If you eat cereal, you have watched the Cheerios effect in action. Maybe it wasn’t the little o’s bobbing around your milk bowl, but you’ve probably seen bits of some cereal swim toward each other, crashing into each other to form a little clump. It’s almost like there’s a magnet in your breakfast. There isn’t. But there is a physics breakthrough that’s shaken up the world of science in recent years and set off a chain of events that could one day lead to a cure for cancer. But let’s back up a minute. The Cheerios effect is the name Harvard researchers came up with back in 2005 to address a phenomena observed at breakfast time for centuries.
Dominic Vella and L. Mehadavan were interested in what’s called self assembly, essentially why objects—like Cheerios—will move toward one another and form a unit when suspended in liquid.
“The effect was actually well known beforehand, but the mechanism was not properly understood,” Vella explains. That’s where breakfast cereal came in. It’s common across American households and perfect for demonstrating how floating objects are drawn to one another without any other force pushing them together.
“The novelty in what we did was to show that an object’s density is important in determining whether the Cheerios effect is attractive or repulsive—for example a relatively dense object and a light object repel, while two light objects attract. We also tried to understand how fast the aggregation happens, which is important for understanding the process of self-assembly.”
At the time, Vella and Mehadavan were hailed for breaking down this relationship between gravity and surface tension into language that was easily understood. If you go by sales data, Cheerios is the most popular cereal in America. Explaining scientific theory with a well-known and widely eaten breakfast cereal made it more easily consumed by the masses, including high school students. The duo got their work published in the American Journal of Physics.
The folks at General Mills—maker of the popular cereal—were pretty pleased too, although oddly they didn’t stumble upon the effect until 2014, according to spokesman Mike Siemienas. That’s when the company’s Canadian arm started building a marketing program, built around the idea of connections fostered by Cheerios.
“Cheerios as a brand has always been about bringing families together and family moments,” Siemienas says.
When the marketers realized there was a study that literally said Cheerios pulls people together, he said they realized “we absolutely have to do this.” The cereal was advertised across Canada with slogans like, “We all love to connect. That’s the Cheerios Effect,” and the company created a website where cereal lovers could share their stories of connecting or send out Cheerio-themed messages.
Then came the inverted Cheerios effect. Published in 2016 in the journal Proceedings of the National Academy of Sciences, this study completed by an international team of scientists turned Vella and Mehadavan’s research on its head. What would happen, they pondered, if you put a liquid on a solid, rather than a solid on a liquid? Would liquids perform as solids, pulling together, or would they repel from one another?
The study saw a number of commonalities with its predecessor, says Dr. Siddhartha Das, assistant professor of mechanical engineering at the University of Maryland and one of the study’s co-authors. Drop liquid on a soft surface, like Jell-O, and the liquid drops will attract, in the same way that cereal pulls together in milk or galaxies come together in the universe.
“The attraction of galaxies in the universe is similar to the attraction of the little Cheerios in your milk,” Das says. That’s because the solid hitting the liquid causes a deformation, and “nature abhors any kind of deviation away from equilibrium.” The same holds true for a liquid hitting a solid … to a point. Because Das and his fellow scientists decided to look at the way liquids reacted if they changed up the playing field, reducing the thickness of the solid surface, reaching a point where they found those liquids actually repelled one another.
The interactions between liquids and solids could have a significant impact on future studies, Das says, including cancer treatment. Because if you can manipulate cells, which can be mechanically described as membrane-bounded drops, on soft surfaces (like tissues) inside our bodies, you may be able to figure out how to make those cells repel, rather than coming together to form a clump like your breakfast cereal.
“Cancer treatment can be massively advanced by such an ability to control cells,” Das explains.
Think of that the next time you pour yourself a bowl of cereal and watch those little o’s pull together.