The Title of ‘3 Body Problem’ Has Some Very Cool Physics Behind It

The Three-Body Problem is everywhere: it’s coming to Netflix in March, streaming on Peacock and Prime Video now, and on every bookstore shelf in the form of Cixin Liu’s original novel. But what does the title refer to, exactly? What is a three-body problem?

You can wait and see, or you can get the basics here!

What is the three-body problem in physics?

Isaac Newton planted the seed of the three-body problem when he posed the two-body problem: a question of how two masses in space will behave if the only force acting on them is their mutual gravitational pull. The two-body problem refers to a planet orbiting a star, two stars orbiting each other, or similar situations.

Crucially, the future movements of two bodies can be predicted using mathematics. In other words, the two-body problem can be solved. Throw in another body, and there’s trouble. There’s a lot of math here that I won’t get into, but as mathematician Richard Montgomery explains in Scientific American, the chaotic nature of three bodies in space acting on each other makes it extremely difficult to predict their future movements.

What would it be like to live on a planet in a system in which three stars were all bound together by their mutual gravitational pulls? That’s the question at the heart of Liu’s novel and its adaptations.

What is the three-body problem in 3 Body Problem?

Note: this section contains spoilers for Cixin Liu’s novel The Three-Body Problem.

In The Three-Body Problem—and presumably the Netflix series—people on Earth begin to play a peculiar virtual reality game. In the game, they try to save a civilization from seemingly random disasters like boiling heat waves and deep freezes. The civilization falls prey to the disasters over and over again while its members try to predict stable eras, when conditions are favorable to life on the planet. During chaotic eras, anything can happen.

Through the game, an alien civilization called the Trisolarans inform their human allies that their planet is at the mercy of three suns in orbit around each other. Because of the chaotic and unpredictable nature of the suns’ orbit, the planet is tossed haphazardly among them. When it drifts too far from all three suns, it freezes. When it’s pulled too close, it burns. When the planet is in orbit around just one sun, the climate becomes livable. Thanks to the three-body problem, the Trisolarans can’t predict when stable or chaotic eras will occur, so their only choice is assemble a fleet of starships and find a new home.

And where are they headed? Yep. Earth.

3 Body Problem premieres on Netflix on March 21, 2024.

(featured image: Netflix)