Donnie Darko and the Novikov consistency principle
Let’s begin with a refresher of the Richard Kelly’s masterpiece.
Donnie, the protagonist, survives the fall of an airplane engine on his house, and is thus “selected by the universe” to carry out an important mission: to ensure the collapse of a parallel universe that was formed as tangent to the timeline of the primary universe, where he ironically did not survive.
If you’d like a more comprehensive explanation and refresh of the movie, I highly recommend this video. It functions well as both a summary as well as an explanation of what happened in the movie, since it’s really confusing at times.
The Novikov self-consistency principle is a theory about time travel in physics that essentially contends that “…even if an event exists that would cause a paradox or any “change” to the past whatsoever, then the probability of that event is zero.” Not all physicists buy into the idea that time travel is possible but time paradoxes are not, and with good reason.
However, the movie sets up a nice hypothetical that reconciles the two perspectives: when a paradox occurs, parallel universes are created that are very unstable, and expand in their timeline until one of them collapses and takes over. In a way, it’s akin to Darwinian selection except applied not to evolutionary biology but to general relativity.
Interestingly enough, this approach can be leveraged to enable an advanced type of computation through time-machines. Specifically, solutions to a problem can be sent back through time through an iterative process that creates parallel universes that all collapse into one universe where the optimal answer was sent (Hans Moravec is the scientist behind this theory, and I recommend his paper if you are more interested in the details).
To the outside observer, it looks like the answer magically appeared from the time-machine-turned-computer, and this is due to the Novikov’s consistency principle, for the observer only gets to exist in a universe that is consistent. In reality however, these possibilities played out and just collapsed because they were not the optimal answer.
