Naked Science Forum

General Science => General Science => Topic started by: Harold on 12/01/2011 22:30:03

Title: How do snowflakes maintain symmetry?
Post by: Harold on 12/01/2011 22:30:03

Harold asked the Naked Scientists:
   
Can you please explain to me how the individual 'arms' of a snowflake 'know' what is happening on the others so that they all grow to match and remain symmetrical?

BTW, I love the show (http://www.thenakedscientists.com/HTML/podcasts/).

What do you think?

Title: How do snowflakes maintain symmetry?
Post by: RD on 12/01/2011 23:47:01

The snowflakes are not absolutely symmetrical, they do have hexagonal symmetry *, but the arms are not identical to each other, just similar ... http://en.wikipedia.org/wiki/Snowflake#Gallery

The six radiating arms form from the same initial conditions, at the hub, and are built according to the same rules (laws of physics) and using the same (hexagonal) building blocks (http://en.wikipedia.org/wiki/Fractal_geometry), that is why they are similar. One arm doesn't "know" what the other arm is doing. The arms are variations on a theme: similar but not truly symmetrical.

[ * The hexagonal symmetry, and other 60^o angles, originates in the way the water molecules are packed ... http://en.wikipedia.org/wiki/Close-packing ]

Title: Hear the answer to this question on our show
Post by: thedoc on 12/01/2016 16:32:48

We discussed this question on our  show
Kat Arney put this question to physicist Stuart Higgins...
Stuart - Well, you need a big cloud of gas and water vapour and you need the right conditions - it needs to be nice and cold. And so, at the start of a snowflake, you need a speck, you need a nucleus, so typically this might be something like the dust in a cloud and the water will start to solidify and crystallise around that nucleus. And it just so happens that the way it packs is in a hexagonal structure - a regular hexagon has a symmetry of six and so that’s what gives us this kind of growing six pronged structure of the snowflake.
Kat - And are all snowflakes different? Is this true or is this a myth?
Stuart - It is true to a certain extent, so they have similar structure. So snowflakes will share this common six pronged structure due to the fact that it’s the packing of the water structure underneath. But what happens after that, when these arms spread out and they start to interlink and branch like tree branches, that’s more dependent on the conditions, that could be the temperature and the exact pressure and all the different factors that might affect it. So, the chance of getting those two sets of conditions, to grow the same crystal in the same snowflake twice is very rare.
Click to visit the show page for the podcast in which this question is answered. (http://www.thenakedscientists.com/HTML/podcasts/naked-scientists/show/20160112/) Alternatively, [chapter podcast=1001251 track=16.01.12/Naked_Scientists_Show_16.01.12_1004648.mp3](https://www.thenakedscientists.com/forum/proxy.php?request=http%3A%2F%2Fwww.thenakedscientists.com%2FHTML%2Ftypo3conf%2Fext%2Fnaksci_podcast%2Fgnome-settings-sound.gif&hash=f2b0d108dc173aeaa367f8db2e2171bd) listen to the answer now[/chapter] or [download as MP3] (http://nakeddiscovery.com/downloads/split_individual/16.01.12/Naked_Scientists_Show_16.01.12_1004648.mp3)