There is a little thing that has bothered me for a number of years about snowflakes. Actually, there are two things.
One is the assertion that no two snowflakes are alike. At one level, this seems like it must be true - it is doubtful that any two perceivable objects are exactly identical, given the sheer number of atoms that compose even the tiniest objects (at least objects that are bigger than molecules). But at the level of human perception, it seems to me that many snowflakes must be essentially identical, simply because there are not that many possible shapes that a snowflake can have.
The second bothersome aspect of snowflakes is their six-way symmetry. I understand that the bond angles of the water molecule tend to favor hexagonal ice crystals. However, how do the separate "arms" of a snowflake "know" what each of the other arms is doing, when those other arms are billions of molecule diameters away?
The conclusion to which I finally came, and which seems to be borne out by my investigations into snowflakes here, is that the arms have no idea what the other arms are doing. However, the microclimate in which a snowflake grows in a cloud does not vary significantly within the volume of a single snowflake, although it does vary significantly over the entire cloud. Since the environment, especially the temperature and humidity, is essentially constant at any given moment where the flake grows, all of the arms grow in the same way.
Over time, the snowflake moves into different conditions, and this changes the way the arms grow - but they all change together. These changing conditions are what make the snowflakes unique - the sequence in which these different conditions are visited is much less likely to be duplicated by arbitrary flakes, although one can easily imagine "brother" flakes (hmmm...) that travel together and thus are very similar.
If this idea is accurate, one would expect that some (or even most) snowflakes are not exactly symmetrical, because the growing conditions are not exactly the same across the diameter of the snowflake - just very, very close to constant.
Well, as you can imagine, it is snowing pretty hard today. I am less interested in the shape of each snow crystal than in getting them off of my driveway. I wish I had a flamethrower or something similar - after all, melted snowflakes all look pretty much alike.
You can respond to my ranting here.
Oh the weather outside is frightful, but the rant is so delightful.