Book Corner: The Three-Body Problem

A review and an invitation to discuss.

The first part of this discussion will be spoiler-free and I will alert the reader before heading into spoiler territory.

Over the weekend I finished reading The Three-Body Problem by Cixin Liu. I was aware of a great deal of hype around the book, including the fact that it had won the Hugo award (and was nominated for a Nebula), but I otherwise knew nothing about the book save that it seemed to have universal acclaim. I honestly had no idea what a “three-body problem” was, although in retrospect it is pretty obvious that I should have known it was about celestial bodies. The phrase “two-body problem” is common in academia (the problem of two married/partnered academics seeking to find jobs at the same university) so while I certainly did not think that the book was about a triad seeking academic employment, the title did make me think it might be about some metaphysical or ontological extra-terrestrial issue.

It is really difficult to say what the book is about without spoilers. I will say, true to the hype, that it is a book with ambitious ideas. The book is about a mystery, one might even say several interconnected mysteries. It is not especially predictable, although once the three-body problem is introduced in the narrative a seasoned science fictions reader is not going to be surprised where the origins of that problem lead.

I will say that while the hype about the ideas in the book is reasonable, yet I ultimately found myself underwhelmed. I found the pacing unsatisfying (although the mystery was compelling enough to keep me reading) and I was especially frustrated by the amount of telling and not showing (there is a lot explaining via dialog and not a lot of action/activity in this book).

The characters are mostly indistinguishable from one another. The only ones that stand out as distinct in my mind are Ye Wenjie, a scientist (mostly because of the character’s personal history and her pivotal role in the story), and Da Shi, a police officer (because he is the only character really given any personal traits). Wang Miao, another scientist and basically the main protagonist of the book, is memorable only because he is central to the narrative (but man, he is mostly just an observer).

The dialog is stilted and wooden. Some of these failings may be the fault of the translator (the novel was originally written in Chinese) but I think that, ultimately, they are inherent to the book.

I did read that the novel was originally published in a serialized format, and that might account for some of the pacing issues.


Next

there

are

Spoilers!

So,

beware!


To talk about some specifics for those who have read the book, I will admit that the most evocative section was about the Cultural Revolution and certainly one could see why it caused Ye Wenjoe to lose faith in humanity. The only scenes in the book that really conjured much in the way real drama were the human computer and the slicing of the container ship. It is noteworthy that the ship-slicing doesn’t take place until almost the end.

The scenes in the Three Body VR game are interesting, but also increasingly laborious. At first I thought that the game was being used to help the aliens solve their problem, and so in some ways the fact that it was just a recruitment tool was a bit of a letdown.

In some ways the central idea of the book is pretty mundane: humans make contact with aliens and, whoops! they want to destroy us! Here they come.

I thought that the idea that some members of humanity would be some disillusioned that they would welcome humanity’s destruction was interesting but begged for more development. Likewise, the factionalization of the ETO was interesting, but ultimately like so much in the book, was just something told to us.

The Trisolarans were interesting, as far as they go, but it is super weird that we are given no idea what they are supposed to look like save that they are humanoid and have eyes similar to ours.

For a good discussion of the book, which largely comports with my own views, I would recommend the episode of Space the Nation wherein hosts Ana Marie Cox and Dan Drezner discuss the novel. BTW, I agree with Drezner that the notion that physicists couldn’t handle randomness in the universe to the point that they immediately starting killing themselves to be silly (and agree about his social scientist rant on that subject). Really, like a lot in the book that too seemed like it could have been developed in a far more interesting idea insofar as I did find the whole need for the Trisolarans to slow Earth’s technological advancement to be an intriguing idea.

A question for anyone who read the next two in the trilogy: do any of my criticism (pacing, characterization, dialog, and telling not showing) get any better?

In short, is it worth continuing?

I am intrigued enough by the story to want to know what happens next, but life is short and my stack of books in high and I am seriously wondering if I should just read summaries and move on. Thoughts?

FILED UNDER: Book Reviews, Books, Podcasts
Steven L. Taylor
About Steven L. Taylor
Steven L. Taylor is a Professor of Political Science and a College of Arts and Sciences Dean. His main areas of expertise include parties, elections, and the institutional design of democracies. His most recent book is the co-authored A Different Democracy: American Government in a 31-Country Perspective. He earned his Ph.D. from the University of Texas and his BA from the University of California, Irvine. He has been blogging since 2003 (originally at the now defunct Poliblog). Follow Steven on Twitter

Comments

  1. Teve says:

    I started to order this set. What stopped me was reading a review somewhere that said, “you need an understanding of Modern Chinese History to really get a number of things in these books.” And I have no understanding of Chinese history.

