Snowflakes

by

I think winter is over.  Seriously.   I know that we’ve had a many a snowstorm this late in the season, but this winter has been rather long, and I’m ready for Spring.

Just in case I’m wrong and I have to face yet another storm, here are some pictures of snowflakes that make snow look really appealing.  These aren’t the snowflakes I see, which look like Hey-I’m-going-to-be-late-to-work, but the stereotypical ones that have that pretty six-sided symmetry.  Here’s a great example by dpnsan, taken this January.

snowflake by dpnsan

And here’s one that CaptPiper took last January:

snowflake by CaptPiper

water_molecule_3dSnowflakes have six-sided symmetry because water molecules are made of  one Hydrogen and two Oxygen molecules, in a configuration that looks a little bit like Strong Sad.  According to this science site, the molecules get all cozy:

The oxygen atom has a particularly strong attraction to the electron clouds of the two hydrogen atoms and pulls them closer. This leaves the two hydrogen ends more positively charged, and the center of the “V” more negatively charged. When other water molecules “brush up” against this growing snowflake, strong forces between the negatively charged and positively charged parts of different particles cause them to join together in a very specific three-dimensional pattern with a six-sided symmetry. Each water molecule that joins the snowflake reflects this pattern until eventually we can see its macroscopic six-sided shape.

And that’s how we get results like this (taken with an electron microscope, from the US Department of Agriculture).

snow_crystals_2b

The neat thing about snowflakes is that they don’t have to be so spikey looking.  Sometimes they form regular hexagons:

snowflake by Wilson A. Bentley

The photo was taken by Wilson “Snowflake” Bentley.  He was the first person ever to photograph a snowflake, back in 1885, and he went on to take bunch of pictures that were published by all sorts of places, including Scientific American and National Geographic.  I’ll end with a collection of some of his photos.

snowflakes by Wilson Bentley

In case you’re wondering how people manage to take pictures of things that melt almost as soon as you look at them, there’s a description here.  For some really stunning examples of the finished products, see the photos by David Drexler, Mark Cassino, and F. W. Widall.

Update 3/12: I woke up this morning and the ground was covered in snow.  I might have been a tad premature in saying that winter was over.

5 Responses to “Snowflakes”

  1. David Spector Says:

    I find the above traditional physics explanation of snowflakes (the bond angle between oxygen and hydrogen) woefully inadequate. I don’t know why everyone accepts it (or a variant involving moving through zones of slightly different temperatures). Neither explanation seems to me sufficient to explain why many snowflakes have almost perfect symmetry. It almost seems like the water at the end of each spike knows what the water at the ends of all the other spikes (or at least its neighbor spikes) is doing, kind of like a quantum macrostate (an actual example of a macroscopic quantum state is superfluid helium; see http://en.wikipedia.org/wiki/Superfluid).

    If the entire pattern of a snowflake were determined by the first few molecules of water, then accidental dislocations should occur all along each spike, massively spoiling the symmetry.

    Also, this bonding-angle explanation fails to explain the good approximation to circles that can appear (there is one in the video at http://www.metacafe.com/watch/793880/snowflakes_under_a_microscope/).

    And, continuing my ranting, why is it that almost all snowflake micrographs, from the 1800s until now, show two-dimensional objects? None of the snowflakes are at an angle that would display their three-dimensional form. Thus, we have the common description “six-sided symmetry”. Only a two-dimensional snowflake would have only six sides. If snowflakes actually are two-dimensional, I think that would be quite remarkable. There must be some detail in the third dimension. So, what keeps most of each snowflake in one plane? Bond angles don’t explain that. Bond angles would imply a three-dimensional crystal, like that of salt. Something else must be going on.

    Consider the rings of Saturn, Uranus, etc. They actually are (approximately) in one plane. Physicists tell us that “shepherd moons” (see http://en.wikipedia.org/wiki/Shepherd_satellite) may help create the intricate structure of planetary rings. But is this an adquate explanation? Not really; it’s just a conjecture without a proof. Why are planetary rings always (approximately) in one plane? Is it because any rock in a tilted orbit would be eliminated by collisions with the others? Maybe. But there are other theories (see http://en.wikipedia.org/wiki/Rings_of_Saturn#Formation and http://www.efluxmedia.com/news_Saturn_Has_Moonlets_in_Its_Belts_from_Collisions_09936.html).

