The key idea is that every soldier must separately track the two messages, the forward-message and backward-message, and add them together only at the end. You never add any soldiers from the backward-message you receive to the forward-message you pass back. Indeed, the total number of soldiers is never passed as a message—no one ever says it aloud.
An analogous principle operates in rigorous probabilistic reasoning about causality. If you learn something about whether it’s raining, from some source other than observing the sidewalk to be wet, this will send a forward-message from Rain to Sidewalk wet and raise our expectation of the sidewalk being wet. If you observe the sidewalk to be wet, this sends a backward-message to our belief that it is raining, and this message propagates from Rain to all neighboring nodes except the Sidewalk wet node. We count each piece of evidence exactly once; no update message ever “bounces” back and forth. The exact algorithm may be found in Judea Pearl’s classic Probabilistic Reasoning in Intelligent Systems: Networks of Plausible Inference.
So what went wrong in phlogiston theory? When we observe that fire is hot, the Fire node can send a backward-evidence to the Phlogiston node, leading us to update our beliefs about phlogiston. But if so, we can’t count this as a successful forward-prediction of phlogiston theory. The message should go in only one direction, and not bounce back.
Alas, human beings do not use a rigorous algorithm for updating belief networks. We learn about parent nodes from observing children, and predict child nodes from beliefs about parents. But we don’t keep rigorously separate books for the backward-message and forward-message. We just remember that phlogiston is hot, which causes fire to be hot. So it seems like phlogiston theory predicts the hotness of fire. Or, worse, it just feels like phlogiston makes the fire hot.
Until you notice that no advance predictions are being made, the non-constraining causal node is not labeled “fake.” It’s represented the same way as any other node in your belief network. It feels like a fact, like all the other facts you know: Phlogiston makes the fire hot.
A properly designed AI would notice the problem instantly. This wouldn’t even require special-purpose code, just correct bookkeeping of the belief network. (Sadly, we humans can’t rewrite our own code, the way a properly designed AI could.)
Speaking of “hindsight bias” is just the nontechnical way of saying that humans do not rigorously separate forward and backward messages, allowing forward messages to be contaminated by backward ones.
Those who long ago went down the path of phlogiston were not trying to be fools. No scientist deliberately wants to get stuck in a blind alley. Are there any fake explanations in your mind? If there are, I guarantee they’re not labeled “fake explanation,” so polling your thoughts for the “fake” keyword will not turn them up.
Thanks to hindsight bias, it’s also not enough to check how well your theory “predicts” facts you already know. You’ve got to predict for tomorrow, not yesterday. It’s the only way a messy human mind can be guaranteed of sending a pure forward message.
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1. Judea Pearl, Probabilistic Reasoning in Intelligent Systems: Networks of Plausible Inference (San Mateo, CA: Morgan Kaufmann, 1988).
34
Semantic Stopsigns
And the child asked:
Q: Where did this rock come from?
A: I chipped it off the big boulder, at the center of the village.
Q: Where did the boulder come from?
A: It probably rolled off the huge mountain that towers over our village.
Q: Where did the mountain come from?
A: The same place as all stone: it is the bones of Ymir, the primordial giant.
Q: Where did the primordial giant, Ymir, come from?
A: From the great abyss, Ginnungagap.
Q: Where did the great abyss, Ginnungagap, come from?
A: Never ask that question.
Consider the seeming paradox of the First Cause. Science has traced events back to the Big Bang, but why did the Big Bang happen? It’s all well and good to say that the zero of time begins at the Big Bang—that there is nothing before the Big Bang in the ordinary flow of minutes and hours. But saying this presumes our physical law, which itself appears highly structured; it calls out for explanation. Where did the physical laws come from? You could say that we’re all a computer simulation, but then the computer simulation is running on some other world’s laws of physics—where did those laws of physics come from?
At this point, some people say, “God!”
What could possibly make anyone, even a highly religious person, think this even helped answer the paradox of the First Cause? Why wouldn’t you automatically ask, “Where did God come from?” Saying “God is uncaused” or “God created Himself” leaves us in exactly the same position as “Time began with the Big Bang.” We just ask why the whole metasystem exists in the first place, or why some events but not others are allowed to be uncaused.
My purpose here is not to discuss the seeming paradox of the First Cause, but to ask why anyone would think “God!” could resolve the paradox. Saying “God!” is a way of belonging to a tribe, which gives people a motive to say it as often as possible—some people even say it for questions like “Why did this hurricane strike New Orleans?” Even so, you’d hope people would notice that on the particular puzzle of the First Cause, saying “God!” doesn’t help. It doesn’t make the paradox seem any less paradoxical even if true. How could anyone not notice this?
Jonathan Wallace suggested that “God!” functions as a semantic stopsign—that it isn’t a propositional assertion, so much as a cognitive traffic signal: do not think past this point. Saying “God!” doesn’t so much resolve the paradox, as put up a cognitive traffic signal to halt the obvious continuation of the question-and-answer chain.
Of course you’d never do that, being a good and proper atheist, right? But “God!” isn’t the only semantic stopsign, just the obvious first example.
