On the importance of staring directly into the sunIt's also important to poke the heart of a dead pigeon
There's something very weird about the timeline of scientific discoveries. For the first few thousand years, it’s mostly math. Maybe a bunch of math nerds hijacked the list, but it's pretty obvious that humans figured out a lot of math before they figured out much else. The Greeks had the beginnings of trigonometry by ~120 BCE. Chinese mathematicians figured out the fourth digit of pi by the year 250. In India, Brahmagupta devised a way to “interpolate new values of the sine function” in 665, and by this point we're already at mathematics that I no longer understand. Meanwhile, we didn't discover things that seem way more obvious until literally a thousand years later. It's not until the 1620s, for instance, that English physician William Harvey figured out how blood circulates through animal bodies by, among other things, spitting on his finger and poking the heart of a dead pigeon. We didn't really understand heredity until Gregor Mendel started gardening in the mid-1800s, we didn't grasp the basics of learning until Ivan Pavlov started feeding his dogs in the early 1900s, and we didn't realize the importance of running randomized-controlled trials until 1948. Oh, and for 13 centuries, people thought that rotting meat turns into maggots, until Francesco Redi did this:
What took us so long? How did all this low-hanging fruit go unplucked for centuries? Our ancestors weren't stupid—they were absolutely nailing it in math, racking up centuries of top-notch numbers stuff, even while they were like , “I hope my meat doesn't rot and turn into maggots.” A very straightforward theory of how science works is “we discover things in order from easiest to hardest.” But what makes something hard to discover? I don't mean impossible to discover—you can't see the rings of Saturn without a telescope, for example. I mean cases where it seems like we have everything we need to make a discovery, and yet we take centuries to make it. Why does that happen? I think I have an answer, but we must unfortunately look for it in the toilet. HOW DOES A TOILET WORKHere's one of my favorite psychology studies of all time. You bring people into the lab, and you ask them, “Do you know how a toilet works?” And they say “Uhh yes, I'm not an idiot.” And then you go “Okay, could you please write down, step by step, how a toilet works.” And then you ask them to explain something that requires knowledge of toilets, like “How does pressing the lever on the side of the toilet cause the bowl to empty and then refill again to a certain level?” What participants learn in this study is that, to their horror, they don't really know how a toilet works, at least not nearly as well as they thought they did. This isn't specific to toilets—you can get it with everything from spray bottles to helicopters. Here's one from me: I realized recently that I don’t know how things dry. I know that things dry, of course—I’m not an idiot! But why do they dry? If you leave a wet towel hanging in the bathroom, eventually it won’t be wet anymore. Where does the water go? Into the air, I assume, but I thought liquid water is only supposed to become gas when it gets hot enough. This trustworthy-seeming website informs me it's because temperature is only the average amount of energy in a volume of water, and individual water molecules can have way more or less energy than that because they're all moving around randomly, and so by chance some are going to pick up enough energy to slip their bonds and rocket off into the air.¹ Psychologists have a name for this tendency to think we understand things better than we do: the “illusion of explanatory depth.” We call it an illusion because we live inside a proto-paradigm where we catch people making mistakes and go “aha! a bias!” and then publish a paper on it. (...he said, having recently published a paper called “The Illusion of Moral Decline”.) But this particular illusion is a feature, not a bug. In fact, we can't live without it. Think of it this way: for most of human history, we didn't know why things fall down. People trip, cups spill, buildings topple, and nobody had any good explanations for this, or at least not any true ones. If you didn't have an illusion of explanatory depth, you'd spend your days dumbfounded: “Why do things fall?? Why do you return to earth when you jump?? What's up with clouds—they don't seem to fall at all!! Why do some things fall when in water and some things don't?? Why can birds rise by flapping their wings, but I can't rise by flapping my arms??” You can't live your life if you're always getting stuck on mysteries like this. You'd get so mesmerized by the inexplicability of your porridge falling into your bowl and bubbles rising in your water that you'd forget to eat or drink and you'd die. That's why we need the illusion of explanatory depth: most things have to feel like they make sense, even if they don't, so that we can get on with the business of living. And indeed, people born before the discovery of gravity understood this whole falling business exactly as well as they needed in order to survive. They knew that they'd fall and die if they walked off a cliff, that the things they throw in the air will fall down on people's heads, and that houses tip over if they aren't built properly. Maybe they thought they understood it better than they actually did, but for their purposes, they understood it perfectly well. In fact, I humbly submit that, despite all our progress, the average human today understands the things-falling-down problem only a tiny bit better than the earliest humans did. Take me as a test case: if you asked me why things fall down, I'd go, smugly, “Gravity!” But that's not an explanation. I could go a little deeper: “Well, everything with mass exerts an invisible force on other things, which pulls those things closer. More mass, more force.” But why do things have this invisible force? How do they exert it? Why does it make things come closer? I understand that someone could probably answer those questions, but I cannot. To me, they're just some arbitrary rules of the great board game of life, much like they were to all of my ancestors. SMACK ME IN THE FACE AND TELL ME I KNOW NOTHINGOkay, so an illusion of explanatory depth is extremely important to staying alive. It does, unfortunately, have a downside: it fools you into thinking the universe isn't full of mysteries. This, I think, explains the curious course of our scientific discovery. You might think that we discover things in order from most intuitive to least intuitive. No, thanks to the illusion of explanatory depth, it often goes the opposite way: we discover the least obvious things first, because those are things that we realize we don't understand. That would fit with our incredible ancient progress in mathematics, because math is not obvious. Here's an example: could you please tell me the volume of this figure?
