How long is the coastline of Britain? It sounds like a question with an answer, until you try to measure it. Use a long ruler and you cut across the bays; use a shorter one and you trace into each inlet, finding more length. Shrink the ruler again and the coastline grows once more. The closer you look, the more detail appears, and the detail looks like the whole.
Benoît Mandelbrot called these shapes fractals: objects whose structure repeats across scales. A branch resembles the tree; a tributary resembles the river; a jagged minute of stock prices resembles a jagged year. Self-similarity is one of the most common signatures of how nature builds, from lungs and blood vessels to lightning and snowflakes.
The pattern is recursion made visible: a simple rule applied to itself, over and over, producing endless complexity from almost nothing. The whole is written into every part.
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