A visual guide · 10 models · 30+ stories

Ten ways to travel in time

Every time-travel story picks a set of rules, sometimes without saying so: Can the past be changed? Is there one history or many? Does the body travel, the mind, or just a message? Here are the most important models, from Back to the Future to Attack on Titan, each with a graphic you can play with.

Start the journey ↓
The map

Two questions sort it all out

Horizontal axis: can the past be changed? Vertical axis: how many histories exist? The color shows what travels. Tap a model to jump to its explanation.

01

A single, rewritable timeline

The past is erased and written over

Back to the Future (1985) · Back to the Future Part II · Looper · Frequency

Travels: the bodyPast: changeableHistories: oneGrandfather paradox: yes

There is a single history, and it has no backup. Change the past and everything that came after is overwritten. In 1955, Marty McFly interrupts the moment his parents were supposed to fall in love, and the family photo in his wallet starts to fade: first his brother Dave, then Linda, and finally his own hand.

  • The change spreads like a wave, with a delay that is conveniently dramatic.
  • The traveler remembers the old timeline, which is how he can repair it.
  • It allows the grandfather paradox: if Marty prevents his own birth, who traveled to 1955?

See also: Biff's alternate 1985 in Back to the Future Part II; the scars that suddenly appear on old Joe's body in Looper.

What about physics?No theory allows it. For the past to "change," you would need a second time, a meta-time, in which the change takes place. It is the most narrative model and the least coherent one.
Move the slider: the amber line replaces the original, and the photo loses the family one by one.
02

Self-consistent loop · Novikov principle

Whatever you did in the past had already happened

The Terminator (1984) · 12 Monkeys · Harry Potter and the Prisoner of Azkaban · La Jetée

Travels: the bodyPast: fixedHistories: oneGrandfather paradox: impossible

The past already includes your trips. You can't change it, because whatever you do there was always part of what happened. In 2029, John Connor sends Kyle Reese to 1984 to protect Sarah. Kyle becomes John's father. Without that trip, John would not exist to order it.

  • Self-consistency principle (Igor Novikov, 1980s): only histories without contradictions can happen.
  • Your freedom is "squeezed": if you try to change something, your attempt ends up causing the very thing you wanted to prevent.
  • There is no first cause: the loop holds itself up.

See also: in 12 Monkeys, the young Cole witnesses his own death; Harry sees "his father" cast the Patronus, and it was Harry himself.

What about physics?This is the version physics takes most seriously. General relativity allows closed timelike curves (Gödel, 1949; Morris and Thorne's wormholes, 1988). In 1991, Echeverria, Klinkhammer and Thorne showed that the "billiard ball paradox" has consistent solutions. Hawking, a skeptic, proposed that something in nature forbids these curves: the chronology protection conjecture.
The dot travels the endless loop: John sends Kyle, Kyle fathers John.
03

Attractors · the fate that pushes back

You can change the path, not the destination

Terminator 2 and 3 · Steins;Gate · Final Destination · 11/22/63

Travels: information and memoryPast: partly changeableHistories: many worldlines

The details change, but some events are attractors: history keeps returning to them by different routes. In Terminator 2 they destroy Cyberdyne shouting "no fate"; in Terminator 3 Judgment Day arrives anyway, just later.

In Steins;Gate, Okabe sends messages to the past (D-mails) and jumps between worldlines. But on every line in his "attractor field" his friend Mayuri dies, even if the time and the manner change. To save her he has to cross into another field, with more than 1% divergence.

  • Information travels: messages or memories sent to your past self.
  • The traveler keeps the memory of the abandoned lines.
  • Escaping takes a big change, not a tweak.

See also: Final Destination (death "corrects" its plan); in Stephen King's 11/22/63, the past fights back against anyone who tries to change it.

What about physics?It's fiction, but it borrows a real idea from dynamical systems: attractors, states that trajectories fall into even when they start from very different places.
Field α · all five lines narrow to the same point: the event happens anyway.
04

Branching multiverse

Traveling to the past creates another present

Avengers: Endgame · Dragon Ball Z (Future Trunks) · Loki · Star Trek (2009)

Travels: the bodyPast: untouchable (it branches)Histories: infiniteGrandfather paradox: no

The past doesn't change: it branches. When you arrive, a new history is born from that point and your original timeline stays intact. Trunks travels to the past, saves the Z Fighters and returns to a future still in ruins: what he saved was another branch.

