Vortex loops, of which smoke rings are a familiar example, occur when a fluid or gas spins in a tornado-like funnel that turns back on itself. The behaviour of'knots' that can form in vortex loops is hard to study, but these important, complex objects have now been created experimentally. Dustin Kleckner and William Irvine of the University of Chicago in Illinois generated vortex loops in water (pictured) by using precisely shaped plastic wings produced with a three-dimensional printer. They watched how these loops change over time; flows in vortices break and reconnect, causing knots to unknot. The evolution of knots is important to our understanding of energy transfer in solar plasmas, electromagnetic fields and turbulent fluids.
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