# Time Dilation

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Jack O'Neill: What day is it?
Daniel Jackson: Well, this might be a little difficult to accept, but since you reported for duty yesterday, two weeks have actually gone by.
O'Neill: Two weeks? [beat] I think I'll sleep in.

Time Dilation is a scientific concept related to relativity which states, basically, that for an observer aboard a spaceship travelling at any speed at all (though only noticeable at appreciable fractions of the speed of light) with respect to Earth (or any inertial reference frame of your choice), time passes more slowly than it would for an observer on Earth. When near-lightspeed travel becomes involved, the effects become quite drastic: A person might go on a space journey that seems to him to last one year and, on returning, find that 10 years have passed on Earth. It is, in effect, Time Travel, most effectively to the future, but since this can also make time be experienced faster by someone faster than everyone else, it can provide a way to go to a relative past.

In general relativity, an additional time dilation effect is caused by gravity. Time passes more slowly nearer to the bottom of a gravitational potential well (e.g., on the surface of a planet) than higher up in one (e.g., in an airplane). This dilation, in addition to the dilation due to differences in velocity, needs to be compensated for by clocks on satellites.

In fiction, this effect is often used to facilitate a variation on Mayfly–December Romance, with the earth-bound partner as the "short-lived" one compared to the space traveller. Such plots can also involve a familial relationship instead of a romance — in this case, the earth-bound character is usually the space traveller's twin or child. On a lighter note, it's also often used for some version of a Stock Joke about how annoying time dilation can make keeping track of time.

This is sometimes extrapolated by science fiction authors to apply to Faster-Than-Light Travel as well, though this does not make much sense physically. Many writers extend this so traveling faster than light means aging backwards, but that isn't how the math says it works. The time scale factor for speeds faster than c is imaginary, not negative. If an object is travelling faster-than-light, though, that means there is always some slower-than-light frame reference that sees the object travelling backwards in time — or possibly moving in the opposite direction, with events on the object occurring backwards.note  The Other Wiki has an article on tachyons, theoretical objects that move faster than the speed of light, and explains how this works.

Compare Year Outside, Hour Inside and Ludicrous Speed. Rip Van Winkle is a related trope in more fantastical works. Year Inside, Hour Outside is the inverse, and tends to show up in softer works or those using magic rather than physics.

Some examples of time dilation in the real world:

• GPS has a small correction for time dilation between the surface of the earth and up in space. A satellite in space experiences 0.6 nanoseconds more for every second on Earth. This is actually how GPS works - by knowing what time each satellite the receiver is getting data from thinks it is, it can use the time dilation to calculate the distance from the receiver to each satellite, which can be used to triangulate the receiver's position.
• Muons are subatomic particles that are similar to electrons but with a much shorter lifespan (about 2.2 microseconds, on average). "Slow" muons can be created in particle accelerators, and "fast" muons are produced naturally in the upper atmosphere by cosmic ray impacts. The fast ones are generated at a high enough altitude that few should reach the surface before decaying, but many do – and the Rossi-Hall and Frisch-Smith experiments confirmed they arrived in numbers that agreed with their lifespans being elongated by time dilation (they travel at between 0.995 and 0.9954c which results in a time dilation factor of around 8.4).

There are a couple of quirks about real-world time dilation that also make it somewhat different from what you see in fiction:

• You have to get pretty darned close to the speed of light to see any significant time dilation effects at all. At 90% of the speed of light, your "gamma factor" — how much slower your clock will seem to a stationary observer — will only be about 2. To get a gamma factor of five million (roughly what you'd need for one minute of your time to equal a decade in "rest time") would require moving at 99.999999999998% of the speed of light.
• Gravitational time dilation is a miniscule effect - so miniscule that it would only be perceivable by a human exposed to incomprehensibly strong gravity (at which case, they would obviously be dead many times over.) As The Other Wiki helpfully points out, even on the surface of the Sun where gravity is 28 times stronger than Earth, a clock would only accumulate a completely negligible 66 fewer seconds over the course of an entire year.
• Time dilation works both ways. To the guy standing on Earth, you're whizzing past him at 90% of the speed of light, so to him your clock seems to only be running at half normal speed. But to you, you're standing still and the Earth is whizzing past you at 90% of the speed of light, so to you the clocks on Earth seem to be running at half normal speed. To you, the people back on Earth are the ones aging more slowly. This seeming paradox is only resolved upon carefully examining the path taken by both observers — or, in this example, by you and your friend back on Earth — and realizing that you had to decelerate and turn back, tracing a path in 4-dimensional spacetime that is not a straight line. According to the odd notion of distance defined in 4-d spacetime, a straight line actually has the longest possible distance, corresponding to the longest possible time. Then you, the traveler, will experience a smaller subjective amount of time than your buddy on Earth.