    1
  2. @Teve: I think reading a brief summary of the Cultural Revolution and having the vaguest of additional knowledge of China would be more than sufficient.

    TBH, there is enough context in the book to tell you what you need to know (including a few useful footnotes from the translator).

    2
  3. de stijl says:

    @Steven L. Taylor:

    I like the idea of a book club.

    @Teve:

    So learn it. It isn’t difficult. A couple of hours to get the gist. One thing to keep in mind is that if you a Westerner, Chinese thought patterns and cosmology structure is very different than what you are traditionally used to / exposed to in the West. Much more adept at acknowledging trait faults in humans. Heroes and villains are flawed.

    There is huge overlap too. But the differences are notable.

  4. Monala says:

    @Steven L. Taylor: not sure I’ll read this series at all, but the best book (in terms of the one that impacted me most deeply) that I read in college was Gao Yuan’s Born Red: A Chronicle of the Cultural Revolution. I’d recommend it for understanding the Cultural Revolution.

  5. Teve says:

    @de stijl: i just don’t read much fiction. I’m currently reading

    The Outlaw Sea – William Langewiesche
    Leonardo da Vinci – Walter Isaacson
    Making Your Own Days – Kenneth Koch
    Evolution – Carl Zimmer

    And catching up on the last 2 Vanity Fairs and 5 New Yorkers, and working on the Passato Prossimo tense in Italian. Fiction is seldom very information-dense, so I don’t read much of it. But that set has gotten a lot of attention, so I might put it back on The List 😀

  6. MarkedMan says:

    @Teve: Chinese history would help. It would also help to know the whole Chinese/Japanese/Korean literary vibe. The idea that a corrupt ruler is better than chaos is very common, and also one of the few safe literary themes in China specifically. And I imagine the idea that democracy is just a phase and ultimately unsuccessful in the VR game went over very well with the censors.

    I wonder if he could get the same book published today, what with the crackdown on non-correct thought and the resurrection of Mao as a heroic figure. Even 10 years ago criticism of the Cuktural Revolution was OK. I don’t think it is now.

    3
  7. Dutchgirl says:

    I listened to the audio version of books one and two. I can listen at work when I’m doing production, so it being too long, stilted, and at times randomly focused on a random details was fine for me. Ultimately, the story arch is interesting and has some new ideas, but the writing is inconsistent and would improve under severe editing. I don’t think it’s a translation problem, as I read quite a few Chinese novels in translation. The second book is better than the first, though. I recommend to keep going unless you have other books on your list that take priority.

  8. Dutchgirl says:

    @Dutchgirl: Apologies for my terrible syntax above. I’m usually better than that, especially when critiquing someone else’s writing.

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  9. Kathy says:

    So it’s not a reference to a solution of the gravitational attraction of three bodies?

  10. Dutchgirl says:

    Kathy, that is the reference. That is why the Trisolarans have to leave their home world.

    1
  11. Slugger says:

    I read a lot of science fiction when I was a teenager. The library in my hometown would not let the under eighteens check out adult books, but they classified sci-fi as juvie lit. I read it because it was the most grown up stuff I was allowed to check out. As an old man, I find contemporary sci-fi juvenile with gadgetry instead of heart. I did read this book because of the hype it engendered. I agree with Professor Taylor’s review. It didn’t grab me. No “sense of wonder.” No insight into my problems. I agree that I may be too far removed from post Cultural Revolution China to appreciate this book, but I’m far removed from Bronze Age warriors and like The Iliad. I’m far from 19th century Russian nobility but like Anna Karenina. I will watch these pages to see if my interest in the rest of this trilogy can be piqued.

    1
  12. Flat Earth Luddite says:

    As Cracker can attest, I’m a written word junkie. Like our host, I’d heard the hype, read some reviews, and got on the wait list at my local library. I tried, oh how I tried. But even a love for writers and their craft couldn’t get me through it. I’ve gone back to it…but like Ulysses, I just don’t grok this one. Hopefully it works better for others.

    1
  13. OzarkHillbilly says:

    ‘Nuff said. I’ve got plenty of books on my “To Read” shelf already.

