(Every day until Christmas, I’ll be posting a science-related image.)
Candles have a long association with the Christmas season, so it seemed fitting to talk about the smoke from a candle for today’s Science Advent installment. In this beautiful image, an ordinary candle was lit, then extinguished. The smoke nearest the slightly glowing wick rises in a a coherent pattern: you could trace the path of a smoke particle along a line. This is known as laminar flow, since the layers of smoke don’t mix together. (“Laminar” literally means “flat”, but in everyday usage, we usually mean layered instead, as in laminated paper or wood laminate.) However, air molecules move randomly, so as the smoke rises, it is increasingly buffeted by these other particles. The result is turbulence, where the layers of smoke mix together and billow. Turbulence is fractal in structure: if you could look closely at the smoke, you’d see that turbulence persists on the microscopic level, equally beautiful and equally complex as at the macroscopic level.