This is a first, scientists have tied water into a knot. Not the kind of knot you struggle with when you can`t get your shoes off but a knot nonetheless. These knots are quite different, first off they don`t have "ends" to untie, they are closed loops, yet it`s something that has eluded scientists for almost 100 years.
From New Scientist:
"Tying a knot in a smoke ring sounds like a feat worthy of those enjoying a certain kind of cigarette. But treat smoke as an example of a fluid, and it becomes a physics problem.
Now for the first time a fluid knot has been created – from water rather than smoke. The achievement will allow us to probe what had been theoretical objects, and this might in turn lead to better models of airflow around aircraft wings, or of strange quantum substances like superfluids.
Unlike the knots in your shoelaces, the knots that physicists and mathematicians talk about are closed entanglements that cannot be untied as they have no ends. The simplest of these are the trefoil, a loop that crosses itself three times, and the Hopf link, two linked loops.
The idea of a knot made of fluid first cropped up in the 1860s when the mathematical physicist Lord Kelvin suggested that atoms might be knots in the ether – a mysterious fluid then thought to permeate the entire universe. That idea fell flat, but since then, knots have become central to many aspects of science, from mathematics to biology. And that has led to renewed interest in the idea of a fluid knot."
"Abstract "Knots and links have been conjectured to play a fundamental role in a wide range of physical fields, including plasmas and fluids, both quantum and classical. In fluids, the fundamental knottedness-carrying excitations occur in the form of linked and knotted vortex loops, which have been conjectured to exist for over a century. Although they have been the subject of considerable theoretical study, their creation in the laboratory has remained an outstanding experimental goal. Here we report the creation of isolated trefoil vortex knots and pairs of linked vortex rings in water using a new method of accelerating specially shaped hydrofoils. Using a high-speed scanning tomography apparatus, we measure their three-dimensional topological and geometrical evolution in detail. In both cases we observe that the linked vortices stretch themselves and then deform—as dictated by their geometrically determined energy—towards a series of local vortex reconnections. This work establishes the existence and dynamics of knotted vortices in real fluids."