Imagine my surprise to see a mainstream media article about snow crystals! Here is the link.
https://www.rt.com/news/326738-designer-snowflakes-lab-california/
It describes the snow crystals grown by Ken Libbrecht in his Caltech lab, and has some great photos.
The text of the article is also worth a read.
Best wishes,
Ken R.
22-Dec-2015
A snow crystal is a single crystal of snow, whereas a snow flake is a clump of snow crystals. Snow crystals show a six-sided symmetry, and often lie in a single plane. There is a book by W. A. Bentley, who photographed snow crystals for about five decades; his 2,400-some photos are in a 1931 book which has been republished by Dover. See the figure for an example, and see the end of this post for pointers to the book and some online resources.
Why are snow crystals symmetrical? There are a couple of hypotheses. (A) One, from Ken Libbrecht at Caltech Physics, is this: “Branches begin to sprout from the six corners of the hexagon… Since the atmospheric conditions (eg, temperature and humidity) are nearly constant across the small crystal, the six budding arms all grow out at roughly the same rate.” Secondly, Libbrecht notes, symmetrical crystals are rare — irregular crystals are much more common.
Another hypothesis (B) is that snow crystals grow upon a charged core, and the charge promotes growth which fills in gaps in the structure. That is, symmetrical growth is a lower energy state, hence encouraged.
These two alternative hypotheses might be tested, by a statistical examination of snow crystal photographs. Consider two arms separated by 60 degrees; call that type 60 symmetry. Or consider two arms separated by 120 degrees; that is type 120 symmetry. Or, opposite arms, type 180 symmetry. If hypothesis A (external conditions) holds, we would expect the context to be roughly constant across the crystal; hence type 60, vs 120, vs 180 symmetry should be about the same across a population of crystals. If hypothesis B holds (charge migration, energy minimum) we would expect type 60 symmetry to be stronger than type 120 symmetry, and type 120 to be stronger than type 180.
So there is interesting work to be done. Opportunity beckons.
Here are some pointers to get you started…
Book: Snow Crystals, by W. A. Bentley and W. J. Humphreys, 1931, Dover reprint 1962. A beautiful book to browse.
Website: http://snowcrystals.com — this website was written by Ken Libbrecht of Caltech Physics, and links to his academic pages at Caltech.
Website: http://www.its.caltech.edu/~atomic/snowcrystals/faqs/faqs.htm — this web page has the hypothesis A which was quoted above, as well as other interesting info, and links to other comparable pages.
Best wishes,
Ken Roberts
01-Dec-2015
Logic, Astronomy, Science, and Ideas Too 