Is It True That No Two Snowflakes Are Alike? Sort Of.

Brilliance | Dec. 10, 2017

Everyone knows the old adage that no two snowflakes are alike. But the truth is more complicated than that. While it would be virtually impossible to actually find two snowflakes that are identical, if you want to get technical, it's possible two nano-snowflakes (with only 10 water molecules as opposed to about 10<sup>18</sup>) could be the same.

The Science Of Snowflakes

There are snowflakes, and there are snow crystals. A snow crystal is a singular crystal of ice, while "snowflake" is the all-encompassing word for either a single snow crystal, or a bunch of snow crystals stuck together, "or large agglomerations of snow crystals that form 'puff-balls' that float down from the clouds," according to Kenneth Libbrecht, a physics professor at the California Institute of Technology, who specializes in snow crystals. Just as a blue jay is a type of bird or a Corvette is a type of car, a snow crystal is a type of snowflake.

So, could two snow crystals be alike? It's complicated. Basically, no. As Libbrecht explains in his oft-cited blog post about the subject, most small snow crystals contain 10<sup>18</sup> water molecules, and some of these water molecules are slightly abnormal. "These unusual molecules will be randomly scattered throughout the snow crystal, giving it a unique design," Libbrecht writes. "The probability that two snow crystals would have exactly the same layout of these molecules is very, very, very small. Even with 10<sup>24</sup> crystals per year, the odds of it happening within the lifetime of the Universe is indistinguishable from zero." By the way, that 10<sup>24</sup>? That's one septillion, or a trillion trillion.

There is a potential exception, Libbrecht says: "a snow crystal with only a handful of molecules," like only ten. That's the nano-snowflake, and considering most snowflakes have 10<sup>18 </sup> molecules, it's not common.

If That's Not Proof Enough

Even after you've broken down the molecular structure of the snowflake, there are outside forces at work, ensuring differences between snowflakes. "Snow crystals are sensitive to temperature and will change in shape and design as they fall from the cloud and are exposed to fluctuating temperatures," according to the Library of Congress's Everyday Mysteries section. "To have two snow crystals or flakes with the same history of development is virtually impossible."

So, basically, it's true that no two snowflakes are alike, but also true that two snowflakes could be alike, if they were nano crystals with no differences in development. But — good news! — snowflakes don't have to be alike to be equally great for snowmen, or sledding. So maybe stop reading for a minute, bundle up, and go enjoy the snowflakes... or should we say crystals?

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