Christopher Nolan’s 2020 film Tenet grounds its “time inversion” in real physics ideas—entropy, the second law of thermodynamics, the grandfather paradox, and Wheeler & Feynman’s 1940 one-electron universe—but physicist Kip Thorne, who advised on the script, warned the movie isn’t meant to be scientifically accurate. Reversing entropy to send a bullet back into a pistol is visually stunning, and impossible.
Let me start by asking a hypothetical question: How extraordinary would it feel if you could move backward in time? Seems a bit contradictory? Complex? Chaotic?
This concept of “time inversion” was beautifully and intensely portrayed in the 2020 film Tenet, directed by Christopher Nolan. To anchor the script in real science, Nolan brought in Nobel laureate physicist Kip Thorne—the same consultant who shaped Interstellar—to read the screenplay and weigh in on the concepts. Nolan himself has been candid about the result: as he told Esquire, “we’re not going to make any case for this being scientifically accurate. But it is based roughly on actual science.” The filmmakers creatively use the concepts of entropy, thermodynamics, and paradoxes to visually portray the mesmerizing phenomenon of objects moving backwards in time.
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The Mind-Boggling Plot
Imagining people moving backwards in time is somewhat possible, but how is it possible to show objects moving backwards in time? Imagine a bullet traveling back into a pistol or a truck reconstructing itself after running into an accident. This manipulation of time has been depicted in the movie by using concepts explained in physics like entropy, the laws of thermodynamics, the infamous grandfather paradox and more.
Physics Or Fiction?
The plot of this movie is undoubtedly mind-bending, but the question remains… is time travel of this kind actually possible in real life? By breaking down the theories of physics adapted in the movie, one can try to figure out whether time inversion is achievable or not. Spoiler alert: It’s not. Scientific concepts are blended with fiction and theoretical speculations to make this movie.
The first thing anyone watching Tenet needs to understand is that inversion in the movie is achieved due to entropy. Entropy, fundamentally means the measure of the order of randomness everywhere (yes, even in the Universe!). By reversing this entropy, a loop is formed, which enables everyone and everything to travel backward in time. This loop is a depiction of the flow of time – meaning that everything happening in the present has already happened in the past.
Wheeler-Feynman’s One-electron Universe
This is where things get really weird. In the spring of 1940, John Wheeler famously telephoned a young Richard Feynman and said, “I know why all electrons have the same charge and the same mass… because they’re all the same electron!” The idea: every electron and positron in the Universe could be a single particle weaving back and forth through time, with positrons being electrons moving backwards. Wheeler never seriously pursued it, but Feynman did borrow the seed of it for his 1949 paper interpreting positrons as electrons travelling backward in time.
Tenet flirts with this idea—the “inverted” people and bullets are essentially objects whose arrow of time has been flipped. The catch? Wheeler-Feynman’s one-electron universe is now considered a charming thought experiment, not a working theory (for one, the Universe contains far more electrons than positrons). It’s evocative, not predictive.
The Second Law Of Thermodynamics
Here’s the real-physics problem at the heart of Tenet. The second law of thermodynamics states that the entropy—disorder—of a closed system can only increase or stay the same over time. Eggs scramble; they don’t unscramble. Heat flows from hot to cold, not the other way around. This statistical asymmetry is, as far as physicists can tell, the actual “arrow of time.”
Tenet imagines a future technology (the “turnstile”) that locally reverses an object’s entropy so that, from its perspective, time runs backward. Visually, it’s spectacular. Thermodynamically, it’s impossible: you can’t just decide to run the second law in reverse for a person while the rest of the Universe keeps going forward. That would require a violation of one of the most robustly tested principles in physics.
The Infamous Grandfather Paradox
The film also dances around the classic grandfather paradox: if you travel back in time and kill your grandfather before your parent is born, you cease to exist—but then who killed your grandfather? Logically, the timeline tears itself apart.
Nolan’s sidestep is the self-consistent loop: in Tenet, time is a closed circle in which everything you do in the past has already happened. The protagonist’s choices in the “inverted” timeline are the same choices that produced the present. This is essentially Igor Novikov’s self-consistency principle, a serious idea in theoretical physics that lets time travel and causality coexist—at the cost of making free will look very different.
Quantum Mechanics
The film name-checks quantum mechanics, with characters muttering about particles like antiparticles and the wavefunction of the Universe. Quantum mechanics genuinely does permit some odd time-symmetric behavior at the particle level—Feynman’s positron-as-backward-electron is one example—but it offers no mechanism by which macroscopic objects (people, cars, freight ships) can have their entropy reversed.
What Tenet takes is the vibe of quantum physics: entanglement, superposition, the strangeness of the small. What it doesn’t take is the part of quantum mechanics that says “these effects do not scale up to billiard balls.”
The Ultimate Conclusion
Tenet incorporates an imaginative exploration of time manipulation with a complex narrative. The film takes some creative liberties in explaining scientific concepts and does venture into realm of science fiction. There is no doubt that scientists are continuing to unravel the mysteries of time and the Universe, but as of now, the current understanding does not align well with the portrayal of concepts like time inversion and reverse entropy, as shown in the movie.
This intense work of fiction certainly generates curiosity in the viewer’s mind about the nature of time and potential possibilities that lie beyond our current scientific grasp. When it comes to entertainment value, Tenet emerges as a clear winner, captivating audiences with its mesmerizing visuals, intricate storytelling, and mind-bending concepts.
