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When It Comes To Snowflakes And Popcorn Kernels, Is It True That No Two Are Alike?

From "Studies Among the Snow Crystals ... " by Wilson Bentley, "The Snowflake Man." From Annual Summary of the "Monthly Weather Review" for 1902.
NOAA's National Weather Service (NWS) Collection

Here at the Curiosity Desk, we love nothing more than taking on a story inspired by a question from you. Today we turn to Steve Deveau, a loyal listener from Swampscott, who reached out with a two-part question.


It’s common knowledge that no two snowflakes are alike, but is it true? Is there anything that prevents any two from being identical?

For this, I turned to Daniel Cziczo, associate professor of atmospheric chemistry at MIT's Department of Earth, Atmospheric and Planetary Sciences (EAPS). He said the answer lies in understanding how snowflakes form.

"There [are] very special particles. They are called ice nucleating particles," he explained, wryly adding, "You can tell we’re scientists and not poets."

When atmospheric conditions are right, these ice nucleating particles — which might be bits of mineral dust or biological material in the clouds — rapidly transform into ice crystals that attract water molecules.

"And depending on what the temperature is, and what the humidity is, and how those molecules of water knit together on the surface of these particles, you start to grow snowflakes," said Cziczo.

That “growing” process can take anywhere from seconds to minutes. And scientists know that flakes tend to form into certain basic shapes, based on certain conditions.

But within those common snowflake shapes is a mind-boggling amount of variation in detail, affected by everything from the temperature, to the humidity, to the length of time it takes for one to form. So, while it is theoretically possible that two snowflakes would be exactly alike it is, in a word, unlikely. How unlikely? 

"Incredibly unlikely," he said. "The real chances of that happening are infinitesimally small. Almost zero."

That the chances are that low is even more astounding when you consider that a single, hefty shovel-full of snow — like the kind we just got pummeled with here in New England — consists of about half a billion individual flakes. 


What about popcorn? Popped kernels aren’t constrained to crystalline shapes like snowflakes. Are they all unique, too?

For that answer, I met up with Vayu Maini Rekdal, a Ph.D. candidate in biochemistry at Harvard University.

"I would consider myself a scientist, a chef, and an educator working at the intersection of cooking and science," he said. "I love popcorn. I think I have a popcorn addiction."

Looks like I found the right guy.

Rekdal says that popcorn pops thanks to the one-two punch of the hard, outer shell — called the pericarp — and it’s more complex innards.   

"You have lots of nutrients, you have water and starch," he explained. "It’s really the water and starch that are crucial for how popcorn work."

When popcorn kernels are heated, that water turns to steam. And the steam is trapped inside by the pericarp.

"That steam starts interacting with the starch inside that seed," said Rekdal. "And what happens then is a process called gelatinization."

As a gooey, dough-like, gelatin forms inside, it also begins to swell.  

"And a certain temperature that swelling is so powerful that it needs to go somewhere, and this is the force that’s required to break through that tough shell," Rekdal continued.

So why doesn’t this gooey gelatin jut splatter apart into space when it comes flying out?

When it breaks through, it meets the relatively cooler air and instantly solidifies. And that is the white, crunchy, beautiful, fluffy food that we know as popcorn. 

As for the million-dollar question: Is each one unique? Well, physics suggests that kernels, all similarly shaped, do have natural weak points.

"It’s more likely, the probability is higher that it would break at a certain point rather being equally probable across the kernel," said Rekdal.

But, like snowflakes, each kernel is just a little different — inside and out. Plus, there are small variations in the temperature, even if you are heating it all inside the same vessel. 

Rekdal's conclusion?

"I think it would be rare to find two popcorn [kernels] that look exactly the same, but I think that’s something that science doesn’t yet know," he said. "Whoever wants to figure that out, it’s an exciting project."

Our thanks to Swampscott’s Steve Deveau for his question that led to this story. What’s yours? Email the Curiosity Desk at — we may just look into it for you. 


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