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Three Worlds Collide
Eliezer Yudkowsky
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Three Worlds Collide

4.3  ·  Rating Details ·  507 Ratings  ·  32 Reviews
Three Worlds Collide is a story I wrote to illustrate some points on naturalistic metaethics and diverse other issues of rational conduct. It grew, as such things do, into a small novella. On publication, it proved widely popular and widely criticized. Be warned that the story, as it wrote itself, ended up containing some profanity and PG-13 content.
Published January 30th 2009
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Jul 10, 2012 Elius rated it it was amazing
Shelves: sci-fi, short-story
I wish Eliezer Yudkowsky was a full time writer. So many good ideas!

This novella was about humans encountering the alien race of Babyeaters - who are civilized but eat their babies, and the humans, as soon as they learn of this, are morally shocked about the custom that is taken to be natural. Most of them want to wage war to save the babies (so cliche) and relieve them of their pain! But then, another alien race arrives, the Maximum Fun-Fun Ultra Super Happy People. One that thinks even having
Sep 05, 2013 Scott rated it really liked it
An interesting science fiction long short story (100 pages). It reminded me of I, Robot, except instead of quaint 1950s charm ("positronic brains") it has awkward references to internet culture ("Any suggestions get reddited up from the rest of the crew?"). I made an EPUB version for ereader users.
Jun 28, 2015 Ana rated it really liked it
Shelves: sci-fi, 2015
This review has been hidden because it contains spoilers. To view it, click here.
Zach Toad
Jan 25, 2015 Zach Toad rated it really liked it
Insanely thought-provoking, but didn't quite get all the references to game theory other than talk about the prisoner's dilemma. I wish I had a college level game theory course under my belt before reading this. The play with ideas in metaethics was very well-done, however. Relevant, too, to all our political conflict over whether to intervene or not in foreign affairs.
Not sure that it brought me any closer to answers!
Shayan Kh
Sep 26, 2015 Shayan Kh rated it really liked it
Yudkowsky is officially one of my favorite thinkers. Too bad he doesn't write more often. I liked the way he shaped hpmor, although I didn't like the whole story. But this time around, he presented a very disturbing version of prisoner's dilemma, in a sci-fi about different kinds of sentient beings, and how their morals might be radically different from ours. It is very thought provoking and I really enjoyed this piece of work.
I hope He writes more stories. I'm definitely gonna read his work.
Andy McKenzie
Nov 26, 2012 Andy McKenzie rated it liked it
Some good portions and does challenge your assumptions. He's done better elsewhere I think.
Simona Vesela
Oct 02, 2016 Simona Vesela rated it it was amazing
I loved it. If playing the classic prisoner's dilemma, you cooperate with a single individual. Almost always. You defect only in fear. But what if you really-really want to defect and you are playing against aliens for whom you are morally disguising, and you feel the same about them.
Amazing story, well written, strange, thought-provoking. Nice to accompany it with the original reader comments on Less Wrong.
I recommend it
Naive Skeptic
Aug 12, 2016 Naive Skeptic rated it it was amazing
Three Worlds Collide is a work of rationalist fiction written by Eliezer Yudkowsky, a fellow at the Machine Intelligence Research Institute. Originally written to explore questions of ethics it features two distinct possible endings. Unlike many other authors Yudkowsky, does encourage the reader to make up their own mind. Instead tells the reader which ending is preferable and why. It is up to the reader to see the entire picture. If the reader thinks Yudkowsky is wrong about the conclusion they ...more
Dione Basseri
So, I was all set to give this story a full five-stars and recommend it to anyone who asked for a unique bit of science fiction. It's so novel. Humanity meets two new races at once, both with radically different senses of morality, and they must find a way to fit into this expanded universe of thinking. One species where overpopulation is rampant, leading to baby-eating as a means to thin out the masses, so much so that eating babies is considered good. Another where information is shared ...more
Verbin Pybir
Sep 12, 2016 Verbin Pybir rated it really liked it
Thought provoking, with the different alien species representing different mindsets and worldviews.
Jan 01, 2016 Jeremy rated it it was ok
I find the characters impossible to relate to. You might say that's beside the point for this particular story, but I think it exactly is the point for a case of first contact with an alien (in all senses) culture. Here, I felt that all the species were alien.

The story describes certain alien behaviors that produce visceral emotional reactions in the characters (and for good reason, probably). And yet I had no emotional reaction myself, which I don't think was the reader's fault.

The author can b
Eric Herboso
Oct 08, 2012 Eric Herboso rated it it was amazing
This short story describes a spaceship of humans in the future who make first contact with not one, but two intelligent alien races. The result involves spirited debate as each of the three realize they all have very different views on which moral facts are true.

