by BRIAN HALL
“—so now that we’ve established that planets are abundant in the galaxy, the next question is how many of them might be habitable. But since we can’t land a shuttle on any of these planets and open the door and sniff the air, like in Galaxy Quest, we need to devise a series of questions that we can apply to the data we collect from these incredibly distant objects. I want to elaborate a little on some of the excellent points Kasting makes on this subject—”
While he talks, he glances at the box in the corner of his laptop screen which shows him how many students have clicked in: 96 today, out of a total enrollment of 109, so 13 absent. He allows students to miss three of the semester’s twenty-seven lectures without penalty, which means if no student exceeded the limit, an average of 12 students would be missing every class. Of course some students do exceed the limit—on average, about 9 percent—and their grades suffer. He announces at the first lecture that laptops cannot be used in the first eight rows because there are still about a quarter of the students who take notes by hand—these also tend to be the more studious ones—and having someone else’s laptop screen in your field of view can be distracting, especially when that person is chatting on Facebook. Mark isn’t naive, some healthy fraction of the approximately seventy students with open laptops are not paying attention. He doesn’t let himself worry about it. Anyone who can spend all that money on college tuition, or have someone else do it for them, and then ignore what’s taught in their classes is a lost soul, as far as he’s concerned. Merely to satisfy his own curiosity, he sometimes asks a multiple-choice question based on something he has said in the past ten minutes, and after the students hit their iClickers, he throws the results up on the screen as a bar graph. Occasionally there might be a genuine misunderstanding, but usually the 15 percent or so who are laughably off-base—for example, the ones guessing today that the current estimate for the number of planets in the Milky Way is around one million—are right now shopping for spring sweaters or playing Angry Birds or hoping to learn what happened between Audrey and Brendan at the rad party last night. (He is under no illusion that his lingo is up to date. “Rad” probably went out years ago. Maybe Angry Birds, too. And come to think of it, these kids were probably ten when Galaxy Quest was made.)
“—Ward and Brownlee caution us that there may be reasons why Earth is not ‘average’ at all. And what we’re learning right now about other stellar systems suggests that the arrangement of our solar system may also be unusual, perhaps even quite rare. We have to be careful about overusing the Copernican Principle, which assumes that we, as observers, are not in some privileged position. For example, it’s often said, even by astronomers, that our Sun is an average star, but that’s not true. Most stars are part of binary or trinary systems, in which stable planetary orbits are either extremely unlikely or impossible. Sol is more massive than 95 percent of the stars in the Milky Way. Planets in the habitable zones around smaller stars, such as red dwarfs, are tidally locked, which is likely unconducive to life. Stars more massive than Sol, because of the luminosity-mass relationship, have exponentially shorter lifetimes, and also emit a larger fraction of their light as ultraviolet and x-ray radiation. Both of these facts probably make the development of complex life unlikely.”
And on he goes—or maybe, on and on and on he goes—tossing up images on the screen, tossing out iClicker questions, checking his timer against his place in the outline. Sure enough, he falls behind and has to skip over a fascinating bit about the dinosaurs, and another about interstellar travel and planetary resource depletion, which he very much regrets. In the last ten minutes he hurriedly dismantles the Drake Equation, invokes the Fermi paradox and ends with a foreboding speculation about the Great Filter.
If he can find the idea moving that three Jersey barriers might hope to be pretty, it’s probably no surprise that he struggles against being audibly emotional in the lecture’s last minute, which concerns whether humans are alone in the universe, and the chances of their survival as a species. Like his aphasia, this troublesome excess emotionalism plagues him more each year. It is profoundly embarrassing to think that he can move himself to tears with his own words. He steadies himself by focusing on the faces in front of him, many of which seem bored or distracted. Is he being unfair to them? Just as he doesn’t want to become a weepy old man, he doesn’t want to become an old fart, continually comparing the younger generations invidiously to his own.