In Endgame, Banner explains it: changing the past doesn't change their present, it just creates an alternate reality. That's why the Stones have to be returned.

  • No grandfather paradox: you kill the grandfather of another branch.
  • Going back "home" requires an extra mechanism (or isn't possible at all).
  • Every trip multiplies the histories. In Loki, an agency, the TVA, is dedicated to pruning them.
What about physics?It connects with the many-worlds interpretation of quantum mechanics (Everett, 1957). In 1991, David Deutsch proposed that on a quantum closed timelike curve the traveler would arrive in another branch, and the paradoxes would dissolve.
Tap a line in the graphic to send someone to that moment: a new branch is born.
05

Genetic travel · memory through blood

The memory travels, not the body

Attack on Titan (Shingeki no Kyojin) · Assassin's Creed · Dune (Bene Gesserit memory)

⚠ Contains spoilers for the ending of Attack on Titan
Travels: memoryChannel: the bloodlinePast: fixedHistories: one

Nobody moves through time. What travels is memory, through the blood. All Eldians, descendants of Ymir Fritz, are connected to the Paths: a dimension outside of time, a sandy desert with a tree of light, where all their lives converge. Through it flow the memories of those who inherit the power of the Nine Titans.

  • Inheritance forward: each new holder receives memories from the previous ones.
  • The Attack Titan also sees memories of its future heirs.
  • Curse of Ymir: each holder lives only 13 years after inheriting.
  • The loop closes: from the Paths, Eren shows the future to his father Grisha and pushes him to act. Eren Kruger was already talking about "Mikasa and Armin" before they were born.

Relatives: the Animus in Assassin's Creed reads ancestral memories stored in DNA; the Reverend Mothers in Dune can access the memories of all their female ancestors.

What about physics?Pure fiction, but with a powerful idea: a biological network linking different moments of the same lineage. Inside, it works like Novikov: the future Eren sees cannot be changed; he only fulfills it.
Memories pass from holder to holder: from Kruger to Grisha, from Grisha to Eren.
06

Reset loop

The world resets; you don't

Groundhog Day · Edge of Tomorrow · Re:Zero · Palm Springs · Majora's Mask

Travels: the mindPast: repeatsHistories: one, on a loop

Phil Connors wakes up on February 2 at 6:00 a.m., again and again. In Edge of Tomorrow, Cage resets the day every time he dies. The world remembers nothing; the protagonist keeps it all.

  • There is a trigger: death, the alarm clock, alien blood.
  • Getting out requires a condition: learning, changing inside, winning.
  • Subjective time grows without limit: estimates say Phil spends years, maybe decades, in the same day.

See also: Subaru's "Return by Death" in Re:Zero, Happy Death Day, Russian Doll; in video games, Majora's Mask and Outer Wilds, where the loop is the mechanic.

What about physics?None. But it is the model that most resembles learning: trial and error with memory. That's why it works so well in video games.
Each turn is the same day. The radius grows with what the protagonist remembers; the world always goes back to zero.
07

Inverted entropy

You don't jump to the past: you travel it backward

Tenet (2020) · The Curious Case of Benjamin Button (in spirit) · Merlin in Arthurian legend

Travels: the body, invertedPast: fixedHistories: one

A turnstile inverts the entropy of a person or an object. To the rest of the world, you move in reverse: bullets fly back into the gun, normal air doesn't work for you and you have to breathe through a mask. To get back to the present you have to live again, backward, all the time you rewound.

  • For a while, several versions of you coexist: the one going and the one coming back.
  • "What's happened's happened": the model is consistent, like Novikov.
  • The temporal pincer: one team moves forward and another backward, and they pass information to each other.
What about physics?It has a real inspiration: Wheeler and Feynman imagined that a positron is an electron traveling backward in time. In a Feynman diagram, a single zigzag line looks, from outside, like a pair that is created and then annihilates. The microscopic laws are almost time-symmetric; the arrow of time comes from entropy.
The protagonist always moves forward in their own time; it's the world that, at times, runs in reverse.
08

Ontological loop · bootstrap paradox

Things nobody created

Dark · Somewhere in Time (1980) · Predestination · Interstellar

Travels: an object or an ideaPast: fixedOrigin: none

A special case of the closed loop, with a problem of its own: something exists without ever having been created. In Somewhere in Time, an old woman gives Richard a watch in 1972; he travels to 1912 and leaves it with her when she is young. Who made the watch? Nobody.

