Tenet is a movie directed by Christopher Nolan that is mainly based on the inversion of time. In this setting, people cannot travel to any point in time at will; instead, they can only move backward to a specific moment and then proceed forward from there. The future world is in lack of resources, so the future people developed inverse materials and wanted to fight with the past to seek survival. Andrei Sator, a Russian who acts as the bridge to communicate with the future, takes part in the destruction of their current world, and the protagonist of this story together with Neil and his team, takes on the mission to prevent it.
 
To me, this movie surpasses any other Nolan movie. The story itself is very complicated yet intriguing: to fully understand it, you have to figure out how time inversion works in this universe, and the timeline of each character. Another amazing part of the movie is its use of sound effects and the combination of its original soundtracks and the visual images. For example, in an operation scene involving four large moving trucks, the sound one would hear in a car moving at high speed is clearly audible; the breathing noise of Nolan himself is sampled and altered so that it represents Sator’s sense of pressure; when the film depicts anyone moving backward in time, the timbre of the instruments is how they would sound after the recording is played backward. These amazing details provide a great auditory experience, especially for one fond of electronic music, and they are also important clues about the development of the plot.
 
A notable element in Nolan’s films is the use of physics, and in "Tenet," it's entropy, specifically reversed entropy. Some criticized this as lacking any physical basics, as it’s true that, according to the second law of thermodynamics, the entropy in the universe is always increasing, and time flows in a single direction; however, in the microscopic view of particles, on-going research proves the possibility of reversed entropy. Yet even though this is a science fiction movie, thinking too much about physics simply diminishes the joy of watching the film. One quote from the movie provides the tenet for us to watch this movie: “don’t try to understand it, just feel it”.
 
The most important questions brought by this movie, therefore, lie not in physics, but in philosophy. After the protagonist learns the presence of such inversed materials, he poses the doubt, “but cause comes before effect.” In other words, does the reverse of time mean that the law of causation is no longer true? This is, in fact, a question asked by physicists and philosophers hundreds of years ago, when the development of relativity seemed to challenge this law. The movie itself provides an answer to this question by saying that no matter the flow of time, the cause of any event is always the initiator of the event, no matter in what direction they perceive it. However, we can still dive deeper into this question, and ask ourselves questions about free will: when one conducts some particular actions because they know that their future selves have already done it, are they still pursuing the action out of their free will, and do their “cause” becomes the product of the effects? Of course, it seems obvious that another choice is to not pursue the action that they know their future selves have done, but the characters in this movie believe that if they quit, a multiverse may be split out, and the fate of their universe is no longer definite. Not all of the questions are answered in this movie, and the answers provided are not necessarily “correct”; but we, as the audience, have the freedom to ponder the question and provide our interpretations.  
 
Another criticism people would give to this movie is that, compared to Interstellar, Tenet seems to lack emotion between characters. I disagree with it — I think the relationship between the protagonist and Neil surpasses any ordinary friendship or even love. When the protagonist first met Neil, Neil had already known him for years; when Neil met the protagonist for the first time in his life, the protagonist had already known him for years too. It’s because Neil was recruited by the Protagonist, and sent back through time to help the operation. He saved the protagonist for three times and had to pay his own life during the final time. When the “young” protagonist said his goodbye to the “old” Neil, tears were already in his eyes, but will he feel sadder when he, after decades and years of further interacting with the “young” Neil, had to send him back to the operation, knowing there’s no way for him to come back? There’s no way to find an answer to this question in the movie, but the entanglement of the fate between the two men, the idea that one had memories of their past when the other first met him, and the sense of destiny, all makes the emotions in this movie no less than any of other Nolan’s movies.