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Rationality: From AI to Zombies #4
Mere Reality
Mere Reality is the fourth book contained in the ebook Rationality: From AI to Zombies, by Eliezer Yudkowsky. It focuses on practical and philosophical questions related to science and the character of physical law.
Mere Reality contains six sequences of thematically connected essays, plus the stand-alone essay A Technical Explanation of Technical Explanation. These are all collected in the Rationality: From AI to Zombies ebook, but the essay names below also link to the original blog posts.
The previous book in the series is The Machine in the Ghost, and the next book is Mere Goodness.
Mere Reality contains six sequences of thematically connected essays, plus the stand-alone essay A Technical Explanation of Technical Explanation. These are all collected in the Rationality: From AI to Zombies ebook, but the essay names below also link to the original blog posts.
The previous book in the series is The Machine in the Ghost, and the next book is Mere Goodness.
- GenresNonfiction
457 pages, ebook
First published January 1, 2015
4 people are currently reading
74 people want to read
About the author
Eliezer Yudkowsky
48 books1,946 followersEliezer Yudkowsky is a founding researcher of the field of AI alignment and played a major role in shaping the public conversation about smarter-than-human AI. He appeared on Time magazine's 2023 list of the 100 Most Influential People In AI, was one of the twelve public figures featured in The New York Times's "Who's Who Behind the Dawn of the Modern Artificial Intelligence Movement," and has been discussed or interviewed in The New Yorker, Newsweek, Forbes, Wired, Bloomberg, The Atlantic, The Economist, The Washington Post, and many other venues.
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Displaying 1 - 5 of 5 reviews
May 7, 2024
Not quite as good as #1 or #3, more on the level of #2. Mostly just provided interesting food for thought, but no revelatory insights (especially in the latter half of the book). Engines of Cognition was really interesting, but doesn't seem all that useful. I think I've always been something of a physical reductionist, but the discussion here really helped me refine my thinking and give a name to the idea, group it all under a coherent heading. I think the most important thing I got out of this book was a new view of what math and science really are - I used to ask questions like "isn't it crazy that the universe actually behaves in accordance with what math predicts?" whereas now it seems obvious that math is actually just a formal system whose axioms and rules of inference we're tweaking to predict reality. Math doesn't pop out of nowhere a priori and reality just happens to follow - math is built to follow reality. Science is similar, an extension of math, just extra rules and axioms. There's still a bit of a bootstrapping problem there, but things are a lot clearer now.
Notes:
• One system cannot gain information about another subsystem without doing thermodynamic work on it - otherwise you could build a Maxwell's demon and break the first law of thermodynamics.
○ Knowledge from faith is incompatible with this formulation of the laws of physics
○ Similarly, this also seems to rule out any a priori reasoning that could be used to make empirical predictions
• The "Mind Projection Fallacy": projecting properties of your mind onto the real world, as if they were real things that exist outside your head.
○ Aristotelian categories (just a cognitive tool to group clusters)
○ Inherent desirability of gold (If I want it, it must be intrinsically desirable, right? @Spain ~1500)
○ Probability (mathematical tool to predict things too complicated to do mechanistically)
• "reductionism" here means that there is nothing that can't be predicted from fundamental laws, with enough compute. There's nothing about a 747 that can't be predicted at the quark level, it's just impractical to do it that way.
○ "The laws of physics do not contain distinct additional causal entities that correspond to lift or airplane wings, the way that the mind of an engineer contains distinct additional cognitive entities that correspond to lift or airplane wings."
• Science is the hard magic system of our world. A university STEM department is like their magic school
• Telling someone (or telling yourself) to ignore a certain argument doesn't work.
○ "When a driver said he had liability insurance, experimental jurors awarded his victim an average of four thousand dollars more than if the driver said he had no insurance. If the judge afterward informed the jurors that information about insurance was inadmissible and must be ignored, jurors awarded an average of thirteen thousand dollars more than if the driver had no insurance"
○ That is a really bad sign for rational discourse huh
○ Makes the Gish gallop (and first-mover advantage in general) way stronger
• "It is always best to think of reality as perfectly normal. Since the beginning, not one unusual thing has ever happened. The goal is to become completely at home in a quantum universe. Like a native. Because, in fact, that is where you live."
• Particle/wave duality is a historical artifact, not a true thing about the universe. Particle intuition and wave intuition both kind of capture quantum behavior sometimes, but the best fitting model is entirely different from either.
