You’ve watched this week’s video, on “The Science of Snowflakes”, right? A lot of people have asked this question:
"Okay, so snowflakes have six sides because physics, but why are they symmetrical?!”
Here, “symmetrical” means that each of a snowflake’s six arms has a similar, often nearly identical set of fractal plates and branches. What gives? If randomness and the intermolecular physics of water molecules are the only things guiding the formation of a snowflake, how does one arm have any idea what another is doing?
In your head, you might think snowflakes all look like this:
(photo by Alexey Kljatov)
Well, as the images up top show, most snowflakes don’t look like that. Snow crystals usually aren’t completely symmetrical. Instead, they are quite irregular and lumpy, full of conglomerations and corrections. The hexagonal crystal structure holds up in all cases, but the sort of perfect fractal sculpture you’ve been led to believe defines a snowflake? It’s a half-truth, at best.
Sorry. I probably should have been more clear about that in the video!
The world’s great snowflake photographers through the years, from Wilson Bentley to Kenneth Libbrecht to Alexey Kljatov, have, for the most part, chosen to only show you the most beautiful examples of snow crystals. Sometimes they wait hours, sifting through thousands of flakes with (literally) bated breath, just to capture that one perfect frigid starburst. They aren’t trying to trick you, many artists’ eyes just prefer the symmetrical ones.
That being said, even in irregular snowflakes, when it comes to the branches, sub-branches, and sub-sub-branches, there’s still a remarkable amount of symmetry. What’s up with that? Let’s retrace the path of a snowflake and see if we can find an answer.
As a speck of dust falls through cold air of a particular humidity, it acts as a nucleus of crystallization, capturing water molecules from the air into the growing crystal. And, as we saw in the video, the precise hydrogen bond angles between water molecules give us the familiar hexagonal shape, an emergent pattern that exists from the molecular to the macro scale.
All those branches off of the hexagon, each plate, dendrite, arm, prism, or whoozywhatsit that grows from the central plate, each forms at a particular combination of temperature and humidity. Consult the following:
Very cold? We get columns. Cold and high humidity? Dendrites. Cold and medium humidity? Sectored plates. Still, none of this explains how two separate arms can form complementary patterns. I know … Get to the point, Joe.
The current thinking, and I must emphasize that this part remains somewhat of a mystery, is this: During a particular snowflake’s delicate dance down to Earth, all six branches will pass through the same tiny, specific pockets of humidity and temperature, all six branches will be subject to the same air currents, all six branches will experience a nearly identical (but not totally identical) evolution.
Imagine if we played human evolution back six times! We would get similar results, perhaps, but not identical. Snowflakes really are a hell of a metaphor, man.
And when all that doesn’t work? When the journey doesn’t result in the perfect six-sided mirror reflections that float through the snow flurries of our imaginations? Well, imperfection is a part of life, whether you’re a snowflake or a human being. In both, artists tend to show us the ideal, but we must remember that there is beauty in the flaws.
And so we return to the images above, and we appreciate them anew.