Are no two snowflakes alike?

This is a bold statement to be coming from scientists, usually world-champion hedgers. Snow is not a well understood phenomenon but, in a funny way, it is our ignorance — or rather the reason for our ignorance — which makes this claim such a good bet.

It may seem incredible, pondering in your armchair, that of all the snowstorms in history, from the highest snow-capped mountains to the deepest Antarctic valleys, there have never appeared two snowflakes exactly alike.

However there are two factors that support the idea. The first is the vast, vast number of shapes snowflakes can take on. That really can’t be overstated. It’s vast. Just because something is elaborate, though, doesn’t mean it’s unique. After all, people are even more elaborate than snowflakes, but identical twins are alike. There has to be something about the way snowflakes form that makes it unlikely two will ever crystallise in just the same way.

Crystal formation is not well understood. One reason for this is the number of factors that affect crystal growth. For snow these include the pressure, temperature, humidity and concentrations of trace chemicals. These interact with one another to determine the pattern of growth the crystal will follow and small changes in any of them can lead to radically different crystal shapes.

These are hallmarks of a chaotic system. At the molecular level snowflake formation is explained by relatively simple rules. Zoom out, though, and things become extremely difficult to follow.

A snowflake’s ornate shape is a record of its history. From moment to moment on its journey from the clouds to the ground it encounters slightly different atmospheric conditions — themselves part of a chaotic system — each leaving a mark on the final shape. To share the same shape two snowflakes would have to experience pretty much exactly the same conditions in the same order.

In principle this still doesn’t exclude the slim possibility of two identical snowflakes. It is assumed, though, that the odds involved make winning Lotto look pedestrian and everyday. For all intents and purposes, no two snowflakes are alike.

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