Chins are funny. Every human has one; no human knows why.
No other primate (extinct or extant) has a chin. Everyone else’s mouth curves inward at the bottom, making chins a curiously and uniquely human trait. There are a few popular ideas for why chins evolved, but none of them holds water. Or food. None of them holds whatever’s in your mouth like your trusty chin does. The proposals that say chins served an evolutionary purpose (whether mechanical or sexual) don’t hold up to scrutiny, while what seems like the best idea (that chins were simply exposed as our ancestors’ faces shrunk) is difficult to prove. It’s a chin-undrum. (That’s conundrum, but chin.)
All I know, really, is that when I’m outside in a blizzard, I need to keep my chin covered because of our old friend the square-cube law. Chins have a lot of surface area, so they lose heat quickly, but they only get warmed at the same rate as the rest of the body (which has less surface area compared to its volume than a chin does). Combine those and it means that chins, ears, fingers, toes, and noses lose heat faster than it’s supplied.
Emperor Penguins have learned the square-cube law, too; it’s why they huddle by the thousands through the Antarctic winter instead of letting every individual fend for themselves. Each member of the huddle has some of their body exposed to the wind and some exposed to other (warm) penguins. Less heat escapes to the wind than it would if everyone were alone. This shielding works so well, in fact, that the penguins at the center of the huddle can get too warm! They move away from the middle to cool off.
When they move to the edge, those on the edge get to shuffle their way toward the middle. They get to warm up and stay alive after bearing the brunt of the cold, the same way members of a household might rotate shoveling duty when it’s really cold outside so that no one gets frostbitten.
This is one where any pair would have been fun to dive into. But I’ve been programming a lot recently, so blueprint it is.
Blueprints are plans, originally for buildings but now metaphorically for just about anything. Real architectural blueprints, though, are always at a certain scale—dimensions are 1/10 the length they’ll be in the final building, say. And that scale is critical. the strength of a material goes up with its cross-sectional area (the square of its length) while weight increases with volume (the cube of length). This critical relationship between squares and cubes is known, sensibly enough, as the square-cube law. It means materials get heavier faster than they get stronger. A building built 15 times larger than a 1/10-scale blueprint will collapse like a house of toothpicks.
This isn’t just about engineering, either. An elephant is not simply a large mouse. The square-cube law means that an elephant shrunk to inches long would have absurdly thick legs, while a mouse inflated to 20 feet long couldn’t stand. (In another consequence of the same law, the giant mouse would explode while the tiny elephant froze.) (Also, it helps us know how big dinosaurs were.) In a computer, of course, you can make materials and legs any strength, regardless of size. But too-small supports will look weird: You can’t have giant simulated animals walking on string-bean legs. Even giraffe legs are thicker than you might imagine.
Chaos is another tricky thing to do in a computer. Chaotic systems turn tiny changes at one moment into enormous divergences later on, and computers have to make small approximations all the time—whether that’s something like rounding 1/3 to 0.3 or breaking time into discrete moments. But on the other hand, the advent of fast computers was one reason chaos was discovered when and how it was: Chaotic systems are often much easier to study in a computer than experimentally, since experiments always have little uncertainties. This is why fluid dynamics is dominated by simulations.
I could say more about chaos and I’m sure I will eventually, but suffice to say for now that one of the early chaotic systems studied both experimentally and computationally, was, of course, a dripping faucet.
I miss recess. Also Recess. That theme really brings me back.
A recess is more than a great TV show from my childhood. It’s another word for a hidden gap. Recesses surround us, in bookcases and closets and cabinets. But recesses get much smaller than that, too. The proteins in our bodies fold into complicated shapes that no one understands even today, but we know enough to say the recesses in those structures are part of how proteins do their work.
Smaller still, surfaces are pitted and pocked all over the place on atomic and molecular scales. These bumps (and larger ones) are the source of friction, as we saw a couple posts ago. But let’s zoom out from that scale to a paper towel. We find recesses there, too. If you take a maker and make a dot on a paper towel, you’ll see the dot expand even after you take the marker away. This happens as ink flows in and out of recess between the fibers of the paper towel, pulled along those fibers by capillary action: Each molecule gets pulled forward by the fiber a little in front of it and pulls the molecules behind it along, too. (That’s loosely stated, but we can’t do everything all the time.)
Capillary action is why notes written in pen on paper towels start out neat and end up looking like ransom notes. Paper towels are made to be particularly good at pulling liquid along the fibers. That way, the part that’s actually touching the source of the liquid can keep sucking up more instead of saturating, and the paper towel cleans up whatever spilled. Paper, though, is made a little differently. Its fibers don’t shuttle liquid around quite as much and ink generally sits more on top than soaking in. But ink still bleeds a bit, even with the best of papers. If you don’t want closed es and gloomy qs, write in pencil on stationery.
Of course, pencil smudges. But that’s neither here nor there. (If anything, it’s both.)
Growing up, I thought adults who said “nor’easter” were bad at saying “northeaster”. I was wrong.
Just about all nor’easters—a sort of winter tropical storm, for those not from New England—count as blizzards. But a blizzard is more than a bad snowstorm. It’s a winter storm with high winds and enough snow in the air to keep visibility fairly low for at least three hours. Since light bounces off snowflakes, the more snow in the air, the closer something has to be for most its light to get to you without being bounced all over the place first. Whether that snow came from the clouds or it was picked up from the ground by wind doesn’t come into play in defining the storm.
Snow muffles sounds just as it bounces light, but for a different reason. The coordinated vibration of molecules that forms a sound jiggles water molecules in the snow around and becomes random vibrations (heat). (Also, winter storms tend to have funny temperature distributions that refract sound upwards and away from our ears.) During a blizzard, with howling winds and sound-absorbing snow everywhere, you can only hear really loud stuff from afar—loud stuff like thundersnow.
