The Stone Loves the World

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 f_life 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