Sir John Pendry is a paradigm-breaking researcher in nano-optics who has demonstrated how wave properties hold the key to making objects invisible.
Waves interacting with static structures have long been studied in many settings: ultrasonics, acoustics, optics, radar and ocean waves to name a few. More recently interest has turned to time dependent systems in which the system parameters vary on a time scale comparable to the period of the waves or even faster. Of particular interest are systems where the material components do not physically move but whose parameters are phased in time from point to point. Because of the absence of physical motion, disturbances can be created that move with any desired velocity. In the case of optics this can mean faster than light and it can create several paradoxical phenomena including apparently (but not truly) acausal behaviour of signals. I shall discuss recent results from my own background in electromagnetism and optics, but will also point out the general nature of our results, particularly in acoustics, where realisation of some of the theoretical concepts can more readily be achieved than in optics.