This week, a video by self-described “science guy” Steve Mould went viral on social media. Using a violin bow, a metal plate, and a cup of dry couscous, he demonstrates something that usually takes a rare neurological condition to experience: he shows us what musical notes look like.
“This is a pretty random distribution of couscous,” Mould explains, “but when I take my bow, and I play this metal square like an instrument, this random distribution will suddenly become decidedly non-random.”
Sure enough, as he draws the bow along the edge of the square, the couscous grains seem to vibrate themselves into a stunningly regular geometric pattern. And when he holds the plate and bow further left or right along the edge, new patterns arise.
So what’s going on?
“This is a problem of wave dynamics,” explains Mould in the video. “The equations that describe the motion of this plate are here… that’s how the plate moves when you bow it.”
“If you look at the plate here, the parts that are moving jiggle the couscous around… until they reach parts of the plate that aren’t moving.”
This experiment is actually well over 300 years old, with quite an epic history. The phenomenon was first discovered in 1680 by the prolific scientist and Isaac-Newton-nemesis Robert Hooke – and he used a method virtually identical to Mould’s.
Over a century later, in 1787, Hooke’s experiments were repeated by the physicist and musician Ernst Chladni. But although he could produce the striking patterns – now known as Chladni figures in his honor – a mathematical explanation eluded him.
It wasn’t long before this caught the eye of one of the most powerful figures on Earth. After Chladni demonstrated his experiments in Paris, Napoleon issued a challenge: Whoever came up with the best mathematical explanation for the phenomenon would win the Prize of the Paris Academy of Sciences.
There was just one problem: Joseph-Louis Lagrange, one of the most prominent mathematicians, well, ever, had declared the problem so difficult that it would need a whole new branch of mathematics to solve it. A question that even the great Lagrange found intimidating would be far too hard for any normal mathematician, people thought, and scholars abandoned the problem en masse – with one exception.
Enter one Sophie Germain. Forced due to the prevailing sexism of her time to submit her early work under a man’s name, Germain eventually became one of the most important mathematicians in history, making contributions in number theory and pioneering the field of elasticity theory. And, despite Lagrange’s warnings, she decided to take on the problem of the Chladni figures.
“The maths that explains it comes from Sophie Germain,” Mould told IFLScience. “She did amazing work figuring out how standing waves like this work.”
Her eventual explanation in 1816 made Germain the first woman to win any prize from the Paris Academy of Sciences – although, as a woman, she was still barred from attending sessions.
Mould’s demonstration has received thousands of views this week, with people offering other examples of musical physics.
So what is it that’s so inspiring about this experiment?
“[Standing waves are] a really important part of lots of physics. Especially quantum mechanics,” says Mould. “But on a human level, patterns appearing out of nowhere is just really cool!”
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