Unless you're a math whiz, I assume the answer does not spring to mind. Maybe you get a sense of , “I think I learned how to do this in high school, I bet I could get it if I thought for a little bit.” Or maybe, like me, you just get a sense of despair. Either way, there's no illusion of explanatory depth here; this problem absolutely smacks you in the face with the realization that you don't know the answer, and it would at least take some work to figure out. And that's exactly what you need to discover something—to realize that you don't know it yet. Perhaps that's why the ancient Egyptians nailed this one ~4,000 years ago! I'm sure that progress in math still requires intuition and insight. (Indeed, the mathematician Henri Poincaré reports that he came up with Fuschian groups—whatever those are—suddenly and almost magically while he was getting on a bus.) But math, perhaps more so than any other intellectual pursuit, emits very strongly what we might call ignorance signals, signs that there's something you don't know. Maybe it's all the numbers and symbols, the funny shapes, the level of abstraction, the amount of stuff you have to hold in working memory, the heaviness you feel in your head when doing mental math—whatever it is, it seems to have helped us do a lot of good math very early in our intellectual history. Other subjects, however, emit fewer ignorance signals. Compare this mathematical discovery from the second century:
With this physics discovery from 1586:
The first one is a method of evaluating polynomials, and I don't even know what it means to evaluate a polynomial (“Hey, nice polynomial you got there”?) The second one is an experiment showing that heavier things and lighter things fall at the same rate, which seems like the most obvious experiment in the world. So why did we only discover it 12 centuries later? The answer, I believe, is that we had an illusion of explanatory depth for weight but not for polynomials. It makes perfect intuitive sense that heavier things should fall faster—after all, it's harder to hold them up! Most people never encounter a situation where they have to know whether one thing will fall faster than another; if you knock over a full glass and a half-full glass, for instance, they'll both be empty glasses rather quickly. Plus, some things obviously fall slowly, like feathers and flower petals, so there's a precedent for things falling at different speeds. So why bother tossing stuff off the Leaning Tower of Pisa? If that didn't satisfy your curiosity and you also happened to be born after 322 BCE, you had an excellent guide for explaining why things fall down: Aristotle. According to him, things fall down because the human world is made of four elements, each with its natural place: earth at the bottom, then water, then air, then fire. Things move in the physical world when they're forced out of their natural order—earth in water will sink, air in water will rise. This sounds silly to us today, but as the physicist Carlo Rovelli explains in this terrific article, Aristotle actually did a great job:
So yes, Aristotle's system suggests that heavy things should fall faster than lighter things because they have more “natural motion” toward their rightful place. This turns out to be wrong. But it was very hard to notice why it was wrong because Aristotle's physics mostly made sense otherwise. There simply weren't enough ignorance signals to make it seem reasonable to check whether heavy things actually fall faster. I mean, if you stepped into the Pantheon (built in the second century, a few hundred years after Aristotle) and beheld its magnificent architecture that stayed up perfectly well—and still does—you probably don't find yourself thinking, “We need a new system of physics.”² GO BLIND, GET HIGH, INVENT PSYCHOLOGYWhich brings us to psychology. No offense to the mathematicians, but most of us find people way more interesting than numbers. So why did we spend centuries studying numbers, while we've only recently started studying people? Maybe it's because psychology is the domain with the deepest illusion of explanatory depth. You open your eyes and see stuff, and although this requires lots of complicated calculations and several anatomical miracles, it doesn't feel mysterious at all. You hear a song and remember the lyrics years later, and this seems totally natural. You and your spouse watch the same movie and have different opinions about it, and the explanation seems obvious: you're right and they're wrong. It's so easy to accept the wild workings of the mind at face value, or to generate ad hoc explanations for them, that you might never realize you have no idea how any of this works. While philosophers have occasionally made these illusions deeper by spinning up spurious theories of psychology, I bet most of our illusion of explanatory depth for psychology comes preinstalled or is acquired quickly through experience. The brain's greatest trick is convincing you that it's not doing any tricks at all, blocking your conscious access to most of what it does and then giving you a perfectly reasonable account for what's going on behind the curtain:
