Write Back to the Future

Doc Brown: It's a very interesting story, future boy. But there's just one little thing that doesn't make sense: If the me of the future is now in the past, how could you possibly know about it?
Marty: You sent me a letter.

— Back to the Future Part III

So, your friend couldn't get through the one-way time portal before it closed, and as you're standing there wondering what to do, this guy from the Post Office comes up and says that he's got this letter, posted 80 years ago, and addressed to you. Turns out your friend spent ten years building a machine to stop the Big Bad, and he sealed it away right beneath where you're standing now. As you read it, you can't help but marvel that the message actually made it through the postal service.

Write Back To The Future is when a time-traveler stuck in the past sends a message along The Slow Path to their compatriots in the future. It may be a way to get them back; it may be the solution to the problem they're looking for; it may just be an assurance that they had a full and rewarding life in whatever century they got stuck in.

Usually, the message shows up right after the relevant time-travel. In especially clever instances, it may appear before said travel.

The likelihood of this actually working depends on the method used to send the message. If you just drop a letter in a drawer, you're betting that nobody's going to move stuff around for the next sixty years, the desk isn't going to get moved, destroyed, or sold off, et cetera. On the other hand, if you put it in a safe deposit box in a major bank or even behind a loose brick in the masonry, it should be there decades later. Another method is to make many copies of the message to ensure that at least one survives (e.g. publishing it as an advertisement); this requires composing a message whose real meaning is only apparent to the intended recipient.

Often, but not always, part of a Stable Time Loop.

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Examples:

Anime & Manga

• Rave Master. When Haru, Elie, and Sieg Hart travel unintentionally 50 years into the past, Sieg manages to send Haru and Elie back to the present at the cost of returning himself. He then proceeds to write letters to all their friends in the present, informing them of the final battle so they may help the hero. Then he sits down on a stone in order not to change the past and guards the only place where that time travel would be possible, becoming the skeleton they saw the very first time they came there.
• In Amakusa 1637, the Time Travelers that remain in the past leave sealed cellphones to be found in the future.
• Marnie's diary serves as an unintentional message to the future in When Marnie Was There

Card Games

• The game Chrononauts revolves around time travel, and uses this trope. One of the cards is a "Memo from your Future Self," and acts like a counterspell via going back and time and stopping the previous card from being played.

Comic Books

• In a Big Finish Judge Dredd/Strontium Dog crossover, Johnny Alpha returns to his own time by leaving notes giving his exact location for his employers to find. Ready to leave, he gives such a note to Dredd, then immediately starts accusing him of betrayal when he fails to dematerialize. It turns out that without his help, Dredd won't survive to deliver the note.
• Superman Vs. The Terminator: Death To The Future #1 has Cyborg Superman leaving information for the future Skynet in a graveyard sculpture.
• In the Return of Bruce Wayne story arc, Batman time-travels forward and leaves clues to his whereabouts in and around the past location of Wayne Manor.
• Zorglub uses this system in the Spirou & Fantasio one-shot "Swams of Time", as after building a time machine to travel to the end of the XIXth century, he is unable to return. He gives a book with all the instructions for building a new time machine to the grandfather of one of the heroes' friends, with instruction to give it to the Count of Champignac on a certain date in the future, which the man actually does, by proxy of his grandson.
• Clara does this at the beginning of the "Continuum Conundrum" arc in Back to the Future, sending a letter from 1893 to Marty in 1986, to inform him that Doc has gone missing. Marty also tries this in the same issue by leaving a note in a canister at Doc's secret lab, concluding that if Doc is time traveling and visits the lab in the future, the note should still be there for him to find.
• Done in a West Coast Avengers story when the team is stuck in the past with a broken time machine that can only go further into the past. They plan to keep going backwards until they reach ancient Egypt, where time-traveler Rama-Tut can repair it. When they stop in 1776, they meet an ancestor of their member La Esperita. They write a message to La Esperita on a piece of silk (that would last longer than ordinary paper) and ask the ancestor to keep it in her family Bible. When the WCA reach Egypt, Rama-Tut is of no help — but Hawkeye has a conversation with the moon god Khonshu. In the present, Khonshu's hero Moon Knight suddenly has a vision, jets off to California, introduces himself to La Esperita, and tells her to read the message in her Bible.
• One Star Trek comic had Captain Kirk stranded in the distant past on an uninhabited alien planet. He spends the next several decades hauling rocks up to the top of a plateau (even carving a staircase to make the trips a bit easier) and arranging them in the shape of a Starfleet insignia big enough to be seen from space. Back in his own time, the Enterprise spots the insignia while scanning planets looking for Kirk, finds his skeletal remains, and is able to date them in order to travel back in time and retrieve him shortly after he'd been stranded to begin with.

Comic Strips

• Calvin and Hobbes: Calvin writes a letter to his future self, expressing envy at having experienced life 20 Minutes into the Future. When he receives the letter, some days later, he feels sorry for his past self.