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## Slower than light-speed examples:

Anime & Manga
• Gunbuster, the original giant robot time dilation story. They even call it the Urashima effect (though it was changed to the "Rip Van Winkle effect" on the DVD to avoid telling an enormous story). Be sure to have tissues nearby anytime it comes up.
• Str.A.In.: Strategic Armored Infantry, since there's no FTL travel in the series.
• In The World of Narue, Narue's elder sister Kanaka came to stay with them on Earth. Unfortunately, Narue and her father had access to FTL travel while Kanaka snuck aboard a ship traveling normal lightspeed. The result is that when Kanaka reaches earth, enough time has passed there that Narue, the younger sister, is now physically older.
• One episode of the Dirty Pair TV anime had a space travel magnate try to separate his son from a lover he disapproved of by launching her on the prototype of a slower-than-light "Time Dilation Tour" ship he had handy. The plan was that she'd only return after the son had aged the fifty years of the trip. The Lovely Angels can't stop the launch, but freed the son in time for him to follow his love on another of the ships. The father finally gets on the final ship because he can't live without his son.
• Towards the end of Futaba-kun Change!, three characters depart for the Shimeru clan's home world on a high-speed spaceship. While they see the journey as a few days at most, eight years pass on Earth.
• In Episode 9 of Wish Upon the Pleiades, Nanako must retrieve an Engine Fragment at the edge of the solar system, traveling at 99.999% of lightspeed. While it only feels like half a day to Nanako, three months pass on Earth while she's gone. Luckily, the girls manage to bring Nanako back to right before she left through inertia shenanigans, along with the Fragment.
• The Aratrum takes millennia to get from Tau Ceti e back to Earth due to relativistic effects in Godzilla: Planet of the Monsters.

Comic Books
• The Alan Moore comic The Ballad of Halo Jones deals with this in the war period of Halo's life. The planet Moab has such an extreme gravitational field that all the soldiers have to wear high pressure armor to fight. When the Amazon Brigade marches towards combat, the fight is frozen but gradually speeds up as they get closer to it, being at normal speed by the time they arrive. Every time Halo goes out on a mission for an afternoon, she misses another birthday. She ends up getting promoted this way, and she returns one last time to find that war ended months ago.
• The Marvel/Epic comic series The Alien Legion had the members of Force Nomad fighting a battle in the event horizon of a black hole. There they met a race of aliens that had been there for decades, but all their star charts were millions of years out of date. They helped our guys get out, but their system of measurements was incomprehensible to all but one of them (This was because it was amazingly ancient, and so was the translator's race). They were able to leave after a short time, but discovered that fifteen years had passed on the outside. During that time, they had been declared dead and Tamara's infant daughter was a teenager in her own platoon.
• The origin story of X-O Manowar: a Visigoth soldier is enslaved by aliens on a slower-than-light ship. Seven years passed on the ship, but 1600 years passed on Earth by the time he returned.
• This ends up striking in Sonic the Hedgehog (Archie Comics). At one point, Sonic is transported over a million light years away from Mobius. He spends a fairly short time making his way through inhabited space until he makes it to a special Portal Network that allows him to instantly warp back to Mobius. However when he arrives, he's horrified to discover that thanks to relativity over a year has passed on Mobius and without him around Dr. Robotnik has pushed things to the brink of nuclear war.
• "Years for Gustave", a story in the anthology Speculative Relationships Volume 2, a long-lost astronaut has been through so much time dilation that his wife went through massive Bio-Augmentation and Lightspeed Leapfrogged him in order to intercept his off-course ship.
• Disney Ducks Comic Universe: An Italian Donald Duck comic used this to explain the absence of Della Duck. She left Huey, Dewey and Louie with her brother Donald for what was supposed to be one afternoon and never came back. Turns out she went on a rocket flight and is oblivious to the fact that her sons have grown older during her 10-minute trip.
• In All-Star Superman, Superman shoots the now superpowered Lex Luthor with a gravity gun that makes him dense enough to warp time and make his powers run out quicker.
• Invader Zim (Oni): Issue 28 is built around an experimental Irken device called the Time Accelerator (or the "Time Thingy" as it's nicknamed). It generates a field which causes time to move faster the closer you get to it. And when it ends up exploding near the end of the issue, it causes Zim to age into an elderly state.

Fan Works
• A Changed World has Eleya rescue 23rd century Bajorans and Klingons that have been trapped in the gravity well of a black hole since 2271, while in the outside world it is now 2410. The resulting Fish out of Temporal Water situation, especially the clash between pre-Occupation casteist Bajorans and post-Occupation pro-Federation Bajorans, drives the second half of the story. Also, as a logical consequence of the functions of the warp drive (it moves space around the ship to defy the light barrier), USS Bajor is able to use warp fields to shield itself from the worst of the black hole-induced time dilation; they're predicted to only lose a few hours during their rescue attempt.

