What synchronizes the growth of the six arms?
Nothing. The six arms of a snow crystal all grow independently, as described in the previous section. But since they grow under the same randomly changing conditions, all six end up with similar shapes. If you think this is hard to swallow, let me assure you that the vast majority of snow crystals are not very symmetrical. Don’t be fooled by the pictures — irregular crystals (see the Guide to Snowflakes) are by far the most common type. If you don’t believe me, just take a look for yourself next time it snows. Near-perfect, symmetrical snow crystals are fun to look at, but they are not common.
