The astronomical problem plays a big role in new Netflix series 3 Body Problem.

By Chris Farnell

Published: Thursday, 21 March 2024 at 19:00 PM

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Scientific concepts make for great titles. To name a few – Event Horizon, Red Dwarf, Terminal Velocity, Half-Life, Dark Matter (twice, one TV series in 2015 and again later this year, although recent research suggests that one might have missed the boat).

It is easy to see why. They’re thematically rich, make you sound intelligent and, of course, they sound cool.

So it isn’t surprising that 3 Body Problem, the Netflix series and The Three-Body Problem, the book it is based on, have gone down this route.

The trouble is, it does beg the question, “What does it actually mean?”

For instance, in science the event horizon is the radius around a black hole where gravity is too intense for light to escape. It is a point of no return – good horror movie title.

Dark matter, the unknown form of invisible matter necessary to make our current model of the universe make sense, is a bit more vague in terms of relevance, but still works as announcing: “Here’s a load of mysterious unknown stuff.”

With the three-body problem, the immediate answer is a pretty straightforward one. The series is about first contact with a civilisation in a star system with three suns – the three bodies.

If you’re happy with that, well, you’re welcome. Never let it be said we bury the important information at the end of the article.

However, to understand the deeper implications of the title, you need to understand what the three-body problem is. For that, we are going to have to talk about physics and, more importantly, maths.

What is the three-body problem?

A lot of physics is the art of taking complex physical processes and coming up with equations that describe how those processes work and what will happen when they do.

The big one we all know about is E=MC². That tells us that the energy of an object is equal to its mass, multiplied by the speed of light, squared.

Another is F=ma, which tells us that the force acting on an object will be equal to that object’s mass times its acceleration. Isaac Newton’s big contribution to science is that he defined a lot of physical processes this way, taking a big share of the credit for the classical model of physics.

In many ways, classical physics is physics on easy mode. It doesn’t include relativity with its time dilation and immovable speed of light. It is miles away from quantum mechanics and all the headaches associated with that. It depicts the universe as a vast, predictable clockwork machine.

This brings us to the two-body problem. The two-body problem is a simple question. If you have two objects floating in space (such as the Earth and the Moon), and you know their mass and velocity, how do you predict how they move?

Applying Newton’s theories, it is pretty straightforward to write an equation that will predict the movements of any two objects in space. The biggest variable is where each of the objects is, and by writing an equation that describes where those objects are relative to their combined centre of gravity, you know everything you need to know.

Ed Miller/Netflix

Take the Earth and the Moon. If you know their mass, you know how much gravity they exert, so once you know where the centre of gravity is between them you can predict how they will move and predict the Moon’s orbit around the Earth.

So, it should be fairly easy to extrapolate the solution to three bodies, right?

But once you have a third body in play, its position changes where the centre of gravity is for all three objects, and that is just one of the extra variables it introduces.

Can the three-body problem be solved?

Now, if this seems like a pretty abstract problem to solve, think about two bodies, say, the Earth and the Sun, and then a third body, like a huge chunk of ice and rock flying near the two. Suddenly we are all really quite invested in finding a way to know where that third object is going to move.

Only our solar system has hundreds of bodies, all of them moving all the time and exerting their own gravity. To make things more complicated, we have sent our own bodies, satellites and spaceships and probes, flying about up there as well.

We have found ways to solve individual three-body problems. Sometimes we use a fudge – a spaceship’s mass relative to a planet’s is practically nothing, and so a problem predicting the movement between two planets and a spaceship can be solved mostly like a two-body problem.

Ed Miller/Netflix

Scientists have also found solutions for the orbit of three objects in an equilateral triangle, not unlike the stars our aliens come from in 3 Body Problem.

We have even been able to model the movement of every object in the solar system for billions of years into the future, but doing that has taken volumes of separate equations to describe what everything in that model is doing.

Physicists hate that – they want one equation, however complex, that will describe how a system will behave every time, but in over three hundred years they haven’t been able to find one.

Of course, these days we have enough computing power at our disposal that we don’t necessarily need one either, but it still presents an interesting challenge.

So, how is this relevant to the story of 3 Body Problem?

Well, aside from the obvious interpretation relating to the trinary start system, the title also reminds us that while two objects acting upon each other might be predictable, when a third party comes into play, things are anything but.

We’ll let you draw your own conclusions about what that could mean for a story about a first contact scenario…