But sounds dissipate with distance even without snow. Some of the coordinated vibration of a sound wave always turns into heat as sound travels through the air. Higher frequencies are especially susceptible: They start with more rapid vibrations at the outset, so it’s easy for those to get out of sync and become random noise. Also, it takes more energy to sustain more rapid vibrations, so the sound runs out of energy sooner. This means treble dissipates too quickly to be heard from a great distance. The farther you are from something, as a result, the lower-pitch it tends to sound. (Side note: This is also why people who live upstairs from you always tend so sound like they’re stomping and grunting rather than squeaking.) (Second side note: This is tangentially related to something I talked about for the Museum of Science [24:17 in that video is the question and then my answer], where you can tell the angle of a lightning bolt from the sound of the thunder.)
What’s true for natural processes is also true for natural processes that humans have a hand in—there’s nothing to be gained in separating us from nature, after all. So if you’re far from an outdoor concert, you’ll hear more bass drums, low voices, and low guitar chords. And if you’re close to a tank when it fires out of the big barrel, you’ll hear a wide spectrum of noises. But if you’re a ways away, you’ll mainly hear a boom. Hopefully you’re far away in the right direction.
A cutlass is a sword, and swords have to be sharp. (It’s also a kind of car, which has to be sharp in a different way to cut through the air.) But we’ve been sharpening things far longer than we’ve had swords. Members of our genus have sharpened tools for millions of years. We’ve gotten good at it by this point. We’ve gotten so good at it that the Ancient Greek philosopher Democritus used a knife to reason his way to a fledgeling atomic theory.
Here’s what he said: When you cut into an apple, some of the apple ends up on either side of the knife. But the only way the knife can get between the two parts of the apple is if there was already space between them. So there must be bits of matter with empty space between them. QED—or whatever the Ancient Greek version of QED was. It’s not quite the argument we’d use today, but it’s neat, even when summarized as fleetingly as I just did.
Modern atomic theory came from the dual directions of physics—where atoms explained temperatures and sounds and a bunch else—and chemistry—where atoms explained reactions. Chemical reactions seemed to consume the input elements in certain ratios, and we now know it’s because a certain number of atoms of one element would always react with the same number of atoms of the other: Two oxygens and one carbon became carbon dioxide, say.
Fire, as we know from the other day, is a complex collection of chemical reactions involving oxygen. But fires need two other ingredients. They need heat and, of course, they need fuel.
When I proposed to my now-wife, I didn’t have a ring. Finding the ring size of someone who doesn’t wear many rings seemed hard, getting and keeping one in secret seemed harder, and I didn’t see the point when really I just wanted to marry her. She said yes anyway. (I think she liked me.)
That made me her fiancé, but, in one of English’s few remaining vestiges of nouns with grammatical gender, it made her my fiancée. Most fiancés have fiancées with diamond rings, both because of some pretty impressive marketing and because diamonds are well suited for finger adornment. When cut right, diamond can exhibit total internal reflection, where (loosely speaking in a way that would make some people mad) an incoming ray of light bounces around multiple times inside the diamond before coming out. This property makes diamonds seem to glint and shine from all angles, which in turn makes them glimmer when they’re on something that moves around a lot—like a finger.
Some diamonds are synthetic and some form from asteroid impacts, but let’s ignore them so that I can say: Diamonds are forged deep within the planet, when buried carbon is squeezed by immense pressures from something like colliding (or newly forming!) tectonic plates. The incredible pressure shoves carbon atoms into their most rigid possible arrangement—so tightly and perfectly packed that it’s nearly impossible to move an atom out of the way. This makes diamonds incredibly hard to scratch. But it also makes them relatively rare, at least compared to normal rocks. So as cool as it would be to live in a diamond house, it’s just not happening.
Instead, we make homes out of much more common stuff. We use wood where there’s a lot of wood. We use stones, sand, and water (and other stuff) to make concrete. We use mud and clay to make bricks. We use sand again to make windows. All of them make for a pretty sturdy shelter. And, honestly, I’d rather have privacy than a diamond house, anyway.
Science is beautifully interwoven. The light we use to understand the Big Bang is the same kind of light we use to heat up leftovers. The telescopes we use to see distant galaxies focus light the same way an inflated balloon can focus sound. The low pitch of rumbling thunder sounds the way it does for the same reason upstairs neighbors tend to sound like grumbling brutes rather than dainty mice. And so on. The more deeply we investigate the inner workings of our material universe, the more interconnected its processes and its physics seem to be.
In this blog, I want to explore some of those interconnections. My plan is simple: Every week, I’m going to go to this Pictionary word generator, set “Number of Things” to 3, “Category” to either Medium or Hard, depending on how I’m feeling that week, and hit “Generate Pictionary Words.” I’ll pick two of the words that pop up and write a little arc of physical connections from one to the other. I’ll post a screenshot of the result from the website, too, just to keep myself honest.
The goal, I suppose, is to be somewhere between an educational read and a good, regular writing exercise. Hopefully it turns out to be both. I can’t promise perfect rigor; I’ll do my best to source claims and double-check my writing, but there’s always a chance I read something wrong in my haste or just write something wrong. I certainly won’t always use semicolons correctly. Why expect anything more from my physics? If someone reads the blog and points out an error, I’ll correct it in the next post—and if that error breaks the chain from one topic to the next, I’ll find another way to connect them. I’ll also thank them for reading, because that’s about the nicest thing a person can do when another humans writes something.
On that note, whether you’ve read this far or skimmed to the end of this introductory post, thank you for reading.