Steve Kass

There is still no good answer to the question “Why can’t we walk straight?”, observed Robert Krulwich’s recorded voice at a recent live taping for Radiolab at The Greene Space. Robert’s observation ressounded¹ today on the “NPR sciencey blog” Krulwich Wonders.

For 80 years, scientists have been trying to explain this tendency to turn when you think you are going straight. … Try as they might, and they’re still trying these experiments, nobody has figured out why we can’t go straight.

When I was a kid, Someone thought they’d figured it out. One’s dominant leg took longer strides, They taught me. I also learned, or maybe inferred, that I should find a leftie to walk with me should I ever need to cross a desert in the fog, at night, or while blindfolded.

But hearing Robert talk about this twice in as many weeks, I realized that They’d been wrong, and that crossing a desert in the fog was not a challenge I’d be ready to meet. (Also, I only then realized that a leftie might not be handy when the challenge arose, anyway.)

Ignoring my sudden and deepening nonplus, I focused on the question. Analogy time.² Robert’s headlineworthy version of the question is an oversimplification of the quandary, but I’ll notwithstand that fact for now.

Why can’t we fly? (Some animals can.) Because we don’t have small bodies, hollow bones, and wings (like some flying-capable animals do); nor do we have really tiny invertebrate bodies and wings (like some other flying-capable animals do).

Why can’t we hear high-pitched sounds? (Some animals can.) Because human ears (unlike the ears of the animals that can) aren’t physically able to convert high-pitched sounds into nerve impulses.

So why can’t we maintain our direction over long distances without a visual point of reference? (Some animals, especially flying-capable ones, can.) Because (unlike those animals) humans never underwent any evolutionary pressure to develop a mechanism to do so?

Robert mentioned one of the trying scientists by name: Jan Sousman. Jan’s article, Walking Straight into Circles, recently appeared in the journal Current Biology (a cornucopia of articles at the titles of which biologists surely titter: Olfaction: When Nostrils Compete; Metastasis: Alone or Together?; Addiction: Flies Hit the Skids; Flagella and Cilia: The Long and the Short of It; and Melanocyte Production: Dark Side of the Schwann Cell).

Jan and his coauthors wrote a wonderful paper. Among many beautiful sentences and figures, they report that their subjects’ “walking trajectories show exactly the kind of behavior that would be expected if the subjective sense of straight ahead were to follow a correlated random walk.” They also mention J. R. R. Tolkien’s The Lord of the Rings: The Two Towers to point out that the belief “that people who get lost end up walking in circles is widespread.”

So “because we can’t” isn’t really such a good answer. Our proprioception (that sixth sense that allows us to touch our noses in the dark when we haven’t had too much to drink) does provide a subjective sense of straight ahead. However, it isn’t very reliable for very far or for very long.`

¹ I initially wrote reappeared, which on rereading, sounded (or more sensibly, looked) wrong, because Robert’s voice never appeared (as in became visible to the eye) in the first place. Unable to solve the Miller Analogy SEE : REAPPEAR :: HEAR: with an existing word, I had to invent the perfect answer: res̈ound (which should appear as the word resound with an umlaut/trema/diaeresis over the s). This answer is in fact all the more perfect (not to mention very unique) for having been invented by a “greater New Yorker.” Unfortunately, as much as I like the idea of using ¨ to estop a preceding prefix from losing its strict meaning, it fails in practical terms. Very few consonants appear in Unicode preëquipped with the dots, and Unicode’s zero-width combining diaeresis, the solution in theory, is unworkably fussy.

² Yay!

Science overload — always a welcome thing — happened at The Greene Space last night. On the menu? Radiolab Live: Symmetry, with guest artist John Cameron Mitchell singing Origin of Love from Hedwig and the Angry Inch.

Hosts Jad and Robert dwove¹ expertly, pointing out many wonderful (mostly asymmetric) sights left and right. Looking-Glass milk, carvone, tartaric acid, and Jimmy Carter, to name a few.

I pulled out my notebook twice during the show: first, to jot down a hairy pun, and second, to sketch a schematic of the cloud chamber I owned as a kid. I’ve retired the pun and won’t divulge it here; it served its intended purpose. (Andy responded, “Ow. Even I’m offended.”) But I have a bit more to say about the cloud chamber.

In my hasty schematic, I labeled the head of the pin AMERICIUM, but subsequent research suggests that it was radium, not americium, on the head of the pin. Fortunately, I never suffered from pica. The kit also contained a chunk of uranium ore.