• Quantum configurations are another example of an ontological shift (scientific revolution) that makes accurate predictions where old tools (particles and waves) tried really hard but ultimately just couldn't hack it
• Kolmogorov complexity and Solomonoff induction proven equivalent to Minimum Message Length! Both support the "minimize rules" rather than "minimize entities" version of Occam's Razor
• Science is built to not have to trust rationality (to a certain extent). Just go directly to the source and see what Nature actually does, rather than trying to armchair it out.
Freud got only the top part of the Bayes factor, Popper swung too far and focused on only the bottom
Notes:
• One system cannot gain information about another subsystem without doing thermodynamic work on it - otherwise you could build a Maxwell's demon and break the first law of thermodynamics.
○ Knowledge from faith is incompatible with this formulation of the laws of physics
○ Similarly, this also seems to rule out any a priori reasoning that could be used to make empirical predictions
• The "Mind Projection Fallacy": projecting properties of your mind onto the real world, as if they were real things that exist outside your head.
○ Aristotelian categories (just a cognitive tool to group clusters)
○ Inherent desirability of gold (If I want it, it must be intrinsically desirable, right? @Spain ~1500)
○ Probability (mathematical tool to predict things too complicated to do mechanistically)
• "reductionism" here means that there is nothing that can't be predicted from fundamental laws, with enough compute. There's nothing about a 747 that can't be predicted at the quark level, it's just impractical to do it that way.
○ "The laws of physics do not contain distinct additional causal entities that correspond to lift or airplane wings, the way that the mind of an engineer contains distinct additional cognitive entities that correspond to lift or airplane wings."
• Science is the hard magic system of our world. A university STEM department is like their magic school
• Telling someone (or telling yourself) to ignore a certain argument doesn't work.
○ "When a driver said he had liability insurance, experimental jurors awarded his victim an average of four thousand dollars more than if the driver said he had no insurance. If the judge afterward informed the jurors that information about insurance was inadmissible and must be ignored, jurors awarded an average of thirteen thousand dollars more than if the driver had no insurance"
○ That is a really bad sign for rational discourse huh
○ Makes the Gish gallop (and first-mover advantage in general) way stronger
• "It is always best to think of reality as perfectly normal. Since the beginning, not one unusual thing has ever happened. The goal is to become completely at home in a quantum universe. Like a native. Because, in fact, that is where you live."
• Particle/wave duality is a historical artifact, not a true thing about the universe. Particle intuition and wave intuition both kind of capture quantum behavior sometimes, but the best fitting model is entirely different from either.
• Quantum configurations are another example of an ontological shift (scientific revolution) that makes accurate predictions where old tools (particles and waves) tried really hard but ultimately just couldn't hack it
• Kolmogorov complexity and Solomonoff induction proven equivalent to Minimum Message Length! Both support the "minimize rules" rather than "minimize entities" version of Occam's Razor
• Science is built to not have to trust rationality (to a certain extent). Just go directly to the source and see what Nature actually does, rather than trying to armchair it out.
Freud got only the top part of the Bayes factor, Popper swung too far and focused on only the bottom
June 15, 2022
Some highlights from this book:
205 If You Demand Magic, Magic Won’t Help
Presumably most readers of these novels see themselves in the protagonist’s shoes, fantasizing about their own acquisition of sorcery. Wishing for magic. And, barring improbable demographics, most readers of these novels are not scientists. Born into a world of science, they did not become scientists. What makes them think that, in a world of magic, they would act any differently?
181 Universal Fire
Matches catch fire because of phosphorus. Phosphorus is highly reactive; pure phosphorus glows in the dark and may spontaneously combust. Phosphorus is thus also well-suited to its role in adenosine triphosphate, ATP, your body’s chief method of storing chemical energy. ATP is sometimes called the “molecular currency.” It invigorates your muscles and charges up your neurons. Almost every metabolic reaction in biology relies on ATP, and therefore on the chemical properties of phosphorus. If a match stops working, so do you. You can’t change just one thing.
202 Joy in the Merely Real
If we cannot take joy in things that are merely real, our lives will always be empty.
201 Savannah Poets
What men are poets who can speak of Jupiter if he were like a man, but if he is an immense spinning sphere of methane and ammonia must be silent? That’s a real question, what kind of poet can write about Jupiter the god, but not Jupiter the immense sphere?
