Fabric of Reality Book Club
Discussion started by Zelalem Mekonnen
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With an account, you can revise, criticize, and comment on ideas, and submit new ideas.We discuss David Deutsch’s first book, The Fabric of Reality.
Can't think of how it could be otherwise. Do you have any examples of inexplicit explanations?
Let's fuck with your intuitions a little bit:
Say "stop" when it's no longer an explanation:
Didactic chapter in plain English with examples and edge cases, distilled into a concise technical note with formal definitions, invariants, and pseudocode.
Literate program interleaving prose and code, or a heavily commented Python implementation with docstrings and tests.
The same code stripped of comments/tests and then minified or obfuscated (e.g., Python one‑liner, obfuscated C), up through esolangs and formalisms (Brainfuck, untyped lambda calculus with Church numerals, SKI combinators).
Operational specifications with minimal labels (Turing machine tables), then hand‑written assembly without labels and self‑modifying tricks, down to raw machine code bytes/hex and binary blobs with unknown ISA or entry point.
The same bits recast as DNA base mapping with unknown block codec, unknown compression, encrypted archives indistinguishable from noise, arbitrary bitstrings for unspecified UTMs, or physical media (flux/RF) without modulation specs.
Haha not a programmer so understood maybe half of it, but I think I see what you mean. There'll always be inexplicit parts to every explanation. My concept of explanations is that there must be at least some explicit part for it to be called an explanation. That's why genes aren't explanations.
My point is rather that it's not so clean a line between explicit and inexplicit. You're a doctor, so imagine the steps being something like:
- Extensive description of patient's symptoms, test results, conclusion, etc, in English.
- Same as above but mostly made out of quick notes by attending doctors and nurses.
- Only a collection of test names and test results. Test results accompanied by Chinese.
- Just a collection of numbers coming out of tests, without saying which test.
Arguably all the information is always there, and can be read off, but with increasing difficulty, requiring you to learn another language, or do a series of deductions.
Yeah nice, seems true. There's no objective explicit/inexplicit ratio for knowledge, it depends on the person's background knowledge.
The important thing is to be able to make predictions about images on the astronomers’ photographic plates, frequencies of spectral lines, and so on, and it simply doesn’t matter whether we ascribe these predictions to the physical effects of gravitational fields on the motion of planets and photons [as in pre-Einsteinian physics] or to a curvature of space and time.
I’m getting conflicting results online for this quote. Some sources that quote the same passage say singular ‘effect’, others use the plural like Deutsch does.
I don’t have access to the original text, so I can’t say for sure if this is possibly a slight misquote or if different people are just quoting different editions.
I don't think a gene has problems. It does not have ideas.
A gene doesn’t have problems in any conscious sense, but it always faces the problem of how to spread through the population at the expense of its rivals.
Maybe that answers your question, Erik.
How could we integrate that vision with Popper's definition (paraphrased): a tension, inconsistency, or unmet explanatory demand that arises when a theory clashes with observations, background assumptions, or rival theories, thereby calling for conjectural solutions and critical tests.
The rival theories and clashes sound like competition between genes – or more precisely, between the theories those genes embody.
Basically, genes contain guesses (in a non-subjective sense) for how to spread through the population at the expense of their rivals. Those guesses are met with selection pressure and competition.
Yeah, thanks! Are ideas also guesses of how to survive in the mind and across substrates, or is there more to ideas?
In the neo-Darwinian view, any replicator’s primary ‘concern’ is how to spread through the population at the expense of its rivals. This view is what Dawkins (IIRC) calls the gene’s eye view, and it applies to ideas as much as it does to genes. Any adaptation of any replicator is primarily in service of this concern.
So I think the answer to your question, “Are ideas also guesses of how to survive in the mind and across substrates …?”, is ‘yes’.
Most people (except in Alzheimer's, etc.) don't run out of memory in the brain. If there's no scarcity for the space of ideas, why do they have to compete?
Everyone has scarce memory. Everyone’s brain has limited storage space.
Of course, memory isn't infinite. But most people don't seem to run out of it in their lifetimes. Is it more accurate to say that ideas compete for working memory, which is scarcer?
I have speculated in the past that ideas compete for attention, but they also compete for any kind of memory, be it something like RAM or hard-disk memory. The RAM-like memory in the brain is presumably closely related to working memory, if not the same.
The reason most people don’t (permanently) run out memory (of either kind) isn’t that memory isn’t scarce but that there’s a pruning mechanism in the mind. And again, there’s competition. That competition can involve predatory ideas which disassemble the source code of other ideas and use it for themselves because that’s cheaper than to construct source code from scratch.
Makes sense, thanks Dennis. Constant pruning is the explanation that retains scarcity and competition, while making the brain seem to have much more memory than it does.
That pruning mechanism is what constitutes natural selection in the mind.
The pruning mechanism is part of it, but there’s more. Again, there’s also competition between ideas and even predatory behavior that can result in the elimination of ideas. All such phenomena taken together constitute natural selection in the mind.