Fan Works

• In the fanfic "Homecoming", Doc sends another cross-decade letter telling Marty about his plans and sending him some family documents it wouldn't do for a historian to find.
• In the Ranma ½ fanfic, Exact Change by Ozzallos, Nabiki does this.
• In The Lord of the Rings fic Don't Panic!, Penny, trapped in Middle-earth, thinks of writing forward in time to let her mother know she's alive. Elrond informs her that it would be impossible, since even with elvish magic, parchment will only last an Age or so.
• Discussed and carried out in "Every Good Fairytale": Sherlock Holmes promises to write to his wife, two centuries into his future. Beth is positive they'll survive, as her family possesses Watson's journals, and she turns out to be right.
• In the Ghostbusters fic Future Shocks by Fritz Baugh, the Ghostbusters of the year 2024 travel back in time to the year 1986 to help the original team overcome the machinations of a time traveler. In a sequel set almost twenty years later, Winston and Ray exploit this trope to once again get aid from the 2024 team, who claim that the message was lost behind a cabinet for several years, and good thing too, as it arrived before their first time using time travel.
• In Quick to the Trigger, the old archaeological dig Dr. Oliver went to in Egypt now has a word carved in one of the bracelets that reads Trueheart. Kotaro states that it's the effects of their friends who traveled back to Ancient Egypt to signify that things are going right on their end.
• The Doctor Who fanfic Epistolary: The Fifty Years Before You Were Born is an extended version of this trope. Amy and Rory, after being trapped in the past following "The Angels Take Manhattan", exchanged correspondence with Bracewell from "Victory of the Daleks", who agreed to keep their letters and other diary entries safe for the Doctor to read later, thus providing a legacy for the Doctor to remember them by. Many of their letters are addressed directly to the Doctor, with the signature line, "Love across the stars."

Films — Live-Action

• In the movie 12 Monkeys, as Cole prepares to travel from the future, he is given the telephone number of an answering machine whose tape was found in archaeological research; the whole end-of-the-world problem ensured the tape was not erased for reuse. Problem is, they don't tell him the details, so he expects someone "in the know" to answer...
• Back to the Future:
  • Marty tries to do this in the first film, with a "Do Not Open Until 1985" letter talking about how Doc gets gunned down. Doc tears it up while proclaiming he can't let it influence the future. He later tapes it back together and reads it.
  • Probably the best-known modern example is the letter Marty receives from Doc Brown at the end of Back to the Future Part II: Doc is in the DeLorean time machine when it gets struck by lightning, sending Doc to 1885 and stranding Marty in 1955. Doc writes a letter to be delivered to Marty's exact time and place to let him know that he's happy where he is, making this an example of "I'm happy in the past." Doc sent the letter simply for Marty's benefit, and in Part III it is revealed that it includes with it a map to the location where he hid the DeLorean after landing in the past and instructions for repairing it so Marty can return home to 1985. Later, however, Marty finds evidence that Doc is killed a week after writing the letter, prompting him to go to 1885 to save him. The courier who delivers it clarifies that it was left in the care of Western Union with specific instructions on where and when to deliver the letter. There was apparently a betting pool as to whether the recipient would even be there (the courier lost).
• In Dino Time, after the protagonists go back in time and end up stuck in the past, they plan to carve an image into a rock to show their parents how to get the time machine to work. Oddly, they don't get a chance to carve the message, but somehow it got there anyway.
• Frequency: A police officer uses an old ham radio in his home to talk to his father using the same radio 30 years ago, allowing them to change events in the mean time.
  • The officer enlists his father to stop a killer before he murders their own mother and wife. The father fails in his first attempt, but after hearing that the killer touched his father's wallet, he figures that the killer's prints are on it, and instructs the father to hide the wallet in a very out-of-the-way spot in the home, where the son finds it.
  • After the ham radio is destroyed, the father communicates with the son one more time by burning a message into the oak table both of them are using.
• A variant in Indiana Jones and the Dial of Destiny as it isn't the time travellers but the inhabitants of the past who create a time machine and puzzle to keep it hidden to specifically make sure someone comes back in time from the future to only that point in time.
• Inverted in The Lake House: the letters time-travel; the people take The Slow Path.
• In Looper, Joe (and Jesse by force) write on their arm with a knife in the main time of the film so that the resulting wounds, after healing, show up on their older selves' arm telling them where to go to settle the situation.
• Edward Johnston does this in Timeline, the film of the Michael Crichton novel. Also, one main character muses over what the life story of a knight buried in a recently-discovered grave might be. At the end, it is revealed to be his own grave, with an inscription to those of his friends who returned to the present.
• At the end of Waxwork II Lost in Time, Mark sends the time-door opener to his Love Interest this way.