The transhuman technologies—molecular nanotechnology, advanced biotech, genetech, Artificial Intelligence, et cetera—pose tough policy questions. What kind of role, if any, should a government take in supervising a parent’s choice of genes for their child? Could parents deliberately choose genes for schizophrenia? If enhancing a child’s intelligence is expensive, should governments help ensure access, to prevent the emergence of a cognitive elite? You can propose various institutions to answer these policy questions—for example, that private charities should provide financial aid for intelligence enhancement—but the obvious next question is, “Will this institution be effective?” If we rely on product liability lawsuits to prevent corporations from building harmful nanotech, will that really work?
I know someone whose answer to every one of these questions is “Liberal democracy!” That’s it. That’s his answer. If you ask the obvious question of “How well have liberal democracies performed, historically, on problems this tricky?” or “What if liberal democracy does something stupid?” then you’re an autocrat, or libertopian, or otherwise a very very bad person. No one is allowed to question democracy.
I once called this kind of thinking “the divine right of democracy.” But it is more precise to say that “Democracy!” functioned for him as a semantic stopsign. If anyone had said to him “Turn it over to the Coca-Cola corporation!,” he would have asked the obvious next questions: “Why? What will the Coca-Cola corporation do about it? Why should we trust them? Have they done well in the past on equally tricky problems?”
Or suppose that someone says “Mexican-Americans are plotting to remove all the oxygen in Earth’s atmosphere.” You’d probably ask, “Why would they do that? Don’t Mexican-Americans have to breathe too? Do Mexican-Americans even function as a unified conspiracy?” If you don’t ask these obvious next questions when someone says, “Corporations are plotting to remove Earth’s oxygen,” then “Corporations!” functions for you as a semantic stopsign.
Be careful here not t
o create a new generic counterargument against things you don’t like—“Oh, it’s just a stopsign!” No word is a stopsign of itself; the question is whether a word has that effect on a particular person. Having strong emotions about something doesn’t qualify it as a stopsign. I’m not exactly fond of terrorists or fearful of private property; that doesn’t mean “Terrorists!” or “Capitalism!” are cognitive traffic signals unto me. (The word “intelligence” did once have that effect on me, though no longer.) What distinguishes a semantic stopsign is failure to consider the obvious next question.
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35
Mysterious Answers to Mysterious Questions
Imagine looking at your hand, and knowing nothing of cells, nothing of biochemistry, nothing of DNA. You’ve learned some anatomy from dissection, so you know your hand contains muscles; but you don’t know why muscles move instead of lying there like clay. Your hand is just . . . stuff . . . and for some reason it moves under your direction. Is this not magic?
The animal body does not act as a thermodynamic engine . . . consciousness teaches every individual that they are, to some extent, subject to the direction of his will. It appears therefore that animated creatures have the power of immediately applying to certain moving particles of matter within their bodies, forces by which the motions of these particles are directed to produce derived mechanical effects . . . The influence of animal or vegetable life on matter is infinitely beyond the range of any scientific inquiry hitherto entered on. Its power of directing the motions of moving particles, in the demonstrated daily miracle of our human free-will, and in the growth of generation after generation of plants from a single seed, are infinitely different from any possible result of the fortuitous concurrence of atoms . . . Modern biologists were coming once more to the acceptance of something and that was a vital principle.
—Lord Kelvin1
This was the theory of vitalism; that the mysterious difference between living matter and non-living matter was explained by an élan vital or vis vitalis. élan vital infused living matter and caused it to move as consciously directed. élan vital participated in chemical transformations which no mere non-living particles could undergo—Wöhler’s later synthesis of urea, a component of urine, was a major blow to the vitalistic theory because it showed that mere chemistry could duplicate a product of biology.
Calling “élan vital” an explanation, even a fake explanation like phlogiston, is probably giving it too much credit. It functioned primarily as a curiosity-stopper. You said “Why?” and the answer was “Élan vital!”
When you say “Élan vital!,” it feels like you know why your hand moves. You have a little causal diagram in your head that says:
But actually you know nothing you didn’t know before. You don’t know, say, whether your hand will generate heat or absorb heat, unless you have observed the fact already; if not, you won’t be able to predict it in advance. Your curiosity feels sated, but it hasn’t been fed. Since you can say “Why? Élan vital!” to any possible observation, it is equally good at explaining all outcomes, a disguised hypothesis of maximum entropy, et cetera.
But the greater lesson lies in the vitalists’ reverence for the élan vital, their eagerness to pronounce it a mystery beyond all science. Meeting the great dragon Unknown, the vitalists did not draw their swords to do battle, but bowed their necks in submission. They took pride in their ignorance, made biology into a sacred mystery, and thereby became loath to relinquish their ignorance when evidence came knocking.
The Secret of Life was infinitely beyond the reach of science! Not just a little beyond, mind you, but infinitely beyond! Lord Kelvin sure did get a tremendous emotional kick out of not knowing something.