I didn’t play with the cloud chamber quite as much as I did with some of my other dangerous toys like the Creepy Crawlers Thingmaker (my favorite childhood toy of all, no contest), the Wham-O Air Blaster (which became increasingly dangerous each time my brother thought of something new, like pencils, to fire from it), the Vac-U-Form, the chemistry set — mercury (I especially enjoyed freezing bits of it with dry ice), carbon tetrachloride, ammonium dichromate, and potassium permanganate were among my favorite chemicals — the Slip-’n-Slide, the lawn darts, or the Clackers.

Nor was the Atomic Energy Lab the radium-containing possession I carried with me most often as a child. That distinction goes to the radium-dial watch Dad gave me in junior high school. The watch was stolen from my gym locker one morning in 1970, unfortunately — but perhaps unfortunately for the thief more than for me.

The only radium I know I own any more is in the painted dial of the Jefferson Electric Golden Hour clock in my bedroom. The radium is no doubt decaying apace and will continue to do so for centuries to come. But alas, the zinc sulfide phospor has broken down, and the dial no longer glows.

¹ The verb dweave (past tense dwove) and the noun dwive will be coined in a future installment of “Word of the Day.”

Internet news aggregator robots never leave me alone. Internet news aggregator robots, never leave me alone.

Every day or more, one of the news aggregator robots gets both my attention and my goat. Here’s one of today’s missiles: “CDC: Most Teens Choose to Abstain,” at cbn.com. The first paragraph:

A recent study shows that most teenagers are virgins, contradicting claims from family planning groups that most young people do not abstain from sex and more sex ed should be taught in schools.

Image by Kelley Boone, some rights reserved (CC-BY-SA 2.0)

This kind of blabbery drives me nuts. They might has well have said, “A recent study shows that the earth is flat, contradicting claims from Unitarians that the planets revolve around the sun and astronomy should be taught in schools instead of the Bible,” when in fact a recent study showed no such thing, and even if it had, it wouldn’t contradict what the Unitarians supposedly said. Maybe if I’d been on the debate team I’d know how to respond more effectively.

If I were a fundamentalist Christian who wanted to justify abstinence education, I wouldn’t quote or misquote studies, nor would I attempt to use logic. I’d be honest: “According to my church, the world is flat, most young people abstain from sex, and abstinence should be taught in schools right after study hall and before creationism. That’s what I believe, because faith in the church is my guiding light.”

Studies be damned, science be damned, the church is the ultimate authority. I might have more respect if they put it that way more often. (I would still object if it got to the point of the Constitution be damned and laws be damned.) Why should fundamentalists care a whit about the fact that science is consistent, well-founded, and predictive? Why should they care about evidence from studies and measurements, if faith, not intelligence, is their life’s compass? I can disagree, disapprove, and be dismayed, but I have no appeal. We live on different planets; we grew up in different universes.

Anyway, for readers who might appreciate facts and figures, let me explain the CBN’s vulpigeration.

What is “sex,” anyway? For its study, the CDC defined “sex” to be heterosexual vaginal sexual intercourse¹ only (though the boy need not stay on top). Many English speakers would call a bunch of other things people do naked with others sex, but the CDC’s restrictive definition should suit the Christian Broadcasting Network in two ways. First, this definition doesn’t infringe on the way CBN might define another word, “sodomy.” They might prefer it for that bunch of other things people do naked with each other. Second, it yields higher virgin percentages. As far as the CDC and CBN.com are concerned, you’re a virgin if you haven’t been part of any penis-in-vagina hanky-panky, even if you’ve gotten plenty naked and nasty with one or more hims or hers.

Fact: Most young people do not abstain from sex. (Or “sex.”) Not during their entire youth, which is what CBN.com suggested. According to the CDC study, most (65% of) boys aged 18-19 and most (60% of) girls in the same age group have had heterosexual vaginal sexual intercourse. The CDC numbers suggest that most young people do abstain from sex “sex” until about age 17 or 18, but abstaining until you stop abstaining is not the same thing as abstaining. Using the CBN.com logic, you could say that all people abstain from sex, ’cuz they all do — until they stop, and most stop, as we know from all the babies being born and abortions being performed. Few babies (or aborted fetuses) are incarnate nowadays.

¹ Additional information available on the internet.

While my part of the world was embroiled in a heat wave last week, brutal midwinter cold was gripping Vostok Station high atop the mountains and ice of central Antarctica. At times, it was more than two hundred degrees colder in Vostok than it was here in the U.S. Northeast.

A few days earlier, by coincidence, I’d installed the last of my three SodaStream carbonators and ordered two refills. On the 7^th, in the middle of the heat wave, the local distributor exchanged my empties, leaving me with four pounds of freshly compressed carbon dioxide and two questions.