Films — Live-Action
• The first 80% of Flight of the Navigator plays time dilation straight, David is taken on a space ship that travels at relativistic speeds, so when he is brought back to Earth, 8 earth-years have passed for his family but only 4 1/2 hours for him. The last few scenes are just straight up Time Travel, which is, of course, impossible.
• Used for a cheap gag towards the end of The Ice Pirates.
• Planet of the Apes has the astronauts travelling two thousand years into the future at near light speeds though Beneath the Planet of the Apes retcons this into a wormhole to allow backwards time travel in Escape from the Planet of the Apes.
• A major plot point of Interstellar involves the gravitational dilation of time around a black hole. The first case happens on Miller's planet, which is located very close to the black hole, which means that an hour on the planet's surface is equal to 7 years on the outside. Cooper and Brand spend only a short while on the planet. Upon their return to orbit, they meet Rommily, who has been waiting for them for 23 years and didn't think they were coming back. Later, Cooper attempts a Spaceship Slingshot Stunt around the black hole. Upon exiting the event horizon, he comments that this maneuver just cost them 51 years (for the people back on Earth), while taking only minutes for the ship. By the time Cooper is reunited with the rest of humanity, he finds out that he is officially 125 years old, while still looking to be in his 40s. His son has died decades ago, and his daughter is now an old woman on her deathbed.
• Happens by accident in the Soviet sci-fi classic Moscow — Cassiopeia with the original crew of the Generation Ship ZARYa ("dawn" in Russian, although it's also an acronym) ending up arriving to their destination when the ship is accelerated to near-light speeds (The Captain mistakenly calls it Faster-Than-Light Travel, but it's clear that it's this trope instead). When they then contact mission control on Earth (using some sort of Subspace Ansible), they are greeted by a former classmate of theirs, who is now a forty-something woman.
• Discussed in Close Encounters of the Third Kind when the aliens return the abductees, some of whom have been gone for decades, but don't look any older.
Scientist 1: They haven't aged a day. Einstein was right.
Scientist 2: Einstein was probably one of them.

