Three Body Problem is a lot of fun, but if you are that concerned by it you should seek out the broader Fermi Paradox dialogue which does not favor this solution, and not just because it's unwanted. Isaac Arthur's Fermi Paradox Compendium on youtube is probably a good place to start and I'm pretty sure his Dark Forest video covers the major points. In any case, I have them here too:
If the universe is teeming with alien life, why isn't it here? It looks like it will take millions of years to colonize the galaxy but the likely variation in emergence/evolutionary timelines is some decent fraction of billions of years (considerably more than 4 billion years, the starting gun is metallicity not the formation of Earth). In particular, if there is highly capable space-faring life at Alpha Centauri, why haven't they probed their neighboring star system in a billion years even though it was completely trivial to do so relative to subsequently displayed technological feats?
Also: it's really hard to configure the rules of a Dark Forest so that the optimal strategy is "hide" rather than "grow, grow, grow -- and hope you grow fast enough by the time it matters," and it's spectacularly hard to make that so universal across all aliens that none of them "wins" and colonizes the galaxy per the previous paragraph.
Finally, Cixin Liu had to break the speed of light to make his story work (and then carefully avoid the implications to #1 and #2 above, which both get worse if c is no longer a constraint). I am all for doing what it takes to tell the story, and even more delighted by his deeper exploration of this concept further down the line, but one must remember to adjust the likelihoods of it all according to the likelihood of the premise, which seems quite low according to our present understanding.
This is a nit pick and doesn't change your argument, but Alpha Centauri would not have been our neighboring star system for a billion years. Stars move relative to each other in our stellar neighborhood at about 30 km/s, or one light year every 10,000 years.
Yep, good reminder! Of course, as you point out, it doesn't change the argument because probing (or simply direct observation, if they must hide) would still be trivial, both at larger distances when we weren't quite neighbors and on the shorter timescale when we were. Trivial next to mustering an interstellar invasion fleet on the turn of a dime, at any rate. Besides, if they were itching for a fight then the original "decent fraction of billions of years" timeline still applies to the question of "why didn't they grow and colonize?"
If the universe is teeming with alien life, why isn't it here? It looks like it will take millions of years to colonize the galaxy but the likely variation in emergence/evolutionary timelines is some decent fraction of billions of years (considerably more than 4 billion years, the starting gun is metallicity not the formation of Earth). In particular, if there is highly capable space-faring life at Alpha Centauri, why haven't they probed their neighboring star system in a billion years even though it was completely trivial to do so relative to subsequently displayed technological feats?
Also: it's really hard to configure the rules of a Dark Forest so that the optimal strategy is "hide" rather than "grow, grow, grow -- and hope you grow fast enough by the time it matters," and it's spectacularly hard to make that so universal across all aliens that none of them "wins" and colonizes the galaxy per the previous paragraph.
Finally, Cixin Liu had to break the speed of light to make his story work (and then carefully avoid the implications to #1 and #2 above, which both get worse if c is no longer a constraint). I am all for doing what it takes to tell the story, and even more delighted by his deeper exploration of this concept further down the line, but one must remember to adjust the likelihoods of it all according to the likelihood of the premise, which seems quite low according to our present understanding.