The Constant

""It's called a constant. Desmond, you have no constant. When you go to the future, nothing there is familiar. So if you want to stop this, then you need to find something there...something that you really, really care about...that also exists back here, in 1996.""

- Daniel Faraday, Lost

When you Time Travel, or you spend some time as a Human Popsicle, or even just leave a place for a long time, things tend to change a lot. But even when almost everything has changed, there's some character or thing that exists in both time periods, not because of time travel, but because they remained there the whole time. They are The Constant, and they connect two different-looking settings together and prove they're the same place.

Frequently the work will go out of its way to make a point of The Constant, and in our examples we focus on these intentional, obvious Constants. If the time-traveling character didn't realize they were in the same place until discovering The Constant, then you have Earth All Along.

If the time travelled was too short, there may be so many Constants that it's unremarkable. For example, it's not uncommon for the entire cast from the past to switch to Future Badass versions of themselves in the future. On the other hand, there is no minimum time difference - a city may be reduced to an unrecognizable place overnight by a terrible weapon, except for The Constant proving it was there. Or as Nena would say, "If I could find a souvenir / Just to prove the world was here."

If the time traveled is very long, the Constant will typically be a structure or an immortal rather than an ordinary person. If it is a person, it's usually the Identical Grandson or a variation thereof (such as My Grandson, Myself).

Compare Earth All Along, Monumental Damage Resistance. Often invokes Never Recycle a Building.

If everything inexplicably survives in a slightly distressed state, it's a case of Ragnarok Proofing.

If the Constant in question ends up being destroyed in real life (e.g. the World Trade Center), can result in a Funny Aneurysm Moment.

Anime and Manga

 * The Sacred Tree in Inuyasha. In the past, it's where Kagome meets the titular Inuyasha; hundreds of years in the future, it's still tended by her grandfather, even though a modern city has grown up around it. The nearby Bone-Eater's Well also exists in both times and acts as a Portal to the Past while it's at it.
 * In the movie Pokémon 4 Ever, the young woman Sammy meets is an old woman 40 years later when he meets her after a time trip.
 * Cowboy Bebop: When the de-frosted (on two levels) amnesiac Faye Valentine returns to Earth, she meets an old classmate of hers, now an old lady.

Art

 * An American artist once released a poster with a series of pictures showing how a patch of land developed over a hundred years from open prairie into a busy city. Through it all one thing remained: A slowly growing tree.

Comic Books

 * The American Flag in The Ultimates. The newly thawed out Captain America is despondent over how different things are. Technology has advanced massively, his high school friends, fiance and army buddies are in their 80s and modern morality is completely different than the 1940s. That is until Nick Fury points out the American flag over a cemetery and comments that one thing hasn't changed. (Well, except those two extra stars from 1959.)
 * Robert Crumb's Mister Natural once had an immensely satisfying meditation in the desert. It starts when he arrives in a desolate spot, spreads out his blanket and assumes the lotus position. Some indeterminate time later, construction workers arrive to build a road past him. He remains transfixed even when junk thrown from passing cars bounces off his head. Eventually a small town grows up around him, and after what appears to be years of development he is finally noticed as a policeman brusquely orders him to move, he is blocking the traffic. (Apparently they managed to build the sidewalk under him.) The guru's only answer is a slowly rising hum that after a few panels causes the officer to flee in panic as the buildings around them crumble into dust. Once the location is back to its original state (you know, apart from the fact that the "sand" now consists of pulverized concrete, glass and asphalt) Mr. Natural stops humming, gets to his feet, stretches and yawns, declares "That was a good one!", rolls up his blanket and wanders off.