Literature
• The short story "Shore Leave Blacks" by Nancy Etchemendy is about the pilot of near-lightspeed spacecraft dealing with the problems this causes her, as she ends up leaving behind not only a husband/lover (I forget which) but a son who will be her age or older by the time she returns.
• Flatterland, an unofficial sequel to Flatland, illustrates this concept with the story of the Paradox Twins. One of them travels at near-lightspeed to the moon and back (or something like that) and returns to find his twin older than he is.
• Time for the Stars by Robert A. Heinlein is about a pair of telepathically linked twins, one of whom goes on a near-lightspeed colonization trip and ends up substantially younger than the other one.
• The International Fleet in Ender's Game relied on this trope specifically. Mazer Rackham, the last great military leader Earth had in the wake of the Second Invasion, was needed to train the genius who would lead Earth's counterattack, so they put him in a spaceship, got him up to a relativistic speed for 25 years, and then he turned around and came home. Only about eight years passed for him, 50 for everyone else.
• At the end, Ender moves to a colony planet with the journetly taking two years from his perspective but 50 to the rest of the universe.
• The sequels take place 3,000 years after it, but involve many of the same characters as they've spent most of their life on spaceships traveling at relativistic speeds. However, he got the bit about this trope working both ways wrong. Relativity and Subspace Ansibles don't mix well.
• Alastair Reynolds plays with time dilation a lot in his novels. The most notable example is probably Pushing Ice, which involves a near-future spaceship encountering an advanced alien artifact which accelerates to such a degree that they end up millions of years in the future.
• This is The Gentle Giants of Ganymede's premise, when humanity runs into a shipload of Ancient Astronauts who had been forced to circle around the solar system for the last several million years due to an emergency hyperspace jump gone wrong, until their engines finally ran out of fuel.
• In the Noon Universe, FTL travel is impossible. All ships travel at near-light speeds and return centuries later (objective time). This all changes when the crew of a starship decides to try something new. Normally, constant or slowly increasing acceleration is maintained for most of the voyage. The captain of the ship decides to try high acceleration for most of the trip (about 10g) in order to reverse the effects of time dilation, as this would fall outside of the Special Theory of Relativity. According to the captain, General Theory of Relativity allows for this. This works, and the ship returns to Earth six months later; however, several years pass for the crew.
• In Captain French, or the Quest for Paradise, the only way to travel between the stars is with the use of a relativistic drive system. It does not require any acceleration (i.e., works like the lightspeed in Star Wars, only with STL) and takes only seconds for the crew. However, decades, if not centuries, pass in the outside universe. It still takes months of travel to and from the edges of star systems in order to minimize the risk of Critical Existence Failure. For this reason, space travel is only done by colonists and space traders and no interstellar government is possible. The titular protagonist mentions once intercepting a message sent out from one world about a scientist claiming to have proven Fermat's Last Theorem. While French admits that this is probably a big deal for a mathematician, the message has no commercial value to him as a space trader. In fact, in all his millennia of travel, he has only intercepted about two dozen interstellar messages, as sending them requires putting up a powerful relay satellite in orbit as well as maintaining it for little or no return. As such, the various human worlds are isolated with an occasional space trader passing through every half-a-century or so. Of course, given that aging has been eliminated in this 'verse, it's entirely possible for a planetbound person to meet the same space trader who comes back 200 years later.
• Sergey Lukyanenko:
• Line of Delirium duology (very loosely based on Master of Orion), all ships must decelerate before exiting hyperspace. Failure to do so would result in the ship exiting at near-light speeds and experiencing extreme time dilation. There are also cases of warships escaping from battle using their sublight engines, being forced to accelerate to near-light speeds when their hyperdrive is damaged. The crew of one such human warship commits suicide when they find themselves in a post-war galaxy over 100 years after they left.
• This is the premise behind the short story prequel Shadows of Dreams, when a Psilon battleship decelerates from near-light speeds near a small human colony, believing that Psilons and humans are still at war.
• The Honor Harrington books occasionally mention time dilation, though generally in the context of reducing perceived travel time in hyperspace by a few days or as an extra wrinkle of a few minutes during combat rather than as a significant alteration to characters' lives.
• The biggest impact that its had on the story so far is that it nearly torpedoed the title character's career before it got started. Dealing with the math involved nearly caused her to flunk out of a compulsory astrogation course in the Academy.
• A major shocker in the ending of the Heechee Saga book Gateway is that the protagonist's friends, whom he betrayed, are still at the edge of a black hole, still just having realized that he's betrayed them, still just having realized that they're going to die there — and they'll be in that state until long, long after he's dead.
• This is the central premise of the novel The World at the End of Time. Everything starts when Wan-To, a plasma-based lifeform that's at war with some other such entities, sends out some copies of itself to decoy its enemies by moving some stars around. One such copy winds up in the star of a human colony. Since this particular copy had no instructions on when to stop, it accelerates the stars and everything in orbit around them to really relativistic speeds. When it finally decides to decelerate, after about 4,000 years or so, ten duodecillionnote  years have passed in the outside universe, more than enough for the rest of the stars to all die.
• Time dilation is one of the quirks of the distorted planet in The Inverted World, which is in the shape of a rotating hyperboloid. North of optimum, where the circumference of the world grows exponentially smaller and the speed of its rotation correspondingly slower, time moves faster. South of optimum, where the circumference of the world grows exponentially larger and the speed of its rotation correspondingly greater, time moves slower.
• In Poul Anderson's Tau Zero, the runaway Bussard ramjet Leonora Christine is going so close to the speed of light that the crew witness the final end of the universe. (They also manage to survive it and end up in the next universe born after ours dies.)
• And they then take their time about slowing down... so that after the Big Crunch and Big Bang, there is time for stars and planets to form and life to evolve to a reasonably advanced level before they finally finish their journey.
• There is a novel where the main character is an astronaut on a ship equipped with an antimatter drive, allowing it to rapidly accelerate to relativistic speeds. Their goal - go to the nearest galaxy and return. Realizing she can't live without him, his girlfriend decides to put herself into an induced coma, a form of extreme cryogenics. Against all odds, her pod is recovered from the ruins of the lab thousands of years later, and she is revived. By this time, FTL travel is discovered, so the humans travel to the other galaxy and rescue her boyfriend, who has been trapped in a stasis field.
• Inverted in The Clockwork Rocket by Greg Egan, which takes place in a universe where the laws of physics are different from ours, and traveling quickly means more time passes. The protagonists take a trip in a high-speed Generation Ship in order to have enough time to develop the technology they need to avert a coming disaster.
• In the Star Trek Expanded Universe novel Enterprise, Uhura uncovers that the reason why Janice Rand seems so nervous and inexperienced is that she's chronologically just 16 years old. When she was a child on a civilian ship, the warp drive was damaged and the ship had to accelerate to high relativistic sublight velocity to reach the nearest starbase, meaning she didn't age in time with her calendar age. Because this is such a rare occurrence, Starfleet apparently never thought to log the discrepency.
• The Star Carrier series takes this into account with high velocities, but as with the Honor Harrington example it's more of a few lost minutes or hours during high-velocity transits of star systems. Ships keep track of both subjective and objective time, with the pilots of space fighters doing a near-c attack run watching the minutes on the objective time clock blur past in a flash.
• A later book shows a race that has developed projected time dilation fields as a response to the race having an extremely slow metabolism compared to most other races. To them, every other being is The Flash, so their solution is to use time dilation to slow them down to their level. They can also slow them down even more as a way to immobilize enemies. Their "time twister" ships can project a field in a spherical manner for a short distance away from the ship, which helps it survive non-direct nuclear explosions (the blast is slowed down, which means the ship is exposed to smaller amounts of deadly radiation for a longer period of time instead of a quick burst of a lot of it). The field can also be turned into a directed long-ranged version, although this limits it to a cone.
• Robert Charles Wilson's Vortex ends with Vox Core being turned into a starship with the time dilation bubble around it to keep the three occupants alive as it escapes the dying Earth and travels to a faraway human colony. By the time it reaches the colony, hundreds of thousands of years pass outside the bubble. Isaac then leaves the other two with the humans and takes off to explore the galaxy on his own. He ends up not only witnessing the end of the universe, but his consciousness, as well the that of humanity and many other races survives to live in the multi-verse, although he ends up performing a Heroic Sacrifice to save a character in an alternate universe.
• The Spin from the original novel is also a planet-wide time dilation field that slows down Earth to a crawl compared to the rest of the universe. The protagonist's two friends immediately recognize the implications: in a mere 20 years on Earth, millions of years will have passed outside, and the Sun will have expanded to consume the planet. However, they take this as an opportunity to terraform and settle Mars within a realistic timeframe, hoping that the Martian colonists can use the time to come up with a solution. Unfortunately, Mars is also placed in its own Spin, after the Hypotheticals notice life on it. The real purpose of the Spin is to preserve the human race until such time as the Hypotheticals can bring in an Arch, connected to a Portal Network that they have build to allow organic races to expand and give them time to create Hypothetical-like technology.
• In Poul Anderson's Time Lag, the dilation effect is enough that Elva uses it to persuade Bors to bring her during the second attack — she will be old when he returns — and make her contemplate how she is a Fish out of Temporal Water at the ending.
• A non-relativistic example in The Alloy of Law with Cadmium Allomancy, which creates a bubble about the size of a small room within which time passes more slowly. Used to freeze The Dragon in place while a small army was summoned to capture him.
• In The Lost Fleet and its spinoffs, it is mentioned that since spaceships can be travelling at up to a quarter of light speed, time dilation and relativistic distortion can be a problem. Every ship in a formation likely has a different time on their internal clocks from the others, and is seeing a slightly different sensor return than everyone else. It's mentioned that until Geary was found, the art of compensating for time dilation to allow for tactical maneuvering more complicated than Attack! Attack! Attack! was a lost art.
• We Are Legion (We Are Bob): Since the SURGE drive allows ships to move at near-light speed, time dilation is common. Furthermore, the Bobs can adjust their frame rate so that years pass like days. Some of them have different opinions on using it—Riker stubbornly sticks to real time unless absolutely necessary, while Homer is happy to adjust his frame rate to meet his needs from moment to moment.
• The Short Story "Vvremya" in The Four Horsemen Universe has a mining company set up an operation on a planet in close proximity to a black hole. Part of their crew balk at this and stay behind in a shuttle in a higher orbit, intended to be picked up a few weeks later. Nobody thinks to calculate for time dilation, and when the miners return everyone aboard has long since starved to death because 97 years have actually gone by.
• Kea's Flight: It takes about 23 years for the Flying Dustbin to travel from Earth to New Charity III. During that time, more than a thousand years pass on Earth.
• In Chindi by Jack McDevitt, a Love Interest of Priscilla Hutchins is stuck on an alien spacecraft that's constant accelerated up to a quarter light speed. Hutch has a "Eureka!" Moment about how to save him, but she's knows it's too late as he's Almost Out of Oxygen. Then her spaceship's Artificial Intelligence points out that thanks to his trope, time is moving slower on the alien spacecraft so he actually has several hours left.
• The original Planet of the Apes is thought to be the Trope Maker with the astronauts taking centuries to reach Betelgeuse that was two years from their own perspective. Ulysse makes a return trip to Earth to find it's been overrun by apes in his absence.