------
189 Dissolving the Question
Many philosophers share a dangerous instinct: If you give them a question, they try to answer it. Like, say, “Do we have free will?” The dangerous instinct of philosophy is to marshal the arguments in favor, and marshal the arguments against, and weigh them up, and publish them in a prestigious journal of philosophy, and so finally conclude: “Yes, we must have free will,” or “No, we cannot possibly have free will.”
191 Righting a Wrong Question
When you are faced with an unanswerable question—a question to which it seems impossible to even imagine an answer—there is a simple trick that can turn the question solvable. Compare: “Why do I have free will?” “Why do I think I have free will?” The nice thing about the second question is that it is guaranteed to have a real answer, whether or not there is any such thing as free will.
236 Privileging the Hypothesis
In large answer spaces, attention without evidence is more than halfway to belief without evidence.
--------
207 The Beauty of Settled Science
And thinking you can jump right into the frontier, when you haven’t learned the settled science, is like trying to climb only the top half of Mount Everest (which is the only part that interests you) by standing at the base of the mountain, bending your knees, and jumping really hard (so you can pass over the boring parts).
209 Is Humanism a Religion Substitute?
When someone sets out to write an atheistic hymn—“Hail, oh unintelligent universe,” blah, blah, blah—the result will, without exception, suck. Why? Because they’re being imitative. Because they have no motivation for writing the hymn except a vague feeling that since churches have hymns, they ought to have one too. And, on a purely artistic level, that puts them far beneath genuine religious art that is not an imitation of anything, but an original expression of emotion.
229 Quantum Explanations
Talking to aspiring young physicists about “wave/particle duality” is like starting chemistry students on the Four Elements.
249 No Safe Defense, Not Even Science
Of the people I know who are reaching upward as rationalists, who volunteer information about their childhoods, there is a surprising tendency to hear things like, “My family joined a cult and I had to break out,” or, “One of my parents was clinically insane and I had to learn to filter out reality from their madness.” My own experience with growing up in an Orthodox Jewish family seems tame by comparison but it accomplished the same outcome: It broke my core emotional trust in the sanity of the people around me.
221 Zombies! Zombies?
Native Chinese speakers can remember longer digit sequences than English-speakers. Chinese digits are all single syllables, and so Chinese speakers can remember around ten digits, versus the famous “seven plus or minus two” for English speakers.
225 Belief in the Implied Invisible
Lex parsimoniae: Entia non sunt multiplicanda praeter necessitatem. That was Occam’s original formulation, the law of parsimony: Entities should not be multiplied beyond necessity.
Interlude: An Intuitive Explanation of Bayes’s Theorem
Karl Popper’s falsificationism—this is the old philosophy that the Bayesian revolution is currently dethroning. Karl Popper’s idea that theories can be definitely falsified, but never definitely confirmed, is yet another special case of the Bayesian rules.
205 If You Demand Magic, Magic Won’t Help
Presumably most readers of these novels see themselves in the protagonist’s shoes, fantasizing about their own acquisition of sorcery. Wishing for magic. And, barring improbable demographics, most readers of these novels are not scientists. Born into a world of science, they did not become scientists. What makes them think that, in a world of magic, they would act any differently?
181 Universal Fire
Matches catch fire because of phosphorus. Phosphorus is highly reactive; pure phosphorus glows in the dark and may spontaneously combust. Phosphorus is thus also well-suited to its role in adenosine triphosphate, ATP, your body’s chief method of storing chemical energy. ATP is sometimes called the “molecular currency.” It invigorates your muscles and charges up your neurons. Almost every metabolic reaction in biology relies on ATP, and therefore on the chemical properties of phosphorus. If a match stops working, so do you. You can’t change just one thing.
202 Joy in the Merely Real
If we cannot take joy in things that are merely real, our lives will always be empty.
201 Savannah Poets
What men are poets who can speak of Jupiter if he were like a man, but if he is an immense spinning sphere of methane and ammonia must be silent? That’s a real question, what kind of poet can write about Jupiter the god, but not Jupiter the immense sphere?
------
189 Dissolving the Question
Many philosophers share a dangerous instinct: If you give them a question, they try to answer it. Like, say, “Do we have free will?” The dangerous instinct of philosophy is to marshal the arguments in favor, and marshal the arguments against, and weigh them up, and publish them in a prestigious journal of philosophy, and so finally conclude: “Yes, we must have free will,” or “No, we cannot possibly have free will.”