Film
""The one constant through all the years, Ray, has been baseball. America has rolled by like an army of steamrollers. It has been erased like a blackboard, rebuilt and erased again. But baseball has marked the time.""
 * The Christopher Reeve movie Somewhere in Time features an elderly hotel employee who recognizes the hero from his childhood - much to the hero's confusion, because from his perspective that event hasn't happened yet (he later goes back in time and meets a boy in the lobby who is clearly the same guy).
 * In Inception, the folks who enter dreams carry a "totem", a small personal item that they alone know the exact size and weight of, to help them remember if they are in reality or dream state if need be. For instance, lead protagonist Dom carries a top that will spin endlessly in a dream, but topple in reality. Growers of Epileptic Trees may find some fertilizer in the observation that.
 * The Statue of Liberty in the Planet of the Apes movie that features so prominently in the Planet of the Apes Ending.
 * The Clock Tower in Back to The Future in a major example of this trope, as it appears under construction in 1885, working just fine in 1955, broken and run-down in 1985, transformed into a casino-hotel in the alternate 1985, and as a piece of high-tech modern art in 2015.
 * Doc Brown serves as one in the first film, as well, moreso than Marty's parents or Biff, as he is aware that Marty has been time-travelling.
 * In the George Pal version of The Time Machine, the protagonist finds a couple of constants during his early trips into the near future, including his friend Filby, and a shop near his laboratory that is featured in the time-travel montage whipping through a succession of window displays (later spoofed in the Discworld series, as described below). However, on his main excursion into the distant future he finds that everything has changed.
 * In the Guy Pierce version of The Time Machine, he meets an AI librarian from the New York Public Library who is still there in the overgrown, recognizable ruins of New York thousands of years later.
 * In Demolition Man, Spartan meets the helicopter pilot who air-dropped him into his final mission before becoming a Human Popsicle. Despite Spartan's difficulty adapting to the future, he never bothers to sit down with the old guy and pick his brain.
 * Like Star Trek below, Star Wars gives the audience a few constants when telling a story in a new time period: The Phantom Menace has no Rebellion and no Empire, with a strange Republic and Trade Federation in their places; but we know it's the same 'verse because we see Obi-Wan from the beginning, and Artoo and Threepio, Yoda, and Tatooine later on.
 * Both the film Field of Dreams and the novel Shoeless Joe, make note that baseball has still remained the same. In the movie, Terrance Mann even calls it this trope.
 * Both the film Field of Dreams and the novel Shoeless Joe, make note that baseball has still remained the same. In the movie, Terrance Mann even calls it this trope.


 * This is subverted in a scene in the comic I ♥ Marvel: Web of Love, where Captain America is seen watching a basketball game on TV with his Avengers pals and Mary Jane Watson-Parker. Confused by the rules added to the game since the 1940s and the resultant new tactics, he comments that at least baseball remained unchanged. Then Luke Cage brings up the designated hitter rule...
 * Inverted in the James Garner film, Thirty Six Hours. The existence of something that should have vanished in a few days,, is what convinces Maj. Pike, that he hasn't spent the last few years in a fugue state, as his German interrogators are trying to convince him he has in order to extract information from him.

Literature
"Though under earth and throneless now I be, Yet, while I lived, all earth was under me."
 * The Hitchhiker's Guide to the Galaxy: Marvin the Android serves as The Constant in The Restaurant At The End Of The Universe (both the book and the place) over a few hundred million years. He's understandably bitter about it.
 * In Susan Cooper's novel The Dark Is Rising, the immortal Will Stanton meets the character Hawkin hundreds of years in the past. Hawkin undergoes a Face Heel Turn and becomes the Walker, condemned to Walk the Earth until it's time for him to fulfill his destiny in the present.
 * In Diana Wynne Jones' The Homeward Bounders, the Old Fort - in particular, the statue on the grounds - are the Constant.
 * Katharine Kerr's Deverry series:
 * In Daggerspell, a battle is fought among the ruins of a fortress at the edge of the grasslands. Several books later, we are shown in A Time of Exile, in a story set a few hundred years prior, how the building of that fortress started a small war, and why it was abandoned. Brangwen's grave is another straight example.
 * Averted when Nevyn, now a royal adviser, tries to find his old quarters in the royal broch in Dun Deverry - and cannot, because the complex has been repaired and expanded so many times over the centuries since he was condemned to Walk the Earth.
 * In The Chronicles of Narnia: The Silver Chair the heroes are directed by Aslan to go to the Ruined City of the Giants and look for a sign that would tell them where to go. Not seeing anything, they are trapped in a snowstorm and forced to hide in a series of trenches. They realize their mistake later when returning to the site, they see the trenches were actually letters on a giant inscription:


