Science explains the principles of TENET: Entropy, annihilation and inversion of time

Christopher Nolan's Tenet deals with entropy, particle physics, and the nature of time. Here's a breakdown of the actual science behind the movie.

Instellar director Christopher Nolan's latest sci-fi film Tenet offers a unique take on the genre of time travel movies, but how strong is the science in the movie? What is entropy? Nolan once again enlisted theoretical physicist Kip Thorne, who also served as a consultant at Interstellar, to advise on the script and ensure that Tenet was anchored in the real laws of physics and time, while also taking some liberties. creative with them.

John David Washington plays the protagonist, a CIA agent who is recruited by a mysterious organization called Tenet. You learn that a war is being fought from the future, where the technology has been invented that allows objects and people to be 'reversed', reversing the flow of their entropy so that they travel backward in time rather than backward. ahead. Tenet was also created in the future, and its goal is to stop the antagonists from activating an apocalyptic weapon that will end the past and present.

To help moviegoers understand the concepts of Tenet, Screen Rant spoke with Dr. Lucian Harland-Lang, a theoretical particle physicist at the University of Oxford. Specifically, he works in the field of phenomenology, applying theoretical physics to the real data that is collected in the Large Hadron Collider. And while Tenet may not sound like a movie about particle physics, particle behavior actually gets to the heart of its time travel mechanics.

What is Entropy?

Entropy in TENET

Entropy is a term in thermodynamics that is more simply defined as the measure of disorder. The more disordered the particles are, the greater their entropy. Liquids have a higher entropy than solids and gases have a higher entropy than liquids, and the universe becomes increasingly chaotic over time. Mathematician James R. Newman called this “the general tendency of the universe toward death and disorder,” while physicist Arthur Eddington coined the rather poetic term “the arrow of time.” Harland-Lang describes entropy as a “probability argument.” Because energy particles are constantly moving, the entropy of a closed system can only increase over time, never decrease.

Think of an egg that has fallen to the ground. As time progresses, the egg may break apart (becoming messier), but it will never re-form as a whole egg (becoming less messy). Entropy flow is the only thing preventing this from happening, since all other laws of physics are symmetric – anything that can happen forward can also happen backward. “You do not see eggs re-forming on the ground and jumping again, but brought to a logical conclusion, physically speaking, that would be allowed by the laws of physics,” explains Harland-Lang.

Because of this symmetry, there is actually a nonzero chance that the egg can repair itself. But for every molecule in the egg there is only one way to reform itself, and billions and billions of ways to break down. Multiply those billions by the billions of molecules in an egg and the probability weighs so much in favor of breaking and against reforming that you will never see a broken egg reform. For the same reason, you will never see a bullet come out of a wall and return cleanly to a gun, or you will see a car repair itself perfectly after a collision. “In effect, there is zero probability of that happening,” says Harland-Lang. But it is not zero. This is how you fix this paradox that, technically speaking, all these things that you are not used to seeing could happen. They just wouldn't. “

In the Tenet production notes, Nolan says the film is based on the idea “that if you could reverse the entropy flow of an object, you could reverse the time flow of that object.” While he does not claim the film is scientifically accurate, he says it is based on “credible physics.” Having seen the movie, Harland-Lang more or less agrees with that assessment: “It's not 100 percent science-based. Is it inspired by it or is it an analogy. If you could reverse the entropy flow of an egg, the egg would not begin to literally travel back in time. But entropy and time are so closely linked that if people see a broken egg reunite, jump off the floor and return to the kitchen counter, it would appear that time was moving backwards through the egg. “

Theoretical physics of TENET

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Tenet's core idea that people and objects have their time invested is based on a theory by physicists Richard Feynman and John Wheeler. They are actually named in the movie when Neil reflects on the meaning of the inversion and what the tourniquets do, although it is a disposable line that is easy to miss. Specifically, Neil is referring to Feynman and Wheeler's idea that positrons could be electrons moving backwards in time.

Electrons are particles that have a negative charge and positrons are antiparticles that have the same mass as electrons, with an equal but opposite positive charge. There are other types of antiparticles that reflect other types of particles, such as antineutrons and antiprotons. Collectively, these antiparticles are known as antimatter. Positrons can be found in natural phenomena like cosmic rays, or created in a particle accelerator like the Large Hadron Collider. Structurally they are the mirror image of electrons, and Feynman-Wheeler theory postulates that if you could force the arrow of time to go backwards in search of an electron, it would look like a positron. Going back in time, it could coexist with its former self or even collide with itself.

Tenet wisely doesn't get too bogged down in explaining all this. Instead, it uses the idea of ​​a war in time and machines that allow people to reverse direction in time as an analogy for the Feynman and Wheeler model. This is particularly seen in the two versions of the Oslo Freeport fight scene, where the protagonist fights a mysterious inverted man who is later revealed to be himself. By showing the fight scene twice, Tenet changes our understanding of what we are seeing. The first time, the audience thinks that the protagonist and the man he is fighting are two different people. The second time, we realize that we are seeing the same person in different states of being. This is what Feynman and Wheeler proposed: that what we perceive as a particle and an antiparticle could actually be the same particle moving back and forth in time.

