A physicist on the science of Christopher Nolan’s ‘Tenet’


Like many of Christopher Nolan’s films, “Tenet” focuses on a guess from real science. Where “Interstellar” looked at wormholes and time travel, “Tenet” wonders if it is possible to reverse the entropy of an object – or a human – to allow it to back down. time. In writing “Tenet,” Nolan took some suggestions from Nobel Prize-winning physicist Kip Thorne, who also advised on “Interstellar,” but ultimately the filmmaker decided to forgo some elements of reality. “I asked Kip Thorne to read the script and he helped me with some of the concepts, although we’re not going to argue that this is scientifically correct,” Nolan noted in the film’s press notes. “But it’s pretty much based on real science.”To find out how science-based ‘Tenet’ action is, we asked Professor Claudia De Rham, theoretical physicist at Imperial College London, to discuss some of the key plot points and determine if we will ever live in a world. where time reversal is possible.

Warning: the main story spoilers to come. If you haven’t seen “Tenet” yet (and most of us haven’t!), We suggest you read this review or this enthusiastic fan article instead. And come back when you saw it.

What did you think of “Tenet”?

I love a good science fiction movie and I love a good action movie. For me, it was a bit too much science fiction as an excuse for acting and directing. He was trying to be smart without really being smart. It’s science fiction, so I get it, “We want to make a movie and we don’t need it to be physically possible.” I can accept that, but maybe it was a bit too much for me – the plot didn’t really make sense. It was more difficult for me to appreciate it as much as other films of the same style.

Overall, how is science holding up?

There is an element of physics. There is an element of science. He tries a little. Compared to previous films, like “Interstellar”, the gap is perhaps greater. It’s much less anchored in physics. There are a lot of times they use scientific jargon and it’s just jargon with no content. If you watch “Interstellar” and other films like that, it has a bit more depth. … All is not completely wrong. It is true that you think your clock is ticking, that the way you experience time is changing. This relates to the notion of entropy, and it’s not necessarily incorrect to say that if you could reverse or reverse your entropy, maybe you could be thinking of things that go back in time. This item you can accept. But the consequences have not been logically explored at all.

At a basic level, what is entropy?

Entropy is the measure of the level of order or level of information. There is a really basic law in physics that tells us that entropy is always increasing. On average, things are more and more disorganized. This is why we age – our bodies slowly become disorganized more and more. That is why it is much easier to destroy something than to build something. On a physical level, if you have a box and put gas in it, the gas will start to take up all the space. It will spread and become more and more disorganized. When entropy increases, it means that things are less and less organized.

If you have an object, like a bullet, is it possible to reverse its entropy?

A refrigerator, for example, is a device where you lower entropy to keep things cooler – when things are cooler, they have less entropy. If you think of ice, it’s cooler, static, and well-organized. When you heat it the entropy increases and it becomes liquid, then it becomes a gas and it becomes less organized. A refrigerator or freezer the opposite for you. So we know that it is very possible to have devices that reverse entropy. But that doesn’t mean time flies the other way around in your fridge. When I put food in my fridge, it doesn’t get fresher every day. But it is certainly possible to have a device that decreases the entropy of an object. The connection to rolling back the internal clock of this object is a bit of an extrapolation. But that’s part of poetry, right? This is science fiction fiction.

In the film’s press notes, Nolan says that all the laws of physics are symmetrical except for entropy. Is it true?

This is especially true. For most of the laws of physics, there is temporal symmetry. Anything that can go forward, you can think of going back. Entropy is the only thing we experience – so we associate it with the way we experience time – in one direction. Overall, entropy is always increasing instead of decreasing. So you can imagine an alternate world where entropy is always decreasing and everything is going the other way as opposed to us. People in the alternate world would live the other way around. That’s fine in itself, but when you start to interact and come in contact with this world, it doesn’t make sense from a physical point of view.

If a person could go back in time, would they be unable to breathe normal air?

The way you breathe is that you have a balance between the oxygen in your lungs and that in your body. It is true that if you have time to go back, you want the reverse process to happen as well. So it’s true, I think, that you would need to bring your own tune with you. So if you want to go back in time, you have to take your air with you, but you also have to take everything else with you. The way you see an object, or someone else, you have light coming from the sun, hitting that object and coming back to you. You see the object because the light hit the object and then it hit your eye. But if you are immersed in what you think is an upside down world and you haven’t taken all the light with you, then you would feel like the first light comes out of your eye, hits the object. then hits the sun. So you wouldn’t see the object. You would just see the light first.

So going back in time would be a real struggle.

It would be a struggle. While it is true that you would need to take your air with you, you would need a lot more with you. Like the car. He backs up, but the car has not passed through the machine and the car is backing up with him. He would need to take the car with him [through the device].

Kenneth Branagh in the movie “Tenet”.

(Melissa Sue Gordon / Warner Bros.)

What if there was an explosion as you were backing up, like in the car chase scene, would that result in ice rather than fire?

This is absolutely not what would happen. It’s like saying, “If something was white, it would turn black.” It’s not as if everything turns out to be the opposite of each other. The reason we feel heat is because molecules in the air hit a surface. This is what we feel, the constant shock of particles on us. Yes [the molecules’] time passed relative to us, they were hitting the other way, but they were still hitting. We would still feel them hitting and we would still feel that notion of warmth.

Did you find it believable when Robert Pattinson’s character says he has a degree in physics?

What he said were random words. It was “radiance” and “positron” with no real content. The only real word he said was “entropy,” but he didn’t explain anything. He says he has a master’s degree in theoretical physics. It’s not much to have a master’s degree in theoretical physics. Don’t tell him that, but having a master’s degree in theoretical physics doesn’t mean you understand everything in the world.

When his character evokes the theory of “parallel worlds”, what does he mean?

Anytime you make a decision or something happens, like you wake up in the morning and decide whether to go for tea or coffee, you can imagine that there is a continuum of parallel worlds. In each of them a particular reality takes place. Here you decide to have coffee this morning, but in another world you decide to have tea, and in another world you decide to wake up five minutes late. With every physical process and every interaction, whatever can happen happens, and there is a multiple of worlds with every possible realization coming in. When he talks about multiple worlds, that’s what he has in mind – that the reality that we are in has something going on here, but there is another reality where something else can happen. to be produced. And maybe there is a connection between the two if you turn back time or reverse time. If you change the decision you made, you might be moving to a different parallel reality. At some point in the movie, they want to explore that possibility, but at the end of the day their conclusion is “What happened, happened”. That there is only one reality and there is no way to change it: “This is the reality that we are in and it is fixed.”

In general, is time travel a scientific possibility?

You have to explore it, but you know it’s impossible. In this particular case, they might call it time travel, but what they have in mind is simply to reverse your entropy. Reverse your notion of time and use it as a device. So there is this notion, or there is the notion of more closed time curves where you go back in time to any other point in your past or your future and you can do it multiple times. It depends on what nature will be fundamentally. Our understanding of everything at the moment runs counter to all of that. The structure of the world and the way we understand time and the way we understand what everything is made of and how it connects to each other, it wouldn’t make sense if it were possible to imagine a return back in time.


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