How can water molecules in a snowflake influence other molecules positioned thousands of molecules away to form the same macroscopic shape and create a six-pointed design?
鈥� They cannot. There is no spooky power at work here. Ice forms into hexagonal crystals because of the sixfold symmetry of the crystal lattice it forms at or below freezing at a pressure of 1 atmosphere (a number of other ices form at extreme pressures that dance to different lattice tunes).
The crystal itself does not care about the water molecule far away. It is concerned only with the one that might fit a gap in its lattice, which is how crystals grow. If the molecule is moving too fast, it will not settle into the gap. It is much like the ball on the roulette wheel that bounces here and there until it has lost enough energy to be unable to escape from one of the numbered indentations. Similarly, the water molecules bounce and jostle until one has lost enough energy to settle into the gap in the lattice.
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鈥淏ecause the history of each snowflake is different, the shape of each one is unique鈥�
In an environment where heat is slowly being withdrawn, molecules will fill the lattice gaps in an orderly manner and the snow crystals we know and love will grow with that sixfold symmetry.
Differences in temperature and pressure in the microenvironment of each snowflake will create enough variation to ensure that the crystals will not be identical, but they can be very similar.
A high-speed freeze will result in a dense mass of interlocked crystals that create ice with no apparent crystalline structure. This is seen in fast-frozen ice cubes, which appear clear. But in a slow-freezing, 鈥渃onstrained鈥� system, such as on a pane of glass or a pond surface, gradual cooling will create the typical hexagonal crystal pattern at the advancing edge of crystallisation.
Bill Jackson, Toronto, Ontario, Canada
鈥� Snowflakes begin with a dust particle or similar nucleation site around which water freezes to produce a 鈥渟eed鈥� ice crystal with six-sided symmetry. Water vapour freezes more quickly at the corners of the hexagonal shape, so arms begin to grow from these corners. The arms can grow at varying rates if the crystal is exposed to different atmospheric conditions. As the snowflake moves in the cloud in which it is forming, it goes through regions of different temperature and humidity, which cause the alternate preferential growth of different crystal faces.
The accumulation of these different phases of growth determines the final complex snowflake shape. Because the snowflake is small, each side of it experiences roughly the same local conditions and so grows in the same manner, resulting in an almost symmetrical snowflake, although of course nothing of this size can be perfectly symmetrical. However, because the history of each snowflake is slightly different, the final shape of each one is unique.
Simon Iveson, Pembangunan Negeri University, Yogyakarta, Indonesia
鈥� Simple answer: they don鈥檛. Photographers search long and hard to find snowflakes that are close to symmetrical. The vast majority are not. Read the experience of one of the world鈥檚 greatest snowflake hunters at
Colin Dooley, Spain