The time travel rules of Tenet make sense but the movie doesn’t go out of its way to explain its mythology or the full details of its story. As a result, some movie goers might have some trouble filling in the blanks of what has happened off screen and how exactly the time travel element of it all work. If you just can’t wrap your head around what exactly happened, when it happened, or how the time travel of it all happened, we are going to break it all down for ya in the simplest terms possible. In the video above, both the time travel rules from Tenet and the ending are explained.
Let’s talk about time travel.
Think of time as a straight line. All matter and streams of consciousness are moving as independent lines along that straight line and can only operate parallel to it. We’ll call that that main straight line the dominant timeline. As individuals, our experiences and memories can only progress within our personal timeline. Our timelines may already be laid out in the dominant timeline and we are simply moving through it with out own consciousness but that’s a question of free will for later.
As our personal timeline grows or we move through it, we are consuming experiences as time passes. In all instances, a personal timeline can only operate in a direction which is parallel to the dominant timeline. This was symbolically represented in the opening sequence of Tenet when two trains were passing the protagonist, each going in opposite directions.
In Tenet’s mythology, the plutonium device and the algorithm is able to reverse an object or person’s entropy in time. So, while a persons trajectory continues to move forward from their perspective, the line which represents their timeline now grows in the opposite direction by comparison to the dominant timeline, overlapping with its previous self. This line would have already happened on the dominant timeline. Actions would be seen to anyone moving in the traditional direction through time as being backwards, but for the person or object, it is happening in their own real time and moving forward as they carry out the actions.
When you reverse your entropy again, you would now be moving through time in the same direction as the dominant timeline. This would mean there are multiple versions of yourself in this timeline, until you reach and surpass the point in time which you originally started to go backwards.
You continue to age the throughout the journey. For example, if I reversed my entropy right now and continued in that backwaerds direction through time for 6 months, then set myself back to a traditional entropy in line with the dominant timeline, forward, when I arrived back at this very moment — I would be a year older despite existing at the same point in the dominant timeline from which I left. No time would have passed for a person or object which did not travel through time.
As your line grows, it is new to you, and this brings up the question of free will because it would seem to imply that the dominant timeline has everything already mapped out for us – we just have to experience it.