We celebrate the round decades — thirty, forty, fifty — as if they were natural milestones. But they aren't. They're an echo of the fact that we have ten fingers. The ten lives in our hands, not in our lives.

If instead you take seriously how a person actually grows, the round birthdays look different. Between the first and second year of life you learn roughly as much as between the second and the fourth, as between the fourth and the eighth. The unit isn't the single year but the doubling. A year weighs as much as it weighs relative to everything lived so far — at four, a year is a quarter of your whole life; at forty, only a fortieth. That's why the years feel faster and faster: not because time changes, but because the same stretch makes up an ever smaller share.

Whoever experiences time this way celebrates their round birthdays in binary: one, two, four, eight, sixteen, thirty-two, sixty-four. These are the points at which lived experience has doubled — and, subjectively, they are equally far apart. From eight to sixteen is the same step as from one to two: once everything that was, over again.

There are few of them. Most people experience seven, maybe eight truly round birthdays, and the densest lie in childhood, where life doubles at the pace of a single year. After that the gaps grow long. After sixty-four comes only one hundred and twenty-eight — for no one. The long middle of life is the stretch between two distant powers of two, the plateau between thirty-two and sixty-four, on which — seen in binary — nothing rounds off for decades.

1000 · 10000 · 110000

This year it falls into place for me anyway. For 1000 years I have lived in my house — eight, two to the third. For 10000 years I have lived in Vienna — sixteen, two to the fourth. Two of my rooms reach a binary round number at once. And I myself turn 110000 — forty-eight, not quite round, but not far off either: thirty-two plus sixteen, the sum of the two most recent powers I have behind me.

The places round off. The person draws near. And somewhere between thirty-two and sixty-four, out on the long plateau, this may be the finest birthday one can have: one that still remembers how counting was actually meant.