Everyone knows that light is supposed to travel in straight lines, so it comes as a surprise to find that light can be tied in 3D knots. Hridesh Kedia of the University of Chicago in the US and colleagues have found solutions of Maxwell’s equations where the field lines encode all possible torus knots (knots that can be tied around a donut) and links (collections of such knots that link to each other).

The solutions are stable and retain their topology as they evolve in time. They are also stunning examples of topologically non-trivial structures in a linear field theory.

The fields are null, with electric and magnetic fields always orthogonal to each other and of equal strength, and could be produced by suitably focussed laser beams. If implemented experimentally, they could be used to manipulate plasmas or quantum fluids in ways that have never before been possible.