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Great Scott! This is heavy: Time Travel Part 1.

Updated: Apr 14, 2021

How far ya going? Let's go back 30 years...

Keywords: Time models, Homochronic, Amoebechronic, Repechronic, Autocreation paradoxes, Autodeletion paradoxes, Polchinski’s paradox

Welcome to this blog post. Here we will talk about what our favourite time travel movies look like, from a scientific perspective.

Time Models.

In many time travel stories, I see many alternate timelines and their effects on future events. Many of these alternate realities can be represented with “time models”.

For example, some “time models” are shown below:

Image from

What does this show?

It shows the three types of time travel: Homochronic, Amoebechronic and Repechronic.

Homochronic: A time model where a single timeline is the host and updated “reality document” of all travels in time. Like in Harry Potter, the Prisoner of Azkaban, the actions of the future Harry and Hermione to save Buckbeak do not change the experiences of the past Harry and Hermione (they always did see the executioner swing his axe down and the voyage of time did not change that occurrence of events). Another example is an iconic film, Bill and Ted's Excellent Adventure, (#umustwatchthis) where Bill and Ted's past selves actually see their future selves arriving in front of them, after the famous line "Bill, strange things are afoot at the Circle K"...

Amoebechronic: A time model where voyages in time have a “ripple effect” and produce an alternate reality. A well-known example of this is Back To The Future, where Marty, in succeeding to “re-unite” his would-be parents, brings out a strong-willed character in George, his father, and changes his future lifestyle from one he was going to live in, before the time travel.

Repechronic: This is where a series of time travels are conducted, going back over and over to the same point in time with increasing experience and where future realities are changed, but the time traveller experiences the same present all throughout the series of voyages. This can be seen in the #LYSO(LaughYourSocksOff) movie Groundhog Day, where a weatherman, Phil Connors (Bill Murray, big fan of), lives Groundhog Day over and over again. Another serious and more-death-less-comedy example is Edge of Tomorrow: Live, Die Repeat. Tom Cruise stars as a soldier who has to experience the same fight between aliens and humans hundreds of times, until the cursed soldier defeats the big mama alien 👽 and, as Tom Cruise always does, saves the world.

I personally agree with a Homochronic time travel model since it nullifies most paradoxes.

Please share your thoughts in the comments below: I would like to see which model you most agree with, or whether you agree with something else.


First of all, what is a paradox?

You ever get that feeling where you know something, but just can’t put it on paper?

Well, I often get that when one of my math-friends asks me this question.

I would say that a paradox is where two reasonings are not consistent in their results. For example: “This statement is false”; one reasoning is to follow the literal meaning to the letter and consider that statement to be false. But another reasoning therefore can state that if the statement is false, it is false that the statement is false, so the statement is true. The statement is therefore paradoxical.

What would a time paradox be?

A time paradox would be where a voyage in time produces an inconsistent and/or mutually exclusive set of outcomes.

The “I killed my grandfather” situation is the main paradox that people take as an example. But there are more!

1. Autocreation paradoxes.

2. Autodeletion paradoxes.

These are the main categories of paradoxes in which most paradoxes fall into.

Autocreation: This is where the voyage of time triggers a set of events which solely cause the initial voyage in time to take place, therefore disrupting causality.

Autodeletion: This is where the voyage of time triggers a set of events which actively prevent the initial voyage in time taking place.

Some examples of autocreation paradoxes are:

1. A time traveller from 29/09/2130 goes back in time to stop Event A and, to be prepared, travels a bit before Event A. Then, unwittingly, he actually causes Event A. Knowing that he did this and has completely failed in his mission, he travels back to the future at 30/09/2130. This causes the 29/09/30 time traveller to go back in time… But why did Event A occur? Well, the time traveller caused that to happen by going back because Event A occurred. So, Event A occurred because of Event A. This violates a law of logic that a cause precedes an effect (causality principle), as in this case, the cause is the effect!

2. In Milo Murphy’s Law, Milo’s not-so-close friends Cavendish and Dakota somehow obtain a peach from a random person throwing it at their shoulder. After confronting deadly Pistachions (okay, they are mutant pistachios), they have to go back in time to be safe. Then after seeing their past selves, Dakota, being volatile, threw the peach at the past Dakota and Cavendish… Where did the peach come from? Well, the future Dakota threw it, but that was because he got it in the past because he threw it in the future because…? The peach came from the peach! As before, this violates causality! Another variation of this is where an avid fan of Charles Dickens tries to congratulate the author with the newly published folio edition of "A Tale Of Two Cities". Unwittingly, the fan sends it to Mr. Dickens before he even started thinking about it. Mr. Dickens reads the story and plagiarises his future self. The manuscript he produces is the replica of the folio edition.

Some examples of autodeletion paradoxes are:

1. “I killed my grandfather” paradox: I killed my grandfather before he had any kids, thus negating my own existence.

2. “Assassination of Hitler” paradox: An activist goes back in time to kill Hitler. However, in the future, the to-be time traveller sees that someone has already killed Hitler, not knowing that the assassin was themselves, and does not bother to go back in time to put the mega-twisted sadist out of his misery. A similar scenario would occur in T2: Judgement Day if the evil cyborg (T-1000) succeeded in destroying John Connor (so my dad tells me).

3. This paradox is a variation of Polchinski’s paradox: A time traveller travels back in time to 10 seconds before the time traveller went back in time and convinces him that it is dangerous, so basically stops his past self from travelling back in time.

Polchinski's paradox diagram.

How a homochronic time model can help with nullifying paradoxes:

For autocreation paradoxes, the simplest answer is that the thing in the “causal” loop (Event A, the peach etc.) actually never existed/occurred. This way, the time traveller does not somehow create a peach out of nowhere. Creations like literature, however, like A Tale Of Two Cities, even in a causal loop, have to exist since if they never existed, Mr. Dickens could never plagiarise himself and his manuscript is completely elemental. In this case, the simplest answer is that the time machine splutters, the book falls into a gutter, or anything that prevents the book from the future getting to the writer, happens.

For autodeletion paradoxes, the simplest answer is that the time machine splutters, the gun fails to shoot the bullet, the time traveller becomes mute before convincing his past self or anything that prevents the “deed” to occur happens.

How an amoebechronic time model can help with nullifying paradoxes:

For autocreation paradoxes, the simplest answer is that one enters an alternate reality where the book/peach does not exist and then gives the book/peach to someone (or places it somewhere) so that in both the timelines (the one where said person left and the one where the said person entered) the 📖 /🍑 exists.

For autodeletion paradoxes, the simplest answer is that after the “deed”, one enters a timeline where the deed is successful, but not the timeline from which he came. Every thing that was a victim of the deed was erased in this timeline.

Again, please share your thoughts in the comments below!

See you again in Part 2!


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1 comentario

anna stow
anna stow
27 abr 2021

interesting 👌

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