Live-Action TV
• In Andromeda, the titular ship and its captain spend three centuries at the edge of the event horizon of a black hole where only a few seconds pass. Enough time for a massive civil war and the subsequent collapse of civilization.
• The Bellerophon, Earth's earliest starship, travelled half the speed of light across the galaxy for 3000 years, but far less passed on the ship.
• In fact, the crew still looks fairly young, implying that they were traveling at much higher speeds than mere .5c (you wouldn't experience much of this trope at that speed). The ship can, apparently, accelerate ridiculously fast using its massive fusion engine (lacking weapons, the ship actively uses the exhaust as a weapon), although they often need to replenish their fuel. Strangely, it's pointed out in an earlier episode that the Andromeda herself can achieve such speeds fairly quickly.
• It's stated in the pilot that the time dilation effect was amplified by the usage of Artificial Gravity aboard the ship.
• A later episode established that more time passed on the ship than previously thought, but the events involved Dylan's memories being wiped.
• Battlestar Galactica (2003): The "Final Five" went on a sublight journey that took 2000 years from an outside perspective, but a lot less to them.
• Carl Sagan laid it out, along with the other bizarre effects that come with approaching the speed of light, in an episode of Cosmos: A Personal Voyage, Travels in Space and Time.
• Doctor Who: "World Enough and Time"/"The Doctor Falls" takes place aboard a Generation Ship slowly escaping the pull of a black hole. Because of the increased gravity near the black hole's event horizon and the length of the ship, time passes much more slowly in the ship's command center than in the lower decks. This is bad news, as said decks are now inhabited by malevolent creatures who have years to plan attacks while only days or minutes pass in the higher-level decks.
• In The Orville's third-season episode "Twice in a Lifetime", the Orville uses time dilation to travel forward in time from the 21st to the 25th centuries when the device they used to travel back in time is destroyed.
• Multiple incidents in the Stargate-verse.
• Our page quote comes from the aptly titled Stargate SG-1 episode "A Matter of Time". Opening an outgoing wormhole to a planet near a black hole caused the gate to lock up due to the differences in the speed of time on either side of the wormhole, time to slow down immensely inside the mountain, and the black hole's gravity to start sucking everything in the vicinity into the stargate. They solved it by detonating a bomb near the gate, causing an overload that made the wormhole jump to another receiving gate, whereupon they disengaged normally. Gen. Hammond sums it up quite well:
Hammond: Captain, relativity gives me a headache.
• Prior to "Unnatural Selection", the Asgard used a time dilation device to try and lock away the Replicators in a "bubble" where "one year to the Replicators would be about ten thousand years to the rest of us". The replicators managed to reverse the device's function, allowing them to experience hundreds of years while less than one years went by outside. SG-1 had to go in and correct the problem.
• Briefly mentioned as a problem in "Memento" if the Prometheus, stranded in deep space hundreds of light-years from Earth after hyperdrive failure, tried to hoof it home. Of course, relativity was kinda secondary to the fact that they didn't have enough supplies for that anyway.
• In the series finale "Unending", Carter uses the time dilation device from "Unnatural Selection" to trigger Year Inside, Hour Outside and give her enough time to develop a plan to save the Odyssey from the three Ori warships pursuing it.
• In an episode of Stargate Atlantis, the crew encountered a group of actual Ancients flying at 99.9% of the speed of light (their hyperdrive did not function), which is the reason why they were alive in the present time, despite the rest of their race being wiped out/ascending long ago.
• Starhunter has a couple of examples, some of which result from the fact that ships in the series accelerate to relativistic speeds to get from planet to planet.
• The "relativity is a pain in the neck" joke gets used at least once in the first series when Rudolpho, the protagonists' boss, complains that they're a couple weeks behind on their bills, and the crew responds that from their point of view they've got a couple of days still.
• At the end of the first season the protagonists end up being trapped in Hyperspace, and at the beginning of the second season one of them comes out 15 years later the same age, and much of the season is her searching for her uncle, who is still trapped there. At one point it's suggested that by the time they find him his son maybe be twice his age.
• One episode features a middle aged man who hires the bounty hunter protagonists to rescue his kidnapped parents, whose kidnappers had been traveling at very fast speeds for 50 years causing them to age only 8 months, meaning he's now twice their age.
• The Twilight Zone (1985): In "Quarantine", although 304 years have passed on Earth, Joshua estimates that it has only been five or ten years for the 1,000 people aboard the American spacecraft launched during the nuclear war in 2043.

