Active matter: this microscope image shows part of a cluster of self-propelled particles, colour-coded according to their distance from the centre. (Courtesy: Jie Zhang, Ricard Alert, Jing Yan, Ned S ...

Torque wrench: artist’s impression of the Casimir torque (purple streaks) acting on two solids (blue) against a background of quantum fluctuations (silver spikes). (Courtesy: Jeremy Munday) A very ...