While the theory behind this is scientifically sound, Harland-Lang cautions that Feynman and Wheeler were not literally arguing that the universe is full of particles that travel in reverse time, only that theoretically it could be. “Basically, a positron is something that moves forward in time,” he clarifies. “It is not that there are time travel every time we see a positron in the world.” The theory is a device for interpreting what we see when we look at electrons and positrons, and Tenet translates it by replacing particles and antiparticles with inverted people.

What do the turnstiles do?

Science explains the principles of TENET: Entropy, annihilation and inversion of time

The effect of the tourniquets on Tenet is not to individually invert each particle in a person's body. If they did, the protagonist would turn into antimatter and explode upon contact with the outside world. In a reaction known as annihilation, the collision of matter and antimatter results in the destruction of both particles (an electron and a positron, for example) and the release of energy. We've only seen this at the atomic level, but increasing its destructive potential would be devastating.

Harland-Lang refers to the Angels and Demons plot, in which a bomb containing just one-eighth of a gram of antimatter has enough firepower to blow up the Vatican. “I haven't sat down to do the math,” says Harland-Lang. “But I think that the amount of energy of a person who completely annihilates himself with the rest of the world would destroy the entire world.” In fact, if a 200-pound man like the protagonist were to turn into antimatter, the resulting explosion would be equivalent to around 3,800 megatons of TNT. To put that in perspective, the most powerful nuclear weapon ever created and tested, the USSR's Tsar Bomba, the detonation of which smashed windows and collapsed roofs hundreds of miles from the blast zone, had a yield of 50 megatons, not ending with the explosion of the protagonist the moment he goes outside after being inverted, it is safe to say that the turnstiles do not create antimatter.

It seems that what they really do is create a closed system in which a person's body continues to experience normal entropy, but can go back in time within the bubble of their closed system. Think of it as creating a small universe the size of a protagonist where time flows in the opposite direction to the larger universe. If the protagonist went through a turnstile and remained inverted for a long time, from a normal perspective he would look like an old man who miraculously defies the second law of thermodynamics by getting younger. However, within his closed system, he would be aging normally.

All inverted objects in Tenet share the properties of this closed system, allowing them to interact. The protagonist must be given an inverted oxygen tank containing inverted air to breathe, because it would be impossible for him to breathe air that is experiencing a flow of time opposite to his own. It is also important that the entrance and exit of the turnstile are in different places, because if they were in the same place, a person entering the turnstile would collide with his inverted self coming out of it and things would get complicated. But what if instead of creating a closed system within the universe, it reversed the flow of time and entropy of the entire universe? That's where Tenet's doomsday weapon comes in.

The algorithm and annihilation

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The first time the protagonist goes through a turnstile on Tenet, he is warned not to interact with his forward-moving counterpart because, as an electron and a positron collide, if the two touch, it would result in annihilation. Again, this is more of a science analogy than a scientifically accurate one. If the protagonist's body had turned into antimatter, it would in fact annihilate itself if it touched its non-inverted self, but it would also annihilate itself if it touched any other kind of matter. As Harland-Lang explains, “Each electron is essentially identical, and any given electron, if it met any other given positron, would annihilate. The electrons in Protagonist's body are no different than the electrons in Neil's body, or Sator's, or the electrons in the air around us. “

Annihilation is also at the heart of Tenet's MacGuffin: a thick, nine-part metal shape called the Algorithm. It is explained that the same scientist who created the turnstiles in the future also discovered a way to reverse the entropy flow of the entire world. Fearful of what his contemporaries would do with this information, he divided the algorithm into nine parts, inverted them and sent them to the past. The effect of activating the algorithm would be massive annihilation. Each particle of the world would be reflected simultaneously in time and collide with its past self coming in the opposite direction. All those pairs of particles would cease to exist and there would be a release of energy on an unfathomable scale, although, in theory, this explosion would head backwards in time, leaving the world intact after the algorithm was activated.

Is Tenet Scientifically Accurate?

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The big question audiences may have when leaving Tenet is whether the movie is scientifically accurate or not. Could you, by reversing the entropy flow of an object or person, make it begin to move backward in time from the point at which it was reversed? “I mean, the short answer is, I don't think so, no,” says Harland-Lang. “But envisioning a world where you could do this, Tenet raises some interesting questions about time and our experience in it.”

“He's definitely open to question whether… although, as I've described, entropy gives us a natural conception of time intuitively, if that's really so directly related to how we experience time. That is a question. And even if that's the case, even if those things are intimately linked, yet the time is there and moving on. “

This brings us back to the idea that entropy is the arrow of time. If you were lost in time and had no idea in which direction it was flowing, you could observe the entropy of a closed system. The direction in which the entropy of that system increased would be the direction in which time moves. And because our indicators of the passage of time – people aging, eggs hatching, mountains eroding – are the result of entropy, it is very difficult to separate our experience of time from our experience of entropy. To us, they seem the same.

Just as Interstellar was intended to accurately portray what it would be like for a person to travel through a black hole, Tenet imagines what it would be like for a person to travel backwards through time. This leads to some pretty mind-blowing fight scenes, but it's also a fascinating gateway to some much more important ideas. | Cinema, comics and series