Textbooks usually show magnetic fields as simple loops around current-carrying wires, but what happens with the many convoluted wires that make up electrical circuits? Quite remarkably, Makoto Hosoda of Osaka City University in Japan and colleagues have shown that typical magnetic fields are wildly complicated and, indeed, chaotic. Even two circular current loops at right angles to each other produce elaborately knotted fields, which are chaotic in the sense that, when following the field lines from two nearby points, the researchers find wildly diverging trajectories.
Such complex fields are well known in plasma physics, but finding them in simple circuits has come as something of a surprise. The good news is that it might be that the chaos avoids the build-up of fields that could otherwise disrupt small devices, allowing them to operate stably.