    The reason I’m raising these questions is to encourage critical thinking. Few schools teach critical thinking to our young children. As a result, they believe that guesses like these are complete explanations. Even adult scientists don’t question them and don’t embark on more serious and long-term research (until the exceptional scientist comes along to find out why objects rise in shaking sand, or why each type of lightning always has the same fractal shape. Our children also believe that Coca-Cola and Pepsi-Cola are good to drink, and that, while tabacco and alcohol are bad for you, it’s perfectly okay to smoke and drink with your buddies after school.

    Anyway, thanks for all the lovely photos of snowflakes, even though they show no detail in the third dimension. It’s not your fault🙂 .

    • Ray George Says:

      Dear David, I had a personal epiphany practically identical to your ‘Snowflake’ insight. I was, at the time, experimenting with fractal and stochastic heuristics viz a viz programming ‘Snowflake’ algorithms.(Among many others). My speculations finally settled on ‘Spooky action-at-a-distance’ of a EPR kind (Perhaps!!!)

  2. Ξ Says:

    David, I really really like the idea that the molecules at each of the six points talk to each other. The reason that I quoted was that I wasn’t completely sure I understood the explanation, and your question is making me think that’s because it’s not an easy question.

    As for the 3D aspect, I have seen some photos in 3D that look columnar, but when we have a snowfall that has these big six-sided ones, to the naked eye they do look flat. I think they’re essentially planar, and I suspect that photographing them from the side would be quite tricky indeed [though it wouldn’t surprise me if someone, somewhere, had done it].

  3. Ξ Says:

    I ran across an article from Scientific American a few years ago that at least mentioned the reasons molecules seem to know what the other molecules are thinking.

    During this process, the molecules (in this case, water molecules) align themselves to maximize attractive forces and minimize repulsive ones. As a result, the water molecules arrange themselves in predetermined spaces and in a specific arrangement. This process is much like tiling a floor in accordance with a specific pattern: once the pattern is chosen and the first tiles are placed, then all the other tiles must go in predetermined spaces in order to maintain the pattern of symmetry.

    The rest of the article is here.

  4. David Spector Says:

    Concerning snowflakes being “essentially planar”, what does that really mean? Nothing in nature is two-dimensional, including snowflakes. They have some degree of thickness. In the rare oblique pictures of snowflakes, there is interesting detail in that third dimension. This is never discussed.

    Further, what constrains snowflakes to be so thin and so planar? When we do see a snowflake that has a sharp “bend”, why are the two portions of the snowflake individually almost planar?

    Concerning the SA article, I think it is reasonable for it to state that temperature and humidity are the main factors in determining the pattern of a snowflake (although the best known explanation does omit humidity). But, concerning the global perfection of snowflake symmetry, this article is just as vague as all the other explanations I’ve seen.

    It’s as though these professors want to prove that physics has a simple explanation for every phenomenon in nature, so they make up something that sounds plausible. On close inspection, all the explanations fall apart due to “hand waving” (a lack of rigor). They focus on supposedly relevant principles but omit a sufficient amount of actual explanation.

    The part of this article that I believe is the statement that hydrogen bonds (proton-electron cloud attraction) cause a sixfold symmetry. The part I don’t believe is that they also explain the fact that each of the six arms are identical (except for minor dislocations, which are always corrected).

    The question remains: why is each arm virtually identical?
    The answer to this specific question at http://www.scientificamerican.com/article.cfm?id=why-are-snowflakes-symmet isn’t science. It basically says “during formation of a snowflake, each adsorbed molecule of water must go in one and only one place due to electrical attraction and repulsion.” This begs the question entirely. I’m shocked to see such a pseudoscientific statement published by SA.

    I admit that crystalline structures have been well understood for many years. But the familiar case of solid crystals growing in liquid don’t make “arms” like snowflakes. Can all crystals growing by adsorption in a cold fog make arm patterns, or is this restricted to water?

    And what causes the corrections of dislocations?

    Maybe it’s time for physicists to admit that they don’t really know and are unwilling to experiment sufficiently to discover the reason?

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