“—I’m sorry, I see that I’ve gone over five minutes, so I’ll stop there. Remember my office hours are tomorrow, four to six, and Monday, three to five. See you next Tuesday.” They instantly come alive, chatting and bustling toward the doors. Detention’s over, thinks the old fart. He closes his laptop, hits the button to raise the screen.
“Professor?”
Two students with decent questions. One of them he’s talked with before, clearly bright. He is being unfair. Who knows how blank-faced he looked when he was twenty and underslept and absorbed in his own thoughts? Who knows how blank-faced he looks now?
Back in his office, he does what he always does after a lecture, typing up notes on ways he might make it better, maybe reach a greater percentage of those faces. Life in the universe! The fate of humankind! Why can’t he get them as excited as he is? He googles Galaxy Quest and sees it’s much older than he realized: most of his students were only two when it came out, no one has any idea what he’s talking about, it’s a lame attempt at humor anyway—the old man trying to be “with it”—so he cuts it from his notes. (Does anyone say “with it” anymore?)
He often wonders what percentage of his colleagues were first drawn to astronomy when they were kids because they were dying to know if there were aliens on other planets. Scientists are people, too, they pass the Turing test every day, and on the subject of extraterrestrial life, more than any other in astronomy, Mark thinks his colleagues’ speculations are distorted by wishful thinking. Sometimes even serious astronomers, if they’re speaking to the general public, will invoke the enormity of the observable universe and say something like, “There must be life out there, because otherwise think of all that wasted space.” What a foolish thing to say! It would make as much sense to contrast the 100 trillion neutrinos passing unscathed through our bodies each second with the approximately one neutrino during our lifetime that will hit something, and say, “But that can’t be. Think of all those wasted neutrinos.” Or when some astronomers get duped by poetry, and say something along the lines of human intelligence being “a way for the cosmos to know itself.” So, just because we happen to be intelligent, the cosmos somehow wants to be intelligent? Just call the cosmos your personal God and be done with it.
It’s probably hardwired in the human brain, this tendency to see life everywhere. Mark read somewhere that babies see a “face” in anything that’s round and has a couple of buttons on it, like smoke alarms. Humans’ instinctive belief that consciousness exists in other humans is probably an evolutionary advantage, helping the species survive through empathetic cooperation. Mark doubts there would be much selective pressure to limit that instinct merely to other humans, and so people evolved to see gods in the sky and spirits in trees. So Percival Lowell saw canals on Mars. So scientists in the 1940s saw Venus’s eternal cloud cover and imagined a warm, wet world conducive to life. So now we detect subsurface oceans on Europa and Enceladus and envision sea creatures.
Kasting, to his credit, is unusual in openly admitting his bias. In the excerpt Mark had his students read, Kasting writes somewhere—Mark searches the file, finds it—“I am one of those people who, like Carl Sagan, would like to believe that life is widespread in the universe.” Mark flags this, adds a note: Life tends to see life. Maybe he should include a few sentences on this. But where to fit them in? He already doesn’t have enough time to say everything he wants to about the Drake Equation. Sometimes he toys with the notion of devoting an entire lecture to the Drake Equation.
He hates
the Drake Equation.
The textbook Mark uses presents a modified version of the equation, which he finds useful for an introductory course:
Nciv = Nhp x flife x fciv x fnow
To put it in words, the number of civilizations extant in the galaxy today equals the number of habitable planets in the galaxy, times the fraction of those planets on which life has arisen, times the fraction of those planets on which life has progressed to civilization, times the fraction of those planets whose civilization is extant right now. (As opposed to, say, a billion years ago.)
The Drake Equation is the one bit of “math” regarding the search for extraterrestrial intelligence that most people know, if they know anything. And since it’s “math,” they have the feeling it tells them something quantitative. But this would be true only if we had a likely range of values for the various terms, which we don’t. Mark thinks that even a few of his colleagues fall into the trap. They plug in numbers that they know are wild guesses, they acknowledge that the resulting number is also a wild guess, and yet that result is a specific number, and numbers are alluring. To be fair to Frank Drake, a fine astronomer, he intended none of this. He was merely formulating a way to think about the problem.