Literature

• Mid-20th-century SF author Jack Finney used this at least three times:
  • In one of his stories, the main character sends people into the past who wanted to "emigrate" there. They would get themselves in photos — usually around the edges of group photos, for some reason — to let him know they'd arrived safely. A Javert-like cop discovers what the protagonist is doing, and is about to stop him, so the protagonist sends him back in time. The protagonist later finds an old photo with the cop in it, looking very angry.
  • In "The Love Letter", a man in the present day sends out an unaddressed letter complaining of his loneliness, and then a few days later finds a hidden compartment in his antique desk containing a letter from a lonely Victorian woman who received a strange, unmarked letter and wished she knew who to reply to. He writes another unaddressed letter, and again finds a hidden compartment in his desk that contains a letter from the Victorian woman. He realizes that there's one last unopened compartment, and writes to the lady explaining that this will be their last exchange and he wishes for something to remember her by. When he opens the last compartment, he finds a photograph of her, and nothing else. Some time later, it occurs to him that there is one more place she could send him a message — and the story ends with him in a cemetery, reading the Public Secret Message engraved on her headstone.
  • In "The Third Level," an ordinary guy tells how he discovered that Grand Central Station has a third level, which allows you to travel back in time to the late 1800s. He gets some vintage money and tries to find the third level again, planning to stay in the past, but never does. Then a friend of his disappears. That night the narrator is looking through his stamp collection (most of which are on unopened, empty envelopes) and finds one he never saw before. This one isn't empty, either — it contains a letter from his friend, telling how he did find the third level.
• The novel Good Omens has a variation, where the author of the "deliver this message to this specific person at this address on this date" message is not a time traveler, but has the ability to see the future. And includes extra messages, addressed by name, for the three people who try to open the message before it reaches its intended recipient, threatening to reveal their sordid secrets (cheating with the secretary, left his squad to die, swindled a widow). Agnes Nutter predicted events of future generations, leaving a record for her descendants to consult, one prophecy at a time, in centuries to come. By the time the story is set, intervening generations have annotated many of these documents, including some ribald comments on the page that predicts Agnes's modern-day descendant will have sex with a particular other character.
• Terry Pratchett uses variations on this theme in Going Postal. It begins with the con-man tasked with reforming the moribund city Post Office looking at great drifts of decades' worth of undelivered mail, and wondering how the heck he's going to do it all. He makes a start by delivering one randomly chosen letter: it's a thirty-year-old response to a marriage proposal that never arrived. So the two people involved each married somebody else, but now that they're both widowed they decide to remarry to each other. Then he discovers the reason why the Post Office collapsed: a quasi-magical Sorting Engine that went haywire and began sorting mail that hadn't even been written yet, pulled back from the future, or else letters from other worlds, or else letters from other phases of Multiversal space and time. This so disrupted causality that the whole ordered system collapsed.
• The novel Timeline had several of these. The first clue that time travel is happening is when the head scientist visits the time travel corporation, and suddenly his archaeologists find a thousand-year-old parchment with his handwriting on it, as well as his glasses. This kicks off the plot. At the end of the book, the archeologists find the grave of one of their team who stayed in the past, with a message for them in the epitaph.
• Robert A. Heinlein:
  • Lazarus Long uses this trick in Time Enough for Love, when he's sent back in time to the early 20th century. It's a complicated set of multiple letters inside letters (with different instructions and dates on which to be opened), since he's writing it to a time two thousand years into the future. The recipients of the letters then use the date they stop being sent to pinpoint when to rescue him.
  • Part of the plot of The Door into Summer
• In D. J. MacHale's The Pendragon Adventure series, the third book, The Never War, has lead character Bobby Pendragon send his journals detailing what happens during his stay on "First Earth" (Earth, circa 1937) to his friends/acolytes/helpers Mark and Courtney by locking them in a safe deposit box in the town's bank.
  • Also in the eighth book The Pilgrims of Rayne where Aja Killian leaves a message hoping the future will find it.
• In Isaac Asimov's The End of Eternity, Cooper sends a hidden message through an ad in a magazine, to inform Harlan of where (or to be exact, when) he is.
• Inverted in The Riftwar Cycle book Into a Dark Realm. Pug has a magical box which he uses to send his past self messages.
• This trope is mocked in Life, the Universe and Everything when Arthur and Ford end up on Earth shortly before it's blown up. Arthur gets the idea to warn himself, but Ford points out that it wouldn't work by doing an impression of the hypothetical phone call "'Hello, me? It's me. Please don't hang up.' *shrug* He hung up. This is NOT my first temporal anomaly, you know."
• Done without the time travel — sort of — in Joe Haldeman's The Forever War, in which Marygay leaves a note for William at the front of his army record, knowing that this will be kept safe to give to him if he survives the war, even though near-lightspeed travel has caused their personal timelines to diverge and therefore he's hundreds of years in her future.
