Two Snowflakes May Be Alike After All

An anonymous reader writes "LiveScience is reporting that it may be possible for two snowflakes to be alike after all. For anyone who studies probability, this seems reasonable, given that the article mentions that 10^24 snowflakes fall in any given year. The article contains links to fascinating snowflake pictures. From the article: 'A typical snow crystal weighs roughly one millionth of a gram. This means a cubic foot of snow can contain roughly one billion crystals ... "It is probably safe to say that the possible number of snow crystal shapes exceeds the estimated number of atoms in the known universe," Nelson said. Still, while "no two snowflakes are alike" might hold true for larger snowflakes, Nelson figures it might ring false for smaller crystals that sometimes fall before they have a chance to fully develop. "How likely is it that two snowflakes are alike? Very likely if we define alike to mean that we would have trouble distinguishing them under a microscope and if we include the crystals that hardly develop beyond the prism stage--that is, the smallest snow crystals," Nelson said.'"

Comments

Nancy Knight, 1988

[Anonymous Coward]

Nancy Knight, 1988

"The old saw that no two snow crystals are identical was disproved in 1988, when National Center for Atmospheric Research scientist Nancy Knight found two that apparently were. The twin crystals were found by accident when Knight was examining samples collected at 6 kilometers (20,000 feet) over Wisconsin for a cloud-climatology study. Thick, hollow, and columnar, the crystals seem to have been Siamese twins that grew attached to each other. No satisfying explanation has yet been found." -

http://www.proquestk12.com/curr/snow/snow395/snow3 95.htm

Re:Years ago...

[Whiney Mac Fanboy]

as you'd expect, if two flakes of snow form under virtually identical conditions you end up with two virtually identical flakes.

From snowflake chemistry

Is it true that no two snowflakes are identical?

Yes and no. No two snowflakes are exactly identical, down to the precise number of water molecules, spin of electrons, isotope abundance of hydrogen and oxygen, etc. On the other hand, it is possible for two snowflakes to look exactly alike and any given snowflake probably has had a good match at some point in history. Since so many factors affect the structure of a snowflake and since a snowflake's structure is constantly changing in response to environmental conditions, it is improbable that anyone would see two identical snowflakes.

Re:Number of atoms in the universe

[FallLine]

"It is probably safe to say that the possible number of snow crystal shapes exceeds the estimated number of atoms in the known universe..."

This sort of thing does my head in. Anyone else trying to keep up?

Makes sense to me. The operating word is possible, as in the number of possible arrangements of unique snow crystal shapes likely exceeds the estimated number of actual atoms in the universe that we know of. This isn't terribly different than saying that number of possible lego combinations exceeds the number of legos in the world (well, I don't really know how many lego combinations are possible.... but you get my point). Though IANAA & IANAM :-)

Re:Number of atoms in the universe

[jd]

It's to do with exponentials. Let's say that a particular snow crystal can form in one of fifteen ways. ((That's all the possibilities depicted on this chart). Then, two such crystals covers 225 possibilities (minus those that simply can't be joined for whatever reason). A snowflake with a hundred crystals would have fifteen to the hundred (ie: one googol) possible permutations.

However, is our starting number of 15 reasonable? The standard snowflake crystals are all formed at temperatures just below freezing under fairly normal conditions. The rate at which the water cools will have a major impact, as will any airborne particles around which the snow crystals can condense. (Particles may cause a break in the symmetry or may force the ice to contain patterns that simply aren't possible when only hexagonal ice crystals are present.) There again, anything dissolved in the water will change the chemistry as well. As not everything freezes at the same temperature, it is entirely possible for snowflakes to acquire bubbles and other oddities where something has remained liquid even as the water froze.

Then, there are the exotic states of frozen H2O which are not considered "ice", per se. Water that has frozen under really strange pressures or at extreme rates will not form regular ice crystals, but form other solid states instead. Slashdot has covered a few of these in the past. Is it possible to have a snowflake form from such states? Maybe. Then you add a whole new set of possibilities to the mix, although it would be unlikely that you could get a mixture of regular ice and these exotic states. (Not impossible, though. If the higher-level clouds chucked down snow in the exotic states, which then got added to by regular snowflake crystals, then you could indeed have a mixture. Not sure this could happen on Earth, but there may be planets where this is common.)