that if history was changed, their memories would be updated with the new version instantly though later events imply this is not actually the case.
- In the old series, Gallifrey had the Eye of Harmony, a modified black hole that acted as an unlimited power source, universe-wide navigational beacon, and the mother of all temporal stabilizers. Thus even if they screwed up, the Time Lords had access to enough energy to maintain the desired timeline by brute force if necessary (as seen in "The Five Doctors"). In the new series, the Eye of Harmony has been destroyed, so the Doctor has less to work with.
- "The Unquiet Dead": Rose assumes that the possibility of creating a paradox keeps her safe from being killed over a hundred years before she was born. The Doctor explains that time travel doesn't work like that.
- In "Father's Day", we see that creating a true paradox (which seems to require not only a change to history which undermines the traveller's presence, but that the traveller witnesses himself doing this by being present in the same time zone twice) has the effect of releasing Clock Roaches, which eat everything on your planet. No, really. The earlier example was retconned in the later one with a Hand Wave by the Doctor saying that when the Time Lords were still alive they prevented this sort of thing from happening.
- The series does tend to imply that the "Laws of Time" are more of a legal code than physical law: in "Smith and Jones", the Doctor notes that crossing one's own timeline is dangerous and forbidden, "except for cheap tricks."
- Although there's the recurring concept of fixed events (or "fixed points") as opposed to unfixed ones events that must happen in a specific way, as opposed to ones that could happen any way. The Doctor, of course, has the inherent ability to tell them apart, something only a few others are ever able to do.
- "Blink", the episode that gave us the Timey-Wimey Ball, has a paradox at its heart. The Doctor is only able to tell Sally Sparrow what's going on via DVD Easter Eggs because Sally wrote it all down at the time and gives it to him at the end of the episode.
- Another interesting use of the temporal paradox concept comes in "Last of the Time Lords", in which the Master brings humans back in time from the end of the universe to kill humanity... which would normally make no sense, which is why he turned the TARDIS into a "Paradox Machine" to keep the paradox stable. Destroying this acts as a Reset Button which sets everything on the surface back to the way it was before the machine was activated.
- You really have to give credit to "A Christmas Carol" and how many paradoxes it goes through. Traveling back in someone's personal timeline as they watch from the future. Confusing and rather nonsensical; where're the Reapers in all this?! And then the Doctor brings the past version of Scrooge er, Kazran, to visit his future self. Attempts to follow this seriously may lead to your head asploding.
- But then the Grand Moff (who wrote "Blink", "A Christmas Carol", and other Timey-Wimey eps like "The Big Bang" and "The Girl in the Fireplace") is becoming quite known for his confuddling paradoxes. For instance, look at the contributions to Comic Relief! (Both of which written by him.)
- Lampshaded in "The Girl Who Waited". Amy is trapped in a faster timestream. Rory encounters an Amy who has waited 36 years to be rescued. She is the key to saving a younger Amy who has only waited for one week in the timestream, but saving the younger Amy means the older Amy would never have existed to save the younger Amy.
- The Doctor tries to invoke this in "The Angels Take Manhattan". Since the Weeping Angels feed on time energy, creating a paradox would "poison the well" and kill the Angels off.
- Lost: Subverted when Sayid attempted to kill Ben, which simply caused him to grow up into the man he already was. Played straight with the Compass, which is a textbook example of the abovementioned Object Paradox: looping endlessly between 1954 and 2007.
- In the 3rd series of Misfits has a few these crop up in the Simon/Alisha time-travel arc:
- Future-Simon paid £10,000 to past Seth for the immunity to Alisha's power. He got the money from... Seth in the future. Who gave it to Simon in the future, to go back in time and pay Seth with in the past, etc.
- There's also the photo of Simon and Alisha in Las Vegas, which Future-Simon gives to Alisha, who shares it with Simon from the present, who takes it with him to the past to give to Alisha...