• The protagonist of The Anubis Gates by Tim Powers sends a message from the past to himself, jotting a note on a book in Pig Latin. This isn't so much an attempt to convey information — he'd already seen the note, and been surprised by it, at a previous point in his time-traveling adventure — so much as a way to self-seal a Stable Time Loop and ensure his earlier self will pay attention to that particular book.
• Likewise, at the end of Artemis Fowl: The Time Paradox, Artemis sends back a note to the past Mulch Diggums after he defeats Opal Koboi to break Artemis and Holly out after they were captured by the past Butler.
• In Diana Gabaldon's Outlander series, Claire and Jamie write to their daughter and son-in-law, storing the letters in a chest addressed to their oldest grandchild.
• In The Extinction Gambit, the first novel in The Extraordinaires trilogy, The Retrievers — having met Kingsley and Evadne when they travelled through time to 1666 — leave a message with a Demimonde law firm to be delivered to a girl matching Evadne's description in 1908.
• A Spider-Man/X-Men series of novels called The Time's Arrow trilogy features Spidey and Bishop being trapped in the wild west period and using a photograph of themselves with a written message on it to the present day period on order for the rest of the X-Men to send them another device to the past so they can return home.
• Much of The Dechronization of Sam Magruder by George Gaylord Simpson is the journal of a paleontologist sent back in time to the era of the dinosaurs, kept on engraved stone tablets and finally unearthed by his colleagues in the present.
• In Harry Harrison's A Rebel In Time, protagonist Troy Harmon leaves a message in a bottle to be picked up in the future by the team that sent him back to the U.S. Civil War. The bottle is buried under a particular tree in a certain garden and is dug up successfully, although Harmon's rescuers are much older than he was expecting as it took them that long to rebuild the time machine.
• Gravity Falls: Journal 3 ties up one of the show's loose ends by having a letter addressed to Dipper and Mabel in which Blendin Blandin explains that in order to escape the custody of the Time Police due to his part in causing Weirdmageddon and nearly bringing about The End of the World as We Know It, he had been jumping through time, only to get stuck in the late 1800s and become a pocket watch repairman.
• The Innsmouth Legacy. In Winter Tide, Dr Trumball's mind is swapped with a Yith and she falls in love with another abductee while studying in their Archives. After Trumball is returned to her body, she asks Aphra Marsh (who when she becomes a Deep One will be effectively immortal) to memorise a letter so it can be delivered to that person when they return to their own body thousands of years in the future.
• Blackout: This is a common tactic used by time travelers to send messages forward to their home base at Oxford in the 21st century. If they get in trouble, time travelers will stick coded messages into personal ads in local newspapers, and Oxford historians will comb period news reports to find the messages and use them to figure out where to send retrieval teams.
  • In Connie Willis' time travel books, the historians use so much space in the classifieds trying to communicate with each other and the future that you begin to wonder if any classified ads are "real".
• The story "The Count of Time" in the tie-in novel El tiempo es el que es of The Ministry of Time (based on an unproduced episode), starts with the discovery of a message left in a Medieval manuscript by a time-traveler asking to be rescued from the year 808 AD.
• Star Trek: Federation: After the crew of the USS Enterprise encounters the Enterprise-D in a time distortion, in 2270 Captain Kirk decides to write a letter to the commander of the Federation starship that took part in a rescue operation near the Kabreigny Object in 2366. He has the letter sealed in the Starfleet archives with orders that it not be delivered for a century, making sure that it would not be delivered until well past the time the rescue operation took place from Captain Picard's perspective. Shortly after the destruction of the Enterprise-D in 2371 the letter is unsealed and delivered to Picard on Titan.
• In the German novel The Last Day of Creation by Wolfgang Jeschke, the Americans who have traveled back five million years into the past consider doing this, as their project has Gone Horribly Wrong and created multiple alternate futures. Realising his Different States of America no longer exists, one contemplates writing down what he remembers only to be told the length of time between now and the beginning of "human culture" is so great it will erase any record.
  "The Atlantids have had plenty of ideas as to how to send advice into the future: anachronisms, indestructible time-boxes — chronological messages in bottles, if you like; but nothing seems to have ever arrived. Perhaps they've all been washed up on uninhabited beaches or buried too deeply in the womb of the earth."
• Bruce Coville's Book of... Magic II: What the Dinosaurs Are Like sees two kids using magic go back in time, to separate time periods, to find out what... well, the dinosaurs are like. (The spell, incidentally, also turns them into dinosaurs.) One breaks the spell and returns to the present day when he realizes the K-T Extinction Event is about to happen. The other, who went back much further, stayed in the past, and his skeleton is now in the dinosaur museum as an unidentified species.
• Septimus Heap: Septimus does this in Physik by hiding a letter in a book he knows will still be around in 500 years, and Nicko and Snorri do this in Queste.

