In my own case, as with the majority of my colleagues, I concluded that my work was respectable but not brilliant. Very well. Unfortunately, I now have to decide what to do with the rest of my life. My 35-year-old friends who are attorneys and physicians and businessmen are still climbing toward their peaks, perhaps 15 years up the road, and are blissfully uncertain of how high they'll reach. It is an awful thing, at such an age, to fully grasp one's limitations.
Why do scientists peak sooner than most other professionals? No one knows for sure. I suspect it has something to do with the single focus and detachment of the subject. A handiness for visualizing in six dimensions or for abstracting the motion of a pendulum favors a nimble mind but apparently has little to do with anything else. In contrast, the arts and humanities require experience with life, experience that accumulates and deepens with age. In science, you're ultimately trying to connect with the clean logic of mathematics and the physical world; in the humanities, with people. Even within science itself, a telling trend is evident. Progressing from the more pure and self-contained of sciences to the less tidy, the seminal contributions spring forth later and later in life. The average age of election to England's Royal Society is lowest in mathematics. In physics, the average age at which Nobel Prize winners do their prizewinning work is 36; in chemistry it is 39, and so on.
Another factor is the enormous pressure to take on administrative and advisory tasks, descending on you in your mid-30s and leaving time for little else. Such pressures also occur in other professions, of course, but it seems to me they arrive sooner in a discipline where talent flowers in relative youth. Although the politics of science demands its own brand of talent, the ultimate source of approval—and invitation to supervise—is your personal contribution to the subject itself. As in so many other professions, the administrative and political plums conferred in recognition of past achievements can suffocate future ones. These plums may be politely refused, but perhaps the temptation to accept beckons more strongly when you're not constantly galloping off into new research.
Some of my colleagues brood as I do over this passage, many are oblivious to it, and many sail happily ahead into administration and teaching, without looking back. Service on national advisory panels, for example, benefits the professional community and nation at large, allowing senior scientists to share with society their technical knowledge. Writing textbooks can be satisfying and provides the soil that allows new ideas to take root. Most people also try to keep their hands in research, in some form or another. A favorite way is to gradually surround oneself with a large group of disciples, nourishing the imaginative youngsters with wisdom and perhaps enjoying the authority. Scientists with charisma and leadership contribute a great deal in this manner. Another, more subtle tactic is to hold on to the reins, single-handedly, but find thinner and thinner horses to ride. (This can easily be done by narrowing one's field in order to remain "the world's expert.") Or simply plow ahead with research as in earlier years, aware or not that the light has dimmed. The 1 percent of scientists who have truly illuminated their subject can continue in this manner, to good effect, well beyond their prime.
For me, none of these activities offers an agreeable way out. I hold no illusions about my own achievements in science, but I've had my moments, and I know what it feels like to unravel a mystery no one has understood before, sitting alone at my desk with only pencil and paper and wondering how it happened. That magic cannot be replaced. When I directed an astrophysics conference last summer and realized that most of the exciting research was being reported by ambitious young people in their mid-20s, waving their calculations and ideas in the air and scarcely slowing down to acknowledge their predecessors, I would have instantly traded my position for theirs. It is the creative element of my profession, not the exposition or administration, that sets me on fire. In this regard, I side with the great mathematician G. H. Hardy, who wrote (at age 63) that "the function of a mathematician is to do something, to prove new theorems, to add to mathematics, and not to talk about what he or other mathematicians have done."
In childhood, I used to lie in bed at night and fantasize about different things I might do with my life, whether I would be this or that, and what was so delicious was the limitless potential, the years shimmering ahead in unpredictability. It is the loss of that I grieve. In a way, I have gotten an unwanted glimpse of my mortality. The private discoveries of new territory are not as frequent now. Knowing this, I might make myself useful in other ways. But another 35 years of supervising students, serving on committees, reviewing others' work, is somehow too social. Inevitably, we must all reach our personal limits in whatever professions we choose. In science, this happens at an unreasonably young age, with a lot of life remaining. Some of my older colleagues, having passed through this soul-searching period themselves, tell me I'll get over it in time. I wonder how. None of my fragile childhood dreams, my parents' ambitious encouragement, my education at all the best schools, prepared me for this early seniority, this stiffening at 35.