Music
• Queen's "'39" from A Night at the Opera is about a crewman on a spaceship who travels to a distant planet and returns after a year, only to discover that a hundred years have passed back home and only the descendants of his loved ones remain. It ends on quite a down note.
• Julia Ecklar and Anne Prather's "Pushin' the Speed of Light" is a classic filk on the subject, and a Tear Jerker: "And you've left behind you the world of men with no way in space to go home again."
• "Benson, Arizona", the opening and closing theme to Dark Star, is about a space trucker who uses faster-than-light travel, and time-dilation effects are mentioned in some of the lyrics ("The years go faster than the days", "Now the years pull us apart, I'm young and now you're old").

• The BBC Radio series Earthsearch uses time dilation as a major plot point. The children of a starship's second-generation crew, the sole survivors of a disaster that killed the crew and erased a huge amount of scientific data (including the concept of time dilation itself), return the ship to their home solar system 115 years after it set out, only to find that a million years have passed outside. Oh, and the Earth is missing.

Tabletop Games
• GURPS: Spaceships goes so far as to provide the equation for relativistic time dilation to be used for ships with sufficiently powerful engines.
• Lancer simplifies relativistic time dilation to one-tenth of normal time passage. A ship traveling 20 light-years at .95c experiences two years.

Video Games
• X-Universe:
• Every ship can mount a "Singularity Engine Time Accelerator" which can speed up the flow of time up to 10x, depending on the game settings. Its primary use is to speed up travel time in-system for the player's benefit. Activating the device at high settings is heavy on the CPU and tends to cause Artificial Stupidity.
• In in-game lore, malfunctioning SETA drives can supposedly crank up the effect to several thousand times normal speed: back in the days of X2 and X3 when stations had bulletin boards that featured news articles, one story covered a pilot who lost a year's worth of time when his SETA device went haywire and took several hours for him to shut down.
• Comes up several times in Gravity Rush and Gravity Rush 2. The entire world is located along a massive World Pillar which extends infinitely up and down. At the bottom is a massive black hole, and localized black holes called gravity storms appear randomly. Going up or down the pillar can mess with people's personal times, so when main character Kat goes down the pillar, she thinks she is only gone for a week from her home town when she is actually gone for one year.