1. Is four pounds of CO₂ a lot compared to the amount already inside my condo, not counting the basement?
2. When the temperature drops below -109.3 °F, the sublimation point of carbon dioxide, does it snow dry ice?

I’m happy to share with you the answers.

1. Yes, quite a lot. The volume of my condo, not counting the basement, is about 7,000 cubic feet, or about 200,000 liters, and while I have far too much junk, my place is still mostly full of air. And like air most places, the air in my condo is mostly nitrogen, oxygen, and argon, and about 400 parts per million of it (by volume) is carbon dioxide. My condo contains a fifth of a million liters of air, I figured, so I’ve got a fifth of 400 liters of CO₂, or about 80 liters.

At room temperature, CO₂ is effectively an ideal gas, so I don’t need Google to convert 80 liters to moles, which is going to help with the calculation. A mole of an ideal gas at standard temperature and pressure¹ occupies 22.4 liters, so I’m living with about 4 moles of CO₂. (And maybe a few voles, too, but that’s not relevant here.) A mole of any chemical compound means 600 sextillion molecules of the stuff. Fortunately, we don’t have to do any sextillionary arithmetic. What makes a mole a mole is that it’s the number of Daltons (neutron or proton+electron masses, more or less) in a gram, so the mass of a mole of a chemical compound is simply its molecular weight in grams. The molecular weight of CO₂ is² 12+2×16, or 44, so a mole of CO₂ has a mass of about 44 grams or an ounce and a half.

Four moles of CO₂ in my condo — that’s about six ounces, or less than a tenth of what’s squeezed into my two new Sodastream carbonators.

2. No. The temperature -109.3 °F is the sublimation point of CO₂ at one atmosphere. That’s the temperature at which dry ice in your house or cooler chest (which is pure CO₂ solid under an atmosphere of air pressure) sublimates; it’s not the temperature at which CO₂ in plain air would precipitate into “snow.” Carbon dioxide won’t precipitate out of the air unless it’s cooled to the sublimation point for its partial pressure in air. That’s (see above) about 400 millionths of an atmosphere at sea level, and roughly two-thirds of that at Vostok Station, elevation 11,000 feet. Smart guy David R. Cook at Argonne National Laboratory has generously used some tax dollars to spread the word. He proposes that the temperature would have to be much colder than –110 — in fact about 220 degrees below zero on the Fahrenheit scale (and no, that’s not “twice as cold” as -110) for CO₂ to precipitate at Vostok Station.

Typical partial pressures of CO₂ on earth are unfortunately off the scale of the phase diagrams I could find, so I can’t provide more details or confirm what David says. You can, however, see the trend in the phase diagram below. The boundary between the periwinkle and salmon regions is where CO₂ sublimates or “snows.” The lower the pressure, the lower the temperature.

Public domain image from Wikimedia Commons.

The phase diagram also answers a question I didn’t think to ask.

• Are full SodaStream carbonators filled with liquid or gas? Liquid.

They’re about a liter big, which (using the calculations above) translates to an internal pressure of several hundred atmospheres, which is well within the green region. How cool is that? Liquid CO₂ right here in my house.

Call it chemistry or call it physics, this is all great fun.

Related links: How Much CO₂ is in a Bottle of Soda?, The Influence of CO₂ on the Chemistry of Soda, Soda’s Contribution to Global Warming

¹ Standard temperature and pressure is 20 °C and one (sea level) atmosphere of pressure. That’s close enough to the conditions in my condo. Around room temperature, gas expands at a rate of about 1% per 4 °C rise in temperature. It also expands as you climb above sea level, by about 1% for each 300 feet. The second derivatives are small, and the contributions from the partial derivative of volume with respect to temperature and altitude add, so yadda yadda yadda, we’re within a few percent. It was worth a quick thinking through, though.

² There are a some simplifications here, but again, they don’t affect the overall calculation by more than a percent or two. The value 44 assumes that every molecule of CO₂ is made up of the predominant isotopes of carbon and oxygen, carbon 12 and oxygen 16, and that single atoms of these isotopes weigh exactly 12 and 16 Daltons, respectively. The “official” atomic weights as periodically reviewed by IUPAC would be more accurate, and they give a molecular weight of 44.01. The discrepancy reflects the distribution of isotopes on earth as well as other details that probably involve higher physics and chemistry well beyond my understanding. In addition, it would seem to me that this measurement ought to be called the molecular mass, but when measuring any property of such tiny things, you’re going to run up against quantum mechanics and other complications, so I suppose whoever understands all of this can call it what they want.