Physicists from the University of Rostock, the Cluster of Excellence ct.qmat, the Julius-Maximilians University of Würzburg and the Indiana University Indianapolis (IUPUI) have shown for the first time that light can propagate without any loss in systems that interact with their environment. Previously, it was assumed that such open systems inevitably would exhibit exponential amplification or damping of light and thus lead to the instability of the system.