Webcomics
• In Homestuck:
• At one point John and Jade travel between two windows in the fourth wall, taking what is explicitly stated as three nanoseconds (the time it takes light to travel one yard) to do so from an outside perspective. It is stated to take three years from their own perspective, which is actually not how time dilation works.
• Andrew then claimed that it was 'plot dilation'. Since the characters had started their quest the previous day, but from our side of the fourth wall it had taken three years, they would have to wait until the same amount of time had passed for them to re-join.
• Problem Sleuth is not much better at depicting time dilation either: as a character approaches the event horizon of a black hole, the events for him start to become faster until "all the events in history happen at once", which Andrew himself admitted was unrealistic but more dramatic.
• A Beginner's Guide to the End of the Universe has the protagonist spend just a few days flying to and exploring the Black Star, while hundreds or thousands of years pass in the rest of the universe. By the time he's back, people consider him a legendary character.
• In Relativity, Irina's light speed spaceflight will last six months for her, and three years for her wife Anne.
Anne: I'll be older than you when you get back. Gah that's so weeeird...
• In Heroine Chic, protagonist Zoe spends roughly one day stuck on villain Excelsior's spaceship. When she returns to Earth she finds six weeks have passed; her lease expired and her boyfriend is now dating someone else. According to a time dilation calculator, Excelsior's ship would have been moving at about 99.9717% the speed of light.

Web Original
• Orion's Arm has relativistic space travel at speeds in excess of .9c, but it's usually requires a Transapient tech Reactionless Drive. But it's not much of an issue because people can have essentially unlimited lifespans (average Nearbaseline lifespan is about 3000 years). Also the setting's Portal Network requires the two mouths of the wormhole to be towed into position at sub-relativistic speeds (~.77c).
• SCP Foundation:
• SCP-1272 (Slow-Motion Catastrophe). SCP-1272 is a nongravitational singularity (similar to that of a black hole/hypermass) that tremendously slows down the passage of time inside its area.
• SCP-7074 (Asymptotic Bubble) is a little perimeter of space with two anomalous properties: one is that matter can't escape it, only energy, and the other is that time inside it is constantly getting slower.

Western Animation
• In Generator Rex, César's mobile laboratory was thrown into space, traveling so fast that where 15 minutes passed for him, five years passed on Earth.
• Reversed in My Life as a Teenage Robot. Sheldon was sent to space by accident, and returned a day later as a 75-year-old man. Dr. Wakeman then tried to use a machine to de-age him, but he ended up as a baby, and was sent to space again to return to his normal age.
• Sonic the Hedgehog (SatAM): Word of God says that the unmade third season would have revealed that Mobius was Earth All Along and that Robotnik and Snively survived aliens wiping us out because they were on a colony planet at the time and returned to Earth centuries later because of this trope.

## Examples using FTL:

Asian Animation
• King Shakir: In "Very Remote Shopping Mall", the bus taking Shakir and his party to Door World goes at the speed of light, and Necati sticks his head out the window for a few seconds. When they arrive, Remzi notices that half of Necati's face has aged to the age of a senior citizen, with half of his mustache and one of his eyebrows being white.

Comic Books
• During the Pre-Crisis era, Superman and Supergirl were able to travel through time by flying faster than light.
• Sonic the Comic: When his Sonic clone aged prematurely, Dr Robotnik got him to pretend he was Sonic who'd come back from the future by running faster than light.
• An issue of The Beano has Billy Wizz trying to go back in time by running backwards faster than the speed of light. He thinks he's back in the sixties but then gets chased by an angry curator for wrecking a display in the history museum.
• The Flash: Speedsters like Barry Allen and Wally West time-travel by running faster than the speed of light.

Fan Works
• In Hellsister Trilogy, Supergirl travels back and forth between the present day and the 31st century several times by flying faster than light.
• In A Changed World, USS Bajor is able to use the warp drive to shield itself from the worst of it, though they still apparently lose a few hours. The Bajoran and Klingon ships aren't as fortunate: they've been there since 2271.
• Superman and Man: After watching his 1978 movie, Superman states he doesn't time-travel by altering the Earth's rotation, but by travelling "at hyperlight speed".
If he had wanted to change history, he would have taken a trip back in time himself, by spinning himself at hyperlight speed.

Films — Animation
• This is a recurring element in Lightyear:
• Attempts to reach hyperspeed involve approaching increasing fractions of the speed of light (approaching hyperspeed is expressed as decimals of c), so time dilation kicks in as one uses it. During the first act of the movie, each attempt Buzz makes to reach hyperspeed takes four subjective minutes for him, but just over four years on the planet below.
• When he finally reaches hyperspeed and returns to the planet, he learns that twenty-two years have passed.
• Zurg, an alternate timeline version of Buzz, has worked out how to use it to go back in time, but could only travel so far back and wants Buzz's help to perfect it.

