Icicles are a beauty and a nuisance, a common fixture of cold-climate cities in winter. To scientists, they're a puzzle: no computer could perfectly predict the shape of an icicle before it grows. But here's where things get really weird. When icicles form ripples (and not all of them do), it's always at a wavelength of 1 cm, "no matter how big the icicle is, or how cold it is," University of Toronto physics professor Stephen Morris told me.
"As far as we know, there are no icicles on our world that don't have ripples at 1 cm," he said. "And we don't know why."
Morris is among the world experts on icicles, if not the leading one. He's been studying them for years. In his lab, he's got a one-of-a-kind icicle-growing machine where he can build them with precision for study, controlling temperature, water drip, and more. This machine, which he calls a "Rube Goldberg machine made of Canadian Tire parts," measures and photographs icicles, too.
His team has put together an Icicle Atlas of "something like 250,000 images of icicles, all taken and organized by machine," including 3D-printable files.
"Icicles are all different," he said, yet they follow certain rules as they grow. "They're sort of self-directed. You put the water in, get the temperature at the right level of cold, and the icicle grows itself. It decides what shape to be."
By growing icicles in his lab, Morris and collaborators, including his former graduate student Antony Chen, have come up with an idea about why ripples form: it happens when the water is impure, which is why icicles found in nature are ripply, he said.
Still, the part about the 1 cm wavelength remains an unsolved mystery, he told me. Being able to grow them precisely in the lab means he can continue to study this puzzle.
Actually, icicles aren't all that common in nature, although city dwellers will be very used to them. They tend to occur on buildings, where heat leaks through bad insulation and melts snow, he said. You'll sometimes find them near a waterfall, for example, if you're not in an urban setting. (A 66-foot-tall icicle was just reported in China.)
Why study icicles? There may be applications to this kind of work, particularly for building design, Morris acknowledged. But that's not really what he's after.
"We study them because they're interesting and beautiful," he said. "It's kind of ironic that we understand exotic things like the Higgs boson particle, [yet] icicles remain mysterious, even in the 21st century."
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