Snowflakes

(1) How do snowflakes end up symmetrical? How do the molecules on one side “know” what the molecules on the other side are doing?

(2) I have a freezer and some water. How can I make snowflakes?

From what I’ve read, the reason that snowflakes are symmetrical is because they’re so small. The ice crystals grow according their immediate environment- air pressure, temperature, humidity, all of these affect how an “arm” on a snowflake forms. Generally speaking, these conditions don’t change over the small area encompassed by the snowflake, but do change between flakes. What you end up with is unique snowflakes, with six-fold symmetry.

As for making them in your freezer, I doubt it’d be possible. You’d have to have very humid air, in there, and it would have to be very still as snowflakes are remarkably fragile (in the atmosphere, this isn’t a problem, as there’s not much to bump into). While keeping the air still so the flakes don’t bump into and stick to the walls of the freezer, you’ld have to keep the flakes suspended in the air while they form. Like I said, I don’t think it’d be possible.

Water only produces symmetrical crystals when it condenses into a solid directly from the vapor. I have seen very frosted-up freezers with six sided crystals growing inside, but they don’t have the dendrite structure of a snowflake.