Grab a mug and slosh the morning coffee around and around and a spinning vortex appears. The swirling rings, with their eddies and choppy waves, obey the laws of classical turbulence, which engineers and applied physicists routinely invoke to study how air flows over an airplane wing or how blood flows through tiny vessels.
Shake up a cup of quantum fluid instead and you still get vortices, but nothing like the tornado in your morning brew.
Quantum vortices can look like tiny rings that shatter into even more minuscule rings and then shrink away altogether. Connected one moment, in the next they appear to flex into curved lines — as if snipped with scissors. Sometimes these lines tangle like a ball of cat hair on a rug. And they can cross over each other into a letter X, swap ends and then shoot away with the gusto of a rubber band flinging from the finger of a mischievous third-grader.
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