The Three-Body Problem

The three-body problem is one of the more vexing problems of classical mechanics. In short, if you have a system of three objects that interact with each other, you can’t use classical Newtonian equations to predict their behavior. Effectively, you have a chaotic system. In astronomy, you might imagine three planets or three stars interacting gravitationally. I first encountered this idea in high school soon after reading how Percival Lowell began a search for a ninth planet in our solar system to account for unexplained perturbations in Neptune’s orbit. We knew the planets Uranus and Neptune pulled on each other, but it seemed like a third, similar-size planet must also be pulling on Neptune. This search ultimately resulted in Clyde Tombaugh’s discovery of Pluto, which really proved too small to account for those orbital distortions. As it turned out, those orbital perturbations in Neptune’s orbit came down to measurement error. Still, I got to spend some time wrapping my thoughts around this challenging concept and even wrote a report on it.

One of my co-workers at Kitt Peak National Observatory recently suggested I check out Cixin Liu’s Hugo Award-winning novel The Three-Body Problem. In the novel, Wang Miao is researching nanomaterials when he starts seeing a countdown in the middle of his field of vision, no matter where he looks. The countdown even appears on photographs he takes. However, no one else sees the countdown and no one else takes photos with images of the countdown. His quest to solve this ultimately, leads him to a virtual reality game called “The Three-Body Problem.” In the game, he’s transported to a world which moves between nice predictable day/night cycles to long periods of night and even occasionally periods of searing heat. Fortunately, the people of this strange world can dehydrate themselves in order to survive the periods of environmental extremes. Unfortunately, they only make technological progress during the periods of relative environmental stability. Wang ultimately realizes this is a planet in a system with three approximately equal-size stars. The planet is being passed back and forth among the stars as they do their chaotic three-body dance. Cixin Liu found a fascinating way to allow readers to experience the complexity of the three-body problem.

The novel also tells the story of Ye Wenjie, an astrophysicist who came of age during China’s Cultural Revolution. She’s ultimately pulled into China’s search for extraterrestrial life project and succeeds in making contact with another world. It turns out the world she’s contacted is same one Wang has been experiencing in the game. Those people from the chaotic system yearn for a world as stable as ours. What’s more, because of her experiences in the Cultural Revolution, Ye sees humanity as irredeemable and feels that humans would benefit from contact by the so-called Trisolarans. Through this plot, Cixin Liu explores the question of whether or not contact with aliens would benefit humanity. In the first novel, he provides no simple answers.

In the novel, it’s suggested the Trisolarans come from Alpha Centauri, which really is a three-star system. However, Alpha Centauri isn’t actually a chaotic system. That’s because two of the stars, Alpha Centauri A and Alpha Centauri B, which are each about the size of our sun, orbit a common center as a nicely behaved two-body system. The third star, Proxima Centauri is only half the size of the other two and is in an orbit about 200-times more distant from the two stars than Pluto is from our sun. Because gravity falls off as the square of the distance, Proxima doesn’t induce much chaos in it’s two big brother suns. So, we have to suspend our disbelief for this part of the novel, or assume that the Trisolarans actually come from some other three-star system that just happens to be a little over four light years away.

The novel also presents some interesting thoughts about the so-called Fermi Paradox, which suggests that it’s strange that we haven’t yet found evidence of other advanced life, even though we suspect that advanced life should be common. I do think there are several possible reasons we haven’t found other intelligent life. Cixin Liu points to the shear size scales of the galaxy and the distances between stars as a factor. I think the vastness of the universe is truly hard to comprehend. This same vastness will make interstellar travel a challenge for any civilization and also becomes a factor when we imagine signals traveling out into space.

Another possible answer to the Fermi Paradox is that alien intelligence is so alien that we have a difficult time recognizing it as intelligence. It could be that not all intelligent beings build tools and send out electromagnetic signals. Even if an advanced civilization has expanded to a few star systems and communicates using electromagnetic signals we could detect, it’s also possible that they’ve found a way to deliberately cloak those signals for either benevolent or hostile reasons. I explore a few of these ideas in my novel The Solar Sea and in my Space Pirates’ Legacy novels. You can learn about them all at: http://davidleesummers.com/books.html