eli5: What is the bootstrap Paradox?
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So you watched Back to the Future right?
Marty’s adventures were chock full of different types of paradoxes.
There’s one in particular we can talk about.
He jumps on the stage during his parents big dance. He starts jamming to a song he loved and knew. Chuck Berry’s *Johnny B Goode*.
Instantly the camera cuts to a man off screen calling his favorite cousin: Charlie.
This is where the example stops.
But we can speculate what was being done here. The man of the phone is the musician responsible for the song. The actual Chuck Berry.
Over the phone he’s inspired to create a song that will one day go on to be learned, loved, practiced, and eventually played on a stage. That he’ll hear that will in turn inspire him to create a song that will go on to be loved, learned, practiced, and played on a stage that he’ll listen to that will plant the idea for a song that will go on to…
It’s a circular reference. Who created the song? Where did this new information come from?
It’s when a person who travels back in time and introduces some knowledge that came from their past but the future of the time they traveled to. The information was apparently introduced by the person from the future, but how did they get it in the first place?
A simple example: Let’s say I go back in time and meet Beethoven before he writes his fifth symphony. I hang out with Beethoven, have a good time, and when I leave I forget to bring my copy of Beethoven’s Fifth Symphony with me. Beethoven finds it instead and releases it as his own. If he got it from me, and I got it from him releasing it in the past, then where did it first come from? The story was no beginning. That’s the Bootstrap Paradox
Basically, you have event A which causes Event B. Someone does the time travel thing back to *before* event A, and manages to cause Event A. The paradox is that from outside the loop, you can’t say what event caused what, as it just goes in circles; A caused B, which caused A…ad infinitum. This is why another name for it is a *causal loop.*
The classic example is traveling back in time and becoming your own grandfather. Another you may be more familiar with is the Time Turner scenes in Harry Potter. Remember all the bits of randomness that turned out to be time-traveling versions of themselves (throwing the rock, casting the Patronus, etc)? They could do those things because they traveled in time, but those things had to happen for them to reach a point where they could travel in the first place.
There’s a reason Starfleet has a division dedicated specifically to preventing or resolving such things.
An event that has no ultimate cause due to a time travel loop.
Your future self arrives in a time machine to give you the plans for a time machine, so you can build the machine and go back in time to give yourself the plans.
The plans have no actual original creation. This is a bootstrap paradox.
If you were sitting there and you appeared from the future and handed yourself a box, then you never opened it until one day you get sent back in time where you give yourself that exact same unopened box…
Who physically constructed the box? It didn’t exist until future you came through to give it to yourself, you didn’t make it, and you give it to yourself later after you time travel… so where did it come from?
Who can guess what’s inside the unopened box?
Quite similar to the 51st episode of Futurama where Fry goes back in time and inadvertently becomes his own grandfather and his dad is also his son.
https://futurama.fandom.com/wiki/Roswell_that_Ends_Well
If I go back in time and give Hitler the plans to start WWII, who really started WWII? Is it me because I gave him the plans? Or was it him because I got those plans by studying what he did? Or is it me because I was studying plans that I created in the first place?
It’s a never ending cycle.
Let the Doctor explain it for you
[https://www.youtube.com/watch?v=u4SEDzynMiQ](https://www.youtube.com/watch?v=u4SEDzynMiQ)
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Time travel is not ELI5
In short, time travel messes up things, it creates a loop where the origin of a particular information is lost and cannot be determined.
It’s from a Robert A. Heinlein story called [“By His Bootstraps.”](https://en.wikipedia.org/wiki/By_His_Bootstraps) There’s a college student trying to write an essay and his future self appears and explains that he shouldn’t listen to anything any future selves tells him to do. Then a second future self appears and tells him not to listen to the first future self.
This adventure begins with a loop. The character appears from the future, telling the present day character not to travel to the future. If you went back in time and told yourself not to go to the future — and presumably ignored that advice — why would you again travel into the past to tell yourself not to go?
The catalyst for you doing the thing you immediately regret is yourself. You create and perpetuate a time travel loop that you don’t want to happen.
In the story the character travels into the future discovers this weird guarded palace and is trying to track down the owner of the palace (for a reason I don’t recall). Eventually we learn that >!all of the characters were the same character at different stages in the future.!<
TL;DR: If you are wearing a pair of Doc Martens with the little loop in the back, you cannot pull on them and lift yourself up. The bootstrap paradox examines how time travel can create impossible situations when a character interacts with themselves.
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