 * The city was gradually reduced to ruins, until all that was left was the inscription. Finally all that remained of the inscription was the final two words: "UNDER ME."
 * The long version is according to the antagonist, who is clearly trying to distract the heroes from their quest. The literal meaning is clear: Look under the inscription.
 * And in Prince Caspian, the Pevensies return to Narnia and Susan finds one of their old chess pieces, and they realize that they're in the ruins of Caer Paravel.
 * In Ursula K. LeGuin's short story "April in Paris", the protagonists occupy the same apartment in different centuries. Notre Dame is another Constant.
 * In The Time Traveler's Wife, Claire generally serves as Henry's Constant as he jumps around in time.
 * In H. Beam Piper's Lord Kalvan of Otherwhen, the absence of an expected constant - the stone quarries of an area of Pennsylvania that the protagonist knows quite well, and which could not have eroded while leaving the local geography intact - tips him off to the fact that he has not travelled into the far future as he previously thought, but is in an Alternate Universe.
 * Lampshaded in the Discworld novel Wyrd Sisters. The biggest expense of Time Travel is finding a fashion store that will remain open for 50 years in the exact same place.
 * In Idiocracy a "Fuddrucker's" restaurant serves as the constant. After 500 years of increasing stupidity the name has gradually changed to "Buttfucker's." Oddly, it retains its status as a family restaurant, while Starbucks, H&R Block, and several other businesses have become brothels.
 * A Star Wars novel has someone who was nearly killed at the end of the Clone Wars and put into stasis for at least half a century, awaking long after the original movies. With almost everyone he knew long dead and the galaxy having gone through several wars and governments, he decides to search for a specific Constant, the YT-1300 freighter he was flying on the mission where he nearly died - the ship that has since come to be known as the Millenium Falcon.
 * Robert Rankin's Brentford series has Professor Slocombe, who is implied to have been Merlin and have worked with Sherlock Holmes. Also, the Flying Swan, which shows up on 15th century maps. Ironically, the real-life pub the Flying Swan is based on, the Bricklayer's Arms, has since been closed and turned into housing.
 * In the Usborne Puzzle Adventure The Vanishing Village, the protagonists must find help an 18th century village that's stuck in limbo. The only way they can get into the past is to bring something that originated in the village with them from the present day. It's a spoon, weirdly enough.
 * In the Bolo story "The Night of the Trolls" by Keith Laumer, the protagonist comes out of a long stretch as a Human Popsicle to find that society has collapsed. The first friendly person he meets in the new world is an old man who turns out to be his son, aged considerably in the 80 or so years since the protagonist's stasis began.
 * The old Hermit in A Canticle for Leibowitz, though his immortality is never explained.
 * Most commentators agree that the final section of the book pretty much comes out and says that he's the Wandering Jew.
 * Inverted in the Discworld book Night Watch. Sam Vimes ends up in the past after a Magical Accident, and has to keep things on-track while a criminal who went with him is messing everything up. Right when he's most despairing of ever getting back to where he belongs,
 * On the other hand, many of the important cast members' past selves feature in the story: Fred Colon, M(r)s. Palm, Young Vimes, ...
 * From In the Keep of Time, Smailholm Tower. In an unusual variation, it is also the "time machine", as it were. The interesting implication of this is that the key can only take time travelers to a time period where the tower exists, not before its construction or after it collapses.
 * In Neal Stevensons Cryptonomicon we are treated to three seperate stories. Two during World War II, and one in the modern day. Many of the characters from the modern day are descendants of the characters from World War II. But apart from the younger Waterhouse's stories of his grandfather, there's only one man who appears in both timelines. Enoch Root. Who hasn't aged a day.
 * In Stevensons Baroque Cycle, we meet the far more distant ancestors of the protagonists of Cryptonomic, as the book is set in the 17th century. But even all this way out, there's still one character in common. Enoch Root.
 * Older Than Radio: After sleeping for 20 years, Rip Van Winkle is dismissed as just a loony old man until he is recognized by his daughter, now grown with a family of her own.
 * In The Redemption of Althalus, when the title character first goes to the House At the End of the World, he passes a particular dead tree, when he leaves the House, 2500 years later, the same dead tree is still there, The Goddess Dweia says the gods keep the tree around as a landmark.

Live Action TV

 * The Trope Namer is an episode of Lost ("The Constant") in which Desmond is undergoing rapid Mental Time Travel between two times in his life and must find a Constant in the two times in order to avoid insanity and death. It's.
 * On the same show, Daniel Faraday uses as his Constant.
 * Although there's no Time Travel involved, McCoy appears in "Encounter at Farpoint", the first episode of Star Trek: The Next Generation, as a reminder that the two series take place in the same universe but different times.
 * The same idea occurs with all the other series of Star Trek as well, with a character from a preceding series showing up in the first episode of the new series (Picard in Deep Space Nine, Quark in Voyager, Spock (and a reference to an Admiral Archer) in the reboot. Enterprise, due to taking place earliest in the continuity, used Zefram Cochrane from Star Trek: First Contact.
 * In the two-part Next Generation episode "Time's Arrow", the long-lived Guinan is the link between times (along with Data's severed head).
 * The Next Generation two-parter "Unification", created for an anniversary and features Spock, who is used to link the past and the present.
 * Happens from time to time in Doctor Who due to its time-travel nature. A significant example comes during the last episode of the new Series 5,
 * Captain Jack Harkness has also become the constant for the universe. He can never die. He can never stop existing..
 * In the old series, there was only one actor who crossed the tenures of more than two doctors. The Brigadier. Even The Master and Davros changed actors. But Nicholas Courtney was there as Brigadier Alistair Gordon Lethbridge-Stewart from the second doctor, to the seventh, making his final appearance in the Sarah Jane Adventures. Companions changed, and the Doctor regenerated, but the Brigadier stood there throughout it all, always taking The Slow Path, and always ready to do the best he can.
 * And that's what makes it so heartbreaking when you find out he has died by the time of the Eleventh Doctor.