Overcoming this expertly-maintained illusion requires a big push, which is perhaps why we didn't do it until a German guy stared directly into the sun. Most histories of psychology as an experimental science begin with Gustav Fechner setting up a psychophysical laboratory in the middle of the 1800s. What those histories often fail to mention is that Fechner began as a physicist, but then he suffered a mental breakdown after going blind because he stared at the sun for too long. He was trying to study afterimages, those glowing spots you get in your field of vision when you look at something bright and then look away. If you do that too many times, it turns out, you fry your retinas and get really depressed for three years. Fechner was completely blind for a while, and then he underwent treatment by moxibustion, which is where you put a weed called mugwort on someone's skin and then set it on fire. Besides leaving scars, this treatment somehow ruined his digestion, and he almost starved to death before a family friend figured out a way of preparing ham in a way that he liked; the friend said the idea came to her in a dream. Fechner eventually recovered, but the experience turned him weird. Maybe it was the mugwort, which has psychedelic properties according to this seemingly-trustworthy website³, which would make sense, because when Fechner regained his sight, he acted like someone who had been doing a lot of shrooms.⁴ His first post-blindness project was a book about the mental life of plants. Then he decided to invent a new religion. From the biography that appears at the beginning of the English translation of his landmark Elements of Psychophysics:
Fechner wrote seven books on the topic, but they never caught on, so he decided he should give his new philosophy a “scientific foundation.” For reasons not entirely clear to me now, he thought the most important thing to do was set up a laboratory and do things like: show people two lights that are almost equally bright and then ask them whether they can tell the difference between the lights. I don't know if this ultimately provided vindication for Fechner's philosophy, but he did discover that the “intensity of our sensation increases as the logarithm of an increase in energy,” and thus laid down, for the first time in history, a scientific law of psychology. Fechner's sun-addled realization helped get people to start both a) wondering about how the mind works, and b) believing that you could study it empirically. He and his friends Ernst Weber and Wilhelm Wundt turned the University of Leipzig into the hot place to be for psychology, where they trained most of the prominent psychologists of that generation, who in turn trained most of the prominent psychologists of the next generation. A good chunk of experimental psychologists working today are descendants of Fechner and his friends, including me.⁵ Which is to say: the field of experimental psychology exists today at least in part because a German guy stared at the sun for too long. What Fechner needed, of course, was not to get his eyeballs cooked, but to get his illusion of explanatory depth dispelled. Virtually every human who had ever existed before him felt content enough with their knowledge of the mind to not bother learning anything more about it. A few people had been curious enough to at least advance a few theories, but they didn't think it was necessary to gather data. (Immanuel Kant, in fact, had written only 75 years before that gathering data was hopeless; we would never learn much more about psychology than we already knew.) We could not make progress in psychology until we understood how little we actually understood, and perhaps going blind from staring at the sun, lying in bed for three years, inhaling some burning mugwort, and inventing a new religion makes you realize there are a lot of questions we haven't answered yet. Fechner's intellectual descendants set about answering those questions, many of which could have been answered long before, but nobody had thought to do so. One of the most influential studies in developmental psychology, for example, is about whether babies can recognize faces; you can replicate it with some cardboard, a mirror, and a baby. Actually, while you've got the baby handy, you can also replicate the Little Albert experiment—an early proof of concept that humans can be classically conditioned—by putting on a Santa Claus mask and banging some pots and pans to scare the baby, but please don't do this. The original study on “learned helplessness” used an electrified floor to shock dogs; you could conceivably replicate it with a more ancient way of torturing a dog, but please don't do this either. We didn't need modern technology or advanced mathematics to study these topics—in fact, someone living hundreds or even thousands of years ago probably could have done a half-decent version of almost every study on this random list of famous psychology experiments. The answers were simply waiting for us to go looking for them. PLEASE FEED ME 11 SLICES OF BREAD PER DAYIt's easy to look back on the history of our discoveries and believe that we've moved from an era of mysteries to an era of certainties. No: we've always lived in an era of mysteries, and we've always lived in an era of undue certainties. We know more than our ancestors did, yes, but far, far less than we think we know. So where are our illusions of explanatory depth still the thickest? One is in psychology, where I've argued that we're stuck doing things in ways that used to work but don't anymore, or in ways that never worked at all. Another is probably in dentistry, where we have pretty bad evidence for almost everything. I'd wager that “dark matter” and “dark energy” are going to end up looking silly, but what do I know. The biggest illusions of explanatory depth might be in nutrition and weight loss, where lots of people believe things very strongly for no good reason. For instance, I grew up staring at this image on the back of my cereal box:
