Not the best work of Chris, but still Tenet is one of the films that make your brain go Dooinnnnnnggg…
This is my understanding of the science behind the fiction. I named this, ‘THE FILM REEL THEORY.’
SPOILER ALERT: You wouldn’t get this anyway if you haven’t watched the movie.
So, the concept of the movie revolves around block universe theory, entropy inversion, and stuff. But I think this is what it means exactly: -
Consider the picture above as a normal film reel (don’t judge. Just consider), with ‘n’ number of frames, each being static and motionless. Now think of this entire film reel as your life on earth. The film of your life. Each frame of the film reel depicts your every movement, even the minutest, as a collection of ‘n’ number of static, stagnant, motionless frames. So, at any given point in space, you are just a motionless image on a frame. This means that time is never moving anywhere, but it is us who feel the passage of time due to an increase in entropy (as our universe is intended to work), and there has been no otherwise so far. But if, only if the entropy is reversed, say, the dissipation of energy in the world is inverted, things start seeming to move in reverse, i.e. your film reel will begin to spin backward. So, the motion will be inverted. Funny thing is, you wouldn’t even notice it since even you will be moving in reverse along with the world. Now that’s where Nolan drops in his PROTAGONIST, from the other side (normal entropic world) as a mere observer of the inversion. For him, who is looking at your film reel from far away, you and your world in the film will tend to move in reverse. This is TENET in a nutshell. Correct me if I’m wrong.