Just in the last few years astronomers have gotten to the point where they can replace the first term to the right of the equal sign with a number that’s not pure garbage. He’s seen a rough calculation based on data from Kepler, HARPS, et al. that suggests there are around ten billion habitable planets orbiting Sun-like stars in the galaxy. Maybe the true figure is a billion, maybe it’s fifty billion. But at least we now have a range based on real data.
But if you move on to the next term in the equation—the fraction of habitable planets on which life does in fact arise: right here is the trap. We have an equation in front of us, our undergraduate students are listening, or the TED talk audience is waiting, and let’s face it, this is the only thing non-astronomers care about, and we’re the experts, we have our expensive PhDs to prove it, so we feel the need to say something. But we should resist! We should shrug our shoulders and look sheepish and put down the chalk. Because any number we put in the equation, no matter what disclaimer we utter as we do so, will seem to have more weight than all the numbers we didn’t put there.
Mark makes a note: Specific numbers have weight, mislead—optimism 100%, pessimism 1%??!
Two weeks ago he read an article—written for a general audience, but by genuine astronomers—in which the authors established a range for flife by suggesting “optimistic” and “pessimistic” bounds. Of course, everyone can agree that the optimistic bound is 1—that is, 100 percent of habitable planets will go on to develop life. For their “pessimistic” bound, these two professional astronomers chose .01. Mark could hardly believe his eyes. Given the enormous range of numbers the universe throws at us for our daily perplexity and amazement, 1 and .01 are practically the same number. Scientists have no emotional difficulty in believing the calculation that out of approximately 1023 neutrinos that pass through a human body during a normal lifespan, only one hits something on the way through.
Mark notes down, Remember the neutrinos.
Or the Sun! Maybe that’s a better example. (He notes down: Proton-proton chain.) The chance that any particular proton-proton collision in the interior of the Sun will result in the formation of deuterium is roughly 1 in 1029. That means that the average proton, experiencing approximately one trillion collisions per second, will successfully produce deuterium only once in about three billion years. And yet the Sun indubitably shines—because the particle density in the Sun’s core is about 1026 per cubic centimeter. Thus, every second, for each cubic centimeter, there are approximately 109 successful reactions. And how many cubic centimeters are there in the Sun’s core? The solar core has a radius of about 150,000 kilometers, and there are 100,000 centimeters in a kilometer, and the volume of the sphere is approximately the cube of that times four, so the number of cubic centimeters is approximately 1.4 x 1031. Multiply that by the number of reactions per cc per second, and you get 1.4 x 1040. The real number is somewhat less, because reaction rate decreases as density decreases with greater distance from the Sun’s center: about 4 x 1038 reactions per second. Or to write it out (since unscientific people don’t have any decent sense of orders of magnitude), 400,000,000,000,000,000,000,000,000,000,000,000,000. The point is, mathematical measurements of the universe are flooded with numbers like this. To declare that any number is “big” or that any probability is “small” is to get fooled by human-scale assumptions. Ten billion habitable planets in the Milky Way galaxy sure sounds like a lot, but if the chance of life developing on a habitable planet is one in 1010, then voilà, Earth is unique.
There’s a knock on the door. Mark looks at the time. Yikes, one of his graduate students, an appointment, the Centaurus A project. “Come in.”
Super bright young woman, new this year, parents Bolivian, grew up in Michigan, undergrad at Michigan State, did work on molecular clouds, is new to TRGB measurements, a night owl, always drinking coffee, smokes out on the quad, likes scarves, what’s her name, shit, he knows it, did he write it on his appointment calendar, no, damn it, she told him it meant “sky,” which is kind of neat for an astronomer, not Adriana, not Antonella, not Alexa, Ar-something, not Ariana—
“Hi, Professor, this is the right time, isn’t it?”
“Yes, please, sit.” Ara-something. If he gets the last name, he’ll get it all. Ma—something like macho, macha—Machado! Aracely Machado! “So tell me, Aracely. How’s the work going?”