    1
  14. Lounsbury says:

    I have read the two books, and found the first intriguing the second somewhat frustrating as compared to the first, but worth reading through (as a rather fast reader it doesn’t take that much time for me so I rarely care if a book is long so long as I can digest [contra Ulyssess say…]). The Chinese mode of it neverthelesss is intriguing, although perhaps because I regularly operate in non European languages / cultures more interesting to me.

  15. steve says:

    I liked it. Read lots of sci fi. I do think that some of the Chinese sci fi is a bit hard to get your head around. I also thought LEM was kind of hard when I read him too, at first. It does explore some ideas that have been around in sci fi a long time, just with a slightly different take. (Disclaimer. I actually liked Dahlgren by Delany and the Simmons books also.)

    Steve

  16. MarkedMan says:

    I may have given the wrong impression above. I actually am glad I read the books and thought they explored concepts in interesting ways.

    One unsettling insight into Liu’s mind was his assumption in several places was that if an individual or group could not “win” they would naturally cause everyone else to lose. Not sure if this reflects a norm of modern Chinese thought.

    1
  17. wr says:

    @steve: ” I actually liked Dahlgren by Delany and the Simmons books also”

    With you on that. Nova was one of my favorite books as a teen…

  18. JohnSF says:

    Good book; though at some points I couldn’t help thinking some of the Chinese characters seemed almost more alien than the aliens.
    But it grips as a story, generally.

    It’s only if you step back and consider some of assumptions made that it become wildly improbable; but that has never been a problem with a good SF novel as long as the handwavium is artfully enough applied for immediate suspension of disbelief.
    Which Liu achieves.
    The “alien allies” also seem a bit implausible, politically. But again, not so extremely as to completely defy acceptance as a fiction.

    Definitely worth a read.

  19. Kathy says:

    Given my large, and growing, queue of audio books and ebooks, plus Duncan’s upcoming release of his book on Lafayette and Wyman’s “The Verge”, I think I should give this book a pass, maybe wait for the movie.

  20. MarkedMan says:

    @JohnSF: When I read it, I wondered about the number and power of the traitor humans. Given the Republican politicians willingness to embrace facism and insane conspiracy theories over the past few years, it seems much more likely…

  21. @Kathy: Netflix is making into a series. We shall see–I think it will take some reworking to make it compelling in that format.

    1
  22. @steve:

    I do think that some of the Chinese sci fi is a bit hard to get your head around.

    It may be that my qualms are somehow linked to culture, but I am not convinced. The conceptual parts of the book were, to me, the best parts.

    My main frustrating was lots of telling, little action, and the lack of exploration of character motivations. Perhaps that is indicative of Chinese writing, but I really can’t say.

  23. MarkedMan says:

    @Steven L. Taylor: Hmm. Not sure that is the best idea for Netflix, business-wise. Is it really a good time to promote an author who has expressed support for the Uighur concentration camps?

    According to a June 2019 interview and profile article by The New Yorker, Liu avoids talking about politics. In the same article, Liu argued that democracy was not appropriate for modern China, and individual liberty and freedom of governance is “not what Chinese people care about”, adding “If you were to loosen up the country a bit, the consequences would be terrifying.” He expressed support for policies such as the one-child policy and the Xinjiang re-education camps, saying “the government is helping their economy and trying to lift them out of poverty”. The article reported that Liu had “become wary of touting the geopolitical underpinnings of his work”.

    1
  24. MarkedMan says:

    @Steven L. Taylor: In general, I agree with your assessment of weak character building. However I suspect some of that is simply his assumption that motivation is obvious in some cases. Balancing family against societal good, protecting the state, personal ambition and the failure to achieve potential, are all things discussed a great deal in China. There may be some “goes without saying” aspect to the lack of character motivation.

    2
  25. Rick Zhang says:

    The series explores big ideas and does so in an unconventional way. As you’ve noted, the Chinese mentality and style of writing/pacing is wholly differently from western sci-fi, emphasizing themes of communal action and self-sacrifice for the nation.

    I would at least read the next book, which is the best of the trilogy according to both my wife and I. It’s still slow and more show than tell but has a few big explosive moments and a great wrap up ending. You can skip the third book if you still don’t like the series by that point.

    2
  26. @MarkedMan: Perhaps. I just find that in this book it felt like these motivations were largely assigned to characters because, well, someone had to have motivation X, might as well be character Z.