If you have a group of friends interested in metaethics, I strongly recommend you try printing out hard copies of this short story in sections, and read the story together in person. Each successive section will give you a lot to talk ab
Aug 02, 2015 Lucas rated it really liked it
The science-fiction novella Three Worlds Collide offers a thought-provoking and hysterically funny (and also somewhat suspenseful) blend of Douglas Adams and Star Trek: The Next Generation. The story is about humanity's encounter with two fascinating, truly alien, alien species and the moral dilemma's posed by these encounters. The novella is philosophical, intelligent, populated by a wonderful cast of characters, making the first few chapters are an absolute blast to read. The ending was a litt ...more
Ramprasad Saptharishi
Jul 16, 2016 Ramprasad Saptharishi rated it really liked it
Shelves: scifi, space-opera
This novella was great. The premise is about three worlds with conflicting notions of morality. The dilemmas are some well done that you begin to question a lot about morality that we take for granted.

The first few chapters of the book were just stunning. But one complaint I had was that the rest of the story seemed just ok and the conclusion made me feel a bit disappointed after such an awesome start. But the more I think about it, it feels like it just had to be this way.

Having said all that
Mathieu Roy
Sep 01, 2014 Mathieu Roy rated it it was amazing
Shelves: 6-stars, free, audio
I've read 25% so far and at one point I almost applauded while going to school listening to the podcast version. It's really good!

EDIT: I've now finished it. I really liked it! The aliens are well developed: not simply a similar copy of homo sapien (which is very improbable to happen IRL and yet it's the most often used type of aliens).

ps1: you might not like what you figure out by reading/listening this.
ps2: are we ready to meet intelligent aliens?
Valentin Buck
Jan 18, 2015 Valentin Buck rated it it was amazing
Really really really impressive story!
I have to say, I like stories with intelligent characters who don't behave like complete trope versions of themselves, and this is full of them!
The ethical dilemmas discussed are relevant and exciting, the opposing factions are neither too perfect nor too chaotic, in short, read this story!
There's also a great audio version over at the hpmor podcast.
Bradley Arlt
Oct 29, 2012 Bradley Arlt rated it really liked it
Shelves: scifi
This review has been hidden because it contains spoilers. To view it, click here.
I don't know if I'll feel like this tomorrow, but having just read it, my main thought is that I didn't know I could like fiction as much as I like this. It's such an awesome picture of, as it says, "the past's future" and how a bunch of smart, pretty rational characters would behave.
Basil H
Dec 14, 2014 Basil H rated it really liked it
Yudkowsky is always thought provoking. Went from three to four stars in the last chapter. He could've, though, made a more effective argument for the utility of pain. See "Habit formation preferences"
Karl Nordenstorm
Nov 06, 2016 Karl Nordenstorm rated it it was amazing
Superb, high paced, surprising, haunting
Thore Husfeldt
Dec 16, 2013 Thore Husfeldt rated it liked it
Cute First Contact story with delicious moral dilemmas, evolutionary psychology, game theory, and alien aliens. I can’t help comparing the Maximum Fun-Fun Ultra Super Happy People with the Inchoroi in R. Scott Bakker’s Second Apocalypse epic fantasy series.
Arjun Narayan
Jun 30, 2013 Arjun Narayan rated it it was amazing
Shelves: transhumanist
Short story, reads quickly, and in need of a good editor. Nevertheless, very though provoking transhumanist fiction.
Martin Gehrke
Apr 23, 2015 Martin Gehrke rated it it was amazing
A very interesting read that takes some simple notions to some far reaching logical conclusions. I really enjoyed the pulp culture references.
Feb 22, 2014 Jelly rated it really liked it
Well played out plot. More would spoil the fun or reading/listening to it.

Titles like "Lady Programmer" still sound promising. :)
Mar 22, 2014 Mariam rated it really liked it
Shelves: sci-fi
It was fun and interesting exploration of Prisoner's Dilemma, evolution and evolutionary psychology, and morality and ethics when confronted with a culture so vastly different than our own.
Brooke Judson
Sep 24, 2015 Brooke Judson rated it really liked it
Shelves: short-story, scifi
Cool stuff about aliens and how different cultures may interact with our own! Would definitely recommend reading it if you like scifi.
Nov 11, 2015 Nathan rated it it was amazing
An excellent First Contact story that just keeps the hits coming. Inter-species ethics is heavily explored, and the reader is confronted with genuinely difficult moral problems.
Fadeway rated it it was amazing
Dec 16, 2012
Xaleander rated it really liked it
Mar 22, 2014
Mooncalf rated it it was amazing
Nov 10, 2012
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From Wikipedia:

Eliezer Shlomo Yudkowsky is an American artificial intelligence researcher concerned with the singularity and an advocate of friendly artificial intelligence, living in Redwood City, California.

Yudkowsky did not attend high school and is an autodidact with no formal education in artificial intelligence. He co-founded the nonprofit Singularity Institute for Artificial Intelligence (
More about Eliezer Yudkowsky...

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“You do realize that your brain is literally hardwired to generate error signals when it sees other human-shaped objects stating a different opinion from yourself.” 3 likes
“To die was not to leave the world, not to escape somewhere else; it was the simultaneous change of every piece of yourself into nothing.” 2 likes
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