The life of a vortex knot (in experiment)*

In recent experiments on linked and knotted vortices in classical fluids, we have found that they undergo a spontaneous change in topology: they untie themselves through a series of local reconnections. This outcome is at odds with the notion that fluid helicity (knottedness) should be conserved, as it should be for a dissipation-less fluid. Remarkably similar behavior is found for simulations of superfluid knots using the Gross-Pitaevskii equation. We will discuss our search for the missing helicity and the possibility of a universal driving mechanism for reconnections in topological vortices.