Knots form not only in everyday items such as headphone wires, but also in less-tangible realms, from electromagnetic field lines to the quantum states of electrons in solids. Physicists have even created ‘quantum knots’ in an ultracold gas — and now scientists have observed these structures spontaneously decay to a simpler knotted state.

Building on their team’s earlier creation of quantum knots, researchers led by Tuomas Ollikainen at Aalto University in Finland cooled a gas of rubidium atoms to just a few billionths of a degree above absolute zero. Then, using a magnetic field, the scientists aligned the magnetic axis of the gas along curves that twist — like a skewed bundle of spaghetti — around a series of doughnut-shaped surfaces, which are nestled inside one another. The structure broke apart within a few milliseconds, and the atoms aligned themselves along a simpler, circular pattern called a vortex.

The researchers speculate that this behaviour could occur across a range of phenomena that are similar to quantum knots in terms of their topology, the branch of mathematics that studies knots and their multi-dimensional analogues. Even ball lightning — an atmospheric phenomenon that can last for more than half a minute and might draw its persistence from knotted electromagnetic fields — could, in principle, decay in a similar way.