May. 13, 2021 , 6:45 PM
Play a video of swimmer Michael Phelps in reverse, and you’ll notice right away that his stroke looks dramatically different running forward or backward in time. Such time asymmetry typifies the swimming motion of the vast majority of animals and it’s absolutely essential for bacteria and other microbes. But now, a team of physicists has developed a tiny mechanical swimmer that can inch along, even though its stroke is symmetric in time. The result opens a new conceptual lane in fluid dynamics and could aid in efforts to develop tiny swimming robots for drug delivery and other purposes.
A dark, shape-shifting mass moves above a tree line. Its fluctuations are almost eerie, like something from a science-fiction movie. Upon closer inspection, it appears that the shadowy figure is not one creature but many thousands of birds moving in unison.
“When I give a class, I play this video [of flocking birds] and ask students to stare at it for a while and write down what they observe,” said Daphne Klotsa, a Carolina applied physicist. “One thing we see that’s quite striking is it looks like one organism. You don’t even know what one individual within the system looks like. It looks like one material that’s stretching.”