    There is, to me, a missing depths.

    Actually, I think this does remind me of some of the SciFi of my youth that focused a lot more on some cool idea at the expense of the actual characters in the book.

  27. @MarkedMan: That is its own issue (which I learned about from the Cox/Drezner discussion).

  28. George says:

    I haven’t read the book, but a review I read said the story (and its title) hinges on the insolvability of the three body problem. That’s not encouraging.

    The three body problem cannot be solved analytically, but it can (and regularly is — as in undergraduate level engineering and physics problems and labs) solved numerically (now by computers, before by pen and paper) to however many decimal places you require. The more accuracy needed the more computation time is needed, but for any reasonably advanced civilization (us for instance) it can be solved to more precision than the actual measurements of the physical bodies. Its simply not a problem in practice, as everything from our space program to aeronautics (and a thousand other mechanical engineering technologies) show.

  29. Modulo Myself says:

    (Disclaimer. I actually liked Dahlgren by Delany and the Simmons books also.)

    Man, I loved the Hyperion books when I read them as a teenager, if those are the Simmons books you mean. They just blew my mind.

  30. @Rick Zhang: Thanks for the recommendation. I am leaning towards reading it.

  31. Franklyn says:

    I actually enjoyed the third book the most of the trilogy – though not the ending sequence. The second book with the “wall breakers” might frustrate you somewhat. Perhaps read a synopsis of book 2 and jump to book 3.

  32. becca says:

    My taste in sci-fi runs to Heinlein and David Drake. Swashbuckling space sagas.
    The Three Body Problem trilogy is not my cup of tea, but my husband, the sci-fi fanatic, really got into it.
    Netflix should check out Drake’s RCN series for production. Fun stuff.

    2
  33. MarkedMan says:

    @Steven L. Taylor: The tendency towards cardboard motivation is a reality, at least in the mainstream Chinese stuff I’ve been exposed to. Although I haven’t consumed a lot of Chinese movies and books, I’ve consumed more than the average American, and I find that there is a prescriptive feel to a lot of it, even the ones I enjoyed. There is a sense of the medieval morality play, where certain acceptable themes are played out with specific character types and plot lines. Part of this may be just risk aversion. A director may want to just make a really cool movie and not wind up in jail, so they once again revisit “8th century hero initially fights against the corrupt emperor but then realizes successfully opposing such an emperor will bring about chaos and so selflessly sacrifices their life to preserve the current regime.”

    Oddly, I think we are heading that way a bit in the US, not with the emperor trope but with the medieval morality play. It seems that some under-30’s are strongly opposed to certain characters have any sort of complexity. If someone is the protagonist they can’t harbor any non-acceptable views. If they have an arc with any length it must be a redemption arc, not a growth arc. One commenter on “The Crying Game” thread labeled the entire movie trash because in it, a 1970’s era Irish nationalist had a strong reaction to finding out the beautiful woman he had just met had male genitalia. This is not acceptable in their eyes. I guess he is allowed the “villian” character, or the “hero” character. And although a redemption arc might have been acceptable because his outlook did change by the end of the film, his zealousness and self-abnegation was completely insufficient.

    1
  34. MarkedMan says:

    @becca: I was a hard core Heinlein fan and got a lot of my early perspective from him. But he eventually succumbed to “Old Science Fiction Writers Disease” wherein an author begins to resurrect their favorite characters from previous stories, mash them together in a new story, and make them have sex with each other. In the advanced stages they will even bring in characters from other authors. Huck Finn or Tom Sawyer often show up in the end stages of the disease.

    1
  35. Just nutha ignint cracker says:

    I read a fair amount of foreign fiction–slow reader, so I don’t read a lot of anything–so the fact of his being a Chinese writer would give him an appeal for me. The big problem that I can see from what y’all have said is that science fiction is already a slog by nature for me (though I read quite a bit when I was really young) and that badly written foreign fiction is even more of a slog. I’ve been thinking about reading Klara and the Sun as the reviews seem to show it to be a good read, but that’s a ways off on my list. If the price on Kindle comes down, I’ll order it.

    For right now, I’ll just put my English teacher who doesn’t read literature hat back on and slink away.

    1
  36. George says:

    @Just nutha ignint cracker:

    A couple of science fiction books you might enjoy are David Brin’s “Uplift War” and “Startide Rising” — both have interesting characters and theme’s. Curiously enough I don’t like his other books.

