You’ve probably heard the bit of folk wisdom that claims no two snowflakes are alike, but is it true?
The simple answer is that there is no possible way to answer that question with certainty, because it is impossible to compare every snowflake that has ever fallen, or will ever fall, with every other snowflake.
A more satisfying answer is that, because every tiny snowflake that falls is literally made up of quintillions of water molecules, the statistical likelihood of any two of them having the exact same structure is incredibly slim, even over millions of years.
Snowflakes form when water vapor in the air freezes into a solid and falls to Earth. Their intricate hexagonal patterns reflect the pattern two three-part water molecules — made up of two parts hydrogen to one part oxygen each — create when they bond together. Their exact form is influenced heavily by external factors, such as temperature, humidity, and wind. Given similar conditions it is possible for two snowflakes to be similar enough that they would look roughly identical under magnification, but it would be highly unlikely for the same person to view them.
This principle was demonstrated in the late 19th Century by photographer Wilson Alwyn Bentley, who shot more than 5,000 separate snowflake “portraits” over the course of his career. He perfected a technique of catching the snowflakes on a piece of back velvet and filming them before they could melt. In more than 40 years of capturing snowflake images, Bentley never photographed two that were identical.