But ignorance exists in the map, not in the territory. If I am ignorant about a phenomenon, that is a fact about my own state of mind, not a fact about the phenomenon itself. A phenomenon can seem mysterious to some particular person. There are no phenomena which are mysterious of themselves. To worship a phenomenon because it seems so wonderfully mysterious is to worship your own ignorance.
Vitalism shared with phlogiston the error of encapsulating the mystery as a substance. Fire was mysterious, and the phlogiston theory encapsulated the mystery in a mysterious substance called “phlogiston.” Life was a sacred mystery, and vitalism encapsulated the sacred mystery in a mysterious substance called “élan vital.” Neither answer helped concentrate the model’s probability density—make some outcomes easier to explain than others. The “explanation” just wrapped up the question as a small, hard, opaque black ball.
In a comedy written by Moliére, a physician explains the power of a soporific by saying that it contains a “dormitive potency.” Same principle. It is a failure of human psychology that, faced with a mysterious phenomenon, we more readily postulate mysterious inherent substances than complex underlying processes.
But the deeper failure is supposing that an answer can be mysterious. If a phenomenon feels mysterious, that is a fact about our state of knowledge, not a fact about the phenomenon itself. The vitalists saw a mysterious gap in their knowledge, and postulated a mysterious stuff that plugged the gap. In doing so, they mixed up the map with the territory. All confusion and bewilderment exist in the mind, not in encapsulated substances.
This is the ultimate and fully general explanation for why, again and again in humanity’s history, people are shocked to discover that an incredibly mysterious question has a non-mysterious answer. Mystery is a property of questions, not answers.
Therefore I call theories such as vitalism mysterious answers to mysterious questions.
These are the signs of mysterious answers to mysterious questions:
First, the explanation acts as a curiosity-stopper rather than an anticipation-controller.
Second, the hypothesis has no moving parts—the model is not a specific complex mechanism, but a blankly solid substance or force. The mysterious substance or mysterious force may be said to be here or there, to cause this or that; but the reason why the mysterious force behaves thus is wrapped in a blank unity.
Third, those who proffer the explanation cherish their ignorance; they speak proudly of how the phenomenon defeats ordinary science or is unlike merely mundane phenomena.
Fourth, even after the answer is given, the phenomenon is still a mystery and possesses the same quality of wonderful inexplicability that it had at the start.
*
1. Silvanus Phillips Thompson, The Life of Lord Kelvin (American Mathematical Society, 2005).
36
The Futility of Emergence
The failures of phlogiston and vitalism are historical hindsight. Dare I step out on a limb, and name some current theory which I deem analogously flawed?
I name emergence or emergent phenomena—usually defined as the study of systems whose high-level behaviors arise or “emerge” from the interaction of many low-level elements. (Wikipedia: “The way complex systems and patterns arise out of a multiplicity of relatively simple interactions.”) Taken literally, that description fits every phenomenon in our universe above the level of individual quarks, which is part of the problem. Imagine pointing to a market crash and saying “It’s not a quark!” Does that feel like an explanation? No? Then neither should saying “It’s an emergent phenomenon!”
It’s the noun “emergence” that I protest, rather than the verb “emerges from.” There’s nothing wrong with saying “X emerges from Y,” where Y is some specific, detailed model with internal moving parts. “Arises from” is another legitimate phrase that means exactly the same thing: Gravity arises from the curvature of spacetime, according to the specific mathematical model of General Relativity. Chemistry arises from interactions between atoms, according to the specific model of quantum electrodynamics.
Now suppose I should say that gravity is explained by “arisence” or that chemistry is an “arising phenomenon,” and claim that as my explanation.
The phrase “emerges from” is a
cceptable, just like “arises from” or “is caused by” are acceptable, if the phrase precedes some specific model to be judged on its own merits.
However, this is not the way “emergence” is commonly used. “Emergence” is commonly used as an explanation in its own right.
I have lost track of how many times I have heard people say, “Intelligence is an emergent phenomenon!” as if that explained intelligence. This usage fits all the checklist items for a mysterious answer to a mysterious question. What do you know, after you have said that intelligence is “emergent”? You can make no new predictions. You do not know anything about the behavior of real-world minds that you did not know before. It feels like you believe a new fact, but you don’t anticipate any different outcomes. Your curiosity feels sated, but it has not been fed. The hypothesis has no moving parts—there’s no detailed internal model to manipulate. Those who proffer the hypothesis of “emergence” confess their ignorance of the internals, and take pride in it; they contrast the science of “emergence” to other sciences merely mundane.
And even after the answer of “Why? Emergence!” is given, the phenomenon is still a mystery and possesses the same sacred impenetrability it had at the start.
A fun exercise is to eliminate the adjective “emergent” from any sentence in which it appears, and see if the sentence says anything different:
Before: Human intelligence is an emergent product of neurons firing.
After: Human intelligence is a product of neurons firing.
Before: The behavior of the ant colony is the emergent outcome of the interactions of many individual ants.
After: The behavior of the ant colony is the outcome of the interactions of many individual ants.
Rationality- From AI to Zombies Page 14