The Stone Loves the World

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:

N_civ = N_hp x f_life x f_civ x f_now

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