  37. Steve says:

    Steve- I don’t think it is a matter of understanding Chinese culture per se but rather that there are different points of emphasis and viewpoints than you see in US based sci fi. Takes some accommodation.

    Steve

    1
  38. flat earth luddite says:

    @Just nutha ignint cracker:
    Cracker, come on over to my corner — got a stack of stuff in my “slash & trash” pile, as you well know.

  39. CSK says:

    1. Wooden dialogue.
    2. Characters indistinguishable from each other.
    3. Overload of exposition.

    It sounds as if the author hit the trifecta of unreadability.

    4
  40. MarkedMan says:

    @George: I’ll throw in anything by Frederick Pohl. Character first, but also an amazing view of potential futures. Although I have to admit most of my reading was decades ago and not everything I liked then held up on re-reading. Still, he was almost one of a kind in science fiction then.

  41. JohnSF says:

    Been thinking about this a bit.
    Warning: spoilers!
    Essentially Three Body Problem and In the Dark Forest are two parts of one book; you can’t really consider either in isolation.
    Death’s End is rather more distinct from the others of the trilogy.

    Liu’s has a distinctly pessimistic view of human politics, human nature, and indeed the likely nature of all sentience.
    Zero sum.
    The crab bucket.
    Reductionist (social) darwinism.
    The need for an empowered and motivated state to overcome individual and sectional preferences and focus on collective goals.
    The tendency of such states to nonetheless collapse under the due to the triple loading of self-interest, fanaticism, and complacent groupthink.

    Perhaps not surprising: a study of Chinese history might incline to such judgements, especially the Cultural Revolution that Liu explicitly makes the background of the human part of the story.

    But also the aliens themselves seem to be rather analogous to Chinese history in some respects/
    Cycles of stability and slow progress, punctuated by periods of chaotic collapse; and the problems of engendering collective good among tendencies to self-serving.

    The Trisolarians fear the faster progress of the late-coming human. Another parallel?
    Spoiler alert:

    And the belief of humanity that it could rival the Trisolarians, only to be almost contemptuously crushed certainly puts me in mind of episodes from Chinese (and Japanese) history.

    In many ways the trilogy is a setting for Liu to explicate his own social and historical attitutes.
    It is categorised as “hard SF” but it’s scientific base is very shaky.
    Including the titular problem itself, but above all the evolutionary biology IMO.
    And “smart photons” for that matter.

    Still worth reading though.

  42. JohnSF says:

    @Rick Zhang:
    …themes of communal action and self-sacrifice for the nation.
    What struck me was how much various groups had to be coerced into collective action, and continually policed for backsliding.
    How it accepted that those who do not materially benefit from a policy would, obviously, not support it, even sabotage it.

    It strikes me that if this is representative of Chinese modes of thought, Europeans are more collectivist by a mile. There’s a scenes in the second book IIRC where the fleet commanders are trying to formulate a system for compelling the adherence of military units to the mission.
    I cannot imagine this sort of concern ever even occurring to commanders of the British Armed Forces. Morale issues yes; basic motivation of the corps, no.

  43. Michael Reynolds says:

    Science fiction is hard to write precisely because it generally comes with a mountain of world-building exposition. And that exposition generally needs to be front-loaded. You either come at it head-on with a straight-up, ‘here’s the deal,’ approach which is tedious, or you tease it out which irritates less patient readers who don’t want to be baffled for the first 50 pages.

    In some ways it’s like writing YA. The bitch with YA is that you have a very limited supply of common reference points. Even a very bright 14 year-old reader has a very limited amount of on-board knowledge. You’re constantly being challenged to explain something in a paragraph that could be done with a five word common reference point. Science Fiction generally lacks those short-hand referents as well.

    Most Sci Fi writers ignore character, probably because most of the writers are men with the souls of engineers. They’re much more about the ideas, not so much the people. Add in the fact that science fiction leans toward series of fairly short books, and the writer’s need to re-set with each sequel, and almost inevitably the ideas and world-building crowd out the characters.

    Add the difficulties of science fiction to the difficulties of YA and you have my writing career. I solve it by elevating character and hand-waving most of the science, an imperfect but commercial solution.

