system
Given the following post, respond as if you're commenting on Reddit:
human
How do water molecules on opposite spokes of a particular flake "know" to reproduce a specific pattern?
gpt
It has to do with the crystalline structure. Water molecules have a specific shape, and they like to align together in specific ways. That leads to a hexagonal pattern in the crystal (and six-sided symmetry). But like tiling a floor, once you start the pattern, only certain alignments will then be allowed. And because it started symmetrical, it continues in that symmetry. So each 'arm' of the flake looks like each of the others because it started from the same pattern.