Disorder — where it appears
Named by 3 essays across 2 fields — each of them below, with the objects they name alongside it.
The second moment is the measurement
The mean number of sides in a cellular tissue is six, and Euler's formula leaves it no choice — so it takes the same value on a golden-angle head, a whorled head and a set of random points. The mean squared departure from six varies by a factor of eighty across the same three, and almost nobody reports it.
The six are the spirals
Label every contact between two cells in a seed head with the difference between the two nodes' placement indices. The labels are the parastichy numbers — 34, 55, 21, 89 — and the six sides Euler forces turn out to be about two from one family, one and a half from the next, and one each from two more.
What a summary throws away
Four statistics this collection has relied on turn out to be incapable of varying with the thing they describe — one is invariant to shuffling, one is fixed by a theorem, one is a parameter that stopped mattering, one is a fitted number selected into being wrong. In each case the second statistic was free and nobody had taken it.
Named alongside it
The objects these essays reach for when they reach for this one.
Euler's formulaMeasurementCell areaGolden angleLatticePackingParastichyRational angleRim effectSummary statisticVoronoi cellsWhorled