Wait, do you view the pruning as separate from the mere competition of ideas, or simply its hardware consequences?
Wait, do you view the pruning as separate from the mere competition of ideas…?
Yes. When I say ‘pruning’, I’m referring to a specific mechanism of a meta algorithm in the mind. For more details, see my book A Window on Intelligence, I think chapter 5. There is no such meta algorithm in biological evolution.
Alright, I remember the meta algorithm from your book but can't recall if you adress this criticism: If there's no need for a meta algorithm in biological evolution, why must there be one for the evolution of ideas?
I don’t think the meta algorithm is necessary for the evolution of ideas. After all, there is no meta algorithm across minds, yet ideas (memes) evolve across minds. Inside a single mind, the meta algorithm is inherited from our non-creative ancestors, where (among other things) it acted as a fail safe against erroneous behaviors.
Wait, I've probably misunderstood but in #2228 it seemed like you thought pruning was needed for scarcity, which is needed for competition between ideas and their evolution.
And you equated pruning with the meta algorithm.
And now you say the meta algoritm/pruning is not needed for the evolution of ideas?
Since you’re a doctor, Erik, let me ask: is there a possibility Alzheimer’s could be explained in terms of bad software? Correct me if I’m wrong, but it seems like the prevailing view is limited to bad hardware.
Hmm never thought of that, interesting! I think since the disease involves continuous loss of brain volume, hardware decay seems like the best explanation.
In general I think it makes sense to speak of diseases in neurology (e.g. Alzheimer's, Parkinsons, stroke) as bad hardware and psychiatric disease as bad software. But it could very well be that some of those diagnoses are miscategorised.
Not a doctor. But it's not hard for me to imagine untainted memory but a script with an error such that it can't manage to look up the information.
Yeah that's definitely a possible medical condition, e.g. in psychosis or after having ECT. Don't think it's the best explanation for Alzheimer's though, where the loss of brain volume is so apparent.
Deutsch says our body of knowledge keeps growing both deeper—better explanations—and wider—new fields, more facts, rules of thumb. He thinks depth is winning. It might be interesting to assess what that balance looks like in 2025.
Perhaps it’s premature, but I’d love to discuss:
why DD thinks the four strands already amount to a theory of everything
why DD presents quantum mechanisms as having already subsumed general relativity
what other (proto)strands we could envision and why they are indeed a meaningful addition to the 4 strands
Yeah (3) is interesting. Constructor theory is the contender I can think of for a future fifth strand. Any other suggestions?
Yes, but that inhirent in biology (evolution) right? I see it as part of the evolutionary strand for this reason.
In that same vein, why couldn't we class biology (evolution) under epistemology?
I still see epistemology as distinct, and I'll try to make my case for it. Epistemology explains how humans create explanatory knowledge — unlike biological evolution, which also produces knowledge, but not explanations. Explanatory knowledge is special because it allows us to understand the world. Deutsch even suggests that this kind of knowledge tends toward convergence — a unified theory of everything — implying a deep connection between reality and its capacity to be explained.
Economics, on the other hand, isn’t distinct in the same way. It deals with trade-offs and scarcity — principles already fundamental to biology. Life itself is about managing limited resources and the trade-offs that come with them. Evolution, in turn, discovered increasingly effective strategies for doing so — including cooperation, exchange, and other relationships between and across lifeforms that facilitate these trades.
May have misunderstood, but do you mean that explanatory knowledge corresponds to truth, whereas biological/evolutionary knowledge doesn't?
I think that was refuted by Lucas Smalldon and others: https://barelymorethanatweet.com/
Undestanding does not flow from explanatory knowledge the way you imply. I understand Dutch and English, but a lot of my understanding of it is inexplicit.
You say that trade-offs and scarcity are fundamental to biology. I agree, and this implies economics as a more fundamental science than biology or evolution. It still applies in our computer models, where biological details may not.
Guess: We can generalise economics further and let it be subsumed by epistemology.
When we choose to try to solve certain problems, we always make trade-offs from a place of scarcity. Likewise, our conjectures wouldn't evolve without the competition enabled by scarcity in our minds.
I currently see Constructor Theory as a meta-theory. A different mode of explanation. But it raises an interesting question: does CT actually qualify as a deeper theory than the four strands? Even if we were to express all four strands in constructor-theoretic terms, that alone wouldn’t make it explain more or have greater reach. So when would it truly deserve to be considered a strand/theory of everything?
By the same logic, wouldn't neo-Darwinism also disqualify as a strand, since it's subsumed by Popperian epistemology?
Consequently (they say), whether or not it was ever possible for one person to understand everything that was understood at the time, it is certainly not possible now, and it is becoming less and less possible as our knowledge grows.
If something already isn’t possible, how could it become less possible?
Isn’t possibility a binary thing? As opposed to difficulty, which exists in degrees.