Live-Action TV

• 12 Monkeys:
  • Unintended, but has the same effect. In "Mentally Divergent" Cole was carrying a note with the address of a mental institution he intends to infiltrate in 2015, when he accidentally ends up in North Korea in 2006. In 2015, Cassandra sees a nine year old photograph of the note (which was left behind at the North Korean military base when Cole was transported to 2015) and concludes that Cole will be at the mental institution right now.
  • At some point in 2017, prior to her death, Cassandra made a recording for the scientists in the future, telling them about Leland Goines, the Army of the Twelve Monkeys, and mentioning Cole by name.
• In Babylon 5, after traveling 1000 years into the past and becoming the prophet Valen, Jeffrey Sinclair writes a letter to himself and leaves it in the care of the Minbari, who delivers it to him just before the beginning of the sequence of events that end in him traveling back in time.
• On the flashback episode of The Big Bang Theory Sheldon attempts to do this with the rental agreement he has Leonard sign:
  Sheldon: And initial here, stating that if we ever discover the secret to time travel our first trip will take us to a point five seconds in the future from now.
  [Leonard initials; they sit for a moment, waiting]
  Sheldon: Well, that's disappointing.
• In season 6 of Charmed, when Chris gets dragged back into the future by his fiancée, Bianca, the sisters write a spell to give him back his powers and stick it under a loose floorboard mentioned previously in the episode. Twenty years in the future, Chris pries up the old loose floorboard, finds the note, and returns to the past with his newly-recovered powers. The sequence is also an example of San Dimas Time, as the sisters 'race' to write and place the spell 'before' Chris opens the floorboard, and were surprised when he re-emerged just a few moments after they planted the note.
• Doctor Who:
  • In "Battlefield", the Doctor finds a note in his own handwriting with the body of King Arthur, a message from his future self.
  • "Blink" revolves almost entirely around such messages. First, Sally finds a message addressed to her written behind the wallpaper of a derelict house. When she returns with her friend Kathy, Sally answers the door to someone with a letter for her while Kathy goes upstairs. The letter is from Kathy saying she had a long and happy life, delivered by her grandson; meanwhile, Kathy is sent back in time. Another character is asked to keep a message and take it to Sally by The Slow Path, and DVD Easter Eggs are inserted into seventeen unrelated DVDs which are all DVDs that Sally owns. At the end, she gives a list of these messages to the Doctor, closing the Stable Time Loop.
  • A similar thing happened to companions Amy and Rory Williams in the end of "The Angels Take Manhattan". A mini-webisode, "P.S." has Brian Williams, Rory's dad, receive a letter while watering the plants in his son's and daughter-in-law's house, delivered by their adopted son (who is older than his grandfather), stating that they got stuck in the past and will never see Brian again. Come to think of it, the Angels seem to trigger this trope almost every time they send someone into the past.
  • River Song uses this tactic all the damn time to get the Doctor's attention (mainly because he won't answer his phone), leaving messages in places that are sure to get his attention sooner or later. (It doesn't matter when exactly he finds them, because he can land the TARDIS precisely at the time she asks, even if that was millennia prior.) Occasionally, the Doctor uses the same technique to get a message to River.
  • The Doctor does an indirect version of this to Amy and Rory in "The Impossible Astronaut". Among other things, he invades a crowd scene during the filming of a Laurel and Hardy movie he knows they own so that they'll see him when they watch it, and fools around with an Elizabethan-era noblewoman, lets himself get caught by her husband, and makes an excessively memorable jailbreak after being imprisoned for adultery in order to amuse the Ponds via history book.
  • And in the Big Finish Doctor Who adventure "The Kingmaker", the Doctor and his companions, separated by two years when the TARDIS is stolen (by William Shakespeare) exchange notes by leaving them in the care of the owner of the eponymous tavern. The letters left by Peri and Erimem travel forward to the Doctor in the usual way, while the Doctor leaves his own notes on the assumption that one of his future selves (the "big-eared Northern chap" in a Lawyer-Friendly Cameo) will collect them and deliver them to the past.
  • In "Journey to the Centre of the TARDIS", the Doctor inscribes the words BIG FRIENDLY BUTTON on a temporal probe that he knows is going to end up in the TARDIS control and where the words will be burnt on to Clara's palm.
  • In "The Name of the Doctor", Madame Vastra, needing to draw Clara into a psychic conference, writes a letter to her and arranges for it to be delivered on April 10, 2013. The letter is impregnated with a drug to knock her out.
  • In "The Day of the Doctor", Eleven carves a note into the wall at the Tower of London for Clara to find in the present. It's the activation code for Captain Jack Harkness' Vortex manipulator, which she uses to travel back to free the Doctors.
  • "Survivors of the Flux". While stranded at the start of the Twentieth Century, Yaz, Dan, and Professor Jericho create a message visible from orbit near the Great Wall of China for Karvanista, who along with the Lupari fleet is protecting Earth in 2021. Karvanista sees the message but it only annoys him, as he doesn't have a time machine so what's he supposed to do about it?
• Early Edition:
  • Reversal: the main character mysteriously receives newspapers a day ahead of time. He then spends the rest of the episode trying to avert the tragedies the newspaper describes before they happen.
  • Played closer to straight in one episode when a reporter at the paper in question realizes this is what is going on and writes an article for tomorrow's edition designed to catch his attention today.
• The Eureka 4th mid-season finale had Jack travel back in time again to leave a message to himself to save Allison.
• Inverted in 5ive Days to Midnight. A case is sent back in time in an attempt to Set Right What Once Went Wrong.
• In one episode of Friday the 13th: The Series, a character tries, and fails, to do this, hiding a note in a desk destined to become an antique. It isn't discovered until after she returns to the present.
• At the end of Goodnight Sweetheart, when Gary finds himself trapped in 1945, he writes a message of explanation and apology to Yvonne on the wall of his flat and then wallpapers over it - knowing that they're going to have that wallpaper stripped in the future (where his friend Ron lives in the same flat fifty years later, since Gary still owns it).
• In the Haven episode "Sarah", when Duke is stranded in 1955, he manages to tell Audrey and Nathan what happened by writing a letter addressed to Audrey with instructions that it is not to be delivered until the present day.
• Heroes: Hiro, in the past, writes an account of his adventures on a series of scrolls and hides them in the hilt of a samurai sword. Conveniently, even though Hiro has been carrying the sword for several episodes, Ando only finds the scrolls after Hiro travels to 1671. (And somehow he gets them in the right order, too.)
