2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/105250The recent discovery of light moving backwards in time, when it propagates in a suitable dispersive medium, obliges us to reexamine the Kramers-Kronig relations. In their usual form, they are dealing with usual light (moving forward in time), and they are a consequence of causality. In a similar fashion, we derive the appropriate form of these relations for light moving backwards in time, starting, instead of causality, from a principle of anti-causality, appropriate to such a light.7 pages with 2 figures. Written in October 2001General Physicstext