191 Righting a Wrong Question
When you are faced with an unanswerable question—a question to which it seems impossible to even imagine an answer—there is a simple trick that can turn the question solvable. Compare: “Why do I have free will?” “Why do I think I have free will?” The nice thing about the second question is that it is guaranteed to have a real answer, whether or not there is any such thing as free will.
236 Privileging the Hypothesis
In large answer spaces, attention without evidence is more than halfway to belief without evidence.
--------
207 The Beauty of Settled Science
And thinking you can jump right into the frontier, when you haven’t learned the settled science, is like trying to climb only the top half of Mount Everest (which is the only part that interests you) by standing at the base of the mountain, bending your knees, and jumping really hard (so you can pass over the boring parts).
209 Is Humanism a Religion Substitute?
When someone sets out to write an atheistic hymn—“Hail, oh unintelligent universe,” blah, blah, blah—the result will, without exception, suck. Why? Because they’re being imitative. Because they have no motivation for writing the hymn except a vague feeling that since churches have hymns, they ought to have one too. And, on a purely artistic level, that puts them far beneath genuine religious art that is not an imitation of anything, but an original expression of emotion.
229 Quantum Explanations
Talking to aspiring young physicists about “wave/particle duality” is like starting chemistry students on the Four Elements.
249 No Safe Defense, Not Even Science
Of the people I know who are reaching upward as rationalists, who volunteer information about their childhoods, there is a surprising tendency to hear things like, “My family joined a cult and I had to break out,” or, “One of my parents was clinically insane and I had to learn to filter out reality from their madness.” My own experience with growing up in an Orthodox Jewish family seems tame by comparison but it accomplished the same outcome: It broke my core emotional trust in the sanity of the people around me.
221 Zombies! Zombies?
Native Chinese speakers can remember longer digit sequences than English-speakers. Chinese digits are all single syllables, and so Chinese speakers can remember around ten digits, versus the famous “seven plus or minus two” for English speakers.
225 Belief in the Implied Invisible
Lex parsimoniae: Entia non sunt multiplicanda praeter necessitatem. That was Occam’s original formulation, the law of parsimony: Entities should not be multiplied beyond necessity.
Interlude: An Intuitive Explanation of Bayes’s Theorem
Karl Popper’s falsificationism—this is the old philosophy that the Bayesian revolution is currently dethroning. Karl Popper’s idea that theories can be definitely falsified, but never definitely confirmed, is yet another special case of the Bayesian rules.
October 21, 2025
This collection of essays from the LessWrong blog touch a variety of topics.
Yudkovsky, with his usual curiosity, love of mathematics, and hatred of religion, uses different angles to attack the *truth* and *reality*.
This is actually a good question. What is the difference between *true* and *real*?
Follow some explorations, like the difference between science and magic, the sacred and the mundane, cognitive biases (it would not be LessWrong otherwise) and what constitutes intelligence. I was also delighted to finally read about zombies (and giant lookup tables). A lot of those essays dabble in physics, and especially quantum physics. Yudkovsky extensively writes about the many worlds theory, why quantum physics feels weird, the importance of mathematics to study physics... My own grandfather was a physics researcher and would probably have provided the same advice. Start with mathematics and build from there.
But wait! There's more! There are also whole articles about epistemology (science has to be falsifiable and testable, what constitutes an hypothesis, how to formulate an experiment etc.). If you read Karl Popper before, this will not be very new, but it is explained in a pretty didactic (and fun) way. Lots of examples, as usual in those essays, will make sure to keep you engaged and entertained.
I do not agree with the not-so-subtle ideas regarding libertarianism, cryogenics and disparaging religious people (complete with a long-drawn critique of Einstein for believing in a higher power). Yudkovsky has a really big ego, and sometimes it makes him unsufferable to read. I am pretty big on the whole "let us respect other people's convictions, as long as they are not actively harming others and themselves". Thomas Bayes, who formulated the theorem Yudkovsky is so fond of, was a Presbyterian minister. He was really, really religious - and obviously, a great mathematician and thinker, too.
Anyways. Despite this rant, I really enjoyed reading through this book. Yudkovsky makes me think about a lot of different things. Some of them I know (or rediscovered). Some of them I am now very curious about. I also like his style, even if it is a little bit on the dramatic side. At this stage, it is a given that I *will* read the Sequences until the end. It will not be a waste of my time.