Films — Live-Action

Literature
• Jump drive in C. J. Cherryh's Alliance/Union universe causes some time dilation, jumps take a week or less for the crew and a month or two for planetsiders and stationers. Of course, humans have to be sedated for jump and most other oxygen-breathing species are knocked unconscious.
• Cordwainer Smith's "The Crime And The Glory Of Commander Suzdal": By traveling through non-space, Suzdal and his ship subjectively experiences thousands of years. Even stranger, when the ship heads back to Earth, "time winds up" and the ship comes back as if only a few objective years have passed, making it an Inverted Trope example. And this is only some of the wacky Time Travel hi-jinks in this tale.
• Some levels of hyperspace in the Uplift series.
• Home Fires by Gene Wolfe uses this along with a Mayfly–December Romance. The traveler is a female soldier, and her husband ages a couple of decades to her two years.
• Stanisław Lem's Return from the Stars is about an astronaut who tries to cope with the changed world after returning from a 127-year mission (which lasted 10 years for him).
• In the Hyperion Cantos humanity has a way of circumventing this with portals. The problem is that you have to send a few dozen (or hundred, depending on the route) lightspeed or so ships out to build a portal at the other end. Now, there is time dilation to begin with, and since that version of Hyperspace Is a Scary Place, they also travel as Human Popsicles, so the people sent to build them leave their whole life behind.
• In the short story "Remembering Siri" (included in Hyperion as "The Consul's Tale"), a woman on a backwater planet falls in love with a dashing Space Marine who stops by for shore leave once a decade (in her timeframe). When she dies of old age, he has only aged 5 years, but their son is 43.
• In the fourth book, it helps the protagonist to cut a few years off the age difference between him and his love.
• The Forever War deals with quite a bit of time dilation. In order to travel faster than light a warship has to accelerate to relativistic speeds towards a collapsar. The effects of "subjective" time on the protagonist are explored to a somewhat large degree.
• Ursula K. Le Guin's Hainish Cycle:
• This effect is present in The Left Hand of Darkness; the Ekumenical diplomats consider it a good thing, since if their mission on a particular planet fails, they can hop over to the nearest planet, then turn around and come right back and have a whole new generation of leaders with which to try again.
• In "The Dowry Of Angyar", later incorporated into the novel Rocannon's World, a young woman named Semley goes on a quest to recover the titular lost heirloom, and meets a group of dwarf-like creatures who promise to help her get it back. Since her native culture is at roughly early medieval technological level, and a trip that took her two days turns out to have lasted sixteen years, it looks, for her and her family, like she's been snatched by The Fair Folk. In the story proper, Rocannon, who gave the necklace back, meets Semley's granddaughter.

Live-Action TV
• Star Trek:
• According to The Making Of Star Trek Gene Roddenberry explains the inconsistency in Star dates by saying that time moves differently to ships travelling at warp speed. He admits he doesn't understand his own explanation but it seems to satisfy fans who ask.
• The Slingshot Maneuver involves doing a Gravitational Slingshot around a star at warp speed and arriving at a chosen time period.
• Daphne from Heroes can travel through time by overtaking the speed of light when Ando supercharges her Super-Speed.
• Vipers in Galactica 1980 can go back in time by flying faster than light. Like the Superman example, there's no explanation why spaceships can quickly travel intergalactic distances without being sent through the time.
• Ultraman Mebius: This is the reason why Captain Sakomizu is Older Than They Look. He was originally a space patrol office in Science Patrol, but the effects of travelling at lightspeed have caused him to age more slowly.

Tabletop Games
• Warhammer 40,000: One more scary thing about the Warp is that you can never tell when you will emerge. More than once a fleet has arrived centuries after (or before) departing. This occasionally creates outright paradoxes; one of the most famous is an Ork warlord accidentally ending back where he started just before he left and promptly murdering his past self and stealing a second copy of his favorite gun.

Video Games

Web Comics
• The D.A.V.E. (Dangerous And Very Expensive) drive in Freefall works by reversing time dilation, weeks pass outside while decades pass on board. So passengers spend the trip frozen.
• Quentyn Quinn, Space Ranger:
• The title character misses three years without realizing it while on a long mission through largely uncharted space.
Quentyn: Wait, a Mark IV? But the Mark III isn't due out for another year!
Delivery guy: Oh no. The Mark III came out last year. The Mark IV just hit the shelves last month!
• It's stated that Rangers are given extremely long vacations to catch back up with current events and family, as well as debreif their superiors on a year-long mission (for the ranger) that took 2-10 (for the brass).
• Used to Justify a Time Skip in Lancer: The Knights of Fenris. A squadron of fighter pilots attempts a Hyperspeed Escape through a black hole without adequate power for their "Relativity Compensators," and it looks like they abandoned their post for two entire years. During which the war went badly.

Web Original
• According to Holonet News, ships in the Star Wars universe have "Relativistic Shielding" to stop this from happening. There's an interview with a guy called Bosbit Matarcher who was sent 190 years forward thanks to a shield mishap.
• Atomic Rockets mentions that special relativity means a ship goes back in time if it goes FTL, and reccomends using some Time Travel Tropes as story ideas.

Feedback

# Time Dilation Between Worlds

There is a discrepancy for characters of each world of how long since they saw each other. For Team RWBY it had been weeks but for the Justice League it had only been three days. While connected by communication synchs the dimensions.

How well does it match the trope?