This is the sixth in a series about the human side of science, drawn from interviews with 27 cosmologists. Earlier posts explored, how this project started, the method, the role of wonder and beauty, the craft and how scientists think. This one is about what keeps them going—and the very different ways they live with not knowing.

06: Compulsion, temperament, and not knowing

“It seemed required that I must learn everything about everything. Otherwise, I thought that I was not doing things properly. I felt guilty at not knowing.”—Allan Sandage

“For me, doing astronomy is incredibly great fun. It’s just an incredible joy to get up every morning and come to work and, in some very much larger framework, not even really quite know what it is I’m going to be doing.”—Vera Rubin

Same compulsion. Completely different experience. Sandage is driven by guilt—an anxiety that he is failing some obligation to know. Rubin is driven by joy—the not-knowing is itself the source of delight. Both of them are describing a life they did not choose. Neither can imagine doing anything else. But Sandage’s version seems somewhat dark and relentless, while Rubin’s is buoyant, almost giddy. Marc Davis captures the same energy: “I feel exhilarated every morning.”

The variety of what “driven” means is one of the surprises of this data. Wallace Sargent’s drive came not from wonder but from necessity. His father was a gardener, often ill; the family drew welfare. Science was a path out. The compulsion was material, not spiritual—but no less powerful for that. Andrei Linde’s and Dennis Sciama’s passion erupted after being suppressed—Linde by Soviet epistemology, Sciama by an early career spent on the wrong side of the steady-state debate. When the passion finally found its object, it was all the more intense for having been bottled up.

But compulsion is only half the story. What matters just as much is how these scientists live with the things they cannot resolve. And here the range is extraordinary.

John Huchra is the great deflationist: “The universe is what it is. Just because we can’t think of a good way to form galaxies doesn’t mean that galaxies shouldn’t be there.” No anxiety, no guilt, no metaphysical hand-wringing. The universe is under no obligation to match our theories. Maarten Schmidt takes a similar line, he won’t speculate beyond what his data supports: “I don’t have fairly strong ideas about how things in the universe work if I have had no input on which I can base that.”

Steven Weinberg is breezier about it: “I take a Mr. Micawberish attitude: something will turn up.” It is confident without being dogmatic, a faith in the enterprise rather than in any particular outcome. Robert Wagoner sits at the other end, burned three times by wrong observations: “I try not to prejudice myself because I’m trying to measure q? with supernovae. So I don’t want to get hung up with any prejudices.” Martin Rees holds multiple hypotheses at once with apparent ease, never needing to choose. Margaret Geller was “sort of afraid of astrophysics because you could never be sure.” She became a scientist despite that fear, not without it.

These are not degrees of a single quality. They are qualitatively different relationships with not-knowing: Sandage’s anxious precision-seeking, Huchra’s deflationary pragmatism, Weinberg’s casual confidence, Wagoner’s earned wariness, Geller’s fear-despite-commitment. Each one is a viable way of doing science. None of them is the “right” temperament. The discipline needs all of them.

My own epistemic temperament is probably closest to Rubin’s end of the spectrum, though in a different key. Comfort with ambiguity is what drew me to design and to education—fields where the problems never fully resolve and the best you can do is muddle through with as much grace as you can manage. I’ve come to believe that the muddling is not a failure of method. It is the method. What makes it bearable, even fun, is accepting that there is no choice but to act anyway—to design the school, teach the class, write the paper—knowing full well that your understanding is incomplete. These cosmologists remind me that even at the highest levels of science, the relationship with uncertainty is personal, idiosyncratic, and never fully settled.

Next: the social and structural forces—mentors, accidents, and outsiders—that shaped these scientific lives: The Ecosystem