And they talk. Aracely is one of two graduate students (the other is Gerhardt, easy to remember his name because he’s not in the room) who are helping Mark crunch reams of Hubble Telescope and ground imaging data on the Centaurus A galaxy group. Last year they published a paper showing that 29 of the 31 dwarf galaxies of Cen A lie in two planes. The ongoing project is to get increasingly precise information on the positions and motions of the Centaurus A dwarf galaxies, and in particular to determine how many of them are rotating in the same direction. If nearly all of them do, it will suggest there is something wrong with the CDM model of galaxy formation, which in turn would raise questions about the behavior of gravity on the largest scales. Imagine if the theory of gravitation had to be revised. That would be super exciting.
After Aracely takes off, Mark emails colleagues for an hour, eats his lunch at his desk, reads some of the day’s online science articles written for the general public. Since he deals so often with undergrads, he likes to keep up with popular conceptions and misconceptions. He avoids poisoned clickbait relating to anything political. He’s intrigued by the algorithms that search engines use to determine, from his browsing history, what links to tempt him with. Since language is tricky for computers, they often make comical mistakes. He just read a piece on supermassive black holes, and embedded in it was a link to an article the computer determined might be related: Don’t miss: Can women really have 100 orgasms in a row? He notes this down. Alas, he could never use it in a lecture. Writes next to it, “Gravity = bliss.”
He spends the rest of the afternoon happily (blissfully, in fact) engaged in Centaurus A work, stopping now and then to lope down and up the three floors of stairs to keep his mind fresh. Gerhardt comes by for an anxious consult. He’s capable, but high-strung, not needing direction so much as reassurance. It took Mark forever to figure this out. Actually, a colleague had to point it out to him. Beth walks by his open door, innocent of coffee and printouts.
At 7:00 p.m. he knocks off. A thin film of snow coats his car. As often happens with snowfall on a cold and windless day, many of the crystals are undamaged. In the light of the parking lot sodium lamps they glint like minuscule silver coins lying flat, several sheets deep. Or maybe, being hexagonal, they’re more like tiny parquet tiles. He takes off his glasses and leans close (the great thing about being nearsighted is this ability to
focus on something an inch from your nose) and examines their varied shapes. He blows lightly and watches them swirl aloft like kites, then float back down to lie flat again. He remembers a scene in some movie, a man—was he a rabbi?—talking about holding on to a sense of the miraculous in the ordinary, and the man gestures out the window of his office and says something like, “Will you just look at that parking lot!”
He sweeps the flakes gently with his gloved hands from the car windows, trying not to damage them. They fall, tumbling and twinkling. He’s never learned to like the light from sodium lamps, partly because their color rendering index sucks, but maybe more because the powdery orange color reminds him of Bayer Children’s Chewable Aspirin, whose taste he hated when his mother made him take it. He can still visualize with a pang the teal-white glow of the mercury vapor street lamp that stood across the street from his house when he was growing up. It looked so lunar and lovely and lonely in the rain at night. His town started changing over to sodium when he was in high school, and since he couldn’t believe anyone would do it for aesthetic reasons, he went to the library to research the motive. Subsequently he went around saying to his classmates, intending it as a parody of a fatuous conversation opener, “Say, did you know that sodium lamps give off 12 percent more light than mercury lamps for half the energy cost?” He thought it was funny. God help him, he even did it at school dances. No wonder the girls ran from him.
He liked that scene in the movie about the parking lot, but his beef with popular culture is that it’s always religious or spiritual people who say things like that, things about transcendence. Whereas in his experience, scientists are more likely than anyone else to feel wonder in the contemplation of mundane phenomena.
He heads downhill into town. The city hasn’t salted the street yet, so he creeps along at fifteen miles per hour. Three years ago a truck lost control on this very hill and smashed into the porch of the church at the bottom of the slope. The nose of the truck knocked out both pillars holding up the gable, substituting as support its own cab roof, and the fit was so perfect, the porch superstructure didn’t tilt an inch. Mark found himself hoping they’d leave the truck where it was, as a bold new design element. It would be no quirkier than one or two of the newest buildings on campus.
