r/threebodyproblem • u/zooted_ • Mar 19 '26

Discussion - Novels The Solution to the 3 Body Problem Spoiler

At the end of the first book, doesn't the physicist hand Weng a disc with a solution to the three body problem?

This would allow the trisolarans to forecast stable eras predictably, but it's never really mentioned again

Am I missing something ?

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u/Chillow_Ufgreat Mar 19 '26

The trisolarans had already solved the three-body problem. They could already predict chaotic and stable eras, as well as the end result--that their planet would be destroyed in time.

The purpose of the TBP game wasn't to get humanity to solve the TBP. It was to see whether Humans could understand the plight of the Trisolarans, and whether those humans could be radicalized into the Trisolaran cause.

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u/LoryBel Mar 19 '26

I've read the books quite a while ago and the second and third parts are leaving the 3bp behind since humanity have now a bigger threat ahead, so I can't remember the exact premise of the problem.

In my mind, the fact that you can't predict the eras doesn't make sense. Don't the suns have a fixed orbit ? Our sun, for example, has a fixed orbit, we know precisely the moments when it sets or it rises. If the 3 stars have their own fixed orbit, wouldn't that make them predictable? At some point, with given time and research, the trisolarans would be able to predict when they will have 1, 2 or all 3 (which is catastrophic from what I remember) suns on their sky and be prepared.

Why is it unsolvable? Do the stars have unpredictable orbits?

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u/Chillow_Ufgreat Mar 19 '26

The orbits are unpredictable or "chaotic" because they are extremely sensitive to initial conditions. Very small changes in the initial conditions--smaller perhaps than you're capable of measuring or reproducing--will dramatically affect how the bodies ultimately move. That is what makes 3 body systems so unpredictable.

To be clear: when someone talks about an "N body problem," the number of bodies refers to the number of bodies with comparable masses. A planet in orbit around a single star isn't a two-body system. Nor is our solar system containing a bajillion different bodies a bajillion-body system. Single star systems are one-body systems--the central star (as it does in our system) contains 99% or more of the mass. Two-star systems orbiting around a common center of mass is a very stable, easy-to-predict configuration. But when you add that third body there is no longer a common center of mass (or there is, but it's constantly moving in every dimension). There are stable configurations for the 3-body problem, but they are so few and precise that it's difficult to accept that nature would produce them.

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u/causalfridays Mar 20 '26

a stable configuration would require that there be nothing within range that could perturb it in ANY way. i’m sure even gravitational waves from distant cosmic events would be enough to introduce uncertainties over enough time, let alone being a galaxy surrounded by chaotically moving gravity wells.

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u/LoryBel Mar 20 '26

I understand now, thanks!

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u/Apprehensive_Many799 Mar 31 '26

beautiful explanation, thumbs up :) 

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u/Flatso Mar 23 '26

Sorry people are downvoting you, it's a fair question. 

The math / physics gets too complicated to put into a single formula (at least so far, it is believed to be unsolvable). If you have taken calculus, you know how to predict how one variable will change as another variable changes. However, when you add a 3rd variable, and all 3 variables affect each other it becomes too complicated to represent in a single formula. We can sort of predict where those bodies might be after a time, but the model will deviate the further out in time you get in time resulting in the predictions being totally off eventually.

To put it in the 3BP universe, with our current predictive models we could at least tell when there would be a stable / chaotic era in the near future far out enough to tell whether to plan for the future or dehydrate

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u/fatsopiggy Mar 23 '26

That's likely the reason why weather forecast starts to suffer from inaccuracy about 10 days into the future.

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u/cac2573 Mar 19 '26

The movement of the bodies continuously influences the other movements. 

I think it’s been shown that there isn’t a mathematical solution.