    2
  44. Zachriel says:

    @George: The three body problem cannot be solved analytically, but it can (and regularly is — as in undergraduate level engineering and physics problems and labs) solved numerically (now by computers, before by pen and paper) to however many decimal places you require.

    That would depend on the specific system. It’s quite easy to imagine a system that’s poised on the edge of a knife, that is, where small errors or uncertainties in current observations could lead to wildly divergent projected outcomes over timescales of concern. This is a common problem, such as predicting the trajectory of Earth-crossing asteroids.
    https://www.sciencephoto.com/media/624864/view/chaotic-planetary-orbits-animation

    1
  45. de stijl says:

    @Michael Reynolds:

    In my experience and to my preference world building exposition gets dropped in by dribs and drabs. Incidental dialog alluding to something you have not fully described. Let the reader figure it out.

    Maybe just drop the whole process and let the reader figure it out with context.

    I was gonna say exposition is boring. It isn’t. It’s often fascinating if well thought through. But it bogs down everything.

    I am in the camp of only referring to the salient bits and let the reader fill in the blanks for the rest.

    YA is technically adult and does not mean you have to hand-hold everybody through the initial stage setting.

    When I was 13 I could figure out a lot stuff on my own dime.

    The mechanisms of exposition are clunky.

  46. @Michael Reynolds: @de stijl: The issue in this novel was not exposition linked to world-building. My major gripe is that a lot of the book, period, was people just talking and explaining.

  47. becca says:

    @MarkedMan: I get that about Heinlein, but Farnham’s Freehold will forever color my opinion. Loved that book.

    David Drake is a war historian and he recreates historical campaigns in space, so not pulp sci-fi but more space cowboy (with strong women characters).

  48. George says:

    @Zachriel:

    Sure, that’s the basis of chaos theory — a non-linear (ie coupled) system where small differences in initial positions can radically change the trajectories of the multiple bodies, typically because of multiple . However that applies to systems that can be solved analytically as well (for instances even a very simple system like the damped, driven pendulum). There’s nothing unusual or special about the three body problem in that regard, and in practice its a limitation of measurement technology.

    In the case of asteroids we haven’t found it important enough to put the resources into measuring their locations and momentum more accurately — the limitation isn’t the three body problem, in that we could determine their paths far more accurately if it became important.

  49. George says:

    @Michael Reynolds:

    That’s an interesting point. I suspect many readers of science fiction (including myself when I was younger) would be happy to read a book about just speculative application of some idea to future civilization and technology, with little or no time spent on characters. For instance, Isaac Arthur does just that on Youtube, and seems to have a large following (about 650,000 subscribers).

    https://www.youtube.com/channel/UCZFipeZtQM5CKUjx6grh54g

    But I’ve never seen books written in that style (the speculative ones tend to be more “Chariot of the Gods” types than speculative science).

  50. JohnSF says:

    @Steven L. Taylor:

    My major gripe is that a lot … was people just talking and explaining.

    My big gripe with life, a lot of the time.
    🙂

  51. JohnSF says:

    @JohnSF:
    On the other hand, probably better than “living in interesting times”

  52. Zachriel says:

    @George: There’s nothing unusual or special about the three body problem in that regard, and in practice its a limitation of measurement technology.

    Observation is necessarily limited and subject to error. The point, of course, is that for a sufficiently chaotic system, there is no way to make specific predictions beyond a certain point. The tame nature of the Solar System in its middle age is not indicative of other systems or even the Solar System in its youth. A slight change in trajectory and the Moon may never have formed as it did.

  53. George says:

    @Zachriel:

    The solar system is relatively easy to predict (at least for its larger objects) because 99% of the mass is in one object. That allows using perturbation theory to make good linear approximations for planetary motion (ie a system of two body problems). Even in the case of the moon, its enough smaller than the earth and distant sun that chaotic elements are fairly minor. The three body problem becomes much more chaotic (as do pendulums and in fact just about every other real system) when the forces involved are on the same order of magnitude.

    And they still come down to having the technology to measure accurately enough to run numerical models. For instance, the earth isn’t really a point mass (or even uniform sphere), and internal distributions of core masses etc have a small but non-zero effect on the moon. A sufficiently advanced technology could measure that and numerically solve the moon’s motion to great accuracy. It just strikes me as an odd thing to concern wrt aliens with the technology to make it it earth (haven’t read the book so I’m just basing my comments on a review) — solving the three body problem for celestial orbits is not going to be a major problem for them.