Video Games

 * Leene's Bell in Chrono Trigger and the Black Omen, later in the game (but previously chronologically). Also the Sun Cave, the Nu and, of course, Lavos.
 * In Dark Cloud 2, there is almost always an overly obvious Constant: That baby Lapras-looking thing you saved helped to form the labs! That girl was the sage all along! etc.
 * The video game series Legacy of Kain has the nine Pillars of Nosgoth, while they don't remain in a constant state (the ruination of the pillars is a major plot point) they remain as a constant on the landscape of the environment and a general marker for the time period. Along with the Pillars, Ariel's soul is present in every game but Blood Omen 2, and her state (bound to the Pillars) is constant, a reminder of Kain's decision not to sacrifice himself.
 * The ruined tower in Sheratan in Baten Kaitos Origins serves as a constant for Sagi, who can eventually use it to travel back and forth in time.
 * Happens several times to the immortal Kaim, in Lost Odyssey. A couple of incidents in the 'Dreams of a Thousand Years' section involve him meeting someone as a child, then crossing their paths again, 60, 70 or 80 years later, where they're old and dying, and he's still as young as ever. In the main game story, he also meets a wise old king - whom, as it turns out, he first met when he was a brash young prince, and taught a few things about combat, survival, and life in general.
 * In Day of the Tentacle, the same house exists for over 400 years, from the days of the Founding Fathers to the future where the tentacles have taken over the world, although it's much more metallic in the future. Also, many objects in the house can be found in more than one time period. This is often used by the main characters to affect one or more future time periods. For example, since only inanimate objects can be passed through the Chron-O-John, the only way to send a hamster to Laverne in the future is to put it in the freezer, which is still around 200 years from now. Apparently, no one has bothered to look inside in all this time. The time machine is still in the basement in the future (though it's broken and useless), and the laundry room doesn't change in the slightest - the coin-operated dryer Bernard sets running in the present is still going two hundred years later (he fed it a lot of change).
 * The Legend of Zelda games Ocarina of Time and Oracle of Ages play with this trope a lot. It's possible the Deku tree is an example across the games, if the one in Wind Waker is the same one in Ocarina. (More likely, it's the tree that grew out of the Deku Sprout, since the old one died.)
 * Across both wildly divergent timelines in the Command & Conquer series, Tiberium and Red Alert, there is a corporation called Futuretech.

Western Animation

 * King Bumi from Avatar: The Last Airbender. Aang knew him as a kid, got frozen in ice for 100 years, and then meets up with Bumi again as an old, crazy king. An episode is resolved by the revelation of this Constant.
 * Similar to Avatar but across a much longer time period, there is an episode of Samurai Jack where Jack visits a temple he had been to in the past. Not only do the martial artist students practice the same traditions, but there is even a monk there, thousands and thousands of years old, that Jack met when he was there.
 * And when Jack finally finds his homeland.
 * Futurama has several Constants: the subterranean ruins of New York, the pizzeria where Fry used to work, the various heads of celebrities preserved in jars, and so on. The biggest one is probably . And Fry's dog...who we'll skip over before we start to tear up.
 * Applied Cryogenics somehow manages to survive for 1000 years without a power failure (or apocalyptic destruction), despite the "No Power Failures Since 1997" sign on the wall in the pilot episode, and that we see the world reduced to medieval levels twice during that time.
 * That was probably doing.
 * In the Justice League episode "Hereafter", Superman is hurled forward some 30,000 years. He soon finds the immortal Vandal Savage as the sole survivor of the human race...who also happens to be responsible for the extinction of the rest of it. Savage feels understandably guilty about the whole thing, and sends Supes back to stop his past self.
 * There is also the Watchtower which, in a subtle Chekhov's Gun, has survived reentry to crashland in the jungle.
 * Demona in Gargoyles.

Web Comics

 * Narbonic has one where Dave has to find a Constant, so he can get returned to the present.

Web Original

 * In Darwin's Soldiers: Pavlov's Checkmate, the main team is trapped in 1990, and needs to send a message to a teammate still in 2010. They do this by noticing a file cabinet that they recall seeing in 2010, and slipping a note inside it.
 * In Fine Structure, Anne Poole is the Constant for over 20,000 years.

Real Life

 * The Pyramids of Giza. They are 4600 years old. They have been around since the dawn of civilisation and are still here.
 * The Ziggurat of Mesopotamia.
 * The Sun. The next time you sit down on the grass, and enjoy the warmth of the sun, remember, that your great-grandparents did this as well. And their great grandparents. And theirs. All the way back to those earliest, simplest forms of life, for whom that standard and none-too-remarkable star was their only source of warmth and energy. It existed 200,000 years before our planet coalesced in it's orbit. When we think of something as old, we call it 'as old as the hills'. The Sun watched the hills form.
 * That was bloody poetic.
 * It has four or five BILLIONS years more to go. Only after then it will go red giant and ultimately go poof.