- In Quantum Leap, it appears that Sam is affected by the changes he makes to history only after he leaps, and this has some bearing on his occasional manifestation of previously unmentioned skills (and previously unmentioned/nonexistent family members). Al, on the other hand, seems to be affected instantly, but only when probability of a new event becomes sufficiently high. This is best demonstrated when one episode sees Sam assumes Al's identity while he was on trial for murder, but a chain of events results in Sam unintentionally preventing a key witness from testifying, making it increasingly likely that Al will be found guilty; when the probability reaches 100%, Al is replaced by another character, whose words suggest his version of the project is very different from Sam's, but Al reappears when Sam reduces the probability of his conviction and execution down to 20%.
- A particularly freaky one occurs in Stargate Universe; the crew of the Ancient ship Destiny have been planning to abandon the ship, but learn that their attempt to do so will apparently kill them all apart from one man and throw the ship itself back in time by twelve hours. Just as they witness the future ship, one of the crew realises that they can use this opportunity to replenish their supplies, and manage to carry out various repairs to 'their' Destiny by travelling to the other Destiny via the Stargate and salvaging various components and supplies from the future ship.
- 12 Monkeys: Discussed frequently by the characters. Most notably, Cole must avoid 'corrupting' Cassandra's timeline too much because that would prevent her from recording the message that led to his time-travel mission. Then again the paradox that would be caused by preventing the plague seems to concern no one.
- The final seasons reveal that the events of the series are the result of a massive Stable Time Loop that causes the time travelers to cross their own timeline over and over again and shape their lives in ways that assure the continuation of the loop. Cole is revealed to be a product of the loop and its cause. He is the son of a time traveler and everything he does ends up ultimately causing the chain of events that leads to his birth. The only way to prevent all of this is to remove Cole from existence and thus stop the Stable Time Loop from ever existing.
- The 2008 miniseries The Andromeda Strain not only implies that the outbreak in the future is set off by the sample in/from the past, it also implies that the virus itself may posses at least some rudimentary intelligence!
- Doctor Who:
- In the Trope Naming episode for Timey-Wimey Ball, the Doctor was just reading from a script in the past, written down by the protagonists in the present and given to him in the future, so that both sides can communicate across 40 years (he leaves a recorded message, with pauses for the protagonists to "answer", they write down what everybody is saying, they then give the transcript to the Doctor in the future so that he knows what to say on the message and what they're saying back). In this, he famously describes time as a "ball of wibbly-wobbly... timey-wimey... stuff", allegedly pausing because he can't think of what to say, but actually embarrassed that the Stable Time Loop invented THAT for him to say. He did not describe time that way, TIME described time that way!
- Comic relief special "Time Crash": the Tenth Doctor and the Fifth Doctor meet. Ten knows what to do about a certain problem because when he was Five, he had experienced these events and watched his future self do it. When one of the Doctors points out how that makes no effing sense, they both say "Wibbly-wobbly, timey-wimey" and move on.
- In "The Big Bang", the Doctor avoids the physical paradox by throwing away a note written by his future self and placed in the past, but the information on the note is still the source of the information on the note.
- In "Space" and "Time", the two-part mini adventure where the TARDIS materializes inside itself, the Doctor knows he needs to create a controlled temporal implosion, but doesn't know which lever to use to trigger the implosion. Cue the arrival of a future Doctor with said knowledge. The Doctor then uses the lever and then quickly runs into the Police Box, becoming the future Doctor telling his past self which lever to use. Now, answer me this. Where exactly did the knowledge of which lever to use come from?
- In "Under the Lake"/"Before the Flood", an ontological paradox, referred to in this as a bootstrap paradox, is the central theme of the second episode. The Doctor's ghost is revealed to be a hologram created by the Doctor's Sonic Sunglasses, and everything the ghost said was programmed in by the Doctor. The thing is, the Doctor only knew to create the hologram because he saw the ghost and was told what it said. So, when exactly did the Doctor come up with the idea for the ghost and what it said? Also in "Before the Flood", the Doctor gives a hypothetical example of this paradox featuring Beethoven.