• In the pilot episode of Journeyman, the protagonist uses a time capsule to the future to prove to his wife that he's been time traveling: he digs under the brick patio in their backyard (which they put in right after they moved into the house) to reveal a toolbox containing a newspaper from 1997 and her engagement ring.
• Korean Drama Nine: Nine Time Travels involves a man who obtains some magic incense sticks that can be used for round-trip time travels exactly 20 years into the past. He wants to Set Right What Once Went Wrong, and one of his goals is to alert his teenage self about his health, since his 2013 self is dying from brain cancer. Unfortunately he only gets to give a cryptic warning before complications ensue. His 18-year-old self from 1993 resorts to scrawling messages around the house, asking his 2013 self to come back and explain.
• The Diffy family in Phil of the Future attempts to do this when their time machine breaks down for an extended period of time in the early 21st century. Phil and Pim's school plans to bury a time capsule that isn't supposed to be opened for 100 years. Their parents Lloyd and Barbara recognize the capsule as an odd thing they both found by accident on a date before they were married, and plot to use this trope to create a Temporal Paradox so they don't get stuck in the past. It fails, because one student put in a can of spring-loaded snakes as a prank, causing Lloyd to spill the drink he and Barbara brought on their picnic, and Lloyd uses his note from the past to wipe up the spill and never reads it.
• One episode of Quantum Leap had Sam and Al switching places, and Sam was locked in the imaging chamber. Sam had Al write a letter to a lawyer with the code to unlock the door, which opened immediately when Al put the letter in a mailbox.
• An episode of the revival Quantum Leap (2022) series had Ben write a letter intended to warn a woman (who herself was a recurring character and a Secret-Keeper of Ben's) of her husband's impending death from a treatable heart defect as he had leaped out before he could tell her directly. It works, but then he dies soon after in a car wreck.
• This was done in reverse in the Stargate SG-1 episode "1969". General Hammond gives a note to Carter as they set out on a mission that ends up sending them to the aforementioned year. It ends up being read by his younger self, who takes the message to heart and helps the team out. In other episodes, the team uses this trope to send a warning to the past not to travel to a certain planet, and on another occasion, they record a video message of themselves to explain their situation to the alternate timeline that resulted from their meddling with past events.
• This also comes up in an episode of Stargate Atlantis. Due to a freak cosmic accident, Sheppard is transported 48,000 years into the future. In order to help him come back to the present, McKay programs a sophisticated, artificially intelligent simulacrum of himself and leaves it in Atlantis where it waits until Sheppard arrives.
• Data's head was used for this, in the Star Trek: The Next Generation two-parter "Time's Arrow"; with Data's head having been blown off before his body and the rest of the crew went through the now-closed portal, Picard is able to use an iron filing to tap a binary-coded message into the neural net of the damaged head to warn the Enterprise not to destroy the portal and how they might use it to bring him home, correctly assuming that his crew will use the head they salvaged when this mission began to repair Data.
• This was attempted in the Star Trek: Voyager episode "Eye of the Needle". A very narrow wormhole led almost home, but 20 years into the past. The crew wrote messages to home and gave them to someone on the other end of the wormhole, to pass on to Starfleet 20 years later, in the present. Unfortunately, that someone died several years before the USS Voyager left, and the messages were never delivered.
• Supernatural:
  • In 6.18 "Frontierland", Sam receives a message (and a parcel with a plot device) from Samuel Colt, whom he met in 1861.
  • In 7.12 "Time After Time", Dean is accidentally transported to 1944 by Kronos. He leaves a message to Sam in the house they were squatting in before the time-shift, thus helping Sam with the ritual required to bring him back. He remembers where Sam placed his sleeping bag and carves "Sam" into the wall near the floor. When Sam lays down to get some sleep, his eyes look straight at that section of the wall and he figures out that a letter is hidden in the wall.
• Timecop: During the protagonist Jack Logan's investigations in the past, he would frequently send back intel to his colleagues at the time agency by hiding coded messages in things like newspaper ads.
• Wyatt does this on Timeless when the team are in 1962, in an effort to prevent his wife's death. It doesn't work, in large part because Western Union stopped their telegram service a few years before Wyatt's wife was killed. In a later episode, Rufus reveals that there is an established protocol for using this technique in case the team gets stranded.
• Used pretty well in the sci-fi action series Time Trax — the main character was able to arrange for someone to be taken to the future by dosing the person with the needed time travel drug, then leaving a coded classified ad in a paper that his team in the future was monitoring. Unfortunately, this conflicts with the show's insistence that "time travel" is actually "interdimensional travel" to a time-shifted parallel world. What this means is that nothing they do affects their own reality, so leaving messages in this world's newspapers would not cause them to magically appear for their colleagues to read in the future.
• Torchwood:
  • In the episode where Jack and Tosh fall through a crack into the 40s, Tosh leaves notes for the others to find that contain the data they need to work out how to get them back. Requires extensive Willing Suspension of Disbelief, as the message is in two parts: one in an electrical box and one in a tin can in a basement. The chances of them going undisturbed for about sixty years, and Gwen managing to find them both in one day, in the right order, boggles the mind.
  • Similarly, in the series 2 episode "To the Last Man", 1918 Torchwood leaves "time-locked" instructions for 2008 Torchwood to follow regarding the 1918 soldier who's been cryo-frozen in the vault for all this time (except 1 day a year).
  • The Torchwood website advises agents not to try this:
  As well as the danger of tangentially altering the timeline in some way, it relies on your messages being undisturbed for decades and subsequently found at the correct time. This is harder than it might seem.
• The Twilight Zone (1985): In "The Junction", Ray Dobson is extremely grateful to John Parker, another miner from 1986, for saving his life while they were trapped by a cave-in on September 16, 1912. In order to return the favor, he writes a letter to John's wife Melissa and leaves it with the church with instructions that it be delivered on September 15, 1986, the day before John became trapped. Although Reverend Bailey had every intention of delivering it on the day in question, he was called away and forgot to do so. By the time that he gets it to Melissa, John is already trapped in the mine. However, Ray's letter includes the location where he and John were trapped in 1912 and John is rescued in time.