In Predestination (based on a Heinlein short story) the protagonist is their own mother and their own father. In Dark, the 33-year cycles chain together: those who travel cause exactly what will push them to travel.

  • Compatible with Novikov: there is no contradiction.
  • But the information comes from nowhere: a song, a formula or a set of coordinates that nobody invented.
  • And then there's entropy: the watch ages on every lap and yet it has to be the same watch.

See also: in Interstellar, Cooper sends from the tesseract the coordinates that lead him to the mission that leaves him in the tesseract.

What about physics?Consistency allows it; thermodynamics hates it. An object going around a loop should wear out, and yet when the loop closes it would have to be as good as new.
The watch goes around: Elise keeps it for 60 years, Richard takes it to the past. Count its age… and its date of manufacture.
09

Time dilation · the time travel that does exist

To the future, with no return

Interstellar · Planet of the Apes (1968) · The Forever War · Contact

Travels: the bodyDirection: future onlyParadoxes: noneStatus: confirmed

The only time travel measured in the lab. The faster you move, or the closer you are to a large mass, the slower your clock runs compared with everyone else's. In Interstellar, on Miller's planet, next to the black hole Gargantua, one hour equals seven years on Earth.

  • Only forward: you reach other people's future, but there's no way back.
  • The twin paradox: the one who travels comes back younger than the one who stays.
  • Two causes: speed (special relativity) and gravity (general relativity).
What about physics?Confirmed. In 1971, Hafele and Keating flew atomic clocks on commercial airliners and measured the difference. GPS satellite clocks run ahead by about 38 microseconds per day; without correcting for it, your location would drift by kilometers every day.
The marks on the blue line are years lived aboard the ship: the faster it goes, the farther apart they are.
10

Block universe · nonlinear perception

All of time exists at once

Arrival · Slaughterhouse-Five · Watchmen · Story of Your Life (Ted Chiang)

Travels: nothing; the way of seeing changesPast: fixedHistories: one, complete

There is no travel because there is no flow: past, present and future exist together, like the pages of a closed book. Louise Banks learns the heptapods' language and begins to perceive her whole life at once. Dr. Manhattan lives all his moments at the same time. Vonnegut's Tralfamadorians look at time the way we look at a mountain range.

  • "Now" is a human perspective, not a property of the universe.
  • Knowing the future gives no power to change it: Louise chooses her life knowing how it ends.
  • It is the silent backdrop of models 02, 05, 07 and 08: they all assume a fixed block.
What about physics?It is a common reading of relativity (eternalism): since there is no universal "now," each observer slices the block differently. Einstein called the distinction between past, present and future “a stubbornly persistent illusion.”
A human sees a single slice, the now, and remembers the earlier ones. The future can't be seen.
Compare

All ten, side by side

A single story can mix models: The Terminator starts as a closed loop (02), and its sequels make it rewritable and then an attractor. Dark combines an origin-less loop with parallel worlds.

ModelWhat travelsCan the past be changed?Grandfather paradox?Real physics?Key example
01 RewritableBodyYes, it's overwrittenYesNoBack to the Future
02 Closed loopBodyNoImpossibleSpeculative (CTCs)The Terminator
03 AttractorsInformation, memoryDetails yes, fate noAvoids itselfNoSteins;Gate, T2
04 MultiverseBodyA new branch is createdNo (a different grandfather)Speculative (many worlds)Endgame, Dragon Ball
05 PathsMemory through the bloodlineNoNoNoAttack on Titan
06 ResetMindEvery day, from scratchNot applicableNoGroundhog Day
07 InversionInverted bodyNoNoInspired by it (Feynman)Tenet
08 No originObject, informationNoNoConsistent, but clashes with entropyDark, Predestination
09 DilationBodyYou only go to the futureNoYes, measuredInterstellar
10 BlockNothing (perception)NoNoAn interpretation of relativityArrival