- The Series 9 finale "Hell Bent" a few episodes later hinges on the Doctor trying to save Clara Oswald from being Killed Off For Real ... an event he witnessed. Because he would not be doing this if she were still alive, the Time Lords fear a potentially Reality-Breaking Paradox will be created. Everyone, even Clara herself, feels that he is going much too far in trying to save her and is terrified he'll beak the universe. He does manage to save her without ruining reality she exists in a timey-wimey state where she can continue to live normally even though 'time doesn't pass' for her. She must eventually return to die where and when history marks her Final Death, but as she puts it, she's taking the long way around. It's a Bittersweet Ending, though when she realizes what he's potentially risking, Clara wipes the Doctor's memory of her so he won't continue to be, well, hellbent on protecting her.
- A Reverse Grandfather paradox occurs in the Farscape episode "Kansas": In order to convince his dad to not go on the Challenger mission, Crichton sets up a scenario he remembers from his childhood where he was trapped in a burning building and his dad saved him. When the time for the rescue actually occurs, Dad gets injured and older John has to save both his father and his younger self.
- As of the season 3 finale of Fringe it is revealed that the machine left by the first people actually came to be scattered in the past by a future Walter Bishop who sent his machine back through a wormhole leading to the Paleolithic era. This means that the machine both came from nowhere and is infinitely old.
- In the Game of Thrones episode "The Door" it is revealed that the reason why Hodor can only say that word is because Bran warged into his head when he was a child at the same time they were attacked by White Walkers, thus causing him some sort of damage. Hodor is actually a contraction of Meera's orders: Hold the Door.
- The Kamen Rider Fourze/Kamen Rider Wizard crossover film Movie Wars Ultimatum contains two separate Object Loops, both caused by the Fourze portion being set five years in the future and having the Future versions of Gentaro, Ryusei, and Nadeshiko coming back to the present to team up with Haruto (Wizard):
- First is the Fourze Connect Ring. When Future-Gentaro comes upon the Wizard plot, he simply pulls the ring out of nowhere and uses it to help Haruto fight off the film's Big Bads. Before returning to his own time, Future-Gentaro asks Haruto to give his present self the ring (as well as the present Fourze Driver, which he borrowed from his present self).
- Second, and more confusing, is Gentaro's class photograph. Future-Gentaro says that he was inspired to become a teacher by a picture of himself with a class of students; when he shows it to his friend Kengo, the latter remarks on how dog-eared it is. When Future-Gentaro pulls his past self aside to borrow the Fourze Driver, the photo falls out of his jacket, and at the end of the movie we see that Present-Gentaro found it. While we do see the photograph being taken, this happens after Future-Gentaro returns to his time, meaning the photo still technically appears ex nihilo.
- As Lost season 5 deals with a Stable Time Loop, this type of paradox is emerging. Kate, Sawyer, and Juliet save Ben's life, allowing Ben to grow up and turn the wheel, which causes the time travel in the first place. There may be physical examples as well: in the future, Richard gives Locke a compass. Then Locke travels to 1954 and gives it back to Richard. While it's possible Richard now has two compasses (and must later give Locke the "newer" one,) or the compass was never created.
- The other major season 5 storyline has a similar problem. Jack's goal is to set off a bomb that will prevent their plane from crashing, meaning they'll never come to the island; completely erasing everything that's happened on the show. This means Jack will never have been there to detonate it. Interestingly, it is suggested that the explosion may end up doing the opposite of what Jack wants and leads to the plane crashing. The blast ends up creating an alternate timeline where they never went to the island.
- Since the flash-sideways were revealed to be purgatory, it is more likely that the blast was responsible for (or at least contributed to) the "incident" that ultimately led to the plane crashing on the island.
- Happens in "Catch-22" when Desmond set out into the jungle after a parachutist on the island and made sure all of the details of his quest exactly matched his vision of the event. The events of the vision only happened because he saw the vision. Also, Daniel Faraday is sent by his mother, Eloise Hawking, to the island, even though she knew full well that she would be the one to kill him when he arrives.
