Mini Lesson 5: Paradoxes
I originally meant for this lesson to be only on paradoxes, but then I decided to switch to complete time travel paradoxes. Have fun!
Grandfather Paradox
There are several paradoxes on time travel, but one of the most famous ones is the grandfather paradox which was first by Nathaniel Schachner in his short story Ancestral Voices and by René Barjavel in his 1943 book Le Voyageur Imprudent. Imagine the following scenario:
There are several paradoxes on time travel, but one of the most famous ones is the grandfather paradox which was first by Nathaniel Schachner in his short story Ancestral Voices and by René Barjavel in his 1943 book Le Voyageur Imprudent. Imagine the following scenario:
You create a time machine, then start assembling a gun. You load the gun, go back in time right before you assembled the gun and kill yourself.
Clearly, there are several problems with this scenario. First of all, if the revolver has actually not been assembled, then with what have you killed yourself, and the second part is, "Is it really possible to kill yourself in the past, if a time machine would have existed?"
This is an example of the classical grandfather paradox, seen below:
This is an example of the classical grandfather paradox, seen below:
Someone creates a time machine. They go back in time and kill their grandfather before their father/mother were born.
If you have killed your own grandfather, you would have never been born, thus never gone back in time and your grandfather would still be alive! It's a paradox! There have been several movies and books mentioning the grandfather paradox, "Back To The Future" is one of the most famous examples of time loops and paradoxes.
The proposed "solution" to the grandfather paradox is to travel not in straight lines through time, but through closed-timelike curves (CTC). In simple terms, CTC is a path of spacetime that returns to its starting point. They came from Einstein's theory on general relativity. You can read more about them here
The proposed "solution" to the grandfather paradox is to travel not in straight lines through time, but through closed-timelike curves (CTC). In simple terms, CTC is a path of spacetime that returns to its starting point. They came from Einstein's theory on general relativity. You can read more about them here
Predestination Paradox
The predestination paradox is another time loop. It is often called a "casual loop". Some instances of the predestination paradoxes and self-fulfilling prophecies, and below cosmologist Igor Novikov has explained it better than I ever can:
The predestination paradox is another time loop. It is often called a "casual loop". Some instances of the predestination paradoxes and self-fulfilling prophecies, and below cosmologist Igor Novikov has explained it better than I ever can:
the billiard ball moves in a path towards a time machine, and the future self of the billiard ball emerges from the time machine before its past self enters it, giving its past self a glancing blow, altering the past ball’s path and causing it to enter the time machine at an angle that would cause its future self to strike its past self the very glancing blow that altered its path. |
An example of the predestination paradox is in Harry Potter and The Prisoner of Azkaban. Harry sees himself cast the patronus charm, saving his younger self in the process. Thus, when he goes back in time he does the same.
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