What is the three-body problem? The science behind Netflix series explained
(Credits: Netflix)

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What is the three-body problem? The science behind Netflix series explained

Liu Cixin’s renowned trilogy has been successfully adapted into the Netflix series 3 Body Problem. Often touted as “hard sci-fi”, the story follows a group of scientists and thought leaders tasked with finding a solution to save humanity in the face of an extraterrestrial invasion threat.

Created by David Benioff, D. B. Weiss, and Alexander Woo, this series offers a fresh perspective on the Hugo Award-winning Chinese novel, The Three-Body Problem. While staying true to the essence of the original work, the show boasts a diverse cast, with characters drawn from the pages of the book, albeit with some notable alterations.

The story starts with Ye Wenjie, portrayed by Rosalind Chao, whose traumatic experiences during the Chinese Cultural Revolution propel her into a world of military secrecy and scientific intrigue. As Wenjie’s decision to make first contact with an alien civilisation reverberates across the cosmos, a group of contemporary scientists, including Jin Cheng (Jess Hong), Augustina ‘Auggie’ Salazar (Eiza González), Saul Durand (Jovan Adepo), along with Will Downing (Alex Sharp) and Jack Rooney (John Bradley), find themselves confronting an existential threat to humanity.

As Liam Cunningham’s Thomas Wade and Benedict Wong’s Clarence ‘Da’ Shi lead and aid humanity’s efforts towards the incoming San Ti (the race of aliens who are arriving from the land of three suns), the story requires understanding one fundamental physics problem.

What is the three-body problem?

At the heart of both the Netflix series and Liu Cixin’s novels lies the concept of the three-body problem. In astrophysics, the three-body problem refers to the challenge of predicting the motions of three celestial bodies that interact with each other through gravitational forces. 

While the dynamics of two bodies can be accurately described using Newton’s laws of motion and gravitation, adding a third body introduces complexities that defy straightforward solutions.

…but 3 Body Problem involves four celestial bodies

In Cixin’s novel The Three-Body Problem, the titular problem refers to a scenario where a planet orbits three suns, creating a complex gravitational interaction involving four celestial bodies. At first glance, this may seem contradictory to the traditional definition of the three-body problem, which typically involves only three bodies interacting gravitationally. However, the inclusion of the planet in this system does not fundamentally alter the essence of the problem.

In astrophysics, the term ‘n-body problem’—mentioned by Jin and Jack in the third episode ‘Destroyer of Worlds’—refers to any scenario where multiple celestial bodies interact gravitationally. While the classic three-body problem is often used as a simplified model for studying gravitational dynamics, the principles and challenges extend to systems with more than three bodies.

The inclusion of the planet orbiting three suns in the 3 Body Problem does not invalidate the concept but rather expands upon it.

Why is the three-body problem unsolvable?

The inherent complexity of the three-body problem stems from its chaotic nature. Unlike the two-body problem, where orbits are predictable and stable, the gravitational interactions between three or more bodies often lead to erratic and unpredictable behaviour. Even tiny variations in starting positions or velocities can result in vastly different outcomes over time.

Furthermore, the three-body problem lacks a general analytical solution that can be applied universally. While mathematicians have devised numerical methods and approximation techniques to tackle specific scenarios, there is no overarching formula (not yet, at least) that can provide definitive answers for all possible configurations of three interacting bodies.

Stephen Wolfram noted in A New Kind of Science, “And even now it remains conceivable that the three-body problem could be solved in terms of more sophisticated standard mathematical functions. But I strongly suspect that in fact nothing like this will ever be possible.” In short, the unsolvability of the three-body problem underscores the inherent limits of human knowledge and computational capabilities.

You can read our review of 3 Body Problem before watching the show on Netflix.