- The Compass is a textbook example of the abovementioned Object Paradox: looping endlessly between 1954 and 2007.
- In Red Dwarf, Kryten's last words (in a timeline that is eventually undone) are the words he knew he would say because he saw his future self die earlier in the episode. Somehow, though he only said it because he knew he was going to, "enig" turns out to be important, short for "enigma". Of course, Red Dwarf is hardly anyone's idea of "hard SF".
- In Star Trek: The Next Generation's two-parter "Time's Arrow", a 500-year-old duplicate of Data's own head is found in a mine shaft underneath San Francisco, prompting the Enterprise to investigate how it got there. Data gets sent back to 19th-century San Francisco and loses his head in that cave. An Object Loop is averted, because the head takes The Slow Path and is rejoined with Data's headless body after the mission, so it never goes back in time again. But it is still a Reverse Grandfather Paradox because the discovery of the head in the cave is what triggered the mission that ended with the head in the cave. Similarly, Picard only joins this mission because Guinan implores him to go, because she knows he will meet her for the first time in the 19th century, because she implored him to go there, because he met her there, and so on.
- An episode of The Twilight Zone (2002) named Cradle of Darkness has a time traveller woman in the mission to kill Hitler as a baby. Realizing that it was Hitler's upbringing under an authoritarian and racist father which made him bad, she kills herself and the baby, causing the paradox when the Hitlers' maid servant bring home another baby bought to a beggar mother who resembles Hitler.
- In an episode of Wizards of Waverly Place, Harper travels back in time from the future. At the end of the episode, present Harper sees a hat that future Harper is wearing. She asks where she got it, and future Harper gives present Harper the hat. But then you begin to wonder where the hat came from in the first place.
- In a Mighty Med episode when Kaz and Oliver travel back to the '50s, it is them who inspire Horace's love for bridges.
- When, in the Red Dwarf episode "Tikka To Ride", Lister attempts to explain the temporal paradox of the last season finale, the camera explodes. Repeatedly.
- In the Star Trek universe, time travelers (and the writers) are generally immune to the effects of changes they make to the timeline, and can therefore find themselves in an Alternate Universe where they should not exist (as in "The City on the Edge of Forever" (TOS), "Yesterday's Enterprise" (TNG), or "Cold Front" (Enterprise)).
- Star Trek: Deep Space Nine has an episode with Chief Miles O'Brien going forward in time a few hours and then, when he feels he's about to die, sends his future self in the past to take his place and prevent the disaster.Chief Miles O'Brien and Chief Miles O'Brien: I hate temporal mechanics.
- One way this could work is that the original Present Miles was from and the Past he goes to have become Alternate Universes. The "first" universe, what was called the Present, Miles would never return to. However, the show just continues in the changed Past universe.
- And in "Trials and Tribbleations":Lucsly: So you're not contending it was a pre-destination paradox?
Dulmer: A time loop? That you were meant to go into the past?
Sisko: Um... no.
Lucsly: We hate those.
- Narrowly averted in the episodes "Past Tense I & II", where-in Sisko successfully impersonates a historical figure after the man is killed (saving Sisko's life no less) before he can make the Heroic Sacrifice for which history remembers him. That Sisko bears an uncanny resemblance to historical record of the man's appearance becomes something of a Brick Joke in later episodes.
- Deep Space Nine had plenty of other time-travel episodes, mainly due to the presence and involvement of the Wormhole Aliens/Prophets of Bajor who existed outside of time preventing any danger from a paradox. In the resolution of "Accession", the hand-wave itself is even lampshaded ("the Prophets work in mysterious ways")
- Kirby Buckets does both in one episode. The Grandfather Paradox takes place when Shredlock kills his past self in a gutiar duel, causing him to disappear. The Ontological Paradox is when Kirby gives Mac McAllister his nickname.