That's right: the government said I should eat eleven slices of bread per day.⁶ Gulping down half a loaf of Wonderbread every day sounds crazy to many people now, but those people also believe many things that will probably sound crazy sometime soon. Eat a lot of fat/no don't! Eat a lot of meat/no don't! Eat only at certain times/no, eat whenever you want! I was once at a dinner where a professor politely refused a plate of potatoes because she was “trying to lose weight,” and I had to giggle because I had just read about a bunch of people who lost weight eating only potatoes. At least there are few things we all agree on—I mean, nobody thinks you can lose weight by eating croissants all day! (Oh, wait.)⁷ Look: we don't really know what's going on here, which is fine. What's not fine is believing that we know what's going on, because then we'll never do what it takes to actually figure it out. The first step in solving the mysteries is believing in the mysteries. WAKE UP AND SMELL THE MUGWORTIt's hard to overcome your illusions of explanatory depth, just like it's hard to hold your breath for a long time—our urge to make sense of things and our urge to breathe are both there for good reason, and our brains don't trust us to turn those urges off at will. It takes practice. Fortunately, we have lots of role models. And now we can better understand what made them so successful: their ability to understand how little they understood. Francesco Redi, the man behind the rotting meat experiment, describes it well:
Unfortunately, the illusion of explanatory depth takes many shapes. Our ancestors believed that the Bible or Aristotle had everything figured out. We got over that, but now some people believe that science itself has everything figured out. We've done all the easy stuff, this line of thinking goes, and so it's only the hardest discoveries that remain. Oh, how I hate this idea! It's just the illusion of explanatory depth dressed in a lab coat. And this incarnation is the worst of all. If you think you know how a toilet works when you actually don't, whatever—you still know enough to go #2 without embarrassing yourself. But if you think you know how science works when you actually don't, you're sunk—you literally can't do it if you think it's impossible. Somewhere out there is our modern-day version of the rotting meat experiment. There are ideas that are simply too obvious to see, obscured by our theories that seem to make more sense than they actually do. Wherever our convictions are strong and our evidence is weak, there is a breakthrough waiting to happen. And then hundreds of years from now, our descendants will look back and say, “I can't believe it took them so long!” So wake up and smell the mugwort! It's a new day and the sun is shining—time to go stare directly at it! 1 I accept this explanation in the same way I begrudgingly accept the long list of arbitrary rules that precedes every new, complicated board game. “Settlements and cities may only be placed at the corner of the terrain hex—never along the edges.” Okay, fine. “When placing a greenery tile, you increase the oxygen level, if possible, and also your TR. If you can’t raise the oxygen level you don’t get the increase in TR either.” Got it. “Water molecules can randomly gain enough energy to evaporate.” Sure, whatever! 2 Thomas Kuhn writes beautifully about this. He's trying to figure out why people had followed Aristotle's system of physics for so long when it seems so dumb, and then finally it clicks for him that Aristotle's system makes a lot of sense from the inside:
3 It also, apparently, cures farts. 4 Drugs show up curiously often in the history of scientific breakthroughs. 6 This was, in fact, merely a passing phase in federal dietary guidelines, which began by specifying five food groups, which then became seven food groups, then four, then six, then up to five, then back to four, then six again, then five with seven subgroups, and most recently six with 10 subgroups. 7 “All you have to do is burn more calories than you consume,” is perhaps the most smugly dispensed piece of dieting advice, but it's true only in the most useless sense, like “all you have to do to make your car run is to fix your car.” For more, see these three great posts from fellow bloggers ExFatLoss and SMTM.
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On the importance of staring directly into the sun
Thursday, 2 October 2025
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