Radio

• In The Hitchhiker's Guide to the Galaxy (1978), Ford and Arthur do this by accident when trapped on prehistoric Earth. Arthur drops his towel during an earthquake, it gets fossilized in a lava flow, then thrown out into space when the planet is blown up by the Vogons two million years later and picked up by the Heart of Gold, where Zaphod interprets it as a message and comes to rescue them. The Heart of Gold is powered by the Infinite Improbability Drive, so things like this are par for the course.
  • According to the Retcon in the Tertiary Phase, though, this all happened in the artificial universe in Zarniwoop's office, thereby explaining why the 'real'' Ford and Arthur are still on prehistoric Earth when the Phase begins. (The actual reason is that the Tertiary Phase was based on the third book, while most of the 2nd radio series never happened in the books, and the Retcon was attempting to incorporate the 2nd radio series into the continuity)

Roleplay

• In Darwin's Soldiers: Pavlov's Checkmate, Shelton's antimatter copy (long story)) uses this to inform modern-day Shelton that he's trapped in 1990.

Tabletop Games

• In Continuum, this is a common solution to being "stuck" in the past while your Span recovers; the Scribes specialize in this. Also, taken to extremes, a way of "instant messaging" with fellow spanners. Have an example of this in action.
• This is also a recommended tactic in GURPS Time Travel and GURPS Infinite Worlds, where the authors suggest giving the message to a law firm to hold until the proper time. Other possible channels exist, they note, but a good lawyer won't even blink at the request.

Theater

• Harry Potter and the Cursed Child features this in the final act, when some of the characters have become stranded in the past. Specifically, they find themselves just before the pivotal event when Voldemort is to attack infant Harry and his parents. They manage to signal present-day Harry to their whereabouts by (somehow) acquiring his baby blanket long enough to write an invisible message on it. The message was written using a material that would remain unseen until it reacted with a rare potion ingredient that spilled on it just before their departure from the present day, the blanket having been kept as a keepsake.

Video Games

• In Back to the Future: The Game Marty once again does this in Episode 5 by giving young Emmet Brown a newspaper from the future, with instruction not to look at it until he receives the Key to the City (which the newspaper depicts). The subtle message being that Marty was stuck in the past and needed Doc to go back and pick him up.
• Chrono Trigger uses this with the Rainbow Shell. Leene leaves a message with it meant for Marle, which she reads 400 years after it's written.
• In Criminal Case: Travel in Time, the team does this while stranded in The '60s by opening a trust fund account for their boss then leaving a distress message inside the vault for him to read in 2029. It works, but unfortunately, the timeline had already been altered by the Big Bad, turning 2029 into a Bad Future where he the boss holds no power.
• In Dark Cloud 2, the diary and letters that Max is writing to his mother... since Elena, like Monica, is from 100 years into the future, and was forced to return there while Max was still an infant.
• In Dark Fall 2: Lights Out, Parker (your character) reads Drake's diary and discovers a threatening message addressed to him. Drake's foreknowledge is explained because he was being manipulated by Malakai, a time-traveling sentient space probe from the future.

Visual Novels

• Steins;Gate: The future gadget lab receives a letter from Suzuha, after she is trapped in the past and loses her memory.

Webcomics

• Casey and Andy: President Cleveland sends a message forward a century, to deliver a crotch-punch to his archenemy. And husband to his wife.
• In Narbonic, Dave's mind is bouncing around in time. His 16-year-old self gets a message on how to return to his own time, which was written by his 6-year-old self on the men's room wall (which wasn't cleaned in the next ten years).