Yudkovsky, with his usual curiosity, love of mathematics, and hatred of religion, uses different angles to attack the *truth* and *reality*.
This is actually a good question. What is the difference between *true* and *real*?
Follow some explorations, like the difference between science and magic, the sacred and the mundane, cognitive biases (it would not be LessWrong otherwise) and what constitutes intelligence. I was also delighted to finally read about zombies (and giant lookup tables). A lot of those essays dabble in physics, and especially quantum physics. Yudkovsky extensively writes about the many worlds theory, why quantum physics feels weird, the importance of mathematics to study physics... My own grandfather was a physics researcher and would probably have provided the same advice. Start with mathematics and build from there.
But wait! There's more! There are also whole articles about epistemology (science has to be falsifiable and testable, what constitutes an hypothesis, how to formulate an experiment etc.). If you read Karl Popper before, this will not be very new, but it is explained in a pretty didactic (and fun) way. Lots of examples, as usual in those essays, will make sure to keep you engaged and entertained.
I do not agree with the not-so-subtle ideas regarding libertarianism, cryogenics and disparaging religious people (complete with a long-drawn critique of Einstein for believing in a higher power). Yudkovsky has a really big ego, and sometimes it makes him unsufferable to read. I am pretty big on the whole "let us respect other people's convictions, as long as they are not actively harming others and themselves". Thomas Bayes, who formulated the theorem Yudkovsky is so fond of, was a Presbyterian minister. He was really, really religious - and obviously, a great mathematician and thinker, too.
Anyways. Despite this rant, I really enjoyed reading through this book. Yudkovsky makes me think about a lot of different things. Some of them I know (or rediscovered). Some of them I am now very curious about. I also like his style, even if it is a little bit on the dramatic side. At this stage, it is a given that I *will* read the Sequences until the end. It will not be a waste of my time.
May 5, 2022
This has been my least-favourite instalment in the series so far. That probably explains why I've been slogging away at it for two years now. Or perhaps the fact that I've been sporadically slogging through is why I enjoyed it less. It's excessively long — about double the length of most other books in The Sequences.
The earlier essays examine the nature of truth and the beauty of reality, which is largely a defence of reductionism and an exploration of the idea that reality is “mundane.” What followed was a series of painfully esoteric essays on P Zombies and a severe bludgeoning on why Many Worlds is so obviously more plausible than Quantum Decoherence from a Bayesian perspective. The book then returns to its earlier form with the essays on science and rationality, which were fascinating and thought-provoking — particularly as someone currently attempting novel scientific research.
The book ends with A Technical Explanation of Technical Explanations, a 16000-word monster that is both deeply insightful and crushingly extensive. I was relieved to be done with it and with this instalment as a whole.
Sections in Book IV: Mere Reality
O Lawful Truth
P Reductionism 101
Q Joy in the Merely Real
R Physicalism 201
S Quantum Physics and Many Worlds
T Science and Rationality
Section Q (Joy in the Merely Real) and Section T (Science and Rationality) are the real gold of this book, in my opinion. But the standout essays were probably Einstein’s Speed, That Alien Message, Mind Projection Fallacy, and Mundane Magic. (But there are some other good ones that don't spring to mind).
The earlier essays examine the nature of truth and the beauty of reality, which is largely a defence of reductionism and an exploration of the idea that reality is “mundane.” What followed was a series of painfully esoteric essays on P Zombies and a severe bludgeoning on why Many Worlds is so obviously more plausible than Quantum Decoherence from a Bayesian perspective. The book then returns to its earlier form with the essays on science and rationality, which were fascinating and thought-provoking — particularly as someone currently attempting novel scientific research.
The book ends with A Technical Explanation of Technical Explanations, a 16000-word monster that is both deeply insightful and crushingly extensive. I was relieved to be done with it and with this instalment as a whole.
Sections in Book IV: Mere Reality
O Lawful Truth
P Reductionism 101
Q Joy in the Merely Real
R Physicalism 201
S Quantum Physics and Many Worlds
T Science and Rationality
Section Q (Joy in the Merely Real) and Section T (Science and Rationality) are the real gold of this book, in my opinion. But the standout essays were probably Einstein’s Speed, That Alien Message, Mind Projection Fallacy, and Mundane Magic. (But there are some other good ones that don't spring to mind).
February 20, 2019
Made me curious about the world we live in.
Displaying 1 - 5 of 5 reviews