title: Observation of image pair creation and annihilation from superluminal scattering sources.
abstract: The invariance of the speed of light is one of the foundational pillars of our current understanding of the universe. It implies a series of consequences related to our perception of simultaneity and, ultimately, of time itself. Whereas these consequences are experimentally well studied in the case of subluminal motion, the kinematics of superluminal motion lack direct evidence or even a clear experimental approach. We investigate kinematic effects associated with the superluminal motion of a light source. By using high-temporal-resolution imaging techniques, we directly demonstrate that if the source approaches an observer at superluminal speeds, the temporal ordering of events is inverted and its image appears to propagate backward. Moreover, for a source changing its speed and crossing the interface between subluminal and superluminal propagation regions, we observe image pair annihilation and creation, depending on the crossing direction. These results are very general and show that, regardless of the emitter speed, it is not possible to unambiguously determine the kinematics of an event from imaging and time-resolved measurements alone. This has implications not only for light, but also, for example, for sound and other wave phenomena.
authors.affiliation: School of Engineering, University of Glasgow, Glasgow G12 8LT, UK.; School of Engineering and Physical Sciences, SUPA, Heriot-Watt University, Edinburgh EH14 4AS, UK.
authors.forename: Matteo
authors.initials: M
authors.lastname: Clerici
authors.affiliation: Department of Physics, Illinois Wesleyan University, Bloomington, IL 61701, USA.
authors.forename: Gabriel C
authors.identifier: 0000-0003-1126-3968
authors.initials: GC
authors.lastname: Spalding
authors.affiliation: School of Engineering and Physical Sciences, SUPA, Heriot-Watt University, Edinburgh EH14 4AS, UK.
authors.forename: Ryan
authors.initials: R
authors.lastname: Warburton
authors.affiliation: School of Engineering and Physical Sciences, SUPA, Heriot-Watt University, Edinburgh EH14 4AS, UK.
authors.forename: Ashley
authors.identifier: 0000-0002-5110-258X
authors.initials: A
authors.lastname: Lyons
authors.affiliation: School of Engineering and Physical Sciences, SUPA, Heriot-Watt University, Edinburgh EH14 4AS, UK.
authors.forename: Constantin
authors.initials: C
authors.lastname: Aniculaesei
authors.affiliation: Department of Physics, Illinois Wesleyan University, Bloomington, IL 61701, USA.
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Richards
authors.affiliation: School of Engineering and Physical Sciences, SUPA, Heriot-Watt University, Edinburgh EH14 4AS, UK.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Leach
authors.affiliation: Institute for Micro and Nano Systems, University of Edinburgh, Alexander Crum Brown Road, Edinburgh EH9 3FF, UK.
authors.forename: Robert
authors.identifier: 0000-0002-0398-7520
authors.initials: R
authors.lastname: Henderson
authors.affiliation: School of Engineering and Physical Sciences, SUPA, Heriot-Watt University, Edinburgh EH14 4AS, UK.
authors.forename: Daniele
authors.initials: D
authors.lastname: Faccio
mesh_terms: D001696:Biomechanical Phenomena; D008027:Light; D009038:Motion; D055095:Optics and Photonics; D010825:Physics
keywords: Physics; optics; speed of light