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What is the ‘3 Body Problem’? Astrophysicist explains concept behind hit Netflix show

Netflix’s big budget adaptation of Liu Cixin’s novel from the creators of “Game of Thrones” shows what happens when a still unsolved quantum mechanics question plays out on a galactic scale.

3 rings on a black background.
Based on Liu Cixin’s book series, “3 Body Problem” takes a science fiction approach to complex quantum mechanics and astrophysics concepts, including the three-body problem. Netflix Photo

“3 Body Problem,” Netflix’s new big-budget adaptation of Liu Cixin’s book series helmed by the creators behind “Game of Thrones,” puts the science in science fiction. 

The series focuses on scientists as they attempt to solve a mystery that spans decades, continents and even galaxies. That means “3 Body Problem” throws some pretty complicated quantum mechanics and astrophysics concepts at the audience as it, sometimes literally, tries to bring these ideas down to earth. 

However, at the core of the series is the three-body problem, a question that has stumped scientists for centuries. 

What exactly is the three-body problem, and why is it still unsolvable? Jonathan Blazek, an assistant professor of physics at Northeastern University, explains that systems with two objects exerting gravitational force on one another, whether they’re particles or stars and planets, are predictable. Scientists have been able to solve this two-body problem and predict the orbits of objects since the days of Isaac Newton. But as soon as a third body enters the mix, the whole system gets thrown into chaos.

“The three-body problem is the statement that if you have three bodies gravitating toward each other under Newton’s law of gravitation, there is no general closed-form solution for that situation,” Blazek says. “Little differences get amplified and can lead to wildly unpredictable behavior in the future.”

Headshot of Jonathan Blazek
The three-body problem has been a compelling question for scientists for centuries because of it is seemingly simple yet deceptively complex, says Jonathan Blazek, assistant professor of physics at Northeastern University. Photo by Matthew Modoono/Northeastern University

In “3 Body Problem,” like in Cixin’s book, this is a reality for aliens that live in a solar system with three suns. Since all three stars are exerting gravitational forces on each other, they end up throwing the solar system into chaos as they fling each other back and forth. For the Trisolarans, the name for these aliens, it means that when a sun is jettisoned far away, their planet freezes, and when a sun is thrown extremely close to their planet, it gets torched. Worse, because of the three-body problem, these movements are completely unpredictable.

For centuries, scientists have pondered the question of how to determine a stable starting point for three gravitational bodies that would result in predictable orbits. There is still no generalizable solution that can be taken out of theory and modeled in reality, although recently scientists have started to find some potentially creative solutions, including with models based on the movements of drunk people.

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