In my Nature article Physicists twist water into knots, Dustin Kleckner and William Irvine, physicists at University of Chicago, Illinois, break new ground by capturing the twisting and knotting of a vortex in water. They do so, in part, through the use of a three-dimensional printer and laser-scanned air bubbles injected into the fluid. Better understanding these complex vortices is important to elementary particle physics and understanding why the Sun’s outer atmosphere is hotter than its surface.
From the article:
Capturing images of the knot was another technical tour-de-force. Fluid dynamicists often use coloured dye to trace the motion of fluids, but Kleckner and Irvine injected tiny gas bubbles into the water that were drawn to the centre of the knotted vortex by buoyancy forces. A high-speed laser scanner capable of producing CT-scan views of the fluid at 76,000 frames per second enabled the researchers to reconstruct the 3D arrangement of the bubbles, thus revealing the knots.
“The authors have managed a remarkable achievement to be able to images these vortex knots,” says Mark Dennis, an optical physicist at the University of Bristol, UK, who has made knotted vortices from light beams. The new study, he adds, transforms abstract notions about physical processes involving knots into testable ideas in the laboratory.