Western Animation

• In Danny Phantom episode, "The Ultimate Enemy" Jazz (in the present) sends a message to Danny, who's trapped 10 years in the future. She used a particularly foolproof method, too: she used the boo-merang, an item designed to target Danny Phantom specifically, with a message that she attached using her Iconic Item (her headband).
• Dexter's Laboratory used a short-term version of this, as Dexter (after opening a space gate to an alien world and being eaten by an alien blob) sends Dee Dee back several hours with a message... but past-Dexter doesn't get it until it's too late (which is to say, just after writing the letter in the first place), due to Dee Dee's ditziness and his own irritability.
• David Xanatos, from Gargoyles, makes his fortune via this trope. After he's zapped back 1020 years in time by the Phoenix Gate, he leaves a package in the care of the Illuminati, to be delivered to his younger self 1000 years in the future (1975). The package contains a single coin (worth thousands of dollars by the time the younger Xanatos receives it and uses it for his first investments, but near worthless for its era), and a lengthy letter to be delivered twenty years after that (1995, one week before the beginning of the episode) that details what he will have to do to ensure that he is sent to the past to send the coin and the letter in the first place.
• Used in a multi-part Time Travel story arc in Adventures of Sonic the Hedgehog. A couple times, Sonic and Tails are stranded in an impossible situation. Sonic's solution: write a note to their contact in the future, bury/hide it right where they stand, and the solution will be beamed to them the exact second they finish.
• In the Phineas and Ferb episode "It's About Time!", Phineas and Ferb get trapped in the prehistoric past and send messages back to the present by scratching them into the mud next to a dinosaur footprint they know is going to become fossilized and end up in the local museum.
• Teenage Mutant Ninja Turtles: Fast Forward: In one episode, the turtles have to deal with dozens of time portals opening up in future New York. The turtles get separated through time, with Donatello landing in modern-day New York. Having nothing but time on his hands, he quickly figures out how to control the device creating the portals and mails instructions to his brothers in the future. Apparently, in the century that it sat in the post office, it gained an iconic status. In the episode's Cold Open, the postal workers cheer when the countdown reaches zero, and they draw straws to determine who gets to deliver the legendary letter.
• An interesting variation occurs in one episode of the original Ninja Turtles. Carter needs to contact time-travelling allies Landor and Merrik, but they're twenty years in the future. Carter sends a radio message into space, with the intent of bouncing it back to Earth via a star ten light years away. It works.
• Though not quite the same thing, an episode of the Superfriends has some of the super-heroes trapped in the prehistoric past. To get a signal to the heroes in the present, the trapped heroes bury their communicator in the ground at the precise location where the Hall of Justice will be built thousands of years from now. At that time, the heroes in the present begin to hear a signal coming from the ground. Somehow, this tells them that their friends are trapped in the past. Even as a kid watching this, none of it made any sense.
• At one point The Tick and Arthur are stranded in the prehistoric past. Arthur takes months, years carving a message into the hardest stone he can find in the hopes that the message would survive millions of years of erosion to be discovered in the future The Tick breaks it. For those who're curious, some hard granite erodes at a rate of approximately one inch every million years; since they were cohabiting with Australopithecus, letters would probably have to be carved at least a foot deep and wide spaced to still be legible today, assuming they were left exposed to the elements.
• In the Futurama episode "The Late Philip J. Fry", Leela discovers that Fry's been sent into the future, unable to return. She goes into a cave and blasts a pattern of holes in the ceiling. The resulting stalagmite formations over millions of years spell out a touching message for him.
• The Day My Butt Went Psycho!: In "The Flushinator", Zack writes a message in wet cement, asking his future self to travel back in time and hide a futuristic freeze ray in the bushes beside the sidewalk. He then reaches into the bushes and finds the freeze ray there.
• Milo Murphy's Law: In "Missing Milo", Milo ends up time-traveling to the future. His friends in the present see him on TV from an episode that originally aired fifty years ago. After seeking out the creator of the TV show, he admits to Milo being there in the past, and gives them a letter that Milo wrote to his friends, instructing him to give it to them in fifty years. When Milo gets back to the present, he admits that he never wrote the letter, and was never in the past. Sarah takes it to mean that Milo must time travel again at some point in the future. Milo agrees and decides to give the letter to the TV show creator when he goes back in time the next time. Finally fulfilled in the show's next season, where he successfully delivers the letter.
• In the Family Guy episode "The Big Bang Theory", Stewie and Brian head back in time to the life of Leonardo da Vinci in order to prevent his assassination, which due to a variety of reasons is the lynchpin that would cause all of spacetime to fall apart. When they ultimately fail, only for reality to remain intact, they deduce that Stewie — a descendant to Da Vinci — is meant to take Da Vinci's place for the time being, and so he sends Brian to their present-day home. It too remains intact before there's a knock on the door: a representative from The Vatican delivering a message from "Da Vinci himself", who did so with instructions it be on their current exact time and date. The message — written a week after Brian left — has Stewie explain that he placed himself in a cryogenic stasis device in their basement, instructing Brian to dig him up.
• Men in Black: The Series has one episode where Jay, Kay, and Elle needed to stop a giant radioactive alien bug from reaching and destroying Phoenix in two hours, but in the present time it was way too big to take down so Jay and Kay travel back in time to the Wild West era when the alien was just an easily breakable egg hidden in an Abandoned Mine. Unfortunately they got captured by the back-then Boom Town sheriff and thrown into jail, berift of their normal advanced weapons (even if they weren't afraid of messing up the timeline by intoducing future alien tech for civilians to witness) and time travel in the series operates under San Dimas Time rules so they can't go back in time and try again. Kay's solution is to bury a small machine into the dirt floor of their jail cell, which emerges by itself at a preset time back in the present day of the now-Ghost Town where only Elle is around to see the message of "follow us back in time — we need help."
• Miraculous Ladybug: The season five episode "Reunion" has three instances of this. After Alix escapes into time in order to safeguard the Bunny Miraculous, she hides a letter and photos of her adventures behind a painting for her father to find in the present day. Then Ladybug hides a letter for Alix, asking her to look up something two hundred years into the future. Finally, Alix goes into the past and leaves the reply under a statue in the museum, so Ladybug can make use of it.

Real Life

• In 2015, Robert Rodriguez directed a Louis XIII Cognac brand-sponsored science fiction film starring John Malkovich that is not supposed to be watched until 2115 (it is kept in a safe). The century-long span matches the time it takes for a bottle of Louis XIII Cognac to be properly aged before its release to consumers.
• Stephen Hawking tried this in his "Time Traveler's Party" experiment. He held a reception for future time travelers, but didn't publish the time (12:00 on 6/28/2009, for any future people reading this) until after the party, so the only people who could show up would be time travelers. No-one did (or he's not telling). Alternatively, since it's an established fact no one showed up, no time travelers want to go, for fear of causing a paradox (and as of 2018 we will never know the answer.)

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